Process-related instability mechanisms for the hydrogenated amorphous silicon thin film transistors

Thin film transistors (TFTs) with various hydrogen concentrations in the amorphous silicon (a-Si:H) films and different silicon nitride (SiN/sub x/) gate compositions have been stressed with dc bias to realize the process-related device reliability. For the positive gate bias stress, the instability phenomena mainly come from the electron trapping in the SiN/sub x/. On the other hand, for the negative gate bias stress, the hydrogen-enhanced state creation in the a-Si:H films due to the defect pool effect will be offset by the hole trapping in the SiN/sub x/. Consequently, the reliability of the TFTs was improved by using the SiN/sub x/ gates with less trap sites and reducing the hydrogen concentration in the a-Si:H films,.