arXiv subjects

Yasutaka Matsuo

Publications and source records attributed to Yasutaka Matsuo.

5 recordsLinked to original sources

arXiv2025

Indium Hydroxide Ceramic Targets: A Breakthrough in High-Mobility Thin-Film Transistor Technology

Thin-film transistors composed of a hydrogen-containing indium oxide active layer are promising candidates for backplane devices in next-generation flat panel displays, offering higher definition and faster operation. However, the hydrogen incorporation process during film deposition poses challenges for scalable and industrial development due to both safety and controllability issues. Here, we demonstrate that using indium hydroxide ceramic as the target material for film deposition overcomes the difficulties associated with hydrogen gas usage. We sintered commercially available indium hydroxide powder using a conventional ceramic process at 150-250°C in air and utilized it for the deposition of hydrogen-incorporated indium oxide films via pulsed laser deposition. The resulting indium oxide films, after thermal annealing, contained a sufficient concentration of hydrogen and exhibited very high electron mobility due to significantly grown grains. Furthermore, we confirmed that the fabricated thin-film transistors exhibited comparably high performance to those produced using the gas-phase hydrogen incorporation method. This approach offers a practical pathway for hydrogen-containing indium oxide-based thin-film transistors in next-generation flat panel displays.

cond-mat.mtrl-sci↗

arXiv2024

High-performance solid-state electrochemical thermal switches with earth-abundant cerium oxide

Thermal switches, which electrically turn heat flow on and off, have attracted attention as thermal management devices. Electrochemical reduction/oxidation switches the thermal conductivity (\k{appa}\) of active metal oxide films. The performance of the previously proposed electrochemical thermal switches is low; on/off \k{appa}\-ratio is mostly less than 5 and \k{appa}\-switching width is less than 5 W/mK. We used CeO2 thin film as the active layer deposited on a solid electrolyte YSZ substrate. When the CeO2 thin film was reduced once (off-state) and then oxidized (on-state), \k{appa}\ was about 2.2 W/mK in the most reduced state, and \k{appa}\ increased with oxidation to 12.5 W/mK (on-state). This reduction (off-state)/oxidation (on-state) cycle was repeated 100 times and the average value of \k{appa}\ was 2.2 W/mK after reduction (off-state) and 12.5 W/mK after oxidation (on-state). The on/off \k{appa}\-ratio was 5.8 and \k{appa}\-switching width was 10.3 W/mK. The CeO2-based solid-state electrochemical thermal switches would be potential devices for thermal shutters and thermal displays.

cond-mat.mtrl-sci↗

arXiv2024

Solid-State Electrochemical Thermal Transistors with Large Thermal Conductivity Switching Widths

Thermal transistors that switch the thermal conductivity (\k{appa}) of the active layers are attracting increasing attention as thermal management devices. For electrochemical thermal transistors, several transition metal oxides (TMOs) have been proposed as active layers. After electrochemical redox treatment, the crystal structure of the TMO is modulated, which results in the \k{appa} switching. However, the \k{appa} switching width is still small (< 4 W/mK). In this study, we demonstrate that LaNiOx-based solid-state electrochemical thermal transistors have a \k{appa} switching width of 4.3 W/mK. Fully oxidised LaNiO3 (on state) has a \k{appa} of 6.0 W/mK due to the large contribution of electron thermal conductivity (\k{appa}ele, 3.1 W/mK). In contrast, reduced LaNiO2.72 (off state) has a \k{appa} of 1.7 W/mK because the phonons are scattered by the oxygen vacancies. The LaNiOx-based electrochemical thermal transistor exhibits excellent cyclability of \k{appa} and the crystalline lattice of LaNiOx. This electrochemical thermal transistor may be a promising platform for next-generation devices such as thermal displays.

cond-mat.mtrl-sci↗

arXiv2024

Reliable operation in high-mobility indium oxide thin film transistors

Transparent oxide semiconductors (TOSs) based thin-film transistors (TFTs) that exhibit higher field effect mobility (uFE) are highly required toward the realization of next-generation displays. Among numerous types of TOS-TFTs, In2O3-based TFTs are the front-running candidate because they exhibit the highest uFE ~100 cm2/Vs. However, the device operation of In2O3 TFTs is unreliable; a large voltage shift occurs especially when negative gate bias is applied due to adsorption/desorption of gas molecules. Although passivation of the TFTs is used to overcome such instability, previously proposed passivation materials did not improve the reliability. Here, we show that the In2O3 TFTs passivated with Y2O3 and Er2O3 films are highly reliable and do not show threshold voltage shifts when applying gate bias. We applied positive and negative gate bias to the In2O3 TFTs passivated with various insulating oxides and found that only the In2O3 TFTs passivated with Y2O3 and Er2O3 films did not exhibit threshold voltage shifts. We observed that only the Y2O3 grew heteroepitaxially on the In2O3 crystal. This would be the origin of the high reliability of the In2O3 TFTs passivated with Y2O3 and Er2O3 films. This finding accelerates the development of next-generation displays using high-mobility In2O3 TFTs.

physics.app-ph↗

arXiv2020

Giant enhancement of THz wave emission underdouble pulse excitation of thin water flow

Simultaneous measurements of THz wave and hard X-ray emission from thin and flat water flow when irradiated by double femtosecond laser pulses (800 nm, 35 fs, transform-limited, 0.5 kHz, delay times up to 15 ns) were carried out at the transmission and the reflection sides of the flow with THz time-domain spectroscopy and Geiger counters. THz wave emission spectra show their dynamic peak-shifts toward the low frequency with the highest intensity enhancements more than 1.5 x 10^3 times in |E|^2 at the delay time of 4.7 ns between the two pulses, while X-ray intensity enhancements are limited to about 20 times at 0 ns under the same experimental conditions. The mechanisms for the spectral changes and the intensity enhancements in THz wave emission are discussed from the viewpoint of laser ablation on the water flow induced by the pre-pulse irradiation.

physics.app-ph↗