Nanoscale SQUIDs-on-chip for high-resolution magnetic imaging

Scanning quantum interference device (SQUID) microscopy enables local imaging of current distributions and the magnetic responses of quantum materials. Typical tunnel junction SQUID designs only tolerate external magnetic fields below about 10 mT and offer spatial resolution on the order of 1 μm. We are developing wafer-scale fabrication of niobium nanoscale SQUIDs with superconducting weak links patterned by electron beam lithography in a planar geometry. Niobium-compatible deep silicon etching defines the probe tip. This approach is expected to enable deep submicron spatial resolution and operation in magnetic fields approaching 0.25 T. Moreover, the planar fabrication provides a path toward integrating additional on-chip circuitry, such as field coils for measuring local magnetic susceptibility.