Vladimir Bulovic Massachusetts Institute of Technology
Seth Coe-Sullivan QD Vision, Inc.
Ioannis (John) Kymissis Columbia University
John Rogers University of Illinois, Urbana-Champaign
Max Shtein University of Michigan
Takao Someya University of Tokyo
G1: Materials and Substrates
Monday PM, November 26, 2007
Fairfax A (Sheraton)
9:00 AM - **G1.1
Recent Advances in Performance of Solution Processed Small Molecule OLED Materials.
Ian Parker 1 , Eric Smith 1 Show Abstract
1 , DuPont Displays, Santa Barbara, California, United States
9:30 AM - **G1.2
Printing and Patterning of Quantum Dots using Thermal Inkjet Techniques.
James Stasiak 1 , Garry Hinch 1 , Tom Etheridge 1 , Tim Strecker 1 , Steven Simske 2 Show Abstract
1 Advanced Materials and Processes Laboratory, Hewlett-Packard Company, Corvallis, Oregon, United States, 2 Digital Printing and Imaging Laboratory, Hewlett-Packard Company, Fort Collins, Colorado, United States
Monday, Nov 26New Presenter *G1.2 @ 8:30 AMPrinting and Patterning of Quantum Dots using Thermal Inkjet Techniques. Tom Etheridge
10:00 AM - G1.3
Liquid Precursors and Large-Area Processing for CuInSe2 Based Photovoltaics.
Jennifer Nekuda 1 2 , Maikel van Hest 2 , Alex Miedaner 2 , Calvin Curtis 2 , Ryan O'Hayre 1 , David Ginley 2 1 Show Abstract
1 , Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Labratory, Golden, Colorado, United States
CuInSe2 represents an important thin film solar cell material. Here we report on the use of liquid precursors to produce the binary and ternary selenides. Liquid In-Se and Cu-Se metal organic decomposition (MOD) precursors were deposited using large area deposition techniques including ultrasonic spraying and ink jet printing. The precursor films produced via these deposition methods were subsequently rapid thermal processed (RTP) under atmospheric pressure conditions to make crystalline In2Se3, Cu2Se, and CuInSe2 (CIS) thin films. The resultant films were characterized by x-ray diffraction, scanning electron microscopy, inductively coupled plasma spectroscopy, and optical reflection spectroscopy. Details of the film deposition, processing, and characterization will be discussed. This synthesis approach does not require either expensive vacuum deposition systems or the use of toxic gases (i.e. H2Se), therefore, it holds great promise for economically and environmentally viable production of large area CIS thin films.
10:15 AM - **G1.4
Alkyl Substituted Fused Thiophenes – Structures and Properties.
Mingqian He 1 , Susan Gasper 1 , Feixia Zhang 1 , Michael Sorensen 1 Show Abstract
1 , Corning Incorporated, Corning, New York, United States
Over the past several years, a new series of alkyl substituted fused thiophene compounds have been designed and synthesized. The alkyl groups greatly enhance the solubility of the thienoacenes, thus making them suitable candidates for solution processing. Placement of the alkyl groups at the β position of the fused thiophene ring system leaves the α positions available for further reaction, such as polymerization. Among these compounds, tetrathienoacenes with dialkyl groups ranging from six to eighteen carbons have been characterized in detail. Single crystal X-ray results reveal that most of the compounds possess a parallel layered structure with the exception of the dihexyl substituted tetrathienoacene. Vapor phase deposition of the alkyl tetrathienoacenes on both treated and non-treated silicon wafers has been performed and mobility measurements demonstrate that these compounds are organic semiconductor materials. Ongoing efforts to elucidate structure-property relationships in order to optimize device performance will be presented.
10:45 AM - G1.5
Solution-Processable Organic Fluorescent Dyes for Multi Color Emission in Organic Light-Emitting Devices.
Junji Kido 1 , Makoto Higashidate 1 , Ken-Ichi Nakayama 1 , Yong-Jin Pu 1 Show Abstract
1 Organic Device Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Four novel fluorescent dyes, bis(difluorenyl)amino-substituted carbazole 1, pyrene 2, perylene 3, and benzothiadiazole 4, were synthesized by C-N coupling with palladium catalyst. These dyes are soluble in common organic solvents, and their uniform films were formed by spin-coating from their solutions. Their glass transition temperatures were enough high (120 – 181 degrees) to be amorphous film for organic light-emitting devices (OLEDs). These solution processable dyes exhibited strong photoluminescence (PL) in the film (1: sky blue, 2: blue green, 3: yellow, and 4: deep red). Optical and electrochemical properties of the compounds were investigated with photo-electron spectroscopy in air and cyclic voltammetry. The energy levels obtained from both measurements were well consistent, and the levels were related with the electronic properties of the central core; electron-donating carbazole compound showed lowest ionization potential and electron-withdrawing benzothiadiazole compound showed largest electron affinity. The simple double layer devices were prepared using these fluorescent dyes as an emitting layer and bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (BAlq) as hole blocking layer. Electroluminescent colors were same as that of PL spectra in the each compounds. These results suggest that solution processable fluorescent dyes are one of candidate for multicolor light-emitting diodes as well as conjugated polymers or dendrimers.
11:30 AM - **G1.6
Materials and Processes for Large-Area Transparent Flexible Barrier Substrates.
Martin Rosenblum 1 Show Abstract
1 , Vitex Systems, Inc., San Jose, California, United States
A critical requirement for large-area roll-to-roll manufacture of optoelectronic devices is the supply of high-quality, low-cost flexible substrate material. For the majority of the devices (e.g., organic photovoltaic cells, OLED displays, etc.) proposed for this type of manufacture the substrate material must provide a barrier against water vapor and/or oxygen for the design life of the product. Polymer-based substrate materials provide low-cost and high quality, but lack significant barrier performance. Metal foil substrates provide an excellent barrier, but at a high cost and with uncertain surface quality. A solution has been developed to the barrier limitation of the polymer-based substrate materials. The necessary barrier property is obtained with the application to the substrate of a multilayer thin-film composed of layer-pairs of an inorganic barrier material and an organic material. This structure overcomes the inherent limitation of the inevitable point defects in any single-layer barrier film. These multilayer films have demonstrated their performance in application as the encapsulant for flexible OLED displays and for the manufacture of OLED micro-displays. The materials and processes used for generating the encapsulant are adaptable to large-area roll-to-roll manufacture of flexible barrier substrate. The primary feature of the thin-film barrier, its organic/inorganic multilayer structure, also provides the opportunity for alternative materials and processes suitable for expanding its application. In the most widely used implementation of the multilayer barrier, an organic precursor is deposited onto the substrate where it condenses as a liquid and is converted, in-situ, to a polymer solid. The polymer layer performs several functions. It acts as a smoothing and planarization layer when in the liquid state. The planarization is particularly effective in reducing the generation by small particles of defects in the barrier layer. The polymer layer effectively decouples defects between adjacent barrier layers. Reactive sputtering is used for the deposition of the aluminum oxide barrier layers. The nucleation and growth of the aluminum oxide film is uniform because of the clean, smooth surface of the freshly deposited polymer. The result is that barrier performance is maintained even as the individual barrier layer thickness is reduced to 20 nm. The reduction of barrier layer thickness contributes to cost-effective manufacture through an increase in line-speed for a given capital cost. Both the organic and inorganic layers are transparent as well as index matched to reduce interference effects. The thin-film processes must be stable and uniform at high deposition rates. The challenges and possible solutions will be discussed for the robust, high-yield manufacturing of flexible barrier films.
12:00 PM - G1.7
Planarization Materials for Active Matrix Thin Film Transistor Arrays.
Deborah Yellowaga 1 , Ahila Krishnamoorthy 1 , Amanuel Gebrebrhan 1 , Mehari Stifanos 1 , Richard Spear 1 , Marie Lowe 1 , Pete Smith 2 Show Abstract
1 , Honeywell Electronic Materials, Sunnyvale, California, United States, 2 , Honeywell Specialty Materials, Morristown, New Jersey, United States
Traditional plasma based dielectric films used in flat panel displays are conformal, taking the shape of underlying layers, creating an uneven surface. There are several disadvantages to having a non-uniform surface in an active matrix thin film transistor (TFT) array in a liquid crystal display. One disadvantage is that it creates different thicknesses in the liquid crystal layer, which results in different response rates and reduces resolution for the display. By creating a planar surface below the pixel, not only is resolution improved by creating a uniform liquid crystal layer, but it also allows for the size of the pixel to be increased, and the larger aperture creates a brighter image. Planarization layers also have applications for flexible displays, as they can be used to planarize and insulate metal foil substrates and form a planarizing protective layer on plastic substrates. Organic polymer materials that have been proposed as planarization layers typically have high moisture uptake and out-gassing, which can reduce the lifetime of the display. Also, organic polymer based planarization materials typically have poor adhesion to metal and metal oxide surfaces, and will dewet completely from the surface in the presence of particles. In this paper, Honeywell will demonstrate the development of hybrid inorganic/organic films that have excellent planarization and electrical properties, while maintaining optical transparency, low moisture uptake and low out-gassing.
12:30 PM - G1.9
Improvement of Durability in Silicon Nitride Barrier Films for Flexible OLED Displays under High Temperature and High Humidity Conditions.
Kunio Akedo 1 , Atsushi Miura 1 , Koji Noda 1 , Hisayoshi Fujikawa 1 Show Abstract
1 , Toyota CRDL., Inc., Aichi Japan
Organic light emitting diode (OLED) displays with thin-film barrier layers and plastic substrates are expected to find applications in next-generation wide-area flat-panel displays that are thin, lightweight, and flexible. Inorganic thin films created by a chemical vapor deposition (CVD) method have been regarded as being well suited to this application because they offer a high barrier performance, high transparency, and good coverage. Indeed, silicon nitride (SiNx) films have already been shown to be well suited to OLED barrier films. The transparent SiNx barrier films, which are usually applied to the light-emitting side of the flexible OLEDs, are fabricated by a plasma-CVD method with SiH4, NH3, and N2 gases at low substrate temperatures. In automotive applications, however, the barrier films are required to show high durability despite severe conditions including high temperatures and humidities. Unfortunately, under such conditions, the transparent SiNx barrier films, especially when they are deposited in high deposition rate over 100 nm/minute, are easily oxidized and the impermeability against vapor is getting worse. When SiNx films are deposited without NH3 gas, it is possible to suppress the oxidation by vapor, but the transparency falls down. To overcome this problem, we have developed a multi-layer structure consist of SiNx films in two different deposition conditions, that is, the transparent SiNx layer deposited with NH3 gas and the ultra-thin SiNx layer (cap-SiNx) deposited without NH3 gas which caps over the former layer. In this structure, the transparent SiNx layer, which is easily oxidized under high temperature and high humidity conditions, is not oxidized as a result of the investigation by fourier transform infrared spectrophotometer (FT-IR) analysis, because it is protected from vapor by the cap-SiNx layer. On the other hand, the transparency can be maintained because the opaque cap-SiNx layer is enough thin to be transparent to visible light. An important point of this structure is that the interface between the transparent SiNx layer and the cap-SiNx layer makes an important role in the high barrier performance. When another layer except SiNx films is inserted between them, the barrier performance deteriorates because the transparent SiNx layer is oxidized by the vapor through the pinholes in the cap-SiNx layer. Therefore, the interface is considered to work as the stopping point of the leakage through the pinholes in the multi-layer barrier film. Thus, the multi-layer SiNx film indicates the specific features as a high barrier performance and high transparency, and makes it possible to apply flexible OLED displays to automobile use.
12:45 PM - G1.10
Development of Amorphous Polymer as High FET Mobility Materials.
Takumi Yamaga 1 , Toshiya Sagisaka 1 , Yoshikazu Akiyama 1 Show Abstract
1 , RICOH CO. LTD., Yokohama Japan
The organic field-effect transistors (OFETs) are widely useful, because the films are easy to fabricate in large scale with low-cost by solution process. Although the characteristics of some OFETs have been intensively investigated, the materials such as polythiophenes used in the OFETs still have various problems. We synthesized stilbene polymers that consist of the triarylamine and phenylene-vinylene structure, and examined their OFETs properties. The OFETs are made on the glass or plastic substrate with bottom contact structure. The poly-paraxylylene film is deposited on gate electrode as a gate insulator. The source and drain electrode made of Au with the channel size of 140 um (W) x 10 um (L) are formed. The active layer consists of the stilbene polymer is fabricated by spin coating or Inkjet printing with using a 1wt% mesitylene solution. The OFETs shows the FET mobility of 0.007 cm^2/Vs by the low voltage operation as VG and VDS are –20V. The threshold voltage and on-off ratio are given nearly 0V and >10^5, respectively. The DC bias stress tests are performed for the OFETs under ambient air condition; there is nothing for some degradation. This results come from the material’s ionization potential of approximately 5.4eV. The transistor properties are improved by the addition of small molecules in the stilbene polymers. The OFETs showed the FET mobility of 0.02 cm^2/Vs with high stability. The family of stilbene polymers and those small molecule mixture systems has a potential to become promising candidate for printable OFETs’ material.
