Meetings & Events

fall 1997 logo1997 MRS Fall Meeting & Exhibit

December 1 - 5, 1997 | Boston
Meeting Chairs:
 Harry A. Atwater, Peter F. Green, Dean W. Face, A. Lindsay Greer 
 

Symposium U—Ferroelectric Thin Films VI

Chairs

Seshu Desu, Virginia Polytechnic Inst
Christopher Foster, Argonne National Laboratory
Robert Jones, Advanced Matls Group
Randolph Treece, Superconducting Core Tech
In Yoo, Samsung Advanced Inst of Tech 

Symposium Support 

  • Blake Industries, Inc. 
  • Inorgtech, Ltd. 
  • MKS Instruments, Inc. 
  • Motorola, Inc. 
  • Samsung Advanced Institute of Technology

* Invited paper

SESSION U1: HIGH PERMITTIVITY MATERIALS FOR DRAMs 
Chairs: Robert E. Jones and Scott R. Summerfelt 
Monday Morning, December 1, 1997 
Salon A/B (M)

8:30 AM U1.1 
LEAKAGE DEGRADATION IN BaxSr1-xTiO3 DIELECTRIC CAPACITORS WITH OXIDE AND METAL ELECTRODES. Noburu Fukushima, Kazuhide Abe, Mitsuaki Izuha and Takashi Kawakubo,Toshiba Corporation, Materials and Devices Laboratories, Kawasaki, JAPAN.

Leakage degradation under DC stresses in epitaxially-grown Ba1-xSrxTiO3/SrRuO3 capacitors with various top electrodes was examined. Epitaxial capacitors employed in this study exhibit higher dielectric constant arising from optimized lattice deformation caused by lattice mismatch between Ba1-xSrxTiO3 and SrRuO3; dielectric constant for SrRuO3/30nm thick Ba1-xSrxTiO3/SrRuO3 all oxide capacitor was 550, which corresponds SiO2 equivalent thickness of 0.21nm. In addition, this type of capacitors have interfaces of higher cleanliness between dielectrics and electrodes, which are expected to provide opportunities of more simplified discussions on reliability issues for thin film capacitors. Dielectric breakdown properties and DC stress-induced leakage degradation properties were examined in room temperature and elevated temperatures. Various kinds of leakage degradation were observed and categorized in anode degradation and cathode degradation. The degradation in capacitors with oxide electrodes was markedly suppressed compared to that in capacitors with metal electrodes such as Pt or Ru. This higher degradation resistance yielded longer lifetime in capacitors of this type and the estimated life time at 458K for SrRuO3/ Ba1-xSrxTiO3/SrRuO3 capacitor was 3E8 seconds, which exceeds required specification for DRAM application. These differences were discussed on the basis of a supposed degradation mechanism in which oxygen vacancy generation at anode interface is taken into account as well as vacancy accumulation at cathode interface.

8:45 AM U1.2 
EFFECT OF FILM COMPOSITION ON THE ORIENTATION OF (Ba,Sr)TiO3 GRAINS IN THIN FILMS PREPARED BY MOCVD. Debra L. Kaiser, Mark D. Vaudin, John E. Bonevich, Sandra A. Claggett, John T. Armstrong, National Institute of Standards and Technology, Gaithersburg, MD; Alexander L. Roytburd, Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD.

Barium strontium titanium oxide thin films of various compositions were deposited by metalorganic chemical vapor deposition (MOCVD) on (100) MgO substrates using a variety of growth conditions. The conventional x-ray diffraction patterns from films that had molar ratios (Ba+Sr)/Ti significantly different from one showed only the presence of crystalline Ba_1-xSr_xTiO_3(BST, x0.058). The second phase material in these films did not give discernible x-ray diffraction peaks and was likely to be amorphous. The orientation of the BST grains in the films was found to be strongly dependent upon film composition: films with (Ba+Sr)/Ti0.73 contained onlyaaxis BST; films with (Ba+Sr)/Ti0.42 contained onlycaxis BST; and films with 0.68(Ba+Sr)/Ti0.72 contained bothaandc axis BST. These orientation results will be discussed in terms of residual stresses in the films.

9:00 AM *U1.3 
REVIEW OF (Ba,Sr)TiO3 FOR DRAM. Scott R. Summerfelt, Components and Materials Research Center, Texas Instruments Inc., Dallas, TX.

The reduction in cell area coupled with the requirements for nearly constant capacitance results in the need for more capacitance per cell area. In the past, the principal method to increase capacitance per cell area was to use new processes (rugged poly-Si), more process steps (crown capacitor structure), and ever taller capacitors. Current efforts focus on using medium dielectric constant materials such as Ta2O5 which allow roughly 50% more capacitance per area compared to traditional SiO2 / Si3N4 (ON) dielectrics using the traditional poly-Si electrodes. Further improvements in increasing the capacitance density of Ta2O5 require the use of metal bottom electrodes. Much greater capacitance densities using perovskite materials such as (Ba,Sr)TiO3 can be achieved. These high dielectric materials require oxygen stable lower electrodes such as Pt, Ir, or conductive oxides such as RuO2. Even with these high dielectric constants, three dimensional devices must be built although the capacitors can have a simpler structure and be much shorter compared to those built with medium dielectric constant materials. The three dimensional structures require a conformal MOCVD BST deposition processes be developed. There are many possible choices of structures, electrodes, diffusion barriers and even MOCVD process routes (high temperature deposition versus low temperature deposition and high temperature anneal). Each decision impacts the others. This presentation will summarize progress in these critical areas and compares the advantages and disadvantages of the various choices.

10:00 AM U1.4 
AN IMPORTANT FAILURE MECHANISM IN MOCVD (Ba,Sr)TiO3 THIN FILMS: RESISTANCE DEGRADATION. C. Basceri, S.E. Lash. C.B. Parker, S.K. Streiffer, A.I. Kingon, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC; M. Grossmann, S. Hoffmann, M. Schumacher, and R. Waser, Aachen, GERMANY; S. Bilodeau, R. Carl, and P.C. van Buskirk, Advanced Technology Materials Inc., Danbury, CT; S.R. Summerfelt, Texas Instruments, Dallas, TX.

We have investigated the intrinsic resistance degradation behavior of fiber-textured MOCVD (Ba,Sr)TiO3 thin films appropriate for use in DRAMs and integrated decoupling capacitors, as a function of voltage (field), thickness, temperature, and the A:B site ratio. At constant field and for a given stoichiometry, the measured degradation lifetime decreases with increasing film thickness, resulting from a decrease in the activation energy with respect to temperature for thicker films. Predicted resistance degradation lifetimes obtained from both conservative temperature and voltage extrapolations to DRAM operating conditions of 85C and 1.6V exceed the current benchmark of 10 years for all of the films studied. The relationship between stoichiometry and degradation lifetime and the effect of annealing after degradation will be presented. Furthermore, the mechanism for modification of the leakage behavior caused by resistance degradation will be discussed.

10:15 AM U1.5 
NOVEL OXIDATION METHODS FOR THE CHEMICAL VAPOR DEPOSITION OF HIGH DIELECTRIC BARIUM STRONTIUM TITANATE. Frank DiMeo Jr., Steven Bilodeau, Bryan C. Hendrix, Jeffrey F. Roeder, Charles P. Seegel, and Thomas H. Baum, Advanced Technology Materials,Inc., Danbury, CT.

In the past ten years, there has been a significant worldwide effort to develop complex-oxide thin films for next generation microelectronic applications. Impressive progress has been made in understanding perovskite materials such as PbZrTiO3 and BaSrTiO3 and in producing thin films with good properties. Significant hurdles, such as lowering the deposition temperature below 600 C, remain for integrating these materials with silicon device processing technology. This paper reports on the use of novel oxidation methods in conjunction with chemical vapor deposition to lower the total thermal budget required to produce high dielectric BaSrTiO3 thin films. Chemical vapor deposition is an attractive method for fabricating these films because it offers the advantages of conformal coating and large area deposition. In order to accommodate the low volatility of the group II precursors required for BaSrTi03 , we have employed a liquid delivery system developed at ATMI. The decomposition efficiency of the chosen precursors are only mildly substrate temperature dependent, changing from 8.5 to 10 over a temperature change of 125ÝC. As the deposition temperature is lowered, however, the decomposition efficiency drops, consistent with reaction-kinetic control of the film growth. We have investigated the use of ozone as a co-reactant gas to improve decomposition efficiency and film oxidation at lower temperatures. The use of ozone concentrations of less than 1 in oxygen was found to have significant effects on the decomposition of the precursors. The effect of ozone treatment during and after deposition on film properties such as dielectric constant and leakage current will be reported.

10:30 AM U1.6 
INVESTIGATION OF DIELECTRIC CONSTANT AND DISPERSION IN THIN BST FILMS. Sufi Zafar, Peir Chu, Bruce White, Robert Jones, Peter Zurcher, Bo Jiang, David Gentile, Deborah Taylor, Bradley Melnick and Sherry Gillespie, Materials Research and Strategic Technologies, Motorola, Austin, TX.

In recent years, there has been an increasing interest in high dielectric materials such as barium strontium titanate (BST) for memory and chip capacitor applications. Two important properties of the BST capacitors for memory applications are dielectric constant and dispersion. The dielectric constant influences the charge storage capacity whereas the dielectric dispersion is usually the dominant cause of charge dissipation in high dielectric films. In this presentation, we report the dependence of the dielectric constant and dispersion on the measurement temperature and frequency for sputtered BST thin film capacitors with platinum electrodes. The dielectric constant and dispersion also are investigated as a function of BST film thickness and sputtering conditions. These measurements show a correlation between the dielectric constant and dispersion: dispersion decreases with increasing dielectric constant. A simple model with series bulk and interface capacitors is proposed to quantitatively explain this correlation. Based on this model, the influence of interfacial and bulk properties on the measured parameters of the BST capacitors are successfully predicted.

10:45 AM U1.7 
STOICHIOMETRIC EFFECTS OF SPUTTERED BARIUM STRONTIUM TITANATE FILMS. B.A. Baumert, L.-H. Chang, T.-L. Tsai, T.P. Remmel, C.J. Tracy, D.F. Sullivan, and E.P. Ehlert, Materials Research and Strategic Technologies, Motorola, Mesa, AZ.

Barium Strontium Titanate films have been deposited by rf magnetron sputtering and have been studied with respect to Ba/Sr ratio as well as A/B site ratio. Typical results measured for Ba0.25SrO.75TiO3 films show a dielectric constant of 236 at 100 kHz, a leakage current density of 6.36xlO-II at 1 V, and a Curie-von Schweidler exponent n of 0.9948. X-ray diffraction shows the films to have a lattice parameter larger than that expected for a bulk ceramic sample. This parameter varies with Ar/02 ratio, pressure, and A/B site ratio. Extensive electrical and materials characterization has been done and will be reported.

11:00 AM U1.8 
DEPLETION DEPTHS OF SrTiO3 AND Ba0.7Sr0.3TiO3 THIN FILMS MEASURED WITH PHOTOEMISSION SPECTROSCOPY. M. Copel, IBM, Yorktown Hts., NY.; J. Baniecki, Columbia Univ., New York, NY; P.R. Duncombe, D. Kotecki, D.A. Neumayer, R. Laibowitz, T. Shaw, IBM, Yorktown Hts., NY.

Numerous groups have applied intensive efforts to implement perovskite ferroelectrics as charge storage devices for microelectronics. We have used x-ray photoemission to probe the band bending caused by Pt metallization of SrTiO3 and Ba0.7Sr0.3TiO3 (BST) thin films synthesized by chemical solution deposition (CSD) and metal-organic chemical vapor deposition (MOCVD) on Pt coated substrates. Substantial band-bending is observed upon contact formation, sweeping the carriers out of the film. For films thinner than the depletion width, the bands are pinned by the back contact with the substrate, which provides a convenient method for measuring depletion widths. The carrier density can be inferred from the depletion width. In this talk we will present results exploring the effect of acceptor dopants on carrier density, and relate this to leakage characteristics of metal-insulator-metal devices.

11:15 AM U1.9 
ELECTRICAL AND MICROWAVE PROPERTIES OF Mn IMPLANTED (Ba,Sr)TiO3 THIN FILMS. J.D. Baniecki, Columbia Univ., New York, NY; R.B. Laibowitz, T.M. Shaw, P.R. Duncombe, D.A. Neumayer, M. Copel, D.E. Kotecki, IBM, Yorktown Hts., NY; H. Shen, Siemens, Hopewell Jct., NY; Q.Y. Ma, Columbia Univ., New York, NY.

Thin films of barium strontium titanate (BST) are being intensively studied for their use in high density DRAM circuit applications. In order to optimize the electrical properties of the BST thin films, it is important to understand what effect impurities and dopants have on these films. Ion implantation is an effective way to introduce dopants into BST thin films because of the uniformity and precision of which the dopant concentration can be controlled and the ability to selectively choose the dopant location. We have used ion implantation to dope Ba.7Sr.3TiO3 thin films with Mn. Dopant concentrations were varied in the range of 0.1at% to 2at% Mn. The thin films (less than 100nm thick) were prepared by chemical solution deposition (CSD) and chemical vapor deposition (CVD). Pt electrodes were used for all the electrical measurements. X-ray diffraction studies show that the implantation process makes the film amorphous, but subsequent rapid thermal annealing for 2 minutes at 750 C in O2 recovers the damage. Microwave measurements of the complex permittivity were made to characterize the dielectric relaxation of the films. Using on chip calibration standards and a lumped impedance model for the parasitics of the test structure, microwave measurements could be made up to 20GHz. Time domain measurements of the relaxation currents were also made which confirmed the results in the frequency domain. Other electrical measurements such as leakage, long term resistance degradation, and C-V will be presented. Our initial results for an implantation of 0.5at% Mn show no significant effect on dielectric relaxation and indicate that the film obeys a Curie-Von Schweidler relaxation law with the exponent approximately 0.96. The leakage current, however, is significantly affected by the Mn doping being reduced by a factor of 10 for an implantation of 0.5at% Mn. Comparisons will be drawn between the implanted and non implanted films and the effect of the the different concentrations of the Mn dopant on dielectric relaxation, leakage, and resistance degradation.

11:30 AM U1.10 
MICROSTRUCTURAL CONTROL OF (Ba,Sr)TiO3 FILMS FOR GIBABIT DRAM APPLICATION. H. Shen, Siemens Components, Hopewell Jct., NY; D. Kotecki, R. Laibowitz, T. Shaw, K. Saenger, R. Murphy, M. Zaitz, C. Parks, L. Tai, IBM, Hopewell Jct., NY.

(Ba,Sr)TiO3 films were deposited on Pt coated SiO2/Si wafers by MOCVD method. Nucleation and growth experiments were conducted to investigate the factors controlling the final microstructure. It was found that it is possible to have much larger grain sizes than the film thickness itself by controlling the nucleation and growth process. I-V and C-V measurements show that BSTO film deposited under optimized conditions have high capacitance (>100 fF/um2) and low leakage current (<10 nA/cm2) and are suitable for Gigabit-scale DRAM application).

11:45 AM U1.11 
A STUDY ON THE IMPROVEMENT OF CHARACTERISTICS OF BST THIN FILMS FABRICATED ON IRIDIUM ELECTRODE. Deok-Sin Kil, Byung-Il Lee, Seung-Ki Joo, Div. of MS&E, College of Engineering, Seoul National University, Seoul, KOREA.

Recently, BST thin films have drawn special attention as a promising candidate for ULSI DRAM capacitor due to their high dielectric constant as well as paraelectric properties at room temperature. In this work, we studied the characteristics of BST thin films sputter-deposited on Ir/poly-Si/Si substrate, and applied newly developed two- step process for deposition of BST thin films on the same substrate. All the films were crystallized at 650C for about an hour in oxygen ambient in order to obtain the perovskite structure. The BST thin film of about 600 deposited at 350C has shown considerably small oxide equivalent thickness of 5.2, compared with that of 7.3 for the film deposited on Pt/SiO2/Si substrate, as well as low leakage current density of 410-8A/cm2 at 1.5V. With the increase of deposition temperature from 350C to 600C, the oxide equivalent thickness decreased remarkably from 5.2 to 3.5. In the case of the films deposited at 700C, oxide equivalent thickness was much smaller(3.1), but the leakage current density was increased significantly from 10-8A/cm2 to 10-4A/cm2. According to our previous study on the characteristics of BST thin films deposited on Pt substrate, electrical properties such as dielectric constant and leakage current density could be effectively enhanced by two step process. We prepared the BST thin films on Ir electrode by two-step process and investigated the characteristics of thus prepared BST thin films. BST thin films were fabricated by two-step process, which was composed of 200 bottom layer deposited at 700C and 300 thick top layer deposited at 500C. For that film, we could obtained very small oxide equivalent thickness of 3,0 and low leakage current density of 710-8A/cm2. In this work, the change of electrical characteristics according to the process parameters will be discussed in detail.

SESSION U2: DOMAINS AND SIZE EFFECTS 
Chairs: Susan Trolier-McKinstry and Sufi Zafar 
Monday Afternoon, December 1, 1997 
Salon A/B (M)

1:30 PM U2.1 
COMPOSITIONAL CONTROL OF FERROELECTRIC DOMAIN STRUCTURES AND PHENOMENOLOGICAL MODEL ON THE DOMAIN EVOLUTION IN HETEROEPITAXIAL PLZT THIN FILMS. Kyeong Seok Lee, Young Min Kang, and Sunggi Baik, Dept. of Materials Science and Engineering, Pohang Univ. of Science and Technology, Pohang, KOREA.

The mechanism and control of ferroelectric domain formation in heteroepitaxial (Pb1-xLa_x)(Zr_yTi_1-y)O_3(PLZT) thin films grown on MgO(001) substrates have been investigated as a function of composition and temperature. Periodic 90^domain structures were developed and systematically changed to the final equilibrium state when the film transform from cubic phase to tetragonal phase during cooling after deposition. Experimental observation of the 90^domain evolution in the films has been carried out in-situ and ex-situ using conventional and synchrotron X-ray diffraction and the results demonstrated that the most important parameter affecting the domain structure and its abundance is the transformation strain at the Curie temperature, which can be varied systematically by changing the concentration of La and/or Zr in PLZT system. Other factors including the selection of substrates, deposition temperature, and cooling rate also influence the domain structures but their contributions are relatively minor. Phenomenological model regarding the 90^ domain evolution as a nucleation and growth process will be presented.

1:45 PM U2.2 
NANOSCALE INVESTIGATION OF POLARIZATION RETENTION LOSS IN FERROELECTRIC THIN FILMS VIA SCANNING FORCE MICROSCOPY. A. Gruverman, JRCAT-ATP, Tsukuba, JAPAN; S.A. Prakash, S. Aggarwal, R. Ramesh, University of Maryland, College Park, MD; O. Auciello, Argonne National Laboratory-Materials Science Division, Argonne, IL; H. Tokumoto, JRCAT-NAIR, Tsukuba, JAPAN.

Scanning force microscopy (SFM) was used to investigate the mechanism of retention loss in ferroelectric thin films using direct nanoscale SFM piezoresponse imaging. Experiments were conducted by performing local polarization reversal within individual grains of PZT films with subsequent imaging of a resulting domain structure at various time intervals. A conductive SFM tip was used for domain switching and imaging in the SFM piezoresponse mode. The dynamics of backward switching in the grain, which proceeds through lateral domain wall motion, was investigated. It is shown that the stability of switched domains depends essentially on their position relative to the grain boundary. A domain of less than 50 nm in lateral size, switched in the center of a grain, is unstable and reverts back to the original state in a few minutes. On the other hand, if the domain switching is generated near the grain boundary, the domain appears to be stabilized by the boundary, such that it does not switch back to its original state for several hours.

2:00 PM *U2.3 
SIZE EFFECTS IN FERROELECTRIC FILMS FOR DRAMS AND NONVOLATILE MEMORIES. Angus I. Kingon and S.K. Streiffer, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC.

The potential for ferroelectric thin films for both DRAMs and nonvolatile memories has been demonstrated. Nonvolatile memories are in limited commercial production, and DRAMs which utilize superparaelectric (Ba,Sr)TiO3 (BST) films are in development for Gbit generations. In both of these applications, size effects are of importance. We first discuss thickness effects in BST films for DRAMs. Thicknesses are limited due to geometric constraints, and thin films are desirable in order to maximize the capacitance densities. In addition, a number of film properties improve with decreasing thickness, and data are presented to illustrate this point. On the negative side, relative dielectric constants decrease significantly with decreasing film thickness. This effect has been investigated in detail, and reasons for the behavior are discussed. The resultant compromises are presented. 
In the case of PZT and SBT films for nonvolatile memories, optimum film thicknesses appear to be significantly greater. In this case, the increase of coercive field with decreasing film thickness is of importance in terms of operating voltage, yield and degradation. The outlook for low voltage operation (below 3.3 volts) is discussed. For high density nonvolatile memories, the capacitor areas will need to decrease significantly. Limits are discussed in terms of grain sizes, switching behavior, and switched charge.

3:00 PM *U2.4 
THE IMPACT OF DOMAINS ON THE DIELECTRIC AND ELECTROMECHANICAL PROPERTIES OF FERROELECTRIC THIN FILMS. S. Trolier-McKinstry, C. Fan, J. Lacey, J-P. Maria, J.F. Shepard Jr., T. Su and F. Xu, MRL, Penn State, Univ. Park, PA.

In ferroelectric thin films for microelectromechanical systems, it is important to understand which mechanisms contribute to the observed piezoelectricity. In soft PZT (PbZr1-xTixO3 ceramics, over half the room temperature response is associated with domain wall contributions to the properties. However, studies on bulk ceramics have demonstrated that the number of domain variants within grains and the mobility of the twin walls depend on the grain size. This leads to a degradation in the dielectric and piezoelectric properties for grain sizes below a micron. This has significant consequences for thin films since 1 m is often the upper limit on the observed lateral grain size. In addition, since the pertinent domain walls are ferroelastic, the stress imposed on the film by the substrate could also, in principle, clamp the piezoelectric response. To investigate these factors, controlled stress levels were imposed on PZT films of different thickness while the dielectric and electromechanical properties were measured. It was found that for undoped sol-gel PZT thin films, the extrinsic contributions to the dielectric and electromechanical properties make very modest contributions to the film response. No significant enhancement in the properties was observed even when the film was brought through the zero global stress condition. Instead, the minor stress dependence observed appeared to be due to a shift in the morphotropic phase boundary. Comparable results were obtained from laser ablated films grown from hard and soft PZT targets. Finally, little twin wall mobility was observed in AFM experiments. The consequences of this, as well as alternative methods to increase the available piezoelectric coefficients and achievable strains in ferroic films will be presented.

3:30 PM U2.5 
HIGH-RESOLUTION OPTICAL MICROSCOPY OF SrxBa1-xTiO3 THIN FILMS. Charles Hubert, Jeremy Levy, Dept. of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA; Adrian C. Carter, Wontae Chang, Jeffrey M. Pond, Jim S. Horwitz, Douglas B. Chrisey, Naval Research Laboratory, Washington, DC.

The local polarizability of ferroelectric thin films (SrxBa1-xTiO3) has been studied at room temperature using confocal scanning optical microscopy (CSOM) and apertureless near-field scanning optical microscopy (ANSOM). The thin films were deposited onto MgO substrates using pulsed laser deposition. Gold interdigitated electrodes were patterned on top of the ferroelectric films with gap spacings from 5 to 12.5 microns, allowing measurements to be taken as a function of electric fields up to 80 kV/cm. The CSOM images of nominally ferroelectric (x=0.8) or paraelectric (x=0.5) samples reveal regions of strain-induced polarization at micron and sub-micron dimensions. Electric field-dependent measurements show little or no ferroelectric domain switching for either the paraelectric or ferroelectric samples. However, samples which have been annealed at temperatures 1200 ƒC in flowing oxygen exhibit both switching and hysteresis. ANSOM images have also been obtained which show features as small as 10 nm, and can be used to study the dielectric response of individual grains. These results will be discussed within the context of understanding the mechanisms for dielectric loss in ferroelectric thin films.

3:45 PM U2.6 
DOMAIN WALL PINNING BY GRAIN BOUNDARIES DURING ELECTRIC FIELD POLING OF KNbO3 THIN FILMS. Venkatraman Gopalan, Center for Materials Science, Los Alamos National Labs, Los Alamos, NM; Rishi Raj, Dept. of Mechanical Engineering, University of Colorado, Boulder, CO.

We present evidence for grain-boundary pinning of domain walls as controlling the electric field poling behavior of KNbO3 thin films. Two epitaxial film systems are compared: (a) film on MgO(100) substrate with KNbO3(110)//120 SrTiO3(100)//MgO(100) and (b) film on SrTiO3(100) substrate with KNbO3(110)//SrTiO3(100). Quantitative measurement of the area fractions of four domain variants in each film system was made using in-situ second harmonic generation measurement while applying an external electric field at room temperature. While the film system (a) showed reversible domain wall motion, the film system (b) showed some permanent poling after the removal of the external field. Transmission Electron Microscopy revealed a network of low angle grain boundaries of 1.5-2 misorientation along the substrate cubic axes in the growth plane of the film system (a) and also a network of 60 and 120 domain walls intersecting these grain boundaries at 45 in the film growth plane. These features were found to be absent in the film system (b). We present a model based on the pinning of 60 and 120 domain walls by low angle grain boundaries that explains the observed electric field poling phenomena.

