Processing and properties of BST thin films for tunable microwave devices

Dielectric nonlinearity and low losses of ferroelectric thin films with perovskite structure have made them prospective candidates for electric field tunable microwave devices. In this paper, we present the correlation between preparation conditions, microstructure and dielectric behavior of Ba0.5Sr0.5TiO3 (BST) thin films deposited by RF magnetron sputtering on (001) MgO and LaAlO3 single crystal substrates. The composition, crystallinity and morphology of the thin films were analysed by Rutherford backscattering (RBS), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The dielectric measurements were carried out using interdigital capacitors (IDC) with Au electrodes on thin films at 1 MHz. By optimizing the processing, a tunability defined as tu%=ε0−εEmaxε0 of 22% at Emax=10 kV/mm and a low loss tangent of 0.0023 have been achieved. In addition, the role of mismatch stress (both compressive and tensile) on the dielectric properties of the thin films is also discussed.