G2: Processing I
Monday PM, November 26, 2007
Fairfax A (Sheraton)
2:30 PM - **G2.1
A Novel Atmospheric Process for Metal Oxide Thin Film Transistors.
David Levy 1 , Diane Freeman 1 , Shelby Nelson 1 , Thomas Pawlik 1 , Peter Cowdery-Corvan 1 , Lyn Irving 1 Show Abstract
1 , Eastman Kodak, Rochester, New York, United States
3:00 PM - G2.2
Zinc Oxide and Related Compounds: From Materials to Devices.
Rodrigo Martins 1 , Pedro Barquinha 2 1 , Luis Pereira 2 1 , Goncalo Goncalves 2 1 , Elvira Fortunato 2 1 Show Abstract
1 CEMOP, Uninova, Caparica Portugal, 2 CENIMAT I3N, FCTUNL, CAPARICA Portugal
3:15 PM - G2.3
Mask- and Solvent-Free Vapor Phase Printing of High Efficiency White Organic Light Emitting Diodes.
Michael Arnold 1 , Gregory McGraw 1 , Richard Lunt 1 , Stephen Forrest 1 Show Abstract
1 , University of Michigan, Ann Arbor, Michigan, United States
We demonstrate the growth of phosphorescent, white organic light-emitting diodes (WOLEDs) directly patterned by organic-vapor jet printing (OVJP). In OVJP, a hot inert carrier gas transports organic small-molecules in the vapor phase through a narrow nozzle to a cooled substrate, resulting in the local condensation and spatially patterned growth of thin films. Feature sizes <25 μm, deposition rates of 25 Å cm(2)/s, and high material yields (>10%) are readily achieved without the use of shadow masks or the complications of liquid solvents. By picking up the vapor of different organic materials in parallel carrier gas streams and then mixing them in a long flow stream, the co-deposition of multiple species is possible. The mixture can be controlled by tuning the source temperature and carrier gas flow rates. Here, we present WOLEDs consisting of parallel stripes of red, green, and blue OLEDs composed of iridium-based phosphorescent dopants co-deposited with the hosts 1-3-bis(carbazol-9-yl)benzene (mCP) or 4-4'-bis(carbazol-9-yl)biphenyl (CBP). External quantum efficiencies comparable to those of single color devices grown by vacuum thermal evaporation are reported (~8.0 ±0.5% for tris[2-(2-pyridinyl)phenyl-C,N]-iridium (Ir(ppy)3) based devices, for example). The theory, simulation, and experimental results of this WOLED printing method are discussed.
3:30 PM - G2.4
Developing Materials Diversity in Transfer Printing for Flexible Electronics.
Daniel Hines 1 2 3 , Adrian Southard 3 4 , Andrew Tunnell 3 1 , Michael Fuhrer 3 4 , Ellen Williams 3 2 Show Abstract
1 Laboratory for Physical Sciences, University of Maryland, College Park, Maryland, United States, 2 NanoCenter, University of Maryland, College Park, Maryland, United States, 3 Dept. of Physics, University of Maryland, College Park, Maryland, United States, 4 Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States
The ability to use a wide variety of substrate, dielectric and semiconductor materials will be important in achieving the promise of flexible electronics. For fabrication using transfer printing, each new material combination requires establishing the conditions needed to achieve differential adhesion. Here we demonstrate successful transfer printing for a variety of flexible electronic devices using four different non-traditional semiconductors with variable substrate and dielectric materials. Pentacene (Pn) organic thin-film transistors (OTFT) with mobilities in the range of 0.2 cm2/Vs have been fabricated with both poly(methyl methacrylate) (PMMA) and poly(4-vinylphenol) (PVP) dielectric layers on polyethylene terephthalate (PET) substrates. Poly(3-hexylthiolphene) (P3HT) OTFTs with mobilities in the range of 0.03 cm2/Vs have also been fabricated with PMMA and polystyrene (PS) dielectric layers on PET substrates and with a polycarbonate (PC) dielectric layer on a PC substrate. The contact resistance of these printed devices is in the range 0.18 MΩ-cm, lower than the 0.56 MΩ-cm measured for devices on a SiO2 dielectric with normal evaporated top or bottom contacts. In addition, both carbon nanotube and graphene TFTs have been successfully fabricated with a PMMA dielectric layer on a PET substrate. The fabrication of these devices constitutes an important step toward illustrating the simplicity and flexibility of the transfer printing process. Additionally, we have successfully incorporated vias into the printing process, which will allow the transfer printing process to be extended to the fabrication of hybrid electronic circuits onto flexible substrates.
3:45 PM - G2.5
Large Area Carbon Nanotube Films.
Gregory Konesky 1 Show Abstract
1 , SGK Nanostructures, Inc., Hampton Bays, New York, United States
Carbon nanotube films can be used in a wide range of applications, from fuel cells and storage batteries, electron field emitters for displays, e-beam and x-ray sources, heat sinks, heat pipes and heat spreaders, and chemically robust filtering membranes.Present approaches to carbon nanotube film production rely on filtration of a suspension to the desired thickness. Creating this suspension, however, requires the use of toxic and hazardous reagents and lengthy processing times. Carbon nanotubes tend to attract each other through van der Waals forces, making them difficult to separate and disperse in solution. Once dispersed, the solution typically has a limited shelf life.We describe an approach of uniaxial die pressing that incorporates a sacrificial layer to prevent binding to the compression surfaces. Water, or other solvents, act as a release agent. No binder is used. The process is scalable in terms of film thickness and area. Electrical resistivity of the film can be used to monitor the compressive state of the film and typically exhibits three orders of magnitude decrease from the uncompressed powder state. Development of a roller-based extrusion process employing these principles for continuous film production is described.
4:30 PM - **G2.6
All Additive Printing of Flexible Backplanes for Large Area Displays.
Ana Arias 1 , Jurgen Daniel 1 , Brent Krusor 1 , Fred Endicott 1 , Alberto Salleo 2 , Robert Street 1 Show Abstract
1 , Palo Alto Research Center, Palo Alto, California, United States, 2 , Stanford University, Palo Alto, California, United States
5:00 PM - G2.7
Arrays of Organic Single Crystal Transistors Patterned from Solution.
Stefan Mannsfeld 1 , Armon Sharei 1 , Shuhong Liu 1 , Mark Roberts 1 , Jason Locklin 2 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Palo Alto, California, United States, 2 Department of Chemistry, University of Georgia, Athens, Georgia, United States
For microelectronic applications such as sensor arrays or small-scale displays, low-cost production techniques for organic field effect transistor devices are desirable. We recently reported a materials-general method of fabricating large arrays of patterned organic single crystals by physical the vapour-phase transport deposition technique . However, for some organic semiconductor materials, vapour-phase deposition is not producing satisfactory results. Here, we present a new patterning technique by which arrays of working field effect transistor devices based on organic single crystals can be produced by casting a molecular solution onto specially treated transistor device substrates. These transistor substrates comprise arrays of source-drain gold electrodes on rigid or flexible substrates with a chemically modified dielectric surface. Our patterning technique works by creating small droplets of the molecular solution within an immiscible host liquid into which the transistor substrate is submerged. After removal of the substrate, the molecular solution droplets wet the electrode areas exclusively and after evaporation of the solvent, organic crystals nucleate from these droplets completing arrays of single crystal OFET devices.
References: A. L. Briseno, S. C. B. Mannsfeld, M.M. Ling, R. J. Tseng, S.H. Liu, C. Reese, Y. Yang, F. Wudl, Z. Bao, “Patterning Organic Single-Crystal Transistor Arrays” Nature 444, 913-917 (2006).
5:15 PM - G2.8
Reliable and Cost-Effective Dispensing Technology for Large-Area Patterning.
Bo Li 1 , Patrick Clark 1 , Kenneth Church 1 Show Abstract
1 R&D, nScrypt Inc., Orlando, Florida, United States
5:30 PM - G2.9
Large Area Processing with Ink Jet Technology.
Michael Grove 1 , Don Hayes 1 , Virang Shah 1 Show Abstract
1 , MicroFab Technologies, Inc., Plano, Texas, United States
Patterning materials over large areas on flexible plastic substrates, or even rigid ones, where multiple layers of different materials are applied in order to create active devices brings with it the real challenge of accurate materials placement. The additive process of printing expensive materials reduces costs associated with the losses of subtractive processing, but focuses the technological necessity on the precision of materials alignments on target substrates. During this decade, both materials and their print processing have developed to a near commercial level for optical and electronic devices, and industrial success will be assured when their production enjoys the economies of scale that large area processing can bring.While large area processing usually brings plastic substrates' problem to mind, large glass panels used in LCDs are not completely rigid and need careful handling. As LCD fabs have gone to larger glass sizes, deletions that occur during screen print processing, which would normally mean loss of yield, are now recovered in some cases by ink jet printing the missing materials. Because of current ink jet production of large area billboard-size prints on plastic substrates, and multi-meter wide textile prints, especially on silk, it is reasonable to examine the application of ink jet printing to the manufacture of large area optical and electronic device panels, or rolls. Billboard printing and large area textile printing enjoy an advantage over electronic device manufacturing as in their case the inks are bing printed onto a blank surface while organic electronic or optical devices normally must be aligned with existing structures such as, for example, antennae for RFID devices. The technology to enable that, however, does exist.If the substrate is originally equipped with a set of fiducial marks, or is so imprinted during the placement of an initial device or feature such as an antenna, current precision optical inspection and recognition equipment can feed that data into an automated ink jet printing system even if the substrate has distorted in processing The critical section of that printing system, which is the array ink jet print heads and motion system, will need to be more sophisticated than the equipment that produces billboards and printed textiles. Array printheads were invented in the 1990s that, along with the necessary electronics, can operate each orifice independently of the rest and even precisely adjust the volume of ink in each and every drop to a different quantity. Real-time rotation of the printheads can correct for distortions. MicroFab Technologies has demonstrated these aspects of ink jet printing. Array printheads of the basic type have been in production for some years.
5:45 PM - G2.10
Toward Inkjet Printed Polymer Solar Cells.
K. Steirer 1 2 , Maikel Van Hest 1 , Reuben Collins 2 , David Ginley 1 Show Abstract
1 NCPV, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Applied Physics, Colorado School of Mines, Golden, Colorado, United States
Printed electronics are rapidly becoming a reality and potentially can revolutionize devices and circuits. Here we investigate the feasibility of inkjet printing a single organic contact layer and absorber layer for an organic photovoltaic device. Poly(3,4-ethylene dioxythiophene)-Poly(styrene sulfonate) (PEDOT:PSS), used as the effective electrode, is inkjet printed and analyzed via optical profilometry, microscopy and UV/VIS spectroscopy. The PEDOT:PSS layer is optimized by varying solution concentration, substrate temperature, drop spacing and contact angle. Printing of poly-(3-hexyl)-thiophene (P3HT), the organic absorber layer, has been investigated similarly and the results are reported. Further, we discuss a general approach outlining the basic principles of printing organic thin films from solution. This includes critical rheologic properties as well as film print quality, stable drop formation, contact angle and surface energy of the system.
G3: Poster Session I
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - G3.1
Processing Light-Emitting Dendrimers for Organic Light-Emitting Diodes.
Chih-Lei Chen 1 , Stuart Stevenson 2 , Ruth Harding 2 , Ifor Samuel 2 , Paul Burn 1 3 Show Abstract
1 Department of Chemistry, University of Oxford, Oxford United Kingdom, 2 Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews United Kingdom, 3 Centre for Organic Photonics and Electronics, University of Queensland, Brisbane, Queensland, Australia
Organic light-emitting materials are being intensively investigated for use in organic light-emitting diodes (OLEDs). The materials investigated fall into three main classes based on structure and processing, namely molecular, polymeric, and more recently dendrimeric.1 These materials can also be divided on the basis of emission process, that is, fluorescence or phosphorescence. Phosphorescent molecular emitters have led to a breakthrough in efficiency.2 However, the disadvantage of molecular materials is that they are processed by evaporation, making the patterning of large area displays very difficult. OLEDs based on solution-processed dendrimers comprised of phosphorescent cores, conjugated dendrons and surface groups can be very efficient.3 By using a modular approach to the preparation of the dendrimers it is possible to engineer the properties of these nanomaterials at the molecular level to optimise their performance. The dendrimers to be reported in this presentation have the light-emitting core providing the structural element to give three-dimensional nanoparticles. The dendrons then provide a rigid structural scaffold to control the intermolecular interactions of the light-emitting cores and the surface groups give rise to processibility of the dendrimers. We will report a study on the use of the surface groups to crosslink the dendrimers giving rise to insoluble dendrimer films and allowing multilayer structures to be made. We will describe the strategies for the synthesis of phosphorescent dendrimers with biphenyl and crosslinkable surface groups and show how we can understand the effect of the crosslinking process in these nanomaterials. Finally, we illustrate how dendrimers can be incorporated into multilayer devices.1. E. Holder, B. M. W. Langeveld, U. S. Schubert, Adv. Mater., 2005, 17, 1109.2. M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest, Nature, 1998, 395, 151.3. S.-C. Lo, N. A. H. Male, J. P. J. Markham, S. W. Magennis, O. V. Salata, I. D. W. Samuel, P. L. Burn, Adv. Mater., 2002, 14, 975.
