Julia R. Greer California Institute of Technology
Joost Vlassak Harvard University
Jurgen Daniel Palo Alto Research Center
Ting Tsui University of Waterloo
I1: Flexible Electronics
Monday PM, December 01, 2008
Room 209 (Hynes)
9:30 AM - **I1.1
Enhancement of Organic Thin Film Transistor Performance using Nanocomposite Dielectrics.
Ashok Maliakal 1 Show Abstract
1 , LGS, Florham Park, New Jersey, United States
The performance of organic semiconductor based transistors is critically dependent on the interface between the semiconductor and the gate dielectric. Engineering this interface can have a profound impact on measured mobilities, on/off ratios, threshold voltage, and subthreshold slope. In most organic thin film transistors, the organic semiconductor is deposited on top of the dielectric film, and as such the morphology of the organic semiconductor layer depends on the chemistry and morphology of the underlying dielectric film. We have explored the effect of titanium oxide core-polystyrene shell nanoparticle (TiO2-PS) films and blends of TiO2-PS with titanium oxide homopolymer on the performance of various organic semiconductors in thin film devices. In several cases the presence of TiO2-PS nanoparticles, even in small concentrations results in substantial enhancements in measured mobilities, coupled with reductions in threshold voltage and subthreshhold slope. These enhancements are seen to correlate with morphological changes in the organic semiconductor thin film.
10:00 AM - **I1.2
Stability Measurements on InZnO TFTs Deposited at Room Temperature using High Rate Sputtering.
Bill Milne 1 , A. Flewitt 1 , P. Beecher 1 , C. Ducati 2 , J. Dutson 3 , M. Thwaites 3 , S. Wakeham 3 , S. Speakman 4 Show Abstract
1 Electrical Engineering, Cambridge University, Cambridge United Kingdom, 2 Department of Materials Science, Cambridge University, Cambridge United Kingdom, 3 , Plasma Quest Ltd., Hampshire United Kingdom, 4 , 3T Technologies Ltd. , Essex United Kingdom
10:30 AM - I1.3
High Mobility, Flexibility, and Tunable Conductivities from n and p-channel Polymer-based Transistors in Air.
Jia Sun 1 , Byung Jung 1 , Howard Katz 1 , Rodney Devine 2 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States
We discuss two approaches to increase the mechanical flexibility of organic semiconductors. First, we present the perfluorophenethyl side chain for transparent naphthalenetetracarboxylic diimides as offering mobility up to 0.3 cm2/Vs in air and low hysteresis. Transistors on flexible substrates and using poly(methyl methacrylate) dielectrics can be operated while being rolled and unrolled around objects just a few mm in radius, with negligible change in performance parameters. Morphological effects near bottom contacts are controlled with synergistic surface treatments on both the contacts and the dielectric surfaces, important for patterning and also for radiation testing. Second, we incorporate flexible, insulating polyolefins in blends with known thiophene-based semiconductors. The polyolefins not only confer their mechanical properties to the blends, in many cases they also induce increased mobility by creating well-ordered semiconductor phases, even at very high polyolefin weight fractions. For example, blends of polystyrenes and poly(bisdodecylquaterthiophene, PQT12) show maximum mobility under certain conditions at 70% polystyrene, and significant drops in mobility only occur with >90% polystyrene. Once again, these measurements were made in the open atmosphere. The use of dopants and polymer additives of various architectures to tune polythiophene mobilities and conductivities independently over a wide range will be demonstrated. This tuning is useful for nontransistor applications such as spintronic devices and thermoelectrics, where the optimum values can be quite different from those commonly assumed for transistors.
11:15 AM - I1.4
Relationship Between Strain and Band Structure in Strained-Silicon Nanomembranes.
Feng Chen 1 3 , Chanan Euaruksakul 1 , Ming-Huang Huang 1 , Boy Tanto 1 , Don Savage 1 , Franz Himpsel 1 , Max Lagally 1 , Feng Liu 2 , Bingjun Ding 3 Show Abstract
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , Xi'an Jiaotong University University , Xi'an, Shaanxi, China, 2 , University of Utah, Salt Lake City, Utah, United States
The influence of uniaxial and in-plane biaxial strain on the conduction bands of Si is explored using elastically strained single-crystal Si(001) nanomembranes (SiNMs) and high-resolution x-ray absorption measurements with electron yield detection. Strain alters the band structure and hence the mobility of charge carriers, as well as band offsets in heterostructures. In addition to the biaxial lattice-induced tensile strain in the Si layer of SiNMs, their extreme thinness (~10s of nm) makes them flexible, allowing us to apply strain into the membranes by mechanically bending them (or the host onto which they are transferred). We use UV Raman spectroscopy to determine the amount of strain in each sample and X-ray absorption spectroscopy with the Si2p or 2s-to-conduction band transition to measure energy shifts and the degeneracy splitting of several conduction band valleys. The surface sensitivity of absorption spectroscopy with electron yield detection makes the method suitable for studying very thin strained layers and the top few nm of bent membranes without averaging over the whole layer. The strain-induced splitting of the conduction band minimum and the energy shifts of two higher conduction bands near L1 and L3 are clearly resolved.  Conduction band shifts and 2p core level shifts for uniaxial strain in different directions and biaxial strain in SiNMs are measured and contrasted, and compared to theory where it exists. Supported by DOE, NSF and CSC C. Euaruksakul et al., PRL submitted
11:30 AM - I1.5
Electrical Response of Polycrystalline Silicon Thin Film Transistor on Steel Foil under Mechanical Strain.
Po-Chin Kuo 1 , Abbas Jamshidi-Roudbari 1 , Miltiadis Hatalis 1 Show Abstract
1 Electrical and Computer Engineering, Lehigh University, Bethlehem, Pennsylvania, United States
Poly-Si TFT on steel foil technology has been successfully demonstrated as a platform for high performance flexible electronics because of its high device mobility, stability and compatibility with high temperature CMOS process. This work investigates the effects of mechanical strain on electrical characteristics of poly-Si TFTs. We fabricated poly-Si TFTs of both types on steel foil substrate and strained the TFTs by bending the samples outward and inward to fit the outer and inner surfaces of cylindrical tubes with various radii. The strain ranging from -1.2% to 1.1% was applied parallel to the channel direction. The electron mobility increased under tensile and decreased under compressive strain while those of the hole were reversed. Both the electron and hole mobilities saturated at higher levels of tensile strain but this phenomenon was not observed under compressive strain. For p-channel TFTs the normalized threshold voltage and subthreshold slope increased in tension and decreased in compression; however, these trends were not apparent for n-channel TFTs. For TFTs of both types the off current decreased under tensile but increased under compressive strain. All TFTs remained functional under each level of applied strain showing that this technology is suitable for flexible electronics application.
11:45 AM - I1.6
Highly Density SWNT Networks Assembled on a Flexible Parylene-C Substrate.
Chia-Ling Chen 1 , Xugang Xiong 2 , Huiyan Pan 1 , Ahmed Busnaina 2 , Mehmet Dokmeci 1 Show Abstract
1 ECE, Northeastern University, Boston, Massachusetts, United States, 2 MIE, Northeastern University, Boston, Massachusetts, United States
Single-walled carbon nanotubes (SWNTs) with their attractive properties such as large surface to volume ratio, high packing density and long-range order may serve as potential building blocks for the next generation of devices. The integration of ordered arrays of carbon nanotubes onto rigid as well as flexible substrates offers many opportunities for fabricating novel functional devices of high performance and small size. The transfer of vertically or horizontally aligned carbon nanotube structures often requires multiple steps of site-selective CVD nanotube growth and conformal contact printing or solution casting methods. Here, we present the realization of direct patterning of SWNTs architectures on to flexible Parylene-C substrates by utilizing surface controlled microfluidic assembly technique. The fabrication process starts by depositing a 10µm thick parylene-C on top of a 15mm×15mm Si chip. Next, O2 plasma treatment is utilized to render the surface properties of the as-deposited Parylene-C from hydrophobic to hydrophilic. Contact angle measurements of the O2 plasma treated Parylene-C substrate shows that after the O2 plasma treatment, Parylene-C surface became hydrophilic with contact angle of about 6° and stayed hydrophilic for at least 2 hours. Next, we created photoresist patterns (down to 4um) utilizing photolithography. Due to the hydrophobic nature of the photoresist surface, surface controlled microfluidic assembly technique is utilized to assemble SWNTs inside the patterned hydrophilic trenches. The patterned substrate was then vertically submerged into an aqueous solution containing SWNTs using a dip-coater. After assembly, two-terminal I-V measurements were conducted and the resistance varied from 15KΩ to 21KΩ with a repeatability test of the variation <1%. The highly organized nanotube lateral structures were formed directly on the flexible substrate without utilizing any printing, transfer or chemical functionalization techniques. This lithography based chemical free patterning technology is versatile and has direct applications in the realization of nanotube based sensors, field effect transistors (FETs) and interconnects for flexible electronics.
12:00 PM - I1.7
Characteristics of All Polymer Flexible FET.
Shinya Oku 1 , Takeomi Morita 1 , Shuichi Nagamatsu 2 , Wataru Takashima 3 , Keiichi Kaneto 1 Show Abstract
1 Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu Japan, 2 Department of Computer Science and Electronics, Kyusyu Institute of Technology, Iizuka Japan, 3 Research Center for Advanced Eco-fitting Technology, Kyushu Institute of Technology, Kitakyushu Japan
Organic field-effect transistors (O-FETs) are attractive to many researchers because of their lightweight, flexible, pattern able characteristics as well as printable functionalities. Toward realizing flexible O-FETs, both of the substrate and the insulator should be plastic materials instead of rigid Si or glass wares. Polyimide is one of suitable materials for the gate-insulator, because of the high heatproof as well as high dielectric breakdown field. Substrate should also be tough enough against thermal procedure. In this study, we mention the current- voltage characteristics of all plastic O-FETs consisting of pentacene and PTCDI-C13 as p- or n-channel materials, respectively, with polyimide as gate insulator and polyethylene naphthalate (PEN) as plastic substrate.
Leak current on the O-FET on PEN film was found in the range less than 10−11 A, indicating that the polyimide layer can be utilized as gate insulator for O-FETs. Capacitance per area was found to be 4.0 nF/cm2 at 100 kHz measured with LCR meter, which was used for estimating mobilities. Clear transfers as well as output characteristics were obtained for both p- and n-O-FETs. The hole mobility and the on/off ratio were estimated to be 0.60 cm2/Vs and more than 105 in Pentacene FETs. In case for n-type OFETs using PTCDI-C13 as channel, the electron mobility and the on/off ratio were found to be 0.10 cm2/Vs and 106, respectively. Those O-FET parameters were similar to those used Si/SiO2 substrate, in which the hole mobility of 1.0 cm2/Vs, the on/off ratio of 107, and the electron mobility of 0.07 cm2/Vs and the on/off ratio of 105, respectively. The findings indicate that employing of PEN and polyimide as substrate and gate insulator, respectively, is suitable for conserving high performance of both of the p-type and n-type organic semiconductors.
