Effects of Ti Doping on the Electrical Properties and Gate-Bias Stability of Amorphous Zinc-Tin-Oxide Thin-Film Transistors

Abstract

Multicationicoxide semiconductors are receiving considerable interestin electronic and optoelectronic devices owing to their tunabilityof physical properties by the cation compositions. Here, we investigatedthe effects of Ti doping on the electrical properties and gate-biasstability of amorphous zinc-tin-oxide (a-ZnSnO, Zn/Sn = 7:3) thin-film transistors (TFTs) using a cosputteringprocess. Particularly, by using cosputtering, controllable dopingof Ti in a-ZnSnO films was possible in the rangeof 0.87-3.87 atom %. From various electrical analyses, it wasfound that the key metrics of Ti-doped ZnSnO (TiZnSnO) TFTs, suchas field-effect mobility and gate-bias stability, were highly dependenton the Ti concentration, showing a mobility-stability tradeoff.Based on X-ray photoelectron spectroscopy analysis, the mobility-stabilitytradeoff is ascribed to the suppression of oxygen vacancy formationby Ti doping. Considering the overall electrical performance and stabilityof TiZnSnO TFTs, which were processed at 450 degrees C, the optimalTi concentration was determined as similar to 1.14 atom % with Zn, Sn,and O concentrations of 15.87, 22.92, and 60.07 atom %, respectively.The device exhibited a field-effect mobility of 8.2 cm(2) V-1 s(-1), a subthreshold slopeof 0.208 V decade(-1), an on/off ratio of 3.38 x10(8), a hysteresis of 2.8 V, and a threshold voltage shiftof +5.61 and -2.24 V under positive- and negative-bias stresses,respectively.