A Terraced Scanning Superconducting Quantum Interference Device Susceptometer with Sub-Micron Pickup Loops

TL;DR

This paper introduces a terraced scanning SQUID susceptometer with sub-micron pickup loops, achieving high spin sensitivity by integrating advanced fabrication techniques and optimized design for precise magnetic measurements at cryogenic temperatures.

Contribution

The paper presents a novel terraced tip design and fabrication process for scanning SQUID susceptometers with sub-micron pickup loops, enhancing spin sensitivity and measurement capabilities.

Findings

Achieved ~70 electron spins per root Hertz sensitivity at 4K.

Integrated flux-locked feedback and background subtraction in the device.

Fabricated pickup loops of 600 nm to 2 μm using focused ion beam.

Abstract

Superconducting Quantum Interference Devices (SQUIDs) can have excellent spin sensitivity depending on their magnetic flux noise, pick-up loop diameter, and distance from the sample. We report a family of scanning SQUID susceptometers with terraced tips that position the pick-up loops 300 nm from the sample. The 600 nm - 2 um pickup loops, defined by focused ion beam, are integrated into a 12-layer optical lithography process allowing flux-locked feedback, in situ background subtraction and optimized flux noise. These features enable a sensitivity of ~70 electron spins per root Hertz at 4K.