Highly stable hafnium–tin–zinc oxide thin film transistors with stacked bilayer active layers

Hf–Sn–Zn–O (HTZO) thin films were prepared on SiO2/SiNx substrates at room temperature by the direct current (DC) magnetron sputtering of Hf-doped Sn–Zn–O targets. The characteristics of films with different amounts of Hf were analyzed. Amorphous HTZO films were obtained by increasing the Hf content, while polycrystalline films have not shown with Hf doping. With the proper Hf concentration in the HTZO films (∼2.0 atomic % Hf/(Hf + Sn + Zn + O)), HTZO films demonstrated good performance as an oxide semiconductor channel material in thin film transistors (TFTs) with a field effect mobility (μFE) of 10.9 cm2V−1 s−1, an on/off current ratio of 109, and a subthreshold voltage swing of 0.71 V/decade.