Effect of W addition on the electrical switching of VO₂ thin films

Vanadium Oxide has been a frontrunner in the field of oxide electronics because of its metal-insulator transition (MIT). The interplay of different structures of VO₂ has played a crucial role in deciding the magnitude of the first order MIT. Substitution doping has been found to introduce different polymorphs of VO₂. Hence the role of substitution doping in stabilizing the competing phases of VO₂ in the thin film form remains underexplored. Consequently there have been reports both discounting and approving such a stabilization of competing phases in VO₂. It is reported in the literature that the bandwidth of the hysteresis and transition temperature of VO₂ can be tuned by substitutional doping of VO₂ with W. In this work, we have adopted a novel technique called, Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) to deposit VO₂ and W- doped VO₂ as thin films. XRD and Raman spectroscopy were used to investigate the role of tungsten on the structure of VO₂ thin films. Morphology of the thin films was found to be consisting of globular and porous nanoparticles of size ∼ 20nm. Transition temperature decreased with the addition of W. We found that for 2.0 at % W doping in VO₂, the transition temperature has reduced from 68 ^o C to 25 ^o C. It is noted that W-doping in the process of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration.