Flexible High-Performance Amorphous InGaZnO₄Thin-Film Transistors Utilizing Excimer Laser Annealing

Abstract

We have investigated an excimer laser annealing (ELA) process for use in fabricating high-performance amorphous InGaZnO4 (IGZO) thin-film transistors (TFTs) on flexible plastic substrates. We numerically estimate the temperature increase of the IGZO film and substrate as a function of laser energy density. This is one of the most important measures for optimizing ELA conditions in order to apply plastic-based TFT fabrication. Because the optical absorption coefficient of IGZO film is three orders of magnitude higher than that of plastic substrates with respect to 308-nm laser light, it is possible to selectively increase the temperature of the IGZO film. The temperature of the IGZO film is estimated to increase to approximately 1500 °C at typical laser energy levels. Furthermore, incorporating a SiO2 buffer layer (some hundreds of nm) between the IGZO film and the plastic substrate is found to effectively suppress thermal damage to the substrate. We have experimentally investigated the properties of IGZO films irradiated with various excimer-laser energy densities. X-ray diffraction patterns and carrier densities of the IGZO films are found to significantly vary with laser energy density. We have used calculations and experimental results to optimize the ELA process; this has enabled us to produce high-performance IGZO-TFTs having a field-effect mobility of 15.6 cm2 V-1 s-1.