Chung-Ming Wu

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

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.

Ultraviolet-Patternable Polymer Insulator for Organic Thin-Film Transistors on Flexible Substrates

In this work, we describe the fabrication of pentacene-based organic thin-film transistors (OTFTs) on a flexible substrate using a UV-patternable polymer material, mr-UVCur06, as the gate insulator. The device structure is poly(ethylene terephthalate) (PET)/indium–tin oxide (ITO)/mr-UVCur06/pentacene/Au (source/drain). In addition to its solution-processable capability, mr-UVCur06 is directly patternable by UV light in a low-temperature process. The OTFT has an on–off ratio that approaches 105, and its pattern resolution can reach 5 µm. Additionally, UV/ozone post-treatment of the patterned mr-UVCur06 can illuminate the organic contaminants from its surface and significantly improve the performance of OTFTs. Moreover, the effect of UV/ozone post-treatment on the polymer dielectric is confirmed using a Fourier transform infrared (FT-IR) spectrometer. Owing to its highly desired characteristics such as photopatternability and low-temperature process, mr-UVCur06 is feasible for low-cost, large-area flexible device applications.

Improving the efficiency of organic light emitting diodes using quantum well structure

The luminous efficiency of OLEDs with a MQW structure have been investigated and improved. The efficiency of OLEDs with the quantum well structure is 90 % higher than the standard device. We suggested that the improvement due to the MQW structure confine carrier in each well without decreasing the mobility of electrons.