9:00 PM - G3.10
Easily Synthesized Air-stable Naphthalenetetracarboxylic Diimide Semiconductors with High Electron Mobility.
Kevin See 1 , Alan Becknell 2 , Joseph Miragliotta 2 , Howard Katz 1 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 , JHU APL, Laurel, Maryland, United States
New naphthalenetetracarboxylic diimides (NTCDIs) were synthesized with excellent electron-carrying properties. Simple one-step procedures were utilized to synthesize a variety of n-channel materials. Vacuum-deposited thin films were employed as active materials in transistors, showing electron mobilities at or above .05 cm2/Vs and on/off ratios of 104 to 105. Two compounds, each with perfluoroalkylated N-benzyl substituents, show strong ordering by x-ray diffraction correlating with the high electron mobilities. Film morphologies were determined by atomic force microscopy or scanning electron microscopy. Mobilities and on/off ratios were maximized in part by varying the substrate temperatures during deposition. High substrate temperatures near 100 C were found to result in the most favorable morphologies and the highest mobilities, combined with excellent reliability. Additional strategies for enhancing the device performance were attempted, including self assembled monolayers on silicon dioxide insulators with both alkyl and perfluoroalkyl end groups to promote large grain growth of the fluorinated molecules. Another approach involved the use of polymer blends containing poly(3-hexylthiophene) and polypropylene as both an interfacial layer as well as the insulator itself. The goal was to utilize the polypropylene to reduce the hole mobility of the P3HT, resulting in a slightly electron donating layer as opposed to a hole-dominated transport layer.One derivative in particular, on which the fluorinated chain is separated by one benzene ring and three methylene groups, sheds some light on the function of the fluorinated chains in promoting the air stability of these n-channel compounds. Our results are consistent with the presence of the fluorinated moiety providing an inert barrier to water and oxygen that can potentially act as electron traps. Because of the remoteness of the fluoroalkyl group from the conjugated core, the effect cannot be resonance or electronic induction.Device parameters were corrected for contact resistance by fabricating devices with varying channel lengths on the same substrate using custom made shadow masks. Additionally, contact resistance can potentially be correlated to molecular structure as compounds with drastically different end chain lengths of 1 and 10 carbons were synthesized. In addition, the application of NTCDI derivative-based devices as chemical vapor sensors will be briefly discussed. NTCDIs functionalized with phenolic receptors that can chemically bond to analyte vapors were utilized in bilayer structures with well-characterized fluorinated semiconductors. The use of this receptor-functionalized semiconductor heterostructure enhanced the sensitivity of transistors relative to devices based on the fluorinated molecules alone.
9:00 PM - G3.12
Electro-fatigue Analysis of Dielectric Thin Films on Flexible Polymer Substrates.
Albert Pinyol 1 , Damien Gillieron 1 , Vinodh Mewani 1 , Yves Leterrier 1 , Jan-Anders Manson 1 Show Abstract
1 Composites and Polymers Technology Lab, Institute of Materials, Swiss Federal Institute of Technology - Lausanne (EPFL), Lausanne Switzerland
The development of flexible electronics demands an in-depth study of their mechanical integrity to avoid failure during manufacture and operational life. Most devices, including rollable thin-film solar cells and flexible displays, are polymer-based multilayer structures that comprise inorganic thin films such as SiNx, poly-Si and ITO . The objective of this work is to investigate the behavior of this class of layered composites under fatigue loading, which is greatly complicated due to the extreme thinness of the films of interest. To this end, a novel electro-fatigue method is presented, based on the fragmentation test . In this latter technique, a quasi-static tensile load is applied to the layered composite film in situ in an optical or electron microscope to provide an accurate determination of critical damage events. It is rather time consuming, and was recently adapted to enable simultaneous electrical measurement and damage detection, in case of conductive coatings . In the present work, the method is extended to the case of dielectric coatings with focus on 50 to 800 nm thick SiNx coatings on polyimide substrates, using an ultrathin conductive probe layer. A careful selection of the conductive probe layer was carried out to avoid artifacts resulting for instance from a change of the residual stress state of the investigated coating. The method was successfully calibrated using a conventional tensile frame and the best results were obtained using a 10 nm thick evaporated carbon layer. It was applied to a broad range of polymer substrates (PI, PET, PEN, ARILYTE) and dielectric thin films (SiNx, SiO2, Al2O3). It was found to be limited to polymers with a glass transition temperature higher than the temperature reached during carbon deposition, and to dielectric coatings with a thickness an order of magnitude larger than that of the carbon probe layer. An electro-fatigue set-up was eventually designed and constructed to enable automatic cycling testing of conductive and dielectric thin films on polymers, and preliminary results will be discussed. Detailed analysis of the onset of tensile damage reveal the existence of very long stable cracks in the brittle coating and a progressive transition towards unstable failure, that invalidates classic fracture mechanics models (ch. 6 in ). The consequence of this process is that sub-critical cracks may grow under fatigue loading until catastrophic failure, the details of which being essential for proper theoretical analysis . The present method should therefore be useful for accurate insight into critical processes that control the lifetime stability of flexible electronic devices. G.P. Crawford (ed) Flexible Flat Panel Displays, J. Wiley, Chichester (UK) 2005 Y. Leterrier, Prog. Mater. Sci. 55 (2003) 1 Y. Leterrier, et al, Thin Solid Films 460 (2004) 156 D.C. Cairns and G.P. Crawford, Proc. IEEE 93 (2005) 1451
9:00 PM - G3.13
MS2 (M = Mo, W) Thin Film Fabrications by Solution Processed Deposition via Spin Coating Techniques.
Wooseok Ki 1 , Jing Li 1 , Xiaoying Huang 1 , Yong Zhang 2 , David Young 2 Show Abstract
1 Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States, 2 , National Renewable Energy Lab, Golden, Colorado, United States
Soluble synthetic techniques have been widely used to fabricate thin films of inorganic materials, such as thin film transistors (TFTs) and photovoltaic solar cells, because of numerous desirable features, including low cost, large area and flexible devices. However, it has been a challenge to synthesize metal chalcogenide based thin films via solution processed depositions, due to the limitation of their solubility in organic solvents. Here we have successfully fabricated transition metal dichalcogenide (MS2, M = Mo, W) thin films by using new soluble precursors via spin coating techniques . The new soluble precursors, (CH3NH3)2MS4(M = Mo, W), were dissolved in organic solvents and spin coated onto substrates. After thermal decomposition, uniform and continuous MoS2 and WS2 thin films were formed with the thickness of ~70nm and ~50nm, respectively. Both organic solvents and spin coating sequences played an important role in surface morphology of the films which affected electrical properties. Electrical conductivity was largely improved when multi-step spin casting procedure was applied compared to single step spin casting. Structural, electrical, optical absorption, and transport properties of the thin films were characterized.  W. Ki, et al., J. Mater. Res., 22, 1390 (2007)
9:00 PM - G3.14
Mechanical Limitations of Materials for Steel Foil Based Flexible Electronics.
Po-Chin Kuo 1 , Jeff Spirko 1 , Ta-Ko Chuang 1 , Miltiadis Hatalis 1 Show Abstract
1 , Lehigh University, Bethlehem, Pennsylvania, United States
Thin steel foils have been successfully demonstrated as outstanding substrate materials for flexible electronics because of their high mechanical strength, flexibility, light weight and thermal stability. This work investigates mechanical limitations of thin film materials on steel foil substrates. We characterize a three layer structure consisting of 100μm thick stainless steel foil as the substrate, followed by 1μm thick spin-on-glass passivation layer and 0.3μm thick patterned aluminum interconnect layer on top with varying widths between 10- 35μm by means of a bending experiment. A collapsing radius test method was adopted for the bending experiment and an elliptical curve fit was used to facilitate the strain measurement. The failure strain of aluminum interconnect layer was detected by monitoring the continuity of the test circuit during the experiment. The corresponding results reveal that the passivation layer cracked at a tensile strain of 0.46% and delaminated at a compressive strain of 0.68%. The metal interconnect layer ruptured at a tension strain of 1.26% and delaminated from substrate at a compressive strain of 1.22% due to the delamination of the passivation layer underneath. We determined that the failure of the aluminum interconnect under tension was due to localized elongation caused by cracking of the passivation layer underneath and concluded that a wider interconnect could withstand a larger strain. The stainless steel foil plastically deformed at a relatively small strain of 0.13%; thus, the use of stainless steel with reversible bending capability for flexible electronics is mostly limited by the minimum elastic bending radius of the steel substrate. The flexibility of steel foil based devices can be effectively improved by decreasing the substrate thickness.
9:00 PM - G3.15
High Performance Lateral Laser-crystallized Polycrystalline Si1-xGex Thin Film.
Hsing-Hua Wu 1 , Po-Tsun Liu 2 , Chao-Chun Wang 1 Show Abstract
1 , Department of Photonics & Institute of Electro-Optical Engineering, Hsin-chu Taiwan, 2 , Department of Photonics & Display Institute, Hsin-chu Taiwan
9:00 PM - G3.16
Ink-jet Printable Hybrid Dielectric Materials for Organic Thin Film Transistors.
Sunho Jeong 1 , Dongjo Kim 1 , Seong Hui Lee 1 , Jooho Moon 1 Show Abstract
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
Using a thermally-crosslinkable organosiloxane-based organic-inorganic hybrid material, an ink-jet printable gate dielectric layer for organic thin-film transistors (OTFTs) has been developed. The dielectric inks were composed of the sol-gel derived hybrid precursors. Ink compositions were carefully controlled to ensure a stable jetting behavior. Non-uniform deposition of the dielectric layer after solvent evaporation, so-called coffee-ring effect, can be prevented by utilizing the mixed solvent system. 1-propanol was incorporated as a main solvent to disperse hybrid precursors, and ethylene glycol and 2-methoxyethanol were added as a high-boiling-point solvent and high-contact angle solvent, respectively. The current–voltage characteristic and capacitance–voltage characteristics were measured to investigate the electrical property of the ink-jet printed hybrid dielectric. To fabricate coplanar-type flexible OTFTs, the hybrid dielectric layer was printed on the Au/Cr/polyimide substrate, followed by deposition of Au/Cr source/drain electrodes through a shadow mask. Either α,ω-dihexylquaterthiophene or soluble pentacene was then drop-cast. An electrical performance of the fabricated transistors was measured to obtain electrical parameters such as on-off ratio, mobility, and threshold voltage, and the relationship between the electrical parameters of the device and process variables for ink-jet printing the dielectrics was analyzed.
9:00 PM - G3.17
PMN-PT Thick Film Structures Prepared by Electrophoretic Deposition.
Danjela Kuscer 1 , Marija Kosec 1 , Janez Holc 1 Show Abstract
1 Electronics Ceramics Department, Jozef Stefan Institute, Ljubljana Slovenia
Perovskite PMN-PT materials exhibit a high dielectric constant, good piezoelectric properties and can be used in electro-optical devices, multilayer capacitors, sensors and actuators. In order to use it for electronic applications, it is necessary to downsize the final device. To achieve this, the active material has to be miniaturized and integrated into the substrate. The electrophoretic deposition has been shown as a successful method for the preparation of integrated ceramic films on and substrate with thicknesses from few microns to few milimeters. In order to obtain a high-quality deposit with homogeneous microstructure, it is necessary to control the properties of the powder, the properties of the suspensions as well as the sintering conditions.The mechanochemical synthesis has been shown as a successful method for the synthesis of nano-sized powders with high-degree of chemical homogeneity. We have synthesised the lead-magnesium-niobate–lead-titanate (PMN-PT) perovskite powder with the composition close to morphotropic phase boundary using high-energy milling. The stoichiometric mixture of the constituent oxides has been milled in a planetary high-energy mill up to 64 hours at ball-impact energy of 560 mJ/hit. The milling parameters were based on the model proposed by Burgio et all (1) and calculated by Rojac et all (2). The milled powder prepared after 64 hours of milling consists of PMN-PT crystalline phase with the particle size up to 30 nm in a matrix of amorphous phase. The ethanol-based suspension was prepared from the PMN-PT powder high-energy milled for 64 hours by using electro-steric stabilization. Zeta potential and viscosity of the suspension were measured as a function of type and amount of additives to determine the suspension with the optimal properties. The deposition process was performed from the optimized suspension at a constant voltage. PMN-PT was deposited on platinized alumina substrate at typical deposition time of few minutes. After the deposition, the green deposit was dried and fired at temperatures between 850 and 1000 oC in atmosphere with different partial pressure of PbO. The phase composition and the microstructure of sintered thick-film structures were characterised by X-ray powder diffraction analysis and scanning electron microscopy. We have found out that at optimised sintering conditions the single-phase PMN-PT layers with a thickness of 20 to 40 micrometers have been obtained. The thick-film structures are dense with high-degree of chemically homogeneity. The functional propertis of the sintered thick-films prepared by electrophoretic deposition has been measured and compared to the results obtained on the films prepared by screen-printed method.1.N. Burgio et all, Il Nuovo cimento, 13(4),(1991), 459-476. 2.T.Rojac et all, J.Eur.ceram.Soc., 26 (2006), 3711-16.