4:00 PM U2.7 
RETENTION LOSS MECHANISMS IN LEAD BASED FERROELECTRIC THIN FILMS. A. S. Prakash, B. Yang, S. Aggarwal, R. Ramesh, Dept of Mat. Sci. and Nucl. Engg., University of Maryland, College Park, MD; A. Gruverman, H. Tokumoto, Joint Research Center for Atom Technology, Tsukuba, Ibaraki, JAPAN; O. Auciello, Argonne National Laboratory, Materials Science Division, Argonne, IL.

Reliability issues confronting the ferroelectric memory technology such as fatigue and imprint have been solved using oxide electrodes. However retention loss issues in FRAM technology have not been comprehensively addressed. In an effort to understand the retention loss mechanism, we are exploring the use of scanning force microscopy (SFM) to directly image ferroelectric domains, in conjunction with electrical measurements. The piezoresponse images were obtained before and after inducing polarization in the films by applying a DC voltage between the bottom electrode and the SFM tip. Using SFM, we have studied the time dependent backswitching, i.e. retention loss, of nanodomains. These nanoscale investigations were modeled with a stretched exponential type behavior and the exponent was found to be less than unity. This suggests that the retention loss occurs through a random walk type process of the domain walls. The macroscopic retention experiments were carried out using RT66A and the loss was modeled with a stretched exponential fit. The exponent was found to systematically vary with doping, crystallinity and retention voltage . The difference in exponents between electrical and SFM studies is understood in terms of the difference in depolarizing fields and neighboring grain effects.

4:15 PM U2.8 
ELECTRO-MECHANICAL MODEL OF DOMAIN STRUCTURE IN FERROELECTRIC THIN FILMS. N. Sridhar, D.J. Srolovitz, Department of Materials Science & Engineering, University of Michigan, Ann Arbor, MI; J.M. Rickman, Department of Materials Science & Engineering, Lehigh University, Bethlehem, PA.

We consider the effects of electrostatic and elastic driving forces on the equilibrium domain structure in epitaxiaI ferroelectric thin films. The elastic stresses arise as a result of lattice parameter mismatch with respect to the substrate and the electrostatic effects are created by the spontaneous polarization of the film below the transition temperature. We present exact analytical results for the energy release due to the formation of a periodic array of twinned domains as well as that for a single embedded twin domain in a thin film. While the analysis is applicable to general misfit strain tensors and arbitrary spontaneous polarization vectors, we specifically analyze the energetics of domain formation for a tetragonal film on a cubic substrate. Examination of the elastic and electrostatic fields show that domain boundaries can be represented by a much simpler idealized defect model. We present results for the dependence of the domain structure as a function of the film thickness the polarization vectors, the boundary energies, and the misfit strains. Finally, we perform a thermodynamic analysis of the effects of applied electric and elastic fields on the equilibrium domain structure.

4:30 PM U2.9 
THE EFFECTS OF FILM THICKNESS ON THE HIGH AND LOW-FIELD STRESS RESPONSE OF LEAD ZIRCONATE TITANATE THIN FILMS. Joseph F. Shepard Jr., Fan Chu, and Susan Trolier-McKinstry, Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, PA.

Lead zirconate titanate (PZT) thin films are currently employed in non-volatile ferroelectric memories (FRAM's) and are intended to be used as the active material in a number of microelectromechanical systems (MEMS). Several groups have reported that both the piezoelectric and dielectric characteristics of ferroelectric thin films improve with an increase of film thickness (above 0.5 m) though the reasons for those improvements are unclear. Previous investigations on the effects of biaxial mechanical stress have indicated that non-180 domain wall motion is limited in 0.4 m thick 52/48 PZT films. It is possible that some of the improvements noted in thicker films (i.e. films thicker than 0.4 m) are associated with an increase of this extrinsic contribution to the properties. To evaluate the domain wall mobility in thicker films, the high and low-field characteristics of sol-gel PZT from 0.4 to 5.0 m thick were measured as a function of applied biaxial stress (140 MPa). The stress response of each film was then correlated to film thickness and microstructure, and the results interpreted in terms of extrinsic domain wall contributions.

4:45 PM U2.10 
FATIGUE IN EPITAXIAL PZT FILMS: EVOLUTION OF THE DOMAIN STRUCTURE.Vladimir Shur, Sergei Makarov, Nikolai Ponomarev, Ekaterina Nikolaeva and Eugeny Shishkin, Ural State University, Ekaterinburg, RUSSIA: Leonid Suslov and Nikolai Salashchenko, Institute of Physics of Microstructures, RAS, Niznii Novgorod, RUSSIA.

The paper deals with the experimental investigation and computer simulation of fatigue in PZT/YBCO epitaxial heterostructures. Variation of the characteristics of initial domain structure existing between switching pulses and the main parameters characterizing the domain kinetics were extracted from the switching current data. The investigated epitaxial heterostructures PbZr0,52Ti0,48O3/ YBa 2Cu3O7-x were deposited by laser ablation on monocrystalline (001) SrTiO3. The original modification of Kolmogorov-Avrami theory was used for the description of domain structure evolution in finite samples. The mathematical treatment of the switching current data allows to obtain the dependence of domain wall motion velocity and concentration of remnant and arising domains on the number of switching cycles. We propose that the 90o domain walls are practically immovable and divide the switched area into stripe regions. Its influence on the kinetics of c-domains was taken into account. Two main mechanisms of fatigue in epitaxial heterostructures were proposed: first, the increasing of incomplete switching of c-domains and second, the arising of the number of 90o domain walls in the initial domain structure. Computer simulation of the incomplete polarization reversal was used for studying the evolution of switching current pulses during fatigue. The research was made possible in part by Grant No.96-02-19588 of the Russian Foundation of Fundamental Research.

SESSION U3: POSTER SESSION: 
BST/DRAM 
Chairs: Orlando Auciello and B. A. Baumert 
Monday Evening, December 1, 1997 
8:00 P.M. 
Salons G-K (M)

U3.1 
BARIUM-STRONTIUM TITANATE THIN FILMS PREPARED BY SOL-GEL TECHNIQUES. A.S. Sigov, K.A. Vorotilov and V.A. Vasiljev, Moscow State Institute of Radioengineering, Electronics, and Automation (Technical University), Moscow, RUSSIA; M.I. Yanovskaya and L.I. Solovjeva, Institute of Physical Chemistry, Moscow, RUSSIA.

The sol-gel techniques for the BST films preparation is discussed. The film structure and morphology, as well as the transformations during heat treatment, were characterized by X-ray diffraction, SEM, TEM, and ellipsometry. Capacitance-voltage, charge-voltage and current-voltage characteristics, as well as frequency and temperature dispersion of dielectric constant and losses are used for characterization of electrical properties of the films. Evolution of film microstructure in the process of heat treatment is governed by the solvent evaporation, organics pyrolysis, polycondensation of hydroxyls, structural relaxation, and crystallization processes. These processes were characterized by the study of shrinkage, refractive index, and IR spectra of the films prepared from alkoxide and modified alkoxide precursors with a different degree of modification by 2-ethylhexanoic acid. It was shown that solution chemistry strongly effects on evolution of the film structure and the crystallization behavior and causes different microcrystalline structure and as a result different electrical properties of the films. In particular, we discuss an effect of the grain size (determined by TEM and by coherent X-ray scattering) on the permittivity of BST films. An effect of Ba/Sr composition on electrical properties of BST films with different thickness and crystallized at different temperatures has been discussed as well.

U3.2 
COMPOSITIONAL AND PHYSICAL CHANGES ON PEROVSKITE SURFACES. S.P. Chen, Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM.

The surface composition of BaTiO3, SrTiO3 and CaTiO3 perovskite (100) surface is determined by shell-model calculations. The TiO2-ending surface is preferred for BaTiO3 and SrTiO3, while CaO-ending surface is preferred for CaTiO3. These preference for specific compositions are found to affect the growth conditions and ferroelectric properties of these perovskite materials.

U3.3 
DEPOSITION OF BARIUM STRONTIUM TITANATE FILMS USING CHARGED LIQUID CLUSTER BEAM. M. Cich, Q. Feng, K. Kim, Thin Film and Charged Particle Research Laboratory, Dept of Electrical and Computer Engineering; H. Choi, S.T. Hwang, Beckman Institute for Advanced Science and Technology, Univ. of Illinois, Urbana, IL.

A novel technique utilizing electrical atomization of a liquid precursor for deposition of (Ba,Sr)TiO3 has been developed. The precursor used was a sol solution prepared using modified barium, strontium, and titanium alkoxide precursors with controlled hydrolysis and polycondensation reactions. This technique offers possibilities for effective coating of non-planar structures. The effects of film deposition conditions (flow rate and voltage) on film morphology and electrical properties are presented.

U3.4 
MOCVD OF SrTiO3 MATERIALS FOR DYNAMIC RANDOM ACCESS MEMORY APPLICATIONS. Kanchana Vaydianathan and Alain Kaloyeros, Center for Advanced Thin Film Technology and Physics Department, The University at Albany-SUNY, Albany, NY; John J. Sullivan, Bin Han and James Loan, MKS Instruments Inc., Andover, MA.

SrTiO3 and (Ba,Sr)TiO3 have been extensively investigated as high dielectric constant materials for applications in memory cell capacitors for dynamic random access memory (DRAM) devices. The need for a viable deposition process without the use of solvents as a carrier medium for the solid sources has led the present investigators to develop a non-solvent based, non-intrusive CVD process for the deposition of these films. This paper reviews our recent work in the development of a CVD process for the growth of SrTiO3 thin films on Si and Pt/SiO2/Si substrates using Sr(thd)2 and Ti(thd)3 as the source compounds (thd - 2,2,6,6,-tetramethyl-3,5-heptanedionate). Two approaches are being considered and compared for the ``dry'' delivery of the source compounds, one using a specially designed solid source delivery system and another using N2O in combination with conventionlal pressure based bubblers. In particular, results comparing the two approaches will be presented from CVD SrTiO3 process optimization and associated structural and chemical characterization of the resulting thin films using RBS, XRD, SEM, XPS.

U3.6 
PREPARATION AND CHARACTERIZATIONS OF BST THIN FILMS WITH HYBRID BOTTOM ELECTRODES. Joon-Hyung Ahn, Jeong-Ho Park and Ho-Gi Kim, Korea Advanced Institute of Science and Technology, Department of Materials Science and Engineering, Taejon, KOREA; Won-Jae Lee, Korea Advanced Institute of Science and Technology, Electronic Ceramic Materials Research Center, Taejon, KOREA.

Ruthenium oxide has attracted much attention as an electrode alternative for high dielectric integrated circuit application due to its good thermal stability and excellent etching properties. However leakage current density of dielectric thin films deposited on RuO2 bottom electrode is about an order of magnitude larger than that on Pt. Therefore a hybrid electrode structure composed of Pt and RuO2 has been used to improve the leakage properties of high dielectric thin films. In this study, the effect of the sputtering conditions and the thickness of each component layer on hybrid electrode properties, such as crystallinity and microstructure were investigated to determine the stable and optimum hybrid electrode structure. Finally the dependence of structural and electrical properties of BST thin films upon the hybrid electrode structure were investigated. Using rf-magnetron sputtering, high dielectric BST thin films were deposited in the same deposition condition on such hybrid electrodes to study the effect of bottom electrodes.

U3.7 
FERROELECTRIC PROPERTIES AND CRYSTAL STRUCTURE OF YBa2Cu3O7/BaxSr(1-x)TiO3/Au HETEROSTRUCTURES. Christoph Schwan, Frank Martin, Gerhard Jakob, Juan Carlos Martinez, and Hermann Adrian, Johannes Gutenberg-Univ, Inst für Physik, Mainz, GERMANY.

Ferroelectric perovskites are considered promising for future nonvolatile memory devices. The use of the oxide superconductor YBa2Cu3O7 (YBCO) as base electrode is motivated by its zero resistance and good fatigue behaviour. The c-axis length of the sputtered BaTiO3 (BTO) thin films in this work is 3% larger in comparison with the bulk material. The rocking curve of YBCO (005) yields a full width at half maximum (FWHM) of 0.32 and the best value for BTO (002) is 0.38. scans of the YBCO/BTO heterostructures on MgO substrates indicate for YBCO an in-plane orientation parallel and 45 rotated to the MgO lattice. BTO grows on YBCO epitaxial. In addition to the cubic unit cell Ba0.5Sr0.5TiO3 (BST) films on YBCO show at room temperature a portion with hexagonal structure. AFM measurements of 300 nm thick BST films present for deposition temperatures of 750C and 475C a surface roughness of about 5 nm and 30 nm respectively. The breakdown field of the BTO films with a FWHM of 0.92 exceeds the value for thin films with a higher degree of crystalline order nearly by a factor of 10. By increasing voltage the BTO films change from interface (Schottky) to bulk (Poole-Frenkel) limited current. The YBCO/BTO bilayer exhibit a superconducting transition temperature of 85 K. Ferroelectricity of BTO was confirmed by capacitance, pulse and hysteresis loop measurements. Using a Sawyer-Tower circuit, we obtain a coercive field of 30 kV/cm and a remanent polarization of 1.25 C/cm2. After 1012 polarization reversals the BTO films possess at 20 Hz nearly a factor 20 higher permittivity than in the original state. This behaviour can be explained by unpinning of the domain walls by the cycling field.

U3.8 
COMBINATORIAL SYNTHESIS OF FERROELECTRIC AND DIELECTRIC DEVICE LIBRARIES. I. Takeuchi, H. Chang, Y. K. Yoo, P. G. Schultz, and X.-D. Xiang, Lawrence Berkeley National Laboratory, Materials Science Div, Berkeley, CA; R. P. Sharma and T. Venkatesan, University of Maryland, Dept of Physics, College Park, MD.

The most pressing issues in development of DRAMs and integrated capacitors include finding optimum ferroelectric and dielectric materials as well as the electrode materials. In order to systematically address these issues, we have implemented the combinatorial synthesis technique where thin film libraries (individual chips containing thousands of different compositions on different sites) are fabricated. Films are deposited by a multi-target pulsed laser depostion system with a rastering laser beam which facilitates very high thickness uniformity over 1 inch square area. At each site, a different multilayer combination of precursor materials is deposited using photolithography and automated high-precision in-situ metal shutters. Chips are then thermally processed ex-situ to induce controlled crystal growth of the materials. RBS is used to confirm proper diffusion of the precursor materials. XRD of the films reveals that they are epitaxial with good crystallinity although traces of mixed orientations are often present. In order to directly evaluate the performance of materials with different compositions, we have fabricated device libraries out of combinatorially synthesized ferroelectric and dielectric thin films. Films are relatively smooth with mean roughness < 20 nm over 100 (m)2 area for thickness of 500 nm which are suitable for multilayer device fabrication. LaAlO3 and MgO substrates are used, and La0.5Sr0.5CoO3 is used as the bottom electrode. After the films are capped with Pt, capacitors with sizes 100 m x 100 m are patterned everywhere by ion milling. Systems under study include BaxSr1-xTiO3 where x is varied continuously from 0 to 1 and others with varying amount of different dopants. Dependence of the device characteristics on composition will be discussed.

SESSION U4: POSTER SESSION: 
DOMAINS AND SIZE EFFECTS 
Chairs: Orlando Auciello and B. A. Baumert 
Monday Evening, December 1, 1997 
8:00 P.M. 
Salons G-K (M)

U4.1 
SIZE AND SURFACE EFFECTS ON FERROELECTRIC THIN FILMS AND NANOPARTICLES WITH FIRST ORDER BULK PHASE TRANSITIONS. Juan D. Romero, Luis F. Fonseca, Univ. of Puerto Rico, Dept. of Physics, San Juan, PR.

Monte Carlo simulations were carried out to calculate the average polarization of ferroelectric thin films and nanoparticles as a function of temperature. The transverse Ising Hamiltonian including two- and four spins interactions were used to study first order phase transitions. The changes on the temperature dependence of the average polarization for films of different thickness and particles of different size were studied, and the dependence of the Curie temperature on the size of the particles and thickness of the thin film is discussed. Averages of the polarization over each layer of the films were performed below the Curie temperature to calculate their variation as a function of the distance of the layer to the surface of the film for samples of different thickness. A decreasing in the layer polarization as compared with the inner layers is obtained at the surface of the film. For nanoparticles, the polarization at different sites were averaged over Monte Carlo cycles (MCC) giving information about the MCC-averaged polarization at different positions in the nanoparticle and its dependence on the size of the particle.

U4.2 
FERROELECTRIC POLYMER LANGMUIR-BLODGETT FILMS-TWO DIMENSIONAL FERROELECTRICS. A. Bune, Stephen Ducharme, Department of Physics and Astronomy, University of Nebraska, Lincoln, NE; V. Fridkin, L. Blinov, S. Palto, A. Sorokin, S. Yudin, and A. Zlatkin, Institute of Crystallography, Russian Academy of Sciences, Moscow, RUSSIA.

Ultrathin ferroelectric films are particularly interesting for the study of ferroelectricity in the domain between three to two dimensions and also offer new effects. Existing theory predicts that there is a minimum size for the existence of ferroelectricity. In this work we have shown ferroelectricity (phase transition behavior, polarization reversal) in polymer Langmuir-Blodgett films of vinylidene fluoride(70%) and trifluoroethylene(30%) copolymer as thin as 10(2 monolayers). We investigated influence of thickness of the films(size effect) on ferroelectric phase transition and observed shift Curie temperature to the lower temperatures for thinner films and completely new phase transition at 20C, connected with surface layers. The films have potential applications as acoustic and electromechanical tranducers, infrared imaging, high energy capacitors, and nonvolatile computer memory.

U4.3 
FORMATION OF ULTRA SMOOTH Bi-BASED FERROELECTRIC FILMS AND THEIR SIZE EFFECT ON DIELECTRIC CONSTANT. Hitoshi Tabata, Takeshi Yanagita and Tomoji Kawai, Institute of Scientific and Industrial Research, Osaka University, Osaka, JAPAN.

Bi-base layer structured ferroelectrics are very interesting materials not only to apply to the non-volatile memory (FRAM) but also to make clear the origin of the ferro-, di-electric properties. For the practical device application, there is a serious problem that the dielectric constant decreases with decreasing the film thickness. To elucidate this problem, the formation of well defined surface & interface is essential. We have formed Bi-based ferroelectric films, such as Bi2VO5.5(n=1), Bi2SrTa2Og, Bi#3TiNbOg(n=2) and Bi4Ti3O12(n=3), with changing a film thickness systematically by a pulsed laser deposition technique. Surface morphology of the film was observed by AFM. The Bi2VO5.5(n=1) film show an atomically smooth surface with a flat terrace of 3000-4000 wide, and steps of 8 and 17 which correspond to half and one unit cell, respectively. An X-ray diffraction pattern corresponding to Laue-function can be observed in the Bi2VO5.5 film with a thickness of 80. THese results indicate that these films are constructed with an atomic order accuracy from the first stage of the film growth. Even in these well crystallized films, the dielectric constants decrease with decreasing the film thickness. The dielectric constants of other Bi-based films (n=2,3) decrease with decreasing film thickness in the same ratio. It is considered that the size effect (combination between surface energy and bulk one) plays an important role in determing dielectric properties.

U4.4 
DIRECT NANOSCALE IMAGING OF DOMAIN SWITCHING DYNAMICS IN FERROELECTRIC THIN FILMS VIA SCANNING FORCE MICROSCOPY. A. Gruverman, JRCAT-ATP, Tsukuba, JAPAN; S.A. Prakash, S. Aggarwal, R. Ramesh, University of Maryland, College Park, MD; O. Auciello, Argonne National Laboratory-Materials Science Division, Argonne, IL; H. Tokumoto, JRCAT-NAIR, Tsukuba, JAPAN.

In the present paper we present results of studies using scanning force microscopy (SFM) to perform nanoscale nondestructive imaging of domain structures after polarization reversal. Domain imaging was carried out in tetragonal PZT films with different structures using the piezoresponse mode of the SFM method. It has been shown that the imaging resolution of the SFM piezoresponse mode depends on the film thickness and microstructure. By varying the width of the voltage pulse, applied to the conductive SFM tip, we could induce full or partial switching of an individual film grain. Polarization reversal in the area as small as 30 nm in diameter was performed. Effect of film crystallinity on domain structure and its dynamics has been investigated.Lateral growth of reversed domains and their interaction with grain boundaries is directly observed. The implications of the observed domain structure and switching behavior on ferroelectric capacitors operation will be discussed.

U4.5 
EVOLUTION OF THE DOMAIN STRUCTURE DURING SWITCHING IN THE FERROELECTRIC THIN FILMS. Vladimir Shur, Sergey Makarov, Nikolai Ponomarev, Eugenii Rumyantsev and Natalia Tonkachyova, Ural State University, Ekaterinburg, RUSSIA.

We review our experimental and theoretical investigations of the fast kinetics of domain structure in ferroelectric thin films. It is well known that the switching process in ferroelectrics is the complicated evolution of the domain structure. The domain kinetics during switching in wide field range was studied by proposed method in polycrystalline and epitaxial PZT and PLT thin films, prepared by sol-gel, laser ablation and magnetron sputtering on different substrates. Using our original modifications of Kolmogorov-Avrami formula we extracted the field dependence of sideways domain wall motion velocity and concentration of remnant and arising domains from the switching current data under the action of rectangular and triangular field pulses (in the constant and linear increasing field). The influence of the geometry and sizes of initial domain structure on domain kinetics during switching was demonstrated. The method was used for investigation of the degradation during periodical switching in terms of changes of the domain kinetics scenario. We discuss the relations between the structure of the investigated films and the domain kinetic parameters.

U4.6 
POLYDOMAIN STRUCTURES OF EPITAXIAL PbTiO3 FILMS ON MgO AND SrTiO3 SUBSTRATES. S.P. Alpay, A. S. Prakash, S. Aggarwal, R. Ramesh, and A.L. Roytburd, Dept. of Mat. Sci. and Nucl. Eng., University of Maryland, College Park, MD; P. Shuk, M. Greenbalt, Dept. of Chemistry, Rutgers University, Piscataway, NJ.

The concept of elastic domain stability maps, which show stable domain regions in coordinates of misfit strain and the tetragonality of the lattice of the ferroelectric phase, is employed to describe the domain structures observed in epitaxial PbTiO3 films grown on MgO and SrTiO3 by pulsed laser deposition. Relative domain fractions are estimated by taking into account misfit dislocation generation at the growth temperature through an effective substrate lattice parameter. The domain structure of the films is investigated by using x-ray diffraction at various temperatures. Experimental data indicate that the film consists of a c/a domain pattern from room temperature to the cubic-tetragonal transition temperature. In this temperature range, films on MgO have more c-domains than films on SrTiO3. Theoretical predictions are in good agreement with experimental results.

SESSION U5: BARRIERS AND ELECTRODES I 
Chairs: Christopher M. Foster and R. Ramesh 
Tuesday Morning, December 2, 1997 
Salon A/B (M)

8:30 AM U5.1 
CHARACTERIZATION OF HIGHLY TEXTURED PZT THIN FILMS GROWN ON LaNiO3 COATED Si SUBSTRATES BY MOCVD. C.H. Lin1, B.M. Yen1, C. Malone1, Haydn Chen1, T.B. Wu2, H.C. Kuo2 and G.F. Stillman2 1Department of Materials Science and Engineering, Materials Research Laboratory, University of Illinois at Urbana-Chempaign, Urbana, IL; 2Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL.

Highly textured PbZrxTi1-xO3 (PZT) thin films with x= 0.2-0.6 were grown on LaNiO3 coated Si substrates at 550-600 C by metal organic chemical vapor deposition (MOCVD). The crystalline orientation of PZT thin films with various Zr concentration were characterized by X-ray diffraction (XRD). The microstructures were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The dielectric constants and hysteresis behavior of these thin films were also measured. The relationship between growth rate and the preferential orientation are discussed. Furthermore, the dependence of the electrical properties on Zr concentration, preferential orientation and growth temperature are demonstrated.

8:45 AM U5.2 
MOLYBDENUM SILICIDE - CONDUCTING BARRIER FOR VERTICAL INTEGRATION OF LEAD BASED FRAMS ON Si-CMOS. Sucharita Madhukar, S. Aggarwal, S.C. Zhang, S. Choopun, R.P. Sharma, A.M. Dhote and R. Ramesh, Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD.

