A Simple Methord Synthesizing VO2 With Almost Coincident Hysteresis Loops On Si

Vanadium dioxide(VO2)is a kind of strongly associated electronic materials that can exhibit an attractive and ultrafast insulator(monoclinic phase)-metal(rutile phase)transition(IMT)at around 68℃.Along with the occurrence of this reversible and stable phase transition,many properties of VO2,including the resistance,optical transmittance,infrared and thermal capacities also change dramatically.On that account,VO2 has been widely studied and applied to photoelectric switches,smart windows,sensors,memory devices and other fields in recent years.In order to meet the requirements of specific functional devices and explore more new possibilities,many methods have been developed for the synthesis of high quality VO2 thin films,including molecular beam epitaxy,pulsed laser deposition,atomic layer deposition,and DC reactive magnetron sputtering,etc.Unfortunately,these methods are faced with the problems of expensive equipment,complex operation or long experimental period inevitably,which limits the practical application of VO2 severely.In most cases,when VO2 is used as a device,especially a sensor or switch,rapid and accurate response is particularly important.However,a wide hysteresis loops width will directly limit its performance,which is very unfavorable for the application of VO2-based devices.Although doping is a relatively reliable way to reduce the hysteresis loops width of VO2 thin films,such as titanium,tungsten,boron doping and so on,the concentration is generally hard to control accurately.Besides,it is not difficult to find that there have been many studies on the orders of magnitude,temperature point,sharpness,and hysteresis loops width of the phase transition of VO2 thin films.As one of the most representative materials,titanium dioxide(Ti O2)has a considerable influence on the all phase transition features of VO2 thin films,and relevant research have been mature increasingly.However,considering the large-scale commercial application of VO2-based devices,it is very significant to prepare VO2 thin films on Si O2/Si or Si substrates to meet the requirements.In contrast,the reports of VO2 thin films with ultra-narrow phase transition hysteresis loops width on Si O2/Si or Si substrates have been rarely seen so far.Moreover,according to the previous experimental results,the hysteresis loops width of VO2 thin films grown on Si O2/Si or Si substrates are not less than 10℃ basically.In this paper,the almost coincident hysteresis loops of VO2 thin film including a Ti O2 buffer layer was deposited successfully on Si substrates by a simple and controllable sputtering oxidation coupling method.Here,the thickness of VO2 and Ti O2 were 60 and 100 nm,respectively.XRD measurement results show that the peak of rutile phase Ti O2 begin to appear while the thickness of buffer layer increases to about 60 nm,which is more compatible with the lattice structure of VO2 and conducive to the growth of VO2 films.Combined with the analysis of XPS spectrum,it is found that the VO2 films formed on different substrates include quite a few V5+ and relatively few V3+ impurity phases.In addition,theoretical analysis indicates that an inversely proportional relationship exists between the hysteresis loops width and the average grain sizes of VO2 thin films,The SEM images confirm this point well revealing the average grain sizes of VO2 thin films does increase with the thickness increase of Ti O2 buffer layer.Therefore,it can be considered that the Ti O2 buffer layer has influence on the VO2 thin film properties from three aspects of lattice structure,phase content and average grain sizes,resulting in the hysteresis loops width narrowing.This work provides a new idea for the applications of VO2 films and devices in integrated circuits and other fields.