Fabrication of high quality ferromagnetic Josephson junctions

TL;DR

This paper reports the fabrication and optimization of high-quality ferromagnetic Josephson junctions with ultrathin barriers, achieving high yield and uniform current transport through advanced techniques.

Contribution

The study introduces a fabrication process that enhances junction quality and homogeneity, including the use of a Cu layer to improve interface smoothness.

Findings

High yield of junctions with less than 2% spread in critical current density

Successful optimization of junction insulation and current homogeneity

Implementation of ion-beam-etching and anodic oxidation techniques

Abstract

We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2 nm thin Cu layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with jc spreads less than 2% was obtained.