Effect of oxygen partial pressure on electrical characteristics of amorphous indium-gallium-zinc-oxide thin-film transistors

The authors report on the fabrication and the electrical characteristics of thin-film transistors (TFTs) with an amorphous indium-gallium-zinc-oxide (a-IGZO) channel, which was deposited by sputtering using an IGZO target at different oxygen partial pressures. The effect of different oxygen concentration on the device performance of a-IGZO TFTs was investigated. With decreasing zinc and increasing oxygen content, the threshold voltage (V_T) shifted in the positive direction. Such a positive V_Tshift suggests that the number of oxygen vacancies in the a-IGZO film decreased. The subthreshold swing degrades due to an increasing tailing of trap states. At a relatively high IGZO power of 110 W and an oxygen flow rate of 4%, a threshold voltage of 1.8 V, an on-off current ratio of 3.4 × 10⁴, and a field-effect mobility of 4.4 cm²/(Vs) were observed.