Amorphous NdIZO Thin Film Transistors with Contact-Resistance-Adjustable Cu S/D Electrodes

Xinyi Zhang,Junbiao Peng,Xuan Zeng,Zimian Lin,Rihui Yao,Honglong Ning,Zhuohui Xu,Kuankuan Lu,Tian Qiu,Zhao Yang

doi:10.3390/membranes11050337

Abstract

High-performance amorphous oxide semiconductor thin film transistors (AOS-TFT) with copper (Cu) electrodes are of great significance for next-generation large-size, high-refresh rate and high-resolution panel display technology. In this work, using rare earth dopant, neodymium-doped indium-zinc-oxide (NdIZO) film was optimized as the active layer of TFT with Cu source and drain (S/D) electrodes. Under the guidance of the Taguchi orthogonal design method from Minitab software, the semiconductor characteristics were evaluated by microwave photoconductivity decay (μ-PCD) measurement. The results show that moderate oxygen concentration (~5%), low sputtering pressure (≤5 mTorr) and annealing temperature (≤300 °C) are conducive to reducing the shallow localized states of NdIZO film. The optimized annealing temperature of this device configuration is as low as 250 °C, and the contact resistance (RC) is modulated by gate voltage (VG) instead of a constant value when annealed at 300 °C. It is believed that the adjustable RC with VG is the key to keeping both high mobility and compensation of the threshold voltage (Vth). The optimal device performance was obtained at 250 °C with an Ion/Ioff ratio of 2.89 × 107, a saturation mobility (μsat) of 24.48 cm2/(V·s) and Vth of 2.32 V.

Highlights

Amorphous oxide semiconductors (AOS) are widely used as the active layer of high performance and flexible thin film transistors (TFTs) [1] because of their high mobility, uniformity and the insensitivity of their electrical properties to mechanical strain
Cu source and drain (S/D) electrodes were utilized in the device with an optimized neodymium-doped indium-zinc-oxide (NdIZO) layer, and the interface contact was investigated by the transmission line method (TLM) method
In order to ensure the accuracy of the experiment, the annealing temperature should still be used as a variable in the follow-up preparation of the device, and further study could be conducted on its influence on the threshold voltage, contact resistance and other electrical performance parameters of the thin film transistor

Summary

Introduction

Amorphous oxide semiconductors (AOS) are widely used as the active layer of high performance and flexible thin film transistors (TFTs) [1] because of their high mobility, uniformity and the insensitivity of their electrical properties to mechanical strain. Due to the advancement in micro-nano manufacturing technology, the pursuit for higher carrier concentration and shorter channel length (L) is inevitable This increases the influence of the RC on the electrical properties of the metal oxide thin film transistor, such as carrier mobility [17]. Saturation mobility (μsat) is often presumed to be free of contact effects, which is reasonable at sufficiently high VGS-VT This has been shown to be incorrect for high contact resistance, especially at the point of the turn-on, for the presence of a Schottky barrier, and where nontrivial Rc causes gated contact resistance [18,19]. Cu S/D electrodes were utilized in the device with an optimized NdIZO layer, and the interface contact was investigated by the transmission line method (TLM) method

Materials and Methods

Film Deposition

Thin Film Transistors

Findings

Conclusions