Study of Thermal properties of VO2 and multilayer VO2 thin films for application in Thermal Switches.

Ultrafast nature of the phase transition near room temperature in VO$_{\mathrm{2}}$ makes it attractive material for applications in electronics and optical devices however utilization of corresponding drastic change in thermo-physical properties are rarely reported. In this study we investigate thermal and electronic properties of VO$_{\mathrm{2}}$ thin films on various substrates across the transition temperature to seek possibility of utilizing VO$_{\mathrm{2}}$ based thermal switches for applications in thermal devices. In addition, the interfacial heat transfer in VO$_{\mathrm{2}}$/metal multilayer thin film is mediated by phonons at low temperature, and when temperature is elevated beyond phase transition temperature, the interface thermal conductance is mediated mainly by both phons and electrons. VO$_{\mathrm{2}}$-multilayers approach is studied to utilize the switching interface thermal conductance in order to obtain higher thermal conductivity switch ratio than what can be achieved in intrinsic VO$_{\mathrm{2}}$. Thermal conductivities and interface thermal conductance of VO$_{\mathrm{2}}$ and VO$_{\mathrm{2}}$ multilayer thin films are measured using the time-domain thermoreflectance (TDTR) method. We will discuss interplay of phononic and electronic component to thermal conductivity in the light of Wiedemann--Franz law across the metal to insulator state of VO$_{\mathrm{2}}$ films.