The Investigation of Indium-Free Amorphous Zn-Al-Sn-O Thin Film Transistor Prepared by Magnetron Sputtering

Abstract

The indium-free amorphous oxide semiconductor thin film transistor (AOS-TFT) with aluminum (Al) electrodes shows broad application prospects in new-generation display technologies, such as ultra-high definition large-screen display, OLED display and 3D display. In this work, the thin film transistor (TFT) with a zinc-aluminum-tin-oxide (ZATO) semiconductor as the active layer and an Al electrodes as the source and drain (S/D) was investigated. The optical, electrical and semiconductive properties of the ZATO films were evaluated by atomic force microscopy (AFM), ultraviolet–visible spectrophotometry and microwave photoconductivity decay (μ-PCD), respectively. The result shows that the film is smooth and transparent and has low localized states and defects at a moderate oxygen concentration (~5%) and a low sputtering gas pressure (~3 mTorr). After the analysis of the transfer and output characteristics, it can be concluded that the device exhibits an optimal performance at the 623 K annealing temperature with an Ion/Ioff ratio of 5.5 × 107, an SS value of 0.15 V/decade and a saturation mobility (μsat) of 3.73 cm2·V−1·s−1. The ZATO TFT at the 623 K annealing has a −8.01 V negative shift under the −20 V NBS and a 2.66 V positive shift under the 20 V PBS.