Relaxation oscillation SQUIDs with high delta V/ delta Phi

Relaxation oscillation SQUIDs (ROSs) based on Nb/Al, AlO/sub x//Al/Nb Josephson tunnel junctions have been designed and fabricated. The hysteretic SQUIDs (superconducting quantum interference devices) have a maximum critical current of about 130 mu A and an inductance of 20 pH. A voltage modulation of 40 mu V and a flux to voltage transfer delta V/ delta Phi of 4 MV/ Phi /sub 0/ have been measured in these SQUIDs. Double relaxation oscillation SQUIDs (DROSs), which are based on two hysteretic SQUIDs, showed transfer coefficients up to 77 mV/ Phi /sub 0/. The intrinsic white flux noise of the DROSs is smaller than 3-5 mu Phi /sub 0// square root Hz. It is noted that the results are very promising for a next generation of SQUID systems with simplified read-out.>