A model for threshold voltage shift under negative gate bias stress in amorphous InGaZnO thin film transistors

School of Electronic and Information Engineering, South China University of Technology, 510640 Guangzhou, P.R. China

^a e-mail: phrhyao@scut.edu.cn

Received: 21 July 2015
Revised: 17 October 2015
Accepted: 18 November 2015
Published online: 18 December 2015

Abstract

In the amorphous InGaZnO thin film transistors (a-IGZO TFTs) with high concentration of oxygen vacancy, the energy level of oxygen vacancy-related donor-like states in a-IGZO films near the gate insulator moves upwards under the negative gate bias stress (NGBS). The electrons in the donor-like states above the midgap are emitted to the conduction band, making the donor-like states positively charged. These positively charged donor-like states accumulate near the interface of the a-IGZO films and gate insulator and screen the gate voltage, thus leading to the negative shift of the threshold voltage (V_th) of a-IGZO TFTs. In this article we establish a physical model of V_th shift in the negative direction under NGBS, and the results are consistent with the experimental results.