12:15 PM - I1.8
Ag-Ge-S Formation on Flexible Substrates for Microscale PMC Memory Circuits.
Sunil Baliga 1 , Michael Kozicki 1 , Gary Tompa 2 , Elane Coleman 2 Show Abstract
1 , Center for Applied Nanoionics, Arizona State University, Tempe, Arizona, United States, 2 , Structured Materials Industries, Inc., Piscataway, New Jersey, United States
Programmable Metallization Cell (PMC) memory stores data by growing or dissolving a metallic electrodeposit between two electrodes using a programming current, thus switching between multiple well-defined resistance states. Of significant interest is applying this technology to flexible circuit structures. For this application, a large area, low temperature film formation technique is desirable. In this paper, we present our results on the fabrication and electrical characterization of PMC memory on plastic substrates using a scalable Chemical Vapor Deposition (CVD) technique. Specifically, we have applied enhanced CVD techniques to form the Ge-S host material on polymer structures at temperatures of ~120 °C and then used a room temperature photo-diffusion method to incorporate the Ag. We will present the results reviewing the method of film growth, film characterization and processed device results.
I2: Flexible Displays
Monday PM, December 01, 2008
Room 209 (Hynes)
2:30 PM - **I2.1
Printed Organic Transistors for Low-cost Tags, Displays, and Sensors: Technology, Modeling and Challenges.
Vivek Subramanian 1 , Alejandro de la Fuente Vornbrock 1 , Huai-Yuan Tseng 1 , Shong Yin 1 Show Abstract
1 Electrical Engineering & Computer Sciences, University of California, Berkeley, Berkeley, California, United States
Printed organic transistors are promising for use in electronics on plastic for such applications as displays, RFID tags, and embedded sensors. Printing potentially enables the fabrication of such systems at very low cost through the use of entirely additive process techniques. Using inks based on metallic nanoparticles, polymers, and soluble oligomer precursors, we demonstrate printed organic transistors on plastic with performance approaching that of amorphous silicon thin film transistors. By careful design and synthesis of nanoparticles, it is possible to formulate inks that sinter at plastic-compatible temperatures to produce metallic contacts with conductivity approaching that of sputtered / evaporated thin films. These therefore make excellent contacts and interconnects for organic-transistor-based circuits. Use of crosslinked polymer dielectrics, coupled with optimized substrate preparation and printing processes allows for the realization of thin gate dielectrics enabling low-voltage transistor operation. Finally, using oligomer precursor semiconductors allows for the realization of printed transistors with relatively high mobility (>0.1cm^2/V-s), while ensuring good process compatibility and stability.The physics of transport in organic semiconductor materials, as well as the non-ideal contacts to the same result in the need for improved compact models for transistor behavior. We report on our development of simple compact models that fit experimental data well, and account for numerous major behaviors observed in these devices. Multiple trap and release mobility models are implemented to correctly fit field-dependence of mobility. Barrier lowering and non-ohmic contact models are implemented to correctly model effects of source/drain electrodes. Leakage models are implemented to model trap-induced device leakage, and geometric corrections are modeled to account for printed-induced non-Manhattan device structures. Finally, we discuss reliability and other challenges impacting the viability of printed electronic devices, including bias stress effects, variability, and device scaling issues. Thus, through this work, we provide a comprehensive overview of the status and outlook for printed organic transistors for use in low-cost displays, tags, and sensors.
3:00 PM - **I2.2
Mechanical, Electrical, and Chemical Stability of Components of Flexible Displays.
Sigurd Wagner 1 , James Sturm 1 , Bahman Hekmatshoar 1 , Kunigunde Cherenack 1 , Prashant Mandlik 1 , Lin Han 1 , Jeff Silvernail 2 , Rui-Quing Ma 2 , Michael Hack 2 , Julie Brown 2 Show Abstract
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Universal Display Corporation, Ewing, New Jersey, United States
3:30 PM - I2.3
Flexible Audible Display using ITO on PVDF and Its Interface Analysis.
Dong-Hee Park 1 , Sang-Yub Ie 1 , Won-Kook Choi 1 Show Abstract
1 , Korea institute of science and technology, Seoul Korea (the Republic of)
Poly-vinylidene fluoride (PVDF) film is widely used as a flexible substrate for pressure sensor, actuator, and film speaker due to its piezoelectricity, the high transmittance more than 80% and the highest dielectric constant among all polymers. To realize the flexible audible display (FAD), it is needed to prepare highly transparent conducting layers with the good electrical properties, usually by not a dipping method or attachment of metal foil film but a vacuum process like sputtering deposition. In this research, Indium-Tin-Oxides (ITOs), as a transparent conducting layer for the display devices, is deposited on PVDF film at lower temperature condition than room temperature with the vacuum web coating . Under the optimized working pressure and the oxygen-argon pressure ratio, our ITO on PVDF showed a good electrical property of sheet resistance about 170 ohm/sq at 100 nm thickness. And it showed a good mechanical durability of only 12% drop of resistance after the 10000 bending cycling test. This results from the increasing the peel strength due to newly formed chemical bonding occurred by incident energetic ions during the sputtering process. By the x-ray photoelectron spectroscopy (XPS) analysis, C-F chain in PVDF is reduced and replaced by carbon-oxygen bonding or carbon-metal bonding, or fluorine-metal bonding . We can also find the 50 nm thick amorphous layer, by the TEM analysis on the interfacial region of PVDF film and deposited ITO layer. OLED device with Al/LIF/Alq3/ NPB/ 2T-NATA structure is fabricated on ITO/PVDF and shows the turn-on voltage at 3.5 V and the maximum luminescence of 1011.2 cd/cm^2 at the driving voltage 13 V. Sound pressure level of 25×25 mm^2 ITO on PVDF is over 80 dB in 700 Hz-10kHz.
I3: Processes on Flexible Substrates I
Monday PM, December 01, 2008
Room 209 (Hynes)
4:15 PM - **I3.1
Demonstration of All Printed 13.56 MHz RFID Tags.
Gyoujin Cho 1 2 , Jaeyoung Kim 2 , Minhoon Jung 1 2 , Joonseok Kim 1 , Chaemin Lim 1 2 , Namsoo Lim 2 1 , Heewon Kang 2 1 , Soojin Lee 2 1 , Donghwan Kim 2 1 , Kyunghwan Jung 2 1 , Junghye Kim 1 , Youngkwan Song 1 , Kwangyong Lee 1 , Yousun Jung 1 , Dongsun Yeom 2 1 Show Abstract
1 School of Applied Materials, Sunchon National University, Sunchon, Jeonnam, Korea (the Republic of), 2 Printed Electronics Research Center, PARU. Co., Sunchon, Jeonnam, Korea (the Republic of)
Roll to roll (R2R) printed electronics has been considered as a pathway toward the mass production of ultra-low cost RFID tags for item-level tracking of consumer goods. However, up to present, the demonstration of all R2R printed RFID tags have not been successful yet because of three major obstacles. The most critical one is the lack of R2R printable rectifier to provide stable DC 10 V @ 13. 56 MHz. Second, stable thin film transistors (TFTs) with the switching speed of 100 Hz under 10 V DC power are not roll to roll printable yet. Third, the overlay registration accuracy of R2R printers can not be comparable to that of current photolithographic process. In this presentation, I would like to show the most practical ways to solve those obstacles based on novel designed materials, and the world first R2R printable 13.56 MHz operated 1 bit RFID tags will be demonstrated.
4:45 PM - I3.2
Growth of Epitaxial γ-Al2O3 and NiAl2O4 Films on Flexible, Single-crystal-like Metallic Substrates by Pulsed Laser Deposition.
Junsoo Shin 1 , Amit Goyal 1 , Sung-Hun Wee 1 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Lab., Oak Ridge, Tennessee, United States
Alumina (Al2O3) is widely used for structural applications because it offers excellent electrical insulation properties together with high hardness, thermal stability and good wear resistance. Epitaxially grown γ-Al2O3 thin films show promise as an oxygen-diffusion barrier for device applications such as a buffered layer between dielectric materials and metallic tapes, protecting the underlying metallic electrodes or the cubic substrates from oxidation. Moreover, γ-Al2O3 thin films have a good lattice match with many perovskites or spinels with ferroic and/or multiferroic properties. For this reason, epitaxial growth of γ-Al2O3 thin films on Si substrates has already been reported by several groups using molecular beam epitaxy (MBE). On the other hand, the growth of nickel aluminate spinel (NiAl2O4) film is reported here for the first time even though NiAl2O4 is a promising candidate for use as an anode electrode material in aluminum electrolysis. This is because of a unique combination of electrical conductivity and chemical diffusivity. We have successfully fabricated single orientation, epitaxial NiAl2O4 and γ-Al2O3 thin films, on flexible, biaxially-textured metal tapes using pulsed laser ablation (PLD). Under the optimum conditions, NiAl2O4 and γ-Al2O3 thin films were epitaxially grown on three different types of flexible, single-crystal-like, metallic templates: (a) IBAD-MgO/Hastelloy: non-textured Hastelloy with MgO layer, biaxially textured by ion-beam-assisted deposition (IBAD), (b) Homo-MgO/IBAD-MgO/Hastelloy: IBAD-MgO/Hastelloy with homoeptiaxial MgO layer, and (c) PLD-MgO/Ni-W: biaxially textured Ni - 3 at.%W metallic substrate with epitaixal MgO buffer layer grown by PLD. These biaxially textured, NiAl2O4 and γ-Al2O3 films on flexible, single-crystal-like substrates are promising for subsequent epitaxial growth of various complex oxide films used for electrical, magnetic and electronic device applications. Research sponsored by the Laboratory Directed Research & Development (LDRD) Program of ORNL, managed by UT-Battelle, LLC for the U. S. Department of Energy.
5:00 PM - I3.3
Laser Direct Drawing of Silver Microwiring on a Double-Decker-Shaped Polysilsesquioxane Film using Silver Nanoparticle Ink.
Mohammod Aminuzzaman 1 , Akira Watanabe 1 , Tokuji Miyashita 1 Show Abstract
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Recent years have witnessed an explosion of interest in the application of polymers as the substrates for various electronic and display devices. The advantages of polymers are their mechanical flexibility, light weight, enhanced durability, roll-to-roll fabrication and low cost compared with rigid materials (such as silicon and glass). Hybrid polymers have drawn great attention because they offer the opportunity to prepare high-performance multifunctional advanced materials through the combination of properties of organic and inorganic segments. Recently, a new approach to construction of nanohybrid materials based on polyhedral oligomeric silsesquioxne (POSS) as an inorganic moiety has attracted a lot of interest. Double-decker-shaped silsesquioxane (DDSQ) is a new family of silsesquioxane consisting of nanometer-sized Si-O-Si cage structure functionalized with a wide variety of organic groups. DDSQ-based hybrid polymer (Double-decker-shaped polysilsesquioxane, DDPSQ) possesses many fascinating properties such as high thermal stability, good mechanical properties, low dielectric constant, excellent transparency, excellent flexibility and so on. Due to these fascinating properties, DDPSQ can be used as a potential candidate substrate for various flexible electronic devices. For such applications drawing of conductive metal (Au, Cu, Ag) patterns on a DDPSQ substrate is required. Herein, we have described fabrication of Ag microwiring with submicron resolution on a DDPSQ film by laser direct writing. The line width of the Ag-wiring fabricated by this laser direct-write maskless technique can be controlled flexibly by changing the objective lens magnification and the focusing point. With an objective lens magnification 100x, Ag microwiring with a line width of about 5 μm has been achieved. The Ag-wiring shows an excellent adhesion to DDPSQ surface as evaluated by Schotch tape test. The resistivity of the Ag-wiring is determined to be 4.3x10-6 Ω cm ,which is comparable that of bulk Ag (1.6x10-6 Ω cm).
