Impact of Oxygen Flow Rate on the Instability Under Positive Bias Stresses in DC-Sputtered Amorphous InGaZnO Thin-Film Transistors

The effect of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">O₂</tex></formula> flow rate (OFR) during channel deposition is investigated on the electrical instability of the amorphous indium–gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) under positive gate bias stresses. From the transfer curves measured before and after bias stresses, we can observe that the high OFR degrades the electrical stability and causes the large threshold voltage shift <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">(Δ VT)</tex></formula> in a-IGZO TFTs. To elucidate the origin of the observed phenomenon, we extract and compare the subgap density of states (DOS) in devices with various OFRs. The extracted DOS shows that the subgap states become higher with the increase of OFR in a wide range of bandgap, and the enhanced electron trapping due to the increased number of trap states is considered as the cause of larger <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">Δ VT</tex></formula> in higher OFR devices.