Improved reliability of a-IGZO thin-film transistor under positive gate bias stress by utilizing NH3 plasma treatment

In this paper, the degradation mechanisms of the bottom-gate amorphous InGaZnO thin film transistors (a-IGZO TFTs) under positive gate bias stress (PBS) are investigated. The PBS-induced degradation can be attributed to the electron capture at the interface of the gate insulator and a-IGZO and the generation of oxygen interstitial defects (O-i) in a-IGZO. The oxygen interstitial defect density (N-Oi) can be calculated by the degradation of SS during recovery after PBS. It is found that the proportion of degradation caused by O-i increases with the increased a-IGZO thickness. By utilizing NH3 plasma treatment, the threshold voltage shift was reduced by >40 % under PBS (@V-G = 5 V, t = 1000s). Further analysis shows that NH3 plasma treatment can effectively suppress the electron capture at the interface and the generation of O-i during PBS. Thus, PBS reliability of a-IGZO TFTs is improved by the proposed method.