Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar:O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.