Transient Thermal Properties Research Of Vanadium Dioxide Thin Film

Vanadium dioxide is a phase change material with excellent property.Its phase transition temperature from the insulating phase to the metallic phase is very close to the room temperature.With the phase change,its thermal,optical,electrical and magnetic properties will change dramatically,therefore,VO₂ has great potential application value,which can be widely used in the fields of thermal switches,optical switches,energy information storage and other microelectronic devices.However,the development of microelectronic products is moving towards a more portable,smaller and higher-performance direction,which brings about the problem of power consumption,therefore,it is of great significance to study the thermal properties of materials,especially the transient thermal properties that are closest to the actual usage.In the past few decades the optical,magnetic,electrical and even electron migration properties of VO₂ thin films during the phase transition have been studied in detail,but few reports have been reported on the thermal properties of VO₂ films before and after the phase transition,such as the measurement and study of transient thermal diffusion curves.This limits the application and development of VO₂ thin films in the thermal field.At present,there are mainly two methods for measuring the thermal properties of materials at the micro-nano scale:contact and non-contact.Contact measurement methods mainly include periodic heating method,3?method,suspended thermal conductivity method and short line method;Non-contact measurement methods mainly include flash method,photothermal reflection method and photoacoustic method.But these methods are unable to obtain the transient thermal diffusion curve of the material and solve the accurate thermal conductivity,which leads to great limitations in the study of the transient thermal properties of the material.In view of the above problems,this study attempts to study the transient thermal properties of VO₂ thin films by combining experiment and simulation.For this purpose,this work firstly prepared four sets of high quality VO₂ film samples with different thickness by polymer-assisted deposition?PAD?method,then transmission and reflectance properties of the samples at different temperatures were measured.Through the tested results of Resistance-Temperature?R-T?curve,Raman and XRD spectra of four groups of VO₂ thin film samples,the electron interaction,lattice deformation and lattice defects in VO₂ thin film with different thickness were analyzed in depth.Then,the transient thermal diffusion curves of four groups of VO₂ thin film samples were tested and analyzed by using the NanoTR thermal analysis system.The thermal diffusion curves and their changes in the range of 297K-353K of VO₂ thin film were obtained,and the thermal conductivity of the four groups of samples before and after the phase transition was obtained by fitting the thermal diffusion curves with the thermal analysis software.Finally,a simplified two-layer transient heat conduction model of VO₂ thin films was established by using ANSYS finite element analysis software,and the thermal diffusion curves of four groups of VO₂ thin films with different thicknesses at 297K and 353K were simulated after verifying the model with standard samples.By comparing experimental and simulation data,the thermal conductivity of VO₂ thin film before and after the phase transition is obtained.In the study of the change of thermal conductivity of VO₂ film caused by different film thicknesses,combined with the heat conduction mechanism in the crystal,the electron-electron heat conduction,phonon-phonon heat conduction and phonon scattering in VO₂ film were analyzed.By excluding the influence of interface contact thermal resistance,it is confirmed that the influence of film thickness on lattice deformation leads to the change of thermal conductivity of VO₂ film.