Improved Properties of Oxide Thin-Film Transistor By Electrohydrodynamic-Jet Printing

Abstract

Oxide Semiconductors have been paid attention to suitable TFTs for OLED because of higher mobility than a-Si TFTs, lower leakage current than LTPS TFTs and even low cost. These oxide thin films can be obtained by simple solution process and applied to printed electronics. Printing process is a way to reduce cost and process time effectively over tranditional vacuum process and photo-lithography by direct patterning. Nevertheless, semiconductor films, in most study of solution processed oxide TFTs, are fabricated by spin coating, which is inadequate for electronics industry. For this reason, researches for various printing methodes on oxide TFTs are needed certainly. Electrohydrodynamic-jet(EHD-jet) technique is avilable to form a fine pattern by electric fields between metal stage and tiny orfice tip. We opimized EHD-jet printning conditions for ZTO solution and fabricated with addition patterning technique ZTO TFT sucessfully showing better and stable features than spin coated one. The effects of speed and temperature of stage on printed pattern width was examined. As the stage temperature accelerated vaporization rate of solvent, printed pattern width was narrower and thicker. Thus, it is essential to optimize printing conditions for any solutions to obtain stable printing state. EHD-jet printed TFTs and patterned TFTs showed similar electrical characteristics with spin coated ZTO TFT but much improved contact resistance and leakage current. We investigated the origin of low leakage current based on the overlap of semiconductor with source and drain electrodes and related fringe effect. Electrical characteristic of ZTO TFT show a mobility of 6.9 cm2/Vs, an on-to-off current ratio of 4.7 x 108, a threshold voltage of 7V and a subthreshold-swing of 0.4 V/dec. Hysteresis behavior and passivation effect were also characterized.