Meetings & Events

Spring 1999 logo1999 MRS Spring Meeting & Exhibit

April 5-9, 1999 | San Francisco
Meeting Chairs: Katayun Barmak, James S. Speck, Raymond T. Tung, Paul D. Calvert

Symposium BB—Multicomponent Oxide Films for Electronics



Dave H.A. Blank
Applied Physics
Univ of Twente
Enschede, 7500 AE NETHERLANDS

Chang-Beom Eom
Dept of Mech Engr & Matls Sci
Duke Univ
1104 Engineering Bldg
Durham, NC 27708

Marilyn E. Hawley
Matls Sci & Tech Div
Los Alamos National Lab
MS G755
Los Alamos, NM 87545

Darrell G. Schlom
Dept of MS&E
Penn State Univ
149 Mtls Res Lab-103 Steidle Bldg
University Park, PA 16802-5005

Stephen K. Streiffer
Materials Science Division
Argonne Natl Laboratory
MSD 212/C212
Argonne, IL 60439-4838

Symposium Support

  • Argonne National Laboratory
  • Los Alamos National Laboratory 


Proceedings published as Volume 574
of the Materials Research Society
Symposium Proceedings Series.
* Invited paper


Tuesday, April 6, 8:30 - 11:45 a.m.
Salon 7 (Marriott Hotel)
tutorial will cover the four main vapor-phase-deposition methods currently used in industrial and research laboratories for fabrication of high-quality complex oxide films. The tutorial will begin with a general overview of vapor phase-deposition methods followed by in-depth descriptions of each of the four techniques (PLD, Sputter Deposition, MOCVD, and MBE) by the respective instructors. Each of the four segments will include background information, a description of the method, the current state of the art, new trends, and unique advantages and limitations, e.g., for fabrication of particular oxide materials or metastable phases, scalability, unusual geometries, and integration in multistep hybrid device fabrication schemes. The intention of the tutorial is to give the attendee a fundamental background on each method, the strengths of each technique, the ease/difficulty/cost of setting them up, and future directions.

Masashi Kawasaki, Tokyo Institute of Technology (PLD)
Julia M. Phillips, Sandia National Labs (Sputter Deposition)
Jeffrey F. Roeder, Advanced Technology Materials, Inc. (MOCVD)
Jean-Pierre Locquet, IBM Zurich Research Laboratory (MBE)

Chairs: Andrew D. Kent and David C. Larbalestier
Tuesday Afternoon, April 6, 1999
Salon 7 (M)
1:30 PM *BB1.1 TRANSITION METAL OXIDES. T.H. Geballe , Applied Physics Dept., Stanford University, Stanford, CA.

The wide range of electrical and magnetic properties of transition metal oxides were subject to experimental, theoretical and practical uses long before the birth of materials science. Today more than ever the field is thriving with many experimental and theoretical challenges and opportunities. The intense interest in the high- temperature superconducting cuprates has focused much attention on how to deal with transport by strongly interacting charge carriers. There are no simple models with predictive powers for understanding the magnetic and electrical properties of transition metal oxides generally as have been long available for covalent semiconductors. It is even more difficult to model the behavior across the interfaces in heterostructures which are designed to have device potential. It is thus necessary to rely upon experiment and to study very simple interfaces in which reliable measurements can be made.

2:15 PM *BB1.2
PHYSICAL PROPERTIES OF FERROMAGNETIC PEROVSKITE MANGANITES. H.Y. Hwang , Bell Laboratories, Lucent Technologies, Murray Hill, NJ.

In recent years, static and dynamic lattice distortions have been shown to significantly influence the magnetotransport and magnetic properties of ferromagnetic manganites. The resistivity, Hall effect, and spin dynamics have been systematically studied for single crystals with decreasing TC, and we show that their behavior can be understood in terms of the tendency toward charge localization and ordering. These materials are also characterized by complete spin polarization in the ferromagnetic ground state, a property currently being explored for utilization in spin-dependent tranport phenomenon. The intergrain magnetoresistance observed in polycrystalline samples reveals the strong role of second-order tunneling via interfacial spins at the grain boundaries, and these interfacial spins dominate the temperature dependence of the low-field magnetoresistance.

3:15 PM BB1.3
FIRST PRINCIPLES INVESTIGATION OF MULTIFERROISM IN PEROVSKITE MANGANITES. Nicola A. Hill , Materials Department, UC Santa Barbara and Karin M. Rabe, Dept. of Applied Physics, Yale University.

We present results of our first principles calculations which indicate the simultaneous occurrence of ferromagnetism and ferroelectricity in perovskite structure bismuth manganite, BiMnO3. Many rare earth perovskite manganites exhibit strong coupling between either their magnetic and structural, or magnetic and electronic order parameters, and the Colossal Magnetoresistive (CMR) effect is thought to be related to the resulting magnetically induced structural and metal-insulator phase transitions. Similarly, the strong coupling between the ferroelectric and structural order parameters in many ferroelectric oxides has led to their widespread use in transducers and actuators. However the existence of strong coupling between all three of the electric, magnetic and structural order parameters (leading to ferroelectricity, ferromagnetism and ferroelasticity) is rather rare. Using a plane wave pseudopotential (PWPP) implementation of density functional theory (DFT) within the local spin density approximation (LSDA), we determine the origin of the differences between BiMnO3 and the conventional rare earth manganites, which are antiferromagnetic and do not have ferroelectric ordering. Our results indicate that covalent bonding between the bismuth and oxygen ions both promotes the ferroelectric distortion, and over-rides the Jahn-Teller facilitated antiferromagnetic super-exchange found in the conventional manganites. We discuss recent experimental results which support this hypothesis. Our study illustrates that LSDA calculations can provide detailed understanding of the fundamental physics underlying complex phenomena such as multiferroism. This knowledge in turn assists in the search for new multiferroic materials, and in optimization of their properties for specific device applications.

3:30 PM BB1.4
THE ROLE OF NICKEL AND ZIRCONIUM DOPING ON THE PROPERTIES OF BARIUM ZINC TANTALATE CERAMICS. Nate Newman , Gang Rong, ECE Dept., Northwestern University, Evanston, IL; David Cronin, Trans-Tech Inc., Adamstown, MD.

Ba(Zn1/3Ta2/3)O3 ceramic material is widely used in current microwave communication applications due to its large-dielectric constant ($\sim$30) and ultra-low loss tangent (<10-4 @10GHz). Nickel doping is commonly utilized to adjust the temperature-coefficient of resonance-frequency, $\tau$f, to near-zero. Zr is also added to reduce the annealing time required to attain low loss. In this paper, we report the influence of these transition metal impurities on the electrical, optical, magnetic and structural properties of Ba(Zn1/3Ta2/3)O3 ceramics. The nickel ion is found to be paramagnetic with an effective magnetic moment of 3.223+0.046. Discrete internal transitions between nickel 3d orbitals dominate the optical properties of Ni-doped Ba(Zn1/3Ta2/3)O3. Transitions from the 3$\Gamma$2(F) Ni2+ ground state to the 4$\Gamma$3(F), 3$\Gamma$1(D), 5$\Gamma$1(D) and 4$\Gamma$3(P) excited states result in absorption at $\sim$1.55, 1.75, 2.50, and 2.80 eV, respectively. The ligand field strength of the neighboring oxygen ions, denoted in crystal field theory as 10Dq, ranges from $\sim$7300 cm-1 for small Ni concentrations (0.25% atomic concentration) to $\sim$7700 cm-1 for large Ni concen- trations (1% atomic concentration). A significant increase in the continuum background in the visible spectral region is correlated with an increase in the microwave loss tangent. The physical origin of this is attributed to alterations in the local environment of Ni due to the presence of point defects. This finding suggests that point defects play an important role in microwave loss in practical dielectric material.

3:45 PM BB1.5
SUBSTRATE-INDUCED CHANGES IN THE COLOSSAL MAGNETORESISTANCE PROPERTIES OF ULTRATHIN FILMS OF (La,Ca)MnO3. J. Aarts , S. Freisem, T. Nojima, Kamerlingh Onnes Laboratory, Leiden University, Leiden, THE NETHERLANDS; H. W. Zandbergen, Laboratory of Material Science, Delft University of Technology, Delft, THE NETHERLANDS.

Ultrathin films (6 nm) of La0.73Ca0.27MnO3 on SrTiO3 exhibit properties quite different from the bulk. They are ferromagnetic insulating (FI), without showing the insulator-to-ferromagnetic metal transition which occurs in bulk material, and which is responsible for the `colossal magnetoresistance' (CMR) effects. On the other hand, the resistance is still strongly reduced upon applying a magnetic field, which is unusual for the FI state. Electron microscopy shows that such films are perfectly crystalline but that their structure is different from the bulk. An important feature is a Jahn-Teller-like distortion of the MnO6 octahedra, which is imposed by the lattice mismatch with the substrate and apparently the cause of the changed physical properties. The occurrence of such structural changes even for a small mismatch (1%) has a number of consequences for growth, relaxation and physical properties of films and multilayers of CMR-type perovskites, which will be discussed.

4:00 PM BB1.6
GROWTH OF METALLIC AND FERROELECTRIC LaTiO3+x THIN FILMS. J. Fompeyrine 1, J.W. Seo1,2, S. Gariglio3, J.M. Triscone3, S. Molitor4, H. Siegwart1 and J.P. Locquet1; 1IBM Research Division, Zurich Research Laboratory, Ruschlikon, SWITZERLAND; 2Université de Neuchâtel, Institut de Physique, SWITZERLAND; 3University of Geneva, Department of Condensed Matter Physics, SWITZERLAND; 4Omicron Vakuumphysik GmbH, Taunusstein, GERMANY.

The electrode materials and the interfaces with the ferroelectric are key parameters for FRAM devices. An alternative route is to make use of only one material, where the physical properties of each layer are tuned from metallic to ferroelectric through its oxidation state, while minimizing the changes in crystal structure. Rare earth (RE) RETiO3+x and related compounds are good candidates for this process, evolving from x = 0 to x = 0.5 through a semiconducting, then metallic and finally ferroelectric state at room temperature. Here, the first systematic study of epitaxial growth in the LaTiO3+x system is reported. MBE-grown epitaxial films are obtained on SrTiO3 and LaAlO3 (100) or (110) oriented substrates, and the value of x is tuned by adjusting the oxygen partial pressure during deposition. The films are metallic for low oxygen pressure ($P = 2 \times 10^{-6}$ Torr), and ferroelectric for high oxygen pressure ($P = 1.5 \times 10^{-5}$ Torr). A TEM analysis reveals a perfect ordering of the additional oxygen layers, parallel to the substrate surface. Using in-situ RHEED monitoring, oscillations of the in-plane lattice parameter are observed and allow the growth mechanism to be clarified. Since LaTiO3.5 possesses a unique polarization axis, the epitaxial orientation of the film implies a unique in-plane polarization. Investigations of ferroelectricity using atomic force microscopy will be discussed.

4:15 PM BB1.7
COMPREHENSIVE STUDY OF LEAD-BASED PIEZOELECTRIC THIN FILMS WITH THE COMBINATORIAL APPROACH. H. Chang , I. Takeuchi, J.W. Li and X.D. Xiang, Lawrence Berkeley National Laboratory, Berkeley, CA.

There have been various attempts in improving piezoelectric properties of multi-component oxides such as PbZr0.52Ti0.48O3. Most of the efforts have involved doping with ``hard'' or ``soft'' dopants. Effects of variations in stoichiometries of various ions have also been explored. However, the number of different dopants and the material phase space to be investigated for optimum piezoelectric performance is large. Thus, combinatorial methods may be the best set of approaches for systematic studies of the effects of compositional variations on piezoelectricity. In these methods, up to thousands of different samples are fabricated on individual substrates. Continuous variations in compositions can also be generated with the composition phase spread method with which the piezoelectric properties of various compositions within a ternary phase diagram can be studied. These samples are analyzed with a scanning optical detection system, allowing the rapid and systematic characterization of the compositional dependence of piezoelectricity. We have fabricated various Pb-based perovskite piezoelectric thin films with epitaxial quality with traces of pyrochlore phases according to x-ray diffraction studies. The dependence of piezoelectricity of [Pb(Mg1/3Nb2/3)O3]0.67-[PbTiO3]0.33 (PMN-PT) on different dopant and dopant concentrations will be reported. Results from phase spread samples of PMN, PT and PbZrO3 will be discussed. Issues involving crystal quality and microstructures of these combinatorial samples will also be discussed.

4:30 PM *BB1.8 (Ni,Zn)Fe2O4 FERRITE FILMS FOR MICROWAVE APPLICATIONS DEPOSITED BY MOCVD ON SINGLE CRYSTAL SUBSTRATES. Angus Kingon , David Gangaware and Reneí Woolcott, Department of Materials Science and Engineering, North Carolina State University and Jeff Roeder, Advanced Technology Materials, Inc.

In this program we are investigating the feasibility of replacing discrete, bulk ferrite components such as convolvers, which are utilized in radar applications, by ferrites which are fabricated by thin film process methods. We report the deposition of (Ni,Zn)Fe2O4 films with the spinel structure on MgO substrates by liquid delivery source MOCVD. The emphasis of the presentation is on the relationships between MOCVD process conditions, the resulting microstructures, and the measured properties of the films. We have found that the MOCVD process window is strongly influenced by the chemistry of the precursors, and in particular the Zn organometallic precursor. The Zn substitution into the film reduces the robustness of the process in comparison with the nickel ferrite endmember (NiFe2O4). The choice of Zn precursors will be discussed. The films retain an epitaxial relationship with respect to the MgO substrate over a wide range of cation stoichiometries. Film microstructures have been characterized by X-ray diffraction, RBS channelling, and atomic force microscopy. Composition and microstructure has been correlated with magnetic properties, in particular the magnetic susceptibilities and magnetic hysteresis loops obtained by vibrating sample magnetometry. Under optimized conditions, magnetic properties approach those of the bulk values. The outlook for the integration into microwave systems will be briefly discussed

Chairs: Chang-Beom Eom and Marilyn E. Hawley
Tuesday Evening, April 6, 1999
8:00 P.M.
Salon 7 (M)
EFFECT OF GROWTH CONDITIONS ON THE THERMAL STABILITY, SURFACE MORPHOLOGY, AND PHOTOELECTRIC WORK FUNCTION CHARACTERISTICS OF IRIDIUM OXIDE THIN FILMS. Babu R. Chalamala , Yi Wei, Robert H. Reuss, Motorola, Inc., Flat Panel Display Division, Tempe, AZ; Sanjeev Aggarwal, Bruce E. Gnade, R. Ramesh, Department of Materials Science, University of Maryland, College Park, MD; John B. Bernhard, Edward D. Sosa, Ambrosio A. Rouse and David E. Golden, Department of Physics, University of North Texas, Denton, TX.

The effect of thermal growth conditions on the stability, morphology and surface work function of iridium oxide thin films grown by annealing the Ir in oxygen ambience is presented. The samples were analyzed using x-ray diffraction, temparature programmed desorption, x-ray photoelectron spectroscopy, atomic force microscopy and photoelectric work function measurements. We found that with increasing temperature during the oxide growth, the surface becomes more IrO2(110) and this is manifested in as a sharpening of the photoelectric energy distributions at 800$^{\circ}$C. The surface work function was determined to be 4.23 eV using ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy analysis shows that IrO2 starts to form at 600$^{\circ}$C accompanied by surface roughening. Annealing the Ir film at 900$^{\circ}$C in O2 ambient leads to complete desorption of the film.


The uniaxial magnetic anisotropy in thin La0.67Ca0.33MnO3 (LCMO) films grown on SrTiO3[001] (STO) substrate has been measured and interpreted to be due to the strain arising from a film/substrate lattice mismatch1. The possibility of producing strained LCMO films grown on LaAlO3 (LAO) substrate with the easy magnetization axis along film normal has been proposed. We performed first - principles relativistic full-potential linearized augmented plane wave calculations for strained tetragonal ferromagnetic La(Ba)MnO3 with an assumed experimental structure of strained LCMO-films grown on STO and LAO substrates. Self-consistent calculations for the magnetization along [001]-axis were performed, and the local-force theorem for out-of-plane to in-plane magnetization rotation was then used to calculate the uniaxial magnetic anisotropy energy (MAE). The calculated MAE values, $-41 \; \mu eV$ for LaMnO3(STO) and $-53 \; \mu eV$ for BaMnO3(STO), are in excellent agreement with experiment for LCMO films ($-56 \; \mu eV$). For LaMnO3(LAO) we calculated the MAE to be $38 \; \mu eV$ and confirmed the perdiction of Ref.1. We also analyze the applicability of linear magnetoelastic theory for describing the stain dependence of MAE, and estimate magnetostriction2 in LCMO-films. [1] J. O'Donnell, Appl. Phys. Lett. 72 1775, (1998); [2] A. B. Shick, Phys. Rev. B R14259, (1997).

STUDIES OF BaTiO3 FILMS ON (100) SrTiO3 SUBSTRATE. S.P. Chen , Los Alamos National Laboratory, Los Alamos, NM.

The structures, c/a ratio, energetics, and dielectric properties of BaTiO3 films (1 to 10 layers) on the (100) surface of SrTiO3 substrate were studied by an ab initio (LAPW) and shell-model calculations. The results will be compared with available experiments.


We have grown thin films of La1-xCaxMnO3 using off-axis sputtering for x $\leq$ 1/3 onto (100)-oriented NdGaO3 and SrTiO3 substrates by cosputtering from individual targets of LaMnO3 and La2/3Ca1/3MnO3. As-deposited films of La2/3Ca1/3MnO3 have a peak resistance temperature and Curie temperature of $\approx$ 260 K. We see a difference in the peak temperature between the two substrates of $\approx$ 15 K, with samples on NdGaO3 having higher peak temperatures. As the value of x is reduced from 1/3, the peak resistance temperature decreases until x $\approx$ 0.15, when the peak temperature has an upturn. Even down to x=0 we still observe a metal-insulator transition (at 185 K) for films on NdGaO3, while samples on SrTiO3 show only activated behavior. As the value of x is reduced, the out-of-plane lattice constant increases for films on both substrates, and there is a marked reduction in the x-ray peak width for the x=0 samples on NdGaO3. We will discuss the low temperature resistivity as well as the magnetoresistance for the samples as a function of the Ca doping.


All perovskite La1-xSrxCoO3/Pb(Ta0.05Zr0.48Ti0.47)O3(PTZT)/ La1-xSrxCoO3 ferroelectric capacitors were deposited on Pt/TiO2/SiO2/Si(001) substrates by pulsed laser deposition. The grain orientation of PTZT films are strongly influenced by the cation ratio of La1-xSrxCoO3. The PTZT films deposited on La0.75Sr0.25CoO3(tetragonal structure) coated substrates prefer (110)-orientation, and those deposited on La0.5Sr0.5CoO3 and La0.25Sr0.75CoO3 (cubic structure) coated substrates prefer (001) and (110)-orientation. SEM studies on the surface and cross-section show diffrence in morphology and grain microstructures. The relative growth mechanisms for the ferroelectric films PTZT were discussed.

EFFECTS OF A Bi4Ti3O12 BUFFER LAYER ON SrBi2Ta2O9 THIN FILMS PREPARED BY METAL ORGANIC DEPOSITION. G.D. Hu, J.B. Xu , I.H. Wilson, W.Y. Cheung, N. Ke and S.P. Wong, Dept. of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, NT, HONG KONG.

Ferroelectric SrBi2Ta2O9 (SBT) thin films with 20 mol$\%$ excess Bi contents have been deposited on the Bi4Ti3O12 (BTO) buffered Pt/Ti/SiO2/Si substrates using metal organic decomposition technique at annealing temperature ranging from 600$^{\circ}$C to 750$^{\circ}$C. No pyrochlore phase was found in the SBT films although the Bi2Ti2O7 phase appeared in the BTO buffer layer. The film with (200) predominant orientation was formed at 650$^{\circ}$C. The effects of the BTO buffer layer and post annealing temperature on the dielectric and ferroelectric properties of SBT thin films have been analyzed.

MULTICOMPONENT TRANSPARENT CONDUCTING OXIDE FILMS PREPARED BY SOL-GEL PROCESSING. Doreen D. Edwards , Warren S. Dabney, Duangsamorn Charoenkul, New York State College of Ceramics at Alfred University, Alfred, NY.

Transparent conducting oxides (TCOs) are use as electrodes in flat panel displays, solar cells, and other optoelectronic devices. The unique combination of transparency to visible radiation and relatively high electrical conductivity is typically achieved by degenerate donor doping of an insulating parent oxide with a band gap greater than 3 eV. Most commercial TCOs use a single-cation oxide as the parent material, typically indium oxide or tin oxide. Over the past five years, several researchers have reported TCOs based on multi-cation parent oxides. In the current work, multicomponent oxide films were deposited by sol-gel spin coating on glass and quartz substrates. The materials investigated include phases in the zinc-indium-oxide system, the indium-tin-oxide system, and the indium-tungsten-oxide system. The influence of processing conditions on the optical, electrical, and electrochromic properties of the films will be discussed.

DIELECTRIC PROPERTIES OF STRAINED (Ba,Sr)TiO3 THIN FILMS. J. Fompeyrine 1, J.W. Seo1,2, R.B. Laibowitz3 and J.P. Locquet1, 1IBM Research Division, Zurich Research Laboratory, Ruschlikon, SWITZERLAND; 2Université de Neuchâtel, Institut de Physique, SWITZERLAND; 3IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY.

