HTS rf SQUIDs with fully integrated planar tank circuits

For the optimization of the operation of rf-SQUIDs a high pumping frequency f(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 LaAlO3 substrates, we measured f(0) at resonance in the range of about 550 MHz to 1.1 GHz and unloaded quality factors Q(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(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 mna in outer diameter, together with a SQUID in flip chip technique we obtained II white flux noise of 50 fT/root Hz for a 150 pH SQUID.