Currently, there is a strong effort to integrate ferroelectrics with silicon and the principal focus is the development of conducting barrier layers to directly grow the ferroelectric capacitors on the poly silicon plug of the transistor. We have investigated the use of refractory metal silicides such as molybdenum silicide which has high electrical conductivity and good oxidation resistance for use as a conducting barrier. We have optimized the growth of molybdenum silicide on poly Si by pulsed laser ablation deposition (PLAD) and studied the effect of deposition parameters on the crystal structure, surface quality and conductivity of molybdenum silicide thin films. Lead based oxide ferroelectric capacitors with La-Sr-Co-O electrodes were grown on molybdenum silicide with and without a Pt layer by pulsed laser ablation deposition. The interaction of MoSi2 and Pt/ MoSi2 with the bottom electrode was studied using XRD, RBS and TEM. The effect of the barrier properties on the crystalline quality and phase of the molybdenum silicide was investigated. The structural properties of this heterostructure were investigated by XRD and TEM. Ferroelectric hysteresis and fatigue measurements were performed on the films grown on MoSi2 barrier to investigate the performance of the ferroelectric capacitors. This work is supported by the NSF-MRSEC.

9:00 AM *U5.3 
CONDUCTING BARRIERS FOR HIGH DENSITY NONVOLATILE MEMORIES. R. Ramesh, Department of Materials and Nuclear Engineering and Center for Superconductivity Research, University of Maryland, College Park, MD.

Over the past two years, we have focused considerable effort on understanding the growth and characterization of conducting barrier layers for the direct integration of ferroelectric capacitors on a poly-Si plug. Our specific focus has been on the materials science of the barrier layers to understand the role of crystallinity and process parameters on the structural and chemical integrity of the barrier layers during the subsequent growth of the ferroelectric capacitor stack. We are using the PZT system with conducting oxide electrodes as a prototypical test system for which at least two different conducting barrier materials systems have been successfully developed. Using both epitaxial and polycrystalline capacitors on these conducting barriers as test vehicles, we have been carrying out systematic studies on the effect of composition, point defect chemistry, strain and other processing variables on the structural integrity and ferroelectric properties A novel aspect of our work is the use of scanning electric force microscopy techniques to understated the microscopic influence of film microstructure on the ferroelectric properties.

10:00 AM *U5.4 
INVESTIGATIONS OF ETCH PROFILES IN ETCHING OF PZT AND Pt THIN FILMS. Chee Won Chung, J.S. Lee, and I.K. Yoo, Electronic Materials Lab., Materials Sector, Samsung Advanced Institute of Technology, Suwon, KOREA.

Reactive ion etching of PZT and Pt thin films have been carried our using fluorine- and chlorine-based gases in an Inductively Coupled Plasma (ICP). Etching process for ferroelectric PZT films was studied to produce good etch profile by varying various process parameters such as etch gas composition, coil RF power, chamber pressure, and susceptor self-bias voltage. Optimum etch process without polymer has been achieved at high coil RF power, low gas pressure, and high seIf-bias voltage. For the etching of Pt thin films, various etch gas combinations have been employed. The redeposit formed on the pattern sidewall by using Cl2/Ar gases was analyzed using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). We found that the redeposit was mainly PtCl2 compound. Based on this result, new etch gas combination has shown clean etch profiles without unwanted redeposition. In addition, Pt etch process was explored with various etch conditions in terms of etch rate, etch selectivity and etch profile.

10:30 AM U5.5 
EPITAXIAL GROWTH AND CHARACTERIZATION OF SrRuO3 THIN FILMS ON (001), (110) AND (111) SrTiO3 BY PULSED LASER ABLATION. C. L. Chen, Y. Chao, Z. J. Huang, Q. D. Jiang, Z. Zhang, W. N. Kang, A. Brazdeikis, Y. Y. Sun, A. Benneker, C. W. Chu, and W. K. Chu, University of Houston, Houston, TX.

SrRuO3 thin films with single crystalline quality have been grown on (001), (110) and (111) SrTiO3 by using pulsed laser deposition. The films have a c-axis oriented with an in-plane relationship of [110]SrRuO3 // [100]SrTiO3 on the (001) SrTiO3 and an a-axis oriented with [001]SrRuO3//[001]SrTiO3 on the (110) SrTiO3, respectively. They have excellent metallic behavior with room temperature resistivity of 310 -cm and a residual resistance ratio of about 7 at 4.2 K, the largest on SrTiO3 substrate reported to date. A clear ferromagnetic transition at 147 K was detected by resistivity and magnetic measurements. However, the transition becomes blurred as the density-of-point defects increases in the films following a 400 KeV proton irradiation with an accumulative dose up to 6.0x1016 ions/cm2. Also, a c-axis layerd provskite SrBi2Ta2O9 thin films have epitaxially grown on the c-oriented SrRuO3 films with (001) SrTiO3 substrates. This research is supported in part by NSF, the Temple foundation, the John and Rebecca Morres Endowment, and the State of Texas through the TcSUH.

10:45 AM U5.6 
STRUCTURAL CHARACTERIZATION OF EPITAXIAL SrRuO3 THIN FILMS. X. Pan, and J. C. Jiang, E. Y. Wang, Dept. of Materials and Engineering, University of Michigan, Ann Arbor, MI; C.-L. Chen, Q. D. Qiang, Z. J. Huang, and C. W. Chu, Texas Center for Superconductivity and Dept. of Phys., University of Houston, Houston, TX.

Highly conductive metallic oxide thin films of SrRuO3 have been grown on (001) SrTiO3 by using pulsed laser deposition. The microstructure of the as-grown films have been characterized by 4-circle X-ray diffraction and plane-viewing and cross-sectional TEM. It has been found that the film grows epitaxially on the (001) surface of SrTiO3 with an in-plane orientation relationship of [110]-SrRuO3 parallel to [100]-SrTiO3. The surface roughness of the films is in the range of about a few nanometers according to the measurements on the cross-sectional micrographs. The atomic structure of the film/substrate interfaces have been studied by cross-sectional HRTEM in combination with computer image simulations. The growth mechanism of the films will be discussed according quantitative image processing and simulations. Data will also been presented on the film growth of SrRuO3 on the R-surface of sapphire.

11:00 AM U5.7 
GRAIN MORPHOLOGY, INTERFACIAL STRUCTURE, AND CATION COMPOSITION HETEROGENEITY OF PZT THIN FILMS DEPOSITED BY MOCVD. I-Fei Tsu, K.L. Merkle, G.-R. Bai, and C.M. Foster, Materials Science Division, Argonne National Laboratory, Argonne, IL; K.C. Liu, Water Chemistry Program, University of Wisconsin-Madison, Madison, WI.

Polycrystalline Pb(ZrxTi1-x)O3 (PZT) thin films with nominal x = 0.5 were grown by MOCVD at temperatures 525C. The preferred orientation grain morphology, interfacial structure, and composition heterogeneity of the PZT films were characterized by XRD, SEM, AFM, and TEM-EDX. PZT films with different preferred orientations were grown under the same condition on (101)- and (110)-textured RuO2 bottom electrodes on (100)Si substrates. The as-grown films showed good ferroelectric properties in Ag/PZT/Ru02 configuration with typical remanent polarizations of 20 - 45 uC/cm2, coercive fields of 35 - 40 kV/cm, and resistivities higher than 1011 ohm-cm at room temperature. Columnar grain microstructure with strongly faceted surface morphology was observed in both types of films. The grain morphology and surface roughness of the PZT films depend on those of the bottom electrodes. Rougher interfaces were observed in PZT/(101)Ru02 where the electrode layers were deposited at lower temperature and/or higher rates. Much higher leakage currents and evidence of Ru diffusion into PZT were observed in these films. Regardless of the bottom electrode orientation, notable cation composition heterogeneity was noticed in both PZT films in length scales of 0.2 - 2 m but not in scales > 40 um. Pronounced Pb composition deficiency was observed in PZT/(110)Ru02 but not in PZTi(101)RuO2. The ferroelectric properties in those two types of films were correlated with the observed microstructure. The grain morphology and cation heterogeneity in PZT were discussed on the basis of diffusion-limited columnar growth mechanism.

11:15 AM U5.8 
PLATINUM TEMPLATE LAYER FOR TEXTURE CONTROL IN PZT FECAPS WITH REACTIVELY SPUTTERED RuO2 ELECTRODE LAYERS. Gerd Norga, Dirk Wouters, Herman Maes, Interuniversity Microelectronics Center, Leuven, BELGIUM.

Because of its large intrinsic remanent polarisation, low processing temperatures, and low switching voltage (1.5 V) attainable by using very thin (50 nm) layers [1], PZT is one of the leading candidate materials for use in future high density nonvolatile memories. The replacement of Pt electrodes by RuO2 has been shown to drastically reduce the electrical fatigue rate of PZT FECAPs. However, Pr of PZT films grown on RuO2 tends to be lower as PZT develops a less favorable texture than PZT(111), grown on Pt(111). Earlier work has demonstrated the influence of power and oxygen partial pressure during reactive sputtering of Ru in O2/Ar on texture development in RuO2. In our experiments, we employed O2 rich (oxidized Ru target) sputtering conditions, which result in RuO2 (101) texture. Sol-gel PZT deposited on RuO2 (101) develops (100) texture, in agreement with data reported by Scott et al. for CVD grown PZT/RuO2 layers [2]. We found that insertion of a 100 nm Pt template layer beneath RuO2 induces (111) texture in PZT without affecting RuO2 texture. By using these RuO2/Pt bilayers as bottom electrode layers, a large improvement in endurance was obtained, while maintaining superior Pr compared to (100) textured films. Issues for integration of these FECAPs in the backend of a 0.5m CMOS process for embedded FRAM will be discussed.

11:30 AM U5.9 
THE EFFECT OF RuO2/Pt HYBRID BOTTOM ELECTRODE STRUCTURE ON THE MICROSTRUCTURE AND FERROELECTRIC PROPERTIES OF SOL-GEL DERIVED PZT THIN FILMS. S.H. Kim, J.G. Hong, J.C. Gunter, S.K. Streiffer, Angus I. Kingon, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC; H.Y. Lee, School of Metallurgical and Materials Engineering, Yeungnam University, Kyongsan, KOREA.

Ferroelectric lead zirconate titanate (PZT) thin films are being developed for a variety of electronic applications, including nonvolatile memories, optical memories, and MEMS devices. The choice of electrode material(s) used for the PZT film has an impact on ferroelectric film quality and device performance: it is well known that the use of conductive oxide electrodes such as RuO2 or La1-xSrxCoO3 helps improve the resistance to polarization fatigue for PZT. However, these electrodes have generally resulted in larger leakage currents and greater susceptibility to dielectric breakdown than precious metal electrodes. In order to improve upon some of these drawbacks, NCSU and other researchers have developed RuO2/Pt hybrid bottom electrodes. When using such hybrid electrodes, film properties are influenced by the thickness / partial coverage of the electrode layers. We have therefore fabricated Pt/PZT/RuO2/Pt heterostructures with different RuO2 thicknesses, using a new alkoxide-alkanolamine sol-gel method for the PZT. The microstructure and ferroelectric properties of the PZT thin films were investigated as a functions of the RuO2 thickness. The effect of the hybrid bottom electrode on microstructure and therefore on the leakage and fatigue characteristics of the PZT thin films will be presented.

11:45 AM U5.10 
A SIMPLE Ru ELECTRODE SYSTEM FOR FERROELECTRIC (Pb,La)(Zr,Ti)O3 CAPACITORS DIRECTLY ON SILICON. Jordana Blacksberg, Timothy Sands, University of California, Berkeley, Department of Materials Science & Mineral Engineering, Berkeley, CA.

Ferroelectric capacitors for Gbit-scale nonvolatile random access memory must be fabricated in direct contact with the silicon pass-gate transistor, necessitating bottom electrodes that also serve as diffusion barriers during high temperature processing of the ferroelectric material in an oxidizing ambient. To achieve these multiple functions, previous research efforts have focused on complex multilayer, multi-component electrode schemes. This work shows that by separating the growth and perovskite crystallization steps, (Pb-4% La)(Zr0.3Ti0.7)O3 (PLZT) capacitors with a simple single-layer elemental Ru electrode can be fabricated. As expected, it was found that direct growth of PLZT on Ru/Si at 620 C is not possible due to reaction layers forming at both the Ru/Si and Ru/PLZT interfaces; Transmission Electron Microscopy (TEM) and X-ray diffraction data indicates the formation of SiO2 and Pb2Ru2O7-x pyrochlore. By using a low temperature deposition process followed by rapid thermal annealing, PLZT capacitors have been fabricated directly on Ru/Si with no observed interface reactions. At lower deposition temperatures (< 400C) and higher pressures (> 50 mTorr) stress leads to film cracking while at higher temperatures reaction phases form. By optimizing stress and interface reactions, a remanent polarization of 15 C/cm2 for Ru/PLZT/Ru/Si structures has been demonstrated for films grown by pulsed laser deposition at 400 C and 50 mTorr O2 followed by rapid thermal annealing at 750 C. X-ray diffraction of the as-deposited films showed the Pb2(zrZTi)2O7-x pyrochlore phase which was converted to the perovskite phase after annealing. SESSION U6: BARRIERS AND ELECTRODES II 
Chairs: Christian D. Gutleben and Katherine L. Saenger 
Tuesday Afternoon, December 2, 1997 
Salon A/B (M)

1:30 PM U6.1 
ATOMIC PEENING EFFECT OF AMBIENT GAS ON PLATINUM FILMS GROWN ON AMORPHOUS SUBSTRATES BY PULSED LASER DEPOSITION. T.Y. Koo, K.-B. Lee, Y.H. Jeong, Department of Physics, Pohang University of Science and Technology, Pohang, SOUTH KOREA; K.Y. Kang, Advanced Research Division, Electronics and Telecommunications Research Institute, Daejeon, SOUTH KOREA.

Platinum is one of the candidate electrode materials to be used with ferroelectric thin films. Since in-situ deposition of electrodes and ferroelectric films is desired, the effect of substrate temperatures and ambient pressures on the quality of platinum electrodes is of particular interest. We studied the effects of substrate temperatures and ambient gas pressures on the preferred orientation of platinum films deposited on amorphous SiO2/Si(100) substrates by the pulsed laser deposition. Even at room temperature, platinum films could be grown under vacuum with (111) preferred orientation. The increase of substrate temperature to 600C induced the additional (100) orientation. While the presence of ambient oxygen or nitrogen gas suppressed (111) orientation at room temperature, it had the opposite effect of enhancing (111) orientation and suppressing (100) orientation at 600C. The effect of ambient gas pressure at high temperatures on the selective enhancement of platinum film crystallinity on SiO2 is proposed to be due to the atomic peening effect of gas molecules.

1:45 PM U6.2 
HILLOCK GROWTH AT THE SURFACE OF Pt/TiN ELECTRODES FOR FERROELECTRIC CAPACITORS DURING ANNEALING IN N2/O2 AMBIENT. Hideo Miura, Yukihiro Kumagai, Hitachi, Ltd., Mech. Eng. Res. Lab., Ibaraki, JAPAN, Yoshihisa Fujisaki, Hitachi, Ltd., Cent. Res. Lab., Tokyo JAPAN.

Hillock growth process at the surface of the Pt/TiN electrodes was investigated to keep flat surface of the electrodes for ferroelectric capacitors. A 50 nm TiN film and a 100 nm Pt film were sputter-deposited on thermally oxidized silicon wafers. Deposition temperature of Pt films was varied from room temperature to 500C in order to change initial internal stress of Pt films from -500 to 1000 MPa. The electrodes were annealed in N2/O2 ambient at various temperatures for 30 minutes. Internal stress change of the Pt films during annealing was measured by detecting the surface curvature change of the films using a scanning laser microscope. During heating, compressive thermal stress developed in the Pt films. Thus, compressive stress increased monotonically in the Pt films deposited at low temperatures, while the initial tensile stress decreased in the films deposited at higher temperatures. Hillocks always started to grow when internal stress of Pt films reached about -1000 MPa during the annealing. Thus, their growth temperature strongly depended on the deposition temperature of Pt films. The hillock growth started at about 300C when Pt films were deposited at room temperature, while it started at about 600C when the Pt films were deposited at 500C. TEM and SEM observations confirmed that delamination occurred at Pt/TiN interface locally first, and then, plastic deformation of the Pt films under compressive stress formed hollow domes, resulting in hillocks. The high compressive stress was almost relaxed during the hillock growth. Since tensile thermal stress developed during cooling, the final residual stress in the Pt films at room temperature was higher than 1000 MPa. It is very important, therefore, to control the initial internal stress in Pt films to eliminate hillock growth at the surface of Pt/TiN electrodes.

2:00 PM *U6.3 
OXYGEN-INDUCED INHIBITION OF NOBLE METAL SILICIDE FORMATION IN METAL/Si AND METAL/SILICIDE STRUCTURES DURING ANNEALING: PROCESS INTEGRATION IMPLICATIONS FOR ELECTRODES IN PEROVSKITE-BASED MEMORY DEVICES. K.L. Saenger, A. Grill, IBM Research, T.J. Watson Research Center, Yorktown Heights, NY; D.E. Kotecki, IBM Microelectronics Division, Hopewell Junction, NY.

We describe the inhibitory effect of ambient oxygen on the noble metal silicide formation expected to occur during high temperature processing of noble metal electrodes deposited directly on silicon or silicides. Reactions of Pt and Ir films with substrates of silicon, tungsten silicide (WSix/Si) and other refractory metal silicides were examined after anneals in atmospheric pressure ambients of oxygen or nitrogen at temperatures of 640 - 700C for various initial noble metal film thicknesses. Metal/silicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, X-ray diffraction, and electrical resistance measurements. While annealing in nitrogen resulted in complete noble metal silicidation in all the samples, some Pt and most to all of the Ir remained after equivalent anneals in oxygen. Oxygen exhibited a greater inhibitory effect on silicidation in thin Ir samples, where no silicide formation was observed. The consistent presence of unreacted noble metal M after oxygen annealing is attributed to the formation of an oxygen-containing M-O-Si barrier which interferes with the silicidation reaction. Qualitative through-film and coupled film/substrate resistance measurements indicated that the M-O-Si barrier layers on the silicide substrates can be at least moderately conductive, a prerequisite for the use of these barrier-free electrode structures in high-density memory applications. We show how the above findings may be exploited in designing noble metal electrode structures suitable for perovskite-based memory devices.

3:00 PM *U6.4 
THE CHEMISTRY OF THE STRONTIUM-BISMUTH TANTALATE / PLATINUM INTERFACE. Christian D. Gutleben, Sony Corporation Research Center, Yokohama, JAPAN. We have known for some time now that residual Bismuth metal present in SrBi2Ta2O9 (SBT) thin films reacts strongly with Pt electrodes. In this talk we will provide a more detailed discussion of the chemical interactions which take place at the SBT/Pt interface. Clean polycrystalline SBT surfaces and SBT/Pt structures were prepared in-situ and examined by high-resolution XPS as a function of Pt coverage. The results show not only that Pt alloys with the residual Bi but also that it reacts disruptively with the SBT crystal to produce a Bi-deficient layer adjacent to the electrode together with a metallic Bi2Pt alloy smoothly graded into the Pt. These effects have a critical impact on both the mechanical and electronic (e.g. I-V) properties of the Pt/SBT interface. As illustration, we provide the valence-band to Fermi-level alignment of this contact from sub-monolayer to thick Pt overlayers.

3:30 PM U6.5 
COMPOSITION AND ELECTRODE EFFECTS ON THE ELECTRICAL PROPERTIES OF SBT. Darin T. Thomas, Norifumi Fujimura, S.K. Streiffer, and Angus I. Kingon, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC.

Strontium bismuth tantalate (SBT) has attracted great interest for non-volatile memory applications due to its minimal polarization fatigue. However, several major issues exist for this material and the electrodes used with it. Chief among these is the relatively high process temperature required to obtain adequate polarization values, which can lead to reactions with Pt electrodes. Therefore, even for physical deposition methods such as sputtering and pulsed laser deposition, a process procedure consisting of low temperature deposition followed by high temperature annealing is usually adopted. This paper describes systematic studies, using pulsed laser deposition, on the effect of film Bi content on the Bi-Pt reaction and on the potential for low temperature processing. The Bi content in the films can be controlled by changing the deposition temperature (Ts) and oxygen gas pressure during deposition. At a Ts of 600C, the films have excess Bi and do not fully crystallize to SBT, resulting in poor remnant polarization (Pr). These films consist mostly of the fluorite phase, plus a small amount of disordered, c-oriented layered perovskite SBT. By annealing over 750C, the films show improved Pr, but Bi precipitation and alloying with Pt is observed. At a Ts of 700C, the as-deposited films are fully crystallized and show saturated hysteresis loops. However, Bi deficiency through alloying results in reduced remnant polarization (2Pr 7.0C/cm2). Finally, alternative electrode configurations which do not react or alloy with the films will be described.

3:45 PM U6.6 
PREPARATION AND ELECTRICAL PROPERTIES OF FERROELECTRIC Pb-Nb-Zr-Ti-O CAPACITORS USING Ir / LSCO ELECTRODES. A.M. Dhote, P.P. Acharya, B. Yang, H. Li, T.K. Song, S. Aggarwal, L. Salamanca-Riba and R. Ramesh, Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD; B. White and R. Jones, Motorola, Austin, TX.

The growth of polycrystalline La-Sr-Co-O/Pb-Nb-Zr-Ti-O/La-Sr-Co-O ferroelectric capacitor heterostructure on Ir/SiO2/Si is demonstrated. Iridium provides the advantage of being a barrier layer for oxygen diffusion into the Si wafer. Incorporation of LSCO, in addition to being a structural template for PNZT, eliminates the possibility of reaction between PNZT and Ir at the interface and therefore eliminates the formation of the undesirable pyrochlore phase. The growth of the ferroelectric heterostructure is achieved at a low temperature in the range of 550-600{deg%%{degC, compatible with existing Si based technology. Transmission electron microscopy studies reveal no interface reaction when LSCO is used as the bottom electrode. Test capacitors show excellent ferroelectric properties and clearly reveal the beneficial effects of the LSCO layer.

4:00 PM U6.7 
EFFECTS OF SPUTTERED Ir AND IrO2 ELECTRODES ON THE PROPERTIES OF PZT THIN FILMS DEPOSITED BY MOCVD. Masaru Shimizu, Satoshi Hyodo, Seiji Nakajima, Hironori Fujisawa, Hirohiko Niu, Dept. of Electronics, Himeji Institute of Technology, Himeji, JAPAN; Hirotake Okino, Tadashi Shiosaki, Dept. of Electronic Science & Engineering, Kyoto University, Kyoto, JAPAN.

Ir and IrO2 thin film electrodes for PZT capacitors were prepared by rf magnetron sputtering using an Ir metal target. Highly (111)-oriented Ir and randomly-oriented IrO2 thin films were successfully obtained on SiO2/Si at deposition temperatures of 350-540C. An IrO2 ceramic as a target was also used to obtain IrO2 films for the first time. PZT thin films were prepared on these electrodes by MOCVD. The effects of the orientation and thickness of Ir and IrO2 bottom electrodes on the growth and electrical properties of MOCVD-PZT films were investigated. From interdiffusion analysis at the interface of PZT/Ir and PZT/IrO2 by SIMS, it was found that the interdiffusion of the PZT component was influenced by the film thickness of the electrodes. The effects of this thickness dependence on the electrical properties of the PZT capacitors and the characterization of interface by DLTS are also discussed.

4:15 PM U6.8 
DIELECTRIC PROPERTIES OF SPUTTERED BST ON IRIDIUM AND IRIDIUM OXIDE ELECTRODES. Bruce E. White, Jr., Peir Chu, Sufi Zafar, David Gentile, Robert E. Jones, Bo Jiang, Bradley Melnick, Deborah Taylor, Peter Zurcher and Sherry Gillespie, Materials Research and Strategic Technologies, Motorola, Austin, TX.

The dielectric constant and dispersion of sputtered barium strontium titanate (BST) thin films deposited on iridium and iridium oxide electrodes have been measured as a function of frequency and dielectric film thickness. Based on the measured variation in capacitance density with BST film thickness, an interfacial capacitance and thin film capacitance have been extracted. The variation of the interfacial capacitance density and the thin film capacitance density with frequency indicates that the majority of dispersion measured for BST deposited on Ir electrodes is due to the interfacial capacitance, in contrast to results found for Pt electrodes. The temperature dependence of the interfacial capacitance and thin film capacitance has also been measured for these electrodes. The implications of these results for charge storage using BST capacitors will be discussed.

4:30 PM U6.9 
MICROSTRUCTURE INVESTIGATIONS AND STRUCTURE-PROPERTY CORRELATIONS IN FERROELECTRIC THIN FILM CAPACITORS. H. Li, B. Yang, A. Dhote, S. Aggarwal, L. Salamanca-Riba and R. Ramesh, Materials Research Science and Engineering Center, University of Maryland, College Park, MD.

