Metal-insulator Transition And Temperature Sensing Characteristics Of Cr-Nb Co-doped VO₂ Epitaxial Thin Film

The reversible metal-insulator transition?MIT?of VO₂ occurs approximately 68?.In the phase transition region,physical properties such as light absorption,refractive index,resistivity,magnetic susceptibility and specific heat are changed.Preliminary studies have shown that VO₂ thin film has high TCR,and easy to be compatible with modern semiconductor process,which is expected to realize large-scale application.Due to the shortcomings of low phase transition temperature?68??,large hysteresis of TCR curve,and poor resolution of light wavelength,the application of VO₂ thin films in temperature detectors and thermal infrared detectors is greatly limited.To resolve the above problems,this paper proposed the strategy of element co-doping to explore the manipulation method of Cr and Nb co-doping on the microstructural properties and the characteristics of MIT of VO₂ epitaxial thin films.We studied the microstructure,temperature-and light-response of the undoped and doped VO₂ epitaxial thin films,and also proposed the design scheme of photothermal detection circuit and the results were obtained following as:1.Microstructural characterizations of VO₂ thin films and the MIT controlled by strain and doping strategy.High-quality and pure Cr or Nb doped VO₂ epitaxial thin films were fabricated by RF magnetron sputtering techniques through changing the target material composition with different doping ratio.XRD,RAMAN,XPS and other characterization methods were used to study the crystal and electronic structure of the films.We found that the Cr or?and?Nb doping did not affect the epitaxial properties of VO₂ films,and VO₂ remained monoclinic in an insulating phase at room temperature.In the analysis of the valence state on the film,it was observed that the doping elements did not change the electron valence state of VO₂.V element still existed in the state of V⁴⁺,and the doped impurity elements Cr and Nb existed in the form of Cr³⁺and Nb⁵⁺,respectively.We also observed that the MIT was suppressed by doping,the thermal hysteresis width was obviously reduced and the TCR curve was linear with respected to the temperature.On the other hand,we realized the strain control of the MIT temperature in the VO₂/Ti O₂ epitaxial thin film system,the phase transition temperature was reduced to near room temperature.2.We performed temperature and light response measurements of the VO₂ thin films.By means of self-built,in-situ optical property measurement platform,we determined the relationship between the temperature and light responsive properties and the doping element and its ratio.It was found that when the doping ratio of Cr:Nb element was close to 2:1,the temperature responsive characteristics?TCR,thermal hysteresis width,linearity?were the best.The TCR?dln R/d T?was up to-3.6%and the thermal hysteresis width was less than 0.5?.Moreover,under the conditions of 20?,60?and 100?,its resistance was nearly linear with the change of light intensity,and it was much more sensitive to the green light with the wavelength of 530 nm.Based on the photothermal characteristics of doped VO₂ thin films,we proposed a circuit design scheme for two-dimensional photothermal detection array,which is expected to be applied to wide-temperature and uncooled photothermal detectors.