RAMP-EDGE JOSEPHSON-JUNCTIONS WITH ND1.85CE0.15CUO4-Y BARRIERS

We have fabricated YBa2Cu3O7-delta ramp-edge Josephson junctions using Nd1.85Ce0.15CuO4-y as the barrier material. In the fabrication proces s we introduced an in situ cleaning process for the ramp surface in th e base electrode prior to the deposition of the barrier layer and the top electrode. In the cleaning process a low energy oxygen and/or argo n ion beam is used. Varying the barrier thickness d, the critical curr ent density J(c) and the normal resistance times area rho(n) of the ju nctions were found to be proportional to exp(- d/xi(n)) and exp(d/xi(r )) with characteristic decay lengths xi(n) = 3.8 nm and xi(r) = 7.2 nm , respectively. For junctions with d > 10 nm, J(c) rho(n) products abo ve 1 mV at 77 K were obtained. The spatial distribution of the critica l current density was imaged directly by low-temperature scanning elec tron microscopy (LTSEM) and showed considerable inhomogeneities on a m u m scale.