9:00 PM - G3.18
Effect of Thermal Treatment Conditions on Microstructure, Electrical and Mechanical Properties of Inkjet-Printed Ag and Cu Interconnects.
Soo-Hong Choi 1 , Jung-Kyu Jung 1 , Inyoung Kim 2 , Hyun Chul Jung 2 , Jaewoo Joung 2 , 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)
Interest in use of inkjet printing for pattern-on-demand fabrication of metal interconnects without complicated and wasteful lithographic or etching processes has been on rapid increase. It is because of numerous advantages of inkjet printing including low cost, environmental-friendliness, and so on. However, inkjet printing is a wet process and an additional thermal treatment, i.e., a drying process is necessary. Since a metal ink is a suspension containing metal nanoparticles and organic capping molecules to prevent aggregation of them, the microstructure of an inkjet-printed metal interconnect ‘as dried’ can be characterized as a stack of loosely packed nanoparticles. Therefore, during being treated thermally, an inkjet-printed interconnect is likely to evolve a characteristic microstructure, different from that of the conventionally vacuum-deposited metal films and that of sintered metal powders. Since microstructure characteristics of an interconnect affects significantly the corresponding electrical and mechanical properties, the optimal conditions for thermal treatment including drying and annealing should be established. In this light, we have characterized the microstructure, electrical and mechanical properties of the inkjet-printed Ag and Cu interconnects. Our results show that the characteristics of microstructure evolution depend heavily on both temperature and time of thermal treatment. Furthermore, evolution of microstructure was observed only after the decomposition of the capping molecules. The electrical resistivity of inkjet-printed metal interconnects as dried was very high, e.g. about two orders of magnitude larger than that of the bulk Ag or Cu. Decrease in electrical resistivity of which magnitude and rate depended on both annealing temperature and time was able to be described using the exponential decay relationship. This suggests that point defects in the metal nanoparticles, such as vacancies, are critical for the electrical performance of the inkjet-printed metal interconnects. We will show that the effect of ambient, e.g. under oxygen atmosphere, on electrical resistivity characteristics can be understood in this respect. The mechanical properties such as adhesion strength at the interface between inkjet-printed metal and substrate material were dependent on the conditions of thermal treatment as well. A four-point bending test method was used to measure the adhesion strength. In specimens as dried, cohesive fracture was observed due to weak bonding between metal nanoparticles. However, there was significant increase in the adhesion strength after annealing treatment. The effect of annealing temperature on adhesion strength will be discussed in terms of point-defect migration as well. Based on these results, the requirements for thermal treatments to obtain the optimal electrical and mechanical properties of inkjet-printed Ag and Cu interconnects will be suggested and discussed.
9:00 PM - G3.19
Electrical and Optical Properties of High Mobility W-doped In2O3 Thin Films.
Ram Gupta 1 , K. Ghosh 1 , S. Mishra 2 , P. Kahol 1 Show Abstract
1 Physics, Astronomy and Materials Science, Missouri State University, Springfield, Missouri, United States, 2 physics, university of memphis, memphis, Tennessee, United States
Transparent conducting oxides (TCO) have been widely used for opto-electronic devices such as light emitting diodes, photo-detectors, touch panels, flat panel displays, and solar cells. Low resistivity, high mobility, and good transparency are the prime requirements for these devices. There is an increasing interest in TCO with high mobility to decrease their electrical resistivity without a significant decrease in the optical transparency. Highly conducting and transparent tungsten doped indium oxide thin films were deposited on quartz substrate by ablating the sintered In2O3 target containing WO3 with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). The effect of growth temperature and oxygen pressure on structural, optical, and electrical properties has been studied. The transparency of the films largely depends on the growth temperature. The electrical properties are found to depend strongly on the growth temperature as well as on oxygen pressure. The temperature dependence resistivity measurement shows the transition from semiconductor to metallic behavior as the growth temperature increases from room temperature to 500 C. The high mobility (up to 358 cm2V-1s-1), low resistivity (1.1 × 10-4 Ω.cm), and relatively high transmittance of ~90 % have been observed on the optimized film grown at 500 C and under oxygen pressure at 1 × 10-6 bar.
9:00 PM - G3.2
High-Performance Scan-Type Stage for Large Substrates.
Ohno Takashi 1 , Azuma Kazufumi 1 Show Abstract
1 , Advanced LCD Technologies Development Center Co.,Ltd, Yokohama Japan
Due to the steady increase in substrate sizes for low-temperature poly-Si devices and LSIs, there are strong demands for larger substrate handling, more accurate positioning and shorter tact time for many processes such as laser crystallization scan exposure, and dopant activation and so on. In order to satisfy such demands, we have developed a high-performance scan-type stage for large substrates. In this paper, we describe the outline of the mechanical structure and also the performance of this stage.The XY moving stage was installed on an air slider of planarized granite. Stroke sizes of the stage were more than 920 mm and 730 mm for scan and step directions, respectively; the stage size was matched to the large glass substrates (4th generation). The stroke in the vertical direction was more than 32 mm, and the stage could rotate for more than ±0.3 degree for alignment. The stage is driven by a newly introduced shaft-type linear motor, which consists of a fixed stainless-steel pipe shaft and a moving cylindrical coil rounded around the shaft. There are thin annular permanent magnets stacked inside the shaft. Since this coaxially aligned structure of permanent magnets and the coil is a nearly ideal configuration for efficient magnetic coupling, this motor could generate a stronger driving force; this enabled rapid acceleration and deceleration of the stage. Since stacked magnets generate parallel and uniform magnetic field along the shaft surface but slight field for transverse direction, electromagnetic force slightly fluctuated along the shaft, independent of the pitch of the magnet plate. This introduced another important advantage of the shaft-type linear motor that cogging, which has a serious impact on processing, was almost eliminated. This fluctuation was further reduced by introducing a real-time feedback system. The shaft-type motor, however, had been said to have the serious difficulty of elongation since its own weight bends the shaft. This problem was solved by using new magnetic materials and an optimized design of physical dimensions of the motor.Experiments have been conducted under stabilized temperature conditions. The maximum scan speed of the stage was more than 500 mm/s with a speed stability of 0.03%, about one order of magnitude better than the reported value of about 0.5%. Acceleration and deceleration times from the halt condition to the constant velocity condition and vise versa were 1.0 s; the scan time was as short as 1.8 s for a 920 mm stroke. The straight extent was always better than ±0.5 μmProjection optics is commercially available for shaping a 30-mm-long excimer laser light beam on a sample surface. If we combine this stage and such optics, the whole area of a 4th-generation substrate surface can be scanned within a little more than 1 minute; that is, extremely high throughput can be expected. For example, to grow arrays of large Si grains, two-dimensional position control is the most important subject.
9:00 PM - G3.3
Fabrication of Transparent Thin Film Transistors using Amorphous Active InGaZnO4.
Woo-Seok Cheong 1 , Chi-Sun Hwang 1 , Sang-Hee Ko Park 1 , Jaeheon Shin 1 , Chun-Won Byun 1 , Doo-Hee Cho 1 , Minki Ryu 1 , Shinhyuk Yang 1 , Sung Min Yoon 1 , Jeong-Ik Lee 1 , Hye Yong Chu 1 , Kyoung Ik Cho 1 Show Abstract
1 , Electronics Telecommunications Research & Institute, Daejeon Korea (the Republic of)
Transparent thin-film transistors (TTFTs) were fabricated using amorphous indium-gallium-zinc oxides (a-IGZO), where a-IGZO acts as a semiconductor active layer. Among deposition methods, sputter system has advantages such as low temperature process and large area. In this study, for optimizing amorphous active films we used simple inverted coplanar device structure, which could be simplely fabricated and be less dependent on the earlier or later processes. The a-IGZO films were made diffrently under the condition of different gas ratios (oxygen/oxygen+argon), working pressures, and rf plasma powers. The microstructures of films and devices were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), FIB (focused ion beam) scanning electron microscopy (SEM) and atomic force microscopy (AFM). Under the room temperature, all the film structures were definetly amorphous, independent upon rf plama powers, gas ratios, and working pressures. The values of film surface roughness (Rrms) were ranged from 0.17 ~ 0.42nm at the 100nm thickness, and the optical transmittances at 550nm were around 80% or higher for most films. The active channel widths of our electronic devices changed from 2.0 to 80.0 μm at the specified gate length (5, 10, 20, 40, 80 μm). The electrode was made by indeum tin oxide(ITO) and ALD grown Al2O3(170nm) was used for the gate insulator. From the various a-IGZO deposition conditions we could find the optimized one, which was positioned in the middle range of rf power, gas ratio, and working pressure. Current-voltage (I-V) properties measured through the gate showed that Ion/Ioff ratio was more over than 106.
9:00 PM - G3.4
Characteristics of Flash Lamp Annealing of Polysilicon Films on Transparent Substrates and Application to Thin-Film Transistors.
Atsushi Sasaki 1 , Daisuke Iga 1 , Tetsuya Ide 1 , Katsunori Mitsuhashi 1 Show Abstract
1 , Advanced LCD Technologies Development Center Co., Ltd., Yokohama Japan
1. Introduction Activation annealing in the polysilicon thin-film transistor (TFT) fabrication process is currently performed using a furnace. There are, however, problems associated with furnace annealing of large-area glass substrates; specifically, it is difficult to increase the dimensions of the equipment, the glass substrate is distorted by the thermal load, and heat treatment requires a long process time. Flash lamp annealing (FLA) has the potential to overcome these problems, since it possesses three useful characteristics. First, the area irradiated by a FLA system can be enlarged by increasing the number of the flash lamps. Second, the irradiation time of FLA is of the order of milliseconds, ensuring that the heating is localized near the glass substrate surface, and thus reducing the thermal deformation of glass substrates. Third, the total thermal processing time by flash lamps is very short, so high throughputs are anticipated. However, most previous studies of FLA have investigated crystalline-Si, and there have been relatively few studies that have reported on FLA of polysilicon. In this study, we report the activation characteristics of polysilicon films on quartz substrates and the application for TFT.2. Experimental The FLA system used in this study consisted of a process chamber and five flash lamps filled with Xe gas. The samples were fabricated on quartz substrates. The polysilicon films were 100 nm in thickness, were crystallized by excimer laser annealing and were implanted using P+or BF2+ ions. The samples were coated with a 450-nm-thick SiO2 film and a 200-nm-thick molybdenum alloy film. The molybdenum alloy film was used to heat the polysilicon film and it was heated by absorbing the flashlight; it was removed after FLA.3. Results and Discussion The sheet resistances of the polysilicon films annealed by FLA at the peak temperature of 1043°C were 240 Ω/sq. for P and 503 Ω/sq. for B. The resistances were nearly the same as the furnace annealing at 600°C for 2 hours. Because glass substrates had low thermal conductivity, the heating of FLA was efficiently localized near the glass substrate surface. Thus, FLA for glass substrates needs not preheating and so the processing time was within 1 minute per wafer. Therefore, The throughputs of FLA would be higher than that of furnace anneal. The high throughputs of FLA are useful for the annealing of large area glass substrates. The TFTs using FLA for the activation annealing had a gate width of 2 µm and a gate length of 0.5 µm. The P-type TFTs had a mobility of 46 cm2/Vs, a subthreshold slope of 157 mV/decade, while the N-type TFTs had a mobility of 114 cm2/Vs and a subthreshold slope of 209 mV/decade. 4. Conclusion FLA, compared to the furnace annealing at 600°C for 2 hours, has nearly equal thermal processability and higher throughputs. Thus, FLA is better suited for thermal treatment of large area glass substrates than furnace anneal.
9:00 PM - G3.5
Nano Glass-based Ink-jet Printable Adhesive for Direct Writing Conductive Patterns on Glass/ceramic Substrate.
