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

Abstract

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, WO3. 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 Ω/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 (IDS) of -7.08 µA, a field-effect mobility (µ) of 0.22 cm2 V-1 s-1, an on–off drain current ratio of 1.8×105, and a threshold voltage of -15.1 V. OTFTs in which WO3 (5 nm)/Ag (10 nm)/WO3 (30 nm) is used as the source/drain electrode greatly outperform OTFTs in which silver is utilized, because the work function of WO3/Ag/WO3 substantially exceeds that of silver.