Short channel effect of solution-processed ZnO thin film transistors : optimization for photolithographic process.

A photolithographic process for the fabrication of short channel solution-processed zinc oxide transistors (ZnO TFTs) was optimized. To avoid damage to the ZnO film by the photolithography, a bottom gate, bottom contact (BG-BC) device structure was adopted. A perhydropolysilazane (PHPS) precursor, thermally annealed and then treated in oxygen plasma, was used as the gate insulator on an aluminum (Al) gate electrode. Al source and drain electrodes, with a minimum channel length of 5 μm were successfully defined using photolithography. A mobility of 1.5×10−2 cm2/Vs, on/off ratio of 106 and good contact between the source and drain (S/D) and semiconductor were achieved for solution-processed ZnO TFTs having various channel lengths, showing no degradation of device properties. The relatively low mobility was attributed to increased roughness of the gate insulator resulting from development during the photolithographic process. These results suggest that short-channel solution-processed ZnO TFTs can be fabricated by adopting optimised photolithographic processes.