Flux noise in ion-implanted nanoSQUIDs

TL;DR

This paper investigates flux noise in nanoSQUIDs fabricated with focused ion beam technology, analyzing how device size and fabrication-induced defects influence noise levels and flux stability.

Contribution

It provides new insights into flux noise sources in ion-implanted nanoSQUIDs and examines the effects of device scaling and fabrication on noise characteristics.

Findings

Smallest device with 50 nm hole has flux noise of 2.6 μΦ₀/Hz^{0.5} at 10^4 Hz

Flux noise influenced by spin fluctuations and flux hopping mechanisms

Scaling effects and focusing influence flux noise properties

Abstract

Focused ion beam (FIB) technology has been used to fabricate miniature Nb DC SQUIDs which incorporate resistively-shunted microbridge junctions and a central loop with a hole diameter ranging from 1058 nm to 50 nm. The smallest device, with a 50 nm hole diameter, has a white flux noise level of 2.6 microphy_{0}/Hz^{0.5} at 10^{4} Hz. The scaling of the flux noise properties and focusing effect of the SQUID with the hole size were examined. The observed low-frequency flux noise of different devices were compared with the contribution due to the spin fluctuation of defects during FIB processing and the thermally activated flux hopping in the SQUID washer.