We report results of microstructure investigations of thin film ferroelectric capacitors, fabricated by pulsed laser deposition and sol-gel processing. These capacitors have been grown on silicon wafers with two types of bottom electrodes namely metallic (Pt or Ir) and metal oxide (LSCO). Epitaxial and polycrystalline films have been studied by transmission electron microscopy. In the case of heterostructures with oxide electrodes, we find no interface reaction at the Ir(or Pt)/LSCO interfaces as well as the LSCO/PZT interfaces, However, in the case of the PZT films grown directly on Ir surfaces, we find direct evidence for the formation of a second phase at the interface Using a combination of X-ray diffraction, electron microdiffraction and microanalysis, we have carried out detailed studies of the heterostructures as a function of electrode material, crystallinity and deposition conditions. In this paper, we report the details of microstructural characterization, and correlation to the processing conditions. This work is supported by the NSF MRSEC, Grant No. DMR 96-32521.

4:45 PM U6.10 
Ir ELECTRODES FOR FERROELECTRIC CAPACITORS. Sung Won Jung, Jaegab Lee, Jiyoung Kim, School of Metallurgical and Materials Eng., Kookmin University, Seoul, KOREA.

The electrode materials for ferroelectric capacitors should be carefully selected, because it gives impacts on ferroelectric characteristics (remnant polarization, coercive field, dielectric constant, leakage current, etc) and reliabilities (fatigue, imprint, retention, TDDB, etc). The most conventional electrode material for ferroelectric capacitors is Pt. However, the capacitor with Pt electrode exhibit a significant problem for fatigue issues. In addition, it is not easy to optimize the dry etch process for Pt electrodes. Recently, there are several alternative electrode materials, Among them, Ir an IrO2 have been attracted due to strong resistance against fatigue and relatively low leakage current(1). A few of papers have reported merits of the hybrid Ir/IrO2 electrodes which have been prepared by reactive sputtering. In this study Ir/IrO2 electrodes were prepared by furnace annealing. 200Nm Ir electrodes annealed at N2 and O2 using furnace and RTA. Both furnace and RTA oxygen annealing on metal Ir electrodes resulted in lower resistivity than that of as-deposited films and nitrogen annealed films. Those annealed films at the oxygen ambient exhibited clear Ir and IrO2 peaks in XRD indicating the presence of both Ir and IrO2. On the other hand, as-deposited and nitrogen annealed films showed only Ir phase. SEM pictures on the oxygen annealed films showed very fine grains (<0.1 m grain size). The oxygen profiles in both oxygen annealed Ir/IrO2 electrode and sputter-deposited hybrid electrode will be reported.

SESSION U7: POSTER SESSION: 
ELECTRODES AND BARRIERS 
Chairs: Seshu B. Desu and Randolph E. Treece 
Tuesday Evening, December 2, 1997 
8:00 P.M. 
Salons E-G (M)

U7.1 
PROPERTIES OF DIRECT CURRENT MAGNETRON REACTIVE SPUTTERED RUTHENIUM OXIDE ELECTRODES FOR PZT FERROELECTRICS. Buntha Ea-Kim, Francisco Ayguavives, Pascal Aubert, Francoise Varnière, Marie Christine Hugon, Bernard Agius, Laboratoire d'Etude des Matériaux en Films Minces, Université Paris Sud-Orsay, FRANCE; René Bisaro, Laboratoire Central de Recherches, Thomson-CSF, Orsay, FRANCE; Francois Abel, Groupe de Physique des Solides, Université VII, Paris, FRANCE.

Physical properties of conducting ruthenium oxide have been investigated using techniques such as in situ Optical Emission Spectroscopy (OES), Rutherford Backscattering Spectroscopy (RBS), Nuclear Reaction Analysis (NRA), X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM), in order to determine the suitability of this oxide as contact metallization of ferroelectric PZT. RuOx thin films have been deposited on SiO2/Si substrates by direct current magnetron reactive sputtering. At the target surface, oxidizing and sputtering processes are in competition leading to different O/Ru ratios in the films, During deposition, in situ OES has been used to follow the dependence of the atomic oxygen O* line intensity (emitted at 777.4 m) on O2/Ar ratios, correlated to the oxygen composition in thin films determined, with a precision of some percent, combining RBS and the 16O(3He,)15O nuclear reaction analysis techniques. In particular, the oxygen content in the films, even on oxygenated substrates SiO2/Si, can be measured using this nuclear reaction. From such investigations at different deposition parameters: total pressure, partial pressure of oxygen, substrate temperature, target-substrate distance, 100 nm thick RuO2 thin films have been obtained <100> oriented with a resistivity of about 40cm. They can be used as a suitable electrode for PZT thin films. After a Rapid Thermal Annealing (RTA), the RuO2/PZT/RuO2 capacitors exhibit good ferroelectric properties with high spontaneous polarization (Ps) and coercitive field (Ec) of about 40 C/cm2 and 60 kV/cm, respectively .

U7.2 
SYNTHESIS OF PHOTODEFINABLE RuO2 PRECURSOR FOR ELECTRODE CONTACTS. Kristen Law, Yvonne Spooner, TPL, Inc. Albuquerque, NM.

A new process for depositing and patterning RuO2 contacts for use in ferroelectric thin film capacitive devices is described. RuO2 has been shown to form a good contact interface with ferroelectric films such as lead-zirconia-titanate; leading to substantially lower fatigue and improved time-dependent breakdown properties compared to devices having platinum metal contacts. However, a lack of convenient processing technology has impeded the implementation of RuO2 in practical devices. A technique is described which incorporates the ease of spin-on deposition, combined with UV patterning to produce crystalline RuO2 films by a less damaging and less expensive process than plasma etching techniques. Three new ruthenium compounds containing photocrosslinkable organic groups have been synthesized which polymerize upon UV exposure. Pattern forming ability of the new precursors has been tested with the use of a simple straight line contact mask. The exposed portions of the precursor films are resistant to ethanol, acetone, and light abrasion. The formation of crystalline RuO2 upon organic pyrolysis was confirmed by x- ray diffraction. Synthesized ruthenium complexes were compared to commercially available ruthenium acetylacetonate and have shown improvement in pattern resolution and clarity.

U7.3 
GROWTH OF LASER ABLATED (SrLa)CoO THIN FILMS ON LaAlO, FUSED SILICA AND SILICON PLATES. J.M.Liu, F.Zhang, M.Wang, Z.G.Liu, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing, CHINA.

Thin films of (LaSr)CoO (LSCO) as oxide electrode for ferroelectric application were recently prepared by pulsed laser deposition. A problem to be overcome for such an application is the poor surface quality of the films. We report our AFM and TEM observations of surface morphology and growth mode of the laser ablated LSCO films on (100) silicon, fused silica and (001) LaAlO (LAO) substrates, respectively, with the optimized deposition conditions. The thin films were found to be well-crystallined, although their prefered orientations depended on the substrates. The cross section image of TEM revealed that the films consisted of columnar grains perpendicular to the substrate surfac. The AFM observations showed that the films on (100) Si achieved the finest grains and high surface quality, whereas the films on (001) LAO and fused silica plates had coarse grains and big surface fluctuations. A detailed analysis of the growth mode of the films on the three types of substrates has been presented.

U7.5 
REACTIVE ION ETCHING MECHANISM OF RuO2 FILM IN O2/CF4 ECR PLASMA. Eung-Jik Leea, Jong-Sam Kima, Jin-Woong Kimb, Ki-Ho Baikb, and Won-Jong Leea, aDept. of Materials Sci. Eng., KAIST, Taejon, SOUTH KOREA; bSemiconductor R&D Lab., Kyundat Electronics Co., Ichon, SOUTH KOREA.

Ruthenium dioxide (RuO2) has been extensively studied recently for the application to the electrode and the diffusion barrier material in ultra large scale integrated (ULSI) because of its high metallic conductivity, chemical stability, and etchability at room temperature. In this study, we investigated the reactive ion etching mechanism of RuO2 film in O2/CF4 electron cyclotron resonance (ECR) plasma. Etch rate of RuO2 were examined as a function of substrate temperature, DC bias applied to the substrate, pressure, and reactant gas flow rates. The etch products and their depth distribution were examined with x-ray photoelectron spectroscopy (XPS) and the concentrations of etching species žn the plasma were analyzed with optical emission spectroscopy (OES). In O2/CF4 plasma, RuO2 film reacts with oxygen radicals and ions to form volatile etch by-products, RuOx(x=3 4), and the formation rate of the by-Product determines the etch rate, i.e. the by-product formation is the etch limiting step. The formation rate of the etch by-product in O2/ CF4 plasma depends on the flux of oxygen radicals and ions arriving at the film surface. The oxygen radical concentration in O2/ CF4 plasma is sensitivity affected by the CF4 mixing ratio, and it shows maximum at CF4/(O2+CF4) ratio of 10% which in turn gives rise to the highest etch rate. The etch rate of the RuO2 film is also influenced by the energy of bombarding ions because they activate the formation reaction of etch products. In CF4 (no oxygen) plasma, the etching of RuO2 film is proceeded through the physical sputtering by energetic ion bombardment.

SESSION U8: Bi-LAYERED FERROELECTRICS 
Chairs: Randolph E. Treece and Rainer Waser 
Wednesday Morning, December 3, 1997 
Salon A/B (M)

8:30 AM U8.1 
STUDY OF C-ORIENTED FERROELECTRIC SrBi2Ta2O9 THIN FILMS USING RF MAGNETRON SPUTTERING. Z. J. Huang, Q. D. Jiang, P. Jin, C. L. Chen, A. Brazdeikis, H. H. Feng, A. Benneker, and C. W. Chu, Department of Physics and Texas Center for Superconductivity, University of Houston, TX.

C-oriented ferroelectric SrBi2Ta2O9 (SBTO) thin films have been synthesized by using rf magnetron sputtering technique on various substrates. X-ray diffraction, atomic force microscope (AFM), and scanning electron microscope (SEM) are used to study the influence of processing gas pressure, substrate temperature, and sputtering power density on the structure, composition, and surface morphology. Our results show that the temperature is critical in controlling the film orientation. AFM image shows very clean, uniform surface consisted of round and curved sheets. The height between two neighboring sheets is about 1.2 nm, half of the unit cell along c-axis, indicating sub-unit cell growth.

8:45 AM U8.2 
CRYSTALLIZATION MECHANISM OF FERROELECTRIC SBT THIN FILMS. Yuji Ikeda, Katsuyuki Hironaka, Chiharu Isobe, Sony Corp, Research Ctr, Kanagawa, JAPAN.

We characterize, via selected area electron diffraction and high resolution TEM, the multistage crystallization process by which SBT (SrBi2Ta2O9) thin films are transformed from initial amorphous phase to the fully formed layer-structured perovskite. During the annealing process at 800C, we found that an intermediate fluorite-like stage is formed after 3 minutes as the SBT precursor crystallizing into the final SBT structure. This new information will be very important for formation and crystallization of ferroelectric SBT films.

9:00 AM *U8.3 
REVERSIBLE AND IRREVERSIBLE CONTRIBUTIONS TO THE POLARIZATION IN SBT FERROELECTRIC CAPACITORS. Oliver Lohse, Rainer Waser, W. Hartner*, G. Schindler*, Institut für Werkstoffe der Elektrotechnik, RWTH, Aachen, GERMANY; *Siemens AG, Semiconductor Group, Munich, GERMANY.

This work presents a survey of the mechanisms of the polarization in ferroelectric thin films which are relevant for application in non-volatile ferroelectric memories (FeRAM). Since the integration of these materials in new memory generations requires small structures and therefore a maximum utilization of the switchable polarization, the distinction between the several polarization mechanisms is of special interest. Standard characterization methods, such as hysteresis loops, -V measurements and fast pulse switching tests are evaluated and used to distinguish between the reversible and irreversible contributions to the total polarization. The respective contributions are described qualitatively and demonstrated at spin-coated SrBi2Ta2O9 thin films and compared with Pb(Zr,Ti)O3 films. Additionally, a method is described to obtain the static hysteresis curve, a precise characterization of the polarization not dependent on the measuring frequency. These data are compared with -V measurements. It is shown, that the standard dynamic hysteresis curve reveals misleading statements about the remanent polarization and the coercive voltage.

10:00 AM *U8.4 
VARIATION OF FERROELECTRIC POLARIZATION PROPERTIES WITH TEMPERATURE IN SrBi2Ta2Og THIN FILMS. Yoichi Miyasaka, Takehiro Noguchi and Takashi Hase, Fundamental Research Laboratories, NEC Corporation, Kawasaki, JAPAN.

Ferroelectric polarization and its fatigue and imprint properties were evaluated in terms of temperature ranging 0 to 150C on SrBi2Ta2O9 thin films, which have attracted considerable attention as a promising material for high-density ferroelectric nonvolatile memories. Decrease in remanent polarization, Pr, with increasing temperature was fairly large on the films having stoichiometric Sr/Ta atomic ratio, even compared to that estimated from the Curie temperature reported on bulk ceramics This is attributed to fast polarization relaxation enhanced by the decrease in coercive field with increasing temperature. The decrease in Pr was fairly improved by modifying the Sr/Ta ratio to 0.8/2. On this composition the decrease within the measured temperature range was only 20%. In contrast to that the films showed almost no fatigue regardless of composition, imprint was significantly observed at high temperature region in a dynamic imprint test. Based on the results of single-shot hysteresis measurement, the imprint is attributed to the internal field induced by the applied unipolar pulses in the test. Although the imprint was observed regardless of composition, the films with modified Sr/Ta ratio can afford sufficient signal margin even after applying 109 imprint pulses, because they maintain relatively large ferroelectric polarization at high temperature region.

10:30 AM *U8.5 
(1-x)SrBi2Ta2O9-xBi3Ti(TaYNb1-y)O9 LAYERED STRUCTURE SOLID SOLUTIONS FOR FERROELECTRIC RANDOM ACCESS MEMORY DEVICES. P.C. Joshi, X. Zhang, S.O. Ryu, T. Sridhar and S.B. Desu, Dept. of Materials Science and Engineering, Virginia Tech, Blacksburg, VA.

Thin films of layered-structure solid-solid solution, (1x)SrBi2Ta2O9-xBi3Ti(TayNb1-y)O9, material have shown much improved ferroelectric properties compared to SrBi2Ta2O9; a leading candidate material for ferroelectric random access memory applications. The higher Pr, higher Tc, and lower crystallization temperature of the thin films of solid solution material promise to solve many problem with the present materials of interest. The films were fabricated by metalorganic solution deposition technique using room temperature processed alkoxide carboxylate precursor solution and characterized in terms of structural, dielectric, and ferroelectric properties. It was possible to obtain a pyrochlore free crystalline phase at an annealing temperature of 600C. The effects of annealing temperature and excess Bi content on the film microstructure and properties were analyzed. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors using Pt as the top and bottom electrode. The films annealed in the temperature range 650-750 C exhibited typical 2Pr and Ec values in the range 12.4-27.8C/cm and 68-84 kV/cm, respectively. The leakage current density was lower than 10 8A/cm2 at an applied electric field of 200 kV/cm. The films exhibited good fatigue characteristics under bipolar stressing at least up to 1010 switching cycles and good memory retention characteristics even after about 106 of memory retention indicating a favorable behavior for memory applications.

11:00 AM U8.6 
MOCVD OF SrBi2Ta2O9 FOR INTEGRATED FERROELECTRIC CAPACITORS. Bryan C. Hendrix, Advanced Technology Materials, Inc., Danbury, CT; Frank Hintermaier, Siemens, A.G., Munich, GERMANY; Debra Desrochers, Jeffrey Roeder, Thomas H. Baum, Peter Van Buskirk, Advanced Technology Materials, Inc., Danbury, CT; Christine Dehm, Nikolas Nagel, Wolfgang Honlein and Carlos Mazuré, Munich, GERMANY.

SrBi2Ta2O9 (SBT) is a promising material for ferroelectric random access memories (FERAM's) because of its inherently high resistance to fatigue and imprint. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformal SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise delivery of low vapor pressure precursors to the process. Precursor decomposition has been examined over a wide temperature range and the effects of process pressure have been examined. Several precursors have been evaluated and the respective processes were compared. The MOCVD process yields the fluorite phase which is transformed to the ferroelectric layered perovskite phase by annealing in oxygen. Dielectric constants () of 200 and remnant polarization (2Pr) up to 16 C/cm2 have been achieved on 150 mm wafers.

11:15 AM U8.7 
IN SITU, REAL TIME ANALYSIS OF THE GROWTH OF SrBi2Ta2O9 ON Pt/Ti ELECTRODES USING MASS SPECTROSCOPIES OF RECOILED IONS. J. Im, O. Auciello, A. R. Krauss, D. M. Gruen, Materials Science and Chemistry Div, Argonne National Lab, Argonne, IL; R. P. H. Chang, Materials Science Dep, Northwestern Univ,

Evanston, IL. The synthesis of ferroelectric thin films by sputter deposition typically requires a background ambient oxygen pressure of 5x10-4 Torr or greater. This background gas limits the use of most current surface analytical methods for the characterization of thin film surfaces during growth. Therefore, we have developed time-of-flight ion scattering and recoil spectroscopies (ToF-ISARS) and mass spectroscopy of recoiled ions (MSRI), which permit monolayer-specific surface analysis under the conditions appropriate for the growth of ferroelectric thin films. Using this technique, the composition, structure, surface segregation and impurities on the top most surface layer of the film can be monitored during growth at pressures up to several mTorr with isotopic mass resolution. In this paper, we present results of studies of SrBi2Ta2O9 (SBT) thin film growth on Pt/Ti/SiO2/Si substrate via ion beam sputter deposition. MSRI analysis of the Pt/Ti/SiO2/Si substrate prior to SBT deposition shows that titanium, silicon, and phosphorus from the n-type silicon substrate segregate to the surface of the top platinum layer when heating the substrate to the deposition temperature of 500600 C. Preliminary studies show a negligible concentration of bismuth but a high concentration of strontium, tantalum, and oxygen on the surface of the SBT film during the initial stages of growth at substrate temperature in the range of 500600 C. On the contrary, when the SBT thin film deposition is performed at room temperature, a strong bismuth signal is found on the growing surface. The implications of these results will be discussed in relation to the subsequent growth of the SBT films and the effect of the interfacial layer on the SBT composition, microstructure and properties.

11:30 AM U8.8 
METAL ORGANIC CHEMICAL VAPOR DEPOSITION OF FERROELECTRIC SrBi2Ta2O9 THIN FILMS. Kwang Bae Lee, Hyun Sook Lee, Kyung Woon Park, Tae Woo Kim, Mi Ran Lee, Sangji Univ, Dept of Physics, Wonju, Kangwondo, SOUTH KOREA; Chong Tak Kim, Sangji Jr College, Dept of Electronics, Wonju, Kangwondo, KOREA; Byung Kwon Ju, KIST, Div of Electronics and Information Technology, Seoul,SOUTH KOREA.

Ferroelectric SrBi2Ta2O9 (SBT) thin films were successfully prepared by means of the metal organic chemical vapor deposition (MOCVD) method. Sr(tmhd)2, Bi(Ph)3 and Ta(OC2H5)5 were used as the precursors for SBT. As-deposited SBT thin films were grown onto platinized silicon wafers at 450C. To get a ferroelectricity, rapid thermal annealing process was carried out at 800C for 30 min in an oxygen atmosphere. In the surface morphology of SBT thin films investigated by using a lateral force microscope, small grains and matrix are found for an as-deposited specimen, while only grains of about 150 nm diameter are found for an annealed specimen. The crystallinity was investigated by using X-ray diffraction (XRD) spectroscopy. While the amorphous halo peaks appear at 2=29 and 33 for as-deposited specimens, polycrystalline XRD patterns without any preferred orientation are found for annealed specimens. The optical gaps of SBT thin films deposited onto fused silica substrates were determined from the measurements of the optical transmission in the wavelength range of 250 to 1100 nm. The optical gaps for as-deposited and annealed SBT thin films are 3.1 and 3.4 eV, respectively. Such an increase of the optical gap by annealing is assumed to be due to the volatilization of Bi dunng annealing and the dense packing accompanied by the crystallization of SBT thin film. The ferroelectric properties, such as the remnant polarization (Pl) and the coercive field (Ec), were also measured by using a ferroelectric tester (RT 66A). For an annealed SBT thin film, Pr and Ec are 9 C/cm2 and 45 kV/cm, respectively, which can be varied slightly with the oxygen partial pressure in the rapid thermal annealing.

11:45 AM U8.9 
FERROELECTRIC THIN FILMS FOR Bi-CONTAINING LAYERED PEROVSKITES. Xiaofeng Du and I-Wei Chen, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA.

Ferroelectric thin films of Bi-containing layered perovskites, such as Bi4Ti3O12, PbBi2Nb2O9 and SrBi2Nb2O9 have been processed on Pi/Si substrates by metal-organic decomposition (MOD) method. By different heat treatment, films of random and c-orientation but with identical composition and thickness have been obtained. Nucleation control has been suggested as the mechanism for the texture evolution. A large anisotrophy of ferroelectric and dielectric properties has been observed which seems to be rooted in the two dimensionality of ferroelectricity in the crystal structure. Physical models have been proposed to systematically compare the polarization anisotropy and other properties of different layered perovskite structures.

SESSION U9: Pb-BASED FERROELECTRICS 
Chairs: Seshu B. Desu and Laura A. Wills 
Wednesday Afternoon, December 3, 1997 
Salon A/B (M)

1:30 PM U9.1 
AN OPTIMIZED PROCESS AND CHARACTERIZATION OF Pb(Zr,Ti)O3 FERROELECTRIC CAPACITOR FOR 1T/1C FERROELECTRIC RAM. Dong-Won Shin, Jin-Woo Lee, Hong-Bae Park, Soo-Ho Shin, Yoon-Soo Chun, Mi-Hyang Lee, Dong-Jin Jung, Yoo-Sang Hwang, Bon-Jae Koo, Sung-Young Lee, and Ki-Nam Kim, Samsung Electronic Co., Semiconductor R&D Center, Kyungki, KOREA.

An optimized process of Pb(Zr,Ti)O3(PZT) ferroelectric capacitor has been investigated in order to develop a highly scaleable 1T/1C ferroelectric RAM(Random Access Memory). The PZT ferroelectric capacitor, Pt/PZT/Pt stack, was formed on the TiO2/SiO2/Si substrate. The PZT thin films were prepared by conventional sol-gel multi-coating method. Physical and electrical properties of the PZT ferroelectric capacitors were characterized by SEM, TEM and RT6000S, respectively. It was revealed that the microstructure of PZT thin film is strongly influenced by sol-gel coating process, especially depending on coating methods of first PZT layer. The second phase was observed in the PZT thin films, which is found to be pyrochlore phase. The size and density of pyrochlore phase, which has low dielectric constant, were significantly reduced by modifying coating methods of first PZT layer. Microstructure of PZT thin flim capacitors were evaluated in detail along with electrical properties such as Pr(remanent polarization), coercive electric field, and dielectric leakage. The sensing Pr window was also introduced for proper sensing margin in 1T/1C ferroelectric RAM. This concept is well verified by 64Kb 1T/1C ferroelectric RAM.

1:45 PM U9.2 
CMOS COMPATIBLE FULLY INTEGRATED PZT CAPACITORS. Joseph T. Evans, Leonard L. Boyer, Robert I. Suizu, Geri Velasquez, Radiant Technologies, Inc., Albuquerque, NM.

The fabrication of high yielding ferroelectric capacitors on CMOS wafers is difficult due to the negative impact of post-capacitor process steps, especially the interlayer dielectric and metal interconnect sinter. Proper selection of the process for each layer of the capacitor structure is necessary to minimize hysteresis damage to the ferroelectric capacitors during their construction. Exploiting process steps developed and tested over a six year period, the authors fabricated integrated PZT capacitors on blank silicon wafers using liftoff processes for the top and bottom platinum electrodes and a combination titanium dioxide/silicon dioxide dielectric between the ferroelectric capacitors and the metal interconnect layer. A 15 minute nitrogen anneal at 450 degrees centigrade after the metal interconnect patterning did not damage the capacitor hysteresis loops. Statistical testing of over 700 capacitors for shorts indicated a defect rate of 127 defects per square centimeter. This is sufficiently low enough to generate a 50% yield in production 64Kbit double-sided-sense nonvolatile memory. At 3.5V the capacitors generated 14 microcoulombs per square centimeter with a standard deviation of 2.3 microcoulombs per square centimeter . The authors have set a target for future lots of 20 defects per square centimeter with 32 microcoulombs per square centimeter at 2.0V with standard deviation of 1.6 microcoulombs per square centimeter.

2:00 PM *U9.3 
NONVOLATILE, REVERSIBLE WRITING OF ELECTRONIC NANOSTRUCTURES IN EPITAXIAL FERROELECTRIC / METALLIC OXIDE HETEROSTRUCTURES USING A FIELD EFFECT. C.H. Ahn, T. Tybell, L. Antognazza, O. Fischer, J.-M. Triscone, University of Geneva, Département de Physique de la Matière Condensée, Geneva, SWITZERLAND; K. Char, Conductus Inc., Sunnyvale, CA; R.H. Hammond, M.R. Beasley, Department of Applied Physics, Stanford University, Stanford, CA.

