Effect of Hf Alloy in ZrO_xGate 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 cm $^{\textsf {2}}\text{V}^{-\textsf {1}}\,\,\text{s}^{-\textsf {1}}$ , a subthreshold swing of 70 mV/dec., and ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ 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. %.