Transparent Organic Thin Film Transistors Using an Oxide/Metal/Oxide Trilayer as Low-Resistance Transparent Source/Drain Electrodes

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This work presents transparent pentacene-based organic thin film transistors (OTFTs) in which an oxide/metal/oxide trilayer provides low-resistance transparent source/drain electrodes. The device structure is glass/indium--tin oxide (ITO)/poly(methyl methacrylate) (PMMA)/pentacene/transparent source--drain electrode. The transparent source/drain electrode consists of a low-resistance metal, silver, that is sandwiched by a high-transmittance oxide, WO<inf>3</inf>. The structure of the transparent source--drain electrode is optimized by tuning the thickness of each layer. The optimized structure has a sheet resistance of 6.2 \Omega/sq. and an optimum transmittance of 70% in the visible wavelength range of 380--780 nm. The pentacene-based OTFT employing optimized transparent source--drain electrode yields an output current (I_{\text{DS}}) of -7.08 μA, a field-effect mobility (\mu) of 0.22 cm2V-1s-1, an on--off drain current ratio of 1.8\times 10^{5}, and a threshold voltage of -15.1 V. OTFTs in which WO<inf>3</inf>(5 nm)/Ag (10 nm)/WO<inf>3</inf>(30 nm) is used as the source/drain electrode greatly outperform OTFTs in which silver is utilized, because the work function of WO<inf>3</inf>/Ag/WO<inf>3</inf>substantially exceeds that of silver.
2013-04-25