Amorphous indium tungsten zinc oxide (a-IWZO) ultra-thin film TFTs (UTFTs) have been successfully fabricated and demonstrated in this work. Tungsten oxide (WO₃)-doped indium zinc oxide was developed because WO₃ doping can form stable semiconducting films with various carrier mobilities and carrier concentration. The novel IWZO UTFTs with high-κ HfO₂ gate insulator exhibit superior potential for the power-saving applications of flat panel displays (FPDs), flexible electronics, and large scale integration (LSI) technologies, owing to its outstanding characteristics of low threshold voltage ~ -0.072 V, high mobility ~ 23.8 cm²/V-s, excellent subthreshold swing ~ 72.6 mV/dec., low voltage operation (low power consumption), high electrical reliability, and small hysteresis.