A planar-type junction of HoBa2Cu3O7−x−La1.5Ba1.5Cu3O7−y −HoBa2Cu3O7−x having an electrode spacing as small as 0.1 μm is fabricated and its electrical characteristics are measured. Supercurrent through the La1.5Ba1.5Cu3O7−y layer is detected up to the temperature of 69 K. A superconducting region extends from the YBa2Cu3O7−x electrodes into a normal La1.5Ba1.5Cu3O7−y layer with a submicrometer scale. The superconducting decay length is 65 nm, which is two orders of magnitude larger than the value calculated from the conventional proximity theory.
We have developed an HTS multilayer structure including a superconducting ground plane and interface-engineered ramp-edge Josephson junctions for single flux quantum (SFQ) circuits, and tried to improve reproducibility in the multilayer and junction process. We found that one of the crucial factors to improve the reproducibility is use of a ground plane with small average surface roughness ( a ) of typically less than 2 nm and a high c above 87 K. By employing La 0 2 Y 0 9 Ba 1 9 Cu 3 O (La-YBCO) thin films deposited by dc off-axis magnetron sputtering, such high quality was maintained for 3-month successive use of a ceramic target. Use of such a high-quality ground plane reproducibly led to SrSnO 3 La YBCO SrSnO 3 La YBCO //MgO multilayer structures with a 2 nm and 100-junction arrays with 1 c spread of 6-17% at 4.2 K depending on the average c level. The run-to-run reproducibility of average junction c and sheet inductance of both the base-and counter-electrodes for three samples was 12%, 3.0%, and 3.4%, respectively, which are substantially smaller than those previously reported.
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