Physico-Chemical Origins of Electrical Characteristics and Instabilities in Solution-Processed ZnSnO Thin-Film Transistors

We investigate the physico-chemical origins that determine the transistor characteristics and stabilities in sol-gel processed zinc tin oxide (ZTO) thin-film transistors (TFTs). ZTO solutions with Sn/(Sn+Zn) molar ratios from 0.3 to 0.6 were synthesized to demonstrate the underlying mechanism of the electrical characteristics and bias-induced instabilities. As the Sn/(Sn+Zn) ratio of ZTO is increased, the threshold voltage of the ZTO TFTs negatively shifts owing to the gradual increase in the ratio of oxygen vacancies. The ZTO TFTs with an Sn/(Sn+Zn) ratio of 0.4 exhibit highest saturation mobility of 1.56 cm²/Vs lowest subthreshold swing and hysteresis of 0.44 V/dec and 0.29 V, respectively, due to the desirable atomic states of ZTO thin film. Furthermore, these also exhibit outstanding positive bias stability due to the low trap density at the semiconductor-dielectric interface. On the other hand, the negative bias stress-induced instability gradually increases as the proportion of tin increases because the negative bias stress instability originates from the ionization of oxygen vacancies. These results will contribute to the optimization of the composition ratio in rare-metal-free oxide semiconductors for next-generation low-cost electronics.