Simple and reliable direct patterning method for carbon-free solution-processed metal oxide TFTs

Masashi Miyakawa,Yoshihide Fujisaki,Mitsuru Nakata,Hiroshi Tsuji

doi:10.1038/s41598-018-31134-w

Abstract

Metal oxide TFT fabrication based on a solution-processing method is considered a promising alternative to conventional vacuum processing and has a number of advantages such as low cost, large-area fabrication, and process simplicity. A simple and reliable, direct patterning method for obtaining a carbon-free aqueous metal oxide film is presented herein. Patterning, which is achieved by selective photoreaction of water molecules under ultraviolet irradiation and by a safe, environment-friendly chemical etching process using a non-toxic organic acid, is followed by an annealing process at a temperature of 350 °C to obtain carbon-free metal oxide TFTs. In–Ga–Zn oxide (IGZO), TFTs on SiO2 dielectrics that were fabricated with a direct patterning method exhibited an average mobility of 4.3 cm2/V·s with good uniformity, which is comparable to TFTs formed by conventional photolithography. The TFTs exhibited stable performance with small (within 0.5 V) shifts in switch-on voltage under positive and negative bias stress. Fabrication of flexible IGZO TFTs by direct patterning was also achieved.

Highlights

Thin-film transistors (TFTs) based on metal oxide semiconductors, such as In–Ga–Zn oxide (IGZO), are highly desirable due to their high mobility, high on/off ratio, and transparency[1,2,3,4]
Photolithography requires multiple steps, involves a time-consuming baking and drying process, and produces a lot of waste, including toxic volatile organic compounds (VOCs) and other waste gases that are emitted into the environment[37]
The patterning method is achieved by the photooxidation of water molecules and nitrate ligands

Summary

Introduction

Thin-film transistors (TFTs) based on metal oxide semiconductors, such as In–Ga–Zn oxide (IGZO), are highly desirable due to their high mobility, high on/off ratio, and transparency[1,2,3,4]. A direct patterning method that limits the amount of organic content in the precursor is critical to reducing carbon impurities in the oxide film for improved performance. The research literature has reported the successful fabrication of metal oxide films for TFT applications by combined UV irradiation and photo-annealing process[31,32,33,34,35]. The precursor was still prepared with carbon-based materials, such as organic solvents, additives, and ligands in metal salts. A direct patterning method for fabricating carbon-free metal oxide thin films was proven using aqueous metal oxide precursors that were prepared without any carbon-related species. We successfully fabricated carbon-free, solution-processed oxide TFTs by direct patterning, which are comparable in performance to TFTs fabricated by conventional photolithography

Methods

Results

Conclusion