No abstract

We have developed a process which incorporates very high quality Nb/Al-oxide/Nb Josephson junctions. The junctions had low subgap conductance yielding V, greater than 50 niV for critical current densities of 1000 A/cm2. Low inductance SQUIDs macle with these junct.ions were apparently free from junction conductance fluctuations, at least for frequencies above 1 He. The SQUIDs exhibited flux noise of currently unknown origin.

A superconducting analog track-and-hold circuit has been designed, fabricated, and tested. Experimental results demonstrate a 1.2-GHz bandwidth and a 25-dB dynamic range. Model calculations indicate that an optimized circuit with a critical current density of 10 000 A/cm2 can achieve a 4-GHz bandwidth and a 35-dB dynamic range.