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.

Figure optionsDownload as PowerPoint slide