Papers

AVS2004 Session TF1-TuM: Thin Films on Flexible and Polymer Substrates

Tuesday, November 16, 2004 8:20 AM in Room 303C

Tuesday Morning

Start	Invited?	Item
8:20 AM		TF1-TuM-1 Mechanisms of Vapor Permeation Through Multilayer Thin-Films G.L. Graff, P.E. Burrows, R.E. Williford (Pacific Northwest National Laboratory) Multi-layer, thin-film organic/inorganic composite barrier layers can achieve water vapor permeation rates (WVTR) of <10^-5 g/m²/day at 25°C/40%RH on polyethylene terephthalate. Using both transient and steady-state vapor permeation measurements combined with classical Fickian diffusion models, we determine the mechanism of vapor permeation through such barrier structures and show the importance of an extremely long effective path length for the diffusing gas. We show that the barrier performance obtained is dominated by lag-time (transient) effects, rather than equilibrium diffusion. The implications for further improvement of flexible thin film vapor barriers are discussed.
9:00 AM		TF1-TuM-3 Multi-layered ITO and SiO₂ Thin Films Deposited on Plastic Substrates by Vacuum Arc Plasma Evaporation T. Miyata, Y. Minamino, T. Minami (Kanazawa Institute of Technology, Japan) Recently, a vacuum arc plasma evaporation (VAPE) method that provides a high rate deposition on large area substrates has been newly developed. This paper describes the preparation of multi-layered structures composed of ITO and SiO₂ thin films deposited on plastic substrates by the VAPE method. Structures such as ITO/SiO₂ and ITO/SiO₂/ITO were prepared for the purpose of improving the optical transmittance of flexible transparent conducting films that exhibit a desirable sheet resistance, e.g., ITO thin films deposited on thick PET films. The ITO and SiO₂ thin films were prepared on PET substrates by the VAPE method using sintered ITO and fused quartz fragments, respectively, as targets. The film depositions were carried out under the following conditions: substrate, PET (glass used as a monitor); substrate temperature, 100°C; pressure, 0.08 to 1 Pa; Ar and O₂ gas flow rates, 20 and 0 to 20 sccm; and cathode plasma power, 4.5 to 10 kW. The optical and electrical properties of the ITO thin films were strongly dependent on the deposition conditions. In addition, the optical transmission spectra of the SiO₂ thin films also were affected by the deposition conditions. By optimizing the deposition conditions, highly transparent and conductive ITO thin films were prepared at 100°C on both PET and glass substrates. The resistivity of ITO thin films increased from 2.9 to 7.8X10^–4Ωcm as the O₂ flow rate was increased from 5 to 20 sccm. In addition, SiO₂ thin films that were prepared on PET substrates under optimized conditions exhibited a high transmittance in the visible region. Using optimized deposition conditions, ITO/SiO₂ and ITO/SiO₂/ITO multi-layered structures with a desirable sheet resistance were prepared on PET substrates based on the theoretical calculation. However, the film thickness of the ITO top layer was determined by the desired sheet resistance. In conclusion, transmittance could be successfully improved in transparent and conductive ITO/SiO₂ and ITO/SiO₂/ITO multi-layered structures prepared on flexible plastic substrates by the VAPE method.
9:20 AM		TF1-TuM-4 Mechanical Performance of Thin Films in Flexible Displays J.S. Lewis, S. Grego, E. Vick, B. Chalamala, D. Temple (MCNC Research and Development Institute) In flexible organic light emitting diode (OLED) based displays, brittle thin films are typically used as transparent conductors, permeation barriers, and transistor backplanes. The use of brittle materials in flexible displays requires the understanding of the mechanical limitations of the materials and the various display architectures. We discuss the mechanical limitations of indium tin oxide (ITO) as a transparent conductor, and present results for a more mechanically robust multilayer transparent conductor made of a dielectric-metal-dielectric (DMD) stack. The DMD structures show dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. Organic light emitting devices fabricated on DMD anodes showed improved performance compared with those made on ITO anodes. The mechanical properties of thin film conductors were investigated by monitoring electrical resistance during flexing, but this approach cannot be used in the analysis of the mechanical failure of transparent thin film permeation barriers. We present a novel approach for etching barrier-coated polymer substrates such that film cracking is readily visible under an optical microscope. We report on the bend test results for sputter-deposited SiO_xN_y barrier films. This work was supported by the Army Research Laboratory (Contract No. DAAD17-01-C-0085).
9:40 AM		TF1-TuM-5 Structural and Mechanical Properties of Dendrimer-mediated Thin Films F.T. Xu, S.M. Thaler, J.A. Barnard (University of Pittsburgh) Dendrimers are three-dimensional, globular, highly-branched macromolecules made up of a central core surrounded by repetitive units all enclosed by a terminal group shell. They can be synthesized with highly controllable sizes (they are monodisperse) determined by the core type, extent of branching, and nature of the end groups, in the range from a few to several tens of nm in diameter. Dendrimers also assemble into monolayers on technologically interesting substrates using simple cleaning, dipping, and rinsing procedures. In this condensed monolayer phase dendrimers can act as surfactants mediating the growth of ultra-flat films, and create novel nanomechanical, adhesive, frictional, and tribological behavior. We have recently reported on the dramatically enhanced quality (superior flatness and adhesion) of metal films deposited on dendrimer monolayers¹. Different tribological responses are also observed in dendrimer-mediated metal thin films². To better understand substrate/dendrimer monolayer/adlayer interactions and how they determine the distinct physical, mechanical, and chemical properties of the resulting dendrimer-based nanocomposites, we are examining the structure and nanomechanical response of metal films formed with and without dendrimer mediation by atomic force and force modulation microscopy. ¹ S.C. Street, A. Rar, J.N. Zhou, W.J. Liu, and J.A. Barnard, Chem. Mater. 13, (2001)3669. ² F.T. Xu, P.P. Ye, M. Curry, J. A. Barnard and S. C. Street, Trib. Lett. 12 (2002)189 .
10:00 AM		TF1-TuM-6 Gas Diffusion Barriers on Polymer Films Using Al₂O₃ Atomic Layer Deposition M.D. Groner, C.A. Wilson, J.D. Ferguson, S.M. George (University of Colorado); R.S. McLean, P.F. Carcia (DuPont CR&D) Polymer substrates are desirable for flexible organic light-emitting diodes (OLEDs). Unfortunately, gas permeability in polymers is high and gas diffusion barriers are needed to reduce H₂O and O₂ permeability. For OLEDs, the desired permeability rate for O₂ is 1 x 10^-5 cc/m²/day. Inorganic films, such as SiO₂ and Al₂O₃, can have extremely low gas diffusion rates and may be excellent gas diffusion barrier candidates if they are continuous and pinhole-free. Low temperature Al₂O₃ ALD has been investigated on a variety of polymer films including PET, PMMA, LDPE, PEN, and Kapton(R). Al₂O₃ ALD films were deposited at temperatures between 100-175°C and yielded thicknesses between 1-25 nm on the various polymer substrates. Al₂O₃ ALD film growth and film properties were characterized using several techniques including quartz crystal microbalance, FTIR spectroscopy and surface profilometry. O₂ permeability through the polymer films was also quantified using MOCON permeation measurements. O₂ permeation rates below the MOCON test limit of 1 x 10^-3 cc/m²/day were measured for Al₂O₃ ALD films ≥ 5 nm thick on PEN and Kapton substrates. New testing methods are currently being developed to measure the extremely low O₂ and H₂O permeation rates required for OLED packaging. Studies are also characterizing the dependence of gas permeation rates on the Al₂O₃ ALD film thickness and growth temperature.