Low-Tc Josephson junctions with tailored barrier

Nb/Al2O3/Ni0.6Cu0.4/Nb based superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions with a thickness step in the metallic ferromagnetic Ni0.6Cu0.4 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-T-c 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. (c) 2007 American Institute of Physics.