Degradation and its fast recovery in a-IGZO thin-film transistors under negative gate bias stress*

Abstract

A new type of degradation phenomena featured with increased subthreshold swing and threshold voltage after negative gate bias stress (NBS) is observed for amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), which can recover in a short time. After comparing with the degradation phenomena under negative bias illumination stress (NBIS), positive bias stress (PBS), and positive bias illumination stress (PBIS), degradation mechanisms under NBS is proposed to be the generation of singly charged oxygen vacancies ( V o + ) in addition to the commonly reported doubly charged oxygen vacancies ( V o 2 + ). Furthermore, the NBS degradation phenomena can only be observed when the transfer curves after NBS are measured from the negative gate bias to the positive gate bias direction due to the fast recovery of V o + under positive gate bias. The proposed degradation mechanisms are verified by TCAD simulation.

Increased Threshold Voltage of Amorphous InGaZnO Thin-Film Transistors After Negative Bias Illumination Stress

“…As shown in Fig. 7(a), the transfer curves after NBIS of 100 s were well fitted by increasing the density of donor-like states distributing in the 10 nm a-IGZO region adjacent to the gate dielectric [26]. The density of state (DOS) parameters for the simulation of the pristine TFT are summarized in Table I and those in the a-IGZO uncovered by the source/drain electrodes for the simulation of the transfer curve after NBIS are summarized in Table II.…”