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.
@article{arxiv.0901.0308,
title = {A Terraced Scanning Superconducting Quantum Interference Device Susceptometer with Sub-Micron Pickup Loops},
author = {Nicholas C. Koshnick and Martin E. Huber and Julie A. Bert and Clifford W. Hicks and Jeff Large and Hal Edwards and Kathryn A. Moler},
journal= {arXiv preprint arXiv:0901.0308},
year = {2009}
}
Comments
See http://stanford.edu/group/moler/publications.html for an auxiliary document containing additional fabrication details and discussion