Operation of high-sensitivity radio frequency superconducting quantum interference device magnetometers with superconducting coplanar resonators at 77 K

We have developed a novel coplanar resonator serving as a tank circuit for radio frequency washer superconducting quantum interference devices (SQUIDs). Two coplanar lines surrounded the circular flux concentrator washer, 13.4 mm in diameter, The SQUID, 3.5 mm in diameter, was coupled to the concentrator in the flip-chip configuration, All parts were fabricated from single-layer epitaxial YBa2Cu3O7 films on LaAlO3 substrates. In this layout, the resonant frequency could be set between 600 and 850 MHz. With SQUID loops of 100X100 mu m(2) (SQUID) inductance L-s=150 pH or 10X500 mu m(2) (L-s=260 pH), we determined at 77 K white flux noise levels S-phi(1/2) of 1.0X10(-5) and 1.5X10(-5) phi(0)/root Hz, respectively. Both figures corresponded to the field resolution of about 30 fT/root Hz. (C) 1997 American Institute of Physics.