Low thermal budget annealing technique for high performance amorphous In-Ga-ZnO thin film transistors

Joong-Won Shin,Won-Ju Cho

doi:10.1063/1.4995973

Abstract

In this paper, we investigate a low thermal budget post-deposition-annealing (PDA) process for amorphous In-Ga-ZnO (a-IGZO) oxide semiconductor thin-film-transistors (TFTs). To evaluate the electrical characteristics and reliability of the TFTs after the PDA process, microwave annealing (MWA) and rapid thermal annealing (RTA) methods were applied, and the results were compared with those of the conventional annealing (CTA) method. The a-IGZO TFTs fabricated with as-deposited films exhibited poor electrical characteristics; however, their characteristics were improved by the proposed PDA process. The CTA-treated TFTs had excellent electrical properties and stability, but the CTA method required high temperatures and long processing times. In contrast, the fabricated RTA-treated TFTs benefited from the lower thermal budget due to the short process time; however, they exhibited poor stability. The MWA method uses a low temperature (100 °C) and short annealing time (2 min) because microwaves transfer energy directly to the substrate, and this method effectively removed the defects in the a-IGZO TFTs. Consequently, they had a higher mobility, higher on-off current ratio, lower hysteresis voltage, lower subthreshold swing, and higher interface trap density than TFTs treated with CTA or RTA, and exhibited excellent stability. Based on these results, low thermal budget MWA is a promising technology for use on various substrates in next generation displays.

Highlights

In recent years, oxide semiconductor based thin film transistors have been intensively studied to address requirements for large-area low-cost processes in the display industry
Oxide semiconductors have higher mobilities than those of amorphous silicon (a-Si), superior uniformity of materials compared to lowtemperature polysilicon (LTPS), and excellent electrical properties, which are advantageous for large area processing.[2,3,4]
Amorphous indium-gallium-zinc oxide (a-IGZO), which has a high mobility even in an amorphous state, has recently attracted considerable attention.[7,8,9], since oxide semiconductor thin films formed at low temperatures have poor electrical characteristics due to the presence of many defects and impurities, post-deposition annealing (PDA) is an essential step when processing high performance TFTs for low-power active-matrix displays (FPD) applications.[10]

Summary

Introduction

This method is effective because energy is directly transferred to the substrate.[11] In this study, we fabricated a-IGZO TFTs using three PDA processes: MWA using microwave energy, RTA using a halogen lamp, and CTA using a high frequency coil.

Results

Conclusion