Double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) have been fabricated with estimated relaxation frequencies up to 14 GHz. Both the intrinsic flux noise and the performance in a flux locked loop with direct voltage readout have been studied. In flux locked loop, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34 h has been obtained for a DROS with a SQUID inductance of 29 pH. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13 h at relaxation frequencies higher than about 3 GHz.
Adelerhof, D. J., Kawai, J., Uehara, G., & Kado, H. (1994). High sensitivity double relaxation oscillation superconducting quantum interference devices. Applied physics letters, 65(20), 2606-2608. https://doi.org/10.1063/1.112582