Title :
Noise performance of high-T/sub c/ DC SQUID magnetometers
Author :
Fife, A.A. ; Anderson, G. ; Angus, V. ; Backhouse, C. ; Betts, K. ; Burbank, M.B. ; Cragg, R.A. ; Ferguson, K. ; Habib, F. ; Kubik, P.R. ; Nomura, J. ; Smith, M. ; Spear, P. ; Westera, W. ; Zhou, H. ; Vrba, J. ; Heinrich, B. ; Curzon, A.E. ; Irwin, J.C. ;
Author_Institution :
CTF Syst. Inc., Port Coquitlam, BC, Canada
fDate :
6/1/1995 12:00:00 AM
Abstract :
High-T/sub c/ DC SQUID magnetometers operating at 77 K have been fabricated from epitaxial YBCO and SrTiO/sub 3/ films and characterized. The DC SQUID washers incorporated either bicrystal or step-edge microbridge junctions of widths down to about 3 /spl mu/m. Three types of DC SQUID magnetometer are described-(a) a single layer device with a direct-coupled loop; (b) a DC SQUID plus flip-chip coupled flux transformer; (c) a fractional turn device with a direct-coupled multi-loop. The 1/f noise in the spectra of uncoupled DC SQUIDs and some magnetometers is significantly reduced by using AC bias modulation. Low frequency energy sensitivities of uncoupled SQUIDs at 77 K have been improved by use of AC bias to 7/spl times/10/sup -30/ J/Hz at 1 Hz (45 pH inductance). For flip-chip coupled magnetometers (15-turn input coil, pick-up coil area 13 mm/sup 2/), excess low frequency noise was observed, only partially reduced by AC biasing, with field sensitivities of 1 pT rms//spl radic/(Hz) and 130 fT rms/spl radic/(Hz) above 200 Hz.<>
Keywords :
1/f noise; SQUID magnetometers; barium compounds; high-temperature superconductors; superconducting device noise; superconducting thin films; yttrium compounds; 1/f noise; 3 micron; 77 K; AC bias modulation; DC SQUID magnetometers; DC SQUID washers; HTS film; HTSC; LF energy sensitivities; YBaCuO-SrTiO/sub 3/; bicrystal microbridge junctions; direct-coupled loop; direct-coupled multi-loop; epitaxial SrTiO/sub 3/ film; epitaxial YBCO films; excess low frequency noise; flip-chip coupled flux transformer; fractional turn device; high-T/sub c/ magnetometers; noise performance; single layer device; step-edge microbridge junctions; 1f noise; Coils; Couplings; Frequency; Inductance; Low-frequency noise; Magnetic modulators; Noise reduction; SQUID magnetometers; Yttrium barium copper oxide;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
