Research On Phase Change Modulation Properties Of Doped Vanadium Dioxide Thin Films

Vanadium dioxide（VO₂）has a reversible phase transition from semiconductor phase to metal phase at 68℃.Its significant changes in infrared optical transmittance before and after phase transition make it have broad application in emerging optical devices,such as optical switches,infrared optical modulators and smart windows.In order to improve the sensitivity、stability and reliability of thermo-switched modulation devices,VO₂ films are required to have higher amplitude modulation、narrow hysteresis width and lower phase transition temperature.As we all know,element doping can effectively regulate the phase transition temperature（T_C）of the VO₂ films.At the same time,it will significantly reduced the superior electrical and optical phase transition properties of the VO₂ films,especially when T_C drops to near room temperature.Therefore,the effective solution for decreasing phase transition temperatures while maintaining superior amplitude modulation is necessary.In this article,the following work is focused on improving the optical phase transition properties of doped VO₂ films:（1）It is studied the effect of W doping on the optical phase transition characteristics of VO₂ films.The results show that W doping has a negative effect on the optical transmittance switching of VO₂ films while effectively reducing the phase transition temperature and reducing the hysteresis loop width.Specifically,as the W doping concentration increased,the infrared amplitude modulation of the VO₂ film prepared on the quartz substrate decreased from 66.21%to 47.24%,decrease 18.97%.The infrared amplitude modulation of the VO₂ film prepared on the glass substrate was reduced from 63.06%to 27.83%,decrease 35.23%.（2）The effects of different annealing temperatures on the thermochromic properties of W-doped VO₂ films were investigated.The results show that proper annealing temperature can improve the crystal quality of the film、increase the particle size and make the grain boundary more obvious.At the same time,VO₂ film with the1.4 at.%ratio of W contents annealed at 400℃ shows a significant improvement in infrared optical amplitude modulation.Compared with undoped VO₂ film,W-doped VO₂ film has lower phase transition temperature（37.4℃）,narrower hysteresis loop width（4.3℃）and excellent infrared amplitude modulation（69.97%）.（3）Adding precursor nano-vanadium oxide seed layer in the W-doped VO₂ film,the results show that 0.15%concentration nano-vanadium oxide seed layer can increase the infrared amplitude modulation from 54.41%to 68.30%,improving 13.89%.The phase transition temperature is 39.0℃,hysteresis loop width is 5.1℃and amplitude modulation is 68.30%of W-doped VO₂ film.（4）Prepared VO₂ buffer layer on the substrate reduces the degree of lattice mismatch between the substrate and the upper deposited film.26nm VO₂ buffer layer increased the infrared amplitude modulation of the W-doped VO₂ film from 54.41%to62.83%,increasing 8.42%.The phase transition temperature is 44.5℃,the hysteresis loop width is 7.8℃and the amplitude modulation is 62.83% of the W-doped VO₂ film.