Characterization of reactive sputtered TiO2 thin films for gas sensor applications

The technology for preparing and characterisation of titanium dioxide (TiO2) thin films with properties appropriate for usage as gas sensors are discussed. For preparing the samples the methods of reactive radio frequency (RF) and direct current (DC) magnetron sputtering were used. The composition and microstructure of the films were studied by XPS, EPMA, XRD and Raman spectroscopy and the surface of the films was observed by high resolution SEM. Thorough profile analyses on the structure changes were performed by XPS. Interactions with the substrate and changes between the different modifications of the crystal structure also were investigated. For measuring the thickness and to identify the refractive indices of the films laser ellipsometry was used. The research was focused on the sensing behaviour of the sputtered TiO2 thin films. Films of various thickness were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was used. This enables highly sensitive gas sensor capable of detecting changes in the molecular range to be constructed. Prototype QCM sensors with TiO2 sensitive films made in our laboratory, showed good sensitivity to ammonia at room temperature, and are currently being tested for sensitivity to other gasses.