Using scanning probe microscopy, we have written nonvolatile electronic nanofeatures in the metallic perovskite oxide SrRuO3.1 The structures were written in epitaxial thin film Pb(Zr0.52Ti0.48)O3 (PZT) / SrRuO3 heterostructures by locally switching the polarization field of the ferroelectric PZT layer with an atomic force microscope (AFM). The resulting field effect changes the sheet resistance of the SrRuO3 layer by up to 300 ohms per square. Using the AFM as an electric field microscope, it is also possible to visualize the charge distribution of the written areas on the PZT surface. Large areas of up to 100 m2 have been polarized and imaged with submicrometer resolution, with the smallest features having a linewidth of 1700 . This approach to local electronic doping is reversible and allows one to write nonvolatile submicrometer electronic features in two dimensions without lithographic steps or permanent electrical contacts required. Applications to ultrathin epitaxial films of the high temperature superconductors will be discussed.

3:00 PM *U9.4 
IS THERE A FUTURE FOR PbZr1-xTixO3(PZT) AS A STORAGE MEDIA? L.A. Wills, Jun Amano, R. Hiskes, S. A. DiCarolis, T. Hidaka*, T. Marayuma*, M. Saitoh*, C. M. Foster** and G.-R. Bai**, Hewlett-Packard Laboratories, Palo Alto, CA; *Hewlett-Packard Laboratories, Kawasaki, JAPAN; **Materials Science Division, Argonne National Laboratory, Argonne, IL.

PbZr1-xTixO3 (PZT) thin films have been studied for many years due to their large remanent polarization and relatively low coercive fields. Commercial FRAM devices are currently being produced with PZT ferroelectrics but are predicted to be replaced with the increasingly popular SrBi2Ta2O9 layered perovskite. While the future of PZT thin films in memory devices is uncertain, the large mechanical coupling coefficient in PZT may secure a long life in electro-mechanical devices. The potential use of PZT in ultra-high density recording media using a scanning probe microscopy (SPM)- based storage technology will be discussed.1,2 Storage densities of 290 Gbit/in2 were demonstrated with the PZT/SrRuO3/SrTiO3 material system.2 The structural and electrical properties of both tetragonal and rhombohedral PZT thin films, which are of interest for ultra-high density recording media applications, will be presented. Finally, there are some fundamental questions that remain unanswered in ferroelectrics; how they may impact the commercial viability of these materials will be presented for discussion.

3:30 PM U9.5 
RETENTION STUDIES ON FERROELECTRIC MEDIA FOR HIGH DATA STORAGE APPLICATION. In Kyeong Yoo, Byong Man Kim, Chang Jung Kim, Electronic Materials Lab., Materials Sector, Samsung Advanced Institute of Technology, Suwon, SOUTH KOREA.

Ferroelectrics are promising candidates for high data storage media. Despite of their potential, memory retention is not guaranteed yet. Depolarization of ferroelectric domain may be one of source for poor retention. Depolarization can be reduced by using top and bottom electrodes for the ferroelectric. However, bare top surface of ferroelectrics is required for data storage application. 
In this paper a multiyer structure of ferroelectric thin film in conjunction with dielectric structure of ferroelectric thin film in conjunction with dielectric film is proposed in order to reduce depolization effect. Polarization and depolarization mechanisms will be reviewed and the principle of ``read'' and ``write'' for the multilayer substrate will be discussed based on the above mechanisms. Finally, memory retention of this substrate will be demonstrate.

3:45 PM U9.6 
LOW VOLTAGE PERFORMANCE OF LEAD BASED FERROELECTRIC CAPACITORS THROUGH LATTICE ENGINEERING. S. Aggarwal, I. Jenkins, A.S. Prakash, T.K. Song and R. Ramesh, Department of Materials and Nuclear Engineering and Center for Superconductivity Research, University of Maryland, College Park, MD; Y. Kisler and S.E. Bernacki, Raytheon Company, Lexington, MA.

The evolution to a high density integrated circuit memory technology imposes low voltage switching and high speed operations of the ferroelectric capacitors. We report on novel, low voltage properties of lanthanum or niobium doped lead zirconate titanate (PZT) ferroelectric capacitors. These ferroelectric films sandwiched between lanthanum strontium cobaltite, (La0.5Sr0.5)CoO3 (LSCO) electrodes were epitaxially grown on yttria stabilized zirconia (YSZ) buffered Si, using a bismuth titanate template. These epitaxial capacitors exhibit much lower switching voltages ( 0.5V ) compared to what has been reported on other PZT systems. The ferroelectric properties of La or Nb doped PZT will be compared in terms of switching dynamics using electric force microscopy. Ferroelectric testing shows excellent fatigue, retention and imprint properties. Pulse width dependent measurements show that the low voltage performance is possible at widths less than 1 sec. The dramatic change in the switching behavior is tentatively attributed to the reduction in the c-axis lattice parameter (due to La, Nb substitution) and the consequent absence of 90 domain walls. This work is supported by the NSF-MRSEC.

4:00 PM U9.7 
IMPROVEMENT OF PZT FERROELECTRIC PROPERTIES BY LASER ANNEALING. Y.F. Zhu, J.S. Zhu, Y.J. Song and S.B. Desu, Department of Materials Science and Engineering, Virginia Tech, Blackburg, VA.

A novel method is developed for lowering the processing temperature of PZT films by using two low-temperature processes: (1) depositing PZT films with various Zr/Ti ratios by sol-gel technique, and annealing the films at low temperature of 475-530C to obtain perovskite phase by using conventional furnace; (2) laser annealing the films to improve their ferroelectric properties at room temperature. KrF excimer laser (248 nm) was used to annealing the PZT films. After laser annealing, the films displayed much better crystallized perovskite and ferroelectric properties. Our results show that the laser annealing can significantly improve crystallization of the perovskite phase, but is hard to directly transfer amorphous or pyrochlore PZT to pure perovskite phase, because the nucleation energy of perovskite phase is much higher than the energy needed to the grain growth, and the energy window between the nucleation energy of perovskite and ablation of PZT is very narrow.

4:15 PM U9.8 
THE EFFECT OF FORMING GAS TREATMENT ON LEAD BASED FERROELECTRIC CAPACITORS. S. Perusse, S. Aggarwal and R. Ramesh, Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD.

Lead based ferroelectric capacitors are currently being considered for non-volatile memory applications. One of the preferred materials for electrodes in these capacitors is Sr doped LaCoO3, or La0.5Sr0.5CoO3 (LSCO). One of the primary barriers to full integration of these ferroelectric capacitors into existing IC design is forming gas (4-10% H2/N2) treatment during manufacturing. We have performed a systematic series of experiments to determine the effects of forming gas treatment (FGT) on the individual layers of the FE stack. We deposited epitaxial lead based ferroelectric materials and LSCO on LaAlO3 substrates by pulsed laser ablation. FGT was performed between 350 C and 450 C for upto 1 hour. Preliminary x-ray diffraction studies show that after FGT, LSCO maintains its structural integrity. Electrical resistivity measurements indicate a small increase after FGT, which is consistent with the formation of oxygen vacancies. Experiments are also being performed on doped and undoped lead zirconate titanate ferroelectric materials.

4:30 PM U9.9 
PROPERTIES OF PTO/YBCO HETEROSTRUCTURE ON BARE SiC SUBSTRATES. M. Duan, J. Linnros, C.S. Petersson, Dept of Electronics, Royal Institute of Technology, Stockholm, SWEDEN; and K.V. Rao, Dept of Condensed Matter Physics, Royal Institute of Technology, Stockholm, SWEDEN.

Both lead base ferroelectrics and SiC are promising materials for high speed and radiation resistant applications. Integrated ferroelectrics on SiC wafer is an interesting topic for investigation due to its possible use in future high-density, non-volatile memories. Comparing with Si and GaAs substrates, SiC has very good chemical stability and would withstand the temperature for depositing the ferroelectric thin film without serious interdiffusion between them, which enable to integrate ferroelectrics on a SiC semiconductor circuit. This study will report the fabrication and characterization of PTO/YBCO capacitors on bare SiC substrates. The lead titanium oxide PbTiO3 (PTO) and high Tc superconductor Yba2CuO7-x (YBCO) capacitor heterostructures were prepared directly on 3C SiC substrates. X-ray diffraction analysis indicated that both PTO and YBCO layer were polycrystalline with perovskite phase. A zero-field cooling (ZFC) curve of YBCO with transition temperature Tc around 60 K was observed by a dc SQUID measurement, which confirmed the superconductivity of the YBCO layer. The ferroelectric properties of the capacitors were characterized by a RT66A apparatus and the ferroelectric hysteresis loops were obtained although somewhat degraded at high electric fields. There was no obvious fatigue being observed up to 1011 cycles.

4:45 PM U9.10 
ELECTRICAL PROPERTIES OF ANTIFERROELECTRIC THIN FILMS. K.Y. Oh, *J.H. Jang, *K.H. Yoon, J.S. Roh and J. J. Kim, Advanced Technology LAB, LG Semicon Co., Ltd., Cheongju, KOREA; *Yonsei University, Seoul, KOREA.

Various compositions of antiferroelectric Pb(Nb,Zr,Sn,Ti)O3 films were prepared by sol-gel process and their physical properties were investigated. It's been reported that some compositions of these antiferroelectric ceramics showed shape memory effects which could sustain the field induced ferroelectric phase even after removing the electric field. These kinds of shape memory effects may be applicable to non-volatile memory devices. Electrical properties, including P-E, C-V, retention and fatigue characteristics were investigated and crystal structures were also studied as function of composition and temperature variations. It showed typical properties of antiferroelectrics, morphotropic and ferroelectrics sequentially as increasing the titanium contents. The results of fatigue test showed more durable characteristics than that of typical ferroelectric films. It may be due to the 180 domain switchings of antiferroelectrics.

SESSION U10: POSTER SESSION: 
Bi-LAYERED FERROELECTRICS 
Chairs: Christopher M. Foster and Robert E. Jones 
Wednesday Evening, December 3, 1997 
8:00 P.M. 
Salons G-K (M)

U10.1 
SYNTHESIS AND CHARACTERIZATION OF WET-CHEMICALLY DERIVED STRONTIUM BISMUTH TANTALATE (SBT) THIN FILMS. J.T. Dawley, R. Radspinner, B.J.J. Zelinski, D.B. Hilliard, G. Teowee, and D.R. Uhlmann, Department of Materials Science and Engineering, University of Arizona, Tucson, AZ; Peir Y. Chu, Bradley M. Melnick, and Robert E. Jones, Jr., Advanced Materials Group, MRST, Motorola, Austin, TX.

Because of its fatigue resistance, large remnant polarization, and low coercive field, strontium bismuth tantalate (SBT) qualifies as a candidate for nonvolatile memory applications. It has been proposed that SBT's unique ferroelectric properties are a result of its layered perovskite structure, which controls the formation of defects that lead to fatigue, and creates a large spontaneous polarization due to the underbonding of bismuth atoms in the perovskite A site. Solution deposition techniques for SBT provide a fast and inexpensive means to evaluate a wide range of compositions and permit the control of composition and microstructure. Evidence in the literature on SBT synthesis indicates that the details of the synthesis route can have a major impact on film properties. In this work, the ferroelectric behavior of SBT films is characterized for several different solution synthesis routes, such as mixed carboxylate and alkoxide-carboxylate routes. Emphasis is placed on establishing relationships between synthesis route, microstructure, and ferroelectric properties.

U10.2 
CHARACTERIZATION OF SOL-GEL DERIVED SrBi2Ta2O9 THIN FILM ON PLATINUM ELECTRODE FOR HIGH DENSITY FRAM APPLICATION. Y. S. Choi, W.S. Kim, H.S. Song, C.E. Kim, YonSei University, Dept of Ceramic Engineering, Seoul, KOREA; W.S. Yoo, B.Y. Kim, Inchon University, Dept of Material Engineering, Inchon, KOREA.

The recent interest in the layered perovskite phase of SrBi2Ta2O9(SBT) as an alternative to PZT for nonvolatile ferroelectric memories stems from the reported negligible fatigue, low switching voltage, minimal tendency to imprint and relatively low dielectric constant, which can be advantageous especially for MFIS or MFMIS structure. However, relatively higher process temperature has been the main issue in the actual IC integration. In this paper, we report a new sol-gel processing method, the use of which results in lowering the crystallization temperature of SBT thin films. The microstructure and electrical properties in relationship to annealed temperature and the Sr deficiency and excess Bi content of SBT thin film were investigated. A reasonable Sol-Gel process and heat treatment window was defined to give acceptable ferroelectric and endurance properties of the layered perovskite films.

U10.3 
A THICKNESS DEPENDENT STUDY OF SrBi2Nb2O9 THIN FILMS. W. Pérez, E. Ching-Prado*, A. Reynés-Figueroa, R.S. Katiyar, D. Ravachandran+, and A. S. Bhalla+. Department of Physics, University of Puerto Rico, Río Piedras, PR; *Department of Applied Physics, Technological University of Panama, Tocumen-Panama, and Research Center of Nuclear Technique (CITEN)-University of Panama, PANAMA; +Materials Research Laboratory, The Pennsylvania State University, University Park, PA.

Thin films of SrBi2Nb2O9 (SBN) with thicknesses of 0.1, 0.2, 0.3 and 0.4 m were grown by Sol gel technique on platinum/silicon substrates, and annealed at 800oC. Raman spectra of the samples present bands around 60, 170, 210, 272, 300, 430, 580, 717, and 839 cm-1 which correspond to the SBN formation. The micro-Raman study indicates that the films are inhomogeneous. The prominent Raman band around 839 cm-1, which is the A1g mode of the orthorhombic symmetry, is assigned to the symmetric stretching of the NbO6 octahedrals. The frequency of this band is found to be different in different places in the same sample, as well as from sample to sample. In general, the frequency and width variations of the Raman bands are discussed in term of ions in non-equilibrium positions, which seems to be related with the crystallization degree in the SBN samples. Also, the Raman study indicates the presence of foreign sharp peaks, which are associated with the coexistence of other phases different than SBN. The thickness dependence of the Raman spectra and the X-ray diffraction are discussed. Also, the experimental results of the SBN/Pt/Si films grown at 800oC are compared with those obtained at 650oC. FT-IR and SEM techniques are also used for structural characterization.

U10.4 
RF-SPUTTERING DEPOSITION AND PROPERTY CHARACTERIZATION OF CaBi2Ta2O9 FERROELECTRIC THIN FILMS. P. Jin, Q.D. Jiang, Z.J. Huang, C.L. Chen, A. Brazdeiskis, A. Benneker, C.W. Chu, Department of Physics and Texas Center for Superconductivity, University of Houston, TX.

We have synthesized ferroelectric CaBi2Ta2O9 thin films using RF magnetron sputtering technique on various substrates. A systematic study of the deposition parameters on surface morphology, microstructures and compositions of thin films has been carried out by using x-ray diffraction, scanning electron microscope (SEM), and scanning probe microscope (SPM). Our result shows that the temperature of substrate plays an important role in controlling the orientation of the films. Particularly, c-orientated films can be grown on MgO(001), SrTiO3(001), Pt(001)/SrTiO3, and Pt(111)/Sapphire. Correlations of deposition parameters and microstructures with ferroelectric properties of thin films are discussed.

U10.5 
SURFACE MORPHOLOGY AND MICROSTRUCTURES OF FERROELECTRIC MBi2Ta2O9 (M=Ca, Sr) and BaTiO3 OXIDE THIN FILMS. Q. D. Jiang, Z. J. Huang, P. Jin, C. L. Chen, A. Brazdeikis, A. Benneker and C. W. Chu, Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX.

We have made a comparative investigation of surfaces of epitaxial grown MBi2Ta2O9 (M=Ca, Sr) and BaTiO3 ferroelectric thin films, using scanning probe microscopes. The crytsallinity and microstructure of thin films are characterized with X-ray diffraction and pole figure measurements. Thin films are deposited by RF sputtering onto well-oriented (001) and vicinal SrTiO3 surfaces exhibiting atomic flat terraces. Morphology of MBi2Ta2O9 thin films consists of round and curved sheets. The averaged diameter of sheets is around 100 nm, while the step size of two neighboring sheets is about half of the c-lattice constant of MBi2Ta2O9 unit cell, indicating a non-unit cell growth mode and reflecting double Bi2O2-layered crystal structure. The surfaces of BaTiO3 thin films deposited at various temperatures display uniform granular grains of 100 nm. Dependency of dielectric and ferroelectric properties on the microstructures of films are discussed.

U10.6 
EVALUATION OF SrBi2.2(NbxTa1-x)2.0O9.0 CAPACITORS FABRICATED BY SELF-PATTERNING PROCESS. Hiroto Uchida, Tsutom Atsuki, Nobuyuki Soyama, Kensuke Kageyama, Katsumi Ogi, Joe D. Cuchiaro*, Larry D. McMillan* and Carlos A. Paz de Araujo*, Central Research Institute, Mitsubishi Materials Corp., Saitama, JAPAN; *Symetrix Corp., Colorado Springs, CO.

Self-patterning process is a selective etching technique to pattern the ferroelectric layer without artifacts on non-planer topographies as CMOS. Conventional spin-on films usually have planarizing character on non-planer topographies and have a film thickness difference due to the position of the structure. Under etching or over etching problems caused by non-selectivity like ion-milling is a major concern. Various size SBNT capacitors down to 2x2 m2 were fabricated from the self-patterning process using photosensitive solution. UV irradiation and self-patterning both effect the film morphology and capacitor performance were evaluated. UV irradiation in the self-patterning process densifies the ferroelectric film which enables us to obtain void free films and evaluate them.

U10.7 
ELECTRONIC STRUCTURE, DEFECTS AND SURFACE PROPERTIES OF SrBi2Ta2O9 AND RELATED OXIDES. J. Robertson, C.W. Chen, Engineering Dept, Cambridge University, Cambridge, UNITED KINGDOM.

The electronic structure of SrBi2Ta2O9 and related oxides such as SrBi2Nb2O9 and Bi3Ti4O12 have been calculated by the tight-binding method. In each case, the band edge states occur on the Bi-O layers and consist of mixed O p/Bi s states at the top of the valence band and Bi p states at the bottom of the conduction band. The main valence band consists of O p states with some Ta (Ti) d admixture, while most Ta (Ti) d states lie in the conduction band. The band gap lies around 4 - 4.2 eV in each case. The main difference between the compounds is that the Nb d and Ti d states lie lower than the Ta d states in the conduction band. The effects of these differences are calculated for the defect states. The surface pinning levels which determine the Schottky barrier heights for metal contact are also calculated.

U10.8 
CRYSTALLIZATION AND ELECTRICAL PROPERTIES OF Bi4Ti3O12 FILMS DERIVED FROM BISMUTH ACETATE AND NITRATE PRECURSOR SOLUTIONS, Chang Jung Kim, C.W. Chung, D.S. Kim, Electronic Materials Lab., Samsung Advanced Institute of Technology, Suwon, SOUTH KOREA.

Ferroelectric Bi4Ti3O12 thin films were fabricated to examine the effect of precursors on crystallization and ferroelectric properties by metalo-organic decomposition (MOD) method with two different bismuth precursors. Bismuth acetate- and nitrate-derived precursor solutions were synthesized by dissolving bismuth acetate and bismuth nitrate in glacial acetic acid and then adding titanium acetate. Films were deposited on Pt coated Si substrate by spin-coating method and crystallized by two step heat-treatments. Surface morphology and crystallographic phase of the films prepared by two precursor solutions were studied by SEM, atomic force microscopy (AFM), and X-ray diffraction. The ferroelectric characteristics of the films were investigated using standardized ferroelectric test systems.

SESSION U11: POSTER SESSION: 
Pb-BASED FERROELECTRICS 
Chairs: Christopher M. Foster and Robert E. Jones 
Wednesday Evening, December 3, 1997 
8:00 P.M. 
Salons G-K (M)

U11.1 
FREQUENCY SPECTRA OF POLARIZATION FATIGUE OF PZT AND OTHER FERROELECTRIC THIN FILMS. Xiaofeng Du and I-Wei Chen, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA.

The effect of fatigue frequency on polarization degradation of (100) oriented PZT and other ferroelectric thin films with platinum electrodes has been investigated. Unlike the standard practice of measuring D-E loops at 60 Hz, special attention has been paid to the hysteresis loop measurements at high frequencies in order to ascertain the switchability of ferroelectric thin films for fast circuit applications. Despite the previous reports that polarization degradation is less severe when fatigued at high frequency, we found the high frequency polarization in PZT to be vulnerable to fatigue at all frequencies. Parallel permittivity measurements also show a loss of high frequency polarizability. Electrical overvoltage stressing and thermal annealing have no rejuvenation effect on the high frequency component of polarization. These results are further quantified by the evolution of coercive field during fatigue modeled using a picture of domain wall movement that is thermally activated. By comparing the threshold field with the applied field, a methodology for fatigue prediction can be developed that applied to all frequencies.

U11.2 
EFFECT OF HEAT TREATMENT PROFILE ON THE PHASE DEVELOPMENT OF PZT THIN FILMS IN RF-SPUTTERING. Il-Woong Koo, Myung-Sik Park, Joon-Hyung Lee, and Sang-Hee Cho, Kyungpook National Univ., Dept. of Inorganic Materials Engineering, Taegu, Korea; Kwang-soo No, Korea Advanced Institute of Science and Technology, Dept. of Materials Science and Engineering, Taejon, KOREA.

In this study, three differnent thermal annealing profiles of in-situ, RTA (rapid temperature annealing), and IPA (in-situ post-annealing) were employed for preparing perovskite phase PZT thin films by rf-magnetron sputtering process, and the evolution of phase development was studied. The RTA was done in a furnace, so the sample was taken out from the chamber after sputtering. Therefore, the IPA had a benefit that can avoid contaminations from the air and other various contamination sources during installing the sample in a furnace and annealing. As a result, in the RTA process, 100% of perovskite phase was formed at 570°Š and 700°Š of substrate and annealing temperature respectively. However, IPA process showed the lowest processing temperature that revealed 100% perovskite phase at 400°Š and 570°Š for substrate and annealing temperature, respectively.

U11.3 
SPACE CHARGE AND CONDUCTION OF RF-SPUTTERED PZT THIN FILMS. Alexandr Zakharov, Evgeny Rogatch, Evgeny Sviridov, Rostov Univ, Inst of Physics, RUSSIA.

Application of ferroelectric PZT thin films is impossible without studing of electroconduction and space charge effects in direct or alternating electric fields. In this work the current-voltage characteristics, relaxation processes of conduction of the film were studied and explained in terms of space-charge-limited-currents (SCLC) theory developed for semiconductors . Ferroelectric thin PZT films were prepared by RF-sputtering in oxygen plasma, which is assumed to suppress the generation of oxygen vacancies. Decreasing of concentration of oxygen vacancies results in low value of electroconductivity of the film (=0.72Ohmcm)-1). The value of electroconductivity evaluated from space charge relaxation time (t=50 sec) was not in a disagreement. It is shown that the temperature dependence of electroconductivity in the range from T=20ƒC to T=100ƒC indicates the extrinsic nature of conduction with impurity energy level Ei=0.8 eV. Also t

U11.4 
ELECTROLYTIC DEPOSITION OF PZT FILMS. Igor Zhitomirsky, Leah Gal-Or, Technion, Israel Inst of Metals, Haifa, ISRAEL.

Ferroelectric thin films have important applications in electronic devices. Recently, a great deal of interest has been generated in the field of electrolytic deposition of ferroelectric films, mainly due to the following advantages of the process: low processing temperature, low cost of starting materials and equipment, rigid control of deposition rate, deposit thickness and uniformity, possibility of deposition on substrates of complex shape as well as on selected areas of the substrate. In the cathodic electrodeposition process a metal ion or complex is hydrolyzed by electrogenerated base to form a deposit on the cathodic substrate. A new approach to the deposition of complex ferroelectric compounds, based on peroxoprecursors, has been developed by the authors. The problem of titania electrodeposition from aqueous solutions was solved by use of a titanium peroxocomplex. Hydrolysis of the peroxocomplex by electrogenerated base resulted in deposition of the corresponding peroxocompound, thermal decomposition of which resulted in the formation of titania films. The important finding was that complex oxide compounds such as ZrTiO4 can be deposited via a corresponding peroxoprecursor. The proposed method for the deposition of ZrTiO4 can be considered as a key step to the deposition of PZT films. Electrodeposition of PZT films via the peroxoprecursor route was achieved on various conductive substrates, including Pt,platinized silicon wafers (Si/SiO2/Ti/Pt), graphite, carbon fiber mats. The films were characterized by XRD, TGA, DTA, SEM, EDS, Auger and other methods. Results of X-ray studies and thermal analysis show that ZrTiO4 and PZT crystallized directly from the amorphous phase, no phase separation was observed. Formation of a perovskite PZT phase was observed at 500circC. The use of peroxoprecursor allows complex oxide compounds of desired stoichiometry to be obtained. By variation of current density and deposition time the amount of the deposited material could be controlled. The electrodeposition process has been quantified in experiments performed with Pt substrates. PZT thin films were deposited as monolayers or multilayers. Possible cathodic reactions which underlie the base generation and the role of hydrogen peroxide in the deposition process are discussed. Obtained results have practical importance for the development of ferroelectric PZT films and composite materials for various applications.

