Influence of Ar/O2 ratio during IGZO deposition on the electrical characteristics of a-IGZO TFT with HfLaO gate dielectric

In this work, the influence of Ar/O₂ ratio during InGaZnO (IGZO) deposition on the electrical characteristics of a-IGZO thin-film transistor (TFT) with HfLaO gate dielectric has been investigated. It is found that lowering the oxygen concentration in the a-IGZO sputtering ambient can effectively improve the device performance, including carrier mobility (μ_sat), threshold voltage (V_th), sub-threshold slope (SS) and on-off current ratio (I_on/I_off). Moreover, the hysteresis (ΔV_H) of the transfer characteristics of the device under forward and reverse sweepings of gate bias voltage can be suppressed, and improvement on its low-frequency noise properties has been found for lower oxygen concentration in the sputtering ambient. As a result, a high saturation mobility of 12.5 cm²/Vs, a low sub-threshold slope of 0.260 V/dec and a small Hooge´s parameter (α_H) of 0.4 have been achieved for the sample with an Ar/O₂ ratio of 24 sccm/1 sccm. All these improvements can be ascribed to the fact that more oxygen vacancies exist in the a-IGZO film deposited in an ambient with less oxygen. These positively-charged oxygen vacancies can induce a higher electron concentration in the a-IGZO film and thus fill up more electron traps at the interface between a-IGZO and HtLaO.