Effect of Hf Alloy in ZrOx 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) thinfilm 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
²
V
^-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. %.