Fabrication of Nanoscale SQUIDs Using Vertical Nb Nanoconstrictions

The measurement of ultra-weak magnetic fields with nanometer-scale spatial resolution is a powerful tool for investigating several biological, chemical and physical systems. Among the available detectors, SQUIDs are the most sensitive magnetic field and flux detectors and are rapidly approaching the quantum sensitivity limit. To reach such sensing capability, technological advances in the fabrication of nanoscale SQUIDs with submicrometric loops are needed. In this work we present a novel process for the fabrication of nanoscale SQUIDs, based on superconducting vertical Nb nanoconstrictions. The fabrication process uses laser lithogra- phy to define the device geometry, focused ion beam to mill the top surface of the Nb in a nanometer-sized region across the width of the film and anodization to define the final thickness of the nanoconstriction and at the same time to embed the ion- implanted amorphous layer produced by the FIB milling step. A preliminary electrical characterization of nano-sized single Josephson junctions and SQUIDs fabricated with this process is also reported.