The Effect of the Active Layer Thickness on the Negative Bias Stress-Induced Instability in Amorphous InGaZnO Thin-Film Transistors

The effect of the active layer thickness (<i>T</i><sub>IGZO</sub>) on the negative bias stress (NBS)-induced threshold voltage shift (Δ<i>VT</i>) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) is investigated and explained by using a subgap density-of-states (DOS) model. The NBS-induced negative Δ<i>VT</i> in a-IGZO TFT with a thinner <i>T</i><sub>IGZO</sub> is larger than that with a thicker <i>T</i><sub>IGZO</sub>. Based on the simulation result with the subgap DOS model, it is concluded that the <i>T</i><sub>IGZO</sub>-dependent Δ<i>VT</i> is originated from the accelerated creation of shallow donor states due to a higher surface electric field in a-IGZO TFTs with a thinner <i>T</i><sub>IGZO</sub>.

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