Fabrication of finely controlled micro groove by focused ion beam for high-Tc superconducting Josephson junctions

For Josephson junctions using a narrow groove on a substrate etched by a focused ion beam (FIB), it is important to control the shape of the groove. We have developed the FIB milling method which has flexibility to produce a variety of groove shapes. The groove shapes are finely controlled by changing the etching time at each line of beam scan under computer control. V-shape grooves with different widths between 205 nm and 650 nm have been formed with the same slope angle on an MgO substrate. A Josephson junction fabricated on this groove shows RSJ-type I-V curves for a 300 nm thick c-axis oriented YBa2Cu3O7 (YBCO) film. The top surface profile of the YBCO film has the same V-shape as the groove on the substrate.