Fabrication of La-Doped YBCO and SrTiO_3-Buffered LSAT Thin Films for Ramp-Edge Josephson Junctions on Superconducting Ground Plane(<Special Section>Recent Progress in Oxide Thin Films by Sputtering)

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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_3aO_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 capacitively shunted junction (RCSJ)-like characteristics were observed in them. An Ic spread of 10.2% (at 4.2K, average I_C = 0.5mA) was obtained for a 1000-junction series-array.
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2004-02-01