Research On Preparation And Characteristic Of Voxthin Films With Thermal And Photo Induced Phase Transition

The phase transition characteristic of vanadium oxide was discovered by aresearcher who worked in bell LABS half a century ago. Of all the vanadium oxide,Vanadium dioxide (VO2) exhibits a metal-insulator transition (MIT) behavior that alarge reversible first-order change in electricity, optical, magnetic, etc occurs at acritical temperature of68℃. So it has been studied to apply in THz switch,photoelectric switch,phase change memory,smart windows and microbolometer.The MIT characteristics of VO2thin films, such as transition temperature,resistivity changing amplitude, hysteresis width, and THz transmittance vary in a widerange due to different preparation method. Besides, the higher the purity of VO2thinfilm, the more difficult it will be to prepare. It will generate vanadium oxide (VOx)thin film mixed with V3+and V5+. In order to improve the phase transitioncharacteristic of thin VOxfilm, we should try to increase the content and improve thecrystalline state of VO2.The VOxthin is prepared on R-sapphire substrate for the first time by magnetronsputtering with Rapid Thermal Process (RTP). The electrical characteristic and THztransmittance of MIT in VOxfilm is studied by four-point probe method and THz timedomain spectrum (THz-TDS). XRD, XPS and AFM are employed to analyze thecrystalline structure, valence state and surface morphology of the film.Results indicate that, as the heat treatment temperature or heat treatment time ofthe vanadium thin film with a thickness of70nm increase in oxygen atmosphere, thevalence state of vanadium oxide thin film becomes higher; the resistance and THztransmission become higher at room temperature as well; the particles on the thin filmbecome bigger due to the agglomerating of it, and the surface roughness is increased.The metal Vanadium film become VOxfilm which has the best properties of phasetransition among them after RTP at450℃for60s in pure oxygen atmosphere. Thesheet square resistance changes2.2orders of magnitude and the THz switching ratioreaches18%and14%in thermal and optical excitation respectively. After RTP at450℃for40s in pure nitrogen atmosphere, the properties of VOxfilm will get better.The crystallization and components of VO2film has been improved and the film becomes compact and uniform. A better phase transition performance is shown thatthe resistance changes nearly3orders of magnitude with a2℃hysteresis width andthe THz transmittance decreases64%and60%in thermal and optical excitationrespectively.