Micro-superconducting quantum interference devices based on V/Cu/V Josephson nanojunctions

We report on the fabrication and characterization of micrometer-sized superconducting quantum interference devices (SQUIDs) based on nanoscale vanadium/copper/vanadium Josephson weak links. Magnetically driven quantum interference patterns have been measured for temperatures in the $0.24–2 K$ range. As DC SQUIDs, these devices obtain flux-to-voltage transfer function values as high as $450 μV/Φ0$ leading to promising magnetic flux resolution $ΦN<3 μΦ0/Hz$⁠, being here limited by the room temperature preamplification stage. Significant improvement in the flux noise performance figures is expected with the adoption of cryogenic preamplification. The presented devices are suitable for operation as small-area SQUIDs at sub-Kelvin temperature, but their design can also be upscaled to include input coils enabling their use as sensitive magnetometers via the adoption of optimized electronic readout stages based on flux feedback schemes.