Perovskites with a high dielectric constant $\varepsilon$ such as (Ba,Sr)TiO3 (BSTO) are promising materials to replace SiO2 in the next DRAM generation. However, the high $\varepsilon$ present in bulk compounds -- related to the proximity of a ferroelectric phase with a Curie temperature close to 300K -- is not easily reproduced in thin films. The main causes for this reduction are believed to be defects, interface & surface effects and lattice deformations. For instance, recent theoretical predictions suggest a doubling (halving) of $\varepsilon$ for a homogeneous expansion (compression) of 0.01 Å and the appearance of a strain-induced ferroelectric state for an expansion > 0.02 Å. Within this framework we used block-by-block molecular beam epitaxy under a beam of atomic oxygen to grow homogeneously strained ultrathin BSTO films on various metallic (including Nb doped SrTiO3) and insulating substrates. The BSTO lattice deformations under compressive and tensile epitaxial strain are characterized using x-ray diffraction measurements and structural refinements. Local strain variations and microscopic defects were analysed using transmission electron microscopy. Finally, we correlated the dielectric properties ($\varepsilon$, leakage, ...) of these films with the lattice deformations.

VOLTAGE SWITCHING IN ULTRA-THIN Pb(ZrxTi1-x)O3 THIN FILMS. Seung-Hyun Kim , Dong-Joo Kim, Jon-Paul Maria, Angus I. Kingon, North Carolina State Univ, Dept of Materials Science and Engineering, Raleigh, NC.

To accomodate the trend of reduced operating voltages in non-volatile memory devices, it is important to study methods of making high quality thin ferroelectric layers which can exhibit fully saturated polarization at <3V applied. Such low-voltage operation has been demonstrated for SrBi2Ta2O9 (SBT) thin films, however much difficulty has been encountered in doing the same for Pb(ZrxTi1-x)O_3(PZT). Recently, we have fabricated high-quality (111)-oriented PZT (Zr/Ti=30/70) films with and without Ca, Sr, and La dopants by chemical solution deposition (CSD). Film thicknesses between 50 and 100 nm were investigated. In general, these ultra-thin films exhibit electrical properties which are comparable to samples that are an order of magnitude thicker. At the 50 nm thickness, P_rvalues in excess of 20C/cm^2, and leakage currents of 10^-7A/cm^2(at 5V) were observed. To achieve these results, special attention was paid to the solution chemistry and to the drying/pyrolysis conditions. Specifically, low molarity solutions and multiple-step drying/pyrolysis conditions were required. Previous reports have indicated that the inability to observe satisfactory electrical properties in very thin PZT thin films resulted from scaling issues. However, these results suggest that with stringent process control, microstructures, crystal structures, and electrical properties consistent with well-prepared thick CSD films can be achieved in 50 nm$ 100 nm layers.{\newline\newline\noindent{\textbf{ BB2.10 }}\newline\noindent... ...\newline\noindent{THICKNESS DEPENDENCY OF FERROELECTRIC PROPERTIES OF SrBi_{2}$Ta2O9 THIN FILMS. Seung-Hyun Kim , D.J. Kim, M. Park, H. Maiwa, J.P. Maria, A.I. Kingon, North Carolina State University, Dept of Materials Science and Engineering, Raleigh, NC; J.A. Christman, R.J. Nemanich, North Carolina State University, Dept of Physics, Raleigh, NC.

Ferroelectric non-volatile memories (FENVMs) offer advantages over conventional non-volatile memories, which include lower writing voltages, faster writing speeds, better endurance, and potentially fewer processing steps. The most recent advance in the development of FENVMs has been the demonstration of fatigue free operation in SrBi2Ta2O9 (SBT) capacitors with Pt electrodes. In comparison to Pb-based perovskites, SBT thin film processing technology is relatively young, thus a satisfactory understanding of the structure-process-property relationships has yet to be developed. In this study, the performance of SBT thin films for ferroelectric non-volatile memory applications is investigated, primarily as a function of film thickness, in the range of 50 nm - 300 nm. A novel chemical solution deposition method (CSD) involving the incorporation of a chelating agent (which provides solution stability) was used to synthesize the SBT layers. Through the thickness series, crystallographic orientation, surface morphology, polarization hysteresis, fatigue, imprint and the field-dependence of permittivity were measured. The results of all measurements will be presented, with specific attention paid to the implications on devices which may require specific capacitor geometries.

CHEMICAL VAPOR DEPOSITION OF STRONTIUM BARIUM NIOBATE THIN FILMS USING METAL ALKOXIDE PRECURSORS*. Ruichao Zhang , Ren Xu, Univ of Utah, Dept of Materials Science and Engineering, Salt Lake City, UT.

Strontium barium niobate, SrxBa1-xNb2O6 (SBN) is a promising material for optoelectronic applications. A new two-step Metal-Organic Chemical Vapor Deposition (MOCVD) processing method has been used in this study to prepare SBN thin films. Two thin layers of single phase SrNb2O6 and BaNb2O6 were deposited alternately on the substrate, and the solid solution of SBN was obtained by the following high temperature annealing. Metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 were used as single source in the deposition of stoichiometric SrNb2O6 and BaNb2O6 thin films, respectively. The stoichiometry control of the SrNb2O6 and the BaNb2O6 thin films were achieved through deposition process control, according to the double metal alkoxide evaporation characteristics. The evaporation behavior of double metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 were studied, and the results were used to compare with the evaporation of single alkoxide Nb(1-OC4H9)5 for better deposition process control. The as-deposited films were amorphous, and annealing was used to induce the crystallization of the films. The orthorhombic phases of SrNb2O6 and BaNb2O6 were obtained at lower annealing temperature around $700^\circ$C and the tetragonal phases of SrNb2O6 and BaNb2O6 were obtained at higher annealing temperature of $1000^\circ$C. The SBN thin film on Si(100) substrate has a highly preferred orientation of (002) direction. Experimental results indicate that the new process allowed a convenient control of the stoichiometry of the multicomponent metal oxide films SrNb2O6 and BaNb2O6, and the preparation of solid solution SBN which contains both multicomponent metal oxides. The molar ratio of strontium and barium can be easily controlled by the thickness of each layer. Key words: MOCVD, strontium, barium, niobate, thin film, metal alkoxide, stoichiometry.
* Supported by National Science Foundation DMR-9526165


PULSED LASER DEPOSITION OF THIN OXIDE FILMS. Valentin Craciun , Joshua Howard, Rajiv K. Singh, Dept of Materials Science and Engineering, University of Florida, Gainesville, FL.

Pulsed Laser Deposition (PLD) has been proven to be one of the most successfully thin film growth technique of the last decade. To improve the properties of the grown films, several deposition parameters such as laser fluence, wavelength, pulse duration, repetition rate, target-substrate distance, substrate temperature and pressure of the ambient gas are usually adjusted. Several reports have indicated that the use of a more reactive deposition atmosphere than the usual molecular oxygen, O2, was beneficial for the quality of grown oxide films. However, the use of very reactive oxidizing species such as ozone and atomic oxygen has been very scarce so far. We have previously shown that the quality of PLD grown oxide films can be significantly improved after a moderate temperature anneal in oxygen under UV radiation illumination. We report here the in-situ use of a low pressure mercury lamp optimized to emit 184 nm radiation for enhanced dissociation of O2 and formation of ozone during the PLD of several oxide thin films (ZrO2, CeO2, ZnO, Y2O3). Investigation of the grown films by XPS, TEM, XRD, and SEM techniques show evidence that the use of the UV lamp has allowed a reduction of the substrate deposition temperatures from the previous optimum values by at least 100 deg C without any measurable degradation of the films properties. This could be an important advantage especially for multilayer structures or temperature sensitive substrate materials.

Abstract Withdrawn.

LOW TEMPERATURE ITO FORMATION WITH OXYGEN CLUSTER ION ASSISTED DEPOSITION TECHNIQUE. J. Matsuo 1, K. Murai2, S. Tamura2, M. Kiuchi2, N. Umesaki2 and I. Yamada1; 1Ion Beam Engineering Experimental Laboratory, Kyoto University, Sakyo, Kyoto, JAPAN; 2Osaka National Research Institute, Ikeda, Osaka, JAPAN.

There is a strong demand to develop low temperature fabrication process of high-quality oxide films, which are widely used in electrical and optical devices. A new technique called ``Cluster Ion Assisted Deposition'' is proposed for low temperature growth of oxide film. In this technique, cluster ions, which can transport thousands of atoms per ion with very low energy per constituent atom, were irradiated on the surfaces during metal deposition. For example, an average energy of a 10 keV cluster ion containing 1000 atoms is only 10 eV, which is adequate to enhance oxidation without damage formation. We have demonstrated Tin doped Indium Oxide (ITO) film formation with this new technique. Very smooth, highly transparent (80% ) and low resistivity ($ < 2 \times 10^{-4}$$\Omega$cm) films were obtained with oxygen cluster ions accelerated at 7 keV. The resistivity is lowest value for the films grown at room temperature, as far as we know. The energetic oxygen clusters dissociate at the surfaces and reacted to the metal atoms with about 10% of them being incorporated, when the kinetic energy of the cluster ion was above 5 keV. This incorporation probability of an energetic cluster is a few orders of magnitude of higher than that of oxygen molecules. Oxidation reaction can be enhanced by energetic cluster ion bombardment which offers a new ion assisted thin film formation technique.

TRANSPARENT CONDUCTING COATINGS MADE FROM REDISPERSABLE, CRYSTALLINE, NANOSCALED POWDERS. C. Goebberta, H. Bishta, M.A. Aegerter a, R. Nonningerb, H. Schmidtb, INM Institut fur Neue Materialien, aDepartment of Coating Technology, bDepartment of Chemistry and Technology of Nonmetallic Inorganic Materials, Saarbruecken, GERMANY.

Electrically conducting films on glass substrates are widely used as transparent electrodes and as heat reflectors. A new wet chemical concept will be presented for the preparation of SnO2:Sb (ATO) and In2O3:Sn (ITO) coatings. It is based on the deposition by spin, dip or spray techniques of a solution containing already dense and crystalline nanoscaled particles fully redispersable in a solvent. The synthesis of these particles is carried out at temperatures < 200$^{\circ}$C in a solution by a controlled growth reaction using SnCl4 and InCl3 as precursors and SbCl3 and SnCl4 as dopant up to a concentration of 10 mole $\%$. The aggregation of the particles is avoided by in situ surface modification with bifunctional organic molecules. The resulting nanocrystalline particles can be redispersed in ethanol at pH<6 (for ITO) or water at pH>8 (for ATO) with solid contents up to 40 wt.$\%$. Single layers with thickness up to 200 nm (ATO) and 400 nm (ITO) has been fabricated. The sheet resistance of the coatings decrease with the sintering temperature. Typical value for ATO coatings fired at 550$^{\circ}$C is 430$\Omega$sq. For annealed ITO coatings, values of R=3 k$\Omega$sq (200$^{\circ}$C), 380$\Omega$sq (550$^{\circ}$C) and 90$\Omega$sq (900$^{\circ}$C) are obtained. Shelf life time stability has been tested up to 40 days at room temperature and 40$\%$ relative humidity. ATO and as fired ITO coatings are stable but the sheet resistance of the annealed coatings steadily increase with time. All coatings have a high optical quality with a transmission in the visible range higher than 90$\%$. These films can be used as transparent electrodes for solar cells, touch screen panels, FOS / CRT coatings or as antistatic coatings on glass or plastic.

A P-TYPE TRANSPARENT CONDUCTOR - COPPER ALUMINUM DIOXIDE. R.E. Stauber 1, P.A. Parilla2, J.D. Perkins2, D. Young2, M. Fu, M. Duncan and D.S. Ginley2, 1University of Colorado, Boulder, CO; 2National Renewable Energy Lab, Golden, CO.

Transparent, p-type-conducting oxide films would enable the fabrication of a new class of electronic devices (potentially with transparent pn junctions) and impact photovoltaic, flat panel and ferroelectric applications. Thin films of CuAlO2 have already been demonstrated to be truly p-type.1 We have successfully reproduced the growth of c-axis CuAlO2 films with pulsed laser deposition (PLD). Phase pure growth is very difficult and X-ray diffraction patterns show that CuO, Cu2O, and CuAl2O4 is also present. The samples with the most (001) - oriented CuAlO2 were deposited in 100mT of oxygen, at a temperature of 713$^{\circ}$C on c-plane sapphire substrates. Preliminary measurements of the Seebeck and Hall coefficients confirm that these films are p-type conductors, though the carrier density of 6x1016/cm3 is quite low. The effect of several other growth parameters including substrate-to-target distance, heater-stage orientation, cool-down conditions, and laser fluence has been studied. There appears to be an exceptionally narrow window for in-situ growth. In-situ and/or ex-situ anneals appear to be one of the critical factors in the formation of the correct phase. We have also grown phase-pure bulk CuAlO2 ceramics by sintering a stoichiometric mixture of Al2O3 and CuO powders in air at 1100$^{\circ}$C for 40 hours, with periodic regrinding and pressing of the pellet. These are also p-type with a carrier density of 4x1015/cm3. Work is underway to optimize the annealing process, with an eye toward extending the phase boundary (which is known at high temperatures and oxygen pressures) down to the temperatures and partial pressures of oxygen appropriate for Pulsed Laser Deposition. 1 H. Kawazoe, et al., P-type electrical conduction in thin films of CuAlO2. Nature 389(30), 939-942(1997).

NUCLEATION AND GROWTH OF SPUTTER DEPOSITED ZnO:Al THIN FILMS ON SODA-LIME GLASS SUBSTRATES. Loren Rieth and Paul H. Holloway, University of Florida, Department of Materials Science and Engineering, Gainesville, FL.

Degenerately doped thin films of zinc oxide are useful in a variety of applications including front transparent contacts to Cu(In,Ga)Se2 thin film solar cells and flat panel displays. Improvement in the electrical properties of the front electrode results in an increased fill factor and higher efficiency solar cells. The interface between the sputter deposited ZnO:Al film and the substrate may have a negative influence on current transport through mechanisms such as interfacial recombination and/or scattering effects. As a first step in gauging the influence of the interface on the performance of sputter deposited ZnO:Al transparent electrodes, the structure of the interfacial region has been investigated during nucleation and growth of these thin films. Films with thicknesses ranging from $\sim$20 to 3000 Å were characterized using Atomic Force Microscopy (AFM), Auger Electron Spectroscopy (AES), and Hall measurements. The films were deposited by RF magnetron sputtering from a ceramic ZnO:Al2O3 (98wt$\%$:2wt$\%$) target onto cleaned 1 inch square soda-lime glass substrates maintained at 150$^{\circ}$C. AES spectra of the thin films do not have silicon peaks indicating they are continuous. AFM results show an increase in surface roughness due to an islanding structure. These results are consistant with the Strankski-Krastanov nucleation and growth mechanism. Hall measurements indicate that the films have carrier concentrations on the order of 1020/cm3, mobilities of <10 cm2/V$\cdot$s, and resistivities on the order of 10-3$\Omega$$\cdot$cm for thicker films. These results are related to their implications on solar cell performance.

Chairs: Xiaoqing Pan and Darrell G. Schlom
Tuesday Evening, April 6, 1999
8:00 P.M.
Salon 7 (M)

[001] tilt grain boundaries in the high-Tc superconductor YBCO, have long been known to have a deleterious effect on the critical current, Jc. In particular, it has frequently been observed that Jc decreases exponentially with increasing misorientation angle. While second phases and oxygen deficiency at the boundaries can obviously cause this effect, a reduction in Jc is still observed at clean boundaries that have been subject to highly oxidizing conditions. These results suggest that there is an underlying mechanism responsible for controlling Jc across these grain boundaries. Here we report the analysis of [001] tilt grain boundary properties based on structural unit models. All [001] tilt grain boundaries have been found to be composed of two distinct structural units. These structural units intrinsically contain under-coordinated copper sites as a result of a 2 x 1 grain boundary reconstruction. The under-coordinated sites are effectively oxygen deficient, meaning that from simple charge compensation, these grain boundaries intrinsically form carrier depletion layers. As the number of reconstructed sites increases linearly with misorientation angle, the effective width of the carrier depletion layer also increases linearly with misorientation angle. From a simple tunneling model, the upper limit of the observed Jc measurements at [001] tilt grain boundaries in YBCO is accurately reproduced. It should be noted that SrTiO3 has been observed to have the same effectively oxygen deficient structural units at [001] and [110] tilt boundaries. These results suggest that intrinsic donor states may exist at all tilt grain boundaries in perovskite materials.

CHARACTERIZATION OF RETENTION PHENOMENA OF MICRON-SIZE ELECTRICAL DOMAINS IN PZT THIN FILMS. Seungbum Hong , Kwangsoo No, Electronic and Optical Materials Laboratory, Korea Advanced Institute of Science and Technology, Taejon, KOREA; Hyunjung Shin, Y. Eugene Pak, Micro Systems Laboratory, Samsung Advanced Institute of Technology, Suwon, KOREA.

The retention phenomena of purposely aligned micron-size domains (defined as ``bits'') in Pb(Zr,Ti)O3 thin films were characterized by atomic force microscopy (AFM) combined with a lock-in amplifier. It is found that the retention loss occurs by ``region by region'' showing local variation of the rate of the loss. Furthermore, the total retention loss can be successfully described by an extended exponential decay which implies a narrow distribution of the relaxation times of the domains. This probably comes from the fact that the micron-size bits are consisted of a few hundreds of domains. Along with the characterization, the effects of the bit size and the poling time per unit area on the retention characteristics were investigated. Based on our observations, it is concluded that the retention time is proportional to both the poling time per unit area and the bit size. This trend is successfully explained by kinetic model developed by our group.

QUANTITATIVE IMAGING OF OXIDE THIN FILMS USING A SCANNING NEAR-FIELD MICROWAVE MICROSCOPE. B.J. Feenstra , D.E. Steinhauer, C.P. Vlahacos, John Lee, S. Aggarwal, R. Ramesh, M. Rajeswari, T. Venkatesan, F.C. Wellstood and Steven M. Anlage, Univ of Maryland, College Park, MD.

Metal oxide thin films exhibit a large variety of phenomena which make them highly suitable for electronic applications. Such applications include high dielectric substrates, non-volatile memories, magnetic recording and superconducting passive devices. For the characterization of these materials imaging techniques are required that span this wide range of physical properties, extending from dielectric and magneto-resistive to superconducting behavior. We have developed a scanning near-field microwave microscope and demonstrated its ability to acquire quantitative information for all of these materials. The operation of the microwave microscope will be explained, and a variety of materials to which our imaging technique has been applied, will be presented. These examples include ferroelectric thin films, such as PbZr0.2Ti0.8O3 and Ba1-xSrxTiO3 for several compositions, CMR films (La0.66Ba0.34MnO3) and high Tc superconducting films (YBa2Cu3O$_{7-\delta}$).

ELECTRON BEAM INDUCED CURRENT/VOLTAGE TECHNIQUE FOR MONITORING FERROELECTRIC AND DIELECTRIC THIN FILMS. Igor Lubomirsky and Oscar M. Stafsudd, Dept. of Electrical Engineering, University of California at Los Angeles, CA.

BaTiO3 thin film is an attractive material for dynamic random access memory (DRAM) and metal-ferroelectric-semiconductor field effect transistors. One of the problems related to the investigation of ferroelectric thin films is a method to detect and measure the spontaneous polarization. Techniques based on electrical measurements (Sawyer bridge, capacitance voltage etc.) measure current related to the change of spontaneous polarization of the ferroelectric film. However, the presence of charged traps makes the current due to the polarization change indistinguishable from the one generated by trap charge/discharge. This problem is especially severe for thin ferroelectric films, where spontaneous polarization is smaller than in single crystals but trap density is much higher. Another method measures thermally generated pyroelectric current. However, an increase or decrease of temperature generates a current related to thermally activated traps, and therefore does not provide accurate information about polarization of the film. A better result may be obtained if we record the AC response of the film to a periodic temperature change. Such a technique is insensitive to the trap related current, and the only observed signal will be the pyroelectric response. This method requires that the thermal time constant of the system be low enough such that significant temperature oscillation is reached. We propose a new Scanning Electron Microscopy technique based on the registration of pyroelectric current induced by an electron beam. The technique is not sensitive to trapped charges and allows fast mapping of domain structures in the ferroelectric films. The depth at which most of the electron beam energy is deposited is a function of the accelerating voltage, therefore it is possible to deliver the energy to a precise depth in the film. This lifts the restriction on thermal inertia of the system, and it allows in-situ monitoring of transformation of domain structure under applied external bias or temperature change. This technique can be easily incorporated into existing in-line wafer control systems.

STRESS AND DEFORMATION OF PZT THIN FILM ON SILICON WAFER DUE TO THERMAL EXPANSION. Ming Zang , Dennis L. Polla, Shayne Zurn and Tianhong Cui, Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN.

