Abstract
We have fabricated YBa 2Cu 3O 7−δ ramp-edge Josephson junctions using Nd 1.85Ce 0.15CuO 4− y as the barrier material. In the fabrication process we introduced an in situ cleaning process for the ramp surface in the base electrode prior to the deposition of the barrier layer and the top electrode. In the cleaning process a low energy oxygen and/or argon ion beam is used. Varying the barrier thickness d, the critical current density J c and the normal resistance area ϱ n of the junctions were found to be proportional to exp(− d/ ξ n) and exp( d/ ξ r) with characteristics decay lengths ξ n = 3.8 nm and ξ r = 7.2 nm, respectively. For junctions with d > 10 nm, J c ϱ n products above 1 mV at 77 K were obtained. The spatial disribution of the critical current density was imaged directly by low-temperature scanning electron microscopy (LTSEM) and showed considerable inhomogeneties on a μm scale.
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