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

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 217 mV/decade, the saturation mobility of ~ 11.4 cm²(Vs)^− 1 and the threshold voltage of 0.1 V 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.