Infrared modulator based on AZO/VO2/AZO sandwiched structure due to electric field induced phase transition

Abstract

Electric field induced semiconductor-metal transition characteristics of VO2 indicate extensive application prospects in smart window,storage device,intelligent radiator,signal generator,optical switch,etc.In order to explore the electric field induced semiconductor-metal transition characteristics of VO2,AZO/VO2/AZO sandwiched structure is prepared to study the problem of optical modulation under the action of applied electrical drive.Firstly,V thin film is fabricated by direct current magnetron sputtering on a ZnO-doped Al (AZO) conductive glass substrate.The operating pressure during sputtering is kept at 3.610-1 Pa,and the sputtering current and voltage are 2 A and 400 V,respectively.The VO2/AZO composite film is prepared by annealing under the air atmosphere for 3.5 h at 400℃.Secondly,another AZO conductive film is deposited by radio frequency magnetron sputtering on the top of the VO2 thin film.Thirdly, Pt electrodes are patterned on the bottom and top of AZO conductive glass by using photolithography and chemical etching processes,and finally AZO/VO2/AZO sandwiched structure is achieved.The crystal structure of the thin film is analyzed by X-ray diffraction (XRD) apparatus.The surface morphologies of the samples were studied by atomic force microscope (AFM).X-ray photoelectron spectroscopy (XPS) system is used to study the relative quantity of the surface elements.The current-voltage characteristics are measured by semiconductor parameter analyzer.The optical properties of the AZO/VO2/AZO sandwiched structure are determined by spectrophotometer.XRD results show that the VO2 thin film has a distinct (011) preferred orientation and well-crystallized structure.AFM results indicate that the VO2 thin film has compact nanostructure and smooth surface with a surface roughness of 5.975 nm.XPS results reveal that the VO2 thin film has high purity.Optical transmittance curves show that the maximum change of the optical transmittance measured from VO2/AZO composite film during the phase transformation is 24% at 800-2300 nm,while the maximum modulation of the transmittance of AZO/VO2/AZO sandwiched structure reaches 31% in the same wavelength range. When applying different voltages to AZO/VO2/AZO sandwiched structure at different ambient temperatures,the current abrupt change can be seen at the threshold voltage.The threshold voltage of the thin film phase transition is 8.1 V at 20℃,while the threshold voltage is 5.9 V at 40℃.However,the threshold voltage is zero at 60℃,which indicates that the semiconductor-metal transition of the VO2 thin film happens at that temperature.It can be found that the higher the ambient temperature,the lower the threshold voltage is.AZO/VO2/AZO sandwiched structure has stable properties with simple preparation technology,and its modulation property meets the performance requirements for electro-optic modulator under applying the electrical drive,which is expected to be applied to the integrated infrared modulator.