Stress and deformation of PZT thin film on silicon wafer due to thermal expansion in anneal process is modeled using 3-D Ansys. For convenience and symmetry, a quarter part of wafer diameter 4 inches, p-type, (100), is studied in this model. The thermal expansion coefficient of each layer changing with temperature in range of 20 to 700 degree C is taken into account. Two designs of a PZT thin film on the wafer are modeled. A PZT/Pt/Ti/silicon dioxide/silicon wafer is to be used for making acoustic emission sensors. The other is a PZT/Pt/Ti/silicon dioxide/silicon nitride/silicon dioxide/silicon wafer, commonly used in fabrication of cantilever beams. In both designs above, thickness of PZT film is 0.4$\mu$, platinum 0.1$\mu$, titanium 0.01$\mu$, silicon dioxide 0.2 and 0.5$\mu$, silicon nitride 1.5$\mu$, and silicon wafer 500$\mu$. Thermal stresses and deformation of the layers at an annealing temperature of 700 degree C are given by means of color distribution on the quarter size of the wafer. For the design without silicon nitride layer, the thermal stress of the PZT film is 298MPa, Pt 1280MPa, Ti 647MPa, silicon dioxide 228MPa, and silicon wafer 0.41-1.67MPa. For the other design having silicon nitride layer, the thermal stresses are PZT 301MPa, Pt 1280MPa, Ti 651Mpa, silicon dioxide 226MPa, silicon nitride 416Mpa, silicon dioxide 226MPa, and silicon wafer 1.05-4.23MPa. The residual stress of the PZT film measured is 200-250MPa for the design without silicon nitride layer, and 336MPa for one having silicon nitride layer. Comparisons of the thermal stress with the tensile or proof stress of material for each layer indicate that the thermal stress of the PZT film is slightly greater than it's bulk tensile stress, Pt's is five times greater, and Ti's is close to. Thermal stresses of the silicon dioxide, silicon nitride and silicon wafer layers are far smaller than their proof stresses. * This work is supported by ONR.

LATTICE DEFECTS IN SrRuO3 THIN FILMS AND THEIR CONTRIBUTION TO FILM RESISTIVITY. Nikolai D. Zakharov , K.M. Satyalakshmi, D. Hesse, Max-Planck-Institut für Mikrostrukturphysik, Halle/Saale, GERMANY; G. Koren, Dept of Physics, Technion Israel Institute of Technology, Haifa, ISRAEL.

Lattice defects present in SrRuO3 thin films have been investigated on cross section samples by high-resolution transmission electron microscopy (HRTEM) in a Jeol 4000 EX microscope. The films were grown by pulsed laser deposition at different substrate temperatures between 700$^{\circ}$C and 850$^{\circ}$C on SrTiO3 (001) substrates in an oxygen ambient of 200 mTorr: Deposition was performed employing a KrF excimer laser with wavelength 248 nm at a pulse energy density of 2 J/cm2. Different kinds of lattice defects, viz. twins, antiphase boundaries, dislocations, and ruthenium vacancies of considerable concentration have been found in these films and they were analyzed in detail. The presence and the density of all of these defects show a systematic dependence on substrate temperature. Moreover, a cubic SrRuO3 phase was identified within some of the very thin (20 nm) films. The atomic structure of the defects was analyzed by the help of image simulations. As an example the antiphase boundaries located at the island boundaries of the films are characterized by a SrO monolayer which is very probably insulating. The results of the structural analysis were correlated with the film resistivities measured by four points probe method. These correlations show that the presence of the cubic phase and of the ruthenium vacancies as well as the antiphase boundaries cause an increase in the film resistivity as compared to those films which are free from these defects. The best films which are free from defects have a room temperature resistivity of only 150 $\mu$$\Omega$$\cdot$cm whereas resistivity reaches up to 650$\mu$$\Omega$$\cdot$cm for the defect-containing films. 

MORPHOLOGICAL EVOLUTION AND TEXTURE FORMATION DURING RAPID THERMAL ANNEALING OF SOL-GEL PZT FILMS. Vladimir Ya. Shur , Elena B. Blankova, Alexander L. Subbotin, Ekaterina A. Borisova, Ural State Univ., Inst of Phys. & Applied Math., Ekaterinburg, RUSSIA; Dierk Bolten, Rainer Gerhardt, Rainer Waser, Rhein. Westf. Technichen Hochschule Aachen, Inst. fuer Werkstoffe der Electrotechnik, Aachen, GERMANY.

The morphological evolution and crystallographic texture formation are studied in sol-gel PZT thin films during rapid thermal annealing (RTA). The mathematical treatment of in situ recorded surface images, elastic light scattering and XRD data reveals the strong correlation between the morphology and the texture. The parameters characterized the texture formation during the transition from pyrochlore to perovskite phase in various annealing regimes have been extracted from the light scattering data. The investigated amorphous Pb(Zr0.47Ti0.53)O3 films have been deposited by sol-gel on Si/SiO2/Ti/Pt substrate. The surface morphology evolution is studied by in situ recording of elastic light scattering data in reflected mode and momentary surface images. Comparison of the scattering data with static images obtained by optical and electron microscopy reveals the dependence of scattered light parameters on the morphology. The observed wide scale range of relief details favors using of fractal formalism for analysis of the angular dependence of scattered light. It is shown that the textured perovskite structure appears the fractal object with wide scale range. The whole phase transformation process consists of separated stages: delay at the beginning, subsequent fast and final slow processes. The mathematical treatment of the data at all stages of perovskite phase growth allows to determine the temperature dependence of essential kinetic parameters. The computer simulation is used for verification of the proposed texture formation mechanism. The research was made possible in part by the Grant of the Ministry of Common and Professional Education of the Russian Federation.

EVIDENCE OF A FERROELECTRIC PHASE TRANSITION IN FIBER-TEXTURED (BaxSr1-x)Ti1+yO3+z THIN FILMS ON Pt/SiO2/Si. S.K. Streiffer , Materials Science Division, Argonne National Laboratory, Argonne, IL; S.E. Lash, C.B. Parker, Angus I. Kingon, Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC; C.E. Bouldin, B. Ravel, D.L. Kaiser, National Institute of Standards and Technology, Gaithersburg, MD; A. Sirenko and X.X. Xi, Dept. of Physics, Pennsylvania State University, University Park, PA.

Although ferroelectric behavior in bulk (BaxSr1-x)Ti1+yO3+z (BST) is reasonably well understood, the dielectric response of this material in thin film form is a subject of considerable investigation. Specifically, polycrystalline BST films deposited on electrode/barrier structures on Si, as for integrated high-permittivity dielectrics, display a nonlinear dielectric response but little or no polarization hysteresis in the film thickness direction, at temperatures at which ferroelectric polarization behavior would be demonstrated in the bulk. This has lead to the assertion that ferroelectricity is suppressed in such thin, polycrystalline microstructures. In contrast, we show here that the temperature dependence of the thickness-direction dielectric response of (100) fiber textured BST films (x=0.7) deposited by liquid-source chemical vapor deposition, is consistent with the existence of an in-plane ferroelectric phase transition at approximately 390K. Coupling between in-plane and out-of-plane polarizabilities below this ferroelectric phase transition is postulated to give rise to the observed departure of the permittivity from Curie-Weiss behavior. Additional structural information pertaining to possible in-plane ferroelectric distortions derived from polarized x-ray absorption fine structure measurements and temperature dependent Raman scattering will be reported, and correlated with the electrical properties.

MICROSTRUCTURE AND NON-STOICHIOMETRY OF BARIUM STRONTIUM TITANATE FILMS FOR DRAM APPLICATIONS. S. Stemmer , Physics Department, University of Illinois at Chicago, IL.; S.K. Streiffer, Argonne National Laboratory, Argonne, IL.; N.D. Browning, Physics Department, Illinois at Chicago, IL; Angus I. Kingon, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC.

The electric and dielectric properties of (Ba0.7Sr0.3)TiO3 (BST) thin film capacitors appropriate for ultra-large scale integration dynamic random access memory (DRAM) applications have been shown to depend on film thickness and film stoichiometry. For the MOCVD grown BST films investigated in this study the resistance degradation lifetime has a maximum at around 52% Ti, while the dielectric constant reaches its highest values near the stoichiometric composition. In this study, we examine possible microstructural origins of this behavior. One of the key issues is the precise mechanism for the accommodation of excess titanium in these films. We analyze variations in the film composition by electron-energy loss spectroscopy (EELS) in a transmission electron microscope equipped with a field emission gun, an annular dark-field detector and a post-column imaging filter. With this instrument, we achieve probe sizes sufficient for sub-0.2 nm spatial resolution in EELS, while simultaneously recording atomic-resolution Z-contrast images in order to accurately position the probe at defects. We compared thin films grown by MOCVD with 51% and with 53% titanium, respectively, and with different film thicknesses. EELS analysis showed a pronounced increase of the Ti/O ratio at the grain boundaries, indicating that at least some excess titanium is accommodated at the grain boundaries. In addition, we found changes in the oxygen near edge fine structure at the grain boundaries which, when compared with reference spectra, are consistent with a titanium enrichment of the grain boundary. We employ low-loss EELS analysis to study dielectric property variations on a nano-meter scale. In addition, we performed through-thickness studies on cross-sectional samples. Finally, we discuss the implications of our atomic scale defect analysis for the electrical and dielectric properties of the films.

FABRICATION ISSUES IN COMBINATORIAL SYNTHESES OF MULTICOMPONENT OXIDE FILMS FOR ELECTRONICS. I. Takeuchi , H. Chang, X.D. Xiang, Materials Sciences Div, Lawrence Berkeley National Laboratory, Berkeley, CA; R.P. Sharma, Y.H. Li, T. Venkatesan, University of Maryland, College Park, MD.

The combinatorial approach to thin film materials generates thousands of compositionally varying samples on individual chips (called materials libraries). This method is effective in applications to oxides since many metal oxide compounds can be formed from amorphous multilayers of precursors. Various thermal processes are developed to fabricate epitaxial, polycrystalline or amorphous libraries depending on the target applications and materials. We rely on extensive x-ray diffraction and RBS spectroscopy to confirm the integrity of the materials. In some instances, intermediate phases seem to block the formation of target compounds. In Ba1-xSrxTiO3, epitaxial films processed from amorphous layers under certain conditions exhibit better dielectric properties than in-situ deposited films. High density capacitor libraries of amorphous composites of Ta2O5 mixed with other metal oxides have been fabricated in search of materials with increased dielectric constant compatible with the silicon technology. We will also discuss characterization issues concerning contact versus non-contact measurements of ferroelectric/dielectric materials libraries. Preliminary TEM results of epitaxial films grown from precursor layers will also be presented.

OXIDE FILM FORMATION ON METALS AND ALLOYS BY THERMAL, ELECTROCHEMICAL AND PLASMA OXIDATION AND PREDICTION OF RESULTING STRUCTURES. David L. Cocke , S. Promreuk, Robert Schennach, M.Y. Mollah, Department of Chemistry, Lamar University, Beaumont, TX; Donald G. Naugle, Department of Physics, Texas A&M University, College Station, TX.

Multicomponent oxide films are needed to meet the increasing demands of the electronics industry. Three main methods that involve oxidation of a metallic substrate are thermal, anodic and plasma oxidation. Today we do not have an adequate fundamental physical-chemical model of how multicomponent oxides evolve on alloys under these oxidizing conditions to design a wide range of materials for electronic devices. The three methods will be discussed in terms of physical/chemical parameters that influence the chemical nature and structure of the resulting oxides. By using surface studies of the oxidation behavior of numerous metals and alloys we have been able to delineate the factors which are most important to the oxide formation process and provide insight into the prediction of oxide layer structures. The electrochemical processes that occur during the materials reaction with a chosen environment will be used to discuss the physical and chemical mechanisms involved. Intrinsic and extrinsic electric fields will be shown to control the chemical and structural nature of the resulting oxide structures. Examples will be presented for a number of metal and alloy systems that have been examined in our laboratory.These include Al, Ti, Zr, Nb, Mn, Cu and Ni and some of their selected alloys. The models that have developed from these studies are providing some predictive power in how the complex oxide overlayer will be chemically speciated and structured.

STOICHIOMETRY AND MELT-TEXTURING IN Ag-BiSrCaCuO POLYCRYSTALLINE THICK FILMS. N.F. Heinig , D.R. Dietderich, J.S. Wang, X.D. Xiang, Lawrence Berkeley National Laboratory, Berkeley, CA.

The superconducting properties of melt-textured Bi2Sr2CaCu2Ox are very sensitive to small variations in composition and heat treatment, and more information about the relationship between these variables is needed. One micron thick films of BiSrCaCuO were grown by pulsed laser ablation, and the stoichiometry was varied by using shutters and different targets. The films were characterized by SEM and EDS, and showed clear gradients in the phase assemblage and composition across each sample. After an ex-situ heat treatment, the films' transport properties at 4.2 K were studied in magnetic fields of up to 12 Tesla, and these results were then correlated to the microstructure.

GROWTH AND MICROSTRUCTURE OF SrBi2Ta2O9 THIN FILMS. S. Srinivas 1, W.J. Kim 2, J.S. Horwit2, R.S. Katiyar1 and D.B. Chriesey2, 1Physics Department, University of Puerto Rico, San Juan, PUERTO RICO; 2Surface Modification Branch, Naval Research Laboratory, Washington, DC.

Ferroelectric SrBi2Ta2O9(SBT) is a promising material for random access memories because of its fatigue free nature exceeding 1x1012 read/write cycles. Inorder to study the influence of the growth conditions on the microstructure, stoichiometry and ferroelectric properties, we have carried out the film growth systematically varying conditions by using a pulsed laser deposition (Kr:F, 248 nm, 30 ns FWHM). Effect of laser fluence (2-0.75 J/cm2), frequency of the laser pulse(4-10Hz), substrate temperature (650-850$^{\circ}$C), substrate type (Si, Si/Pt, Si/Ti/Pt, MgO) and oxygen partial pressure (150-450 mTorr) have been studied using XRD, SEM, EDAX, XPS, AFM. The deposited films were found to be highly c-axis oriented in nature with narrow X-ray omega scans. (FWHM varied between $0.4-0.9^{\circ}$ for SBT (006) peak depending on the growth conditions). Atomic force microscopy(AFM) shows that the films have a smooth surface with homogeneous grains with an average grain size between 50-100nm and an average surface roughness between 0.06-0.3nm. The surface roughness of the films, increased with the increase of oxygen partial pressure and laser pulse frequency. The elemental ratio from XPS measurements was close to the stoichiometry in the films deposited with laser fluence between 1.5-1.0 J/cm2 and with substrate temperatures between 700-770$^{\circ}$C. A discussion of the effect of the deposition conditions on the growth of SBT films will be presented.


V2O5 xerogel have interesting conducting as well as electrochemical properties like the laminar (or 2D ) structure adequate for intercalation reactions. Europium and europium vanadates are well know for their interesting optical and magnetic properties. The V2O5 films after preparation reacted with a solution of EuCl3. As characterization techniques, X-ray diffraction, FTIR, TG/DTA, ESR, luminescence as well as XANES (measured in the Brazilian synchroton facility ) were used. The thermal treatments were made in air at constant temperature ( 333K to 973K) for 15 min. For the as grown samples, the intercalation of Eu is observed to have little effect in the V2O5 laminar structure, however the inter-planar spacing grows from 1.19 nm to 1.33nm for a 10$\%$ Eu content as observed from the X-ray as well as FTIR data. TG/DTA data indicates three de-hydration steps at 393K; between 393K and 543K; and between 543K and 623K, with a re-structuring at 613K. ESR, X-ray diffraction and XANES data on heat treated samples indicates an increase in disorder for treatments up to 573 K for samples containing Eu, in fact Eu seems to suppress partially the de-hydration of the sample. For treatments above 923K, V2O5 micro-crystals are observed, as well as the formation of ferromagnetic EuO. The luminescence for the as grown samples are dominated by the host, however for samples treated above 900K the excitation spectra presents a new shoulder at 300 nm, which when excited shows emissions bands typical of the Eu3. This result may be correlated to the presence of water in the neighborhood of Eu suppressing the luminescence, in good agreement with the XANES data. The increased disorder and de-hydration characteristics may have positive consequences in the Li intercalation/de-intercalation processes in this material.

RAMAN SPECTRA OF RHOMBOHEDRAL BaxSr1-xTiO3. M.V. Belousov , I.E. Kozin, Inst of Physics, St. Petersburg State Univ, St. Petersburg, RUSSIA; V.Yu. Davydov, I.N. Goncharuk, V.V. Lemanov, T.A. Shaplygina, P.P. Syrnikov, A.F. Ioffe Physico-Technical Inst, St. Petersburg, RUSSIA.

Raman scattering spectra of the low temperature rhombohedral phase of BaxSr1-xTiO3 ceramics and films have been studied for the first time. All modes of the rhombohedral phase were identified using polarized Raman scattering spectra of BaTiO3 and Ba0.12Sr0.88TiO3 single crystals. These data allowed us to identify the modes and the symmetry of vibrations in the Raman spectra of BaxSr1-xTiO3 ceramics and films. In these spectra, soft modes of Ti-O bond vibration were found in the dependence on Ba content. The frequencies of these modes vary from 270 cm-1 (E-mode) and 180 cm-1 (A-mode) at x=1 in pure BaTiO3 to zero at x=0.025. This means that the ferroelectric rhombohedral phase is instable at x=0.025 and transforms to nonpolar tetragonal phase of SrTiO3. It is important to note that the lattice constant of SrTiO3 is smaller that that of BaTiO3. At decreasing x, the stiffness of Ti-O bond falls steeply but does not grow, as it is usual at decreasing lattice constant. In our opinion, it is an evidence for a multiwell model of Ti-O potential. This conclusion supports the concept of order-disorder character of transition from ferroelectric to paraelectric phase in BaTiO3.

DOPING AND OXIDATION EFFECTS IN RAMAN SPECTRA OF MANGANITES. V.B. Podobedov , D.B. Romero, A. Weber, J.P. Rice, National Institute of Standards and Technology, R. Schreekala, M. Rajeswari, R. Ramesh, T. Venkatesan, H.D. Drew, Department of Physics, Univ. of Maryland, MD.

Raman scattering from La1-xRxMn0$_{3-\delta}$ compounds (single crystals, ceramics, films) was studied as a function of kind (R) and amount (x) of dopant as well as of oxygen deficit ($\delta$) in the structure. For x = 0.1 to 0.55, nearly linear Raman shift of the Ag mode from 240 to 125 cm-1 was observed in Sr-doped compounds. While intensity of disorder-induced Raman bands was found to be sensitive to the oxygen content, the symmetry allowed related Raman modes exhibit the change in the frequency scale. As an indication of deposition conditions, the lowering of symmetry of the film structures with respect to single crystals and ceramics was detected. We discuss the physical nature of observed effects and their correlation with Tc found from magnetization and resistivity data. We show how experimental data can be used for optical characterization of manganite samples. In particular, film crystallinity, film orientation as well as degradation effect have their signatures in polarized Raman spectra.


Double perovskite structures are among the systems for which the occurence of half-metallic (HM) behavior (i.e. metallic behavior in one spin channel and semiconducting in the other one) is more likely to be expected[1]. HM would be very favorable for magnetotransport and magnetoelectric applications. We present a first-principle (plane-wave and ultrasoft pseudopotentials) study about structural and electronic properties of double perovskites X2RuPdO6, with X=Ca, Ba, La. From experiments, these compounds are metallic and have orthorombic (Pnma) structure. The high density of states at the Fermi level featured in the paramagnetic phase drives these systems towards strong magnetic ordering. We found a large energy gain (more than 1 eV per formula unit) with respect to the paramagnetic phase. The ferromagnetic order is also favoured with respect to the various examined antiferromagnetic arrangements, and characterized by high magnetic moments ($\sim$ 2.5 $\mu_B$) on Ru atoms. From our band structure calculations, it results that an energy gap (Eg= 0.48 eV) whose edge is close to the Fermi energy opens in the minority spin channel of the ferromagnetic phase calculated at the experimental structure. Structural relaxations performed in the cubic symmetry suggest that relaxations might increase the gap and be able to drive the systems towards half-metallicity. [1] W. E. Pickett, Phys. Rev. B 57, 10613 (1998)

TEM STUDY OF PHASE COMPOSITION IN NON-STOICHIOMETRIC (Ba, Sr)TiO3 THIN FILMS. Igor Levin , Debra L. Kaiser, Ceramics Div., MSEL, National Institute of Standards and Technology, Gaithersburg, MD.

Recently, much attention have been focused on the fabrication of crystalline ferroelectric thin films of (Ba,Sr)TiO3. Barium strontium titanate can offer a high capacitance density at a relatively large thickness in dynamic random access memories, as well as it has a great potential for erasable image storage devices and optical applications. Processing of BaTiO3 films can result in a deviation of (Ba+Sr)/Ti ratio from stoichiometric value which has been shown to have a major effect on dielectric properties. However, the way of accommodation of the excess of Ba or Ti in these films has yet to be determined. In the present work, phase composition of non-stoichiometric (Ba,Sr)TiO2+y films deposited by metalorganic chemical vapor deposition (MOCVD), with y=(Ba+Sr)/Ti varying from 0.77 to 1.14, was investigated by high-resolution transmission electron microscopy combined with electron probe microanalytical techniques. The results on both planar view and cross-sectional specimens prepared from films deposited on Pt/SiO2/Si and (001) MgO substrates will be presented.

KINETIC MONTE CARLO SIMULATION OF OXIDE FILM GROWTH. Chaitanya Deo , David J. Srolovitz, University of Michigan, Dept. of Materials Science & Engineering, Ann Arbor, MI.

Compared with other electronic thin films, the growth of oxide thin films from a vapor are very much more complicated. In this talk, we will examine several models for the vapor deposition of oxides which include deposition, desorption, surface diffusion and reaction. These models will be exercised within the framework of a three-dimensional kinetic Monte Carlo simulation in which the relative rates of each event are separately controlled. Models of two and three component oxides will be examined. The goal of this idealized study is to determine the conditions under which crystalline oxides will form, the relative importance of surface diffusion and deposition/desorption, and the effect of such variables as oxygen pressure, growth rate, and sticking coefficient. Finally, we propose an efficient approach to more realistic oxide film growth modeling.

