Enhanced electrical properties of oxide semiconductor thin-film transistors with high conductivity thin layer insertion for the channel region

Abstract

This study examined the performance and the stability of indium tin zinc oxide (ITZO) thin film transistors (TFTs) by inserting an ultra-thin indium tin oxide (ITO) layer at the active/insulator interface. The electrical properties of the double channel device (ITO thickness of 5nm) were improved in comparison with the single channel ITZO or ITO devices. The TFT characteristics of the device with an ITO thickness of less than 5nm were degraded due to the formation of an island-like morphology and the carriers scattering at the active/insulator interface. The 5 nm-thick ITO inserted ITZO TFTs (optimal condition) exhibited a superior field effect mobility (∼95cm2/V·s) compared with the ITZO-only TFTs (∼34cm2/V·s). The best characteristics of the TFT devices with double channel layer are due to the lowest surface roughness (0.14nm) and contact angle (50.1°) that result in the highest hydrophicility, and the most effective adhesion at the surface. Furthermore, the threshold voltage shifts for the ITO/ITZO double layer device decreased to 0.80 and −2.39V compared with 6.10 and −6.79V (for the ITZO only device) under positive and negative bias stress, respectively. The falling rates of EA were 0.38eV/V and 0.54eV/V for the ITZO and ITO/ITZO bi-layer devices, respectively. The faster falling rate of the double channel devices suggests that the trap density, including interface trap and semiconductor bulk trap, can be decreased by the ion insertion of a very thin ITO film into the ITZO/SiO2 reference device. These results demonstrate that the double active layer TFT can potentially be applied to the flat panel display.