Practical low-noise integrated dc superconducting quantum interference device magnetometer with additional positive feedback

• Published in: Applied physics letters Vol. 59; no. 2; pp. 228 - 230
• Main Authors: Ryhänen, T., Cantor, R., Drung, D., Koch, H.
• Format: Journal Article
• Language: English
• Published: United States 08-07-1991
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DESIGN; ELECTRONIC EQUIPMENT; FEEDBACK; FLUXMETERS; MAGNETIC FLUX; MAGNETOMETERS; MEASURING INSTRUMENTS; MICROWAVE EQUIPMENT; SIGNAL-TO-NOISE RATIO; SQUID DEVICES; SUPERCONDUCTING DEVICES 426001 > Engineering > Superconducting Devices & Circuits > (1990-)
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.105974

We have designed and fabricated a low-noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4×4 mm2 chip. The white flux noise of the magnetometer measured in a flux-locked-loop mode using simple, direct-coupled electronics with additional positive feedback (APF) is 6.4×10−7 Φ0/√Hz. The corresponding white flux density noise is 3.9 fT/√Hz. The SQUID flux-to-voltage transfer function with APF is enhanced to 4.7 mV/Φ0 at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 μT/s at 300 Hz have been attained using a two-pole integrator.