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 InGaZnO 4 (IGZO) thinfilm 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 SiO 2 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 cm 2 V À1 s À1 . #

Effects of Excimer Laser Annealing on InGaZnO4Thin-Film Transistors Having Different Active-Layer Thicknesses Compared with Those on Polycrystalline Silicon

“…2), and we can estimate, using a simple calculation, that the carrier density must be less than roughly 2 Â 10 18 cm À3 in order to achieve a depletion width greater than 20 nm. 20) Although a similar tendency was observed for the 50-nm-thick IGZO film, carrier density significantly increased at a lower energy density than that for the 20-nm-thick IGZO film. Figure 5 shows the dependence of the Hall mobility of the IGZO film on laser energy density for film thicknesses of 20 and 50 nm.…”

“…We consider that the significant improvement in the transfer characteristics by ELA is mainly due to the reduction in the trap density below the conduction band in the IGZO films, which is caused by the rise in the temperature of the IGZO films. 16,20) When the laser energy density was roughly 210 mJ/cm 2 , Hall mobility increased significantly, which can be explained by the fact that Hall mobility increases with increasing carrier density. 3) When the laser energy density was 400 mJ/cm 2 , Hall mobility decreased, even though the carrier density was as high as roughly 1 Â 10 19 cm À3 .…”

Microstructural Characteristics of InGaZnO Thin Film Using an Electrical Current Method

“…3,4) The IGZO system has been reported constantly, and most of the reports have focused on the relationship between the atomic ratio and device characteristics. 25) Furthermore, many papers have discussed the annealing effects of IGZO thin films, but the depositing oxygen flow conditions affecting the film matrix have still not been examined.…”

Performance improvements of IGZO and ZnO thin‐film transistors by laser‐irradiation treatment

“…10 In addition, the influence of laser annealing on the electrical properties of IGZO TFTs fabricated by sputtering was reported. 11 In the semiconductor industry, pulsed laser annealing has been applied to improve the structural, optical, and electrical characteristics of polycrystalline semiconductor films. This study investigates the influence of irradiation parameters on the characteristics of solution-based TFTs with ZnO/IGZO as the active layer.…”