Research On Etching Modification Of Vanadium Oxide Thin Films With Phase Transition

Vanadium dioxide（VO₂）is a phase transformation and metal-insulator transition（MIT）material.Below the phase transition temperature（T_C）,VO₂ exists in the monoclinic phase（M）.When the temperature is higher than transformation temperature,VO₂ transforms into the tetragonal rutile（R）phase in metallic state.This transformation not only occurs rapidly,but also is reversible.After VO₂ changes the phase and structure,its physical properties will also change,and show obvious switching characteristics.Based on these characteristics,VO₂ has been widely studied and applied in smart window,terahertz modulation and uncooled infrared detection.In recent years,in order to respond to the national call and achieve energy conservation and emission reduction,smart window is becoming more popular by the day and has become a subject of research.However,there are still some challenges in the practical implementation of smart window:（1）At the same time,it is difficult to achieve the visible light transmittance(T_lum)≥40%and the solar modulation efficiency(ΔT_sol)≥10%;（2）The phase transformation temperature is too high,and it can not be applied at room temperature.With these two challenges in mind,these works have been carried out:（1）The effect of reactive ion etching time on VO₂ thin films was investigated.VO₂thin films of uniform thickness were prepared by magnetron sputtering and then etched with reactive ions for different times.The results show that with the increase of reactive ion etching time,the T_lum of the films continued to rise,but theΔT_sol continued to decline,and finally barely meet the application requirements of smart window;at the same time,the T_C decreased firstly and then increased.Among them,after 6-minute reactive ion etching,the T_lum of sample T2 is 40.52%,theΔT_sol is 12.18%.Therefore,proper reactive ion etching can change the properties of VO₂ films.（2）Effect of complex etching with reactive ion etching followed by acid etching on VO₂ films was studied.The VO₂ films after single reactive ion etching could only barely meet the application requirements of smart window,in order to further improve the performance of theΔT_sol of VO₂ films,after reactive ion etching,it is subject to acid etching treatment.The results show that the T_lum of VO₂ films behind acid etching for different time increased continuously after reactive ion etching for the same time,theΔT_sol increased firstly and then decreased,and both of them could maintain at a high level at the same time;in the mean time,the T_Cdecreased firstly and then increased.Among them,the T_lum of sample S6 that was acid etching for 21 s after reactive ion etching for60 s is 71.47%,theΔT_sol is 14.56%,which far meet the lighting and energy saving requirements of smart window.（3）The effect of reactive ion etching combined with acid etching on VO₂ films was studied.The available datas show that doping W⁶⁺can significantly reduce the T_Cof VO₂films.Therefore,we should consider W⁶⁺doping VO₂ films firstly,and then compound acid etching.The results show that the MIT performance of VO₂ films doped with W⁶⁺of different contents can be significantly improved after reactive ion etching for the same time and acid etching for the same time.Among them,the T_lum of sample FW3 after reactive ion etching for 5 min and acid etching for 14 s is 59.29%,theΔT_sol is 15.89%,the T_C is 31.21℃,the MIT performance is excellent.