5:30 PM - I3.5
Deposition of PZT Thin Films on Copper-coated Polymer Foils.
Gunnar Suchaneck 1 , Zdenek Hubicka 2 , Lubomir Jastrabik 2 , Alexandr Dejneka 2 , Dmitry Kiselev 3 , Andrei Kholkin 3 , Gerald Gerlach 1 Show Abstract
1 Solid State Electronics Lab, TU Dresden, Dresden Germany, 2 Dep. of Optics, Institute of Physics, ASCR ,v.v.i., Prague Czechia, 3 Dept. of Ceramics and Glass Engineering & CICECO, University of Aveiro, Aveiro Portugal
The deposition of complex oxides on metal substrates and polymer foils represents an important extension of the thin-film technology towards substrate materials more compatible with innovative applications. Electronic devices which are directly integrated into printed wiring boards or multi-chip module-laminated structures allow the fabrication of much thinner and sleeker electronics. They decrease manufacturing costs, increase electrical performance, and enhance design flexibility.An increasing interest for deposition of thin films at low substrate temperatures is paid to plasma sources. A quite efficient way of generating homogeneous radio frequency (RF) plasmas is the hollow cathode discharge. Here, the electrons oscillate in the hollow cathode, giving rise to a high plasma density. The plasma expands in a plasma-jet through a nozzle into the reactor chamber. Reactive sputtering occurs through interaction with the material of the nozzle. Thus, the composition of the nozzle material is transferred to the substrate surface. Low pressure RF plasma jets generate a non-equilibrium plasmas with electron temperatures of about 22,000 K, molecules vibrationally excited up to about 5,000 K, and a gas temperature of about 500 K. The non-thermal excitation of the species allows perovskite synthesis without sufficient heating of the substrate. In this work, we analyze the processing of Pb(Zr,Ti)O3 (PZT) thin films directly on copper-coated polymer foils by means of a RF-modulated plasma–jet system comprising a hollow cathode for reactive sputtering. (111) textured PZT films were deposited using a TiOx seeding layer.Structure analysis of the deposited films was performed by XRD diffraction. Surface topography and piezoelectric response (both in-plane and out of plane) were evaluated by scanning force microscopy. Chemical composition was measured by an electron microprobe JOEL JXA 733. Optical measurements were made by means of a J.A. Woollam spectral ellipsometer operating in the rotating analyzer mode. The ellipsometric parameters were measured in the spectral range from 300 to 1000 nm at three angles of incidence. The ellipsometric data were analyzed with the software package WVASE32. Optical constants were calculated for a simple substrate/film model taking into account surface roughness and thickness non-uniformity. The complex dielectric behavior was investigated by means of a Solartron 1260 impedance analyzer. Ferroelectric loop were recorded by a compensated Sawyer-Tower circuit.The application of deposited films as embedded capacitors, piezoelectric actuators and detectors of acoustic emission is discussed.This work was supported by the German Research Foundation (DFG) - Grant GE 779/18-1, by the Academy of Science of the Czech Republic – Grant KJB100100703, by the Grant Agency of the Czech Republic – Grants 202/08/1009 and AV0Z10100522, and by the DAAD-GRICES exchange program.
5:45 PM - I3.6
Ultrathin Insulator Films with Atomically Smooth Surfaces Using Plasma Processing.
Venkat Bommisetty 1 , Rojan Karmacharya 1 , David Galipeau 1 Show Abstract
1 EE, South Dakota State University, Brookings, South Dakota, United States
Ultrathin insulator films with smooth surfaces are critical for next generation microelectronics, nanosensor and biosensor applications [1-3]. HfO2 is widely used as high-k dielectric in microelectronics industry and is currently deposited using sputtering or CVD methods. HfO2 thin films deposited using these methods contain large defect density resulting in increased oxide charge and leakage current. This report presents results of RF glow discharge oxidation of metal Hf thin films for growing atomically smooth HfO2 films. Hf thin films were deposited using both DC and RF sputtering. While RF sputtering produced smoother films at process pressures over 10 mTorr, DC sputtering produced smoother films at low pressures. DC sputtered Hf films of 50 nm thickness (50 W, 2 mTorr of Ar) produced the smoothest film with RMS roughness of about 0.26 nm (over 10 x 10 Sq. micron area). RF glow discharge oxidation (10 W, 10 s, 55 mTorr of O2) produced HfO2 films with 0.33 nm RMS roughness. The surface roughness of both Hf and HfO2 films were comparable to that of the glass substrate, indicating conformal deposition. Surface roughness of HfO2 films increased with oxidation power and duration. Prolonged oxidation at high plasma power produced HfO2 films with large grains. Nanoscale electrical conductivity and breakdown voltage of these films is being studied using current-sensing atomic force microscopy.  R. K. Nahar, et. al., J. Mater Sci: Mater Electron, 18, (615) 2007.  B.Y. Tsuia and H.W. Chang, J. Appl. Phys., 93, 10119 2003.  G. He, et. al., Appl. Surf. Sci. 253, 3413 (2007)
Julia R. Greer California Institute of Technology
Joost Vlassak Harvard University
Jurgen Daniel Palo Alto Research Center
Ting Tsui University of Waterloo
I4: Metallic Thin Films
Tuesday AM, December 02, 2008
Room 209 (Hynes)
9:15 AM - **I4.1
High Ductility of Thin Metal Films on Polymer Substrates.
Zhigang Suo 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard, Cambridge, Massachusetts, United States
When a freestanding plastically deformable metal film is stretched, it ruptures by strain localization, and the elongation is less than a few percent. When the film is deposited on a polymer substrate, however, strain localization may be retarded by the substrate. This talk describes Cu films deposited on Kapton substrates and stretched up to the rupture of the substrates at an elongation beyond 50%. We show that the measured electrical resistance agrees with a theoretical prediction. Micrographs show that the strain localization and debonding co-evolve. We further show that the ductility of the film can be markedly varied by the adhesion between the film and the substrate, the thickness of the film, and grain growth during deformation. 1. Nanshu Lu, Xi Wang, Zhigang Suo, Joost Vlassak, Metal films on polymer substrate stretched beyond 50%. Applied Physics Letters 91, 221909 (2007).2. Nanshu Lu, Xi Wang, Zhigang Suo and Joost Vlassak, Failure by simultaneous grain growth, strain localization, and interface debonding in metal films on polymer substrates. http://imechanica.org/node/3320
9:45 AM - I4.2
Tensile Testing of Ultra Thin Metallic Films on Polyimide Substrates: Plasticity, Fracture and Fatigue.
Patric Gruber 2 , Dong Wang 1 , Cynthia Volkert 3 1 , Ralph Spolenak 4 , Oliver Kraft 1 2 Show Abstract
2 izbs, University of Karlsruhe, Karlsruhe Germany, 1 IMF II, Forschungszentrum Karlsruhe, Karlsruhe Germany, 3 Institute for Materials Physics, University of Göttingen, Göttingen Germany, 4 Department of Materials, ETH Zürich, Zürich Switzerland
Current semiconductor technology demands the use of compliant substrates for flexible integrated circuits. However, the reliability of such devices is often limited by the extensibility of the anorganic components. So far, little experimental work has been carried out to investigate the mechanical properties of thin metallic films on compliant substrates at high strains and cyclic loading. Here, we present experimental results for the yield strength, fracture toughness and fatigue behavior of ultra thin Cu and Ta/Cu film systems on polyimide substrates with 20 to 1000 nm film thickness. The film systems have been tested by a synchrotron-based tensile testing technique (up to 7% total strain) as well as cycling loading (100 Hz, strain amplitude of 0.5 to 1%) and have been characterized by SEM and FIB microscopy. The synchrotron experiments yield the stress-strain curves of the Cu films (as prepared and fatigued) whereas the cyclic tests give the fatigue lifetime. On the other hand, in situ tensile tests in the SEM and stationary FIB investigations reveal the evolution of cracks and fatigue damage in the films. For the thinnest films the deformation behavior during the tensile tests and for cycling loading becomes more and more brittle and multiple cracking is observed. It is shown that the fracture toughness of the Cu films decreases with decreasing film thickness whereas the fatigue lifetime and the yield strength increase. The different size effects may be attributed to an increasing constraint and final lack of plastic deformation by dislocations. This may be corroborated by the observation that the strain hardening is strongly reduced for the thinnest films.
10:00 AM - I4.3
Concurrent Grain Growth, Strain Localization, and Interface Debonding in Metal Films on Polymer Substrates under Uniaxial Tension.
Nanshu Lu 1 , Xi Wang 2 , Zhigang Suo 1 , Joost Vlassak 1 Show Abstract
1 SEAS, Harvard University, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
The ductility of metal interconnects on polymer substrates is of great importance for the reliability of flexible electronics. Previously we have demonstrated that a microcrystalline copper film well bonded to a polymer substrate can be stretched beyond 50% without cracking. The film eventually fails through the co-evolution of necking and debonding from the substrate. Here we report much lower strains to failure (around 10%) for polymer-supported nanocrystalline metal films, whose microstructure is revealed to be unstable under mechanical loading. We find that strain localization and deformation-associated grain growth facilitate each other, resulting in an unstable deformation process. Film/substrate delamination can be found wherever strain localization occurs. We therefore propose that three concomitant mechanisms are responsible for the failure of a plastically deformable but microstructurally unstable thin metal film: strain localization at large grains, deformation-induced grain growth and film debonding from the substrate.
10:15 AM - I4.4
Cyclic Uni-axial Loading of Stretchable Gold Thin-films on Elastomeric Substrate.
