Fabrication and characterization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary Josephson junctions on [110] NdGaO/sub 3/ bicrystal and single-twin substrates

To meet the requirements of high-frequency applications, we have fabricated YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions on 2/spl times/12/spl deg/ [110] NdGaO/sub 3/ bicrystal substrates. Compared to reference junctions made on (100) SrTiO/sub 3/ bicrystals, the specific resistances R/sub n/A of the junctions on NdGaO/sub 3/ 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 YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film formed on twin boundaries of the NdGaO/sub 3/ bicrystal substrate. The electrical properties of these additional weak links have been studied by preparing YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin-film bridges crossing a single twin boundary of a NdGaO/sub 3/ substrate. The critical current densities j/sub c/ were found to be on the order of 1/spl times/10/sup 6/ A/cm/sup 2/. Therefore, even for the smallest twin boundary junctions, a pronounced flux-flow-behavior is observed.