Daehwan Jang 1 , Dongjo Kim 1 , Jooho Moon 1 Show Abstract
1 , Yonsei University , Seoul Korea (the Republic of)
A drop-on-demand ink-jet printer has been used in the production of conductive metal tracks onto various substrates such as glass, polyimide, polytetrafluoroethylene, and alumina substrates. However most of the commercially available silver-based conductive inks are designed for printed electronics on plastic substrate. The printed films well adhere to the substrate with an aid of the polymeric additives added in the conductive inks. When it comes to the use of glass and/or ceramic substrates that requires higher annealing temperatures above 400°C, the polymeric additives no longer exist to promote the film adhesion due to their pyrolysis. Furthermore the metal nanoparticles could be over-sintered and the metal granular films undergo a significant volumetric shrinkage, which may induce crack and/or delamination defects. In this regard, we need the ink-jet printable adhesive materials that can work at higher temperatures. We have developed nanosized glass frit-based additives that can be readily mixed with the water-based conductive ink without disturbing the ink and jetting stabilities. For direct-writing the conductive interconnector/electrode on the glass substrate at 550°C, we have determined proper particle characteristics of the glass frit in which the particle size is ~ 150 nm and a glass transition temperature is 525 °C. We have also prepared well-dispersed nano glass frit-based additive suspensions by adjusting the dispersants and solvent systems. By adding a proper amount of the glass frit-based additive, we have prepared the conductive patterns that well-adhere to the glass substrate after the heat-treatment of 550°C. The glass frit added film is still very conductive and its resistivity is <10μcm. SEM cross-sectional image shows that the glass frit sufficiently melt during the annealing to glue the granular film with the glass substrate. Adhesion strengths of the films are tested according to ASTM D3359 (standard test methods for measuring adhesion by tape testing).
9:00 PM - G3.6
Electrostatic Force Directed Integration of Nanomaterials.
Chad Barry 1 , Jesse Cole 1 , Xinyu Wang 1 , Heiko Jacobs 1 Show Abstract
1 Electrical Engineering, University of Minnesota, Minneapolis, Minnesota, United States
This talk focuses on the development of new tools to direct the assembly of nanomaterials onto predefined locations on a substrate. The assembly strategy is based on patterned surfaces and uses electrostatic forces as the driving mechanism. This work has led to several gas phase nanoparticle integration processes. We expect these processes to work with any material that can be charged. The processes offer self-aligned integration and could be applied to any nanomaterial device requiring site specific assembly. The Coulomb force process directs the assembly of nanoparticles onto charged surface areas with sub-100 nm resolution. The charging is accomplished using flexible nanostructured stamps. Gas phase assembly systems are used to direct and monitor the assembly of nanoparticles onto the charge patterns with a lateral resolution of 50 nm. The fringing field process focuses the assembly of nanoparticles into pre-fabricated openings on a substrate. The fringing fields can be confined to sub 50 nm sized areas and exceed 1 MV/m, acting as nanolenses. Gas phase assembly systems have been used to deposit silicon, germanium, metallic, and organic nanoparticles. These printed nanoparticles act as catalysts for nanowire growth, can be focused and annealed to form conducting interconnects, and are utilized as a precursor for device fabrication.
9:00 PM - G3.7
Poly(bithiophene) from Melt Processed Poly(bithienylsilanes)using Solid-state Oxidative Conversion.
Jia Choi 1 , Gerald Ling 1 , Montgomery Shaw 1 2 , Gregory Sotzing 1 3 Show Abstract
1 Polymer Program, University of Connecticut, Storrs, Connecticut, United States, 2 Chemical Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 Chemistry, University of Connecticut, Storrs, Connecticut, United States
9:00 PM - G3.8
Flexible Organic Light-emitting Diodes with Highly Conductive Polymeric Electrodes and Their Stress Tolerance.
Yutaka Ohmori 1 , Hirotake Kajii 1 , Yasuhiro Sekimoto 1 , Yasuhiro Shigeno 2 , Naoya Takehara 2 , Hiroshi Nakagawa 2 Show Abstract
1 Ctr for Adv Sci & Innov (CASI), Osaka University, Suita, Osaka, Japan, 2 , Hosiden Corp, Yao, Osaka, Japan
Organic light emitting devices (OLEDs) have attracted considerable interest because of their advantages in flexible display. Recently, electrodes fabricated from conducting polymers and metal nano-particles have been developed, and attracted considerable attention for their simple and low-cost solution processes. In this presentation, we discuss fabrication and characteristics of flexible OLEDs with highly conductive polymeric electrodes as an anode and their stress tolerance of the devices fabricated on polymeric substrates. Fabrication and characteristics of OLEDs with highly conductive poly(ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) as an anode have been investigated. The typical device consists of an PEDOT:PSS coated substrate, methoxy-substituted 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB) hole injection layer, 4,4’-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (a-NPD) hole transporting layer, and tris(8-hydroxquinoline) aluminum (Alq3) emissive layer, terminated with a LiF/Al/Ag cathode. Emission patterns of OLEDs with highly conductive PEDOT:PSS, PEDOT:PSS with 4nm-ITO electrode and PEDOT:PSS with hole injection layer have been compared. A hole injection layer of TDAPB was spun over the PEDOT:PSS-coated substrate. The surface emission pattern of an OLED with high conductive PEDOT:PSS with 4nm-ITO electrode as an anode improved, compared with only highly conductive PEDOT:PSS electrode. By inserting the hole injection layer between PEDOT:PSS anode and hole transport layer, the emission pattern and device performance was improved. In the case of the OLED with PEDOT:PSS with hole injection layer, a maximum luminance of more than 10,000 cd/m2 and a current efficiency of more than 3 cd/A have been obtained. Pushing tolerance tests were performed for OLEDs fabricated on polymeric substrates. In the case of the devices fabricated on ITO-coated polymeric substrate, the emission intensity decreased with increasing the number of impact. One of the reasons for the decrease of the emission intensity comes from the destruction of the ITO electrode by the impacts. For an ITO electrode, the star like dark part increased with the number of the impact. While, for the PEDOT:PSS electrode, the device continued to emit light after a pushing test consisting of more than 60,000 steps without the damage of the transparent electrode.
9:00 PM - G3.9
Specialty High Performance Coatings for Optical Fiber Applications via Perfluorocyclobutyl (PFCB) Aryl Ether Polymers.
Stephen Budy 1 3 , Scott Iacono 1 3 , Wade Hawkins 2 3 , Paul Foy 2 3 , John Ballato 2 3 , Dennis Smith 1 3 Show Abstract
1 Chemistry, Clemson University, Clemson, South Carolina, United States, 3 Center for Optical Materials Science and Technologies (COMSET), Clemson University, Anderson, South Carolina, United States, 2 School of Materials Science & Engineering, Clemson University, Clemson, South Carolina, United States
Vladimir Bulovic Massachusetts Institute of Technology
Seth Coe-Sullivan QD Vision, Inc.
Ioannis (John) Kymissis Columbia University
John Rogers University of Illinois, Urbana-Champaign
Max Shtein University of Michigan
Takao Someya University of Tokyo
G4: Processing II
Tuesday AM, November 27, 2007
Fairfax A (Sheraton)
9:00 AM - **G4.1
Low Cost Methods for Fabricating OLEDs.
Hak Fei Poon , Don Foust 1 , Martin Yan 1 , Anil Duggal 1 Show Abstract
, 1 , GE Global Research, Niskayuna, New York, United States
9:30 AM - **G4.2
Carbon Nanotube Network, a New Electronic Material.
George Gruner 1 Show Abstract
1 Physics and Astronomy, University of California-Los Angeles, Los Angeles, California, United States
A random, two dimensional network formed of electrically conducting nanoscale wires, called carbon nanotubes - a carbon Nanonet - is a transparent electronic material, that can be fabricated using room temperature processes. Networks with both metallic and semiconducting attributes can be fabricated, and display high conductivity, high carrier mobility and optical transparency, together with mechanical flexibility, robustness and environmental resistance. Application opportunities include touch screens, solar cells and light emitting diodes; proof-of-concept devices have been fabricated to demonstrate performance. Transistors, with Nanonet conducting channels have also been made with performance characteristics exceeding that of polymer/organic devices. These applications require patterned films, with feature sizes at different length scales. I will discuss and compare the various patterning methods that range from laser ablation through plasma etching to shadow masking and transfer printing.
10:00 AM - G4.3
Polymer Solar Cells with a High-level of Structural Control Fabricated Using a Novel Spray Coating Deposition Technique.
Claudio Girotto 1 2 , David Cheyns 1 2 , Hans Gommans 1 , Barry Rand 1 , Tom Aernouts 1 , Jef Poortmans 1 , Paul Heremans 1 2 Show Abstract
1 Polymer and Molecular Electronics, IMEC vzw, Leuven Belgium, 2 ESAT, Katholieke Universiteit Leuven, Leuven Belgium
Molecular-based solar cells have the potential to provide low-cost energy production on lightweight and flexible substrates. Organic solar cells are either produced by solution processing of polymers or evaporation of small molecules. In the first case, spin coating is considered the most reliable and reproducible method, but is limited to small areas. To realize large-area coverage, various deposition techniques, such as ink-jet and screen or gravure printing, have been proposed and demonstrated. Here, we present a simple method for the deposition of large area devices based upon spray coating, and show that this method is a valid alternative to other techniques.Spray coating is a technique that is well established in graphic arts, industrial coatings, and painting. This high-rate, large-area deposition technique ensures an ideal coating on a variety of surfaces with different morphologies and topographies, and is often used in inline productions. Moreover, the fluid waste is reduced to minimal quantities.To justify the usefulness of this technique, we compared a standard spin coated solar cell based on a mixture of poly(3-hexyl thiophene) (P3HT) and the C60-derivative (6,6)-phenyl C61-butyric acid methyl ester (PCBM) with a spray coated one, where the P3HT:PCBM blend was sprayed by a N2-powered airbrush. Spray coated solar cells were found to have power conversion efficiencies above 2%, a performance which is comparable to that of the spin coated devices.We also performed atomic force microscopy, ellipsometry and absorption measurements to compare the film quality of the two techniques. Significantly, we found that the spray coating technique allows for the demonstration of polymer solar cells with distinct layers, owing to the differences in the kinetics of the solvent evaporation process when compared to other solution based techniques. The small femto-liter scale droplet size intrinsic to the spray-coating technique means that thin films can dry very rapidly, and subsequent films can be deposited despite a common solvent. In the case of techniques that use at least nano-liter scale solutions, (i.e. spin coating and inkjet printing) this process would have the undesired effect of dissolving the underlying layers. This finding also has important consequences for polymer-based light emitting devices, particularly for white light emission, where having multilayered structures is advantageous for high-efficiency devices.We investigated different methods of spray coating, from single-pass to multiple-passes, and varied the concentration of the solutions, in order to optimize the technique, and looked into the effects of thermal annealing to the layers. Then we analyzed the relation between the performance of the devices and the characteristics of the films obtained from the two different depositions techniques to show that spray coating is an excellent alternative to spin coating for the fabrication of large area polymer-based devices.
10:15 AM - G4.4
Patterning Submicron Features on Flexible Plastic Substrates by Optical Lithography.
Maria Peter 1 , Wim de Laat 2 , Peter Giesen 1 , Cheng-Qun Gui 2 , Erwin Meinders 1 Show Abstract
1 , Holst Centre/TNO - Netherlands Organisation for Applied Scientific Research, Eindhoven Netherlands, 2 Special Applications, ASML Netherlands B.V., Veldhoven Netherlands
The ‘System-in-Foil’ program line of the recently established open innovation research centre, the Holst Centre (NL), together with its partners invests large efforts to develop plastic electronics on non-conventional, thin plastic flexible substrates. Optical lithography is one of the technology approaches in the program line “Lithography on Flexible Substrates” to pattern sub-micron features on polymeric substrates. The main challenge is to cope with dimensional stability of flexible substrates, such as the in-plane and flatness tolerances. The technology finds application in all kinds of high-performance flexible products, such as sensor arrays, organic transistors, organic memories and lighting devices. Imaging experiments on 100 micron thick PEN (Dupont Teijin Films) foils were performed with a PAS 5500/100 ASML stepper (i-line 365 nm) equipped with standard reticles having features of sub-micrometer dimensions. Material properties, such as wetting, mechanical deformations, heat expansion, swelling, and moisture uptake of the PEN foil were thoroughly investigated to improve the photolithographic processing. Most of the mechanical properties were studied on a novel in-house built mechanical tester, which allows the detection of in-plane deformations with accuracy below 1 micrometer. The used PEN foil showed a contact angle of 63° with water. Commercially available photoresists could therefore be used for the imaging experiments without the need for a surface pre-functionalization. To overcome handling problems and to assure a good surface flatness (below 5 micrometer) during processing the foils were reversibly glued onto a solid carrier (i.e. 6 inch Si wafers). The optimum process window for sub-micrometer critical dimensions was determined by performing a Focus Exposure Matrix (FEM) experiment in which the energy and focus were increased stepwise. After developing, the samples were coated with a thin gold layer and characterized by Scanning Electron Microscopy (SEM). The optimum imaging conditions were derived from the SEM analysis. In the full paper, we will address several topics related to the developed technology, such as imaging challenges, wafer flatness measurement, substrate deformation and quality of the patterned features (with respect to homogeneity, interface interaction, etc.). In addition, we will show our first demonstrators made with the developed technology, among others the dual detection (DUDE) DNA sensor on PEN foil.
