High-T_c thin films on low microwave loss alkaline-rare-earth-aluminate crystals

It is demonstrated that the alkaline-rare-earth aluminates (K₂NiF₄-type perovskites) are an excellent choice as the substrate material for the growth of high-T_c thin films suitable for microwave and far-infrared applications. The CaNdAlO ₄ and SrLaAlO₄ single crystals have been grown by Czochralski pulling and fabricated into the form of (001)-oriented wafers. The Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O/ss films deposited on these substrates by a single-target magnetron sputtering exhibited very good superconducting and structural properties. Dielectric properties of the CaNdAlO₄ and SrLaAlO₄ crystals at submillimeter-wave frequencies are also presented and compared to measurements of materials most commonly used as substrates for deposition of high-T_c films. The comparison shows that SrLaAlO₄ is potentially the best material for millimeter-wave applications of high-T_c films because it combines excellent dielectric properties with a good lattice match with the Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O crystals