SQUID on cantilever probes based on corner lithography

Superconducting quantum interference devices (SQUIDs) are the most sensitive magnetic flux sensors and are used in scanning SQUID microscopy (SSM) to spatially resolve and map magnetism. Conventional SQUID probes make use of planar silicon substrates which limit their spatial resolution to several micrometers due to an increased sample-pickup area spacing. In order to increase the probes spatial resolution and magnetic sensitivity the SQUID pickup area must be brought in closer proximity to the surface.

Recent advances in the fabrication of SQUID probes for SSM have employed ideas from other scanning probe microscopy techniques like atomic force microscopy and scanning tunneling microscopy to move the SQUID to the apex of a sharp tip. Although these SQUID-on-tip probes have greatly advanced the field of SSM, there are still challenges in the fabrication process such as limited flexibility and one-by-one fabrication.

We have used the principles of corner lithography and molding in silicon wafers to create freestanding superconducting wireframe probes on the wafer scale. By controlling the initial mold size we have direct control over the resulting loop size at the apex of the wireframe. With a focused ion beam we aim to pattern superconducting weak links at the apex of the probe. By integrating the wireframe probe on a silicon nitride cantilever we intend to create a SQUID-on-cantilever probe which will enable simultaneous magnetic and topographic imaging.