MANUFACTURABLE LOW-NOISE SQUIDS OPERATING IN LIQUID-NITROGEN

THE superconducting quantum interference device (SQUID) holds promise for a wide range of applications, including the measurement of magnetic fields generated by the brain and heart, detection of tiny cracks and corrosion currents, and exploration of oil and mineral deposits. Currently available SQUIDs rely on low-transition-temperature (low-T(c)) superconductors, and must therefore be refrigerated to liquid-helium temperature (4.2 K). This difficult cryogenic requirement has presented a barrier to the widespread implementation of SQUID technology. We report here on the development of a high-T(c) d.c. SQUID with a noise level in liquid nitrogen (77 K) that is a significant improvement, at frequencies of practical interest, for SQUIDs produced by a manufacturable fabrication process 1,2. The energy sensitivity of 1.6 x 10(-29) J Hz-1 at 10 Hz is comparable to the best previously reported 3 for any high-T(c) SQUID at 77 K. These high-T(c) SQUIDs are sensitive enough for many of the applications presently possible only with liquid helium devices.