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 (TIGZO) on the negative bias stress (NBS)-induced threshold voltage shift (ΔVT) 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 ΔVTin a-IGZO TFT with a thinnerTIGZOis larger than that with a thickerTIGZO. Based on the simulation result with the subgap DOS model, it is concluded that theTIGZO-dependent ΔVTis originated from the accelerated creation of shallow donor states due to a higher surface electric field in a-IGZO TFTs with a thinnerTIGZO.