Periodically pulsed wet annealing approach for low-temperature processable amorphous InGaZnO thin film transistors with high electrical performance and ultrathin thickness.

Ye Kyun Kim,Won Jun Kang,Hyung Koun Cho,Sung Woon Cho,Myeong Gu Yun,Cheol Hyoun Ahn

doi:10.1038/srep26287

Abstract

In this paper, a simple and controllable “wet pulse annealing” technique for the fabrication of flexible amorphous InGaZnO thin film transistors (a-IGZO TFTs) processed at low temperature (150 °C) by using scalable vacuum deposition is proposed. This method entailed the quick injection of water vapor for 0.1 s and purge treatment in dry ambient in one cycle; the supply content of water vapor was simply controlled by the number of pulse repetitions. The electrical transport characteristics revealed a remarkable performance of the a-IGZO TFTs prepared at the maximum process temperature of 150 °C (field-effect mobility of 13.3 cm2 V−1 s−1; Ion/Ioff ratio ≈ 108; reduced I-V hysteresis), comparable to that of a-IGZO TFTs annealed at 350 °C in dry ambient. Upon analysis of the angle-resolved x-ray photoelectron spectroscopy, the good performance was attributed to the effective suppression of the formation of hydroxide and oxygen-related defects. Finally, by using the wet pulse annealing process, we fabricated, on a plastic substrate, an ultrathin flexible a-IGZO TFT with good electrical and bending performances.

Highlights

The enhancement of the field-effect mobility and electrical stability in amorphous oxide semiconductors is an essential research topic that has recently received great attention in relation to next-generation flat panel displays[1,2], including active-matrix liquid crystal displays and organic light-emitting diode displays[3], as well as flexible electronic applications[4,5]
Hosono group reported that H2O molecules exhibited considerably higher surface reactivity in amorphous InGaZnO (a-IGZO) films than O2 molecules, and the surface reactivity was suppressed by wet annealing at 400 °C26
An excessive supply of H2O induces the formation of OH-related species in a-IGZO, causing a decrease in electrical conductivity and lower field-effect mobility in a-IGZO thin film transistor (TFT), owing to the well-known role of hydroxyl groups as trap sites for electrons[27,28]

Summary

Introduction

The enhancement of the field-effect mobility and electrical stability in amorphous oxide semiconductors is an essential research topic that has recently received great attention in relation to next-generation flat panel displays[1,2], including active-matrix liquid crystal displays and organic light-emitting diode displays[3], as well as flexible electronic applications[4,5]. Low-temperature processable amorphous InGaZnO (a-IGZO) thin films appear very promising, owing to their large area uniformity and the possibility to use flexible substrates, as well as their high field-effect mobility and low off-current level[6,7,8]. We proposed the “wet pulse annealing” technique for low-temperature processable a-IGZO TFTs as a valuable alternative to the conventional dry and wet annealing processes. This process consisted of an artificially periodic exposure to a wet ambient (H2O vapor) and a dry atmosphere (vacuum purge). We successfully employed this approach to fabricate ultrathin a-IGZO TFTs on a flexible polymer with the thickness of a few microns

Methods

Results

Conclusion