Hydrogen as a Cause of Abnormal Subchannel Formation Under Positive Bias Temperature Stress in a-InGaZnO Thin-Film Transistors

This paper analyzes the abnormal degradation induced by hydrogen annealing. Although device performance is enhanced after hydrogen annealing, an abnormal hump is observed in transfer characteristics (I-D-V-G) under positive bias temperature stress (PBTS). Threshold voltage shift (V-TH2) in this hump region increases with increasing stress voltage and temperature. Additionally, V-TH2 is independent of the channel width. A novel hydrogen rupture diffusion model is proposed to explain the degradation. COMSOL simulation and C-V measurement are utilized to clarify the precise degradation position. Moreover, variable S/D spacing (L-SD) devices are designed to support the mechanism. Finally, ISE-TCAD software is carried out to verify the proposed model. Our results from electrical measurement suggest that hydrogen can cause additional instability, which shares a similar conclusion for those by using material analyzation and first-principle simulation.