The Effect Of Film Thickness Modulation And Doping On VO₂Transition Properties

As a typical thermochromic functional material, vanadium dioxide (VO2) single crystals willundergo reversible transitions from the monoclinic structure phase of the semiconductor propertiesto the rutile structure phase of the metal characteristics at about68℃. Accompanied with thephase transition, optical and electrical properties of VO2single crystals will occur mutation. Sincethe phase transition can be completed in10-12s and is repeatedly reversible, VO2has an attractiveprospect.But in practical application, VO2thin film instead of bulk crystal is used to avoid the volumechange accompanied by structure transition, which shows a MIT similar to bulk crystal butgenerally has worse and more uncertain MIT properties. In single crystals, resistance changes4decades with a narrow transition width△T≈1℃, while the magnitude changes of polycrystallinethin film can be a value shock between1-3, at the same time the hysteresis width can be evenwider than36℃.The changeable properties caused by the use of thin film not only broaden thescope of VO2application but also make the applications have more room for improvement. Withthe study on the effect of film thickness modulation and doping on the phase transition of VO2films, some impact mechanisms of VO2phase transition were established, and a simplemodulation of the film VO2phase transition can been achieved.Through strict control of variables, high quality vanadium dioxide (VO2) films with thicknessranging from29-670nm were fabricated on Al2O3substrates by DC sputtering and oxidationcoupling method. In this paper, the enlargement of resistance magnitude and the shrink ofhysteresis width are simultaneously found with the increase of film thickness. The VO2thin filmas thick as463nm not only shows a large resistance magnitude of3.48but also shows a narrowhysteresis width of3℃. The experiment phenomena was related to the transversal grain sizeexpansion with increasing film thickness by excluding other impact factors, and impactmechanisms of grain size on resistance magnitude and hysteresis width were established at thesame time.In addition, we also realized the doping to VO2with sputtering and oxidation couplingmethod, and the influence of Cr and Ti elements on VO2phase transition characteristics have been verified. By the contrast of different change trends of hysteresis width after doping, the effectof doping on the phase transition hysteresis width was concluded.