Microstructure and phase transformation of zinc titanate thin films

ZnTiO₃ have excellent microwave dielectric properties, can be as high-frequency (> 10 GHz) capacitors among the passive components industry. In this study, the microstructures and phase transformations of zinc titanate thin films were investigated. Zinc titanate thin films were synthesized on SiO₂/Si(100) substrates by RF magnetron sputtering using a sintered ceramics target of ZnTiO₃ at various Ar/O₂ mixing ratios (100/0, 90/10, 80/20), the substrate temperatures ranging from 25 to 400 °C and then the as-deposited films were annealed at temperatures ranging from 600 to 900 °C. The samples were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). A single phase of ZnTiO₃ (hexagonal) films could be obtained and existed at substrate temperatures of 400 °C, and annealing temperatures between 700 and 800 °C for 2h. However, it is found the hexagonal ZnTiO₃ decomposes into cubic Zn₂TiO ₄ and rutile TiO₂ at annealing temperature 900 oC. This result is unlike to bulk ZnTiO₃ ceramics which the hexagonal ZnTiO₃ phase remains stable at temperatures below 945°C, and then it decomposes to the cubic Zn₂TiO₄ and TiO₂ phases at 945°C, as indicated in the phase diagram of ZnO-TiO₂. However, the unit cell size of the ZnTiO₃ films crystal is a = ∼5.075 Å, c = ∼13.85 Å. In addition, Zn₂Ti ₃O₈ phase was observed when the substrate temperature is below 300 °C to accompany with annealing temperature at 800 °C.