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

• Half-Corbino a-IGZO TFTs with a-SiOx and a-SiOx/a-SiNx passivation layers are fabricated.
• Short-channel effect of half-Corbino a-IGZO TFT leads to asymmetric electrical properties.
• The impact of Mo/a-IGZO contacts on device properties is discussed.
• The origins of threshold voltage shift during bias temperature stress are studied.
• Electrical stability is improved using the a-SiOx/a-SiNx bilayer passivation structure.

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 4.5 μm achieves a geometrical factor (fg) of ∼2.7, a threshold voltage (VT) of ∼2.4 V, a field-effect mobility (μeff) of ∼15 cm2/Vs, a subthreshold swing (SS) of ∼320 mV/dec and an off-current (IOFF) < 10−13 A. 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 = 15 V 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 −0.5 V under positive (PBTS = +15 V) and negative BTS (NBTS = −15 V) at 70 °C for 10 ks, 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.