Effect of annealing on microstructure and dielectric properties of Zn2Ti3O8 thin films by reactive co-sputtering

Microstructure and dielectric properties of Zn2Ti3O8 films deposited on Pt/Cr/SiO2/Si via a DC reactive magnetron co-sputtering method using zinc and titanium metal targets in O2/Ar atmosphere are investigated. The as-deposited Zn–Ti–O film has an amorphous microstructure. A single Zn2Ti3O8 phase appeared when the films were annealed at 500 °C and 600 °C for 1 h. As the temperature further increased to 700 and 800 °C, it was found that Zn2Ti3O8 and ZnTiO3 phases coexisted. A phase transformation from cubic Zn2Ti3O8 and rhombohedral ZnTiO3 to cubic Zn2TiO4 and rutile TiO2 was observed while a further increase in temperature up to 900 °C. The heat treatment also induces a change in the surface morphology of the thin films observed by scanning electron microscopy. Transmission electron microscopy examination indicated that the film annealed at 700 °C was composed of Zn2Ti3O8 and ZnTiO3 with fine and large grains in microstructure, respectively. The study also reveals that the dielectric constant of the films depends on the annealing temperature. When annealing at 600 °C, the Zn2Ti3O8 films has the following properties at 1 MHz: dielectric constant = 32.9, tan δ = 0.022.