Noise properties of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junction array magnetometers

We have fabricated magnetometers based on the magnetic field dependence of the critical current of 24/spl deg/ bicrystal Josephson junctions from the high temperature superconductor (HTS) YBa/sub 2/Cu/sub 3/O/sub 7/. The field sensitivity is increased with additional flux focusers up to /spl part/I/sub c///spl part/B=130 A/T. Because the voltage modulation and signal-to-noise ratio increases with the number of junctions, serial arrays of up to 105 junctions are employed. At 77 K we obtain a transfer function of /spl part/V//spl part/B=7500 V/T and a white noise level of /spl radic/S/sub B/=1.2pT//spl radic/Hz for the largest array. The 1/f noise component from critical current fluctuations in the junctions is suppressible by a simple flux modulation scheme.