FABRICATION AND CHARACTERIZATION OF BI-EPITAXIAL GRAIN-BOUNDARY JUNCTIONS IN YBA2CU3O7-DELTA

We have fabricated bi-epitaxial grain boundary junctions in YBa2Cu2O7-delta (YBCO) thin films by using SrTiO3 (STO) seed layers on MgO(100) substrate. YBCO film growing over the STO seed layer has a different in-plane orientation from YBCO film without the seed layer, so artificial grain boundaries were created at the edge of the seed layer. The fabricated junctions have high T(c) (up to 80 K), and constant-voltage current steps are observed in response to 12.1 GHz microwave radiation. Moreover, some of the junctions show characteristic current-voltage curves comprising not only an usual Josephson-like characteristic but also a low critical current due to the flux creep. This suggests that the two characteristic parts are likely to be connected in series at the junction region.