Ingrid Graz 1 , Darryl Cotton 1 , Stephanie Lacour 1 Show Abstract
1 , University of Cambridge, Cambridge United Kingdom
Emerging applications of stretchable electronics in hand-held devices or bio-robotics require mechanically dynamic electrical circuits with electrical interconnects robust to large, fast and repeated mechanical deformation. We have evaluated the electrical and mechanical resistance of thin gold films on silicone membranes to extended cyclic uni-axial loading, and found that 50nm thick gold films on 1mm thick silicone substrate remain electrically conducting over 100,000 cycles to 20% tensile strain. The film morphology evolves from a random micron size crack pattern into a square-like (of ~15μm side) crack pattern. The metallic conductors made of 50nm thick gold on top of 5nm thick adhesive chromium, are prepared by thermally evaporation on a 1mm casted silicone membrane. Two different sample types were investigated being 5mm long, and 0.11 and 1mm wide, respectively. Their electro-mechanical characterization is conducted in our customized uni-axial stretchers where we can control the strain rate (up to 2mm/sec), the maximum applied strain (εmax = 10 and 20%), and record the electrical resistance. Prior to cyclic loading, all samples are cycled once slowly (15μm/sec rate) to 20% strain. Then repeated stretching is applied at a rate of 1.5mm/sec. The electrical resistance R0 at 0% strain remains stable throughout the 100,000 cycles. At maximum applied strain (εmax=20%), Rmax decays exponentially over the first 100 cycles then stabilizes to reach a maximum value about twice R0. However, the resistance-versus strain dependence evolves from displaying maximum resistance at maximum strain to actually exhibiting a local minimum in resistance at maximum strain. We believe this behaviour is related to morphology changes in the thin-films over cycling. Scanning electron microscopy (SEM) images taken on the pristine (unstretched) conductors reveal randomly distributed branch-like and shallow cracks. After extended cyclic loading, the crack pattern is very different: pronounced cracks (and holes) have formed in and perpendicular to the stretching direction defining a grid-like network. We will present our experimental data for these highly robust metallic films on silicone including sample fabrication and characterization.
10:30 AM - I4.5
Thickness and Young’s Modulus Characterization of the Plasma Treated Surface Layer of a Stretchable PDMS Substrate.
Stephane Befahy 1 2 , Pascale Lipnik 1 , Michel Troosters 2 , Patrick Bertrand 1 , Sami Yunus 1 , Thomas Pardoen 1 Show Abstract
1 Ecole Polytechnique de Louvain, Université catholique de Louvain, Louvain-la-Neuve Belgium, 2 , Neurotech SA, Louvain-la-Neuve Belgium
Processing a polydimethylsiloxane (PDMS) elastomer as a stretchable substrate for flexible electronic applications requires preliminary surface oxidation before performing a metallization or a chemical grafting. This oxidation, usually obtained by plasma treatment, induces the formation of a “silica-like” layer. This layer is much stiffer than the bulk PDMS substrate and lead to periodic buckling patterns upon thermal or mechanical induced deformation. [1,2,3] The wrinkling and fracture behaviour of the metal layer which control the reliability of the electronic system is directly influenced by this intermediate silica-like layer. In this work, the thickness and the Young’s modulus of the silica-like layer is estimated from simple optical microscopy measurements of the buckling pattern parameters of metallized with gold and un-metallized oxidized PDMS regions, prestretched before the surface treatments. Different plasma conditions are investigated. The measurements are performed on PDMS wires which allow inducing the predeformation by prestreteching or pretwisting the samples. The two unknown parameters are determined using a closed form solution for the buckling of a thin bilayer on top of a thick compliant substrate, following Huck et al. . The thickness predictions, ranging between 10 and 100nm depending on the plasma conditions, are successfully compared to TEM measurements performed on oxidized PDMS sheets welded together by the plasma treatment.  S. Béfahy, S. Yunus, V. Burguet, J.-S. Heine, M. Troosters, and P. Bertrand, The Journal of Adhesion, 2008, 84, 231–239 W. Huck, N. Bowden, P. Onck, T. Pardoen, J. Hutchinson and G.M. Whitesides, Langmuir 2000, 16, 3497-3501 S. Béfahy, S. Yunus, M. Troosters, T. Pardoen, and P. Bertrand, Appl. Phys. Let., 2007, 91, 141911
I5: Thin Films on Flexible Substrates
Tuesday PM, December 02, 2008
Room 209 (Hynes)
11:15 AM - **I5.1
Mechanics of Electronic Eye Camera.
Yonggang Huang 1 , John Rogers 2 Show Abstract
1 , Northwestern University, Evanston, Illinois, United States, 2 , University of Illinois, Evanston, Illinois, United States
The human eye represents a remarkable imaging device, with many attractive design features. Prominent among these is a hemispherical detector geometry, similar to that found in many other biological systems, that enables wide field of view and low aberrations with simple, few component, imaging optics. This type of configuration is extremely difficult to achieve using established optoelectronics technologies, due to the intrinsically planar nature of the patterning, deposition, etching, materials growth and doping methods that exist for fabricating such systems. Here we report strategies that avoid these apparent limitations and we implement them to yield high performance, hemispherical electronic eye cameras based on single crystalline silicon technology. The approach uses wafer-scale optoelectronics formed in unusual, two dimensionally compressible configurations and elastomeric transfer elements capable of transforming the planar layouts in which the systems are initially fabricated into hemispherical geometries for their final implementation. In a general sense, these methods, taken together with our theoretical analyses of their associated mechanics, provide practical routes for integrating well developed planar device technologies onto the surfaces of complex curvilinear objects, suitable for diverse applications that cannot be addressed using conventional means.Reference Ko et al., “A hemispherical electronic eye camera based on compressible silicon optoelectronics,” Nature (in press).
11:45 AM - I5.2
Localized Plasticity Effects on the Delamination of Thin Hard Films on Compliant Substrates.
N. Moody 1 , M. Cordill 2 , M. Kennedy 3 , D. Adams 4 , J. Emerson 4 , D. Bahr 5 , E. Reedy 4 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Austrian Academy of Science, Leoben Austria, 3 , Clemson University, Clemson, South Carolina, United States, 4 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 5 , Washington State University, Pullman, Washington, United States
Reliability of thin hard films on compliant substrates is a key factor governing the use of emerging flexible substrate devices where compressive stresses can lead to delamination and buckling. However, the effects of substrate compliance on film failure are not well defined. We are therefore studying these effects using substrates that span two orders of magnitude in compliance and hard tungsten films where high compressive film stresses trigger delamination and buckling. The results show that failure occurs most readily on compliant substrates with extensive substrate deformation along buckle edges that alters buckle morphology and fracture energies beyond effects suggested by existing models. In this presentation we will use the results to show how localized substrate plasticity affects delamination of films on flexible substrates providing a means to predict device performance. This work was supported by Sandia National Laboratories, a Lockheed Martin Company for the USDOE NNSA under Contract DE-AC04 94AL85000.
12:00 PM - I5.3
Superplastic Materials as Flexible Interconnects.
Noble Woo 1 , Stephan Frank 1 , Ralph Spolenak 1 Show Abstract
1 Department of Materials, ETH Zürich, Zürich Switzerland
Flexible or ‘wearable’ electronics are some of emerging novel products, e.g. flexible displays, integrated sensors and microprocessors in textile. One important common feature is the use of metal interconnects/electrodes on highly deformable substrates. Since global wiring system has to accommodate at least 10% (preferably >50%) of strain along the deformation of substrate, classical interconnect materials such as Al, Au and Cu, cannot accommodate such strains without fracture. We try to overcome this issue by developing thin films alloys that exhibit the following properties: the alloy should have limited superplasticity (50-100%) at room temperature; the electrical conductivity of the alloy should only decrease slightly relative to the pure metal. Potential alloying metals include, but are not limited to Li, Mg, and Zr. In this study a combinatorial approach is employed, which allows co-deposition with multiple sputter sources, to produce sample films with varying compositions as function of position. The alloy composition spreads are deposited on polymeric substrates to enable tensile testing. In-situ tensile testing, in particular, is carried out in electron and/or optical microscopes to determine the onset of cracking as a function of temperature. The combination of in-situ testing and the combinatorial approach for the investigation of alloy compositions in parallel makes alloy development much more efficient. Standard microelectronic 4-point probe technique is used to characterize electrical conductivity locally. Alloys which exhibit room temperature superplasticity will then be determined for its exact composition by Energy dispersive X-ray Spectroscopy (EDX).
12:15 PM - I5.4
Fatigue Behaviors of Inkjet-printed Ag Films on Flexible Substrates.
Ho-Young Lee 1 , Seol-Min Yi 1 , Ji-Hoon Lee 1 , Hwan-Soo Lee 2 , Jung-Bok Kwak 2 , Seung-Min Hyun 3 , Young-Chang Joo 1 Show Abstract
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Central R&D Institute, Samsung Electro-Mechanics, Suwon Korea (the Republic of), 3 Division of Nano-Mechanical System Research, Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of)
As the complexities of electronic packages grow, high reliability of assembled components is critical to maintain final product quality, especially in light of trends toward miniaturization and higher levels of integration. Flexible circuits are widely used in various electronic packages to achieve such goals. Flexible printed circuitry (FPC) is a patterned array of conductors supported by a flexible dielectric film made of high strength polymeric material such as polyimide. The flexibility of FPC provides an opportunity for three dimensional packaging, easy interconnections and dynamic applications. Recently, A lot of concerns have been focused on the inkjet printing of metallic nanoparticles on flexible, large-area substrates to fabricate FPC. Advantages of inkjet printing include ease of mass production, low cost, and flexibility. Most researches on inkjet-printed metallic films have concentrated on the fabrication and the characterization of microstructure and electrical properties. It is known that mechanical properties of thin metallic films are different from those of bulk counterparts. In thin metallic films on flexible substrates, cracks are generated and propagate in those applications due to repeated bending motion, resulting an open circuit. Fatigue behaviors of inkjet-printed metallic films have not yet been studied. Thus, fatigue behavior of inkjet-printed metallic films should be evaluated and confirmed. Inkjet printing is a wet process and an additional heat treatment is required. During the heat treatment, an inkjet-printed metallic films are likely to evolve a characteristic microstructure. Microstructure evolution and oxidation during heat treatment are closely related to the corresponding electrical and mechanical properties. In this work, microstructure characteristics of inkjet-printed Ag films such as grains and pores were investigated as a function of isothermal annealing time, and their electrical and mechanical properties with respect to the microstructure evolution were also investigated. In addition, high cycle fatigue resistance of inkjet-printed Ag films was determined by using specially designed experimental setup which can generate bending strain in the specimen. The fatigue characteristics of the inkjet-printed Ag films were summarized in the form of S-N diagrams with respect to frequency. Significant decrease in fatigue lifetime has been observed due to higher strain in high cycle fatigue. Failure mechanisms are also discussed in terms of microstructure evolution during the heat treatment.
12:30 PM - I5.5
Measuring Adhesion Energies of Metal-Polymer Interfaces
Megan Cordill 1 , Gerhard Dehm 1 2 Show Abstract
1 , Erich Schmid Institute for Materials Science, Leoben Austria, 2 , University of Leoben, Leoben Austria
New emerging technologies in the field of flexible electronic devices require that metal films adhere well and flex with polymer substrates. Measuring adhesion energies of metal films on polymer substrates can be difficult due to the viscoelastic behavior of substrates and the combination of thin film and thin substrate. Common techniques such as stressed overlayers, nanoindentation and four point bending methods are difficult to use for metal films on polymer substrates. Utilizing small scale tensile testing, delamination of the metal film from the substrate can be induced. Chromium films on PI and PET substrates were strained in the tensile direction both ex situ and in situ inside the SEM to observe the strain when fracture and delamination of the films begins. Fracture toughness and adhesion energies are measured using mechanics based models and will be presented.