INVESTIGATIONS ON KTN THIN FILMS BY XRD, XPS AND MICRO-RAMAN SPECTROSCOPY. A.A.Savvinov , I.G. Siny and R.S. Katiyar, University of Puerto Rico, Department of Physics, San Juan, PUERTO RICO; F. Fernandez, Department of Physics, UPR, RUM, Mayaguez, PUERTO RICO.

KTa1-xNbxO3 materials are well-known examples of mixed perovskite systems having potential in device applications. The renewed interest in them, especially in the high quality thin films, is related to their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO3 lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO3 and KNbO3. KTN thin films with several Nb concentrations, on different substrates, and with various film thickness were prepared by pulsed laser deposition. The phase and orientation in our KTN compositions were confirmed by using x-ray diffraction and the resultin compositions were further investegated by x-ray photoelectron spectroscopy techniques.The micro-Raman scattering was employed to study the substrate effect on KTN films, in particularly, and its affect on the symmetry properties, in general. The present paper reports the comparison of the behavoir of different modes in Raman scattering of KTN films of different tickness and composition in a temperature range from 70 K to 580 K.
This work is supported in parts by DEPSCOR (#DAAG55-98-1-0012), DoE (#DE-FG02) and NSF (#NSF-DMR 9801759) grants.

MICROSTRUCTURE OF OXIDE PARTICULATE COATINGS GROWN BY PULSED LASER ABLATION. M. Ollinger , V. Craciun, R.K. Singh, University of Florida, Dept of Materials Science and Engineering, J.M. Fitz-Gerald, Naval Research Laboratory.

A novel method to synthesize nanometric oxide coatings on particulate materials in a dry environment is presented. Over the last 5 years, the synthesis of particulate materials has become a multi-billion dollar industry. Applications for thin oxide coatings range from flat panel display materials and metal hydride based rechargeable batteries to chemical mechanical polishing. The major obstacle in this research area remains in the control of the surface architecture. By controlling the surface architecture (thickness, stoichiometry, adhesion), utilization of the particle properties can be realized. The thin film coatings were synthesized using a modified pulsed laser deposition system to create a plume of nano-particles. This plume was then directed onto a mechanically agitated bed of core particles which were heated using a specially designed heat source. Depositions were performed in oxygen, helium, and argon atmospheres ranging from 50-600 mTorr. silica and alumina were used as core particles. Solid targets of CeO2, Yttria and LaNiO3 were used as ablation sources. The coatings were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS).

CHARACTERIZATION OF SiOxNy ANTI-REFLECTIVE COATINGS USING SIMS AND RBS. Adli A. Saleh , J. Bruce Rothman, J.F. Kirchoff, Charles Evans and Associates, Redwood City, CA; Jiro Yota, Chau Nguyen, Advanced Process Technology, Rockwell Semiconductor Systems, Newport Beach, CA.

Silicon oxynitride (SiOxNy) films formed using plasma-enhanced chemical vapor deposition (PECVD) is proposed as an anti-reflective coating (ARC) for deep ultraviolet (DUV) photolithography. The SiOxNy film is required in order to reduce undesirable light reflections caused by the increased substrate reflectivity at wavelengths in the DUV region. These shorter illuminating wavelengths are needed during photolithography process in order to produce small feature sizes for the gigascale integration of devices. These films reduce these reflections by phase-shift cancellation, which is dependent on the refractive index, extinction coefficient and thickness of the film. Therefore, it is critical that the refractive index, extinction coefficient, and thickness of these films meet the necessary phase-shift cancellation requirements during the lithography process. The refractive index, extinction coefficient, and thickness of the SiOxNy ARC films can be modified by changing the deposition conditions, including the reactants flow rates, pressure, temperature, power and deposition time. Several such films, 100-300 A thick, were deposited on p-type (100) 200 mm silicon wafers using silane (SiH4), nitrogen (N2), and nitrous oxide (N2O) gaseous precursors. Rutherford backscattering spectrometry (RBS) was used to determine the nitrogen, oxygen and silicon average concentrations. Elastic recoil detection spectrometry (ERDS) was used to determine the average Hydrogen content in the film. Secondary ion mass spectroscopy using CsM+ method was then used to deduce the concentration depth profiles.

COMBINATORIAL SYNTHESIS AND CHARACTERIZATION OF Ln1-xBxMnO3. Young K. Yoo , Dept of Physics, Univ of California at Berkeley, CA; Hauyee Chang, Dept of Chemistry, Univ of California at Berkeley, CA; Yi Dong, Jingwei Li, Xiao-Dong Xiang, Materials Sciences Div, Lawrence Berkeley Natl Lab, Berkeley, CA.

Perovskite manganites of the series Ln1-xBxMnO3, with x=n/16, have been synthesized in epitaxial thin films (where Ln is a rare earth ion, B is a divalent alkaline earth ion, and n is varied from 0 to 16). A library of 128 (8 by 16) members, where each row contains a different ternary manganite series, was synthesized by photolithographic masking and sequential pulsed laser deposition with an automated shutter system. Three precursors, BMnO3, Ln oxides, and Mn3O4, were deposited at room temperature and subsequently post-annealed. X-ray data of selected samples shows good epitaxial growth along the (001) plane. Electrical conductivity and magnetoresistance were measured. We used 64 4-point probes for parallel characterization of the library. The measurement identified regions of metallic phases and magnetoresistive properties depending on the A-site average atomic radius. We compared our results with a prevailing theory.

Chairs: Hans Hilgenkamp and Jonathan Z. Sun
Wednesday Morning, April 7, 1999
Salon 7 (M)
8:30 AM BB4.1
MICROMACHINED ARRAY STUDIES OF TIN OXIDE FILMS: NUCLEATION, STRUCTURE AND GAS SENSING CHARACTERISTICS. Balaji Panchapakesan , Don Devoe, University of Maryland, Institute for Systems Research & Department of Mechanical Engineering, College Park, MD; Robin Walton, Richard Cavicchi, Steve Semancik, National Institute of Standards and Technology, Process Measurements Division, Gaithersburg, MD.

Growth of tin oxide by micro-chemical vapor deposition has been investigated as function of the type and thickness of seeding layers using a four-element array of micro-hotplates [1]. Metals including Fe, Sn and Pt of varied thicknesses were vapor deposited as seeding layers. Following vapor deposition, tin oxide was grown on these hotplates in a cold wall CVD reactor[2]. The growth is self-lithographically defined by using the microheaters of selected microelements. By heating a microhotplate to 500 C, thermal decomposition of tetramethyl tin in an argon and oxygen ambient produced tin oxide on the heated surface. Conductance was monitored during growth using the contact pads on the device and growth was terminated when the conductance reached 5 kOhm. Seed layers as thin as 15A produce significant differences in growth rates. Tin oxide films were also grown to ultra-low coverages and examined by SEM to investigate the differences in nucleation and the early stages of growth. Dramatically improved stability and sensitivity to ethanol was observed, for example, for tin oxide seeded with iron. Sensitivity towards different analytes will also be reported. The seed layer metals have been used to produce varied nucleation sites to control the morphology of the sensing film and are not believed to be chemically active as sensing enhancers. Our findings do indicate the possibility of a catalytic effect by the seed layers for tin oxide deposition. This study demonstrates the power of micromachined temperature controlled platforms for performing efficient materials studies, where different materials can be grown and characterized selectively on each individual element. 1. R.E. Cavicchi, J.S. Suehle, P. Chaparala, K.G. Kreider, M. Gaitan and S. Semancik Micro-hotplate Gas Sensor, Technical Digest, Solid State Sensor and Actuator Workshop, 1994. 2. S. Semancik, R.E. Cavicchi, K.G. Kreider, J.S. Suehle and P. Chaparala, Selected-area deposition of multiple active films for conductiometric microsensor arrays, Sensors and Actuators B34, 209-212 (1996)

8:45 AM BB4.2
HIGH ENERGY DENSITY CAPACITORS FABRICATED BY THIN FILM TECHNOLOGY. A.V. Wagner , T.W. Barbee Jr., G.W. Johnson, Lawrence Livermore National Laboratory, Materials Science and Technology Division, Livermore, CA.

Low energy density in conventional capacitors severely limits efforts to miniaturize power electronics. We have successfully applied PVD technology to greatly increase capacitor energy density. The high breakdown strength we have achieved in thin films such as Al2O3, ZrO2 and Ta2O5 allows high energy density to be achieved with these moderately low dielectric constant materials. The small temperature dependence of the dielectric constant, and the high reliability, high resistivity, and low dielectric loss of these dielectric materials make them even more appealing. We have constructed single dielectric layer thin film capacitors, and shown that they can be stacked to form multilayered structures with no loss in yield for a given capacitance. Control of film growth morphology is critical for achieving the smooth, high quality interfaces between metal and dielectric necessary for device operation at high electric fields. Most importantly, high rate deposition with extremely low particle generation is essential for achieving high energy storage at a reasonable cost. This has been achieved by reactive magnetron sputtering in which the reaction to form the dielectric oxide has been confined to the deposition surface. By this technique we can reproducibly achieve an energy density of 14 J per cubic centimeter of Al2O3 dielectric material in 1 KV, 5 nf devices. By further reducing defect density and increasing capacitance we aim to construct, high energy density devices to meet the requirements of applications in power electronics such as snubber and filter capacitors for electric vehicles. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

9:00 AM *BB4.3
COMPOSITIONAL DESIGN OF FARADAY ROTATOR MATERIALS. Vincent J. Fratello , Steven J. Licht and C. David Brandle, Lucent Technologies Bell Laboratories, Murray Hill, NJ.

Bismuth-doped rare-earth iron garnet thick films have become the material of choice for a wide variety of magnetooptic applications including optical isolators and circulators. Garnet compositional design and liquid phase epitaxial growth have been adapted to the requirements of these devices. Properties such as optical absorption, temperature and wavelength dependence of Faraday rotation, index of refraction and magnetic and optical anisotropy can be controlled to a high degree. Introduction of nucleation induced coercivity has even allowed the elimination of a permanent bias magnet. However, in optimizing device performance and film growth, there are often tradeoffs among these properties. Material design is therefore a compromise based on the requirements of device designers.

10:00 AM BB4.4
YMnO3 and YbMnO3 THIN FILMS FOR FET TYPE FeRAM APPLICATION. Norifumi Fujimura , Takeshi Yoshimura, Daisuke Ito, Taichiro Ito, College of Engineering, Dept. of Applied Materials Science, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka, JAPAN.

We have proposed the use of RMnO3 (R: rare earth elements) films for metal-ferroelectric-semiconductor field effect transistor (MFSFET)-type ferroelectric random access memories (Ferroelectric RAMs). It was reported the production of YMnO3 films on Si substrates for MFSFET with confirmation of the distinct ferroelectricity by P-E hysteresis and capacitance-voltage (C-V) measurement [1]. (0001)-oriented YMnO3 films were obtained on a (111)Si substrate using a pulsed-laser deposition method. Although the Pt/YMnO3/Si structure exhibits a very low remnant polarization of 1.2 nC/cm2, it has clear ferroelectric polarization switching type C-V characteristics with a memory window of 1.1V. However, the memory window width of the film had strong sweep rate dependence. We were able to avoid this issue using Y2O3 buffer layer on Si. This paper is going to summarize progress in the ReMnO3 thin films for FET type FeRAM application. [1] N.Fujimura et al, APL 73, 3 (1998) 414

10:15 AM BB4.5
MOTT TRANSITION FIELD EFFECT TRANSISTOR: EXPERIMENTAL RESULTS. A.G. Schrott , J.A. Misewich, B.A. Scott, A. Gupta, T. Doderer, C.C. Tsuei, D.M. Newns, D. Abraham, IBM Thomas J. Watson Research Center, Yorktown Heights, NY.

In this paper we describe the fabrication of oxide-based devices similar in architecture to a conventional FET with source, drain, and gate electrodes and a channel. The distinctive characteristic of our device is the use of a channel material capable of undergoing a field-induced Mott insulator-metal transition at room temperature. Lithographic techniques developed for oxide materials have been combined with pulsed laser deposition of perovskite materials onto single crystal strontium titanate (STO) substrates to fabricate these devices. Materials chosen for the Mott transition channel include La2CuO4(LCO) and YBCO,(p-type); and Nd2CuO4 (n-type). The details of lithographic fabrication and performance at room temperatures will be discussed.

10:30 AM *BB4.6
BIOMEDICAL MEMS APPLICATIONS OF PIEZOELECTRIC THIN FILMS. Dennis L. Polla , Ronald McGlennen, University of Minnesota, Dept of Biomedical Engineering, David Drinkwater, Lorraine F. Francis, Tian Hoe Lim, Dept of Chemical Engineering and Materials Science, Yunwoo Nam, Alex Bonne, Department of Electrical and Computer Engineering and Peter Schiller, Microtechnology Laboratory, Minneapolis, MN.

Piezoelectric thin films have been applied in several biomedical MEMS applications including 1) active tissue monitoring, 2) motorized surgical tools, 3) microfluidic vales and pumps for precision fluid delivery, 4) in vitro fertilization systems, and 5) patient monitoring. The piezoelectric materials are based on 0.6 $\mu$m-thick films prepared by sol-gel and MOD preparation methods. The PZT materials are deposited on silicon substrates with appropriate Ti/TiO2 buffer layers and Ti/Pt electrodes. Solid-state micromachining is carried out using either surface-sacrificial methods or deep reactive ion etching. Often the silicon substrates contain on-chip electronics with analog signal conditioning and telemetry capability. This talk will focus on the materials challenges of applying BioMEMS to real medical applications including materials selection, process design, packaging, and systems integration. Several case examples including human clinical trials will be presented from five medical disciplines.

11:00 AM *BB4.7
WHAT WOULD WE REALLY LIKE TO KNOW ABOUT THIN AND THICK FILMS FOR LARGE SCALE HTS APPLICATIONS? David C. Larbalestier , Applied Superconductivity Center, University of Wisconsin, Madison, WI.

Unlike most oxide film uses, there is a vital requirement for continuous high current density, electrical connectivity for useful HTS films. Stretching the term film just a little, we can say that all useful forms of HTS are as films, since even the filaments of BSCCO-2223 in a multifilament conductor are only some 5 microns thick. Coated conductors of YBCO are certainly films, only 1-2 microns thick. A characteristic of ALL polycrystalline forms of HTS, even in film form, is that current percolates through them. Much work is aimed at understanding the barriers which dictate this percolation and this will form the main subject of my talk. The film geometry is particularly subject to contamination from the bank or substrate material, particularly at grain boundaries and other defect sites. Evidence on this from recent bicrystal studies will be presented. The strong temperature dependence of the phase relationships in BSCCO-2223 imposes cation defect concentrations that may play a strong role in flux pinning. Getting explicit evidence for the role of atomic scale defect structure on the properties of HTS remains a challenging, but still vital task. Work supported by AFOSR, EPRI and NSF through the UW MRSEC on Nanostructured Materials.

11:30 AM *BB4.8
HIGH-Tc SUPERCONDUCTING DEVICES*. J. Talvacchio , B.D. Hunt, M.G. Forrester and R.M. Young, Northrop Grumman STC, Pittsburgh, PA.

We have developed an epitaxial multilayer process with multicomponent insulator, normal-metal, and superconducting oxide films for fabrication of HTS single-flux-quantum logic circuits. The process is based on edge SNS Josephson junctions and is extendible to medium-scale integration since low circuit inductances are provided by an integrated HTS ground plane and there is flexibility in the placement and orientation of junctions. We will use the sequence of major process steps as an outline for describing the choices we made in selection of materials, deposition techniques, parameters for interface formation and junction fabrication, and topics for separate experiments. Although process yield and circuit performance are determined by insulator integrity, step coverage, via critical currents, and other properties of passive components, the reproducibility of junction characteristics is the primary factor in determining the present level of circuit integration. We will compare the reproducibility of SNS junctions with N-layers composed of doped YBCO films with that of N-layers formed by processing of the patterned base electrode edge.
*Supported in part by AFOSR contract F49620-98-2-0234 and ONR contract N00014-96-C-0007.

Chairs: Masashi Kawasaki and Tom P. Pearsall
Wednesday Afternoon, April 7, 1999
Salon 7 (M)
1:30 PM BB5.1/V6.1
ION BEAM ASSISTED TEXTURE CONTROL DURING OXIDE FILM GROWTH. Liang Dong , David J. Srolovitz, University of Michigan, Department of Materials Science & Eng., Ann Arbor, MI.

The orientation of oxide thin films can be modified by the presence of an ion beam during growth. We perform a series of three dimensional molecular dynamics (MD) simulations of film growth on an amorphous substrate to examine how an ion beam can be controlled to determine in-plnae and out-of-plane texture during film growth. We explicitly consider how an ion beam modifies texture in the nucleation/pre-coalescence stage and compare this with observation in the post-coalescence growth stage. We examine issues associated with ion flux, ion energy, ion beam orientation, channeling and ion channel acceptance angles. The goal of this work is to identify the trade-offs between fast growth and sharp texture and between ion beam collimation and ion beam flux. Both generic simulation results and the application of these results to the growth of in-plane texture MgO will be presented.

1:45 PM *BB5.2/V6.2
BIAXIAL TEXTURING AT THE NUCLATION STAGE IN MGO. P.C. Wang, K.B. Do, M.R. Beasley, T.H. Geballe, R.H. Hammond , Stanford University, Stanford, CA.

IBAD of MgO to achieve biaxial texturing is a nucleation effect, as contrasted to the evolution mechanism found in YSZ. We will review the observations of this work at Stanford University.

2:15 PM *BB5.3/V6.3
FERROELECTRICITY INDUCED BY LATTICE MISFIT STRAIN IN HETEROEPITAXIAL (BaxSr1-x)TiO3 FILMS. Kazuhide Abe , Naoko Yanase, Kenya Sano, Takashi Kawakubo, Toshiba Corp., Materials and Devices Research Laboratories, Kawasaki, JAPAN.

It has been demonstrated that ferroelectricity can be induced by lattice misfit strain in heteroepitaxial barium strontium titanate (BST) films with Ba content $x \ge 0.44$ [1]. The BST films were deposited on SrRuO3/SrTiO3 substrates by rf magnetron sputtering at a substrate temperature of 600$^{\circ}$C. XRD analyses showed that the misfit strain normal to surface was more than 5$\%$, and it did not relax even when the BST film was as thick as 100 nm. Ferroelectric hysteresis was observed at 200$^{\circ}$C for a Ba0.6Sr0.4TiO3 film, whereas the original Curie temperature is known to be 0$^{\circ}$C. The ferroelectricity could be measured even when the thickness was reduced to 26 nm.
Based on the results, it was concluded that BST films can be used not only for DRAM application, but also for ferroelectric nonvolatile memory applications. The employment of BST would be advantageous for high density integration of nonvolatile memories, because it is free from unstable elements such as Pb or Bi. We have already obtained epitaxial growth on Si substrate with a multilayer system of BaTiO3/SrRuO3/Pt/(Ti,Al)N/Si [2]. Recent progress in improvement of ferroelectric properties by optimization of epitaxial growth conditions will be shown at the symposium.
[1] K. Abe and S. Komatsu: J. Appl. Phys. 77 (1995) 6461.
[2] N. Yanase, et al., Jpn. J. Appl. Phys. 37 (1998) L151.

2:45 PM BB5.4/V6.4
LUMINESCENT CHARACTRISTICS OF PULSED LASER DEPOSITED EPITAXIAL Eu-DOPED Y2O3 THIN FILMS. D. Kumar , K.G. Cho, Zhan Chen, V. Craciun, P.H. Holloway and Rajiv K. Singh, Department of Materials Science and Engineering, University of Florida, Gainesville, FL; J. Perriere, GPS, Universite Paris VII et VI, FRANCE.

In this paper, we report the growth, structural and luminescent characterization of europium doped yttrium oxide thin films (Eu:Y2O3). The level of europium doping, acting as an activator in the host lattice of yttrium oxide, was four percent by weight. The Eu:Y2O3 films were grown in-situ using a pulsed laser deposition technique. The structural properties of the films were investigated using x-ray diffraction ($\theta$-2$\theta$$\omega$-scan, $\phi$-scan), Rutherford backscattering spectrometry (RBS), and high resolution transmission electron microscopy (HRTEM) . Our results have shown that Eu:Y2O3 films can grow epitaxially on (100) LaAlO3 substrates under optimized deposition parameters (temperature $\ge$750$^{\circ}$C, oxygen pressure $\sim$200 mTorr). The epitaxial growth of Eu:Y2O3 films on a widely lattice mismatched LaAlO3 substrate is explained by considering the atom positions in the lattices of the film and the substrate and domain matching. The photoluminescence and cathodoluminescence measurements carried out on these films have indicated that epitaxial Eu:Y2O3 films are useful for their applications due to improved chemical stability and improved crystalline structure.

