Superconducting Quantum Interference Devices (SQUIDs) can have excellent spinsensitivity depending on their magnetic flux noise, pick-up loop diameter, anddistance from the sample. We report a family of scanning SQUID susceptometerswith terraced tips that position the pick-up loops 300 nm from the sample. The600 nm - 2 um pickup loops, defined by focused ion beam, are integrated into a12-layer optical lithography process allowing flux-locked feedback, in situbackground subtraction and optimized flux noise. These features enable asensitivity of ~70 electron spins per root Hertz at 4K.
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