12:45 PM - I5.6
In situ Electromigration-induced Transient Stress in Pb-free Sn-Cu Solder Joints Measured by Synchrotron Radiation Based X-ray Polychromatic Microdiffraction.
Kai Chen 1 2 , Nobumichi Tamura 1 , King-Ning Tu 2 , Yi-Shao Lai 3 Show Abstract
1 Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Materials Science and Engineering, UCLA, Los Angeles, California, United States, 3 , Advanced Semiconductor Engineering, Kaoshiung Taiwan
Electromigration-induced elastic hydrostatic stress in Pb-free SnCu solder joints has been studied by using in situ synchrotron X-ray white beam microdiffraction. The elastic stress within two different grains, one located at the anode end and the other at the cathode end, was analyzed based on the anisotropy of the β-Sn crystal structure. The stress at the cathode end was almost constant except for temperature fluctuation, while the compressive stress at the anode end was build-up as a function of time in electromigration until a steady state was reached. The effective charge number of β-Sn was estimated to be in good agreement with the calculated value. The measured compressive stress gradient is much larger than that needed in pushing Sn whisker growth.
I6: Processes on Flexible Substrates II
Tuesday PM, December 02, 2008
Room 209 (Hynes)
2:30 PM - **I6.1
Photonic Curing of Thin Films on Low Temperature Substrates.
Kurt Schroder 1 Show Abstract
1 , Novacentrix, Austin, Texas, United States
A novel industrial process for rapidly curing thin films, such as metallic and semiconductor inks, on low temperature substrates is presented which uses intense pulsed light from a flash lamp to briefly heat the film without affecting the substrate. This targeted processing reduces or even eliminates the need for an oven to cure many materials and often shows improved performance. The process is able to cure materials that cannot ordinarily be thermally processed in air such as sintering a copper particle film to form a conductor. Unlike laser curing, the process is broadcast by nature and maskless. Thus, the processing rates are much faster and no critically aligned optics are required. Furthermore, the millisecond timeframe of the process makes it ideal for high speed printing applications for materials even beyond metal inks.An R&D system, PulseForgeTM 1100, has been built to develop curing parameters for various thin film/substrate systems. A commercial system, PulseForgeTM 3100, has also been built to process material continuously up to 200 fpm and handle an arbitrarily wide web in 6 inch increments.Data from both silver and copper based films are presented. Sheet resistances as low as 20 mΩ/‖ and resistivities as low as 4X bulk have been attained with silver. Sheet resistances as low as 150 mΩ/‖ and resistivities as low as 40X bulk have been attained with copper. Typical substrates are cellulose and PET and typical films are 0.5-5 microns thick. Results for other materials are also presented.
3:00 PM - **I6.2
Low-temperature Processing of a-Si:H Thin-film Transistor Arrays for Conformal Flexible Electronics.
William Wong 1 Show Abstract
1 Electronic Materials and Devices Laboratory, Palo Alto Research Center, Palo Alto, California, United States
The development of inexpensive high-performance electronics requiring low-temperature device processing would enable low-cost, large-area flexible electronics for applications such as large-area displays, sensors, and evolving technologies such as electric paper. The recent developments of thin-film transistor backplanes processed on flexible plastic substrates opens the possibility for novel device structures, processes, and applications. The integration of inorganic thin films with flexible organic substrates provides additional functionality to conventional applications such curved sensor arrays for wide-angle, curved focal plane cameras. In this presentation, an overview of low-temperature a-Si:H processing for thin-film transistor array fabrication will be given along with the integration of these backplanes with organic and inorganic sensor materials. The development of a hemispherically shaped image sensor array that incorporates high-performance a-Si:H p-i-n sensor diodes on polyethylene naphthalate (PEN) substrates will also be presented. The flexible arrays were then processed to make a curved hemispherical sensor. The design is based on a geodesic dome, which forms an increasingly good approximation to a spherical section with increasing number of triangular sub-units. We discuss a flexible sensor array based on 45 triangles that can be fabricated flat and bent to shape. The geometrical design, the matrix addressing approach and progress in the fabrication and evaluation of the sensor array will also be presented.
3:30 PM - I6.3
Roll-to-roll Fabrication and Transfer Printing of Dense Horizontally-aligned Carbon Nanotube Ribbons.
Sameh Tawfick 1 , Kevin O'brien 2 , Michael Moebius 1 , A. John Hart 1 Show Abstract
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 , Intel Corporation, Hillsboro, Oregon, United States
Applications of carbon nanotubes (CNTs) in flexible and CMOS-based electronic and energy devices are impeded due to typically low as-grown CNT areal densities, growth temperatures which are incompatible with device substrates, and challenges in large-area alignment and interconnection. Seeking to address these challenges, we present a scalable method for continuous fabrication and transfer-printing of dense aligned CNT ribbons. First, microstructures of vertically-aligned CNTs having controlled diameter (tunable from 2-30 nm) are grown at high temperature on a silicon substrate; and next, a dedicated apparatus is used to continuously transform the CNTs to a horizontal configuration, which simultaneously increases the CNT areal density by up to 50-fold. By controlling the adhesion characteristics of this “rolling” process, the millimeter-long horizontal ribbons may remain on the growth substrate after transformation, or be continuously transferred to a polymer film. Raman spectroscopy suggests that the structural quality of the CNTs is preserved, and the final ribbons have areal density exceeding 10^12 CNTs/cm^2 and a bulk density greater than 50% of the theoretical limit dictated by hexagonal packing of the CNTs. Electrical resistivity of 1.2 mOhm-cm is measured using Pd contacts deposited on the top surfaces of 2 micron thick ribbons; while the resistivity of copper is 100 times lower, significant improvements in the CNT resistivity are expected by optimization of contact conditions. Our roll-to-roll printing apparatus which has been prototyped at the bench scale enables direct film transfer between rigid and/or flexible substrates, without limits to substrate area. For CNT ribbon manufacturing, the growth catalyst remains on the substrate following transfer, and the substrate may be re-processed several times.
3:45 PM - I6: PFS 2
I7: Flexible Optical Devices
Tuesday PM, December 02, 2008
Room 209 (Hynes)
4:15 PM - **I7.1
Quantum-dot Light Emitting Devices on Flexible Substrates.
Peter Kazlas 1 , Jonathan Steckel 1 , Zhaoqun Zhou 1 , Craig Breen 1 , Matthew Stevenson 1 , Seth Coe-Sullivan 1 Show Abstract
1 , QD Vision, Inc., Watertown, Massachusetts, United States
4:45 PM - I7.2
Flexible Infrared Displays Incorporating Quantum Dot/Polymer Composites.
Matthew Panzer 1 , Vanessa Wood 1 , Scott Geyer 2 , Moungi Bawendi 2 , Vladimir Bulovic 1 Show Abstract
1 Electrical Engineering & Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Colloidal semiconductor nanocrystals (or quantum dots, QDs) are attractive for a variety of optoelectronic applications due to their narrowband emission spectra, which can be tuned over a wide range of visible and infrared (IR) wavelengths by altering the QD size and/or composition. The ability to process QDs in solution suggests their high compatibility in devices that can be fabricated on large area, flexible substrates through a printing or a coating process. In this work, we demonstrate that IR-emitting QDs of various peak emission wavelengths can be used together with a commercially-available electroluminescent phosphor to produce a simple, robust, “multicolor” IR display on a transparent flexible substrate.In-house synthesized PbS(CdS) core(shell) QDs are combined with a transparent polymer binder and inkjet-printed to form high-definition QD/polymer composite thin-film patterns that comprise the luminescent layer of our devices. In addition to preventing QD aggregation and self-quenching, the polymer matrix also serves to encapsulate the QD lumophores and protect them from environmental degradation. The device operates by generating, upon electrical excitation, blue photons that are emitted from a doctor blade-deposited electroluminescent phosphor layer, and are absorbed and re-emitted as IR radiation from the patterned QD film. By using QDs of different sizes, a range of peak IR emission wavelengths can be obtained, enabling fabrication of a multicolor display. The use of low temperature processing steps (<50° C) allowed us to fabricate displays on flexible substrates of polyethylene terephthalate coated with indium tin oxide (ITO). Optimization of the phosphor layer is performed to improve the bending radius of the display while maintaining its operational integrity.
5:00 PM - I7.3
Flexible Semiconductor Devices in Microstructured Optical Fibers for Integrated Optoelectronics.
Rongrui He 1 , Mahesh Krishnamurthy 2 , Pier Sazio 3 , Venkatraman Gopalan 2 , John Badding 1 Show Abstract
1 Chemistry, Pennsylvania State University, State College, Pennsylvania, United States, 2 Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania, United States, 3 Optoelectronics Research Centre, University of Southampton, Highfield, Southampton, United Kingdom
Here we present a novel group of flexible semiconductor electronic/optoelectronic devices made in microstructured optical fibers with extreme aspect ratios. These devices are motivated by incorporating the optoelectronic capabilities of semiconductor structures into optical fibers, the backbone for the modern optical communications. The joint of these two key techniques could enable all-fiber networks, in which light generation, modulation, transmission, and detection can all be performed within a fiber.One very important merit that makes optical fibers so practical in long distance communications is that they are very strong and flexible. The semiconductor materials and structures are thereby required to have comparable strengths and flexibilities, if constructed inside the fibers to realize unprecedented optoelectronics functions.Microstructured optical fibers have a complex two dimensional structure of air holes running down the length. We have demonstrated infiltration of a variety of semiconductor materials into the holes via the unique high pressure chemical vapor deposition. In this presentation, we first report the control of the carrier type and concentration in Si and Ge. Based on this control, we are able to make different types of field effect transistors and realize Si/Ge pn junctions in a fiber for the first time. This should be of considerable significance since pn junctions are the basic building blocks for optoelectronics. For example, our preliminary results show that Si/Ge heterojunctions work as in-fiber photodetectors for the 1.55 μm communication light. In the presentation, we will particularly address the flexibility of these in-fiber devices. These devices are wires or tubes with diameters ranging from 0.5 to 10 μm and lengths up to several tens of centimeters. Although being of polycrystalline nature, they show remarkable flexibilities, for example, they can generally stand > 1% strain without breaking. Generally, single crystalline whiskers and nanowires have proven to have strengths close to the theoretical values. The study of the mechanical behavior of these fine grained semiconductor materials should be highly worthwhile; they may expand the material choice for the flexible electronics and optoelectronics.
5:15 PM - I7.4
Fiber Integrated Diodes for Photodetection and Energy Conversion.
Nicholas Orf 1 , Yoel Fink 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Electronic and optoelectronic devices composed of metals, insulators, and semiconductors with sophisticated functionalities have traditionally been confined to planar, often rigid, substrates and are small in size. On the contrary, optical fiber devices typically exhibit greater mechanical flexibility and can be manufactured at lower cost than their planar compliments but have simple structures consisting primarily of insulators. Recently we have fabricated fiber-integrated optoelectronic devices, until now limited to planar substrates, utilizing simple thermal drawing techniques common to the optical fiber industry. This achievement makes it possible to introduce semiconductor device functionalities at fiber-optic length scales, uniformity and cost. I will review a new fiber device based on selenium/zinc selenide heterostructures with applications in energy harvesting and photodetection. The preform-based thermal drawing process is an ideal method of large-area device fabrication because it generates large surface areas cost-effectively. The fiber geometry also makes it possible to weave flexible, large-area ‘fabrics’ that with unique sensor applications.  Abouraddy, et al., Towards multi-material multifunctional fibres that see, hear, sense, and communicate, Nature Materials, 6 336-347 (2007)
I8: Poster Session: Processing and Reliability of Flexible Electronics
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - I8.1
Flexible Electronic Systems Based on Single-walled Carbon Nanotube Thin Films.
