Analysis of Bias Stress Instability in Amorphous InGaZnO Thin-Film Transistors

Abstract

In this paper, we report an analysis of electrical bias stress instability in amorphous InGaZnO (a-IGZO) thinfilm transistors (TFTs). Understanding the variations of TFT characteristics under an electrical bias stress is important for commercial goals. In this experiment, the positive gate bias is initially applied to the tested a-IGZO TFTs, and subsequently, the negative gate bias is applied to the TFTs. For comparison with the subsequently negative-gate-bias-applied TFTs, another experiment is performed by directly applying the negative gate bias to the tested TFTs. For the positive gate bias stress, a positive shift in the threshold voltage (V th ) with no apparent change in the subthreshold swing (S SUB ) is observed. On the other hand, when the negative gate bias is subsequently applied, the TFTs exhibit higher mobility with no significant change in S SUB , whereas the shift of the V th is much smaller than that in the positive gate bias stress case. These phenomena are most likely induced by positively charged donor-like subgap density of states and the detrapping of trapped interface charge during the positive gate bias stress. The proposed mechanism was verified by device simulation. Thus, the proposed model can explain the instability for both positive and negative bias stresses in a-IGZO TFTs.Index Terms-Density of states (DOS), electrical instability, InGaZnO (IGZO), modeling, thin-film transistors (TFTs).

Interface Study on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using High‐k Gate Dielectric Materials

“…Following the positive voltage stress tests, neither shifted to the left nor deteriorated. These results accord with the trend observed for Si 3 N 4 sample and the characteristics of positive gate voltage stress [19][20][21]. This phenomenon is attributed to the interface effect between the gate-insulating layer and the IGZO.…”

Control of electrical properties and gate bias stress stability in solution-processed a-IZO TFTs by Zr doping

“…With increasing addition of Zr, Zr-doped IZO became unstable under PBS, but were stable under NBS. According to previous studies of Si-based TFTs, two main mechanisms for the shift of V th under gate bias stress were reported [31]. One is charge trapping at the interface between the active layer and dielectric.…”

Impact of Long-Term Stress on the Light Output of a WRGB AMOLED Display

“…3) The positive shift in threshold voltage for active pixels needs further investigation but it is suspected that this behavior is a result of bias-stress induced positive threshold voltage shift of the InGaZnO driving TFTs [14]- [17]. 4) Also the negative shift in threshold voltage of the driving TFT for inactive pixels needs further investigation, but it is suspected that this behavior is a result of the thermal and photo-instability of the backplane TFTs.…”