GROWTH AND CHARAC'T'ERIZATION OF YBCO/INSULATOR/YBCO TRILAYERS

Multilevel circuits for high frequency applications of high-T-C superconductors require low dielectric constant insulators between superconducting layers. Initial studies of CeO2 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 CeO2 and SrTiO3 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 Jc = 2 x 105 A/cm(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 SrTiO3.