Correlation between gap state density and bias stress reliability of nanocrystalline TFTs comparing with hydrogenated amorphous silicon TFTs

The disordered bonds may generate a redistribution of trap states, resulting in unstable electrical characteristics such as threshold voltage (V_T), subthreshold swing (SS), and mobility (μ) of carriers. The hydrogenated nanocrystalline (nc-Si:H) thin-film transistors (TFTs) were demonstrated with high electrical reliability for hot carrier (HC) stress and positive bias temperature instability (PBTI) stress and can be explained by trap state distribution of the bandgap. The weak or broken bonds may contribute to the redistribution of trap states and lead to unstable electrical characteristics of the hydrogenated amorphous Si (a-Si:H) TFTs. We conclude that the gap state density of a nc-Si:H layer with stress is the fundamental reliability issue for the development of flexible electronics.