IEEE Access (Jan 2023)
Modeling Phase Changing Property of VO<sub>2</sub> for Reconfigurable Microwave Frequency Selection Applications via Time-Resolved Microwave Conductivity
Abstract
Vanadium dioxide (VO2) is characterized using the time-resolved microwave conductivity (TRMC) method for applications requiring reconfigurable microwave frequency selection. We demonstrate that TRMC is a flexible method for determining the microwave conductivity of thin film compounds of varied thicknesses that are both phase-changing and non-phase changing in nature. The method makes use of Ka-band microwave resonant waveguides to examine how thermally excited samples’ microwave conductivity changes in response to microwave-transmitted power through the system’s sensitivity factor. The sensitivity factor is illustrated by a study of incident waves (electromagnetic fields) on medium and waveguide perturbation analysis in VO2 thin films. The TRMC measurements show a low regime in the microwave conductivity below the transition temperature ( $T_{c}$ ) of VO2 where $T_{c}$ occurs near 65°C; this is associated with the dielectric characteristics of the charge carriers and points to the presence of shallow trap electron states. Longer electron hops enhance charge mobility and, consequently, the barrier energy above $T_{c}$ , where these states are thermally discharged, resulting in a high thermally triggered microwave conductivity regime. The activation energy may come from a variety of complex contributions, like polaronic self-localizations, as well as a dynamic disorder brought on by the thermal oscillations of VO2 molecules. The calculated conductance values are simulated in CST Studio as plane wave incidence on medium to ascertain the fields’ microwave transmission behavior and contrast it with the experimental results to validate the model. Additionally, using the derived conductivities, the characteristics of well-known materials like copper (Cu) were confirmed.
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