Abstract
In this study, we analyzed the threshold voltage shift characteristics of bottom-gate amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) under a wide range of positive stress voltages. We investigated four mechanisms: electron trapping at the gate insulator layer by a vertical electric field, electron trapping at the drain-side GI layer by hot-carrier injection, hole trapping at the source-side etch-stop layer by impact ionization, and donor-like state creation in the drain-side IGZO layer by a lateral electric field. To accurately analyze each mechanism, the local threshold voltages of the source and drain sides were measured by forward and reverse read-out. By using contour maps of the threshold voltage shift, we investigated which mechanism was dominant in various gate and drain stress voltage pairs. In addition, we investigated the effect of the oxygen content of the IGZO layer on the positive stress-induced threshold voltage shift. For oxygen-rich devices and oxygen-poor devices, the threshold voltage shift as well as the change in the density of states were analyzed.
Highlights
Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have made significant progress, in display and mobile electronics, owing to their high mobility, high transparency to visible light, and low process temperatures [1,2,3]
No studies have been reported that analyze the instability for a wide stress voltage region, including a very large gate or drain voltage
Electrons gain sufficient kinetic energy by a large lateral electric field to overcome a potential barrier between the IGZO channel and the gate insulator (GI) [22]
Summary
Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have made significant progress, in display and mobile electronics, owing to their high mobility, high transparency to visible light, and low process temperatures [1,2,3]. Many research groups have reported stress-induced instability characteristics [4,5,6,7,8,9,10,11,12,13,14] Most of these studies have focused on the verification of degradation mechanisms, such as charge trapping, hole trapping, and donor-state creation. A thorough understanding of the effect of oxygen content in IGZO thin films on the degradation mechanisms under various stress conditions has not been reported. Micromachines 2021, 12, 327 ured by reverse and forward read-out conditions, respectively. The effect of different oxygen contents was analyzed by adjusting the oxygen flow rate (OFR) in the deposition process of the IGZO layer on the positive stressflow rate induced.
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