Thermal stability of amorphous InGaZnO thin film transistors passivated by AlOx layers

•a-IGZO TFTs with different thickness passivation-layer were fabricated and measured.•a-IGZO TFTs showed serious threshold voltage shifts at high temperature.•A quantitative model was proposed to explain the threshold voltage shift.•Intrinsic excitation and oxygen vacancy formation domain the threshold voltage variation.•Oxygen vacancy generation became more difficult with thicker passivation layers.

Thermal stability of amorphous InGaZnO thin film transistors (a-IGZO TFTs) passivated by AlOx layers was investigated in this paper. The passivation-layer thickness (0–60 nm) and measurement temperature (298–573 K) were intentionally controlled to study the temperature dependent performance of a-IGZO TFTs with sputtered AlOx passivation-layers. Generally, there was a negative shift in threshold voltage under higher temperatures, which was due to thermally excited carriers through intrinsic excitation and oxygen vacancy formation. A qualitative model was proposed to effectively ascertain the aforementioned two physical mechanisms. With passivation-layer thickness decreasing oxygen vacancy formation became more and more evident while intrinsic excitation could apparently worsen the characteristics of a-IGZO TFTs under the temperature higher than 473 K. In addition, the “passivation-layer thickness effect” for thermal stability of a-IGZO TFTs was theoretically explained by the variation of defect formation energy with the device passivation-layer thickness.

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