U11.5 
DIELECTRIC AND FIELD-INDUCED POLARIZATION BEHAVIORS IN (1-X)PbZrO3-(X)BaTiO3 THIN FILMS PREPARED BY SOL-GEL PROCESS. Jeong Hwan Park, Ki Hyun Yoon, Yonsei Univ, Dept of Ceramic Engineering, Seoul, KOREA; Dong Heon Kang, Suwon Univ, Dept of Electronic Material Engineering, Suwon, KOREA

Dielectric and field-induced polarization behaviors in the (1-x)PbZrO3-(x)BaTiO3 thin films prepared by sol-gel process have been investigated as a function of x. The dense PZ-BT thin films with only perovskite phase were obtained by heat-treating at 700 C for 10 minutes. The antiferroelectric to ferroelectric phase transition field was decreased due to disruption of the long ranged antipolar order as the amount of x increased. Nonlinearities in the dielectric properties were observed in the range of x from 0.05 to 0.1, indicating the region of antiferroelectric-ferroelectric phase boundary. The x=0.05 specimens show the maximum Ps and Pr values which were 45C/cm2 and 31C/cm2, respectively.

U11.6 
MULTIWAFER MOCVD REACTORS FOR THE MASS PRODUCTION OF FERROELECTRIC DEVICES. M. Deschler, B. Schulte, D. Schmitz, G. Strauch, and H. Jürgensen, AIXTRON GmbH, Aachen, GERMANY.

The need for ferroelectric capacitors and FRAMs is rapidly increasing as world wide communication networks are being erected and a higher interpretation of memory chips will be introduced in the next few years. To meet the demand for economical production of thin film structures of ferroelectrics, we developed a metalorganic vapor phase epitaxy (MOVPE) reactor for the deposition of the material films on a large substrate area. We expanded the existing Planetary ReactorsR to be able to take charges of nine six inch wafers or the equivalent (total substrate area of 0.25 square meters). The development of growth processes was supported by numerical simulations. The Planetary ReactorsR is a proven tool in mass production environments for the growth of compound semiconductors. A major achievement is the compensation of the depletion of the gas phase which can result in poor uniformity of the films. By rotating the wafers, the growth rate along the direction of flow is averaged to produce uniform films with a variation of less than 1.5% in composition and +3% in thickness across an area with a diameter of 10 inches. Results on the single wafer reactor (I x 6'') for PZT thin films and the transfer of the process to the mass production scale reactor will be presented.

U11.7 
SUPPRESSION OF THE TETRAGONAL DISTORTION IN THIN Pb(Zr,Ti)O3 FILMS GROWN ON MgO(001). D. Y. Noh and H. C. Kang, Dept of Materials Science and Engineering, and Center for Electronic Materials Research, Kwangju Institute of Science and Technology, Kwangju, KOREA; J. H. Je, Dept of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, KOREA; H. K. Kim, Dept of Physics, Pusan National University, Pusan, KOREA.

The paraelectric cubic to ferroelectric tetragonal phase transformation of thin Pb(Zr,Ti)O3/MgO(001) films was studied in synchrotron X-ray scattering experiments. In the thin epitaxial films, the tetragonal distortion in the ferroelectric phase and the transition temperatrue were significantly suppressed. In sharp contrast to the reported mixture of the a-type and the c-type domains in thicker films, the 250 thick film was purely composed of the c-type domains in the tetragonal phase. We attribute the suppression of the transition to the substrate effect that prefers the c-type domains near the interface, and reduces the tetragonal distortion to minimize the film-substrate lattice mismatch.

U11.8 
EPITAXIAL PbZr0.52Ti0.48O3/YBa2Cu3O7-x/(Y,Nd)AiO3 THIN FERROELECTRIC FILM CATHODES. Alex Grishin, Masaaki Yamazato, Yukihiko Yamagata, Kenji Ebihara, Department of Electrical and Computer Engineering, Kimamoto University, Kumamoto, JAPAN.

Recent advances in technology have enabled distinct breakthrough in new ferroelectric thin film applications interesting both in the study of fundamental physics and microelectronics. One of them is the ability to fabricate high efficient electron cathodes based on thin film conductor/ferroelectric oxide capacitors. Epitaxial thin ferroelectric film cathodes have several stong advantages comparing with their polycrystalline bunk ceramic counterparts: much higher electrical performance and low voltage operation ability. AuPbZr0.52Ti0.48O3(4OO nm)/YBa2Cu3 O7-x(200 nm) thin film cathodes, made by KrF pulsed laser deposition on the single crystal YAlO3:Nd substrates, have been found to be single phase, highly c-axis oriented, and strongly textured in (a, b) plane. They are possessed of high dielectric constant = 920, low loss (100 Hz) = 0.05, low leakage current density and no visible fatigue after 107 switching. Our theoretical study shows that during ferroelectric film switching the effect of strong electron pumping (SEP) in the top metallic electrode occurs. The main attributes of SEP phenomenon are the following: creation of a thin dense electron sheath on the top electrode-ferroelectric interface during ferroelectric charging, its acceleration by a non-uniform electric field after ferroelectric switching and the following electron avalanche on the top electrode-vacuum interface; enhancement of the Coulomb screening and a blockage of electron energy relaxation in the degenerate electron liquid. Furthemore, theory explains high current density, which is 1-2 orders greater than in thermodynamic equilibrium Child-Langmuir regime, as well as the appearance of extremely energetic emitted electrons. Experimental results on electron emission from epitaxial PZT/YBCO/YAlO heterostructures will be presented: nanosecond pulsed emission, retardation effects and the field dependence of switching time.

U11.9 
SUPERIOR-QUALITY EPITAXIAL YBa2Cu3O7-x/PbZr0.52Ti0.48O3 THIN FILMS HETEROSTRUCTURES ON YAlO3:Nd SUBSTRATES. Alex Grishin, Hiromitsu Kurogi, Yukihiko Yamagata, Kenji Ebihara, Department of Electrical and Computer Engineering, Kumamoto University, JAPAN.

Recently we optimized processing conditions to grow high quality thin YBa2Cu3O7-x / PbZr0.52Ti0.48O3 bilayers on MgO () substrates by KrF pulsed laser deposition technique. High degree of c-axis orientation, the critical temperature of Tc = 90.5 K and the current density of jc = l06 A/cm2 in YBCO template layer as well as relatively low loss (100 Hz) = 0.12, high dielectric constant of = 805 and remanent polarization of Pr = 24 C/cm2 indicate excellent characteristics of coexisting superconducting and ferroelectric properties. Nevertheless, low capacitor yield and high scattering of its electrical performance remain a principal problem.

8:30 AM *U12.1 
MICROWAVE APPLICATIONS OF FERROELECTRIC THIN FILMS. D.B. Chrisey, J.S. Horwitz, A.C. Carter, and W. Chang, Naval Research Laboratory, Washington, DC.

Low loss ferroelectric thin films are currently being developed at NRL for use as the active element in a low phase noise voltage controlled oscillator (VCO). The ferroelectric thin films are deposited by pulsed laser deposition and their dielectric properties, such as capacitance, tuning, and loss, are evaluated at frequencies between 1 and 20 Ghz. Thin films of SrxBa(1-x)TiO3 are being used for the construction of the low phase noise VCO (1.5 - 2.5 Ghz) because their bulk properties include low loss, high tunability, and a Curie temperature which can be varied about room temperature. Single phase and oriented films have been deposited onto (100) LaAlO3 and MgO substrates and onto single crystal Ag films. The temperature and electric field dependence of the dielectric constant and the dissipation factor have been measured at 1 MHz. A 75% change in the capacitance can be achieved using a 40 V bias across a 5 µm interdigitated capacitor gap (80 kV/cm). The dissipation factor depends on film composition (the ratio Sr to Ba) and temperature. A loss tangent as small as 1.25 x 10-2 has been measured at microwave frequencies (5 Ghz). The overall success of this effort will require an understanding of the relationship between thin film processing, microstructure, and dielectric loss. A summary of recent progress in ferroelectric thin film microwave characterization will be presented.

9:00 AM *U12.2 
FREQUENCY TUNABLE BANDREJECT FILTERS USING PLANAR YBCO/Sr/TiO3 STRUCTURES. M.W. Cromar, G.A. Koepf, R.M. Yandrofski, Z. Zhang, L. D'Evelyn, M. Heiny, T. Rivkin, M. Rivkin, D. White, X. He, J.B. Thompson, D. Galt and R.E. Treece,* SCT, Inc., Golden, CO.

The performance and effectiveness of military and commercial receivers can be degraded by unwanted signals. Tunable bandreject filter banks comprised of YBCO/SrTi03 structures have been developed to attenuate these signals, thus preserving receiver sensitivity and communication link integrity. Changing the DC bias applied to the SrTi03 film changes the dielectric constant of the film resulting in a very rapid change in the center frequency of the filter. Multi-pole filters with good rejection over a tuning range of several percent of the center frequency have been fabricated and tested. The tuning, rejection, and Q of one-pole filters have been modeled. Measurements of the filter characteristics and descriptions of the tuning models will be presented.

10:00 AM *U12.3 
FIELD TUNABLE DIELECTRIC THIN FILMS FOR MICROWAVE ELECTRONICS. Mark J. Dalberth, Renaud E. Stauber, John C. Price, Charles T. Rogers, Department of Physics, University of Colorado, Boulder, CO; and David Galt, SCT, Inc., Golden CO.

Electric field tunable dielectric materials have significant potential for application to tunable electronics in the microwave frequency region. We have been studying the effect of growth conditions and substrate choice on the microwave dielectric properties of thin film Strontium titanate (STO) and related materials, grown by pulsed laser deposition. We will report the dielectric properties of such films grown primarily on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. Coplanar Ti/Au capacitor structures are fabricated on the films to allow measurement of the complex dielectric function vs. frequency, temperature, and electric field strength. Finished capacitor structures are diced to standard size and then indium-alloy soldered onto a microwave ring resonator. We extract the complex dielectric function near 2 GHz by comparison of the tuning and loss behavior of two nearby resonant modes (only one of which is sensitive to the tunable capacitor). The structure also allows for simultaneous measurement of lower frequency dielectric response (10 kHz to 1 MHz). Film dielectric properties, their relationship to film structure, and prospects for application to microwave electronics will be discussed.

10:30 AM U12.4 
MOCVD OF ALKALINE EARTH TITANATES FOR INTEGRATED RF CAPACITORS. Gregory T. Stauf, Charles G. Seegel, Advanced Technology Materials, Danbury, CT; R.K. Watts, H.M. O'Bryan, Bell Laboratories, Lucent Technologies, Murray Hill, NJ.

Development efforts at ATMI and elsewhere on metalorganic chemical vapor deposition (MOCVD) of BaSrTiO3 (BST) thin films were until recently focused on their use for DRAM capacitors. BST also has the potential to replace discrete ``passive'' capacitors used in portable and wireless applications with integrated capacitors. Bringing thin film devices directly onto Si and GaAs chips shortens lead length and improves overall circuit Q values by reducing inductance, important at RF frequencies. We will discuss the electrical properties of BST thin films which make them suitable for these high frequency applications, as well as the impact of processing conditions on specific film properties. Major processing variables include growth temperature, stoichiometry, and film thickness. By modifying the basic BST stoichiometry, we have demonstrated charge storage densities up to 3,000 nF/cm2 with leakages below 10-8 A/cm2 at 3 V, and second order dielectric nonlinearities below 100 ppm/V2. Q factors are as high as 500 at kHz frequencies, and evidence suggests that low losses can be retained up through the L and S microwave bands (1-4 GHz). These properties make alkaline earth titanate films suitable for use in decoupling and bypass capacitors, as well as switched capacitor filters.

10:45 AM U12.5 
MICROWAVE TUNING QUALITY AND POWER HANDLING OF VOLTAGE-TUNABLE CAPACITORS:SEMICONDUCTOR VARACTORS vs Ba1-xSrxTiO3 FILMS. D. Galt, T. Rivkina, M. Cromar, SCT Inc., Golden, CO.

Thin films of SrTiO3 and Ba0.4Sr0.6TiO3 have been pulse laser ablated onto LaAlO3 substrates. Normal metal coplanar capacitor electrodes were patterned on top of these films and the capacitors were incorporated into weakly coupled microstrip resonators. Resonant frequencies and Q's were measured as a function of bias at room temperature and at 77 K. The microwave frequency capacitance and loss is calculated from the resonant properties and compared with the simultaneously measured 1 MHz capacitance and dissipation. Two-tone intermodulation distortion products were measured and the third-order intercept is referenced to the microwave voltage across the capacitors. Commercially available semiconductor varactors were tested in a similar manner. Tuning quality (the ratio of the relative capacitance tuning to dissipation), frequency dispersion, and power handling of these capacitors is compared.

11:00 AM U12.6 
THE EFFECTS OF ANNEALING AT 1350 C AND COMPOSITION ON THE DIELECTRIC PROPERTIES OF THIN FILMS OF BaxSrzTiO3. Adriaan C. Carter, Wontae Chang, Patricia Loferski, James S. Horwitz, Steven W. Kirchoefer, Jeffrey M. Pond, Douglas B. Chrisey, Naval Research Laboratory, Washington DC.

High quality, thin films of BaxSr1-xTiO3 (BST) were deposited by pulsed laser deposition (PLD) on to single crystal substrates of (100) MgO, (012) LaAlO3, and (100) SrTiO3 followed by annealing in O2 from 1000 C to 1350 C. Silver interdigitated capacitors were patterned on top of the ferroelectric films. The temperature dependence of the capacitance and dissipation factor of the films were measured as a function of bias electric field ( 80 kV/cm) at 1 MHz. Room temperature capacitance and loss measurements as a function of bias electric field ( 80 kV/cm) have also been measured at 1 - 20 GHz. Post deposition annealing significantly reduced dielectric loss and increased the change in capacitance with electric field. However, annealing above 1250 C and annealing for times longer than 2 hours only gave marginal reductions in dielectric loss and marginal increases in dielectric tuning. Chemical analysis studies on films deposited from stoichiometric targets showed the films to be up to 6 deficient in Ba and Sr at typical PLD deposition temperatures (750 C). BST films deposited from targets compensated with excess Ba and Sr showed a 2-fold reduction in dielectric loss while maintaining a 2 to 1 tuning ratio for the capacitance. The physical mechanisms involved with the effects of annealing and non-stoichiometry will be discussed.

11:15 AM U12.7 
NONLINEAR OPTICAL FILMS OF KTN GROWN BY PULSED LASER DEPOSITION ON GaAs FOR INTEGRATED OPTICS. L.A. Knauss, K.S. Harshavardhan, Neocera Inc, Beltsville, MD; H.Y. Zhang, X.H. He, Y.H. Shih, Dept of Physics, Univ of Maryland at Baltimore County, Baltimore, MD.

Nonlinear optical (NLO) components form the basic building blocks of the information technologies of the future. NLO films on GaAs and other III-V (AlGaAs, InGaAs) semiconducting substrates have many potential applications in integrated optics. With the thin film approach it is possible to develop an integrated optics technology in which light sources, nonlinear optical components and detectors may be developed on the same substrate. At present, the growth of device quality films on GaAs remains a major technological challenge. Using Pulsed Laser Deposition (PLD) epitaxial films of prototypical nonlinear KTa0.52Nb0.48O3 (KTN) were successfully developed on single crystalline GaAs substrates for the first time. In order to alleviate chemical and structural incompatibilities between the GaAs substrate and KTN films at the growth temperatures (750C), a novel buffer layer scheme consisting of epitaxial MgO and SrTiO3 buffer layers was successfully developed during this effort. To obtain films with the required stoichiometry, a segmented target geometry was used consisting of KTN and KNO3 targets. The high crystalline quality of KTN films on GaAs was established by detailed 4-circle x-ray diffraction studies. Rutherford Backscattering studies confirmed the composition of the films.Optical measurements have been carried out on epitaxial KTN films on GaAs. Using an Ar+ laser (457.9 nm) operating in the TEM00 mode, we have observed sharp and distinguishable TE and TM propagating modes in KTN films. The refractive index (no) of the film at 488 nm is 2.275 which is close to the bulk value of 2.35. In this presentation, we will discuss the epitaxial growth aspects of KTN films on GaAs and summarize our preliminary optical data.

11:30 AM U12.8 
PZT ELECTROOPTIC WAVEGUIDE DEVICES FABRICATED BY SOLID-PHASE EPITAXY. Keiichi Nashimoto, Shigetoshi Nakamura, Hiroaki Moriyama, Masao Watanabe, Eisuke Osakabe, Optical Devices Laboratory, Fuji Xerox Co. Ltd., Kanagawa, JAPAN.

High quality epitaxial PZT optical waveguides have been grown by solid-phase epitaxy based on metal alkoxide solution process. Optical propagation loss as low as 4 dB/cm was achieved in epitaxial PZT thin film optical waveguides on insulative SrTiO3 substrates. Optical waveguides on conductive substrates, however, seems to be more attractive than those on insulative substrates in terms of electrooptic device applications. Considerable reduction in drive voltage will be expected when top electrode / optical waveguide / conductive substrate structures are realized. In the present study, epitaxial PZT optical waveguides were grown on Nb doped conductive SrTiO3 substrates by solid-phase epitaxy. Waveguide modes were observed by prism coupling technique in PZT optical waveguides on lightly Nb doped SrTiO3 substrates. Propagation loss was relatively large due to free carrier absorption in Nb doped SrTiO3 substrates, as compared with the structure using non-dope insulative substrates. Electrooptic deflection devices were fabricated by preparing prism electrodes on the surface of the PZT optical waveguides. Efficient deflection/switching of coupled laser beam in the PZT optical waveguides was observed by applying voltage between prism electrode and Nb doped SrTiO3 substrates.

11:45 AM U12.9 
EPITAXIAL FERROELECTRIC PLZT/MgO MULTILAYERS ON GaAs GROWN BY PULSED LASER DEPOSITION FOR SPATIAL LIGHT MODULATORS. H.D. Young, R. Ramesh and A. Christou, Materials Research Science and Engineering Center and Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD.

Epitaxial lead lanthanum zirconium-titanate thin films (1 m) and MgO (1.1 m) were deposited on (100) GaAs. Up to ten multilayer periods were grown using an excimer KrF2 laser technique. Deposition parameter optimization in terms of substrate temperature, ambient pressure and deposition rate have been carried out. Atomic Force Microscopy, x-ray diffraction, SEM and optical photoreflectance measurements were used to determine composition, structure, interface roughness and morphology of the deposited films. All films exhibited preferential alignment of the (111) planes parallel to the MgO and PLZT surfaces. Excellent preferred orientation has been obtained for films deposited at temperatures below 600C with small amounts of the pyrochlore phase. Low temperature deposition on GaAs allows one to avoid microcracks from high temperature stresses. Optical measurement revealed an electro-optic effect making these structures candidate as Bragg reflectors and optical modulators.

SESSION U13: MATERIALS FOR 
PIEZOELECTRIC MEMS 
Chairs: Timothy D. Sands and Bruce A. Tuttle 
Thursday Afternoon, December 4, 1997 
Salon A/B (M)

1:30 PM U13.1 
PROCESS OPTIMISATION FOR PIEZOELECTRIC FILMS AND COATINGS. Michael Sayer, Lichun Zou, Brian Leclerc, Marc Lukacs and Tim Olding, Queen's University, Kingston, CANADA; J.H. Schloss, SSI Technologies Inc., Janesville, OH.

Processing of high activity ferroelectric and piezoelectric films requires control of both the sol gel deposition processing and factors associated with the nucleation and growth of the appropriate crystallographic and domain microstructure. Different sol gel routes have been evaluated by measurements of residual carbon content, with low carbon content related to good ferroelectric properties. A poling study of PZT ferroelectric films shows that the piezoelectric properties are a maximum at a poling temperature of 200C and a poling field of 200V/micron. The development of models to assess the poling characteristics of coatings are discussed.

1:45 PM U13.2 
THICKNESS MODE RESONANCE OF PZT COATINGS ON A SUBSTRATE. Marc Lukacs, Tim Olding, Mike Sayer, Queen's University, Dept. of Physics, Kingston, ON, CANADA; Stewart Sherrit, Royal Military College of Canada, Physics Dept., Kingston, ON, CANADA.

A theoretical model using the 1D piezoelectric equations with complex variables has been developed to predict the frequency response of a piezoelectric film on a substrate. The model has been used to evaluate the thickness mode frequency response of composite sol-gel PZT coatings on a substrate of variable thickness. Three substrate/coating structures have been investigated: i) thin substrate with thick coating -this mimics a bulk ceramic resonator. ii) thick substrate with thin coating -this mimics a clamped system. iii) substrate of intermediate thickness -this structure produces a complicated impedance response where the mechanical resonance of the substrate and coating couple with the fundamental piezoelectric resonance of the same coating. Both the intermediate and thick substrate structures are shown to significantly broaden the fundamental piezoelectric resonance. The degree to which material properties can be assessed will be discussed.

2:00 PM *U13.3 
MATERIALS ANALYSIS OF Pb(Zr,Ti)O3 THIN FILM/MICROMACHINED Si STRUCTURES. B.A. Tuttle, T.J. Garino, P.G. Clem, D. Dimos, W.K. Schubert and J.A. Ruffner, Sandia National Laboratories, Albuquerque, NM.

There has been an explosion of technical interest in integrating ferroelectric thin films with Si micromachined technology because of the large number of diverse, near term applications for which these films are the primary media. These applications include acoustic detectors, micropumps and uncooled infrared detectors. Our approach has been to design and fabricate simpler structures to unambiguously determine both piezoelectric/pyroelectric response and to address integration issues for more complex structures. Stress versus thermal history measurements have been performed on a series of PZT films deposited on blanket wafers as a function of composition and thermal processing. From these measurements, film composition and process temperatures are tailored to enhance the yield of microbeam and membrane devices. We have successfully fabricated and characterized Pb(Zr, Ti)O3 thin films on the following platforms: macrocantilever beams, bulk micromachined cantilever beams, surface micromachined membranes and LSCO//SiO2 aerogel composites. In addition, one of the first reports of surface acoustic wave response of PZT films at frequencies ranging from 67 MHz to 180 MHz is presented.

3:00 PM *U13.4 
MICROSTRUCTURE AND TEXTURE EFFECTS ON THE IN-PLANE PROPERTIES OF POLYCRYSTALLINE PZT THIN FILMS FOR MEMS. Loucas Tsakalakos, Timothy Sands, Jordana Blacksberg, University of California, Dept of Materials Science & Mining Engineering, Berkeley, CA; Ulrich Dahmen, Lawrence Berkeley National Laboratory, National Center for Electron Microscopy, Berkeley, CA; Frances M. Ross, IBM T.J. Watson Research Center, Yorktown Heights, NY.

The field of Micro-Electromechanical Systems (MEMS) has experienced rapid growth in the past few years. Various devices such as micro motors, mirrors, sensors, and pumps have been demonstrated, mostly utilizing low piezoelectric constant (dij) materials such as ZnO. Only very recently have materials with greater piezoelectric activity, such as those in the Pb(ZrTi)O3 (PZT) system, been successfully integrated with silicon for use in MEMS. Nevertheless, there are problems associated with piezoelectric fatigue and ferroelastic hysteresis that impact the device reliability. These issues are essentially related to the motion of non-180 domain walls under an applied electric field. It is presently no clear whether these boundaries are mobile in thin films subject to mechanical clamping due to the thermal expansion mismatch between the film and substrate, particularly in the polycrystalline films of interest in devices. We are studying the effect of biaxial film stresses on the ferroelectric/piezoelectric properties and the domain wall mobility by applying an electric field in the plane of PZT thin films grown at 620C on SrTiO3 (STO) and Bi4Ti3O12 (BTO) buffer layers, which in turn were grown on a SaixNy/Si substrate. The buffer layers were deposited by Pulsed Laser Deposition at temperatures between 620-800C and have grain sizes ranging from 20-100nm for STO and 150-200nm for the BTO. The BTO films were found to possess b-axis texture, whereas the STO was completely randomly oriented, and PZT microstructure was indeed found to mimic that of the buffers. When released from the silicon, this membrane structure is well suited for use in Flexural Plate-Wave (FPW) devices such as sensors and micro-pumps. The removal of the metallic ground plane, found in present devices, allows for an increase in the mass sensitivity (inversely proportional to the mass per unit area) of such devices. Ferroelectric measurements will be presented, as well as in situ Transmission Electron Microscopy results of the response of such polycrystalline films under an applied bias and as a function of temperature.

