Oxygen-Related Reliability of Amorphous InGaZnO Thin Film Transistors

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 V
_O
²⁺
. The V
_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 (V
_SD
> 0) is smaller than the forward measurement (V
_DS
> 0) after hot electron injection.