FABRICATION AND CHARACTERIZATION OF YBA2CU3O7-X GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS ON (110)-NDGAO3 BICRYSTAL AND SINGLE-TWIN SUBSTRATES

To meet the requirements of high-frequency applications, we have fabri cated YBa2Cu3O7-x grain-boundary junctions on 2x12 degrees (110) NdGaO 3 bicrystal substrates. Compared to reference junctions made on (100) SrTiO3 bicrystals, the specific resistances R(n)A of the junctions on NdGaO3 were usually several times higher, Furthermore, they showed RSJ -like behavior in a more limited temperature range, which might be due to weak links in the YBa2Cu3O7-x thin film formed on twin boundaries of the NdGaO3 bicrystal substrate, The electrical properties of these additional weak links have been studied by preparing YBa2Cu3O7-x thin- film bridges crossing a single twin boundary of a NdGaO3 substrate, Th e critical current densities j(c) were found to be on the order of 1x1 0(6) A/cm(2). Therefore, even for the smallest twin boundary junctions , a pronounced flux-flow-behavior is observed.