3:30 PM U13.5 
ANTIFERROELECTRIC THIN FILMS FOR DECOUPLING CAPACITOR AND MICROACTUATOR APPLICATIONS. Baomin Xu, Neelesh G. Pai, Paul Moses, L. Eric Cross, Intercollege Materials Research Laboratory, Pennsylvania State University, University Park, PA.

Antiferroelectric thin films have been suggested for use as decoupling capacitors in advanced multichip modules (MCM's) and microactuators in microelectromechanical systems (MEMS), due to the high charge release concurrrent with ferroelectric to antiferroelectric (backward) phase switching, and the large strains associated with antiferroelectric to ferroelectric (forward) phase switching. In this work, we characterized the properties of the antiferroelectric thin films relevant to these applications, with the emphasis on charge release and backward phase transition speed, leakage current, and field-induced phase transition strain. The compositions studied are niobium or lanthanum doped lead zirconate titanate stannate, and the film thickness is about 0.4 m. The samples show ³square" hystersis loop and zero remanent polarization, and the maximum saturated polarization can reach 40C/cm2. The backward phase switching was determined by directly measuring the released charge of the samples. The backward phase switching speed is less than 2.5ns, and half of the stored charge can be released in 10ns. The phase transition strain was measured by using a double beam laser interferometer. The phase transition strain level can reach about 0.4, which is double the strain level of general PZT ferroelectric thin films. These results show that the obtained antiferroelectric thin films are very promising for decoupling capacitor and microactuator applications.

3:45 PM U13.6 
TEXTURE DEVELOPMENT AND ELECTRICAL PROPERTIES OF THE SOL-GEL DERIVED LEAD ZIRCONATE TITANATE THICK FILMS. F. Chu*, S. Trolier-McKinstry*, R.J. Davis** and S. Corbett, *Materials Research Laboratory, **EMPRL, The Pennsylvania State University, University Park, PA; Microsound Systems, Lake Oswego, OR.

Piezoelectric thick films of lead zirconate titanate (PZT) have attracted considerable attention for microelectromechanical systems (MEMS) in sensor and actuator applications. In the present work, crack-free Pb(Zr0.52Ti0.48)O3 (PZT52/48) films with thicknesses greater than 1 m were prepared on Pt/Ti/SiO2/Si substrates using a methoxyethanol-based precursor solution and multiple spin-coating. It was found that for PZT films prepared by multiple rapid thermal annealing, the preferred orientation was not strongly affected by the pyrolysis temperature or the heating rate during thermal annealing as has been previously reported for PZT thin films using a single annealing step. Thus, higher pyrolysis temperatures such as 450C and a lower heating rate (20C/min) did not result in stronger (100) orientation. Instead, pre-annealing the Pt/Ti/SiO2/Si substrates above 600C was shown to favor the <100> orientation. The diffusion of Ti to the surface of <111> oriented Pt, preventing the nucleation of <111> perovskite oriented grains is believed to be responsible for this effect. Electrical characterization showed no difference in resistivity between the PZT films with <111> and <100> preferred orientations. The remanent polarization of <111> oriented films (Pr<111> = 23 C/cm2) is slightly higher than that of <100> orientation dominant films (Pr<111> = 19.6 C/cm2). Whereas the coercive field (Ec) decreases with increasing <100> orientation. THe piezoelectric properties of samples with different orientations and thickness will be reported. It is noted that the preferred orientation becomes weaker with increasing thickness for films thicker than 2 m. The patterning and use of these films for biomedical imaging transducers will also be discussed.

4:00 PM U13.7 
THE INFLUENCE OF FILM THICKNESS AND MICROSTRUCTURE ON THE TRANSVERSE PIEZOELECTRIC COEFFICIENT (d31) OF PZT THIN FILMS. Joseph F. Shepard Jr., Fan Chu, Paul J. Moses, and Susan Trolier-McKinstry, Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, PA.

The wafer flexure technique has been developed for the rapid measurement (less than 10 minutes) of the transverse piezoelectric coefficient (d31) of piezoelectric thin films. The technique is based upon the controlled bending of a clamped silicon substrate coated with a piezoelectric film. Flexure of the wafer results in the transfer of biaxial stress from the silicon to the film and thus the production of an electric charge. The charge produced is monitored electronically and used in conjunction with the applied principle stresses to determine the film's transverse piezoelectric coefficient (d31). For 0.4 m thick 52/48 lead zirconate titanate (PZT) films the wafer flexure method has yielded values from -20 to -77 pC/N depending on the poling conditions (magnitudes are in agreement with laser interferometric techniques). For this study the wafer flexure technique was modified from semi-ac operation (i.e. oscillation of applied stress by hand) to a mechanized ac measurement (i.e. electronic pressure oscillation and lock-in charge detection). Modifications made reduce electromagnetic noise and enhance both the resolution and precision of the device. Lead zirconate titanate thin films from 0.4 to 5.0 m thick were synthesized with 52/48 compositions using a modified sol-gel technique. The transverse piezoelectric constants (d31) of the PZT films were then measured with the improved wafer flexure method and results correlated to film thickness, remanent polarization, and microstructure.

4:15 PM U13.8 
DEPOSITION AND ELECTRICAL CHARACTERIZATION OF EPITAXIAL Pb(Mg1/3Nb22/3)O3 - PbTiO3 (65/35) RELAXOR THIN FILMS. Jon-Paul Maria, Thomas R. Shrout, and Susan Trolier-McKinstry, The Pennsylvania State University, Department of Material Science and Engineering, University Park, PA.

Recent measurements on relaxor - PbTiO3 perovskite single crystals have revealed remarkable electromechanical property values including d33 coefficients > 2000 pC/N, electromechanical coupling coefficients (k33) > 90, and strains as large as 1.7. Though the polar axis of the rhombohedral compositions lies along one of the <111> directions, these values were measured along <100>. These materials are attractive for many solid state actuator applications including those in microelectromechanical devices (mems). The large strains associated with relaxor - PT crystals appear not to result from non-180 domain wall motion; this is promising for thin film applications where the limited domain wall mobility restricts the values of achievable piezoelectric coefficients in lead zirconate titanate. Epitaxial PMN - PT (65/35) thin films were deposited by pulsed laser deposition on (001) oriented LaAlO3 and SrTiO3 substrates using a PbO excess PMN - PT target; SrRuO3 was used as the bottom electrode. Films were characterized by 4-circle x-ray diffraction and electrical property measurements including temperature dependent permittivity and polarization hysteresis. The films were found to be phase pure with full width half maximum values of 0.4, 0.9 and 0.5 in 2, , and respectively. The films deposited on LaAlO3 exhibit the bulk Curie transitions temperature of 155C: room temperature permittivity and loss tangent values were 800 and 3% respectively. A remanent polarization of 20 C/cm 2 is observed. In addition, by modulation of deposition parameters, the Curie transition can be shifted to below room temperature. Strain measurements by double-beam interferometry will be presented.

4:30 PM U13.9 
PIEZOELECTRIC MEASUREMENTS OF PZT THIN FILMS. F. Xu, J.F. Shepard, Jr., T. Su, and S. Trolier-McKinstry, Materials Research Laboratory, Penn State, University Park, PA.

Reliable measurements of the piezoelectric coefficients of thin films are required for designing miniature sensors and actuators. In this papers a charge-based technique for rapidly measuring the d33 coefficients is presented. The samples measured were lead zirconate titanate thin films prepared using a methoxyethanol based sol-gel route and rapid thermal annealing. When a PbO topcoat was used during the crystallization to minimize lead loss, the films showed clear ferroelectric paraelectric phase transformations in the dielectric constant versus temperature curves with near-bulk transition temperatures, and high values of the remanent polarization (>20C/cm2). d33 measurements were made by applying a controlled pressure to the film and measuring the induced charge. For these films, d33 values were generally 150 pC/N. Details on the measurement set-up will be given.

4:45 PM U13.10 
PZT/PVDF COMPOSITES FOR ACTUATOR/SENSOR APPLICATIONS. W.Kowbel, X. Xia and J.C. Withers, MER Corp., Tucson, AZ; B. Wada, J.P.L. and M.J. Crocker, Auburn University, Al.

Currently, smart structures utilize both polymeric sensor and PZT-based actuators. The benefit of self-sensing calls for the development of integrated actuator/sensor composites. This paper addresses the development of this new class of smart materials. Porous PZT ceramics were fabricated by several techniques including tape casting and foaming. PVDF was subsequently infiltrated within the controlled porosity PZT. In addition, PVDF or its blends and PZT powders were in-situ processed to generate controlled piezo and mechanical properties composites. Both actuating and sensing of this new class of composite materials were studied. This paper presents the processes-structure-property relationship on this new class of piezocomposites.

SESSION U14: POSTER SESSION: 
MICROWAVE/OPTICAL DEVICES 
Chairs: Timothy D. Sands and Bruce A. Tuttle 
Thursday Evening, December 4, 1997 
8:00 P.M. 
Salon E (M)

U14.1 
FABRICATION OF TUNGSTEN-BRONZE FERROELECTRIC THIN FILMS BY PULSED LASER DEPOSITION*. Yinhua Li and Robert E. Leuchtner, Physics Department, University of New Hampshire, Durham, NH.

Strontium barium niobium tantalate (SBNT) is tungsten-bronze structured and is a promising material for frequency agile applications, especially at microwave frequencies. We are investigating film growth of SBNT ferroelectrics for frequency agile electronic applications. We have explored a range of compositions of SBNT varying the Ba/Sr and Nb/Ta ratios in order to obtain maximum tuning and low loss of microwave signal at room temperature. Films were deposited using pulsed laser deposition on MgO, Cu, SrTiO3, and on buffer layers of Au or Pt on MgO. A KrF excimer laser beam with wavelength of 248 nm and pulse duration of 30 ns was focused to a spot of 0.11 cm2 on targets. The pulse energy range of 300 to 400 mJ/pulse resulted the laser power of 2.7J/cm2 to 3.6J/cm2. Processing parameters were varied to obtain c-axis film growth. The ambient oxygen partial pressures were 50, 200, and 500 mTorr and the substrate temperature of 650C, 700C, 750C and 800C respectively. The in-situ grown films were in smooth surface with few particulates as observed under a microscope with 1000x magnification. Energy dispensive x-ray analysis and Rutherford backscattering spectrometry were used to confirm the chemical composition of the films to be nominally the same as the targets. X-ray diffraction showed the films were c-axis oriented for growth temperatures above 700C on MgO substrate. Small fraction of a-axis orientation was observed at 650C. The best film obtained on MgO substrate was at 200 mTorr oxygen ambient pressure, 750C substrate temperature which had a rocking curve width of <002> SBNT of 0.4.Au or Pt was first deposited on MgO at temperature 550C, 600C and 750C in 50 mTorr Ar, and then depositing SBNT on it. It was difficult to distinguish the Pt <200> XRD peak from SBNT <002>, so an off-axis XRD scanning method was used to confirm c-axis growth of SBNT. The SBNT/Pt film was tilted 11.9 and the SBNT <203> crystal plane was explored. These results indicate high quality film growth for microwave device application. Some preliminary tuning and loss data will be presented.

U14.2 
FERROELECTRIC/HTS HETEROSTRUCTURES FOR TUNEABLE MICROWAVE FILTERS. C. Couvert1, M. Drouet1, B. Marcilhac2, J.P. Contour1 and E. Jacquet1, 1Unite Mixte de Physique, CNRS Thomson-CSF, LCR, Orsay, FRANCE; 2Laboratoire des Dispositifs Supraconducteurs, Thomson-CSF, LCR, Orsay, FRANCE.

YBa2Cu3O7 / SrTiO3 heterostructures have been grown by Pulsed Laser Deposition (PLD)on LaAlO3 substrates. They have been patterned into tuneable coplanar resonators by standard photolithography and ion beam milling. In these structures, the tuneability is achieved via the change in the dielectric constant of the ferroelectric material (STO). The surface resistance of the as grown superconducting layer was found to be of 0.2 mOhms (at 77K and 10GHz). Non-linearities were not found up to an rf field of 12 Oersteds. Despite their very good Rs, the quality factor Q of the coplanar structures remains about 10 times lower than expected from theoretical calculation. This difference is attributed to the rather poor quality of the underlying STO layer. The study of the tuneability is under progress.

U14.3 
DIELECTRIC AND STRUCTURAL PROPERTIES OF (100) KTaxNb1-xO3 FILMS GROWN ON MgO AND LaAlO3 SUBSTRATES BY PULSED LASER DEPOSITION. Wontae Chang, Adriaan C. Carter, James S. Horwitz, Steven W. Kirchoefer, Jeffrey M. Pond, Douglas B. Chrisey, Kenneth S. Grabowski, Naval Research Laboratory, Washington, DC.

High quality 0.5 m thick KTaxNb1-xO3 (KTN) films were grown on (100) MgO and (100) LaAlO3 substrates by pulsed laser deposition (PLD). Deposited films were smooth, single phase and exclusively (100) oriented. The high volatility of K required excess K in the ablation target. Sintering of the target and post-deposition annealing of the films were done in a sealed Pt coated container. Rutherford backscattering showed the films to have a 1 to 1 atomic ratio of K to Ta + Nb. On top of the KTN films, Ag interdigitated capacitors were deposited. Room temperature measurements of capacitance and dielectric loss as a function of bias electric field (0 - 80 kV/cm) at 1 GHz were made. One MHz capacitance and dielectric loss measurements were made as a function temperature and bias electric field. The results show the strong potential of KTN for use in frequency agile microwave electronics.

U14.4 
CRYSTALLIZATION OF AMORPHOUS THIN BST/Mg0(100) BY R.F. MAGNETRON SPUTTERING : AN IN-SITU SYNCHROTRON X-RAY SCATTERING STUDY. D.Y. Noh, H.H. Lee, J.H. Je, and H.K. Kim, Kwanju Inst of Science and Technology, Kwangiu, KOREA.

The crystallization of amorphous BST/MgO(100) films was studied in a synchrotron x-ray scattering experiment. The amorphous films of various thickness, 300Å, 550Å, 5500Å were grown by R.F. magnetron sputtering at room temperature. The crystallization process of these films was studied by a series in-situ measurement of the x-ray scattering profile during annealing. At around 600C, an intermediate phase, which we suspect to be a metastable pyrochlore phase, was formed. This phase was signifined by rather broad scattering feature near the MgO(200) Bragg peak, which disappeared upon further annealing to higher temperatures. The reflectivity curve measured at the same time showed that the film-substrate interface became very rough as the pyrochlore-like phase was formed, which might indicate that it was nucleated near the interface area. The behavior of the crystallization to the stable perovskite phase was quite different from sample to sample. In the thin 550Å sample, the cystallization occurred at 750C. The crystal film had the <100> preferred orientation. On the other hand, the 5500Å thick sample became crystalline even at 500C with random orientation. Since the crystalline films were close to completely powders, we believe that the crystallization occurred in the bulk region of the film, not near the interface area. The thickness dependence of the crystallizatoin temperature indicates that the substrate effect was dominant throughout the films with thickness less than 1000Å. The scattering profile measured in a crystal film obtained by rapid thermal was very similar to that of the slowly annealed sample.

U14.5 
STRESS EFFECT ON NONLINEARITY AND LOSS IN STO AND BST FILMS. Vladimir Merkulov, Weidong Si, Hongcheng Li, Jeff Lannin, Xiaoxing Xi, Penn State University, Department of Physics, University Park, PA.

STO and BST thin films are normally stressed due to the lattice mismatch and the different thermal expansion coefficients between the film and the substrate. Stress also results from the nonequilibrium nature of the thin film growth. It is likely that stress plays an important role in degrading the tunability and loss properties in STO and BST films from those of the bulk materials. Our recent data indicate that by removing stress from STO thin films, their dielectric properties are improved towards the bulk properties.Raman scattering measurement also suggests important influence of stress on the lattice dynamics in STO and BST thin films.

U14.6 
STUDY OF KTN THIN FILMS OF VARIABLE COMPOSITION GROWN BY PULSED LASER DEPOSITION. Felix E. Fernandez, Manuel Pumarol, Pablo J. Marrero, Univ of Puerto Rico, Dept of Physics, Mayaguez, PR.

Potassium niobate tantalate (KTN) has been known for some time as an attractive material family due to its fast nonlinear optical response and high value of spontaneous polarization. Thin film growth of KTN has so far been limited to certain fixed compositions within the solid solution range. We have explored KTN growth with a range of compositions by depositing submonolayers of KTaO3 and KNbO3 in sequence. The growth technique used was reactive Pulsed Laser Deposition, and KNO3 was also deposited onto the multilayer in order to provide the required amount of potassium. The submonolayer approach was necessary because KTaO3 and KNbO3 will not interdiffuse appreciably. The resulting KTN films, grown on MgO (100) and KTaO3 (100) substrates, were characterized for microstructure by x-ray diffraction, and for composition by Rutherford Backscattering Spectroscopy and Secondary Ion Mass Spectrometry. Optical properties of the films are presented as well.

U14.7 
FERROELECTRIC THIN FILMS EMBEDDED WITH SEMICONDUCTOR QUANTUM DOTS: CONSTRUCTING A NEW CLASS OF OPTOELECTRONIC MATERIALS. Zhou Ji, Lin Yu, Wu Pinggui, Gui Zhilun and Li Longtu, Department of Materials Science & Engineering, Tsinghua University, Beijing, CHINA.

A new material with novel nano-structure was designed and prepared. This structure is based on ferroelectric thin film and embedded semiconductor quantum dots. The composite of BaTiO3 thin film and ZnS nanoparticles(quantum dots) were prepared by a sol-gel process. Ferroelectric, dielectric and photoluminescence properties was investigated. It is shown that both ferroelectric and dielectric properties of the composite thin films are simular to that of pure BaTiO3 thin films, whereas a typical lumescence of ZnS quantum dot was observed in the composite thin films in case it was excited by UV.

U14.8 
LOW FREQUENCY DIELECTRIC MEASUREMENTS AND STRUCTURAL PROPERTIES OF EPITAXIALLY LIFTED-OFF STRONTIUM TITANATE FILMS. Mark J. Dalberth, Charles T. Rogers, Univ of Colorado, Dept of Physics, Boulder, CO.

Using pulsed laser ablation, we have grown epitaxial bilayers of strontium titanate and yttrium barium copper oxide on lanthanum aluminate substrates. Using a selective acid etch, we have removed the YBCO from the middle of the bilayer and lifted off strontium titanate films from their parent substrates. We have transferred these films to a range of different substrates. We have performed X-ray diffraction measurements before and after the lift-off and present data on the change in the out-of-plane stress of the films. Using capacitors patterned on the film's surface, we have measured the dielectric constant of a lifted-off film from 10 kHz to 1 MHz and compared it to the dielectric constant of the film while still a part of the bilayer.

U14.9 
OPTIMIZATION OF FERROELECTRIC AND DIELECTRIC MATERIALS THROUGH COMBINATORIAL SYNTHESIS OF THIN FILM LIBRARIES. Hauyee Chang, Ichiro Takeuchi, Jingsong Wang, Fred Duewer, Peter Schultz, X.-D. Xiang, Lawrence Berkeley National Laboratory, Berkeley, CA.

The potential applications in dynamic random-access memories (DRAMs) and tunable microwave devices have raised tremendous interest in ferroelectrics materials due to their high dielectric constant and nonlinear dielectric properties. However, finding materials with optimized properties is still the limiting factor for large scale commercial applications. In order to systematically and effectively search and optimize ferroelectric materials, we have used recently developed combinatorial synthesis and screening technologies. In this approach, thousands (e.g.1024, currently) of different compositions or compounds are synthesized on a small (e.g. one inch square) substrate using sequential film depositions through a series combinatorial masks followed by controlled annealing processes. Dielectric properties (dielectric constant and loss tangent) are then characterized by high resolution microwave impedance microscopy using a recently developed scanning tip microwave near-field probe. Further characterizations include interdigital electrodes or microstrip based measurements. We based our initial studies on BaxSr1-xTiO3. Analysis of thin films by both X-ray diffraction and RBS, shows uniform diffusion of precursors and epitaxial film growth on the substrates, LaAlO3 and MgO. The correlation between physical properties, such as dielectric constant and loss tangent, and compositions, such as the relative ratios of strontium and barium and the presence of a variety of dopants will be discussed. Studies on other ferroelectric materials, such as SrxBa1-xNbO3 will also be discussed.

SESSION U15: POSTER SESSION: 
MEMS 
Chairs: Timothy D. Sands and Bruce A. Tuttle 
Thursday Evening, December 4, 1997 
8:00 P.M. 
Salon E (M)

U15.1 
SOL-GEL DERIVED ANTIFERROELECTRIC THIN FILMS FOR ELECTRONIC DEVICE APPLICATIONS. Neelesh Pai, Baomin Xu and L. Eric Cross, Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, PA.

Recently there has been an increasing interest in the use of antiferroelectric thin films for power plane decoupling capacitors in very high speed multichip modules (MCMs) as well as in microactuators in microelectromechanical systems (MEMS). Distinctive square hysteresis response was observed in niobium doped and lanthanum doped lead zirconate titanate stannate thin films prepared by modified sol-gel spin coating technique. The effect of different compositions and processing parameters on the various electrical properties like maximum polarization, switching fields, energy storage density, hysteresis, dielectric permittivity, dielectric loss, etc., were studied. We also studied the temperature and thickness dependence of the electrical properties and their aging under DC bias. The changes in dielectric permittivity with temperature and thickness were studied. It was found that by choosing appropriate compositions and suitable processing parameters the loop characteristics could be tailored to suit different applications. We can tailor the loop to have high maximum polarization, high switching fields, high energy storage density and a moderate hysteresis necessary for use in decoupling capacitors in MCMs. We can also modify the loop characteristics to have high maximum polarization, low switching fields, small hysteresis and low loss suitable for use in microactuators in microelectromechanical systems (MEMS). The experimental results indicate that these antiferroelectric thin films are very promising for both energy storage and microactuation applications.

U15.2 
PIEZOELECTRIC PROPERTIES OF SOL-GEL DERIVED PZT THIN FILMS WITH VARIOUS Zr/Ti RATIOS. G. Teoweea, K.C. McCarthya, F.S. McCarthya, D. Davisb, J.T. Dawleyb, R. Radspinnerb, B.J.J. Zelinskib and D.R. Uhlmannb, aDonelly Corporation, Tucson, AZ; bDepartment of Materials Science and Engineering, University of Arizona, Tucson, AZ.

Piezoelectric thin films are useful for application in microelectromechanical devices. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios were prepared on platinized substrates. These films were fired to 650 - 700C to crystallize them into single-phase perovskite film. Dcpending on the Zr/Ti ratio, the PZT films can be tetragonal or rhombohedral perovskite films. Top Pt electodes were then deposited onto thern to obtain monolithic capacitors. Their piezoelectric properties were measured using optical lever-based instrumentation. Large d33 piezoelectric coefficient of up to 500 pm/V was obtained in PZT 53/47 film making it attractive in applications such as thin film transducers, microcantilevers and surface acoustic wave devices. The piezoelectric properties will be discussed with regards to composition and microstructure.

U15.3 
SOL-GEL DERIVED Pb(Zn1/3Nb2/3)O3-PbTiO3 THIN FILMS. G. Teoweea, K.C. McCarthya, F.S. McCarthya, D. Davisb, J.T. Dawleyb, R. Radspinnerb, B.J.J. Zelinskib and D.R. Uhlmannb, aDonelly Corporation, Tucson, AZ; bDepartment of Materials Science and Engineering, University of Arizona, Tucson, AZ.

There has been recent attention on single crystal relaxor ferroelectrics namely Pb(Zn1/3Nb2/3)O3 (PZN) especially with regards to its piezoelectric properties. PZN-based single crystals have beenreported to yield d33 piezoelectric coefficient of as high as 2100 pm/V in contrast with PZT-based ceramics with d33 of < 800 pm/V. Typical relaxor ferroelectrics are difficult to crystallize into single phase perovskite films. The presence of remanent pyrochlore phase tends to degrade the overall ferroelectric behaviors of the thin films. A series of sol-gel derived Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) films. With various PbTiO3 content, were prepared on platinized Si wafers. The resulting capacitors were characterized for their dielectric, ferroelectric and piezoelectric properties. Incorporation of PbTiO3 appeared to aid ill stabilization of the desired perovskite phase. The effects of chemistries (namely composition), microstructure and processing condition will be discussed with respect to the properties observed.

SESSION U16: POSTER SESSION: 
NOVEL FERROELECTRIC DEVICES 
Chairs: Timothy D. Sands and Bruce A. Tuttle 
Thursday Evening, December 4, 1997 
8:00 P.M. 
Salon E (M)

U16.1 
PHASE TRANSITION AND PYROELECTRIC PROPERTIES OF Mn-DOPED (PbLa)TiO3 THN FILMS. Kenji Iijima, Fine Ceramic Research Association, Synergy Ceramics Laboratory, Aichi, JAPAN; Kouichi Niihara, Institute of Scientific and Industrial Research, Osaka University, Osaka, JAPAN.

