Hot-Carrier Effects in a-InGaZnO Thin-Film Transistors Under Pulse Drain Bias Stress

The degradation mechanism of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) under pulse drain bias stress is investigated. Although the degradation mechanism is found to be a dc one, the shift of the transfer curve under the pulse drain bias (0-20 V) is unexpectedly larger than that under dc drain bias (20 V) within the same equivalent stress time. The degradation mechanism is proposed to be tunneling and trapping of electrons in the etching stop layer during the pulse peak time and that in the gate dielectric during the pulse base time under the extended drain electrode region of the a-IGZO TFT, where the occurrence of the latter is triggered by the former. A solution for enhancing the stability of the a-IGZO TFT is also suggested.