Superconducting YBCO films on polycrystalline yttrium-iron-garnet using IBAD-YSZ as a template

Monolithic integration of high quality YBCO films on polycrystalline yttrium-iron-garnet (YIG) substrates represents an advance of great technical significance for magnetically tunable microwave components. We have solved the problem of crystallographic incompatibility between the two materials and the lack of an epitaxial template for the growth of well-oriented YBCO films. Using a buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ), deposited by an ion-beam-assisted-deposition (IBAD) technique, we routinely produced device quality YBCO films on polycrystalline YIG substrates. The YBCO films were c-axis oriented with an in-plane mosaic spread of less than 7° FWHM. The films had transition temperatures above 88 K, transition widths less than 0.3 K, and critical current densities above 10⁶ A/cm² in self-field at 75 K. The surface resistance of the films was ∼0.86 mΩ at 10 GHz and 76 K.