Qing Cao 1 3 4 , John Rogers 2 3 4 Show Abstract
1 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Frederick-Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Random networks and aligned arrays of single-walled carbon nanotubes (SWNTs) can form effective thin films for flexible electronics. They can serve as either conductive or semiconducting materials in these systems , with several attractive properties, including very high carrier mobility, extreme levels of mechanical bendability and excellent optical transparency. They are compatible with low cost printing-like fabrication processes and flexible plastic substrates. Here we report our latest achievements made on utilizing SWNT random networks for developing low-cost high-performance flexible electronics systems. In particular, we demonstrated thin-film transistors (TFTs) based on our nanotube random networks with device mobilities at around 100 cm2/Vs. At the same time, we developed effective ways to yield on/off ratios, in some cases as high as 105, through engineering the layout of SWNT thin films and selective chemical functionalizations. High k dielectrics were utilized to achieve low-voltage, hysteresis-free operations. Unusual transparent and/or stretchable TFTs based on SWNT films have been also demonstrated in some prototype devices. Finally, we successfully integrate these high-performance SWNT TFTs together and demonstrate some complex digital circuits with information processing abilities. These results could be valuable, with many potential areas of application in consumer and other areas of electronics.
9:00 PM - I8.10
Flexibility Evaluation of AlN Passivation Films for Flexible Display.
Hong Rak Choi 1 , Bhaskar Mohanty 1 , Jong Seong Kim 2 , Yong Soo Cho 1 Show Abstract
1 Materials science and engineering, Yonsei University , Seoul Korea (the Republic of), 2 Display Solution Team, LCD R&D Center, Samsung Electronic Co., LTD, Gyeonggi-Do Korea (the Republic of)
Mechanical and electrical properties of a passivating multilayer comprising of an AlN barrier film grown onto a Pt (or ITO) pattern on flexible plastic substrates, nearly PES and PET are investigated. AlN films were prepared by magnetron sputtering with RF power in the range of 150-250W and substrate temperature in the range of 50-150oC. Flexibility of the passivated films was analyzed by means of the bending test. The tests led to generation of mechanical stresses and eventual failure of the coatings, which is manifested by a sudden change of the resistivity and dielectric constant. Thus, the results of bending tests are discussed in correlation with electrical resistivity and dielectric constant of the Pt patterns and an AlN passivation layers, respectively. During the repeated bending cycles, the ratio of change to initial resistance was observed and about 0.32 was obtained over 500 times. The properties of AlN coated films were measured at different bending radius of flexible specimens that ranged from 20 to 50 mm. Microstructure and transmittance of the films were observed using scanning electron microscopy and UV-IR spectroscopy respectively. Influence of the growth condition on the properties and then on the ultimate performance of AlN on flexible substrates has been explained. The effect of internal stresses on the failure mechanisms of the multilayer composite films has also been discussed in detail.
9:00 PM - I8.11
Electrical-mechanical Properties of RF Magnetron Sputtered ITO Films for Flexible Displays.
Seungwoo Han 1 , Jongsung Bae 1 , Seungmin Hyun 1 , Jaewook Kang 2 , Hakjoo Lee 1 Show Abstract
1 Nano mechnical systems research division, KIMM, Daejeon Korea (the Republic of), 2 Surface technology research center, KIMS, Changwon Korea (the Republic of)
9:00 PM - I8.12
Reliability of Nano-scale Au Thin Films on PDMS.
Onobu Akogwu 1 2 , Marcus Eleruja 3 , Auxillia Munhutu 1 4 , David Kwabi 1 2 , Swaminathan Midthuri 5 , Wole Soboyejo 1 2 Show Abstract
1 Princeton Institute of Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey, United States, 2 Mechanical & Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 3 Department of Physics, The Obafemi Awolowo University, Ile-Ife. , Osun State, Nigeria, 4 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 5 Department of Mechanical Engineering, University of Arkansas, Fayetteville, Arkansas, United States
9:00 PM - I8.2
Characterization of Low Voltage Operating IGZO Based Thin Film Transistor with High-k MgO-BST Composite Gate Insulator on Plastic Substrate.
Dong Hun Kim 1 , Nam Gyu Cho 1 , Ho-Gi Kim 1 , Dae-Jin Yang 2 , Jae-Min Hong 2 , Il-Doo Kim 2 Show Abstract
1 Department of Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Center for Energy Materials Research, KIST, Seoul Korea (the Republic of)
9:00 PM - I8.3
Low Temperature Sintering of Binder-free TiO2 Nanoparticles Prepared by Electrospray Method for Plastic Dye-sensitized Solar Cell.
Byunghong Lee 1 , Hyun Ju Kim 1 , Sung Yeon Jang 1 , Sung Mu Jo 1 , Dong Young Kim 1 Show Abstract
1 Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
The low temperature process for plastic-type dye-sensitized solar cell have attracted much attention due to drastic reduction in cost and more extensive application, such as mobile power for wearable electronic device. Various method have been attempted to fabricate flexible plastic DSSCs, such as enhancing the viscosity of TiO2 paste using acid-based chemistry, microwave irradiation of TiO2 films and electrophoretic deposition of TiO2 particle using a solution of TiO2.In our research, we employed the electrospray (electohydrodynamic) method with binder-free well dispersed TiO2 solution. The advantage of electrospraying is that the droplets can be extremely small, down to the order of 10’s nanometers. Through electrospray method, we were successfully prepared on conducting substrate using TiO2 solution developed for sintering at low temperature, 150oC. We also investigated the morphology, surface area, porosity, characteristics of the electron transport and recombination and photovoltaic properties of dye-sensitized TiO2 electrode produced by electrospray. The field emission scanning electron microscope and high resolution transmission electron microscope images after electrospraying shows ball-like structures which have a range of diameters approximately 300-800nm, formed by crystallized 25~50nm particles. The specific surface areas were estimated by using the Brunauer-Emmett-Teller (BET) method, and the pore-size distributions and porosity were determined with the Barrett-Joyner-Halenda (BJH) method by using the nitrogen desorption branches of the isotherms. The binder-free TiO2 ball shows a typical type-IV isotherm with H2 hysteresis between the absorption and the desorption curves. The TiO2 ball film dried at 150oC were relatively larger specific surface area and porosity approximately 63.7m2g-1 and 78.6%, respectively, compared with the TiO2 nanoparticle film calcined at 500oC using organic binder (surface area of 65.3m2g-1 and porosity of 63.1%). The photovoltaic performances of the TiO2 ball dried by 150oC showed a Voc of 0.72V, a Jsc of 6.34 mAcm-2, a fill factor of 67.8% and an efficiency of 3.10% on the conducting glass. The DSSCs of flexible ITO coated PET (ITO-PEN) plastic substrate showed a Voc of 0.83V, a Jsc of 3.52 mAcm-2, a fill factor of 67.7% and an efficiency of 2.0%. Work on high-efficiency plastic-based solar cell is underway. Further improvement of the photovoltaic performance of these TiO2 ball film, the mechanical pressure applied during the hot pressing at 140oC served to decrease the void volume in TiO2 film. The heat treatment under pressure provides two important purposes: The enhancement of connection which is expected to improve electron transport properties, and the hydrothermal effect for the removal of the surface states. Until now a higher energy efficiency of the TiO2 ball based DSSC cell on the FTO/glass substrate with low-temperature treatment at 150oC was achieved as 5.2% under 1 sun.
9:00 PM - I8.4
Highly Flexible and Transparent InZnSnO2/Ag/InZnSnO2 Multilayer Electrode for Flexible Organic Light Emitting Diodes.
Han-Ki Kim 1 , Kwang-Hyuk Choi 1 , Jae-Wook Kang 2 Show Abstract
1 Information and Nano Materials Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, Korea (the Republic of), 2 , Korea Institute of Materials Science, Changwon, Gyeongnam, Korea (the Republic of)
9:00 PM - I8.5
Efficient Organic Photovoltaics on Flexible Substrates.
Jae-Wook Kang 1 , Sung-Pil Lee 1 , Do-Geun Kim 1 , Sunghun Lee 1 , Jong-Kuk Kim 1 , Gun-Hwan Lee 1 , Mi-Rang Park 1 , Han-Ki Kim 2 Show Abstract
1 , Korea Institute of Materials Science (KIMS), Changwon, Gyeongnam, Korea (the Republic of), 2 , Kumoh National Institute of Technology, Gumi Korea (the Republic of)
9:00 PM - I8.6
Thin-film Passivation and Aging Effect of Pentacene Field-Effect Transistors.
Hayoung Jeon 1 , Chan Eon Park 1 Show Abstract
1 Chemical engineering, POSTECH, POHANG Korea (the Republic of)
The thin-film passivation of organic field-effect transistors (OFETs) using a AlOx film grown by atomic layer deposition (ALD) was investigated. Using trimethylaluminium and water, a high-quality AlOx passivation layer was deposited on OFETs at 90'C. Despite the low deposition temperature, the 50nm thickness of AlOx passivation layer exhibited a low water vapor transmission rate (WVTR) value of 0.0434g/m2/day. In addition, mobility of an OFET passivated by AlOx film compared to unpassivated device slightly reduced within 9% indicating that the performance of an OFET is not critically affected by ALD process. Unlike unpassivated devices, electric performance of passivated device after 2 months was almost the same as that of unaged device due to excellent barrier property of passivation layer. To clarify the origin of atmospheric degradation of pentacene FETs, the effects of oxygen and humidity exposure on electric performance and temperature dependent mobility were investigate for unpassivated pentacene FETs in dark condition. In case of pentacene FETs exposed to pure oxygen gas for 6h, no remarkable change was observed in activation energy. In contrast, pentacene FETs exposed to humid condition (RH~70%) for 6h exhibit a sharp increase of activation energy. This suggests that the trap distribution become broader and deeper in the band gap because of H2O in air. The results of these experiments indicate that the major factor critically affecting the degradation of device performances was H2O in air, the adsorption of which causes charge trapping in both pentacene bulk and pentacene/dielectric interface.
9:00 PM - I8.7
Effects of Yield Strength on the Ductility of Polymer-Supported Metal Films.
Nanshu Lu 1 , Zhigang Suo 1 , Joost Vlassak 1 Show Abstract
1 SEAS, Harvard University, Cambridge, Massachusetts, United States
The ductility of metal interconnects on polymer substrates is of great importance for the reliability of flexible electronics. Our experiments show that as thickness reduces, the ductility of metal films degrades. Finite element simulations, however, show that film thickness itself has little effect on the ductility. We look into the film microstructure and find out that as thickness reduces, grain size decreases monotonically, which results in a continuous rise in yield strength according to the Hall-Petch effect. High yield strength will induce early rupture of polymer-supported metal films because macroscopically, there is a large driving force for interface debonding; and microscopically, some brittle fracture mechanisms such as grain boundary and twin boundary cracking are triggered at high stress level.
