Effect of Hf alloy in ZrO_x gate insulator for solution processed a-IZTO thin film transistors

We report the effect of Hf alloy in ZrO_x (HZO) gate insulator on the performance and stability of solution-processed amorphous indium-zinc-tin oxide (a-IZTO) thin-film transistors (TFTs). The Hf concentration in ZrO_x is varied from 0% to 50 %. The optimized concentration is found to be 10% and the TFT with 10% HfZrO_x exhibits the saturation mobility of 4.76 cm²V^-1 s^-1, a subthreshold swing of 70 mV/dec., and I_ON/I_OFF current ratio of 108. The TFT has no hysteresis and a small threshold voltage shift of 0.44 V upon positive-bias-stress at 5 V for 1 h. The improvements are due to the decrease in V_o (O vacancy) and -OH concentrations and the increase in M-O-M (M: metal) bond concentration at the a-IZTO/HZO interface. This is related with the diffusion of Hf into the a-IZTO active layer by the average concentration of 1.44 at. %.