Fabrication of La-Doped YBCO and SrTiO_3-Buffered LSAT Thin Films for Ramp-Edge Josephson Junctions on Superconducting Ground Plane

摘要

The deposition conditions of Y_(0.9)Ba_(1.9)La_(0.2)Cu_3O_y (La-YBCO) and (LaAlO_3)_(0.3)-(SrAl_(0.5)Ta_(0.5)O_3)_(0.7) (LSAT) thin films were studied with the aim of fabricating ramp-edge Josephson junctions on a superconducting ground plane. These films were deposited by a magnetron sputtering method and utilized as a base electrode and an insulating layer under the electrode, respectively. YBa_2Cu_3O_y thick films grown by liquid phase epitaxy (LPE-YBCO) were used for a ground plane. Insertion of a SrTiO_3 buffer layer between LSAT and LPE-YBCO significantly improved the flatness of the film surface. La-YBCO films with a flat surface and T_c(zero) of 87K were reproducibly obtained by DC sputtering. We have fabricated ramp-edge Josephson junctions using these films. Resistively and capaci-tively shunted junction (RCSJ)-like characteristics were observed in them. An I_c spread of 10.2% (at 4.2K, average I_c = 0.5 mA) was obtained for a 1000-junction series-array.