Study of mechanism of stress-induced threshold voltage shift and recovery in top-gate amorphous-InGaZnO4 thin-film transistors with source- and drain-offsets

Bias instability of top-gate amorphous-indium-gallium-zinc-oxide thin-film transistors with source- and drain-offsets is reported. Positive and negative gate bias-stress (V-G_STRESS) respectively induce reversible negative threshold-voltage shift (Delta V-TH) and reduction in on-current. Migration of positive charges towards the offsets lowers the local resistance of the offsets, resulting in the abnormal negative Delta V-TH under positive V-G_STRESS. The reduction in on-current under negative V-G_STRESS is due to increase in resistance of the offsets when positive charges migrate away from the offsets. Appropriate drain and source bias-stresses applied simultaneously with V-G_STRESS either suppress or enhance the instability, verifying lateral ion migration to be the instability mechanism. (C) 2012 Elsevier Ltd. All rights reserved.