3:30 PM BB5.5/V6.5

We have grown YBa2Cu3O7 (YBCO) single layer and La6.4Sr1.6Cu8O20/YBa2Cu3O7 (LSCO/YBCO) bilayer heterostructures on 8$^{\circ}$ miscut (001) SrTiO3 substrates for use in high-Tc SNS junctions. The substrates were annealed at 950$^{\circ}$C in flowing oxygen for 1 hour prior to film deposition. Atomic force microscopy images of the substrates show well-controlled steps with multiple unit cell height on the substrate surface. The use of such miscut substrates was expected to promote step flow growth of the films and develop a step-terrace morphology on the surface of the film. Scanning tunneling microscopy images of both films show the presence of nanoscale steps on the film surface. The YBCO bottom electrode deposited on the miscut SrTiO3 substrate shows a periodic step-terrace pattern with non-unit cell (0.4 - 1.2 nm) step height. LSCO metallic oxide barrier layers grown on such a YBCO bottom electrode followed the morphology of underlying YBCO film. These films also show a step-terrace morphology. However, step bunching occurs in the LSCO film leading to multiple unit cell (5 - 12 nm) high steps and large terraces. The unidirectional periodic nanoscale steps present at the interface between the superconductor and normal metal layer may act as uniform sites for proximity coupling. This work was supported by the ONR Contract No. N00014-95-1-0512, the NSF Young Investigator Award (CBE) and the David and Lucile Packard Fellowship (CBE).

3:45 PM BB5.6/V6.6
LIQUID COMPOUNDS FOR CVD OF ALKALINE EARTH METALS. Roy G. Gordon , Sean T. Barry, Randy N. R. Broomhall-Dillard, Nicholas DiCeglie, Jr., Xinye Liu and Daniel J. Teff, Harvard University Chemical Laboratories, Cambridge, MA.

The first room-temperature liquid compounds useful for the CVD of alkaline earth metal-containing oxides were prepared by reacting metal $\beta$-diketonates with novel ligands. The compounds are monomeric and can be completely flash-vaporized leaving no non-volatile residue detectable at the parts-per-million level. A stable, solvent-free liquid mixture was formed by mixing new liquid barium, strontium and titanium compounds. CVD experiments using direct liquid injection of this liquid mixture deposited films of barium strontium titanate. New liquid CVD precursor compounds will also be presented for other elements, including calcium and magnesium. This approach should also be applicable to the deposition of many other multicomponent oxides containing alkaline earth metals, such as ferroelectrics (strontium bismuth tantalate), metallic conductors (strontium vanadium oxide, lanthanum strontium cobalt oxide), phosphors (calcium tungstate), non-linear optical materials ($\beta$-barium borate), magnetic oxides (barium ferrite), colossal magnetoresistive materials (lanthanum strontium manganese oxide), high Tc superconductors (yttrium barium copper oxide, bismuth calcium strontium copper oxide) and microwave dielectrics (barium magnesium tantalate).

4:00 PM BB5.7/V6.7
INVESTIGATION OF GROWTH EVOLUTION IN c-AXIS SrBi2Nb2O9 EPITAXIAL THIN FILMS. J. Lettieri , Y. Jia, D.G. Schlom, Penn State University, Dept of Materials Science and Engineering, University Park, PA; G.W. Brown, M.E. Hawley, Los Alamos National Laboratory, Los Alamos, NM.

There has been considerable interest in the bismuth-based, layered materials of the Aurivillius homologous series, such as SrBi2Nb2O9 (n = 2 member), due to their superior fatigue-resistance even after significant ferroelectric cycling. This advantageous property makes these films excellent candidates for ferroelectric memories. It has been argued that it is the highly anisotropic crystal structure of this material that makes it superior to other perovskite-based ferroelectrics. Additionally, it has been previously shown through atomic force microscopy (AFM) that c-axis films of SrBi2Ta2O9 (isostructural with SrBi2Nb2O9) grow via a spiral growth mechanism. As a result, studying oriented growths of these materials can provide insight into this growth phenomenon that has been observed in other layered perovskite-like systems. Using pulsed laser deposition (PLD) we have grown phase pure, (001)-oriented epitaxial SrBi2Nb2O9 to begin studying the temporal evolution of the spiral surface morphology. Here, we report on the c-axis growth of this Aurivillius phase with special attention to the interesting growth phenomenon present in this material. AFM, 4-circle x-ray diffraction, TEM, and RBS data will be presented.

4:15 PM BB5.8/V6.8
CONTROL OF MBE-GROWN DyBa2Cu3O7 THIN FILMS USING RHEED INTENSITY OSCILLATIONS. P.A. Kraus , K.R. Nikolaev, W.K. Cooley and A.M. Goldman, Univ. of Minnesota, School of Physics and Astronomy, Minneapolis, MN.

By monitoring the intensity of the RHEED specular point, we have modified the block-by-block growth technique for MBE-grown DyBa2Cu3O7 and related compounds. Computer controlled shutters for each metal source allow for real time corrections to film composition. The relationship between the intensity oscillations and the correct stoichiometry has been empirically determined using Rutherford backscattering spectroscopy. Results of x-ray reflectivity and diffraction for films grown by the standard block-by-block technique will be compared to the RHEED controlled films. Applications of the technique to oxide multilayers will be discussed. (Supported in part by the Office of Naval Research under grant N/N00014-98-1-0098.)

4:30 PM *BB5.9/V6.9
ENGINEERING OXIDE MULTILAYERS USING ATOMIC LAYER BY LAYER MOLECULAR BEAM EPITAXY. J.N. Eckstein , J. O'Donnell, S. Oh, A. Andrus, University of Illinois, Department of Physics, Urbana, IL; I. Bozovic, Oxxel GMBH, Bremen, GERMANY.

Our group has employed atomic layer control of molecular beam epitaxial growth to make films and heterostructures of several different oxide compounds. These range from simple perovskites, such as titanates and manganites to materials with more complicated unit cells like BSCCO-2278. If the composition is controlled within a range of typically <3%, we find that single phase growth occurs, while for compositions outside this range one or more second phase nucleates. Within that range different growth modes can occur. For example in the growth of manganite films on titanate substrates, if the composition is slightly (<1%) Mn-rich, 3D columnar growth occurs and the material self assembles into grains about 30 nm across. Smooth films that show a terraced structure are obtained if the composition is not Mn-rich. By controlling the process to obtain 2-D growth, tunnel junctions with titanate barriers have been grown. The temperature dependence of the tunneling suggests localization at the interfaces. Other oxide systems have also been studied and methods of local control of carrier doping explored. These include doping with non-isovalent ions in specific planes, as well as devising intergrowths or stacking faults that locally change the charge transfer occuring.

Chairs: Albert-Laszlo Barabasi and Stephen K. Streiffer
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)
ANALYSIS OF KINETICALLY DETERMINED THIN FILM MORPHOLOGIES. Paritosh , University of Michigan, Dept. of Chemical Engineering, Ann Arbor, MI; Xingquan Li, University of Michigan, Dept. of Physics, Ann Arbor, MI; Peter Smereka, University of Michigan, Dept. of Mathematics, Ann Arbor, MI; David J. Srolovitz, University of Michigan, Dept. of Materials Science & Engineering, Ann Arbor, MI.

Compared with metals and typical semiconductors, oxides exhibit a wide range of possible crystal structures. These crystal structures impact the types of morphologies that are observed during polycrystalline oxide film growth. In the present study, we examine a model of faceted film growth, in which crystallographically equivalent facets grow at the same rate. We determine the microstructure and morphology of these growing films by tracking the growth fronts of an array of randomly oriented seeds on the substrate as they grow, coalesce, and compete with each other during growth. We examine such microstructure characteristics as grain size, roughness, and crystallographic texture for oxides of different crystal symmetry. These simulations will be performed in both two and three dimensions, using front tracking and level-set methods. The resultant structures are analyzed in terms of simple concepts associated with growth idiomorphs (i.e., the Wulff plot based upon the velocity vectors).

SYNTHESIS OF A&C AXES ORIENTED (Cu1-x,Tlx)Ba2Ca3 Cu4Oy SUPERCONDUCTOR THIN FILMS. Nawazish A. Khan , Y. Sekita, F. Tateai, T. Kojima, K. Ishida, N. Terada and H. Ihara, Electrotechnical Laboratory, Umezono, Tsukuba, Ibaraki, JAPAN.

Predominant single phase of (Cu1-x,Tlx)Ba2Ca3Cu4Oy [CuTl-1234] superconductor thin films is prepared for the first time by employing two step method. In this method the crystalline phase is grown from the sputtered amorphous phase by thallium treatment. This process is carried out at 900$^{\circ}$C for 1hour in the Au capsule. The amorphous phase is prepared by sputtered deposition on the SrTiO3 substrate from the stoichiometric target composition CuBa2Ca3Cu4Ox. The films achieved after thallium treatment are aligned biaxially along a and c axes. The XRD measurements showed a predominant single phase with the c-axis lattice constant of 18.74Å. The c-axis lattice constant value in our CuTl-1234 films is in between that of Cu-1234 (17.99Å) and Tl-1234 (19.11 Å). The pole figure measurements of (103) reflection of the films showed a-axis oriented crystals with Df=0.796o. The composition of the films after EDX measurements is Cu0.3Tl0.7Ba2Ca3Cu4Ox. From the resistivity measurements the Tc is 113K and Jc measurements showed a current density of 1.0$\cdot$106A/cm2 (77K,0T: Jc is determined by the threshold value of 1mV/cm). Preparation of CuTl-1234 films by this method is highly reproducible.

GROWTH AND STRUCTURAL CHARACTERIZATION OF La1-xSrxFeO3$\delta$ THIN FILMS. Jean Fompeyrine 1, Jin Won Seo1,2, Mike Toney3, Joachim Stohr3, Eric E. Fullerton3 and Jean-Pierre Locquet1, 1IBM Research Division, Zurich Research Laboratory, Ruschlikon, SWITZERLAND; 2Université de Neuchâtel, Institut de Physique, Neuchâtel, SWITZERLAND; 3IBM Almaden Research Center, San Jose, CA.

Transition metal perovskites thin films of compounds such as La1-xSrxMnO3 and Ba1-xSrxTiO3 are studied for their interesting and useful magnetic and dielectric properties. Previous work has shown that the properties of both compounds can be tuned using epitaxial strain. Here we report on the growth and the structural characterization of a related perovskite system : La1-xSrxFeO3. For x = 0, LaFeO3 is an orthorhombic weak ferromagnet (Tc = 750K) due to the canting of antiferromagnetically coupled spins. Thin films were grown using block-by-block molecular beam epitaxy under a beam of atomic oxygen on various substrates (SrTiO3, LaAlO3, NdGaO3, MgO) and different orientations. The deposition temperature was varied between 450 and 750$^{\circ}$C. The in-situ reflection high energy electron diffraction patterns indicate almost perfect epitaxial and 2D growth. The high structural quality of these films is confirmed by a detailed structural analysis using X-ray diffraction, synchrotron radiation and Transmission Electron Microscopy. The results indicate that the films are not orthorhombic but are fully strained up to a thickness of at least 200Å. The consequences of the epitaxial strain on the magnetic properties will be reported.

CHANGES OF Tc UNDER EPITAXIAL STRAIN: IMPLICATIONS FOR THE MECHANISM OF SUPERCONDUCTIVITY. J.P. Locquet 1, J. Perret1,2, J. W. Seo1,2, J. Fompeyrine1 and P. Martinoli2, 1IBM Research Division, Zurich Research Laboratory, Ruschlikon, SWITZERLAND; 2Université de Neuchâtel, Institut de Physique, SWITZERLAND.

Recent results demonstrated a relationship between a large change of Tc and small variations of the lattice parameters for La1.9Sr0.1CuO4 ultrathin films grown by molecular beam epitaxy under compressive or tensile strain. First we search for the subtle deviations of the atom positions responsible for the observed behavior. Then we compare our findings regarding charge transfer, anisotropy, in-plane resistivity and superfluid density with trends among the family of the one CuO2 layer compounds. This systematics leads to the following conclusions : i) increasing the distance between the charge reservoir and the CuO2 plane is essential to increase Tc; ii) the electrical coupling from one CuO2 plane to the next CuO2 plane may not be essential for the mechanism of superconductivity; iii) a sufficient density of carriers is present in the underdoped state but the appearance of superconductivity is hindered by a large scattering rate and iv) this scattering is determined by the two-dimensional confinement of the carriers in the CuO2 plane.

PRESSURE TUNED EPITAXY OF ZnO AND ZnMgO ON SAPPHIRE IN PULSED LASER DEPOSITION. S. Choopun , W. Noch, R.D. Vispute, A. Balsamo, R.P. Sharma, T. Venkatesan, CSR, Dept of Physics, Univ of Maryland, College Park, MD; D.C. Look, Wright State Univ, Univ Res Ctr, Dayton, OH; A.A. Iliadis, Dept of Electrical Engineering, Univ of Maryland, College Park, MD; P. Shen, K.A. Jones, Army Research Laboratory, Adelphi, MD.

In recent years, there has been a significant progress in the development of optoelectronic materials and their heterostructure technologies. In metal-oxides, a promising material for UV and blue light emitting devices is ZnO. It has higher exciton binding energy of 60 meV. The exciton radius in ZnO is 1.8 nm versus making ZnO optical properties less sensitive to the defects. In this paper, we discuss the influence of oxygen pressure on the structure, epitaxy, surface, interface, and opto-electronic properties of thin films of ZnO and ZnMgO grown on sapphire by pulsed laser deposition. Results of AFM in conjunction with RBS, ion channeling, and XRD indicate that these film grew three-dimensional, two-dimensional, and textured in the oxygen pressure regimes of 0.1-1x10-4 Torr, 1-10x10-3 Torr, and 1-5x10-1 Torr, respectively. It is also observed that the growth mode strongly affects the electrical mobility, carrier concentration, and the luminescence properties of the films. By tuning the oxygen pressure during the initial and the final growth stages, smooth and epitaxial films with high optical quality, high electron mobility, and low carrier concentration have been fabricated. We also found that the bandgap of Zn(1-x)Mgx (1-x)O films increases linearly from 3.3 eV to 4.0 eV with an increase of x from 0 to 0.2. The alloyed films of composition varying from x=0 to 0.1 had high crystalline and optical qualities, whereas the alloys with x>0.1 showed composition fluctuation within the films, MgO precipitation near surface with rough surface morphology and poor optical properties. Our results represent that the films having composition x=0 to 0.1 can be useful for fabrication of quantum wells for carriers and photon confinement in ZnO. The implication of these results towards the fabrication of the efficient UV-blue lasers, and the possibility of n and p-type controlled doping is discussed.

STRUCTURE AND ELECTRICAL TRANSPORT PROPERTIES OF EPITAXIAL OXIDE CaRuO3 THIN FILMS ON VICINAL (001) SrTiO3 SUBSTRATES. Qing Gan , Chang-Beom Eom, Duke Univ, Dept of Mechanical Engineering and Materials Science, Durham, NC.

Epitaxial CaRuO3 thin films of different thickness (500${\AA}$ - 4000${\AA}$ ) have been grown on miscut (001) SrTiO3 substrates (0$^{\circ}$, 0.8$^{\circ}$, 2$^{\circ}$, and 4$^{\circ}$). We have found that the electrical transport behavior of these thin films showed strong dependence on both the miscut angle of substrates and film thickness. For CaRuO3 thin films with thickness less than 1000${\AA}$ , semiconducting behavior was observed on low miscut substrates (0$^{\circ}$, 0.8$^{\circ}$), however, films on high miscut substrates (2$^{\circ}$ and 4$^{\circ}$) showed metallic behavior. For thicker films ( > 2000${\AA}$ ), samples on different miscut substrates all showed metallic behavior. To understand this strong miscut angle and film thickness dependence, the structure, and film composition have been studied by x-ray diffraction, and Rutherford Backscattering (RBS), respectively. The data from these measurements suggest that the coherency strain plays a critical role in determination of the film structure and stoichiometry attributed to the observed electrical transport behavior dependence on the film thickness and miscut angle of vicinal (001) SrTiO3 substrates. This work was supported by the NSF Grant No. DMR 9802444, the ONR Grant No. N00014-95-1-0513, the NSF Young Investigator Award (CBE), and the David and Lucile Packard Fellowship (CBE)

Abstract Withdrawn.

METAL-ORGANIC CHEMICAL VAPOR DEPOSITION OF METAL OXIDES FROM PRECURSOR SYNTHESIS TO THIN FILMS. John A. Belot , Anchuan Wang, Tobin J. Marks, Northwestern University, Department of Chemistry, Evanston, IL; Paul R. Markworth, Robert P. H. Chang, Northwestern University, Department of Material Science and Engineering, Evanston, IL; Mike P. Chudzik, Carl R. Kannewurf, Northwestern University, Department of Electrical and Computer Engineering, Evanston, IL.

This contribution will describe recent work focusing on the synthesis, characterization, and implementation of metal-organic chemical vapor deposition precursors for oxide film growth. Synthetically, new, highly volatile sources for a variety of metals (lanthanides, alkaline earths, and group IV) will be presented. Furthermore, their MOCVD compatibility will be explicitly demonstrated by the successful deposition of various HTS-related oxides (insulators and superconductors) on both lattice-matched single crystal and metallic substrates.

EFFECTS OF INTERFACIAL STRESS ON THE MICROSTRUCTURE OF EPITAXIAL SrRuO3 THIN FILMS. X.Q. Pan and J.C. Jiang, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI; Q. Gan and C.B. Eom, Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC.

Epitaxial SrRuO3 thin films grown on (001) SrTiO3 and (001) LaAlO3 substrates by 90$^{\circ}$ off-axis sputtering were investigated by plane-view and cross-section transmission electron microscopy. SrRuO3 films grown on the (100) SrTiO3 substrate have a smooth surface and a coherent interface between the film and the substrate. In contrast, films grown on (001) LaAlO3 substrates have very rough surface. In addition, the SrRuO3/LaAlO3 interface is semi-coherent and consists of an array of misfit dislocations owing to the lattice mismatch ($\sim$4.0%) across the film/substrate interface. Furthermore, all six different types of orientation domains exist in the SrRuO3 film grown on (001) LaAlO3. The film, which grows at lower temperature (500$^{\circ}$C), has a smaller domain size and smoother surface in comparison with that deposited at higher temperature (600$^{\circ}$C). The hilly surface morphology and complex domain structures of the film grown on the LaAlO3 substrate can be attributed to the existence of interfacial stresses originating from the large degree of lattice mismatch across the interface. In-situ TEM observations of SrRuO3 thin films have revealed the occurrence of a structural phase transformation around 580$^{\circ}$C. Possible influence of this phase transition on the microstructure of SrRuO3 thin film grown at high temperatures will be discussed.

Abstract Withdrawn.

POLYDOMAIN MICROSTRUCTURE IN PLD THIN FILMS OF FERROELECTIC Pb(Zr0.2Ti0.8)O3. L.A. Bendersky , MSEL, NIST, Gaithersburg, MD; S.P. Alpay, S. Aggarwal, R. Ramesh, A.L. Roytburd, Dept. of Materials and Nuclear Engineering, University of Maryland, College Park, MD.

Pb(Zr0.2Ti0.8)O3 thin films were grown epitaxially on (001) SrTiO3 at 600$^{\circ}$C by pulsed laser deposition. In such films c-domains (with c-axis normal to a substrate) are dominant, and a domains appear as the thin plates alternating with the c-domain and having a (110)-type interface. It is accepted in literature that such films have patches consisting of either a1/c/a1- or a2/c/a2-type alternation. In this paper we will show the existence of a polydomain microstructure where both a1- and a2-domains coexist with c-domains and form a special morphology. TEM characterization of the microstructure, as well as theoretical analysis based on the minimization of elastic energy, will be presented in the paper.


Epitaxial (La1-xNdx)0.7Sr0.3MnO3 thin films have been grown on LaAlO3(001) substrates by pulsed laser deposition with different target-plume-substrate configurations. Like the high-Tc superconducting YBCO films, the manganite films are also featured by the existance of particulate of about micrometer size. Apart from the laser droplets, outgrowths with different shape and size are observed from the as-grown manganite films with the conventional arrangement. We demonstrate that when the substrates are placed within the visible energetic laser plume, the films are outgrowth-free. Resistivity measurements and x-ray diffraction studies show that when deposited in the same O2 pressure, the outgrowth-free films exhibit higher conductivity and better crystallinity than the films with outgrowths. Formation mechanisms of the particulate will be discussed.

INFLUENCE OF ANNEALING ON LATTICE STRAIN, ELECTRICAL TRANSPORT AND MAGNETIC PROPERTIES IN EPITAXIAL La0.8Ca0.2MnO3 CMR FILMS. T.K. Nath , R.A. Rao, D. Lavric, C.B. Eom, Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC.

We have studied the effect of annealing time on 3-dimensional lattice strain, crystallographic domain structure, magnetic and electrical properties of both 250 ${\AA}$ and 4000 ${\AA}$ thick epitaxial La0.8Ca0.2MnO3 (LCMO) thin films grown on (001) LaAlO3 substrates. While short annealing time ($\sim$ 2hrs.) leads to increase of the peak temperature (TP) and Curie temperature (TC) beyond room temperature, longer annealing time ($\sim$ 10 hrs.) restores the TP and TC almost the same values as that of the as-grown films. Furthermore, as the annealing time is increased, the lattice strain relaxes with filmís lattice parameter approaching to the bulk value. A clear correaltion is observed between TP and perovskite unit cell volume for both the films. The films crystalline quality determined by the FWHM of the x-ray rocking curves was improved with the annealing time. The non uniform strain in the films can be correlated with their electrical and magnetic properties. This work highlights the importance of controlling the 3-dimensional lattice strain for optimizing the properties of CMR films. This work was supported by the NSF Grant No. DMR-9802444, the NSF Young Investigator Award (CBE) and the David and Lucile Packard Fellowship (CBE).

