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 (
T
_IGZO
) on the negative bias stress (NBS)-induced threshold voltage shift (Δ
VT
) 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
VT
in a-IGZO TFT with a thinner
T
_IGZO
is larger than that with a thicker
T
_IGZO
. Based on the simulation result with the subgap DOS model, it is concluded that the
T
_IGZO
-dependent Δ
VT
is originated from the accelerated creation of shallow donor states due to a higher surface electric field in a-IGZO TFTs with a thinner
T
_IGZO
.