A simple method for synthesizing VO2 with almost coincident hysteresis loops on Si substrate containing TiO2 buffer layer

Highlights: • VO₂ and TiO₂ thin films were synthesized on Si substrates by a simple and controllable method. • The almost coincident hysteresis loops of VO₂ thin films including a TiO₂ buffer layer was realized on Si substrates. • The reasons for the narrowing of hysteresis loops width of VO₂ were analyzed and summarized from three aspects. -- Abstract: The overlapped degree of hysteresis loops is critically important for the accurate response of vanadium dioxide (VO₂)-based optoelectronics devices. Generally, the hysteresis loops width is not less than 10 ℃ for VO₂ thin films deposited on amorphous SiO₂/Si or Si substrates. In this work, the almost coincident hysteresis loops of VO₂ thin films including a TiO₂ buffer layer was synthesized successfully on Si substrate by a simple and controllable method. Here, the thickness of VO₂ and TiO₂ were 60 nm and 100 nm, respectively. XRD patterns show that the peak of rutile phase TiO₂ begin to appear while the thickness of buffer layer increases to about 65 nm, which is more compatible with the lattice structure of VO₂. Combined with the XPS spectra, it is found that the VO₂ thin 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 size of VO₂ thin film, The SEM images confirm this point well revealing the average grain size of VO₂ thin film does increase with the thickness increase of TiO₂ buffer layer.