Oxygen Dispersive Diffusion Induced Bias Stress Instability in Thin Active Layer Amorphous In–Ga–Zn–O Thin-Film Transistors

We studied the bias stress instability of amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) by varying the active layer thickness (t) from 6 to 100 nm. We found that the stretched exponential relationship between the threshold voltage shift and the stress time can be explained by oxygen dispersive diffusion which is absorbed near the back channel region during an oxygen annealing process in the active layer. For an a-IGZO TFT with t=6 nm, direct exposure of the channel layer to the ambient oxygen greatly increases the bias stress instability and induces hump like characteristics, indicating that the creation of acceptor-like states is the dominant mechanism of the instability of a-IGZO TFTs with a thin active layer.