Noise in DC SQUIDS with Nb/Al-oxide/Nb Josephson junctions

The authors have developed a process which incorporates very-high-quality Nb/Al-oxide/Nb Josephson junctions. The junctions had low subgap conductance, yielding V/sub m/ greater than 50 mV for critical current densities of 1000 A/cm/sup 2/. Low-inductance SQUIDS (superconducting quantum interference devices) made with these junctions were apparently free from junction conductance fluctuations, at least for frequencies above 1 Hz. A correlation between low leakage junctions and low noise from critical current fluctuations was observed. The SQUIDS exhibited flux noise with an unusual frequency dependence of currently unknown origin.<>