OPERATION OF HIGH-TEMPERATURE RF SQUID MAGNETOMETERS USING DIELECTRICSRTIO3 RESONATORS

The operation of YBa2Cu3O7 rf superconducting quantum interference dev ices (SQUIDs) using a dielectric SrTiO3 resonator as tank circuit was tested. At 77 K, we attained for such resonators unloaded quality fact ors Q(0) up to 7000 at resonant; frequencies near 1 GHz, when measurin g without electromagnetic shielding. For a washer SQUID with an area o f 4x4 mm(2) and an inductance of similar or equal to 100 pH, which was properly coupled to the resonator, we measured an approximately 60 mu V peak-to-peak SQUID signal and a white flux noise spectral density o f S-phi(1/2) = 1 x 10(-5)Phi(0)/root Hz, corresponding to a field sens itivity of B-N=105 fFT/root Hz. With an additional single-layer flux t ransformer with a diameter of the pickup loop of 22 mm in flip-chip ar rangement,the field sensitivity was improved to 30 fT/root Hz. (C) 199 5 American Institute of Physics.