This paper investigates anomalous capacitance-voltage (C-V) degradation in amorphous indium-gallium-zinc-oxide (a-IGZO) thinfilm-transistors (TFTs) under hot carrier stress. In vacuum hot carrier stress, both the gate-to-drain capacitance (C GD ) and the gateto-source capacitance (C GS ) curves exhibited positive shifts due to electron trapping in the gate dielectric. In addition, an observed increase in capacitance value at a lower gate voltage in the C GD measurement only can be ascribed to interface state creation. However, when the hot carrier stress was performed in an oxygen-rich environment, the C GD -V G curve showed a significantly positive shift due to the electric-field-induced oxygen adsorption near the drain terminal. The degradation in the C GS -V G curve is due not only to the positive shift, but also the anomalous two step turn-on behavior. This phenomenon can be ascribed to the electron trapping in the gate dielectric and electric-field-induced oxygen adsorption on the channel layer, especially in the area adjacent to the drain terminal. The electron trapping increased the source energy barrier, with the electric-field-induced oxygen adsorption further raising the energy-band near the drain, resulting in a two-step turn-on behavior in the C GS -V G curve.

This study examines the dependence of light-accelerated instability on bias and environment in amorphous indium-gallium-zinc-oxide thin film transistors. When device is in vacuum ambient, the threshold voltage of device after negative gate bias illumination stress (NBIS) showed bias-dependent electrical degradation behavior. However, experimental results show the degradation of electrical characteristic in a-IGZO devices does not only rely on the charge trapping mechanism for NBIS. During NBIS in oxygen, moisturesimulated and atmosphere ambient, the negative shift in electrical characteristic is suppressed when compared to that in vacuum. This implies that the adsorbent gas species in the surrounding environment dominates the electrical characteristic degradation of devices during NBIS, which leading the change of dominant mechanism from photon-created carrier trapping to adsorbed/desorbed gas phenomenon.

This study presents the influence of photo‐thermal pre‐treatment on the electrical characteristic and bias‐induced instability of amorphous Zn‐Sn‐O thin film transistors. Even in the vacuum ambient, the passivation‐free device with photo‐thermal pre‐treatment shows more stability after stress than that without pre‐treatment. This indicates pre‐treatment should be conducted before passivation process.

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