Research On The Preparation And Phase Transition Properties Of Tantalum Element Doped Vanadium Oxide Thin Films

As a functional material that can undergo reversible phase transformation under the excitation conditions of light,electricity and heat,vanadium oxide(VO₂ )thin films have obvious switching properties in both electrical and optical aspects before and after phase transformation.Due to its excellent phase transformation properties,VO₂ films are widely used in smart windows,optical switches and optical modulation.In general,the thermal hysteresis loop width of the prepared VO₂ films is more than 10?,and the difference between the phase transition temperature(60?)and the indoor temperature(30?)is still greater than 30?,so that they can not be used in most fields.Therefore,it is more necessary to adjust the MIT properties of VO₂ films according to the specific application requirements.Considering the potential application of VO₂ films in the field of far-infrared/THz modulation,it is not feasible to simply improve the modulation amplitude of the films without optimizing other parameters,and lower phase transition temperature and narrower loop width of the films are also required.In order to solve this problem,this paper mainly launched the following work:(1)The phase transition temperature and the loop width of VO₂ thin films can be optimized by doping high-priced ions,we studied and analyzed the influence of high-priced transition metal Ta⁵⁺doping on the phase transition properties of VO₂ thin films.By measuring the transmittance of the sample in the far-infrared band,it was found that with the increase of Ta⁵⁺content,the loop width of VO₂ thin film is narrowed,the phase transition temperature is lowered,and the optical modulation amplitude of far-infrared/THz band is slightly reduced.When the doping content of Ta⁵⁺is 0.71%,the phase transition temperature of VO₂ thin film is reduced to 37.5?,the loop width is narrowed to 1.03?,and the THz modulation amplitude is kept at 64.2%,which is more suitable for the application of THz modulator.(2)In the process of preparing VO₂ films by magnetron sputtering,there are high requirements for the process conditions.The different process parameters have an important effect on the growth,crystallization and phase transformation characteristics of VO₂ films.In order to better study the MIT properties of Ta⁵⁺doped VO₂ films,the effects of sputtering time,reactive oxygen content and substrate temperature on MIT properties of Ta⁵⁺doped VO₂ films were studied and analyzed.(3)As a kind of metal ion,W⁶⁺can effectively reduce the phase transition temperature of VO₂ films.The influence of Ta/W co-doping on the MIT properties of VO₂ thin films was analyzed by considering the addition of W element on the basis of Ta element.In the sample TW3-TW6,VO₂ films co-doped with Ta and W were prepared.The phase transition temperature of VO₂ films was further reduced by the addition of Ta in the sample TW4,and the excellent MIT performance of VO₂ films with loop width of 1.19?,phase transition temperature of 30.83?and optical modulation depth of 82.49%was obtained.