Oxygen-related Reliability of Amorphous InGaZnO Thin Film Transistors

Chia-Chun Yen,C W Liu,Cheng-Hsu Chou,Yu-Chieh Liu,An-Hung Tai,Tsang-Long Chen

doi:10.1109/jeds.2020.2993018

Abstract

Effects of oxygen flow on positive bias temperature instability and hot carrier injection are investigated in Amorphous InGaZnO (IGZO) thin film transistors. The oxygen flow can suppress the oxygen vacancy density, but introduce shallow states near the conduction edges. The electron can tunnel into gate oxide via these shallow states. As a result, the IGZO channel with oxygen flow has more electrons trapped in the gate oxide than the channel without oxygen flow, leading to more positive V T shift after positive bias temperature instability. The IGZO without oxygen flow create oxygen vacancy (VO) in the channel. The hole generated by impact ionization during the hot electron injection can be trapped in VO to form $\text{V}_{\text{O}}^{2+}$ . The $\text{V}_{\text{O}}^{2+}$ leads to less positive V T shift for IGZO channel without oxygen flow than with the oxygen flow. Since the impact ionization occurs near the drain, the positive $V_{T}$ shift of the reverse measurement (VSD > 0) is smaller than the forward measurement (VDS > 0) after hot electron injection.

Highlights

Amorphous oxide semiconductors such as amorphous InGaZnO (a-IGZO) are expected for channel materials in thin-film transistors (TFTs) for display and mobile electronics due to their high electron mobility (>10 cm2/V-s), high transparency to visible light, and low temperature process
TFTs as the driving transistors for display applications can be simultaneously exposed to the high drain voltage stress and high gate voltage stress to create hot carrier injection (HCI) near the drain
As for OFIGZO, VT in HCI is larger than its PBTI results due to the additional electron trapping induce by the drain current

Summary

INTRODUCTION

Amorphous oxide semiconductors such as amorphous InGaZnO (a-IGZO) are expected for channel materials in thin-film transistors (TFTs) for display and mobile electronics due to their high electron mobility (>10 cm2/V-s), high transparency to visible light, and low temperature process. At the off-state, the positive high gate voltage stress can cause the electron trapping in the gate oxide, and the positive VT shift is observed (positive bias temperature instability, PBTI). There is no discussion of oxygen flow effects on HCI. The distribution of the defect states of a-IGZO is strongly dependant on the oxygen concentration, diversifying the degradation behaviours of the devices [6]–[10]. The effects of HCI in a-IGZO TFTs with and without oxygen flow are discussed with the comparison of PBTI. The drain voltage dependency, the forward/reverse measurement under HCI, and related mechanisms are reported

DEVICE FABRICATION

CONCLUSION