Effects of low-temperature ozone annealing on operation characteristics of amorphous In–Ga–Zn–O thin-film transistors

Abstract

Effects of low-temperature annealing were examined for amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). In a previous study, we reported that O2 annealing is effective to improve performances of a-IGZO TFTs when annealed at ≥300°C, but causes large negative threshold voltage shift when annealed at ≤ 200°C. Here, we examined effects of ozone (O3) annealing on physical properties and TFT characteristics of a-IGZO in comparison with conventional O2 annealing. We found little differences in chemical composition, band gap and photoemission spectra between the O2 and the O3 annealed films. On the other hand, free electron density was suppressed well by the O3 annealing even at low temperatures ≤200°C. Moreover, even at 150°C, the TFTs characteristics were improved to the subthreshold voltage swing of 217mV/decade, the saturation mobility of ~11.4cm2(Vs)−1 and the threshold voltage of 0.1V by the O3 annealing. It was also found that the effects of the O3 annealing is more effective for thicker channel TFTs, which would be due to stronger oxidation power and the larger diffusion constant of oxygen atoms produced from O3 molecules than those of O2. These results substantiate that the O3 annealing is more effective to improve TFT characteristics in particular for low-temperature processes at ≤200°C.