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Miniature SQUIDs

Sept. 03, 2007 (H2).  Interest in miniature superconducting quantum interference devices (SQUIDs) has been motivated by the possible application of such sensors in high resolution scanning SQUID microscopy and for the study of magnetic nanoparticles. Researchers from the University of Twente, the Netherlands, have recently reported the development of miniature SQUIDs with effective areas as small as 3.6 x 10-2 μm2 [1]. These nanoSQUIDs were based on niobium nanobridges. Figure 1 shows the nanobridge area.  At temperatures of 4.2 K, typical critical currents of 4 to 25 μA and flux sensitivities of 40 – 200 μV/Φ0 were measured for sensors based on 80 nm wide, 50 nm thick and 150 nm long structures. A white flux noise level of 1.5 μΦ0/Hz1/2 was measured for a device with an area of 900 μm2and a critical current of 15 μA. Based on these characteristics the described devices offer good perspectives for an improvement of resolution in the discussed applications.

[1]  A.G.P. Troeman et al., NanoSQUIDs Based on Niobium Constrictions, Nano Lett. 7, 2152-2156 (2007)

Miniature SQUIDs

Fig. 1.  The SQUID nanobridge area.