MAGNETIC-FIELD MODULATION OF CRITICAL CURRENTS IN YBACUO COPLANAR JOSEPHSON-JUNCTIONS USING FOCUSED ION-BEAM

The YBa2Cu3O7-delta co-planer Josephson junctions by Focused Ion Beam were fabricated by changing the width and the thickness of a YBa2Cu3O7 -delta thin film The magnetic properties of the junctions were measure d at different temperatures. In the junction with 300 nm thickness, th e magnetic field modulation of the critical current at 4.2K was not ob served. Near the critical temperature of the junction, the magnetic mo dulation curve was similar to that of a dc-SQUID. From the SEM observa tion, some microshorts were observed on the junction. In the junction with 200 nm thickness, the I-V curve was changed for flux-flow junctio n type to RSJ type. The magnetic modulation curve of the 7 mu m wide j unction at 4.2 K was similar to a Fraunhofer pattern. Thus it is consi dered that the coupling region was changed from a microshort to weak c oupling region, when the thickness of the YBaCuO film was decreased fr om 300 nm to 200 nm.