Compositionally graded BaxSr1−xTiO3 thin films for tunable microwave applications

Compositionally graded BaxSr1−xTiO3 (BST) thin films (from x=0.7 to 1) were fabricated for high frequency tunable applications using a modified sol–gel technique. The structure, surface morphology and compositional gradient of the films were characterised by glancing incidence X-ray diffraction (XRD), atomic force microscopy and Rutherford backscattering. The small signal dielectric constant (εr) and dielectric loss (tan δ) at 100 kHz were found to be 520 and 0.03. Dielectric constant and dielectric loss are relatively stable in a wide range of temperature. Dielectric properties change significantly with applied dc bias field and the graded thin film show high tunability of 40% at an applied field of 230 kV cm−1.