Asymmetrical degradation behaviors in amorphous InGaZnO thin-film transistors under various gate and drain bias stresses

The asymmetrical degradation behaviors of amorphous indium-gallium-zinc oxide thin-film transistors are studied comprehensively under various gate and drain bias stresses. The transfer curve moves to the negative direction after bias stresses are applied, and different types of asymmetrical degradation are observed depending upon the magnitude of the applied gate and drain bias stresses. After the application of gate-to-source (V-GS) and drain-to-source (V-DS) bias stresses of (V-GS = 16 V, V-DS = 16 V) and (V-GS = 22 V, V-DS = 10 V), the forward mode transfer curve exhibits a more negative shift compared to that of the reverse mode, whereas opposite results are observed under the stress condition of (V-GS = 10 V, V-DS = 25 V). From the two-dimensional simulation results and the separately extracted subgap density of states in the source and drain sides of the thin film transistors before and after the application of various bias stresses, the local high electric field-induced nonuniform generation rate of the subgap states near the conduction band edge is considered to be the dominant mechanism causing the asymmetrical degradation of the devices under various gate and drain bias stresses. The generation of the subgap states is observed at different locations depending upon the magnitude of the applied gate and drain bias stresses. (C) 2014 American Vacuum Society.