Low-Tc Josephson junctions with tailored barrier

Nb∕Al2O3∕Ni0.6Cu0.4∕NbNb∕Al2O3∕Ni0.6Cu0.4∕Nb based superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions with a thickness step in the metallic ferromagnetic Ni0.6Cu0.4Ni0.6Cu0.4 interlayer were fabricated. The step was defined by optical lithography and controlled etching. The step height is on the scale of a few angstroms. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate uniform ferromagnetic layer thicknesses and the same interface transparencies for etched and nonetched F layers. This technique could be used to tailor low-Tclow-Tc Josephson junctions having controlled critical current densities at defined parts of the junction area, as needed for tunable resonators, magnetic-field driven electronics, or phase modulated devices