10:30 AM - G4.5
Photolithographic Patterning of Organic Light-Emitting Diode Displays Using an Electron-Injection-Enhancing Protecting Layer.
Feng-Yu Tsai 1 , Chih-Yu Chang 1 , Syue-Jhao Jhuo 1 Show Abstract
1 Materials Science and Engineering, National Taiwan University , Taipei Taiwan
This study demonstrated organic light-emitting diode (OLED) displays that showed improved performance after the electroluminescent (EL) layer was patterned with a standard photolithographic process, which included photo-resist coating, exposure, development, wet etching, and photo-resist stripping. The EL layer, made of poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), was protected during the patterning process with a 1-nm-thick Al2O3 layer formed by atomic layer deposition (ALD), which was not removed after patterning but instead became sandwiched between the EL layer and a subsequently added cathode. Thanks to the excellent surface coverage of ALD, the ALD Al2O3 layer, despite being ultra thin, was able to keep the EL layer and the underlying structure intact throughout the patterning process. Although insulating, the Al2O3 layer's small thickness allowed it to enhance injection of electrons from the cathode to the EL layer, as is consistent with previously reported mechanisms. This enhancement of electron injection in conjunction with a hole-blocking effect of the Al2O3 layer resulted in significantly reduced turn-on voltage (by ~16%) and increased luminous efficiency (by ~120%) compared with unpatterned displays. This result is in contrast with those of related previous studies where the performance of displays was often compromised upon patterning. The technique reported in this study enables standard photolithographic processes to be directly applicable to the fabrication of patterned OLED displays. The inherent capability of ALD for uniform large-area, large-batch deposition at low temperatures will render this technique attractive for practical applications.
10:45 AM - G4.6
Dry Photolithographic Micropatterning Technique for Organic Electronic Devices.
Alexander Zakhidov 1 , Ha Soo Hwang 1 , John DeFranco 1 , Hon Hang Fong 1 , Jin-kyun Lee 1 , Xavier Andre 1 , Christopher Ober 1 , George Malliaras 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
Cost-effective, reliable, scalable micropatterning process is essential for modern organic electronics. All said benefits are inherent to photolithography - micropatterning technique used in the mature and entrenched industry of silicon processing. However due to incompatibilities between chemicals used in photolithography and the vast majority of organics, photolithography have not made a high impact in the field. We propose new dry photolithography micropatterning approach which is chemically fully compatible with majority of organic electronic materials. In this approach a random copolymer, composed of 1H,1H,2H,2H– Perfluoro decyl Methacrylate (FDMA) and tert-Butyl Methacrylate (TBMA) were prepared as negative type photoresist for patterning of organic material utilizing supercritical carbon dioxide. Supercritical carbon dioxide is environmental friendly development media with low viscosity and high diffusivity which does not damage active organic material. Another advantage of this media is the absence of pattern collapse in high aspect ratio sub-micrometer features and possibility of creating extremely high resolution patterning due to absence of phase separation. As a proof of a concept we used proposed technique to successfully demonstrate micropatterned organic light emission diodes.
11:30 AM - **G4.7
Active-Matrix OLED’s with High-Lifetime Amorphous Silicon Transistors on Clear Plastic Substrates.
James Sturm 1 Show Abstract
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Active-matrix OLED displays using amorphous silicon (a-Si) thin film transistors (TFT’s) are very attractive because of the large-scale industrial infrastructure for producing low-cost amorphous silicon backplanes. Traditional drawbacks of a-Si for AMOLED’s include low drive current, poor TFT stability (especially for low-temperature TFT processes on plastic), and the lack of a p-channel device. The drive-current issue becomes less important as OLED efficiencies increase, especially with phosphorescent devices. Clear plastic flexible substrates have traditionally limited a-Si TFT’s in one of two ways. First, substrates with low glass transition temperatures and or high thermal expansion characteristics, such as PEN or PET, have limited the a-Si TFT process temperatures to 200 oC or less. This severely degrades the TFT threshold voltage stability, due to the poor quality of the gate dielectric. The shifting threshold voltage affects the pixel brightness and/or color balance, unless more complex circuits which reduce aperture are used. Second, the lack of a p-channel TFT combined with a conventional “anode first” OLED gives a pixel where the translation of data voltage to OLED current undesirably depends on the OLED voltage, further degrading stability and substantially raising the data programming voltages. In this talk, we present novel clear plastic substrates that can be processed at 300 oC, and that combine the properties of high glass transition temperature, low thermal expansion coefficient (under 10 ppm/oC), and high transmission across visible wavelengths. We show how they can be used to make stable AMOLED active matrix test arrays. For example, raising the process temperature from 200 to near 300 oC leads to ~1000X increase in the overall pixel stability. We also demonstrate a novel method to connect the top OLED cathode to the drive TFT’s on an individual pixel level, so that the circuit limitations of n-channel TFT’s are removed – typical drive currents (microamp) can be achieved at 5V data voltage instead of 15 V. The authors thank the DuPont Company and Universal Display Corporation for collaboration and the US Display Consortium for financial support.
12:00 PM - G4.8
Sub-Micron Resolution Jet Printing Method Based on Electrohydrodynamics
Jang-Ung Park 1 , John Rogers 1 Show Abstract
1 , UIUC, Urbana, Illinois, United States
Research directed toward classes of printing techniques that have their origins in the graphic arts, such as ink jet printing, flexography, and others, for applications biotechnology, microelectromechanics, and electronics have grown rapidly in recent years. This talk describes the use of an electrohydrodynamic jet printing method in which ultrafine nozzles and optimized voltage sequences combine to enable direct, sub-micron patterning resolution. Printing of various material inks, including biomaterials (DNA, protein), suspensions of single walled carbon nanotubes / nanoparticles, and solutions of conducting / insulating polymers, demonstrates some of the features of this method. Simple devices, such as transistors that use aligned arrays of single walled carbon nanotubes and biochips that use spotted arrays of DNA and various proteins, illustrate several of its potential areas of application.
12:15 PM - G4.9
Precise Pixel Patterning and Fabrication of High-Resolution OLEDs via Spin Casting.
Jonghwa Jeong 1 , Debra Mascaro 2 Show Abstract
1 Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States, 2 Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah, United States
Organic light-emitting devices (OLEDs) are being pursued as low-cost alternatives for numerous display applications, including full-color displays and microdisplays. However, the development of low-cost and large-area patterning techniques for organic materials remains a significant research challenge. Organic luminescent materials such as tris(8-hydroxyquinoline) aluminum (Alq3) are most often deposited by thermal evaporation through a shadow mask, which limits pattern resolution and precision. In this research, we demonstrate precisely patterned micron-scale OLED pixels by spin casting. This solution-based patterning technique exploits segregation of the organic molecules into microfabricated wells, and is applicable to fabrication of large-area displays. The single emissive layer is a mixture of Alq3 as the electron transport material and N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) as the hole transport material, yielding typical green Alq3 electroluminescence. Insulating micro-wells are fabricated in SiO2 using standard microfabrication techniques. The SiO2 is deposited onto glass/ITO (bottom-emitting structure) or Si/SiO2/Ag (top-emitting structure) substrates. The wells range in width from 10 μm to 100 μm and in depth from 100 nm to 500 nm. Prior to Alq3/TPD spin-casting, the substrates are treated with octadecyltrichlorosilane (OTS) in order to inhibit adsorption of organic molecules, yielding selective deposition in the wells. In some devices, poly(3,4-ethylendioxythiophene)-poly(styrenesulfonate) (PEDOT) is spin-cast on the substrate to improve device performance by enhancing hole injection and the quality of the anode/organic interface. After patterning the Alq3/TPD pixels, LiF/Al (bottom-emitting structure) or LiF/Al/Ag (top-emitting structure) is deposited as the cathode. In this presentation, we will discuss the electrical and optical properties of the patterned OLEDs, and the extension of the fabrication technique to passive-matrix OLED displays. In summary, we have demonstrated a novel, solution-based patterning technique for fabricating high-resolution OLED pixels for large-area, low-cost display applications.
12:30 PM - G4.10
Electrical and Structural Properties of Laser-crystallized Polycrystalline SiGe Thin Films.
Moshe Weizman 1 , Lars Scheller 1 , Norbert Nickel 1 , Ina Sieber 1 , Baojie Yan 2 Show Abstract
1 , Hahn-Meitner-Institut Berlin, Berlin Germany, 2 , United Solar Ovonic Corporation, Troy, Michigan, United States
12:45 PM - G4.11
Development of a Novel Electrical Pulse Annealing Method for Si/SiGe Heterostructures Fabricated on Flexible Kapton Substrates.
Paothep Pichanusakorn 1 , Prabhakar Bandaru 1 Show Abstract
1 Material Science, University of California, San Diego, La Jolla, California, United States
The processing of thin films deposited at low temperature on flexible/plastic substrate, for electronics and optical device application, is temperature-limited due to the nature of the substrate. Techniques such as laser pulse annealing and rapid thermal annealing (RTA) have been developed to address the crystallization of thin films. However, laser annealing is localized, and difficult to adapt for macro-scale processing. RTA, on the other hand, is associated with structural instability. To circumvent both these disadvantages, we have developed a novel electrical pulse annealing technique, which allows for individual tailoring of device characteristic, and is also applicable for large area, back-end processing. We will present results on annealing of Si/SiGe hetero structures deposited at various temperatures (room temperature to 400°C) on flexible substrates, e.g. Kapton. By inducing electrical pulses in the device structure, we cause local joule heating in the overlayers while minimizing the effect on the substrate. The electrical pulse induces an instantaneous temperature change, providing energy for crystallization, and producing a drastic 40-fold decrease in the electrical resistance. Parameters such as pulse amplitude, width, and duty cycle were varied to tune the heating rate and annealing zones in the material. Comparison of resistance change brought about by pulse annealing with that due to conventional oven heating indicates an increase of at least 200°C of local temperature, due to electrical pulses. Consequently, our technique can be used in concert with conventional heating. For example, oven heating the material to 350°C, and subsequently employing our pulse technique, one could induce crystallization of SiGe films, which is known to occur at 550°C. The electrical pulse annealing method that we have developed could be superior to techniques such as laser, and flash thermal processing, in terms of allowing for lower density of lattice defects, and avoiding dopant metastability
G5: Integrated Processes I
Tuesday PM, November 27, 2007
Fairfax A (Sheraton)
2:30 PM - **G5.1
Solution Processed Organic Thin Film Transistors.
Thomas Jackson 1 Show Abstract
1 Department of Electrical Engineering, Center for Thin Film Devices, and Materials Research Institute, Penn State University, University Park, Pennsylvania, United States
Many large area electronic device applications will be cost sensitive and solution-deposited organic semiconductors can offer important advantages for low-cost processing. However, solution processed semiconductors often lack the molecular-level order important for good carrier transport and large field-effect transistor mobility. Working with J. Anthony (University of Kentucky) we have investigated functionalized pentacenes and related materials that can provide both solution processiblity and good molecular ordering. Solution deposited films of several of these materials show strong molecular ordering and good electronic transport. Using triisopropylsilylethynyl (TIPS) pentacene films deposited by drop casting we have fabricated organic thin film transistors (OTFTs) with mobility >1.5 cm2/Vs and simple circuits including ring oscillators. Using fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (F-TES-ADT) films deposited by simple spin casting we have fabricated OTFTs with mobility >1 cm2/Vs. Spin cast F-TES-ADT films display differential microstructure on or surface features with varying surface energy. The differential microstructure results in variations in mobility of about a factor of 100 and may be useful for low cost device fabrication. Using self-assembled monolayer treated electrodes that encourage large well-ordered F-TES-ADT grains, we have fabricated spin-cast OTFTs with mobility that increases with decreasing gate length and spin-cast circuits including ring oscillators and frequency dividers on both glass and polymeric substrates with propagation delay <5 μsec/stage. Solution-processed organic semiconductors also allow printing or other non-conventional approaches for material patterning. Using TIPS-pentacene and F-TES-ADT we have used surface energy modification to demonstrate non-relief pattern lithography (no photoresist used) at the few micron resolution scale, including organic semiconductor patterning for OTFTs and simple circuits.
3:00 PM - G5.2
Organic Light Emitting Transistors using a Vertical Structure.
