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 2 h. However, it is found the hexagonal ZnTiO₃ decomposes into cubic Zn₂TiO₄ and rutile TiO₂ at annealing temperature 900°C. 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 ¿, c = ~ 13.85 ¿. In addition, Zn₂Ti₃O₈ phase was observed when the substrate temperature is below 300°C to accompany with annealing temperature at 800°C.