An extremely high figure of merit for a pyroelectric infrared sensor was yielded by the Mn-doped (PbLa)TiO3 (PLT) ferroelectric thin film. These films were prepared by a precise control of an ionic structure by rf-magnetron sputtering. Curie temperature of PLT decreases with increasing La content. Ferroelectric phase transition of PLT becomes broad and smear and spontaneous polarization is decreasing with increasing La content. Consequently, figure of merit for infrared sensor is decreasing with increasing La content. It is considered that the broadening of phase transition is due to the incorporation of detect structure by the exchange of Pb2+ to La3+. The defect structure is the cause of microscopic structural fluctuation which is disturbing a long range interference of dipole moment. In this study, the defect structure is compensated by doping a small amount of Mn ions in the PLT structure. The Mn doped PLT thin film shows a sharp and normal phase transition and a square hysteresis loop with large remanent polarization and an extremely large figure of merit was obtained. We will report electrical properties and related nanostructure characterization results of PLT thin films. Research supported by NEDO, under the Synergy Ceramics Project of the ISTF program promoted by AIST, MITI, Japan.

U16.2 
PYROELECTRIC CHARACTERISTICS OF THIN PbTiO3 AND La-MODIFIED PbTiO3 FILMS ON PLATINUM FILMS FOR INFRARED SENSORS. K.K. Deb, Army Research Laboratory, Infrared and Electron Devices Directorate, Adelphi, MD; T. Tamagawa, Y. Di, G. Gui, B.L. Halpern, J.J. Schmitt, Jet Process Corporation, New Haven, CT.

Lead titanate (PbTiO3) and La-modified PbTiO3 thin films were grown on platinized Si(100) substrates under controlled substrate temperature and ambient by a modified Jet vapor deposition process. X-ray diffraction patterns taken on these films showed single-phased perovskite structure. The homogeneity and thickness of these films were also locally examined through a comparative use of micro-probe laser Raman spectroscopy. Pyroelectric and P-E hysteresis curve measurements, as well measurements of the dielectric constant and loss tangent versus temperature and frequency, were performed. It was found that significant pyroelectric currents were detected on all films before poling treatments, and pyroelectric coefficients as high as 84 nC/ cm2 C were observed. The pyroelectric coefficient and dielectric constant varied with La content. The calculated figures of merit, based on the measaured properties , were compared with their ceramic counterparts and thin films of other commonly materials. A consideration of these figures makes the present thin films appear to be highly favorable in performance characteristics for IR detector applications when compared with the corresponding bulk materials or PZT thin films.

U16.3 
CRITICAL ROLE OF SUBSTRATE CRYSTALLINITY ON ELECTRICAL AND DIELECTRIC CHARACTERISTICS OF MIS DIODES USING BARIUM TITANATE BASED THIN FILMS. Yuichi Masaki and Harry E. Ruda, Department of Metallurgy and Materials Science, University of Toronto, Ontario, CANADA; Mark Farrell, Energenius Inc., Toronto, Ontario, CANADA.

Owing to the widespread applicability of ferroelectrics, there has been intense interest in these materials over the past decade. Amongst the many ferroelectric materials, barium titanate (BaTiO3) and BaTiO3-based materials are most widely used in both research and industry. We report on the electrical and dielectric characteristics of two different types of Metal-Insulator-Semiconductor (MIS) structures using BaTiO3-based thin films as the I-layer; for the S-layer, one uses amorphous Si (a-Si) and the other crystalline Si (c-Si). The MIS structure using a-Si has a metal substrate, onto which the a-Si film is deposited. BaTiO3-based thin films were then deposited onto the a-Si by either a sol-gel process or sputtering. After the preparation of BaTiO3-based films, rapid thermal annealing was carried out to induce crystallization of the BaTiO3. During rapid thermal annealing, short wavelength radiation was used to minimize interactions with the underlying a-Si layer. Finally, metal dots were evaporated onto the BaTiO3 as upper electrodes to enable electrical characterization to be made. On the other hand, for the MIS structure using c-Si wafers, BaTiO3-based films were deposited onto the c-Si wafer and rapidly crystallized, followed by the formation of the upper and lower electrodes. This approach therefore enables us to highlight the role played by the substrate crystallinity on the crystallization behavior, crystal structure and electrical properties of BaTiO3-based thin films.

U16.4 
GROWTH AND ELECTRICAL PROPERTY OF YMnO3 THIN FILMS ON Si SUBSTRATES. Takeshi Yoshimura, Norifumi Fujimura, Nobuaki Aoki, Masaki Takaoka, Taichiro Ito, Osaka Pref Univ, Coll of Engineering, Dept of Applied Materials Science, Osaka, JAPAN.

We have proposed ReMnO3 (Re: Rare earth elements) films for metal-ferroelectric-semiconductor field effect transistor (MFSFET) type ferroelectric random access memories (Ferroelectric RAMs) and (0001) epitaxial YMnO3 films on (111)MgO and (0001)ZnO:Al/(0001)sapphire substrates have been obtained. Since YMnO3 has hexagonal crystal structure with unipolarization axis, low dielectric permittivity, and does not have non-volatile element, it supposes to have several advantages compared with PZT and SBT. This paper describes the potential of the YMnO3 film growth on (111)Si substrates with and without some buffer layers. YMnO3 films and the buffer layers were prepared by a pulsed laser deposition method. Since all the YMnO3 films show amorphous feature, some buffer layer were adopted through this work. Y-Mn-O buffer layer deposited with YMnO3 target without introducing any oxygen gas. Although crystalline films can be obtained by using this Y-Mn-O buffer layers, remnant polarizations of the YMnO3 films were quite small. On the other hand, epitaxial YMnO3 films can be grown on the top of epitaxial Y2O3 buffer layers on (111)Si. This epitaxial YMnO3 films on Y2O3 buffer layer show small polarization with saturation. By RHEED, however, precipitation of YMn2O5 was observed at the surface of the film which results in leaky films due to the poor structure. The growth process and the mechanism of YMnO3 films with and without buffer layers and the structure-property relationships will be described.

U16.5 
LASER DEPOSITION OF FERROELECTRIC (METAL) STRUCTURES FOR LOW WORK FUNCTION APPLICATIONS. R. Yanochko, R. Leuchtner, J. Quinn, University of New Hampshire, Dept of Physics, Durham, NH; P. Wurz, Physikalisches Institut, University of Bern, Bern, SWITZERLAND

Low work function surfaces are important for a variety of technological applications such as thermionic converters and neutral conversion surfaces. Thin films or layered structures offer exciting opportunities for development in this area because of the novel types of electronic and crystallographic structures possible at the surface. BaZrO3 films were produced using pulsed laser deposition (PLD). Their material properties were evaluated for potential use as a neutral conversion surface for space applications. Films were fabricated with background ambients of Ar and O2 ranging from 0.05 - 0.30 torr, and at temperatures from 300^)C. Film deposition rate was measured as a function of laser fluence, and background pressure.

8:30 AM U17.1 
EPITAXIAL FERROELECTRIC MULTILAYERS BY PLD: TOWARDS MULTI-LEVEL FERROELECTRIC MEMORY. T.J. Zehnder, A.M. Grishin and K.V. Rao, Department of Condensed Matters Physics, Royal Institute of Technology, Stockholm, SWEDEN.

Recent advances of in situ fabrication of highly crystalline complex oxide thin films by pulsed laser deposition challenge fabrication of multilevel ferroelectric memory cells . These are n-layered ferroelectric capacitors which can store 2n-coded information. We discuss the general principles of multi-level ferroelectric memory and the requirements of a suitable material. Both `write-in' and non-destructive `readout' operations are considered. A systematic study of two-component PbZr0.52Ti0.48O3 and non-doped PbTiO3 multilayers grown by Nd:YAG pulsed laser deposition on the template layer of YBa2Cu3O7-x/LaAlO3 are presented. We evidence optimization of the processing conditions to get global epitaxial quality of multilayers in terms of the observed single phase (00l ) reflections in -2 XRD-scan, narrow rocking curves of (00l ) reflections and strong in (a, b) plane structure as revealed by -scan at oblique geometry. In situ post-annealing of the template YBCO layer is found to be crucial in order to obtain a superior quality of the following ferroelectric layers. Furthermore, asymmetry of polarization loop, caused by built-in electric field, and leakage current have been significantly reduced as well as remanent polarization, P(E) loop squareness and pyroelectric coefficient have been enhanced by proper choice of layers order, thickness, and composition. Preliminary experimental results and theoretical considerations of multi-switching and coherent domain polarization processes in ferroelectric multilayers will also be discussed.

8:45 AM U17.2 
EQUILIBRIUM STRUCTURE AND GIANT PERMITTIVITY IN EPITAXIAL FERROELECTRIC HETEROSTRUCTURES. A. Erbil, School of Physics, Georgia Institute of Technology, Atlanta, GA.

Recent advances in the atomic level growth techniques have made possible the creation of various novel materials which do not exist in nature. These new materials provide an ideal laboratory for fundamental studies and lead to new generation of devices. In this talk, some of the material systems created at Georgia Tech will be described, along with a detailed discussion of a giant permittivity phenomenon recently discovered in ferroelectric superlattices. Epitaxial thin films of various ferroelectric perovskite-type oxides have been successfully grown using the metalorganic chemical vapor deposition (MOCVD) technique. The equilibrium and the dynamical properties of epitaxial ferroelectric thin films have been predicted by using a theory based on a free-energy functional of the Landau-Ginzburg-Devonshire type. A giant permittivity associated with the motion of domain walls is observed in epitaxial heterostructures having alternating layers of ferroelectric and non ferroelectric oxides. At low frequencies, permittivities as high as 420,000 are found. Real and imaginary parts of the dielectric constant show large dispersion at high frequencies. We interpret the observations as a result of the motion of a pinned domain wall lattice at low electric fields and sliding mode motion at high electric fields.

9:00 AM U17.3 
THE CONTROLLED GROWTH OF FERROELECTRIC SUPERLATTICES BY MBE. C.D. Theis and D. G. Schlom, The Pennsylvania State University, Deptartment of Materials Science and Engineering, University Park, PA; M. E. Hawley, Los Alamos National Laboratory, Los Alamos, NM; X. Pan, University of Michigan, Department of Materials Science and Engineering, Ann Arbor, MI.

Superlattices consisting of alternating layers of PbTiO3 and SrTiO3 have been grown using reactive molecular beam epitaxy. Strontium titanate layers are deposited using atomic absorption composition control and feedback from RHEED intensity oscillations. Lead titanate layers are deposited under adsorption-controlled growth conditions. 4-circle x-ray diffraction reveals intense 00l superlattice reflections and narrow rocking curve widths (e.g., 0.13 for the 00 reflecton of a [5 unit cell SrTiO3 / 5 unit cell PbTiO3]11 superlattice). Electrical measurements of the ferroelectric properties were made using La-doped SrTiO3 bottom electrodes grown by MBE (conductivities in the 50 mcm range) and platinum or gold top electrodes. Electrical leakage current in superlattices has been significantly reduced as compared to pure PbTiO3 using the SrTiO3 buffer layers even without using Schottky electrode contacts. For example, a 130 nm film consisting of alternating 10 unit cells of lead titanate and strontium titanate has a resistivity of 51011 cm with a remanent polarization of 4 C/cm2. Data will be presented on the variation of electrical properties as a function of varying superlattice period. AFM and cross-sectional TEM characterization of the superlattices will also be presented.

9:15 AM U17.4 
FERROELECTRIC FIELD EFFECT TRANSISTORS USING Pb(Zr,Ti)O3 AND Bi4Ti3O12 THIN FILMS. D.C. Kim, H.M. Lee, S.M. Cho, and W. Jo, LG Corporate Institute of Technology, Materials Application Group, Seoul, KOREA.

Ferroelectric field effect transistors (FET) were fabricated using Pb(Zr,Ti)O_3(PZT) and Bi_4Ti_3O_12(BTO) thin films. The PZT thin films were grown on Pt, Ir, and IrO_2by the sol-gel technique. Remnant polarization (P_r) and coercive field(E_c) of the PZT films were 25C/cm^2and 60 KV/cm, respectively. On the other hand, the BTO thin films were grown on the same type of bottom electrodes by rf-magnetron sputtering. The BTO films showed P_rof 5C/cm^2and E_cof 50 KV/cm. Reactive ion etching and inductively coupled plasma etching processes were adopted to define a metal-ferroelectric-metal capacitor with 4x4m^2dimension on the gate of n-channel CMOS transistors. From capacitance-voltage caracteristics of the FET, memory window and interface trap charge density were estimated below 5 V and 10^11/cm^2. Drain characteristics of the n-channel FET exhibited different values in accordance with polarization states of the ferroelectric materials, indicating that the ferroelectric FET has a non-volatile memory function.

10:00 AM U17.5 
STRONTIUM BISMUTH TANTALATE BASED FERROELECTRIC GATE FIELD EFFECT TRANSISTOR WITH YTTRIUM OXIDE AS THE BUFFER LAYER. Myoungho Lim and T.S. Kalkur, Microelectronics Research Laboratories, Department of Electrical and Computer Engineering, University of Colorado, Colorado Springs, CO.

Metal-oxide-semiconductor with strontium bismuth tantalate(SBT) as the ferroelectric material has been investigated for non-volatile non destructive-read-out (NDRO) memory applications. Whenever an oxide based ferroelectric film like SBT is deposited and annealed on silicon, a thin oxide layer forms at the ferroelectric silicon interface. Cross sectional transmission electron microscopy analysis shows that the thickness of this thin insulating layer depends on the annealing temperature and time. In addition to this, during annealing inter-diffusion of silicon and ferroelectric was observed. In order to overcome this problem, yttrium oxide was used as the buffer layer between silicon and the ferroelectric thin film. The memory windows of these structures were analyzed by capacitance versus voltage (C-V) measurements. The memory window was found to be dependent on the coercive voltage of the ferroelectric film and the programming voltage depends on the relative thicknesses of buffer layer and ferroelectric thin film. A memory window of 1.8 volts was obtained at the applied bias voltage of 10V. The buffer layer was found to be effective in reducing the charge injection between silicon and ferroelectric. Current versus voltage characteristics show leakage current density of 10 nA/cm2 at the operating voltage and below 1nA/cm2 in the holding state.

10:15 AM U17.6 
EFFECTS OF BUFFER LAYER ON THE FABRICATION AND CHARACTERISTICS OF FERROELECTRIC THIN FILMS. Han Wook Song, Joon Sung Lee, Dae-Weon Kim, Kwangsoo No, Dept of Material Science and Engineering, KAIST, KOREA; Kwang Ho Kim, Dept of Semiconductor Engineering, Cheong Ju University, KOREA; Tae-Hyun Sung, Center for Advanced Studies in Energy and Environment, Korea Electric Power Research Institute, KOREA.

For the MFSFET, the ferroelectric thin films are fabricated directly on Si substrate. But it is very difficult to fabricate the films directly on Si substrate because of the reaction between Si and the constituents of the ferroelectrics. So an buffer layer must be introduced between Si substrate and the ferroelectric thin film, which plays a role of diffusion barrier. A small lattice mismatch with Si substrate is recommended for preferred orientation formation and less defects. The purpose of this study is to find an optimum buffer layer for the MFISFET structure. MgO and CeO2 were deposited as buffer layers using e-beam evaporation and rf magnetron sputtering methods. Major experimental parameters were the substrate temperature, the deposition rate, and the film thickness, etc. The crystallinity and preferred orientation were checked by XRD and pole figure, respectively, and the interface between the oxide layers and Si substrate was investigated by the SEM and the interface trap density measured in C-V curve. PZT thin films were deposited on the buffer layers using the sol-gel and the rf magnetron sputtering methods. The crystallinity and the electrical properties, such as C-V curve and P-E curve, etc., were investigated. The compositional profile near the interface between the ferroelectric thin film and the buffer layer was investigated by AES. By introducing buffer layer between PZT thin film and Si(100) substrate, it was possible to fabricate (100) oriented PZT thin films on Si.

10:30 AM U17.7 
STRUCTURE AND PHYSICAL PROPERTIES OF Bi4Ti3O12 THIN FILMS PREPARED BY APMOCVD AND RTA. H.Wang, S.X.Shang, Z.Wang, M.Wang, Institute of Crystal Materials, Shandog University, Jinan, CHINA.

Ferroelectric Bi4Ti3O12 thin films on Si(100) substrates have been prepared by atmosphric pressure MOCVD and rapid thermal annealing (RTA). The metalorganic precursors used were triphenyl bismuth [Bi(C6H5)3 and titanium isopropoxide . The crystal structure of films were examined by x-ray diffraction analysis (XRD) before and after RTA processes. The leakage current, interfacial properties and memory effect of metal/Bi4Ti3O12/Si/metal structure were studied by I-V and C-V measurements. The results show that the Bi4Ti3O12 film has a (00L) preferred orientation after RTA processes. The C-V hysteresis measurements yielded a 3.5V memory window in response to a 8V programming voltage for a MIS structure.

10:45 AM U17.8 
DIRECT WAFER BONDING AND LARGE AREA PULSED LASER DEPOSITION: AN INNOVATIVE WAY FOR THE INTEGRATION OF FERROELECTRIC OXIDES INTO SILICON TECHNOLOGY. M. Alexe, A. Pignolet, J.F. Scott*, D. Hesse, and U. Gösele, Max Planck Instgiute of Microstructure Physics, Halle/Saale, GERMANY *On leave of absence from: University of New South Wales, Sydney, AUSTRALIA

The last decade has seen a surge in interest in ferroelectric thin films due to the wide range of their potential applications in microelectronics. Because of the high processing temperatures and the presence of heavy metals, the direct integration of ferroelectric films into the silicon technology without damaging the underlying semiconductor devices is a challenge. A possible novel fabrication process of ferroelectric-semiconductor heterostructures based on direct wafer bonding and layer transfer is presented. This new method allows very sharp interfaces and prevents thermal degradation or thermally induced chemical reactions at the ferroelectric-semiconductor interface. Polycrystalline and epitaxial Bi-layered pervoskites and PZT ferroelectric thin films have been deposited on 3-inch p-type Si (100) wafers using chemical solution deposition and pulsed laser deposition. These wafers were then directly bonded to a silicon wafer in a micro-cleanroom. High-resolution transmission electron microscopy shows that the bonded and reacted ferroelectric semiconductor interfaces are structurally improved. Metal-Ferroelectric-Silicon (MFS) structures, whose ferroelectric-semiconductor interface is actually the bonded interface, were built by polishing down and etching the handling wafer away, prior to deposition of a top metallic electrode. Electrical properties, i.e. C-V, I-V and P-E characteristics, were measured on these MFS structures and will be presented as well as their microstructural properties.

11:00 AM U17.9 
(Mn, Sn) DOPED-PZT/YBa2Cu3O7+y HETEROSTRUCTURE FOR IR DETECTOR ARRAY. Y.Q. Xu, N.J. Wu, D. Liu, J.Y. Fan and A. Ignatiev, Space Vacuum Epitaxy Center and Texas Center for Superconductivity, University of Houston, Houston, TX.

(Mn, Sn) doped-PZT (PMS7iT)lYBa2Cu307+y (YBCO) heterostructure on YSZ/Si substrate has been integrated into array for infrared (IR) detector. PMSZT films with good expitaxy on C-oriented YBCO conducting oxide electrode have been successfully grown by a pulsed laser ablation deposition technique. The ferroelectric properties and IR radiation response of PMSZT films have been studied. Good hystersis loops of PMSZT films were observed with the coercive field Ec is 94 kV/cm and the remnant polarization Pr is 15 C/cm2. The dielectric constant of PMSZT film F as s function of temperature was measured in the range of 25-300C and curie temperature TC of PMSZT film is about 185C. The I-V curve shows that PMSZT films have high electrical field breakdown strength with values exceeding 400kv/cm and can be integrated with IC for IR detector array. The PMSZT IR detectors were examined by their lR radiation response dependent upon sample temperature and IR source wavelength. The experimental results given show that the detectors have high pyroelectric coefficient of 23 nc/cm2k, and high pyroelectric figures of merit Fv of 15.5 x 10-11 C*Cm/J and Fm of 9.5 x 10-9 C*Cm/J at 25C. The measured normalized detectivity D*at 2.5 m -19.5 m wavebands ranges from 2.5x108 Cm (Hz)1/2/W to 6.0x108 Cm (HZ)1/2/W.

11:15 AM U17.10 
ORIENTATION EFFECTS ON PYROELECTRIC PROPERTIES OF SOLUTION-DERIVED BISMUTH TITANATE FILMS. Tran D. Khang and Relva C. Buchanan, Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH.

Ferroelectric bismuth titanate (Bi4Ti3O12) thin films with controlled degree of a c-orientation were fabricated on Pt/Si substrate by solution spin-casting technique. The degree of c-orientation of films was characterized by XRD analysis and Raman spectroscopy. The dielectric and ferroelectric characteristics such as dielectric constant, dielectric loss factor, spontaneous polarization, and coercive field decreased over the range of (119-87), (0.04-0.015), (8-4 C/cm2), and (30-20 kV/cm), respectively as the degree of c-orientation of the films increased. Values for the pyroelectric coefficient, voltage responsivity, and voltage figure of merit were evaluated. These properties exhibited strong dependence on the degree of c-orientation of the films and, for a highly oriented film, reached values of 9.5 nC/cm2, 62 V/W, and 0.3 x 10-10C, cm/J, respectively. The inter-correlations between degree of c-orientation, grain morphology, and pyroelectric properties of the films will be discussed.

11:30 AM U17.11 
RESPONSIVITY OF FOUR-LAYER PYROELECTRIC DETECTORS. V.B. Samoilov*, S.J. Kang, and Y.S. Yoon, Inha University, Dept. of Electronic Materials & Device Eng., Inchon, KOREA.

Progress in the technology of ferroelectric materials during the last few years has made it possible to produce thin films with excellent ferroelectric properties. One of the attractive areas of applications for these films is pyroelectric detectors of infrared radiation, because their noise voltage decreases with decreasing sensitive-element thickness. Unfortunately, this beneficial effect on the detectivity D is restricted by an increase of the heat loss in the substrate and the environment with decreasing pyroelectric thickness. It has been shown that for low-frequency applications the pyroelectric layer should not be made too thin. The main issue in the development of thin-film pyroelectric detectors is the thermal insulation of the film. In this research, the temperature distribution under periodic thermal excitation and the pyroelectric response of a four-layer system consisting of front and back semi-finite media, a pyroelectric element, and an intermediate layer are found. Numerical results and approximate expressions are obtained for special cases, such as a detector with an air gap between the pyroelectric layer and the bulk substrate and a detector on a substrate of finite thickness in air environment. The responsivities of detectors with a lead-lanthanum-titanate (PLT) sensing element on either a Si and a SiO2 substrate are calculated as functions of the pyroelectric layer and the underlying layer thicknesses. It is found that the detector with an air gap has a frequency-independent responsivity over a wide frequency range. A correlation is found between the type of frequency response in each frequency region and the corresponding dominant mechanism for heat loss.

11:45 AM U17.12 
GROWTH AND CHARACTERIZATION OF COMPOSITIONAL GRADED Ba1-XSrXTIO3(BST) THIN FILMS BY MAGNETRON SPUTTERING. F. Jin*, G.W. Auner* and R. Naik**, *Electrical Engineering Dept, Wayne State University, Detroit, MI; **Physics Department, Wayne State University, Detroit, MI.

BaTiO3 and SrTiO3 are ferroelectric materials with different Curie temperatures. By tailoring the composition of Ba1-xSrxTiO3 (BST) solid solution, one can adjust the Curie temperature of the BST solid solution and achieve high pyroelectric coefficient at room temperature which is important for uncooled thermal image sensor application. Even more interesting are compositional graded BST thin films which recently have exhibited a dc offset in their P-V hysteresis loop and high temperature sensitivity in a broad temperature range. This new graded ferroeleetric material opens the way for the fabrication of low cost uncooled therrnal image sensors with high pseudo pyroelectric coefficients. 
In this study, BaTiO3 and SrTiO3 targets are co-sputtered on platinum coated silicon substrates in a magnetron sputtering system. BST films with various compositions and compositional gradients are formed. The composition of the BST films is controlled by adjusting the sputter rate of the BaTiO3 and SrTiO3 targets. The desired gradients of the films are achieved by coutinuously adjusting the relative powers sent to the two targets, and thus the sputter rate of the two targets during deposition. The compositions and the gradients of the deposited BST films were verified by electron beam microanalysis and x-ray photo-emission spectroscopy (XPS. The microstructure of the graded films were characterized by x-ray diffraction and SEM. The electrical properties of the deposited films such as dielectric constant, are also measured. The P-V hysteresis loop of the films, measured using a modified Sawyer-Tower circuit, and the calculated pseudo pyroelectric coefficient of the films will be presented.