EPITAXIAL GROWTH OF OXIDE BUFFER LAYERS ON BIAXIALLY TEXTURED-Ni (100) SUBSTRATES BY SOL-GEL PROCESS. T.G. Chirayil , M. Paranthaman, D.B. Beach, J.S. Morrell$\dagger$, E. Sun, A. Goyal, D.F. Lee and E. Specht, Oak Ridge National Laboratory, Oak Ridge, TN; $\dagger$Department of Chemistry, University of Tennessee, Knoxville, TN.

Epitaxial growth of biaxially textured oxide buffer layers and YBCO on rolled-Ni substrates by using the vacuum process has demonstrated high Jc films for the development of second generation superconducting wires. We have used the cost efficient and easily scalable non-vacuum process to epitaxially grow compatible oxide buffer layers on Ni substrates. The precursor solution for the oxide buffer layers was prepared by an all alkoxide sol-gel route and was deposited on the substrates by spin coating or dip coating methods. The processing of the films was conducted in the 800-1160°C temperature range under optimum atmospheres. The oxide buffer layers exhibited a strong c-axis orientation on the Ni (100) substrate and the phi and omega scans indicated good in plane and out of plane orientation. The X-ray (111) pole figure showed a cube-on-cube epitaxy. The optimum processing conditions, the characterization of these films, and their microstructure will be discussed in detail. Attempts will be made to grow YBCO films on these sol-gel grown buffer layers by Pulsed Laser Deposition. This research is sponsored by the U.S. Department of Energy, Division of Materials Sciences, Office of Basic Energy Sciences and Office of Energy Efficiency and Renewable Energy, and Office of Utility Technology-Superconductivity Program. Oak Ridge National Laboratory is managed by Lockheed Martin Energy Research Corporation for the U.S. Department of Energy under contract #DE-AC05-96OR22464.

NOVEL APPROACH TO REACTIVE EVAPORATION OF SUPERCONDUCTING YBCO FILMS. Z. Lu , K. Von Dessonneck, V. Matijasevic, and A. Barfknecht, Conductus Inc., Sunnyvale, CA.

The technique of using a rotating heater with an oxygen pocket (Garching heater) for co-evaporation of YBCO films (1) has been shown to provide a process capable of high-throughput production of high-quality superconducting YBCO films. However, consistent control of cation chemistry is still being researched by many groups. At Conductus, we have built a novel rotating heater which allows us to improve rate control by using conventional quartz crystal monitors for rate control. This new process allows us also to research the deposition conditions for oxidizing individual metal species Y, Ba and Cu. Microwave measurements showed that the films produced by this process are at least as good in quality as those deposited using the standard Garching-type heater. The new process also allows for the use of larger sources, such as electron-beam evaporators in a production environment.
(1) P. Berberich, W.Assmann, W. Prusseit, B.Utz, and H. Kinder, J. Alloys and Compounds, 195, 271 (1993).

THE GENERATION AND DETECTION OF ATOMIC OXYGEN FOR THIN FILM OXIDE GROWTH. N.J.C. Ingle , R.H. Hammond, M.R. Beasley, Stanford University, Dept. of Applied Physics, Stanford, CA; D.H.A. Blank, University of Twente, Dept. of Applied Physics, NETHERLANDS.

The growth of many epitaxial thin film oxides are significantly enhanced with the use of an oxidizing agent such as atomic oxygen, ozone, or NO2. We have pursued the generation of large atomic oxygen fluxes while maintaining vacuum pressures of less that 1 $\times$ 10-4 Torr and minimizing the production of energetic ionized oxygen by a flow-through microwave plasma source. Continuous and real-time detection of the atomic oxygen is achieved by an atomic absorption spectrometer operating at the 130 nm atomic oxygen lines. We have measured the generation of atomic oxygen as a function of microwave power, flow-rate, gas composition, and surface treatment of the plasma confinement tube. A lower limit on the atomic oxygen flux generated is found to be 3 $\times$ 1017 atoms/cm2 sec. This atomic oxygen generation and detection scheme has been used to attempt the epitaxial growth of ``high-pressure`` phases such as CrO2 and SrCu2O3.

STRAIN INHOMOGENEITY IN EPITAXIAL CMR La0.67Ca0.33MnO3 THIN FILMS. R.A. Rao , T.K. Nath, D. Lavric, and C.B. Eom, Department of Mechanical Engineering & Materials Science, Duke University, Durham, NC; L. Wu, and F. Tsui, Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC; XQ. Pan, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI.

The evolution of 3-dimensional strain states, and crystallographic domain structures of epitaxial colossal magnetoresistive La0.67Ca3MnO3 (LCMO) films has been studied as a function of film thickness and lattice mismatch with (001) SrTiO3 and (001) LaAlO3 substrates. The lattice parameters were determined using normal, grazing incidence x-ray diffraction (GID), and also a least-squares fit from many off-axis reflections. The lattice strain at the film surface determined by GID appears to relax faster than the strain at the film interior calculated from the least-squares fit. The unit cell volume of the films is not conserved, and it exhibits a substrate-dependent variation with film thickness. Films grown on (001) SrTiO3 substrates with thickness up to $\sim$250AA are strained coherently with a pure (001)T orientation normal to the surface. (The superscript T denotes miller indices based on the tetragonal unit cell.) In contrast, the 250Å thin films grown coherently on (001) LaAlO3 substrates have a purely (110)T texture. While thinner films have smoother surfaces and higher crystalline quality, strain relaxation in thicker films leads to mixed (001)T and (110)T textures, mosaic spread, and surface roughening. The strain inhomogeneity in the films is also reflected in the double transitions observed in the temperature dependence of magnetization. Transmission electron microscopy studies of the film structure and strain states will also be discussed. This work was supported by the NSF Grant No. DMR-9802444, the NSF Young Investigator Award (CBE) and the David and Lucile Packard Fellowship (CBE).

Chairs: Dave H. A. Blank and Susan Trolier-McKinstry
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)
INVERSE MAGNETORESISTANCE IN MANGANITE/SrTiO3/Co TUNNEL JUNCTIONS. J.M. De Teresa , A. Barthélémy, J.P. Contour, A. Fert, R. Lyonnet, F. Montaigne, A. Vaurés, P. Séneor, UMR de Physique CNRS-Thomson CSF, LCR, Orsay, FRANCE.

We present magnetization and magnetoresistance (MR) measurements on tunnel junctions composed of LSMO (La0.7Sr0.3MnO3) for the bottom electrode, STO (SrTiO3) for the barrier and Co for the top electrode. The oxides are deposited epitaxially by laser ablation and the Co by MBE or sputtering. After deposition, a photolythography method is used to pattern the junction. An antiparallel (AP) configuration between the magnetizations of the electrodes is obtained in the field range between the coercive field of LSMO, for example Hc$\approx$30 Oe at 5 K, and that of Co, Hc$\approx$150 Oe at 5 K. We find an inverse MR: the tunnel resistance is lower in the AP configuration. At 5 K the maximum MR ratio is $\approx$35$\%$ and decreases to 3$\%$ at room temperature. Measurements performed with bias voltages in the range $\pm$1.5 v between the LSMO and Co electrodes indicate that the variation of the MR is small in the negative bias voltage region and more pronounced in the positive one. The temperature dependence of this variation will be shown. The observation of inverse tunnel MR has deep implications for the understanding of spin-dependent tunneling. As the spin polarization of the carriers in LSMO is known to be positive, the inverse MR of our junctions implies that the polarization of the electrons tunneling from or to the Co is negative. This in contrast to the positive polarization generally found for tunneling from or to Co across alumina barriers. However, this is reminiscent of the negative polarization found in some field emission experiments. A plausible explanation is that the tunneling of d-character electrons is favoured in our STO barrier junctions, so that the MR reflects the negative polarization of the d-band density of states in Co, while the s-character electrons are favoured to tunnel in alumina-based tunnel junctions.

GROWTH AND CHARACTERIZATION OF Ba(1-x)Sr(x)TiO(3) (BST) THIN FILMS ON SELECTED ELECTRODE/DIFFUSION BARRIER HETEROSTRUCTURES FOR APPLICATION IN HIGH FREQUENCY DEVICES. P.K. Baumann , S.K. Streiffer, O. Auciello, Materials Science Division, Argonne National Laboratory, Argonne, IL; M.T. Lanagan, J. Giumarra, R.A. Erck, Energy Technology Division, Argonne National Laboratory, Argonne, IL; J. Im, A.R. Krauss, Materials Science and Chemistry Divisions, Argonne National Laboratory, Argonne, IL.

The synthesis of Ba(1-x)Sr(x)TiO(3) (BST) thin films has been investigated for applications such as high-frequency phase-shifters and capacitors for resonant circuits. We have been growing BST thin films with good thickness and composition uniformity using a vertical metal organic chemical vapor deposition (MOCVD) system with the capability of depositing films on up to 4 inch substrates. Accurate control of the composition and reproducibility of the films stoichiometry have been facilitated by means of a liquid delivery system to supply precursors into the deposition chamber. BST films have been grown on Pt/TiO(2) and on Ir/TiN layered electrode/diffusion barrier heterostructures to investigate the effect of the bottom electrode on the microstructure and properties of the BST films. We have used mass spectroscopy of recoiled ions (MSRI) to analyze the electrode systems. We have determined that Ti diffuses to the surface of Ir at substrate temperatures in the range of 400-700 C, while no diffusion has been observed for the Pt/TiO(2) system. The chemical composition and structure of the BST films have been analyzed using Rutherford backscattering spectroscopy (RBS), X-ray fluorescence (XRF), and X-ray diffraction (XRD), respectively, in order to establish correlations with possible effects introduced by diffusion of species to the surface of the bottom Pt or Ir electrodes. A discussion will be presented on the correlation between the chemical and structural properties of the BST films and the BST/electrode interface and the electrical properties, such as the dielectric constant, the dielectric loss and the leakage current. The dependence of these characteristics of the BST films on the growth parameters will be discussed.

DIELECTRIC RESPONSE OF FREE STANDING STRONTIUM TITANATE THIN FILMS FROM 10 KHZ TO 1 GHZ AS A FUNCTION OF TEMPERATURE AND APPLIED VOLTAGE. Mark J. Dalberth , Renaud E. Stauber, John C. Price and Charles T. Rogers, University of Colorado at Boulder, Department of Physics, Boulder, CO.

Using pulsed laser ablation, we have grown epitaxial bilayers of strontium titanate (STO) and yttrium barium copper oxide (YBCO) on (110) neodymium gallate (NGO) substrates. Using a selective acid etch, we have removed the YBCO from the middle of the bilayer and lifted off the STO films from their parent substrates. Using coplanar interdigital capacitors patterned on the surface of the films, we have measured the dielectric constant and loss as a function of frequency (from 10 kHz to 1 GHz), temperature (from 300 K to 4 K), and applied electric field (up to roughly 5 V/$\mu$m). We have seen frequency dependent loss peaks in the films that indicate thermally activated behavior.

BARIUM STRONTIUM TITANATE-MAGNESIUM OXIDE COMPOSITE FERROELECTRIC THIN FILMS FABRICATED BY PULSED LASER DEPOSITION. Costas G. Fountzoulas , Eric Ngo, Poran Joshi and Melanie W. Cole, Army Research Laboratory, Weapons Materials Division, APG, MD.

Bulk barium strontium titanate-magnesium oxide (BSTO-MgO) composites have excellent properties for microwave communication applications including high dielectric tunability and low dielectric loss. In the present work, a pulsed laser deposition technique (PLD) has been used to fabricate BSTO-MgO composite thin films. Thin films were prepared using targets with an optimized BSTO-MgO composition. The effects of different evaporation temperatures of MgO and BSTO on the film stoichiometry and microstructure have been analyzed. The composition of thin films has been analyzed by Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). The structure and morphology have been analyzed by x-ray diffraction and scanning electron microscopy. Both the dielectric tunability and dielectric loss characteristics have been measured. These properties are compared to the bulk material properties to evaluate the potential of the BSTO-MgO composite thin films for tunable microwave devices.

IMPROVEMENT OF THE ELECTRICAL PROPERTIES OF YMnO3 THIN FILMS IN A METAL/FERROELECTRIC/Si STRUCTURE. Woo-Chul Yi , Chang-Su Seo, Sook-Il Kwun, Seoul National Univ., Dept. of Physics, Seoul, KOREA; Jong-Gul Yoon, Univ. of Suwon, Dept. of Physics, Kyung-gi-do, KOREA.

Highly (0001)-oriented films of YMnO3 were grown on Si(100) substrates by a chemical solution deposition at an annealing temperature as low as 650 $^{\circ}$C by using an improved precursor solution and rapid thermal process. Ferroelectric property of YMnO3 film was examined in the metal/ferroelectric/Si structure. Capacitance-voltage measurements exhibited a memory window of 1.9 V at 9 V and a dielectric constant of 25. Polarization-voltage measurements showed a spontaneous polarization of 1.4 $\mu$C/cm2 at 11 V. Current-voltage characteristics showed a leakage current density of 16 nA/cm2 at 3 V. The low temperature fabrication of this YMnO3 film on Si(100) substrate showed a possible application of the material to nonvolatile ferroelectric memory devices in the form of a metal/ferroelectric/semiconductor field effect transistor.

LOW LOSS FERROELECTRIC FILMS GROWN ON POLYCRYSTALLINE FERRITE SUBSTATES FOR DUAL-TUNING MICROWAVE DEVICES. Hua Jiang , Wei Hu, Shaohua Liang and Vladimir Fouflyguine, NZ Applied Technologies, Woburn, MA; Quanxi Jia, Los Alamos National Laboratory, Los Alamos, NM.

Ferrite and ferroelectric materials individually provide magnetic and electrical tunability for adaptive microwave devices. Adaptability would increase significantly if a microwave device could be simultaneously tuned by both magnetic and electrical techniques. However, such advanced devices have not yet been demonstrated by others due to the unavailability of high quality ferroelectric films on polycrystalline ferrite substrates. (Large single crystal ferrite substrates are not currently available.) We have successfully deposited high quality biaxially oriented BaSrTiO (BST) thin films on polycrystalline YIG substrates using both the metal-organic chemical liquid deposition and pulsed laser deposition methods with biaxially oriented MgO (and yttria-stabilized zirconia, YSZ) buffer layers. BST films deposited on MgO buffered YIG substrates showed (100) orientation while (110) orientation on YSZ bufferd YIG substrates. The full width at half maximum (FWHM) of the BST (110) peak on MgO buffered YIG substrate was around 8°. The dielectric loss of the films decreased from a value of 0.015 at zero bias to 0.005 at a dc bias voltage of 40 V, while 25% of dielectric constant change was observed with 40 V bias voltage in the frequency range from 100 Hz to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range (77 K to 380 K). A microwave coplanar phase shifter using a BST film grown on an MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in a wide frequency range (3-20GHz) when an electric bias or a magnetic field was applied to the device. The phase shift per unit length of the device by electric or magnetic tuning was compatible to those of the best electrical or magnetic tunable phase shifters. To the best of our knowledge, this is the first real integrated microwave dual-tuning device.

EXOTIC DOPING FOR ZnO THIN FILMS: POSSIBILITY OF MONOLITHIC OPTICAL INTEGRATED CIRCUIT. Norifumi Fujimura , Tamaki Shimura, Toshifumi Wakano, Taichiro Ito, College of Engineering, Dept. of Applied Materials Science, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka, JAPAN.

We have been interested if ZnO can be applied to monolithic optical integrated circuit by exotic doping (Li, Mg, N, Gd, Mn, Al, B and so on). ZnO is well known as a excellent piezo-semiconductor, a varistor ceramic and a transparent conductive film. In the past few years there has been a significant effort to develop ZnO thin films for next generation electronic and opt-electronic applications. The triggers are the stimulated emission from a ZnO nanocrystalline film [1] and the discovery of ferroelectric phase transition of ZnO:Li bulk materials [2]. We also succeeded to apply ZnO:Li thin films to FET-type FeRAM[3]. Moreover, if we dope the magnetic element like Mn, it should transform to antiferromagnetic phase like usual II-VI group dilute magnetic semiconductors. All above suggest that we have a chance to fabricate optical IC by using just only ZnO. This paper describes our recent results on conductive ZnO with trivalent elements like Al, Sc and B, ferroelectric ZnO:Li, Mg and also discusses the magnetic structure of Gd, Yb and Mn doped ZnO bulks and thin films. [1] Z.K.Tang et al, Solid State Commun. 103 (1997) 459 [2] A.Onodera et al, Jpn. J. Appl. Phys. 35 (1996) 5160 [3] N.Fujimura et al, submitted to APL

LOW MAGNETIC FIELD RESPONSE OF 2D-ARRAYS OF WEAKLY COUPLED FERROMAGNET. Zdravko G. Ivanov , Radoslav A. Chakalov, Tord Claeson, Dept of Physics and Engineering Physics, Chalmers University of Technology and Gothenburg University.

Ferromagnetic thin films with low field response have a high potential for applications as magnetic sensors and information storage media. The effect of high sensitivity of the magnetoresistance (CMR) to low magnetic field has been onserved in La0.67(Ca/Sr)0.33MnO3 polycrystalline thin films and attributed to the properties of grain boundaries. The response in this case is averaged over the range of grain boundaries presented. We have developed a method to fabricate 2D-arrays of weakly coupled ferromagnet. The temperature and magnetic field dependences of resistance and magnetization of those 2D-arrays were measured and compared with the properties of single crystal and polycrystalline films.

MOTT TRANSITION FIELD EFFECT TRANSISTOR: SIMULATIONS OF NANOSCALE DEVICE. D.M. Newns , Y. Snir, W.M. Donath, P.C. Pattnaik, C.C. Tsuei, T. Doderer, J.A. Misewich, A.G. Schrott, B.A. Scott, A. Gupta, D. Abraham, IBM Thomas J. Watson Research Center, Yorktown Hieghts, NY.

The Mott Transition Field Effect Transistor is an FET-like device aiming to exploit the nonlinear behavior of a novel type of channel made from a Mott Insulator oxide material, and the properties of a high dielectric constant gate oxide, to achieve operation at nanoscales (order 10 nm. channel length). Estimated `ON' currents achieved by metallizing the Mott Insulator via the gate voltage are appropriate for logic switching applications. Factors supporting nanoscale function are the very low thickness (<1 nm.) of the metallized channel, absence of pn junction, low dopant scattering and relatively thick gate oxide inhibiting tunneling. We have implemented simulations of device function to evaluate behavior in the nanoscopic regime. Simulations are compared with existing (micrometer scale) device data in order to support understanding of fundamental device physics. Dynamic quantum simulations on very small devices supply information required to evaluate switching speed performance.

OPTIMIZATION OF BaxSr1-xTiO3 FILMS FOR USE IN ROOM TEMPERATURE TUNABLE MICROWAVE DEVICES. C.M. Carlson 1, T.V. Rivkin2, J.C. Price1, P.A. Parilla2, D.S. Ginley2, L.C. Sengupta3, L. Chiu3, X. Zhang3, Y. Zhu3, S. Stowell3, S. Sengupta3, 1University of Colorado, Boulder, CO; 2National Renewable Energy Laboratory, Golden, CO; 3Paratek, Inc., Aberdeen, MD.

Ferroelectric materials such as BaxSr1- xTiO3 (BST) exhibit a high dielectric constant, tunability with bias voltage, and low losses in the paraelectric state. These properties make BST potentially useful in a wide range of applications such as tunable microwave phase shifters, resonators, and filters. By changing the Ba to Sr ratio, the temperature for highest tunability and lowest loss can be set anywhere from a few Kelvin to above 400 K. With the goal of optimizing the performance of pulsed-laser-deposited (PLD) films for room temperature operation, we have grown high quality BST thin films on LaAlO3 (LAO) and MgO substrates. Although LAO is more closely lattice-matched to BST, we obtained films with a higher figure of merit on MgO after a post-deposition anneal. This is significant since MgO not only has certain advantages for microwave devices, but is also less costly. Structural analysis combined with microwave (1-2 GHz) measurements led us to propose that annealing produced BST films on MgO with less strain than films on LAO. When the structural properties are optimized, the limiting factor of microwave performance becomes the imperfections at the interface between the BST and the electrodes. In an attempt to further optimize our devices, we investigated the effects of different electrode geometries and materials including normal metal and lattice-matched oxide electrodes such as LaNiO3.

PREPARATION AND ELECTRICAL PROPERTIES OF PLZT FILMS ON Si SUBSTRATES WITH A CeO2 BUFFER LAYER BY PULSED LASER DEPOSITION. Zhou W.L. , Yu J., Wang Y.B., Dong X.M., Zheng Y.K., Xie J.F., Liu G., Dept. of Electronic Science & Technology, Huazhong University of Science & Technology, Wuhan, Hubei, P.R.CHINA.

(Pb, La)(Zr, Ti)O3 films and a CeO2 buffer layer were prepared by Pulsed Laser Deposition on Si substrates simultaneously through multi-target rotation. Crystalline quality were confirmed by X-ray diffractometry with the substrate temperature and O2 gas pressure as parameters. The surface morphology was observed by SEM. With evaporated Au upper electrodes, a good Capacitance-voltage (C-V) hysteresis curve was obtained with the PLZT film at substrate temperature of 550$^{\circ}$C and CeO2 at 600$^{\circ}$C. The leakage current was also measured. Results demonstrated that the PLZT/CeO2/Si structure is one of the most promising structures for the fabrication of MFSFETs.

OXYGEN DIFFUSION IN TANTALUM OXIDE METAL-OXIDE-METAL CAPACITOR STRUCTURES. J.P. Chang , M.L. Steigerwald, R.M. Fleming, R.L. Opila and G.B. Alers, Bell Laboratories Lucent Technologies, Murray Hill, NJ.