Ken-ichi Nakayama 1 , Daisuke Kimijima 1 , Yong-Jin Pu 1 , Junji Kido 1 , Masaaki Yokoyama 2 Show Abstract
1 , Yamagata University, Yonezawa, Yamagata, Japan, 2 , Osaka University, Suita, Osaka, Japan
The vertical-type organic transistor is a promising device structure that can make the channel length much shorter, leading to low voltage operation and high frequency response. Recently, we have reported a high performance vertical transistor having a simple layered structure composed of organic/metal/organic layers. This device was named a metal-base organic transistor (MBOT), because the inserted middle electrode behaves like a base layer in the bipolar transistors. So far, MBOTs achieved very high current density modulation exceeding 100 mA/cm2 with low voltage operation of several volts.The sandwich structure of the MBOT is very compatible with the organic light-emitting diodes (OLEDs). In this paper, we report a novel type of organic light emitting transistors (OLETs) by means of inserting emissive and transporting materials into the collector semiconductor layer of the MBOT. Many researches on the OLETs have been reported since the first report in 2003. However, most of them are based on the conventional field-effect transistor (FET) structure. Therefore, they inevitably require a large area fine patterning for display application, and high driving voltage because of its long channel length around 10 microns. On the other hand, OLETs using vertical-type MBOT structure realizes simple fabrication process like shadow-mask deposition and large area emission like OLEDs, furthermore, low voltage operation because of its short channel length.The device was fabricated by vacuum deposition. Firstly, OLED layers composed of CuPc/NPD/Alq3 was deposited. Here, an exciton blocking layer of BCP was inserted. Then, the MBOT layers were deposited, the collector layer of perylenetetracarboxylic derivatives (Me-PTC), and the base electrode of aluminum (20nm), the emitter layer of C60 (80nm), and the emitter electrode of Ag (30nm). The final device structure was ITO(C)/CuPc/NPD/Alq3/BCP/Me-PTC/Al(B)/C60/Ag(E).The inserted OLED layers did not prevent the current modulation of the MBOT. The fabricated device showed current modulation around 140 mA/cm2 for base voltage change from 0 V to 1.7V under a constant emitter-collector voltage of 16 V. In addition, a light emission modulation around 170 cd/m2 was observed simultaneously. This emission was attributed to the recombination between injected holes from the collector electrode and the electrons injected from the emitter and transmitted through the base electrode. The current efficiency as an OLED device was still lower than the standard OLED device using the same material. However, it was enough high performance compared to the reported OLETs using FET structure.
3:15 PM - G5.3
Solution-processible Multilayer Phosphorescent PLED Based on Crosslinkable Copolymer Structures.
Silvia Janietz 1 , Hartmut Krueger 1 , Manuel Thesen 1 , Bert Fischer 1 , Armin Wedel 1 Show Abstract
1 Polymer Electronics, FhG-IAP, Potsdam, Brandenburg, Germany
The application of polymer based light emitting devices is very attractive for the preparation of large area and fine-pixel displays. In this case the polymers are of great interest as they are more amenable to the solution processing techniques such as spin coating and printing that could be used for low cost production over large areas. In OLEDs, high quantum efficiencies were obtained, when small, molecular phosphorescent emitters such as iridium complexes were used. The utilization of small organic molecules leads to high performance OLEDs with long lifetime, because multilayer structures could be realized by evaporation techniques. In the case of polymers normally the transport molecules and the phosphorescent complex were blended in a polymer matrix for example PVK or directly attached to a non-conjugated polymer backbone like polystyrene. In such devices the injection and the transport of charges take place in this layer; this could be a critical point. One way to solve this problem could be the separation of the transport layers from the emitting layer like in an OLED based on small molecules. Normally it is not possible to implement multilayers with polymers by solution processing. The introduction of crosslinkable groups on a polymer backbone allows the forming of a network and it becomes insoluble. Copolymers or terpolymers were synthesized which contain additionally molecules with crosslinkable groups in the side chain These newly synthesized copolymers were applied as hole transport layers in the device. The layers are crosslinked after thermal treatment. A second layer could be deposit consisting of copolymers with covalently attached electron-transport and phosphorescent molecules with red, green and blue emission to the polystyrene backbone. Therefore different Ir–complexes and tert.-butylphenyl-5-biphenyl-1, 3, 4-oxadiazole (TBPO) as electron- transport units were selected as components for this polymer based phosphorescent systems. These components were functionalized with styrene groups through multistep organic synthesis. As polymerisation process a radical polymerisation was chosen in THF/DMF and with AIBN as initiator. Several copolymers were synthesized with sufficient high molecular weights and film forming properties. The composition of the copolymers is verified to optimize the device parameters. PLEDs were fabricated with this two layer system and characterized. The relationship between the composition of the two polymer layers and the achieved PLED device parameters will be discussed in detail. The achieved performance is comparable with blend systems.
3:30 PM - G5.4
Electroluminescent Devices from Ionic Transition Metal Complexes for Large Area Displays and Lighting Applications.
Jason Slinker 1 , John DeFranco 1 , Jose Moran-Mirabal 2 , Daniel Bernards 1 , Hector Abruna 3 , Harold Craighead 2 , George Malliaras 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Ionic transition metal complexes (iTMCs) are receiving increased attention as solution-processible materials capable of yielding efficient electroluminescent devices with air-stable electrodes. Here we discuss the potential of integrating iTMCs with display and lighting technology. We have fabricated efficient iTMC devices with laminated electrodes, indicating potential for reel-to-reel processing. We have also demonstrated monolithic and scalable lighting panels from iTMCs. Formed from a single, unpatterned iTMC layer, these panels show intrinsic fault tolerance and operation with dc and ac voltages, even accommodating line power at 120 volts and 60 hertz. Finally, we discuss light-emitting nanofibers from iTMCs formed by electrospinning. Electrospinning enables rapid and direct deposition of mirco- and nanoscale emitters, demonstrating great promise for high-resolution displays.
4:15 PM - **G5.5
Micron-sized, Fine Metal Patterning on Unsupported Flexible Plastic Substrates, the First Step Towards Roll-to-roll Manufacturing of Flexible Large Area Electronics.
Mark Poliks 1 2 , Bahgat Sammakia 2 , Hao Zhang 2 , Peter Moschak 1 , Christopher Chase 2 Show Abstract
1 Research & Development, Endicott Interconnect Technologies, Inc, Endicott, New York, United States, 2 Center for Advanced Microelectronics Manufacturing, Binghamton University, Binghamton, New York, United States
Roll-to-roll electronics manufacturing techniques may eventually lead to continuous production of high quality, flexible, thin film devices at significant cost reduction. This revolutionary approach will enable both ubiquitous and disposable electronic devices. The goal of the Center of Advanced Microelectronic Manufacturing (CAMM) is to develop electronic fabrication tooling and processes to use unsupported flexible polymeric substrates in a roll-to-roll format. As part of setting up the Center of Advanced Microelectronics Manufacturing, we fabricated micron-sized copper and aluminum circuit patterns on poly(ethyleneterephthalate) (PET) substrates by adapting conventional batch processes. For example, 125 µm (5 mil) thick heat stabilized PET polyester (DuPont-Tejin Films Melinex ST507) film was IPA and oxygen plasma cleaned followed by sputtering of 50Å chrome and 3000 Å copper at Endicott Interconnect Technologies (EI). RHEM Shipley 1813, SPR 220 or LC-100 positive photo resists were coated to 1.5 to 3.0 micron thickness on PET substrates, with or without a sputtered copper or aluminum conducting layer, using both spin coating of single pieces or web die-slot coating of PET rolls as long as 1000 feet. Die-slot coating was performed at Frontier Industrial in Towanda, PA. The wavelength of exposure for these resists was 365 nm. The exposure energy was varied. Aqueous TMAH, KOH or NaOH solutions were used for resist development. The resist stripping process was evaluated by using aqueous alkaline solutions, 1-methyl-2-pyrrolidinone or AZ-300T. The smallest feature size produced on unsupported PET substrates was 3 μm lines and spaces. These processes are being scaled-up for roll-to-roll fabrication in support of testing a web based photolithography tool (Azores Corporation) and developer (Hollmuller-Siegmund, ME Baker and Northfield Automation) at the CAMM facility. The Cornell CNF was used to fabricate photolithography masks and to test various processes using test coupons. The Binghamton University based S3IP Analytical Lab was used to characterize the patterned substrates. Recently, C. J. Zhong  and his group have fabricated gold microelectrode devices on glass substrates to explore the use of thin film coatings of monolayer-capped nanoparticles for chemical sensors (volatile organic compound sensing), medical diagnostics and other microelectronic applications. Here we attempt to fabricate copper microelectrode devices using unsupported poly(ethyleneterephthalate) (PET) substrates for use in these low-cost, disposable chemical sensor applications. References1. Wang, L; Zhong, C. J; et al, “Sensing Arrays Constructed from Nanoparticle Thin Films and Interdigitated Microelectrodes”; Sensors, 6, 667-679 (2006). 2. http://camm.binghamton.edu/
4:45 PM - G5.6
Near-Room-Temperature Processed Integrated Metal Oxide Field Effect Transistors for Large Area Electronics.
Annie Wang 1 , Kyungbum Ryu 1 , James Perkins 1 , Ivan Nausieda 1 , Burag Yaglioglu 1 , Vladimir Bulovic 1 , Charles Sodini 1 , Akintunde Akinwande 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
5:00 PM - G5.7
Pulsed Current Annealing Of Lithographically Defined Nano-Crystalline Si Nanowires for Low-Temperature High-Speed Roll-To-Roll Crystallization.
Ali Gokirmak 1 , Nathan Henry 2 , Helena Silva 1 Show Abstract
1 Electrical and Computer Engineering , University of Connecticut, Storrs, Connecticut, United States, 2 , Michigan Technological University, Houghton, Michigan, United States
Achieving defect-free crystalline Si at low temperatures on large areas in a variety of substrates has been attracting significant interest in recent years. We have developed an electrical pulse annealing technique for crystallization of lithographically defined nano-cystaline and/or amorphous Si nanowires.This technique is demonstrated by depositing a thin layer (~ 75 nm) of highly-doped nanocrystalline Si film using a low pressure chemical vapor deposition (LPCVD) process on thick thermally grown silicon oxide on Si substrates. The wires widths in the order of 0.25 μm and large contact pads are patterned using optical lithography and etched using reactive ion etching (RIE). The wire pads are contacted directly with tungsten probes and resistivity change after electrical pulse stressing is measured. The wires are observed under SEM.Our observations show that pulse annealing of few um long wires with pulses in the order of 30-40 V, 1 μs, with current levels of ~ 1 mA/wire results in rapid melting and recrystallization. Preliminary results indicate that two single crystal Si domains are formed along the wire using this process. The melting and recrystallization process causes the wires to acquire a cylindrical shape (from the initial ribbon-like shape) possibly due to surface tension. The wires shape can be left as flat ribbons with extremely smooth surfaces depending on the pulse conditions and the length of the wires which suggests a slightly different mechanism. A significant asymmetry is observed in the melting process which is attributed to significant thermoelectric effects during the pulse period.This process can be economically realized by connecting a large number of devices in parallel and scanning probes with DC biases for roll-to-roll processing. In this approach a pulse will be generated as one of the probes get into and out of contact with the metal contact for an array of wires. The pulse duration will be determined by the metal contact widths and the rate of rolling. We propose electrical pulsing as a low-cost, high-speed, low-temperature processing technique to integrate defect free crystalline Si and other semiconducting materials for large variety of substrates including glass and plastics. Details of the process and the observations and possible approaches for implementation of this process for large scale industrial production will be discussed.
5:15 PM - G5.8
Printing of Semiconductor Bare Die Using a Laser Transfer Technique.
Alberto Pique 1 , Nick Charipar 1 , Ray Auyeung 1 , Tom Sutto 1 , Heungsoo Kim 1 , Scott Mathews 2 Show Abstract
1 Code 6364, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Electrical Engineering, The Catholic University of America, Washington, District of Columbia, United States
Laser forward transfer processes such as laser direct-write (LDW) allow the transfer and embedding of unpackaged patterned semiconductor bare die into flexible substrates. With LDW it is possible to release individual devices from a carrier substrate and transfer them inside a pocket or recess in a receiving substrate using a single UV laser pulse, thus per-forming the same function as pick-and-place tools. However, conventional pick-and-place systems are not able to handle small (< 0.5 mm2) and thin (< 100 micrometers) components, across large area substrates. At the Naval Research Laboratory, we have demonstrated the laser printing of patterned bare die devices of sizes ranging from 0.1 to > 5 mm2 with thicknesses down to 10 microns and with high placement accuracy onto a variety of substrates. Once the devices have been transferred, the same LDW system is then used to print the metal patterns required to interconnect each device. The use of this technique is ideally suited for the integration of dissimilar microelectronic and optical components on flexible substrates. Furthermore, since it is a digitally driven process, the overall circuit design and layout can easily be modified or adapted to a given application or specific form factor. This presentation will show how the LDW process can be used as an effective laser die transfer tool for printing circuits on flexible substrates and describe the analysis of the laser-driven release process as applied to various types of silicon bare dice.This work was supported by the Office of Naval Research.
5:30 PM - G5.9
Line-Scan SLS of Prepatterned Amorphous and Polycrystalline Si films.
