Design And Fabrication Of W/VO₂ Tunable Infrared Absorber

In recent years,great progress has been made in the research on the metamaterial absorber.The optical properties of metamaterial are different due to the artificial material or the composite structure.By changing the geometrical size,surface microstructure and the composition of the metamaterial,it is possible to obtain absorbers with different properties such as infrared absorber,filter absorber,solar cell and so on.In order to make the absorber perform better in the practical applications,the suitable phase transition material is chosen as the dielectric film,so that the tunable performance can be achieved at low and high temperature.As a widely used phase transition material,VO₂ will change from dielectric state to metallic state reversibly when the temperature rises to around 68?,which causes dramatic changes on the structure and properties of the film.Based on the special properties of VO₂ thin film and combined with the plasmon resonance effect of tungsten and the light field penetration effect,two infrared absorbers based on W/VO₂ composite structure were designed and fabricated in this work.?1?Tunable W/VO₂ square lattice infrared absorberThe phase transition material VO₂ was combined with Tungsten to design an infrared absorber based on W/VO₂ square lattice structure.The influence of the structural parameters on the absorption was simulated by FDTD Solution.The thicknesses of VO₂ and W film are both 0.14?m.When the side length and the period of the square lattice are 0.60?m and 1.00?m,respectively,the tunable property is the most obvious.The absorption difference between low and high temperature can reach to 89.74%at the center wavelength of 5.28?m.The theoretical simulation results show that the absorber is polarization-independent at normal incidence and wide-angle absorption at oblique incidence.Compared with the absorber under TM polarization,the absorber has stronger angle-dependence under TE polarization.The electromagnetic field in the absorber is highly localized and exhibits strong absorption at low temperature.While the electromagnetic field is distributed on the surface,the absorption is suppressed at high temperature.In addition,the accuracy of simulation results is verified by the equivalent LC circuit model.The experimental results of the sample are consistent with the simulation.?2?Tunable W/VO₂ planarized absorberIn view of the complicated preparation of the W/VO₂ square lattice absorber,a tunable infrared absorber based on W/VO₂ planarized structure was designed and simulated in the FDTD Solution.The optimal absorption property is achieved with the top VO₂ film thickness of 0.14?m,the middle W film thickness of 0.02?m,the dielectric layer VO₂ thickness of 0.14?m and the bottom W film thickness of 0.10?m,respectively.The absorption tunable range between low and high temperature at the center wavelength of 3.00?m is about 77.10%.It is obvious that the absorber is polarization-independent at normal incidence and wide-angle absorption at oblique incidence.In contrast,the absorber under TM polarization is more pronounced at wide-angle absorption than that under TE polarization.The experimental results of the sample are identical with the simulation results.This planarized structure of the absorber is easy to prepare without lithography or etching.