High dielectric constant materials such as amorphous tantalum pentoxide (Ta2O5) have been widely studied because of their application in dynamic random access memory and capacitors. The major advantages of Ta2O5 are its high dielectric constant ($\epsilon$ 25) and its low deposition temperature (<500$^{\circ}$C). These advantages make Ta2O5 a good candidate for metal-oxide-metal (MOM) capacitors because it is also compatible with the current metallization scheme and can be easily integrated with the existing processes. However, it is crucial that these Ta2O5-based MOM capacitors with a layered stack of metal/barrier/Ta2O5/barrier/metal can withstand subsequent processing at higher temperatures. In this work, we explored the thermal stability of these MOM structures. The structures studied were generally a Ta2O5/barrier/metal multilayer (half of the MOM structure) where the diffusion barrier was TiN, TaN, or WN and the metal was Al, Ti, Ta, W, Pt, or doped Si. All the films used in this work were sputter deposited. The interfacial composition and reaction of tantalum pentoxide with the underlying barrier materials were monitored by X-ray photoelectron spectroscopy (XPS) in situ at elevated temperatures. We found that Ti and Al were able to reduce the Ta2O5 to Ta and form oxides of Ti and Al at 600$^{\circ}$C, through an oxidation/reduction reaction. Oxygen diffused through the TiN barrier and oxidized the titanium metal underneath. There is no detectable oxygen remaining in the diffusion barrier when the titanium layer is present underneath. Thicker diffusion barriers further limit the diffusion of oxygen and therefore postpone the reduction of Ta2O5 to higher temperatures. As judged by the temperatures at which the reduction of Ta2O5 occurs, TaN and WN are more effective oxygen-diffusion barriers than TiN. We observe no reduction of Ta2O5 when Pt, W, or Si was used as the bottom electrode. The mechanism of oxygen diffusion through the barriers will be discussed.

PULSED LASER DEPOSITION OF SUPERCONDUCTOR/ FERROMAGNETIC YBa2Cu3Oy/SrTiO3/La2/3Sr1/3MnO3 HETEROSTRUCTURES. Vítvézslav Trtík , Florencio Sánchez, César Ferrater, Manuel Varela, Universitat de Barcelona, Departament de Física Aplicada i Óptica, Barcelona, SPAIN; Manuel Bibes, Benjamín Martínez, Lourdes Fábrega, Josep Fontcuberta, Instituto de Ciencia de Materiales de Barcelona - CSIC, Bellaterra, SPAIN.

YBa2Cu3Oy/SrTiO3/La2/3Sr1/3MnO3 heterostructures have been deposited on LaAlO3(001) substrates by pulsed laser deposition. The influence of deposition conditions and the effect of post annealing on the properties have been studied. Different characterization techniques have been used to determine and correlate heterostructures properties. A complete analysis of the crystal structure and strain have been carried out with a four circle difractometer. Morphology of each three layers has been individually studied by scanning electron microscopy and atomic force microscopy in order to determine surface roughness and droplet density. Finally, the spin-polarized charge transport properties have been measured.

DRY ETCHING TO FORM SUBMICRON FEATURES IN CMR OXIDES: PrBaCaMnOX AND LaSrMnOX. K.P. Lee , K.B. Jung, H. Cho, D. Kumar, S.V. Pietambaram, R.K. Singh, Y.B. Hahn and S.J. Pearton, Dept. of Materials Science and Engineering, University of Florida, FL; P.H. Hogan, K.H. Dahmen, Center for Materials Research and Technology, MARTECH, Florida State University, FL.

To fabricate spin-valve read heads or MRAM elements based on the CMR oxides, it is necessary to develop dry etch processes for high fidelity pattern transfer. The high bond strengths of these materials make conventional reactive ion etching difficult, but High Density Plasma (HDP) systems offer much higher ion fluxes and separate control of ion density and energy. Effective pattern transfer into PrBaCaMnO3 and LaSrMnO3 has been achieved using Cl2/Ar discharges operated under Inductively Coupled Plasma conditions. Etch rates up to 900${\AA}$$\cdot$min-1 for LaSrMnO3 and 300${\AA}$$\cdot$min-1 for PrBaCaMnO3 were obtained, with these rates being a strong function of ion flux, ion energy and ion-to-neutral ratio. The etching is still physically-dominated under all conditions, leading to significant surface smoothing on initially rough samples. Sub-micron (0.35$\mu$m) features have been produced in both materials using SiNx as the mask.

BARIUM TITANATE CERAMIC/CERAMIC 0-3 COMPOSITES FOR ULTRASONIC TRANSDUCER APPLICATION. M.C. Cheung , H.L.W. Chan, Q.F. Zhou and C.L. Choy, Dept of Applied Physics and Materials Research Centre, The Hong Kong Polytechnic Univ, Hunghom, HONG KONG, CHINA.

Barium titanate (BaTiO3) ceramic/ceramic 0-3 composite thick films ($\sim$10 $\mu$m) for ultrasonic transducer applications were fabricated by a modified sol-gel process. Nano-sized BaTiO3 powder was dispersed in a sol-gel matrix of BaTiO3 to form a 0-3 composite solution. Films were prepared by spin casting and then annealed at various temperatures. The crystallization of the composite film was studied by X-ray diffraction. The dielectric permittivity and the ferroelectric properties of the film were also measured.

OF HYDROGEN DEGRADATION IN Pt/SrBi2(Ta1 xNbx)2O9/Pt CAPACITOR. Akira Furuya , NEC Corporation, Silicon Systems Research Laboratories, Tokyo, JAPAN; J.D. Cuchiaro, Symetrix Corporation, Colorado Springs, CO.

Recently, SrBi2(Ta1-xNbx)2O9 (SBTN) thin films are under evaluation for IC memory applications, since it has been reported to have higher fatigue endurance than any other ferroelectric material such as the lead zirconate titanate (PZT). One of the most important issues for integrating ferroelectric materials into IC memory applications is the degradation of the capacitor ferroelectric properties from reaction with hydrogen. Hydrogen annealing for terminating dangling bonds in silicon or elevated temperature processes which dissociate hydrogen are expected to degrade the electrical properties of the ferroelectric oxide by reduction. Therefore, in this work, we have investigated reducing degradation in Pt/SBTN/Pt capacitors due to hydrogen effects by evaluating the compositional dependence of the Ta/Nb ratio and incorporating TiN as a hydrogen diffusion barrier. To investigate the compositional dependence, the Pt/SBTN/Pt capacitors with the desired composition were fabricated from enhanced metal organic deposition solutions that were spin deposited and delineated with a conventional patterning technique. After annealing the samples in H2 (1$\%$)-N2 ambient at 400 $^{\circ}$C for 10-60 min, hysteresis and current-voltage measurements were conducted to evaluate the degradation. It was observed that the best electrical characteristics were obtained from the capacitor with the Ta/Nb ratio of 1.5/0.5 in this experimental condition. Therefore, the Pt/SBTN/Pt capacitor with the Ta/Nb ratio of 1.5/0.5 was used for the evaluation of TiN barrier effect. After depositing a TiN film on the Pt/SBTN/Pt capacitors, the samples were annealed in H2 (5 $\%$)-N2 at 400 $^{\circ}$C for 10-60 min. Following removal by NH4OH : H2O2 : H2O = 1 : 3 : 1 at 60-70 $^{\circ}$C, hysteresis and current-voltage characteristics of the capacitors were measured. It was found that the degradation was extremely reduced by incorporating a TiN barrier. Moreover, it was revealed that degradation effects decreased with increased density of the deposited TiN film. TiN densities greater than 3.8 g/cm3 in these experiments, kept the degradation in the leakage current to less than 10-6 A/cm2 and the degradation in the remanent polarization less than 20%$.{\newline\newline\noindent{\textbf{ BB7.17 }}\newline\noindent{DETAILED C-V ... ...oindent{\textbf{ BB7.17 }}\newline\noindent{DETAILED C-V ANALYSIS FOR YMnO_{3}$/Y2O3/Si STRUCTURE. Takeshi Yoshimura , Norifumi Fujimura, Daisuke Ito, Taichiro Ito, Dept of Applied Materials Science, Coll of Engineering, Osaka Pref Univi, Osaka, JAPAN.

Metal-ferroelectric-(insulator-)semiconductor field effect transistor (MF(I)SFET)-type ferroelectric random access memories (Ferroelectric RAMs) have attracted much attention due to the advantages of saving electrical power and decreasing memory cell size. RMnO3 (R: Rare earth elements) which we have proposed has low permittivity and does not include volatile elements, it is expected to have several advantages over PZT and SBT for the application to MF(I)SFET. We have reported that c-oriented YMnO3 films are obtained on (111)Si substrates and they show P-E hysteresis and ferroelectric polarization switching type C-V characteristics. However, the memory window of this C-V characteristic are obtained only when bias sweep rate is more than 0.8V/s due to the poor memory retention property.[1] The use of Y2O3 buffer layer improved the crystallinity of YMnO3 films and its electrical properties.[2] Although the memory window of C-V characteristic is obtained at the bias sweep rate below 0.1V/s, the memory retention property was still poor. Detailed electrical analyses and the theoretical study are needed to understand the polarization properties of MFIS structure. Then, detailed C-V measurements and the theoretical analyses were carried out to understand the electrical potential at several interfaces and the polarization state of each layer. A peculiarity of C-V analysis for MFIS structure is discussed and the device structure of YMnO3/Y2O3/Si will be optimized. [1]T. Yoshimura et al, Appl. Phys. Lett., 73, 414-416 (1998) [2]T. Yoshimura et al, Jpn. J. Appl. Phys., 36, 5921-5924 (1997)

CHEMICAL AND MECHANICAL PROPERTIES OF HARD OXIDE COATINGS FOR MEMS. Joseph J. Talghader and Wei Liu, University of Minnesota, Department of Electrical and Computer Engineering, Minneapolis, MN.

Many optical and electronic devices in microelectromechanical systems (MEMS) will require multilayer coatings to control the spectral, phase, and polarization content of light. Such materials for MEMS must be able to withstand high temperatures and undergo photolithographic, wet, and dry chemical processing. In addition, their mechanical and stress properties are critical since they may be deposited on thin polysilicon mirrors or other actuated structures. One class of materials that are robust for coating bulk components are multilayers of hard oxides such as Ta2O5, TiO2, Nb2O5, HfO2, and ZrO2. We have undertaken a study of the chemical and mechanical properties of reactive-sputtered and e-beam evaporated thin films of these materials. The wet and dry etching data show nonuniform etch rates for both e-beam evaporated and commercial reactive sputtered thin-films, indicative of substantial composition changes throughout the film. For example, TiO2 and ZrO2 have wet etch rates which can vary by more than an order of magnitude from the top to the bottom of a layer. The dry etching data for fluorine plasmas shows a similar but less extreme trend. The materials also show good resistance to buffered etches designed for SiO2, offering the possibility that some of them, such as Ta2O5, might be used without passivation during sacrificial etch processes. The magnitude of the stress in the oxide films varies from 16MPa for reactive sputtered ZrO2 to 150MPa for e-beam evaporated TiO2. Bulk modulus measurements for each of these films is also shown. Our data shows that compensated stress coatings can be made for interferometrically flat optical and electronic MEMS devices.

ELECTRICAL NOISE IN ULTRA THIN GIANT MAGNETORESISTORS. Alvydas Lisauskas, S.I. Khartsev, Alex Grishin , Department of Condensed Matter Physics, Royal Institute of Technology, Stockholm, SWEDEN; Vilius Palenskis, Department of Radiophysics, Vilnius University, Vilnius, LITHUANIA.

The colossal magnetoresistance (CMR) effect and large temperature coefficient of resistance (TCR) in rare-earth manganese oxides have triggered great interest because of the potential applications for magnetoresistive read heads and bolometric detectors. Since a metal-insulator (ferromagnetic-paramagnetic) phase transition is responsible for CMR and TCR effects electrical fluctuations become a critical issue which could limit sensor performance. We report on 1/f electrical noise study in the series of epitaxial La0.75Sr0.25MnO3 manganite films (over the range d = 3.2 to 200 nm) fabricated by KrF pulsed laser deposition onto the single crystal SrTiO3 substrates. Hooge's relation for conductance fluctuations have been evaluated in a wide range of transport current I, frequencies and temperatures T. The deviations from Hooge's law increase with a transport current increase and have been found to follow universal I and T behavior. Independent Hall measurements have been employed to deduce the Hooge parameter gamma. The role of built-in strain and oxygen deficiency in ultra thin magnetoresistors on the noise magnitude will be discussed.

THIN FILM DIELECTRICS FOR ELECTRONICS USING COMBUSTION CHEMICAL VAPOR DEPOSITION. Wen-yi Lin , Hai Huang, D. Kacy Cullen, Shara S. Shoup, Donald Cousins, Jerome J. Schmitt and Andrew T. Hunt, MicroCoating Technologies, Chamblee, GA; Robert R. Romanofsky, Fred W. VanKeuls and Carl H. Mueller, Lewis Research Center, NASA, Cleveland, OH.

The Combustion Chemical Vapor Deposition (CCVD) was used to prepare multicomponent dielectric thin films. Barium strontium titanate and strontium titanate thin films were deposited on single crystal substrates. Gold electrodes were patterned to form interdigitated structures for electrically tunable devices, namely, coupled microstripline phase shifters (CMPS). The undoped, as-deposited perovskites were evaluated in transmission mode, utilizing an HP Network Analyzer. Figure of merit of 53$^{\circ}$/dB was obtained from 48$^{\circ}$ phase shift and less than 1 dB magnitude of the transmission coefficient at 20 GHz and 23$^{\circ}$C. Intended for non-volatile ferroelectric memory, lead zirconium titanates were deposited with a seed layer of perovskite structure to prevent the growth of the unwanted pyrochlore phase. A- and B-site dopants for charge compensation were also used to foster the formation of PZT. Strontium bismuth tantalate was also investigated for NVFRAM applications. High-permittivity, polycrystalline ferroelectrics ($\epsilon$=263) were coated for passive devices and potentially for dynamic random access memory. Epitaxial coatings of ceria, yttria-stabilized zirconia, and strontium titanate were deposited onto oxide single crystal substrates for use as potential buffer layers in high temperature superconductor applications. These and other buffer layers will be deposited onto textured metal substrates for practical use in superconducting wire. Preferentially oriented ceria as an intermediate layer between silicon wafer and Pt were also deposited to function as a diffusion barrier. Characterization results from SEM, EDS, XRD, pole figure and electronic analyses will be presented. The capability and potential of the CCVD process for low-cost production is reviewed.

OPTIMIZATION OF MICROWAVE PROPERTIES OF Nd0.67Sr0.33MnO3-y LAYERS FOR MAGNETICALLY TUNABLE MICROWAVE SUPERCONDUCTING FILTERS. Jaroslaw Wosik , Mikhail Strikovski, Lei-Ming Xie, V.V. Srinivasu, John H. Miller, Jr., Texas Center for Superconductivity, University of Houston, Houston, TX; Piotr Przyslupski, Institute of Physiscs, Polish Academy of Sciences, POLAND.

We report on magnetic tunability of superconducting microwave filters controlled by magnetic field-dependent permeability mu(H) of Nd0.67Sr0.33MnO3-y (NSMO) thin films. We grew NSMO single layers and NSMO/YBCO bilayers on (100) oriented LaAlO3 (LAO) substrates using both high-pressure dc sputtering and laser ablation methods. Several films with different Curie temperatures Tf, saturation magnetization 4$\pi$M, and coercitivity fields ranging from 220 K to 60 K, 1000 to 3000 G and 100 to 400 G, respectively, were tested. Both a 13 GHz dielectric cavity resonator and 3 GHz S-shaped microstripline resonator, coupled in a flip chip configuration to the NSMO film, were used to evaluate the tuning parameter K. The correlation between the microwave and magnetic properties of NSMO films will be discussed. Performance of a monolithic device with a YBCO microstrip line patterned on the top layer of the YBCO/NSMO/LAO structure will be also evaluated.

EFFECT OF FORMING GAS ANNEALING ON SrBi2Ta2O9 (SBT) BASED CAPACITORS WITH Ir TOP ELECTRODES. Sridhar Tirumala , Kwang B. Lee and Seshu B. Desu, Materials Science and Engineering Department, Virginia Tech, Blacksburg, VA.

An attempt is made to reduce the degradation of ferroelectric properties of SBT based capacitors, caused by annealing in forming gas, by using Ir and IrO2 top electrodes. A metal organic solution deposition technique is used to fabricate 0.25mm thick SBT film on platinized silicon wafer. Using SBT/Pt thin films processed at 750$^{\circ}$C in oxygen atmosphere, three types of capacitors were fabricated, namely, Pt/SBT/Pt, Ir/SBT/Pt, IrO2/Ir/SBT/Pt. All the three capacitor structures were annealed in forming gas at temperatures ranging from 25$^{\circ}$C to 400$^{\circ}$C. The remnant polarization of Pt/SBT/Pt capacitor was found to decrease by 65% after annealing in forming gas at 400$^{\circ}$C. For the same annealing temperature, loss of polarization of Ir/SBT/Pt was observed to be 8%, while that of IrO2/Ir/SBT/Pt was as low as 3%. Reduced catalytic activity of Ir as compared to that of Pt, in converting hydrogen molecules to hydrogen atoms, could be a reason for the reduced degradation of SBT capacitors during forming gas annealing.

REDUCTION OF DIFFUSION OF O THROUGH POLYCRYSTALLINE PT BY BE DOPING. Roland Stumpf , Motorola, Predictive Engineering Lab, Clarence Tracy, Motorola, MRST.

A serious problem preventing the use of new high dielectric oxide materials (e.g. Barium-Strontium-Titanate=BST) for capacitors as part of future DRAM is the oxidation of or the O diffusion through the electrodes. Pt electrodes do not oxidize but they allow for rapid O diffusion through the Pt film while the dielectric is deposited and annealed. This causes unwanted oxidation below the Pt film. Using first principles electronic structure calculations we first determine the O diffusion mechanism in polycrystalline Pt. We find that O diffuses as interstitial O along grain boundaries (GB) with a barrier of about 0.7 eV in agreement with experiment. To propose measures to reduce the O diffusion we screen ten elements for their potential to retard O diffusion if added to the Pt in small amounts. Among the candidates we find that Be is the most promising since it has a strong tendency to segregate to GB's, it diffuses slower than the O and it retards O diffusion along GB's by two mechanisms. As substitutionally absorbed Be, Be has a high diffusion barrier (about 2 eV) and it forms strong bonds to O. Interstitial Be at the GB repels the O and thus stuffs the GB. Preliminary experimental results confirm our theoretical predictions. General aspects of finding barriers for interdiffusion will be discussed. We acknowledge the use of Sandia National Laboratories computing resources.

Chairs: Vincent J. Fratello and Nathan Newman
Thursday Morning, April 8, 1999
Salon 7 (M)
8:30 AM BB8.1
PREPARATION OF Na0.5K0.5NbO3/La0.75Sr0.25MnO3/SrTiO3

THIN FILM STRUCTURES BY PULSED LASER DEPOSITION. Alex Grishin , S.I. Khartsev and Choong-Rae Cho, Department of Condensed Matter Physics, Royal Institute of Technology, Stockholm, SWEDEN; Ture Lindbck Department of Materials and Manufacturing Engineering, Lulea University of Technology, Lulea, SWEDEN.

The perovskite sodium-potassium niobate (NKN, Na1-xKxNbO3) thin films attract much attention because very low loss tan $\delta$, and strong electric field dependence of rather low dielectric permittivity promise vast variety of applications in a wide operating temperature range. We report on epitaxial Na0.5K0.5NbO3 films grown at first time onto the colossal magnetoresistive La0.75Sr0.25MnO3 (LSMO) template layer on (001) SrTiO3 single crystal by KrF excimer laser ablation of stoichiometric ceramic target. Processing parameters have been optimized to obtain smooth LSMO template layer, avoid NKN-LSMO interdiffusion, preserve NKN stoichiometry against the lost of volatile potassium and sodium and achieve reasonable reliability of NKN film performance. Thickness and roughness of fabricated films have been controlled by AFM and SEM. High degree of c-axis orientation both in template La0.75Sr0.25MnO3 and Na0.5K0.5NbO3 layers as well as strong in-plane texture have been revealed by XRD rocking curves and $\omega$-scan correspondingly. To make vertical capacitive cell gold upper electrodes with the diameter of 0.6 mm have been thermally evaporated on the top of Na0.5K0.5NbO3 layer. Measured resistivity of Na0.5K0.5NbO3 layer was in the range of 109$\Omega$-cm. Temperature dependencies of dielectric constant and loss tan $\delta$, of Au/Na0.5K0.5NbO3(470 nm)/La0.75Sr0.25MnO3(500 nm) capacitor structure measured at 1 kHz have no anomalies in the range 77 to 300K while dielectric constant and loss tan $\delta$ have been found to vary from 175 to 280 and 0.015 to 0.036 correspondingly. Films exhibit polarization loops with typical coercive field Ec of 30 kV/cm, spontaneous polarization Pc (150 kV/cm) of 50 mC/m2 and remnant polarization Pr of 30 mC/m2.

8:45 AM BB8.2
MICROSTRUCTURAL OPTIMIZATION OF FERROELECTRIC THIN FILMS FOR Ku-BAND PHASE SHIFTERS. C.H. Mueller , F.W. Van Keuls, F.A. Miranda and R.R. Romanofsky, NASA Lewis Research Center, Cleveland, OH; C.L. Canedy and R. Ramesh, University of Maryland, College Park, MD.

