Effect of crystallinity on the dielectric loss of sputter-deposited (Ba,Sr)TiO₃ thin films in the microwave range

The crystallinity dependence of the microwave dielectric losses in (Ba,Sr)TiO₃ thin films was investigated. The sputter-deposition temperatures were altered to vary the level of thin-film crystallinity on a Pt/Si substrate. The dielectric losses (tan δ) were measured up to 6 GHz without parasitic (stray) effects by using a circular-patch capacitor geometry and an equivalent-circuit model. The microwave dielectric losses increased from 0.0024 ± 0.0018 to 0.0102 ± 0.0017 with increasing crystallinity. These deteriorated dielectric losses showed a good correlation with the symmetry-breaking defects, as confirmed by Raman spectra at approximately 760 cm⁻¹, inducing microscopic polar regions above the Curie temperature of the bulk (Ba_0.43Sr_0.57)TiO₃.