Half-Corbino short-channel amorphous In–Ga–Zn–O thin-film transistors with a-SiOx or a-SiOx/a-SiNx passivation layers

Abstract

We investigated the electrical properties and stability of short-channel half-Corbino amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). In the linear region, the fabricated half-Corbino a-IGZO TFT with a channel length of 4.5μm achieves a geometrical factor (fg) of ∼2.7, a threshold voltage (VT) of ∼2.4V, a field-effect mobility (μeff) of ∼15cm2/Vs, a subthreshold swing (SS) of ∼320mV/dec and an off-current (IOFF)<10−13A. In the saturation region, asymmetric electrical characteristics such as drain current were observed under different drain bias conditions. The electrical properties asymmetry of half-Corbino a-IGZO TFTs was explained by various geometrical factors owing to the short-channel effect. The reduced VT and increased SS at VDS=15V is explained by the drain-induced Schottky barrier lowering. In addition, the bias-temperature stress (BTS) was performed for half-Corbino a-IGZO TFTs with both amorphous silicon oxide (a-SiOx) single layer and a-SiOx/amorphous silicon nitride (a-SiNx) bilayer passivation (PV) structures. The device with bilayer PV shows a threshold voltage shift (ΔVT) of +2.07 and −0.5V under positive (PBTS=+15V) and negative BTS (NBTS=−15V) at 70°C for 10ks, respectively. The origins of ΔVT during PBTS and NBTS for half-Corbino a-IGZO TFTs with single and bilayer PV structures were studied. To improve the device electrical stability, the bilayer PV structure should be used.