9:00 PM - I8.8
Environmentally Benign Carbon Nanotube Field Effect Transistors on Flexible Substrates.
Nidhi Shrivastav 1 , Selvapraba Selvarasah 1 , Kyle Anstey 1 , Ahmed Busnaina 2 , Mehmet Dokmeci 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Mechanical Engineering, Northeastern University, Boston, Massachusetts, United States
In this paper, we present Single-Walled Carbon Nanotubes (SWNTs) based Field Effect Transistors on flexible polymeric substrates. Environmental protection is also established utilizing a top pin-hole free Parylene-C layer. Flexible electronics is an emerging industry with applications in flat panel displays, bendable/wearable sensors and smart textiles. Most flexible devices are built on polymeric materials that utilize organic semiconductors deposited at low temperatures. Due to the limited mobility of organic semiconducting materials (<1.5cm2/Vs), Carbon Nanotubes (CNTs), with their high current carrying capacity, flexibility and tailorable electronic properties, are a promising candidate for flexible, high speed and low cost electronic devices. Various polymeric substrates have been utilized for realizing flexible devices. Here, we introduce the first Carbon nanotube field effect transistor (CNTFET) fabricated on a flexible Parylene-C substrate. Parylene (poly-para-xylylene) is a light-weight, stress-free, transparent inert film which can be deposited at room temperature and does not produce any out-gassing; also has very low permeability against moisture and gases. Utilizing bottom-gate device architecture, first Cr/Au gate electrodes (75nm/5nm) are deposited on to a 10 µm thick Parylene-C substrate. After the deposition of the 1 µm thick gate dielectric (Parylene-C) layer, source and drain electrodes (Cr/Au-75nm/5nm) are deposited. Then SWNTs are placed between the source and drain electrodes utilizing dielectrophoretic assembly. Finally, the device is encapsulated with a 2 µm thick Parylene-C encapsulation layer and peeled off from the silicon wafer. The CNTFET devices displayed a pronounced p-type behavior. Due to the high mechanical strength of Parylene-C, (E ~ 3GPa), the flexible substrates can be bent into circles with successive reductions in diameter without any deterioration in the performance of the devices, which suggests that our technology holds promise for niche applications in flexible electronics.
9:00 PM - I8.9
Impedance Spectroscopy to Detect Fatigue in Thermal Sprayed Coatings.
Arash Ghabchi 2 , Andrew Gouldstone 1 Show Abstract
2 , SUNY Stony Brook, Stony Brook, New York, United States, 1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
The focus of this research is to understand the microstructural changes that occur under low strain cycling of air plasma sprayed (APS) coatings. APS and other sprayed coatings are becoming attractive for their ability to be deposited on virtually any substrate, including those under flexible or harsh environments. Preliminary data showed that under nominally elastic loading (<< 0.1% strain) of thermally sprayed materials changes occur that are detectable via electrical (resistivity, dielectric constant) measurement methods. This is due to the micro-scale growth of pre-existing defects. To systematically test this, we deposited spinel coatings on tapered cantilever substrates, which were flexed to provide spatially constant in-plane cyclic strains. After different numbers of cycles, dielectric constant of coatings was measured via impedance spectroscopy. Results confirm growth of defects under these low strains, and also a large effect of humidity on different porosity features. We explain this by recourse to physisorption and chemisorptions of water on crack faces. To further quantify the adsorption phenomena electrical measurements were conducted on ceramic TS coatings in environments with different humidities. This investigation could have major implications for coating reliability, as it allows us to characterize how a coating evolves in-service, particularly for functional or electronic applications.
Julia R. Greer California Institute of Technology
Joost Vlassak Harvard University
Jurgen Daniel Palo Alto Research Center
Ting Tsui University of Waterloo
I9: Small Scale Mechanical Properties I
Wednesday AM, December 03, 2008
Room 209 (Hynes)
9:15 AM - I9.1
Extracting Mechanical Properties of Low-k Dielectric Materials with Nanoindentation.
Guanghai Xu 1 , Zhongping Bao 2 , Daniel Pantuso 1 , Yong Xiang 3 , Xi Chen 4 Show Abstract
1 , Intel Corp, Hillsboro, Oregon, United States, 2 , Intel Corp, Chandler, Arizona, United States, 3 , Numonyx, Santa Clara, California, United States, 4 Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, New York, United States
Integrating low-k dielectric (ILD) film within backend of advanced logic products is key to reducing RC delays. However, the drastic deterioration in mechanical properties of ultra thin ILD films has led to serious process challenges and becomes a major reliability concern in both integration and assembly. Nanoindentation technique provides handy means for evaluating mechanical properties of ILD film which must be taken into account when selecting back end ILD materials for reliability and at the same time optimizing for device performance. This paper implemented an exciting framework proposed by researcher which utilized substrate effect at various indentation depths to extract mechanical properties of ultra thin films. Presented here is an effective reverse analysis on nanoindentation testing data with ultra thin ILD films and a few selective materials used in back end. Details of the calibration procedures are also discussed.
9:30 AM - I9.2
Evaluation of Adhesion Between UV-cured SiOC Film and Si Substrate by Nanoindentation Method.
Masaaki Takeda 1 , Nobuhiro Matoba 1 , Manabu Oishi 1 , Mototsugu Sakai 2 Show Abstract
1 Material Characterization Labs, Toray Reserch Center Inc, Otsu Japan, 2 Material Science, Toyohashi University of Technology, Toyohashi Japan
Many interfaces consisting of different thin films have recently become common in small area electronics devices. It is important to quantitatively measure the adhesion strength at the devices to ensure their reliability. In this study, a simple technique for measuring the adhesion using the nanoindentation method by interpreting the energy balance during indentation process was proposed and applied to evaluate the adhesion of three kinds of UV-cured SiOC films on a Si substrate. A SiOC thin film of approximately 500 nm was deposited on a Si (100) substrate by the CVD process and cured by UV irradiation in 60 s and 300 s to improve the mechanical properties. We also prepared a thin film without UV curing for comparison with the cured samples. The indentation experiments were carried out using Nanoindenter (Nanoindenter XP/DCM, MTS Systems Corporation, USA) with a CSM (continuous stiffness measuring) mode up to about 500 nm in indentation depth using a Berkovich indenter. The cross section at the interface of the 60 s cured sample was observed by FIB-SEM (Strata DB235, FEI Company, USA) to confirm the delamination. An AFM (Pacific Nanotechnologies, Nano-R, USA) was used to characterize the morphology of the indents under the non-contact mode. The delamination size was determined from the AFM height profile across the indentation triangle point. The discontinuous points of approximately 300 nm in depth appeared in all the indentation curves (load, Young’s modulus, and hardness vs. indentation depth curves) with a high reproducibility, and it was confirmed that these points reflect the occurrence of an interfacial delamination from the cross sectional observation using FIB-SEM. Moreover, it is clear that a localized plastic pile-up around the contact zone occurred after the delamination by the AFM height images and the height profile of the indent in the UV-cured SiOC films. The total dissipated energies calculated from the load vs. indentation depth curves indicated a good correlation with the indentation load, therefore, the delamination energy can be calculated by subtracting the plastic strain energy from the total dissipated energy. The energy release rates at the interface of the UV-cured SiOC films calculated from energy balance increases with the increasing UV cure time and the results show a high reproducibility. The technique proposed in this study is quite useful to simply and quantitatively measure the adhesion of the thin film in a small area.
9:45 AM - I9.3
Nanoindentation Induced Deformation to Inorganic Thin Films Grown on Flexible Polymeric Substrates for FEDs Application.
Spiridon Kassavetis 1 , Stergios Logothetidis 1 , Hariton Polatoglou 1 Show Abstract
1 Lab of Thin Films - Nanosystems & Nanometrology, Physics Department, Aristotle University of Thessaloniki, Thessaloniki Greece
10:00 AM - I9.4
The Cracking Patterns in ITO on PET Substrates under Different Loading Conditions.
Jin-Woo Park 1 , Gyeom Kim 1 , Geon-Hwan Lee 2 Show Abstract
1 , Yonsei University , Seoul Korea (the Republic of), 2 , KIMS, Chang-Won Korea (the Republic of)
10:15 AM - I9.5
Direct Crack Path Monitoring for Local Investigation of Interfacial Toughness in Transparent Systems.
Davy Dalmas 1 , Damien Vandembroucq 1 , Etienne Barthel 1 Show Abstract
1 , CNRS/Saint-Gobain, Aubervilliers France
We have developped a set-up which allows the direct monitoring of a crack front in a planar interface with heterogeneous toughness. The system is based on a DCB set-up developped for thin film adhesion measurements on glass . An in plane toughness pattern was created by locally removing the low toughness film before gluing the backing. We have measured the crack front morphology as it propagates through the toughness pattern in a weak pinning regime. We show that the crack front can be adequately fitted using the Gao and Rice perturbation model . This latter analysis provides a local measurement of the toughness contrast between the low and high adhesion regions . The present technique therefore opens up for local adhesion assessment in transparent systems as well as high throughput adhesion measurements. However, a major question is still unsolved: we were also able to measure the macroscopic interfacial toughness (at the sample scale) through the standard DCB analysis but we find a significant discrepancy between the local and the macroscopic measurements. Possible causes will be discussed.
E. Barthel, O Kerjan, P. Nael and N. Nadaud, Asymmetric Silver to Oxide Adhesion in Multilayers Deposited on Glass by Sputtering, Thin Solid Films, 473(2) (2005) 272-7.
 H. Gao and J. Rice, A first order perturbation analysis on crack trapping by arrays of obstacle, J. Appl. Mech. 56 (1989) 828
D. Dalmas, D. Vandembroucq and E. Barthel, Controlling the crack front morphology by pinning in patterned heterogeneous interfaces, in preparation.
10:30 AM - I9.6
Investigation of Metal-Polymer Interfacial Cracking using Contact Resonance Atomic Force Microscopy.
Marian Kennedy 1 , Neville Moody 3 , Donna Hurley 2 Show Abstract
1 School of Material Science and Engineering, Clemson University, Clemson, South Carolina, United States, 3 , Sandia National Laboratory , Livermore, California, United States, 2 , National Institute of Standards & Technology, Boulder, Colorado, United States
The response of thin metallic films on flexible substrates to residual stress is strongly influenced by such factors as substrate compliance and strain localization. In these systems, residual stress can cause the formation of two detrimental structures: wrinkles and buckles. Buckles occur when the metallic film separates from the polymeric substrate whereas wrinkles are surface pertubations. A discrete transition from wrinkling to buckling is commonly postulated. However, this has not been demonstrated experimentally, and more complex hybrid structures are possible. Contact resonance atomic force microscopy (CR-FM) was used to determine at what point a 300-nm Au film delaminated from a polyimide film. The CR-FM frequency signal was compared to the local topography in order to identify the edge of the delaminated film. The tops and sides of the buckles showed a constant CR-FM signal corresponding to a delaminated film, while far from the buckle edge, the CR-FM signal indicated an adhered film. At the edges of the blister, CR-FM indicated a transition zone between these two states extending a few micrometers up the sides of the buckle. In this talk, we will discuss these results and show how they are affected by various influences such as interface chemistry and substrate compliance.
