Preparation of (1−x%)(Na0.5Bi0.5)TiO3–x%SrTiO3 thin films by a sol–gel method for dielectric tunable applications

(1−x%)(Na0.5Bi0.5)TiO3–x%SrTiO3 (NBTSx) thin films were deposited on Pt/TiO2/SiO2/Si substrates by a spin-on sol–gel method and rapid thermal annealing. The stock solutions were prepared using sodium acetate, bismuth acetate, strontium acetate, and titanium n-butoxide as precursors, ethanol, and acetic acid as solvents and acetylacetone as the chelating agent. The thermal treatment conditions were determined by thermal analyses of the dry gel powders derived from the stock solutions. Structure and dielectric tunable properties of the films were studied as functions of Sr concentration. NBTSx films exhibit the perovskite structure of a pseudo-cubic symmetry with the lattice parameters increasing with increasing Sr concentration. It was found that the substitution of Sr in Na0.5Bi0.5TiO3 may greatly reduce the dielectric loss while decrease the tunability at the same time. The best figure of merit was achieved in NBTS80 films. The results were discussed and compared with related materials.