Thermal Damage-Free Microwave Annealing with Efficient Energy Conversion for Fabricating of High-Performance a-IGZO Thin-Film Transistors on Flexible Substrates.

Ki-Woong Park,Won-Ju Cho

doi:10.3390/ma14102630

Abstract

In this study, we applied microwave annealing (MWA) to fabricate amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) without thermal damage to flexible polyimide (PI) substrates. Microwave energy is highly efficient for selective heating of materials when compared to conventional thermal annealing (CTA). We applied MWA and CTA to a-IGZO TFTs on PI substrate to evaluate the thermal damage to the substrates. While the PI substrate did not suffer thermal damage even at a high power in MWA, it suffered severe damage at high temperatures in CTA. Moreover, a-IGZO TFTs were prepared by MWA at 600 W for 2 min, whereas the same process using CTA required 30 min at a temperature of 300 °C, which is a maximum process condition in CTA without thermal damage to the PI substrate. Hence, MWA TFTs have superior electrical performance when compared to CTA TFTs, because traps/defects are effectively eliminated. Through instability evaluation, it was found that MWA TFTs were more stable than CTA TFTs against gate bias stress at various temperatures. Moreover, an MWA TFT-constructed resistive load inverter exhibited better static and dynamic characteristics than the CTA TFT-constructed one. Therefore, MWA is a promising thermal process with efficient energy conversion that allows the fabrication of high-performance electronic devices.

Highlights

With the remarkable advances in display technology, flexible or foldable electronic devices are attracting considerable attention
Extensive studies have been conducted on flexible thin-film transistors (TFTs) for backplane driving devices and flexible substrates such as polymer plastics, ultra-thin glass (UTG) and metal foils [1,2,3,4]
Stringent restrictions are placed on the thermal process, which is essential for improving device performance in flexible substrate-based electronic devices

Summary

Introduction

With the remarkable advances in display technology, flexible or foldable electronic devices are attracting considerable attention. Polyimide (PI) is attracting much attention due to its low cost, relatively high thermal stability, and excellent mechanical/chemical properties [5,6,7]. The conventional thermal annealing (CTA) process using an electrical resistance heating furnace has the advantages of low cost and high wafer throughput, and it is mainly used in post-deposition annealing (PDA) after depositing oxide semiconductors. Because this convection heating process requires a long time at high temperatures, it may cause serious thermal damage to the flexible substrate and consequent deterioration of device performance [14,15]. A technology for efficient PDA is essential for improving the electrical properties of a device without causing damage to the flexible substrate

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