바나듐 이산화물 박막 기반 전자 소자의 광열 제어 전류 스위칭에 관한 연구

Abstract

Vanadium dioxide (VO2), one of the representative oxide semiconductors, exhibits a reversible phase transition (PT) between metallic and insulating states at certain critical temperature. These PT characteristics of VO2 can be applied to a novel electronic device for current switching controlled by optical stimulation. In several studies, photothermally induced PT has been triggered by irradiating a focused high-power laser pulse onto a VO2 thin film. In addition, the current flowing through the device could be controlled. However, in recent studies, the rate of improvement in switching performance began to decrease and tends to saturate. As the control method based on the photothermal effect is mediated by light-induced heat, the thermal characteristics of the device are directly related to the switching characteristics. To investigate the factors affecting the switching performance, it is necessary to scrutinize the temperature distribution and temporal variation by fabricating and testing devices with various structures. However, these characteristics are challenging to analyze experimentally owing to some practical limitations. In this dissertation, an in-depth analysis of the switching characteristics according to various conditions was carried out and a solution to improve the switching performance was proposed. First, a VO2 device was fabricated and bidirectional current switching was performed to confirm the upper limit of the performance and obtain the boundary condition for modeling. Second, the fabricated VO2 device was modeled by employing a commercial software. Numerous simulations were performed by changing various conditions. The dimensions of the substrate and thermal conductivity dominantly determined the switching stability and performance. To maintain a stable operation even under repeated switching, it was necessary to select the appropriate dimensions of the substrate and laser power. The material of the substrate must be changed to a material having a higher thermal conductivity to improve the fundamental switching performance.