Realization of a good contact between Au and Bi2Sr2CaCu2O8+y for HTS ramp-edge junctions

The fabrication process of high-T_C ramp-edge type junctions with a Bi₂Sr₂CaCu₂O_8+y (Bi-2212) base electrode and a conventional superconducting counter electrode (Nb, Pb or Pb-In alloy) was investigated. An Au film was deposited as a layer between Bi-2212 and Nb (or Pb, Pb-In). Most of thin films were prepared by a pulsed laser deposition (PLD) method. By optimizing the annealing condition for the junction fabrication process, the higher T_C´s (T_C∼80 K) of Bi-2212 thin films were stably available after all processes. Resistivity of Au thin film could be reduced to about 1 μΩcm at 4.2 K by heating the sample at 300-400°C during the in-situ Au deposition. There were difficulties to realize Bi-2212/Au/Nb (Pb or Pb-In) junctions. However, in case of Bi-2212/Au junctions, the junction interface was much improved by an interlayer process. Good homogeneous conductivity found to be kept in the fabricated Bi-2212/Au junctions, which was reproducible.