Prevention of blistering in preparation of vanadium dioxide films

This paper presents a method for the preparation of VO₂ film. It consists of the following four processes: V₂O₅ sol preparation by a quenching method, V₂O₅ gel film preparation by dip-coating or spin-coating, V₂O₅ film preparation by stove drying in air, and VO₂ film preparation by vacuum heat treatment. The final film prepared by this method is of high quality such as better resistivity switching property than that of those prepared by other techniques. But there is a defect in this method, that is, the film has an inclination to blister after heat treatent. This paper investigated this problem by using DSC, XRD and SEM. It was found that drying before vacuum heat treatment shows strong effect on blistering. The results show that the V₂O₅ gel film undergoes three changes during drying in the temperature range from room temperature to 600°C: evolution of H₂O in the range of room temperature to 140°C, crystallization of V₂O₅ in the range of 260-290°C, and decomposition of V₂O₅ in the range of 330-400°C. Quick evolution of H₂O and crystallization of V₂O₅ were found to be the major reasons fo blistering. To avoid blistering, these two processes should be controlled to occur at a low speed. Drying at >300°C for several hours at a low heating rate (<0.5°C/min) before the vacuum heat treatment was proved to be a good countermeasure to this problem.