10:45 AM - I9.7
Mechanical Robustness of Atomic Layer Deposited and Molecular Layer Deposited Coatings for Microsystems and Flexible Electronics Applications.
David Miller 1 3 , Ross Foster 1 3 , Yadong Zhang 1 3 , Shih-Hui Jen 2 3 , Jacob Bertrand 2 3 , Zhixing Lu 1 3 , Dragos Seghete 2 3 , Jennifer O'Patchen 2 3 , Ronggui Yang 1 3 , Yung-Chen Lee 1 3 , Steven George 2 3 , Martin Dunn 1 3 Show Abstract
1 Mechanical Engineering, Univeristy of Colorado, Boulder, Colorado, United States, 3 DARPA Center for Integrated Micro/Nano-Electromechanical Transducers (iMINT), University of Colorado, Boulder, Colorado, United States, 2 Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, United States
Films grown using the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques are being explored for the purpose of creating high integrity, minimally thick coatings. Applications include encapsulation of MEMS, nano-materials, and microelectronics for improved hermeticity, charge dissipation, and/or improved tribological performance. Further, the use of an optically transparent chemical permeation barrier is of recent interest to the organic light emitting diode (OLED) and flexible electronics industries. We have utilized a series of film architectures, 5-125 nanometers in thicknesses, deposited on polyethylene naphthalate (PEN), to investigate the mechanical robustness of ALD and MLD films. First, strips of ALD alumina coated PEN were tensile tested to different prescribed strains. Each sample was then examined using a novel chemical tag, which renders a high-contrast optical signal specific to where the alumina was damaged. Additional verification was performed using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and oxygen plasma etching combined with optical microscopy. By characterizing the spacing of channel cracks and their geometry, such as secondary transverse cracking seen at greater applied strains, we are able to estimate the toughness of the films as well as their critical interfacial shear strength (substrate adherence). Observed enhanced performance, e.g. critical strain at the onset of cracking exceeding 5%, is made possible by the excellent thickness control for the ALD technique. Second, borrowing from the field of biomimicry, composite coatings composed of alternating layers of ALD alumina and MLD aluminum alkoxide (“alucone”) were explored in order to improve mechanical robustness. The polymer-like alucone films have recently been developed in our group and their mechanical performance is described here for the first time. The composite coatings are evaluated according to the same tensile characterization methods utilized for the alumina coatings. Based on the measured properties of the film materials (determined through nanoindentation), an optimized multilayer composite design was identified using the fracture mechanics approach of Corderro et. al . The optimized architecture as well as coatings of alternate thickness were characterized to validate the approach.References:1. N. Cordero, J. Yoon, and Z. Suo, Appl. Phys. Lett., 90, 2007, pp. 111910.
11:00 AM - I9:SSMP 1
11:30 AM - I9.8
Effect of Geometric Size of Ni-W Nanocrystalline Alloy on its Plasticity.
Dongchan Jang 1 , Julia Greer 1 Show Abstract
1 Materials Science, California Institute of Technology, Pasadena, California, United States
When microstructural features or external sizes of materials are reduced to nanometer scale, they exhibit very different behaviors from their larger counterparts. A typical example is “smaller is stronger” manifested by very high strengths attained during plastic deformation of nano-sized materials. While plasticity mechanisms responsible for these differences remain controversial, the strength increase is due to the larger contribution of surface area and/or interfaces. In addition, conventional strengthening mechanisms such as Hall-Petch relation for plastic deformation of polycrystals, may not be valid at nanometer scale. In this study, the combined effect of internal nano-structure and sample size on plasticity is investigated. Even though these two factors, overall sample size and internal microstructure, have been extensively investigated separately, combination of their effects has never been reported. Here, we present the results of uniaxial compression of nanometer-sized cylindrical pillars with diameters down to ~ 100 nm, fabricated using Focused Ion Beam (FIB). Grain size of these electrodeposited nanocrystalline Ni-W alloys is ~ 60 nm. Pillars are compressed in the nanoindenter under displacement (rate?) control at various strain rates (spanning from what to what?). Site-specific TEM analysis reveals microstructural changes occurring as a result of mechanical deformation.
11:45 AM - I9.9
Study of Nanoporous Gold Electrodes on Flexible Substrates.
Totka Ouzounova 1 , Lu Feng 1 , Christopher Umbach 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Nanoporous gold (NPG) has attracted considerable attention as a material for energy storage , catalysis, actuators  and electrochemical sensors . A common method for porous gold preparation is formation of a precursor AxB1-x alloy followed by chemical or elecrochemical dealloying of one of the elements. For the Au30Ag70 system, the silver is removed and a highly porous structure of gold is formed. NPG can be reliably produced as a thin membrane or as thin film on a rigid substrate, but there are challenges in reproducing the useful properties of NPG on flexible substrates. It has been shown that the NPG membrane can be kept flexible under certain dealloying conditions . This opens new possibilities for manufacturing NPG electrodes as components of devices on flexible supports.We have deposited NPG thin film electrodes on 125 μm thick Kapton substrates. By appropriate deposition and dealloying conditions, we have maintained the flexibility of nanoporous gold on these substrates. DC sputtering was used for Au30Ag70 alloy films on Cr/Au buffer layers to form NPG films with thicknesses from 50 to 400 nm. The adhesion on the flexible substrates depends on the buffer layer thickness. The morphology and crack propagation within the films was observed as a function of substrate elongation by SEM. The resistivity of the films was correlated with the porosity and elongation of the films. Greater resistivity was found with increasing porosity.  M.B. Cortie, A.I. Maaroof, G.B. Smith, Gold Bulletin, 38 (2005) 15.  D. Kramer, R.N. Viswanath, J. Weissmüller, Nano Lett. 4 (2004) 793.  M. Castano-Alvarezet, M.T. Fernandez-Abedul, A. Costa-Garcia, Electroanalysis 16 (2004) 1487.  N.A. Senior, R.C. Newman, Nanotechnology 17 (2006) 2311.
12:00 PM - I9.10
3D-effects on Delamination Along Polymer-metal Interfaces.
Willem-Pier Vellinga 1 , Alexander Fedorov 1 , Jeff De Hosson 1 Show Abstract
1 , M2i/University of Groningen, Groningen Netherlands
Elastic mismatch and residual stresses due to thermal mismatch cause mixed mode I, II and III loading of delamination fronts in applied polymer-metal interfaces. Such interfaces are increasingly common in thin-film, flexible devices. Experimental results on 3D aspects of crack propagation in these mixed mode conditions are scarce. Here we present 1. observations of differing front shapes (concave vs. convex) for samples differing in stored thermal residual energy and work of adhesion, and 2. observations of delamination front geometries accompanied by apparent 3D “pinning” of the delamination fronts 1. These results show important 3D effects in delamination along polymer-metal interfaces. The results are interpreted using results of a simple lattice model of a delamination front propagating along an interface. Observations and lattice calculations indicate that the ratio Gt/G between the “thermal energy release rate” Gt (due to release of elastic energy stored as a consequence of interplay between thermal mismatch and thermal treatment) and the total energy release rate G determines the shape of the delamination front. The observed “pinning” of delamination fronts may be explained by a combination of reduced mode I and increased mode III loading of the front near edges. The lattice calculations also support the interpretation of “pinning” as external forces needed to propagate the delamination front are highest for propagation in the “pinning regions”.  W.P.Vellinga, A.Fedorov, J.Th.M.De Hosson, Thin Solid Films (2008) in press
12:15 PM - I9.11
3D Force and Displacement Sensor for SFA and AFM Measurements.
Kai Kristiansen 1 , Travis Koh 1 , Patricia McGuiggan 2 , Greg Carver 1 , Carl Meinhart 3 , Jacob Israelacvhili 1 4 Show Abstract
1 Chemical Engineering, University of California at Santa Barbara, Santa Barbara, California, United States, 2 Materials, Johns Hopkins University, Baltimore, Maryland, United States, 3 Mechanical and Environmental Engineering, University of California at Santa Barbara, Santa Barbara, California, United States, 4 Materials Research Laboratory, University of California at Santa Barbara, Santa Barbara, California, United States
A new device has been designed, and a prototype built and tested, that can simultaneously measure the displacements and the components of a force in three orthogonal directions. The ‘3D Sensor’ consists of four or eight strain gauges attached to the four arms of a single cross-shaped force-measuring cantilever spring. Finite element modeling (FEM) was performed to optimize the design configuration to give desired sensitivity of force, displacement, stiffness and resonant frequency in each direction (x, y and z) which were tested on a ‘mesoscale’ device and found to agree with the predicted values to within 4-10%. The device can be fitted into a Surface Force Apparatus (SFA), and a smaller ‘microscale’ microfabricated versions should be suitable for Atomic Force Microscopes (AFMs) for simultaneous measurements of the normal and lateral (friction) forces between a tip (or colloidal bead probe) and a surface, or the 3D topography of a surface. Results from adhesive and elastic properties on polymer will be presented showing that the mesoscale prototype functions as expected, suggesting that scaled down (or up) versions should be practicable.
12:30 PM - I9.12
Mechanical and Electrical Reliability of a Chronically Implanted Metal-Polyimide Electrode Array.
John Yeager 1 , Derrick Phillips 2 , David Rector 2 , David Bahr 1 Show Abstract
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington, United States
A flexible electrode array consisting of a thin metal film on a Kapton substrate has been developed for neural implantation in rats. The biocompatible arrays record cortical brain signals over periods exceeding several weeks in order to gather significant neurological data. Four point bend testing of the metal-Kapton system has been used to characterize the interfacial toughness, and therefore the durability, of the array prior to implantation. The effect of several different metallic adhesion layers on gold-Kapton and platinum-Kapton arrays will be presented, showing for example that a 5nm titanium interlayer approximately quadruples the interfacial toughness of gold-Kapton. Mechanical reliability testing in a simulated implantation environment suggested that the electrodes should give reliable recordings for at least 10 weeks. Impedance of the array was characterized as a function of strain, showing no significant increase in impedance up to at least 1% strain, and in some cases even higher. Gold-Kapton arrays were implanted in rats for periods exceeding 100 days, and neural recordings were taken frequently. The electrical performance of the implanted gold-Kapton arrays will be presented in comparison to implanted platinum-Kapton arrays. The flexible array shows excellent long-term electrical reliability, with no decrease in efficiency compared to a control electrode over the course of the implantation. The neural response measurements demonstrated that the electrode array can detect signals from the brain as efficiently as traditional screw electrodes, but with better frequency power for signals higher than 100Hz. The electrode also shows the potential for high resolution mapping due to the tissue proximity and small spacing between channels. A few individual channels of the array failed over time, and failure analysis of the interconnects will be presented.