Mitsuhiro Toyoda 1 , Gabriel Ganot 1 , Ui-Jin Chung 1 , Adrian Chitu 1 , Paul Van der Wilt 1 , Alexander Limanov 1 , James Im 1 Show Abstract
1 Applied Physics & Applied Mathematics, Columbia University, New York, New York, United States
Melt-mediated crystallization of prepatterned Si films represents an established route for manipulating the microstructure of the films. Typically, solidification of strategically patterned Si films has been performed to obtain large-grained or single-crystal regions for producing high performance devices. In contrast to such investigations, this paper proposes -- and evaluates the applicability of -- crystallizing prepatterned Si films with the primary aim of improving the apparent uniformity of resulting transistors. Specifically, we have performed directional SLS (sequential lateral solidification) of prepatterned Si films as a way of ultimately delivering high-mobility/high-uniformity devices that are desired for producing AMLCDs, AMOLED displays, and 3D integrated circuits. Previous investigations have demonstrated that directional SLS can produce high-mobility-enabling Si films that, however, are recently found to contain physically distinct regions with varying densities of planar defects and/or crystallographic orientations; we presently view such microstructural details, which are apparently quite innate to the method, as the main reason behind these high-mobility transistors exhibiting relatively poor device uniformity. By physically confining such a microstructurally distinct region within a narrow stripe of Si and by placing a multiple number of such stripes within the active channel region of a device, the approach proposed in this paper can potentially substantially improve the apparent uniformity of the devices (without affecting the high-mobility character that arises from the directionally solidified microstructure).Experimentally, the samples consisted of approximately 100-nm-thinck Si films that were formed (via PECVD or solution-printing) on SiO2-coated glass substrates and Si wafers. The SLS system consisted of an excimer laser (308 nm wavelength, 30 nsec pulse duration), projection optics, and precision translation stage. Si stripes (tens of nm to tens of um in width) were formed via a photolithography, nano-imprint, or ink-jet printing method. Characterization of the irradiated stripes using SEM, AFM, and TEM reveals that the stripes can indeed be SLS processed, so long as the widths are in the order of a few microns or larger; at smaller widths, enhanced mass flow proceeding at the outer edges was found to lead to agglomeration of the stripes. For such narrow stripes, oxide capping was found to morphologically stabilize the stripes and prevent dewetting from taking place during SLS. We will discuss how the method can potentially be implemented without any additional steps and how the concept may also be applicable to rapid-ZMR of Si films using cw-lasers.
5:45 PM - G5.10
Flipchip Bonding of Si Chip on Flexible PEN Foil using Novel Electronic 100 µm Pitch Fan-out Circuitry.
Jeroen Brand 1 , Erik Veninga 2 , Andreas Dietzel 1 Show Abstract
1 , TNO/Holst Centre, Eindhoven Netherlands, 2 , TNO, Eindhoven Netherlands
The ‘System-in-Foil’ program line of the recently established open innovation research institute the Holst Centre (NL) aims at developing plastic electronics on low cost, flexible polymeric substrates. The technology that is being developed finds application in all kind of flexible products, like sensor arrays and flexible OLED lighting devices. Ultimately, in-foil-systems should be fabricated using reel-to reel (R2R) technology. An important topic in the research program is the development of interconnection technologies for low cost, flexible foils. In our research we currently develop processes for flexible PEN (poly(ethylene)naphthalate) foil substrates. As compared to polyimide, this material is cheaper but it has a lower temperature stability. This makes the interconnection technologies challenging. The successful bonding of a 50 µm thick test chip with an interconnection pitch of 100 µm on a 100 µm thick PEN foil (Dupont Teijin Films) will be presented. The electrical connection with the circuitry was made using a low temperature curing anisotropic conductive adhesive (ACA). The electrical fan-out circuitry itself was fabricated by means of a novel method which involves the use of polymer thick film materials. The involved processes and materials will be discussed and obtained results will be shown for a fan-out circuitry with a pitch of 100 µm and a line width of 50 µm. The technique is newly developed and has clear potential to go to finer pitches. As compared to existing technologies the method has the advantages that it is R2R compatible and that low cost circuitry can be made while still having highly conductive lines. For protection of the package, a covering PEN foil was laminated on top using an UV curing adhesive. This whole package was evaluated with respect to its electrical and mechanical performance.
G6: Poster Session II
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - G6.1
Fabrication of Conductive Polymeric Arrays using Direct Laser Interference micro/nano Patterning.
Andres Lasagni 1 , Diego Acevedo 2 , Cesar Barbero 2 , Frank Muecklich 1 Show Abstract
1 Materials Science, Saarland University, Saarbruecken, Saarland, Germany, 2 Departamento de Química, Universidad de Río Cuarto, Río Cuarto, Córdoba, Argentina
9:00 PM - G6.10
Electroluminescent Properties of a Solution Processable Carbazole-Substituted Iridium(III) Complex.
Noriaki Iguchi 1 , Yong-Jin Pu 1 , Ken-Ichi Nakayama 1 , Junji Kido 1 Show Abstract
1 Organic Device Engineering, Yamagata University, Yonezawa, Yamagata, Japan
A solution processable phosphorescent dendrimer, BCz-Ir(PPy)3, contaning phenylpyridine ligands with carbazole subsutituents was synthesized and evaluated as an emitter material in OLED. In the single layer devices, PEDOT: PSS was used as the hole injection layer. BCz-Ir(PPy)3 as an emitting layer was spin-coated on the PEDOT layer. In the bilayer devices, on the top of the emitting layer, bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine (B3PYMPM) was vacuum deposited as an electron transport layer. Finally, an electron injection layer, LiF, and Al cathode were vacuum deposited sequentially. OLED devices with BCz-Ir(PPy)3 exhibited green emission at 513 nm. The device having an electron transport layer, B3PYMPM, exhibited lower driving voltages compared with the single layer device. The barrier height of the bilayer device from the cathode to the emitting layer, BCz-Ir(PPy)3, was reduced by 0.7 eV by the electron transport layer, B3PYMPM, and B3PYMPM also acts as a hole blocking layer due to its large ionization potential. The bilayer device exhibited high external quantum efficiency of 9.2% and power efficiency of 31 lm/W at 4.0 V and at luminance of 100 cd/m2.
9:00 PM - G6.11
Electrospun Electrochromic Core-Shell Nanofibers.
Muge Acik 1 , Ki-Ryong Lee 1 , Gregory Sotzing 1 Show Abstract
1 Department of Chemistry and Polymer Program, University of Connecticut, Storrs, Connecticut, United States
Previously, we have demonstrated the ability of polythiophene nanofibers prepared via electrospinning of a polymeric precursor to have electrochromic switching capability. Herein we describe the preparation of core-shell nanofibers consisting of a polythiophene core and polyethylene oxide shell via two fluid electrospinning. Furthermore, we will report on our attempts of inversing this geometry having polythiophene as the shell in an effort to have isolated electrochromic switching fiber. More specifically, we have utilized a precursor polymer, poly[(norbornylene-3-terthiophene(30%)-co-norbornyleneacetate-(70%)] [poly(Nb3T-co-NbAc)] and poly(ethylene oxide) (PEO) as two polymers for this study. The primary application purpose of the PEO will be to serve as the polyelectrolyte. THF/DMF (70/30 v/v) was the solvent choice for poly(Nb3T-co-NbAc) and chloroform for PEO for electrospinning. The core-shell fiber dimension was altered by varying electrospinning conditions such as voltage, current, flow rate and distance. Morphologies of the resulting fibers were investigated.
9:00 PM - G6.12
Self-assembly of Nanoparticles into Sub-100 nm Complex Structures through Distortion–assisted Soft Lithography.
Ying Zhang 1 , Jason Reed 3 , Anna Peter 1 , Randy Kaimen 2 , Jay Kikkawa 2 , Shu Yang 1 Show Abstract
1 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Physics & Astronomy, Univeristy of Pennsylvania, Philadelphia, Pennsylvania, United States
In order to harness the unique magnetic, optical and plasmonic properties of inorganic nanoparticles for advanced technology applications, patterning of the nanoparticles in desired 2D or 3D arrays is crucial. By combining convective assembly of nanoparticle colloids with an elastic instability of on a microstructured PDMS membrane during swelling, we self-assemble nanoparticles (e.g. magnetic Fe3O4 and Ag) into complex 2D structures with periodicity ranging from sub-100nm to microns over an area of cm2. By controlling the amount of distortion, we can tune the pattern shapes from circular to ellipsoidal to spear-like. By taking advantage of soft lithography, we can “print” the complex nanoparticle structures onto flat and curved substrates. Theory has been developed to quantitatively explain the pattern formation as well as to test the device performance.
9:00 PM - G6.13
Optical and Electrochemical Properties of an Electrochromic Window Based on PProDOT-Me2 and CeO2-TiO2 Films.
Soo Yeun Kim 1 2 , Minoru Taya 2 1 , Chunye Xu 2 Show Abstract
1 Materials Science and Engineering, University of Washington, seattle, Washington, United States, 2 Mechanical Engineering, University of Washington, seattle, Washington, United States
9:00 PM - G6.14
Conducting Polymers from Processable Silane and Siloxane based Precursors.
Jayesh Bokria 1 , Ki-Ryong Lee 1 , Arlene Tran 1 , Gregory Sotzing 1 Show Abstract
1 Chemistry and Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Of the various thiophene-based conjugated polymers (CPs),poly(3,4-ethylenedioxythiophene) (PEDOT) has received the most attention mainly because of its enhanced stability both in the conductive and insulating states, along with ease of doping, high visible transmissivity in the oxidized form, and high conductivity. Bayer introduced a processable version of PEDOT, Baytron P®, where EDOT was polymerized in the presence of a polymeric counterion, poly(styrene sulfonate) (PSS). This material found commercial application as an optically transparent conductor, low ESR capacitors, and as a hole transport layer in organic light emitting diodes to name a few. However, the counter-ion was limited to PSS, and its strong acidic nature poses several issues such device stability and multilayer device construction where the second layer could be acid sensitive. Herein, we will present a precursor methodology to obtain PEDOT from precursors that, like commercial commodity polymers, can be processed via the vast range of techniques available to the industry. These silane or siloxane based EDOT precursor polymers can be processed as films or patterns on various substrates, and can then be converted in a single step into PEDOT with the retention of its solid state structure. Furthermore, we will also demonstrate that the processed precursors convert into PEDOT simply by exposing to bromine vapor, followed by mild heat. Oxidation peak of the EDOT containing silane precursor polymer was observed at 1.2 V(vs. Ag/Ag+) and this varied very slightly depending on the precursor system, and upon complete conversion, PEDOT redox was observed via cyclic voltammetry and matched the redox behavior for traditionally electropolymerized PEDOT. Optical data obtained from the precursor processed either on a conductive or insulating substrate, and then converted by the several techniques, vide supra, also indicated formation of PEDOT with band gap agreeing with literature reported values. Conductivities of PEDOT obtained from the solid-state conversion of silicon containing precursor polymers were measured to be 20 S/cm.
9:00 PM - G6.15
Large Scale Electrochemical Nanoimpriting Using Solid-state Superionic Stamping.
Anil Kumar 1 Show Abstract
1 ECE, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Nanoscale pattern design finds applications in electronics, photonics, MEMS, and biological and chemical sensors. A plethora of techniques are utilized depending on the application, cost and ease of use. Most of them are capable of generating nanosize features on small area but the cost and complexity of fabricating structures on large area increases dramatically. We recently reported a new nanoimprinting technique called solid state superionic stamping (S4) , which involves a solid superionic conductor to electrochemically etch patterns into metallic films, and has fundamental advantages compared to currently available techniques. To extend this work further, and to overcome the limit of most fabrication techniques of patterning very small areas, we report application of S4 for large area fabrication. The basic idea is to create a relatively small mold and repeatedly emboss it to pattern large area substrates. Preparing a large pattern on the stamps, using, for example, an FIB, is a very expensive and time consuming process. Here, we use a small master pattern fabricated using electron beam lithography and emboss it on a silver sulfide stamp, the solid state superionic conductor responsible for ionic transport during electrochemical etching. Silver patterns are then etched from a thin film by connecting the stamp and film to an external circuit as reported earlier .In our preliminary work, we used 50 nm thick gold structures in the shape of bowties with gap of 20 nm between the triangle tips. Excellent pattern transfer was achieved onto the silver sulfide stamp during embossing. The stamps prepared in this fashion are then used exactly as the ones fabricated with FIB, as demonstrated in our previous work, with very good pattern transfer fidelity and minimal stress related issues. Imprinting with these stamps gives features similar to the ones obtained in our original process, with the added ability to continuously use the mold over and again. A precise alignment during embossing can help utilize stamps with millimeter size areas with nanosize features. A similar control during imprinting the pattern provides very large-area fabrication with good repeatability. After demonstrating a proof of concept, we are currently working on designing the