Low-T_c Josephson junctions with tailored barrier

TL;DR

This paper reports on the fabrication of Nb/Al2O3/NiCu/Nb Josephson junctions with a precisely controlled ferromagnetic barrier step, enabling tailored critical current densities for advanced superconducting devices.

Contribution

It introduces a method to create controlled thickness steps in ferromagnetic barriers of Josephson junctions, enhancing device tunability and performance.

Findings

Uniform F-layer thickness confirmed by experiments

Controlled critical current densities achieved

Potential applications in tunable superconducting devices

Abstract

Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb based superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel junctions with a thickness step in the metallic ferromagnetic \Ni_{0.6}\Cu_{0.4} 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 an uniform F-layer thickness and the same interface transparencies for etched and non-etched 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.