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In this paper, we investigated the influence of both source gas and deposition temperature in plasma-enhanced chemical vapor deposition (PE-CVD) for a SiO2 passivation layer on the electrical properties and reliability of a bottom-gate In–Ga–Zn–O thin-film transistor (IGZO TFT). Two gas chemistries consisting of SiH4–N2O–N2 and tetraethoxysilane (TEOS)–O2 were utilized as the source gases for the PE-CVD SiO2 deposition, and the deposition temperature (${T}_{D}$) was adjusted from 180 °C to 380 °C. The TFT properties were basically identical for both gas chemistries at ${T}_{D}$ of 180 °C. When ${T}_{D}$ increased to 300 °C or higher, the TFTs with the SiO2 passivation deposited by SiH4–N2O–N2 gas chemistry (SiH4-SiO2) drastically changed from the transistor to the conductor. In contrast, the TFT with TEOS-SiO2 passivation maintained its TFT characteristics even at ${T}_{D}$ of 380 °C, despite the degradation of subthreshold characteristics and a negative shift of turn-on voltage were observed due to an electron injection barrier lowering as ${T}_{D}$ increased to 310 °C or higher. We also revealed that a stacked SiO2 passivation that is deposited at a different ${T}_{D}$ is an effective technique to improve the performance and reliability of the IGZO TFT. [ABSTRACT FROM AUTHOR]