Growth and characterization of YBCO/insulator/YBCO trilayers

Multilevel circuits for high-frequency applications of high-T/sub c/ superconductors require low-dielectric-constant insulators between superconducting layers. Initial studies of CeO/sub 2/ thin films as the insulating layer in YBCO/insulator/YBCO structures revealed insufficient isolation between YBCO layers. Trilayer structures employing thin-film composite dielectrics of CeO/sub 2/ and SrTiO/sub 3/ were therefore investigated. Each layer grows epitaxially with a morphology comparable to that of a single YBCO film. Transport critical current density measurements of the top YBCO layer resulted in J/sub c/=2*10/sup 5/ A/cm/sup 2/ at 77 K, a factor of 10 lower than for single films. Trilayer structures had a microwave surface resistance at 10 GHz and 4 K of 50 mu Omega , comparable to that of single films. Preliminary low-temperature measurements of the dielectric constant of composite insulator structures gave values an order of magnitude lower than for pure SrTiO/sub 3/.<
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