Vertical quantum sensor could reveal nanoscale magnetic patterns in quantum materials

Quantum materials possess unique properties that set them apart from conventional materials, including the ability to transmit electricity without loss or to conduct it only along their outer edges with insulating interiors. As quantum computers and sensors rely on such materials, researchers must examine the exact locations of currents and magnetic fields at the nanoscale.

A superconducting ring known as a SQUID is sensitive enough to detect these minute magnetic changes. However, magnetic fields weaken rapidly with distance, requiring the sensor to be brought close to the material to capture the necessary details. The University of Twente was able to overcome this challenge by positioning the sensor on a pyramid structure.

This design allows the sensor to be brought right up to the material being examined without any interference from the surrounding chip. With this method, researchers can image the magnetism at the scale at which quantum materials perform their functions, leading to the development of materials with novel characteristics. The pyramid is created by etching upside-down pyramid-shaped pits into a silicon slice, which is used in the fabrication of computer chips.

Thin films of glass-like material are then applied to each pit, with the film removed, leaving only material at the edges. This results in a frame of fine, precisely aligned wires on the pyramid's tip. The sensor is completed by adding a superconducting layer and cutting two constrictions into the ring at the top. This vertical SQUID sensor on a pyramid tip can be positioned close to a surface to investigate nanoscale magnetic fields in quantum materials.

The wafer-scale fabrication process successfully created rings as small as 100 nanometers, with 80-90% of the tips usable in each production run. The sensor operates in magnetic fields above 1 tesla, which is significant compared to Earth's magnetic field. The sensor's fabrication process, which utilizes wafer-scale production, offers a faster path to creating sensors for other laboratories to use, ultimately benefiting the research on quantum materials.