The characteristics of hydrogenated amorphous silicon field effect transistors using amorphous silicon nitride as a gate insulator has been studied. The threshold voltage increased with time under the positive gate bias and decreased under the negative gate bias. And also rapid quenching produces a decrease in the off conductance and an increase of the on conductance. All above changes are metastable and annealed states are recovered by annealing above the 160℃. The changes of the characteristics of field effect transistor take place by chrage trapping in the silicon nitride and the creation of metastable defect state in the silicon and the interface between the silicon and silicon nitride. These possible origins of instability in amorphous silicon field effect transistor are studied through the isochronal annealing experiment. Annealing temperature dependencies off source-drain current as well as the threshold voltage give the evidence for the multiple annealing stages. The annealing kinetics of these annealing behavior were studied by the hydrogen diffusion model. The annealing peak around 160℃ is the well known annealing temperature of bulk defect therefore this is attributed to the silicon bulk defect. The annealing peak around the 115℃ and the 135℃ are attributed to the interface defect annealing. From the hydrogen diffusion model of kinetics, the method to distinguish the different kind of defect state from the mixed state was proposed.
