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.

Performance improvement of a sol–gel ZTO-based TFT due to an interfacial SnOxdopant layer

“…The μ and SS of the solution-processed Z/S/Z TFT proposed in this work are 14.33 cm 2 V −1 s −1 and 0.13 V dec −1 , respectively, which are also better than the values of 1.47–6.1 cm 2 V −1 s −1 and 0.15–1.39 of the sputtered ZTO TFTs reported in the literature. 21,22,34–36 The above comparison indicates that this study has a significant advancement in ZTO-based TFT technology. The performance of the proposed Z/S/Z TFT is higher than most ZTO-based TFTs fabricated using solution and vacuum sputtering processes.…”

“…This may overcome the bottleneck of m for ZTO-based TFT devices. [20][21][22]29,30,[34][35][36][37][38][39][40]80,81…”

“…The optimal ZATO TFT shows an I on / I off ratio of 5.55 × 10 7 , sub-threshold swing (SS) of 0.15 V dec −1 and μ of 3.73 cm 2 V −1 s −1 . 21 Sharma et al proposed that an as-deposited ZTO film normally has excess electrons, which causes the corresponding ZTO TFT to show poor electrical characteristics. However, the performance of the TFT can be improved by doping Ge in the ZTO film.…”

“…The above literature indicates that an additional doping process is usually needed for improving the performance of a ZTO TFT and the mobilities of the solution-processed ZTObased TFTs are 0.2-3.83 cm 2 V À1 s À1 , [29][30][31] which are normally lower than 1.47-6.1 cm 2 V À1 s À1 of vacuum-processed ZTObased TFTs. 21,22,[34][35][36] It seems that there is still room for improvement in the performance of solution-processed ZTO TFTs.…”