Preparation of ramp-edge Josephson junctions with natural barriers
We have demonstrated ramp-edge Josephson junctions using high temperature superconductors without depositing artificial barriers. We use a surface barrier formed naturally during an etching process by an Ar ion beam. The resistivity of the barrier, which is evaluated in the Nb/Au/YBCO structures, changes over 4 orders in accordance with the gas pressure in the vacuum annealing executed before the deposition of the counter-electrode. All the junctions having YBCO/barrier/YBCO structure exhibit RSJ-like current-voltage characteristics over the entire temperature range of operation. Fraunhofer-like modulation patterns are observed with a very small amount of excess current even at low temperatures except for large junctions. The temperature dependence of J/sub c/ and R/sub u/A are similar to those in HTS grain boundary junctions. Since the junction parameters are controlled by the total pressure during the vacuum annealing, the junctions made through this procedure have a potential for circuit applications.