Oxygen-related Reliability of Amorphous InGaZnO Thin Film Transistors
Chia-Chun Yen, An-Hung Tai, Yu-Chieh Liu, Tsang-Long Chen, Cheng-Hsu Chou, C. W. Liu
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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . The V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> leads to less positive V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> shift for IGZO channel without oxygen flow than with the oxygen flow. Since the impact ionization occurs near the drain, the positive V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> shift of the reverse measurement (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</sub> > 0) is smaller than the forward measurement (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> > 0) after hot electron injection.