Facile Fabrication of High-Performance Thermochromic VO2-Based Films on Si for Application in Phase-Change Devices

This work reports on an alternative and advantageousprocedureto attain VO2-based thermochromic coatings on silicon substrates.It involves the sputtering of vanadium thin films at glancing anglesand their subsequent fast annealing in an air atmosphere. By adjustingthickness and porosity of films as well as the thermal treatment parameters,high VO2(M) yields were achieved for 100, 200, and 300nm thick layers treated at 475 and 550 degrees C for reaction timesbelow 120 s. Comprehensive structural and compositional characterizationby Raman spectroscopy, X-ray diffraction, and scanning-transmissionelectron microscopies combined with analytical techniques such aselectron energy-loss spectroscopy bring to the fore the successfulsynthesis of VO2(M) + V2O3/V6O13/V2O5 mixtures. Likewise,a 200 nm thick coating consisting exclusively of VO2(M)is also achieved. Conversely, the functional characterization of thesesamples is addressed by variable temperature spectral reflectanceand resistivity measurements. The best results are obtained for theVO(2)/Si sample with changes in reflectance of 30-65%in the near-infrared at temperatures between 25 and 110 degrees C. Similarly,it is also proven that the achieved mixtures of vanadium oxides canbe advantageous for certain optical applications in specific infraredwindows. Finally, the features of the different structural, optical,and electrical hysteresis loops associated with the metal-insulatortransition of the VO2/Si sample are disclosed and compared.These remarkable thermochromic performances hereby accomplished highlightthe suitability of these VO2-based coatings for applicationsin a wide range of optical, optoelectronic, and/or electronic smartdevices.