HTS rf SQUIDs with fully integrated planar tank circuits

For the optimization of the operation of rf-SQUIDs, a high pumping frequency f/sub 0/ and a high quality factor Q of the tank circuit are desirable. For this purpose we used a washer rf SQUID or a current-injection loop SQUID integrated with a modified planar hairpin resonator around the SQUID. On LaAlO/sub 3/ substrates, we measured f/sub 0/ at resonance in the range of about 550 MHz to 1.1 GHz and unloaded quality factors Q/sub 0/ from 4000 to about 6000 using several layouts with different diameters. We found that the coupling coefficient k between the SQUID and the resonator can be estimated from the geometrical parameters of the layout. The requirement k/sup 2/Q>1 can easily be met with our design. Our layouts are very flexible, as they make possible the implementation of various single and multilayer antennas. Using a single layer flux transformer, 13 mm in outer diameter, together with a SQUID in the flip chip technique, we obtained a white flux noise of 50 fT//spl radic/Hz for a 150 pH SQUID.