Metastable effects in high-voltage amorphous silicon thin-film transistors

We report on a high-voltage amorphous silicon thin-film transistor by which large drain voltages are controlled by a low gate potential. Under certain stress conditions, the output characteristics of these devices can undergo a parallel shift towards higher drain potentials. This phenomenon, which we call the Vx shift, has been analyzed by comparing numerical computer models to experimental data. Simulations show that the Vx shift is caused by negative charge located in the transistor’s amorphous-silicon layer near the edge of the gate. This charge resides in extra metastable deep traps which are generated by the equilibration of stressed amorphous silicon. As this equilibration mechanism is reversible, the Vx shift can be recovered.