Correlation between passivation film density and reliability of In–Ga–Zn–O thin-film transistors

The effect of the film density of a SiO2 passivation layer on the positive bias stress (PBS) stability of an In–Ga–Zn–O thin-film transistor (IGZO TFT) was investigated by a comparison of the results of the PBS test between ambient air and vacuum. The film density was varied by changing the deposition temperature. The TFT with low-density SiO2 passivation exhibited a more severe threshold voltage shift (ΔV th) under the PBS in ambient air than in vacuum. In contrast, no significant difference in ΔV th was observed from the TFT with a dense SiO2 passivation. Thus, a dense passivation is essential for reducing ambient effects for IGZO TFTs.