Electrically tunable microwave devices prepared by rf-magnetron sputtering

In this work, we have used the Warren-Averbach method to analyze the x-ray diffraction patterns of several Ba_0.6Sr_0.4TiO₃ (BST) epitaxial thin films deposited via 90° off-axis rf-magnetron sputtering. This method allows for the determination of the coherent strains, incoherent strains, crystallite sizes, and defect densities in these films. Results indicate that for BST (60/40) films, the incoherent strain normal to the substrate is smaller on LAO compared to MgO for films 200 Å - 3000 Å thick. However, the opposite relationship holds for the coherent strains. The thickest films showed dielectric constants of 1350 and 925 on MgO and LAO, respectively (at 1 MHz). All showed dielectric loss on the order of 0.007 with the room temperature tunability being 3 times greater for the films on MgO. In-plane measurements of the coherent strain were also completed, showing good agreement with theoretical predictions of the effects of strain on the dielectric properties.