Next-generation low-earth-orbiting satellite communication systems must transmit as well as receive information at much higher data rates than current systems. To achieve high data rate uplinks, low-cost steerable beam phased antennas to track the satellites are highly desirable. Our research focuses on achieving phase and frequency steering by incorporating tunable ferroelectric films into the beam forming networks. The performance of ferroelectric phase shifters is a function of the intrinsic and extrinsic properties of the ferroelectric film, as well as the microwave design. In this paper, we show how film microstructure impacts the tunability and dielectric loss of the films, which in turn impacts the microwave device performance. We have observed that maximum tunability occurs when the ferroelectric films are highly oriented, with minimal film strain. High resolution x-ray diffraction data shows that barium strontium titanate and strontium titanate films are epitaxial when deposited on lanthanum aluminate substrates, and film strain at the substrate/film interface is completely relaxed. The correlation between film microstructure and insertion loss at microwave frequencies is more complex; higher film quality causes the film dielectric constant to increase, which decreases the characteristic impedance and lowers the operating frequency of these phase shifters. Experimental and modeling data showing the correlation between phase shift, insertion loss, and film microstructure will be presented.

9:00 AM BB8.3
HIGH-CONTRAST, LOW-LOSS SiON OPTICAL WAVEGUIDES BY PECVD. H.W.M. Salemink , B.J. Offrein, G.L. Bona, R. Germann, F. Horst, IBM Zurich Research Laboratory, Rueschlikon, SWITZERLAND.

We report on the fabrication of low-loss, high-contrast silicon oxynitride (SiON) optical waveguides, embedded in SiO2 cladding layers and deposited on silicon substrates. The SiON (optically guiding) core layers are deposited by PECVD using SiH4, NH3 and N2O precursors. The relatively high index of this core material (n=1.510) is made by the nitrogen content of approximately 7 atomic % as confirmed by Rutherford backscattering and depth profiling Auger techniques. As a consequence of the hydrogen-containing precursors and the low deposition temperature in the PECVD process, the SiON films are hydrogen enriched and contain N-H chemical bonds. The overtone of the IR absorption band at 3350 cm-1 from this N-H bond leads to unacceptably high propagation losses at the foreseen operating wavelength of the optical devices at 1550$\pm$10 nm. A high-temperature anneal process at 1413 K in a N2 atmosphere largely eliminates the N-H related losses and leads to a propagation loss of 0.15$\pm$0.05 db/cm in planar SiON films. The oxynitride waveguide sandwich consists of three oxidic layers (SiO2/SiON/SiO2) on a silicon substrate and exhibits a polarization-dependent optical propagation (birefringence) due to the incorporated stress as a consequence of the mismatch in the thermal coefficients and the tempering treatment. This birefringence is minimized to an acceptable value of <4$\times$10-4 by a careful optimization of deposition and annealing process steps. The high index contrast of SiON vs. SiO2 allows the manufacture of optical integrated circuits with a much smaller bending radius (1-2 mm) than usual in low-contrast SiO2 technology. Thus, a higher integration or circuit density can be explored, for example in more complex, multistage devices. Results on film material and on devices are presented.

9:15 AM *BB8.4
THIN FILM PYROELECTRIC FOR UNCOOLED INFRARED IMAGING. H.R. Beratan , K.R. Udayakumar, C.M. Hanson, J.F. Belcher, K. Soch, Raytheon Systems Company, Dallas, TX.

Next-generation ferroelectric uncooled IR detector technology is beginning to emerge at Raytheon. After four years of development, arrays of micro-machined thin-film ferroelectric (TFFE) detectors have been produced, tested, and inserted into production systems for imaging demonstrations. System design allows for room temperature operation while sensing radiation in the 8 to 14 micron waveband. Present generation uncooled infrared detector arrays are comprised of 20 micron thick ceramic barium strontium titanate (BST) pixels on 48.5 micron centers and operate in the dielectric bolometer mode. Detector sensitivity is limited by thermal isolation and time constant, while image acuity is controlled by device architecture. No path to reduce pixel thickness, or to increase array density is obvious. Thin-film micromachined pixels operating in the pyroelectric mode offer the potential of improved sensitivity with better image acuity. Material properties have been measured that project to a noise equivalent temperature differential (NETD) of about 10 mK. A description of array architecture, processing, and relevant material properties will be discussed.

10:00 AM BB8.5

CrO2 is theoretically predicted to be a half-metallic ferromagnet (1, 2) and to exhibit double exchange (3) analogous to the CMR manganites. The ambivalent experimental situation about this material is that a high spin polarization of 95% has been found in spin polarized photoemission only at 2eV below the Fermi energy EF (4) without indication of a Fermi edge, whereas a small but finite density of states at EF has been observed recently in photoemission (5). We have deposited epitaxial CrO2 films on Al2O3(0001) substrates by oxide-MBE, CVD and sputtering techniques. The thin films were characterized by x-ray diffraction, STM and SQUID magnetometry. The metallic films have an a-axis orientation and an in plane magnetization. The surface roughness is about 15Å for a substrate temperature of 100$^{\circ}$C. First tunneling measurements indicate a spin polarisation $\sim$ 50% at EF. Magnetotransport properties for 4K$\le$T$\le$400K will be discussed in comparison with CMR-manganites.
(1) K.H. Schwarz, J. Phys. F: Met. Phys. 16 , L211 (1986)
(2) H. van Leuken and R.A. de Groot, PRB 51 , 7176 (1995)
(3) M.A. Korotin, PRL 80 , 4305 (1998)
(4) K.P. K{amper et al., PRL 59 , 2788 (1987)
(5) T. Tsujioka et al., PRB 56 , R15509 (1997)

10:15 AM *BB8.6
FACTORS CONTROLLING TRANSPORT PROPERTIES OF INTERFACES IN HIGH-Tc SUPERCONDUCTORS. H. Hilgenkamp , R. Schulz, C.W. Schneider, B. Getz, A. Schmehl, H. Bielefeldt and J. Mannhart, Exp. Phys. VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, Augsburg, GERMANY.

The electronic transport properties of interfaces in high-Tc superconductors are of central importance for numerous applications of these materials, varying from electronic devices to large-current carrying cables and tapes. Also in many fundamental studies on high-Tc cuprates interfaces play a crucial role. Understanding and control of the transport properties of such interfaces, e.g. grain boundaries and superconductor-normal metal contacts, is therefore of great relevance. An understanding of the transport properties of interfaces in high-Tc cuprates has been obtained by considering their microstructure, the possibility of bending of the electronic band structure in these materials, and the predominant dx2-y2-symmetry of the order parameter in most high-Tc cuprates [1]. These factors control e.g. the critical current density and the normal state resistivity of grain boundaries and their dependencies on boundary-misorientation and on applied magnetic and electrical fields. In addition, these factors also control transport properties of other interfaces involving high-Tc superconductors, such as those of superconducting - normal metal contacts. [1]: H. Hilgenkamp and J. Mannhart, Appl. Phys. Lett. 73(2), 265 (1998).

10:45 AM *BB8.7
SPIN-DEPENDENT TRANSPORT IN MANGANITE TRILAYER JUNCTIONS. Jonathan Z. Sun , IBM T. J. Watson Research Center, Yorktown Heights, NY.

Ferromagnetic manganites provide a model system for the study of spin-polarized transport in half-metals. Epitaxial manganite thin films are used to fabricate trilayer junctions, which reveal several new phenomena, including (1) A large, low-field magnetoresistance; (2) Two energy scales, an order of magnitude apart, for the bias- and temperature-dependence of junction conductance and magnetoresistance; and (3) a spin-current induced switching of the junction magnetic state. These transport behavior can be related to the interface materials sciences of the trilayer junction. For example, the temperature for suppression of junction MR is low compared to the Curie temperature of the electrodes, which is around 360K for La0.67Sr0.33MnO3. This is related to a surface layer with decreased magnetic order. The materials origin for this surface disorder is yet to be understood. The presence of magnetic nanoparticles related to laser ablation leads to the observation in some junctions of a spin-current induced switching of junction magnetic state. I will address these novel physics issues with an emphasis on their relationship to the specific materials properties of the manganites.

11:15 AM *BB8.8
WAFER BONDING INVOLVING COMPLEX OXIDES. Ulrich Goesele , Marin Alexe, Pascal Kopperschmidt, Max Planck Institute of Microstructure Physics, Halle, GERMANY; Qin-Yi Tong, Li-Juan Huang, School of Engineering, Duke University, Durham, NC.

After an introduction to the general concept of wafer bonding, various approaches involving wafer bonding and complex oxides will be discussed, including back-to-back bonding of wafers with a high quality epitaxial thin film on one side for creating substrates with high quality films on both sides and the transfer of ferroelectric oxide layers from one substrate to another by chemo-mechanical polishing and a low temperature wafer bonding approach. The possibility of fabricating single crystalline oxide layers on a convenient substrate (which might be amorphous, polycrystalline or non-lattice-matched single crystalline) by wafer bonding combined with hydrogen implantation induced layer splitting (`smart-cut' or `smarter-cut') from bulk single crystalline oxide wafers will be discussed and first results for lathanum aluminate and lithium niobate will be presented. These single crystalline oxide layers may be used as substrates for the epitaxial growth of lattice-matched oxide layers.

Chairs: Doreen D. Edwards and Ichiro Takeuchi
Thursday Afternoon, April 8, 1999
Salon 7 (M)
1:30 PM BB9.1
ATOMISTIC MODELING OF THIN FERROELECTRIC OXIDE FILMS. D. Fuks , Mat. Eng. Dept, Ben Gurion Univ., Berr Sheva, ISRAEL; S. Dorfman, Phys. Dept., Technion, Haifa, ISRAEL; E.A. Kotomin, Fachbereich Physik, Univ. Osnabruck, Osnabruck, GERMANY and Inst for Solid State Physics, Riga, LATIVA.

A study of the structure and properties of ferroelectric thin films is important for their numerous applications. We present results of first atomistic, shell-model simulations for three ABO3 oxides: SrTiO3, BaTiO3 and KNbO3, with emphasis on relaxation of their (100), (110), and (111) surfaces. Calculated atomic displacements are compared with the LEED experiments available for the SrTiO3, and ab initio calculations for BaTiO3. We demonstrate that considerable atomic relaxation, which affects six near-surface crystalline planes, leads to the surface polarization even in the cubic phase. This means that perovskite surfaces could serve as important factor imposing a long-order in paraelectric crystals and thus reveal properties quite different from the bulk material.
E. Heifets, S. Dorfman, D. Fuks, E. Kotomin, A. Gordon, J. Phys.: Cond. Matt., 10, L347 (1998); S. Dorfman, D. Fuks, E. Kotomin, Thin Solid Films, 318, 65 (1998).

1:45 PM BB9.2
IN-SITU GROWTH MONITORING USING RHEED FOR FABRICATION OF PLANAR REBa2Cu3O7$\delta$ JUNCTIONS. Guus Rijnders , Gertjan Koster, Horst Rogalla and Dave H.A. Blank, University of Twente, Applied Physics, Low Temperature Division, NETHERLANDS.

One of the key-goals in High Temperature Superconducting [HTS] electronics is the development of SIS or SNS junctions. Due to the anisotropy in the coherence length in cuprates, i.e., 10-20 Å in the ab direction and only a few Å in the c-axis direction, a lot of groups have directed their research towards the development of junctions in the ab plane. Different kinds of junctions have been realised by several groups, including grain boundary, ramp-type, step edge and a-axis sandwich-type junctions. The use of these junctions in integrated circuits, e.g., fast electronics and sensors, is hampered with respect to reproducibility and layout-problems. The planar geometry of the c-axis junctions combines the in-situ deposition of, both, electrodes and barrier with the relative easy integration in electronics. To avoid mixing of properties in the anisotropic materials, the roughness of the interfaces should be small compared to the barrier thickness. Moreover, the superconducting properties are easily degraded at the interfaces, which influences the junction properties dramatically due to the short coherence length in the c-axis direction. In this study we have used Pulsed Laser Deposition (PLD) for the deposition of the REBa2Cu3O$_{7-\delta}$ electrodes as well as barrier. To enhance layer-by-layer growth, to our opinion a vital part in obtaining planar junctions, we applied a new deposition technique. This technique is based on an extra modulation of the growth rate. Here, we present the improvement of layer by layer growth using this new interval deposition approach and the influence on the surface morphology of both the REBa2Cu3O$_{7-\delta}$ electrodes and barrier material, using high-pressure RHEED and scanning probe microscopy, respectively.

2:00 PM *BB9.3

The increasing interest in scanning probe instruments (SPM) stems from the outstanding possibilities in measuring electric, magnetic, optical and structural properties of surfaces and surface layers down to the molecular and atomic scale. For the inspection of ferroelectric materials, both the scanning force microscopy (SFM) and the scanning near-field optical microscopy (SNOM) are promising techniques revealing information on the polarization vector and the electric field induced stress within a crystal. Polarization sensitive modes are discussed as is friction force microscopy, dynamic force microscopy (DFM) and voltage modulated SFM. From these measurements, 180$^{\circ}$ domain walls (c-domains) are resolved down to 4 nm, while 3-dimensional polarization mapping in ferroelectric ceramics reveals a 30 nm resolution. In addition, non-contact DFM measurements in ultra-high vacuum are able to resolve ferroelectric surfaces down to the atomic scale. Also chemical heterogeneity at the sample surface is differentiated from ferroelectric domains down to a 5 nm lateral resolution, taking advantage of the short ranged chemical forces. SNOM in contrast, probes the optical properties of ferroelectric crystals both in transmission and reflection. Here image contrast arises from changes in the refractive index between different domains as well as at domain walls. In addition, SPM instruments are used for the local modification of ferroic samples by applying a relatively high voltage to the SPM tip. Domains with lateral dimension down to 30 nm are thus created with the size strictly depending on both the switching and material parameters. With SFM we are able to record nanoscale hysteresis loops while performing switching experiments. These measurements monitor both the successful domain reversal and the coercive field needed for domain nucleation at the sample surface. Also various applications of nanoscale ferroelectric domain switching are discussed including optics and fast ultra-high density data storage devices.

3:00 PM BB9.4
TEMPERATURE AND OXYGEN PRESSURE DEPENDENCE OF THIN FILM EPITAXY OF SrTiO3 AND LBMO ON SrTiO3(001) STUDIED BY AN OBLIQUE-INCIDENCE OPTICAL REFLECTANCE DIFFERENCE TECHNIQUE. Xiangdong Zhu , University of California at Davis, Dept. of Physics, Davis, CA; Weidong Si, Xiao Xing Xi, Qi Li, Penn-State University, Dept. of Physics, University Park, PA.

Using an oblique-incidence optical reflectance technique, we studied the kinetics of the homoepitaxy of SrTiO3 (STO) and heteroepitaxy of LBMO on SrTiO3(001) as functions of temperature (275 - 850 C) and oxygen pressure (0.0003 - 0.62 torr). We found that the homoepitaxy of STO and the heteroepitaxy of LBMO are rate-limited by the oxidation of the as-deposited film, rather than by regrowth (e.g., surface diffusion of monomers). From the rate constants deduced from the measurement, we are able to determine a kinetics-limited phase-diagram for STO homoepitaxy.

3:15 PM BB9.5
LOCAL ATOMIC STRUCTURE IN FIBER-TEXTURED (BaxSr1-x)Ti1+yO3+z THIN FILMS ON Pt/SiO2/Si. C.E. Bouldin , B. Ravel, D.L. Kaiser, National Institute of Standards and Technology, Gaithersburg, MD; S.K. Streiffer, Materials Science Division, Argonne National Laboratory, Argonne, IL; Angus I. Kingon, Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC.

Polycrystalline (BaxSr1-x)Ti1+yO3+z (BST) films are candidates for use as advanced integrated dielectrics in a variety of semiconductor devices. However, a fundamental understanding of factors limiting attainable permittivities in such films has not been developed. Here we report on the local atomic structure in (100) fiber-textured BST (x=0.7) thin films deposited by liquid-delivery metal organic chemical vapor deposition on Pt/SiO2/Si, as a function of Ti composition y. Using polarized x-ray absorption near-edge structure measurements, variations in the Ti local environment are observed as a function of both Ti content and in-plane versus out-of-plane electric field polarization. These atomic-scale structural changes suggest a mechanism that accounts for the Ti composition dependence of the nonlinear dielectric behavior of the films, particularly with regard to the well-known increase in dielectric stiffness with increased excess Ti.

3:30 PM *BB9.6
EPITAXIAL AND ORIENTED Pb(Mg1/3Nb2/3)O3-PbTiO3 FILMS. S. Trolier-McKinstry , J.P. Maria and J.H. Park, Materials Research Laboratory, The Pennsylvania State University, University Park, PA.

[001] Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals on the rhombohedral side of the morphotropic phase boundary have recently been shown to demonstrate extremely high levels of piezoelectric strain. In addition, these single crystals offer significantly higher coupling coefficients and piezoelectric properties than are available in lead zirconate titanate (PZT). Of particular interest from the standpoint of thin film actuators is the low hysteresis in the electrically-induced strain even for strain levels up to 0.6%. This implies that long-range motion of non-180$^{\circ}$ walls is not essential for the observed piezoelectric properties. This is important because the extent of non-180$^{\circ}$ domain wall contributions to the properties appears to be limited in most PZT films. Consequently, in this work, epitaxial and oriented thin films of PMN-PT have been examined for piezoelectric applications. Epitaxial PMN-PT 70/30 doped with 2% Ba were deposited on SrRuO3-coated (001) LaAlO3 substrates by pulsed laser deposition. Two growth regimes were identified. For adsorption controlled growth from Pb-rich targets, the best electrical properties were obtained for deposition at temperatures above 670$^{\circ}$C. Optimized samples exhibited bulk transition temperatures, room temperature dielectric constants greater than 1500, and remanent polarizations of 20 $\mu$C/cm2. Deposition of epitaxial films was also possible from targets containing small quantities of excess PbO (e.g., 3%) at temperatures below 600$^{\circ}$C, due to epitaxial stabilization of the perovskite phase. For samples deposited at these temperatures, energetic bombardment was required to optimize the structural and electrical properties. The PMN-PT films showed piezoelectric d33 coefficients of $\sim$350 pC/N, and d31 of $\sim$ -180 pC/N. A strong polarization bias was identified in many of the films and correlated with bombardment of the film during growth. The properties of these epitaxial films will be compared with oriented films grown by a sol-gel process.

4:00 PM *BB9.7
ENHANCEMENT IN ELECTRICAL PROPERTIES OF BST FILMS USING TAILORED OXIDE ELECTRODES. Jae-Bok Lee, Kyung-Woong Park, Jeong-Hee Park, Duck-Kyun Choi , Hanyang University, Dept. of Inorganic Materials Engineering, Seoul, KOREA.

Selection of a proper electrode for the high dielectric material such as (Ba, Sr)TiO3 is a great concern because the deposition of BST requires high temperature and oxidizing atmosphere. In this study, we suggested the perovskite-type electrodes, which provide the structural match with the BST dielectric material, under the recognition that high leakage current could be associated with the structural mismatch between the BST and the electrode. We studied (Ca, Sr)RuO3 electrode of which the lattice parameter can be tuned to fit into BST by changing the Ca/Sr ratio. We also studied (Ba, Sr)TiO3 electrode which is not only structurally identical but also chemically similar to the BST. In addition, doping effects in the BSR electrode were investigated to minimize the leakage current by the proper modulation of the barrier height. The electrodes were directly deposited on Si substrate and all the films in the experiments were deposited by RF magnetron sputtering technique. Electrical properties were measured from MIM structure. We will address the effect of Ca/Sr and Ba/Sr ratio variations in the electrodes on the dielectric constant and the leakage current. Especially, the interface characteristics between the electrodes and the BST film will be discussed in relation to the electrical properties of BST films.

4:30 PM *BB9.8
OXIDE THIN FILMS FOR CHEMICAL SENSORS: PROCESSING-STRUCTURE-PROPERTY RELATIONSHIPS. Xiaoqing Pan , and Li Fu, Dept. of Materials Science and Engineering, The University of Michigan, Ann Arbor, MI.

SnO2 with the rutile type structure is a wide band gap n-type semiconductor. Owing to its high sensitivity to small concentrations of chemical gases (at ppm levels) as well as high chemical and mechanical stability, SnO2 is widely used as a base material in chemical gas sensors. In particular, SnO2 thin films have recently drawn much interest because of their potential application in microsensor devices. In this paper we present our recent studies on thin oxide films deposited on different substrates including SiO2/Si-(100) and sapphire (various cuts) substrates by electron beam evaporation under controlled deposition conditions. Films deposited below 300$^{\circ}$C are amorphous, while those deposited at temperatures above 350$^{\circ}$C are textured, polycrystalline films with the ($\alpha$-SnO structure. Epitaxial, single crystal films with the ($\alpha$-SnO structure were grown on the R-plane of sapphire at >600$^{\circ}$C. SnO2 films with the rutile-type structure were obtained by post-deposition annealing of as-deposited films at >600$^{\circ}$C in air. The thin film microstructure was investigated using x-ray diffraction and cross-section TEM. The surface and interface characterization was conducted using AFM, SEM, and the state-of-the-art HRTEM techniques. The effects of substrate temperatures and post-deposition annealing conditions on the microstructure and electrical properties of the films were studied. By properly choosing the processing conditions and film/substrate lattice match, SnO2 thin films with different microstructures and surface morphologies can be fabricated. These show different electrical properties, in particular different sensing performances in reducing gaseous environments.

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