Investigating the Back-Channel Effect and Asymmetric Degradation Under Self-Heating Stress in Large Size a-InGaZnO TFTs

Abstract

This paper investigates the back-channel effect and asymmetric degradation of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with a bottom-gate structure under self-heating stress (SHS). In our experiments, the phenomenon initially discovered is that for wide-channel devices, the SHS causes the threshold voltage of the minor channel to shift negatively and the main channel to shift positively in the linear region of the I-V curve. Moreover, the results show that these wider devices also have an obvious asymmetric degradation in the saturation region of the I-V curve. Several experiments are used to examine these abnormal phenomena, including AC self-heating stress applied to the drain and SHS at 77 K environment to verify that sufficient thermal energy exists in the active layers to induce the dual-channel effect and asymmetric deterioration. Silvaco TCAD is also used to simulate the electric field of the system and verify our supposition of the asymmetric degradation phenomenon and explain the physical mechanism in the a-IGZO TFTs.