Electrical and Hysteresis Characteristics of Top-Gate InGaZnO Thin-Film Transistors with Oxygen Plasma Treatment Prior to TEOS Oxide Gate Dielectrics

Abstract

We report the impact of oxygen (O2) plasma time on an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film surface that was carried out before TEOS deposition in order to optimize the performance of thin-film transistors (TFTs). TheO2 plasma time of 60 s possessed the largest on/off current ratio of >108, with a field-effect mobility (µFE) of 8.14 cm2 V−1 s−1, and the lowest subthreshold swing (S.S.) of 0.395 V/decade, with a threshold voltage (Vth) of −0.14 V. However, increases in Ioff and S.S. and decreases in the µFE were observed for the longer O2 plasma time of 120 s. As the O2 plasma time increased, the reduction in the carrier concentration in the IGZO channel layer may have resulted in an increase in Vth for the IGZO TFT devices. With an increase in the O2 plasma time, the surface roughness of the IGZO channel layer was increased, the carbon content in the TEOS oxide film was reduced, and the film stoichiometry was improved. The SIMS depth profile results showed that the O/Si ratio of TEOS oxide for the sample with the O2 plasma time of 60 s was 2.64, and its IGZO TFT device had the best electrical characteristics. In addition, in comparison to the IGZO TFT device without O2 annealing, larger clockwise hysteresis in the transfer characteristics revealed that a greater number of electrons were trapped at the interface between TEOS oxide and the a-IGZO channel layer. However, hysteresis curves of the O2-annealed IGZO TFTs with various O2 plasma times were greatly reduced, meaning that the electron traps were reduced by O2 annealing.