DC-SQUIDs with low noise and large beta /sub L/-values on (Y)ZrO/sub 2/ bicrystal substrate

High-quality YBa/sub 2/Cu/sub 3/O/sub 7/ DC-SQUIDs (superconducting quantum interference devices) fabricated on bicrystal (Y)ZrO/sub 2/ substrates have been operated at temperatures from 10 K to the critical temperature at 89 K. Stable operation with low white noise levels is found even for beta /sub L/-values as large as 60 for these nonhysteretic junctions ( beta /sub c/<<1). In addition, two noise sources were identified in the 1/f noise: (1) a junction critical current dependent noise S/sub v/ approximately I/sub 0/(T)/sup 2.7/ and (2) a narrow peak in S/sub v/(T) centered at 87 K with its origin in vortex motion within the superconductor. Optimum low-noise operation was obtained in a minimum at 85 K with a flux noise S/sub Phi /(10 Hz)=1.5*10/sup -9/ Phi /sub 0//sup 2//Hz.<
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