L. Hao et al., COMPARATIVE NOISE MEASUREMENTS IN YBCO STEP-EDGE AND BI-CRYSTAL GRAIN-BOUNDARY JUNCTIONS, Physica. C, Superconductivity, 232(1-2), 1994, pp. 111-118
A system has been developed for the absolute measurement of excess noi
se in high-T(c) superconducting devices. Grain-boundary Josephson junc
tions of step-edge and bi-crystal type, fabricated in four different l
aboratories, have been characterised and compared in the frequency ran
ge 0.1 Hz-60 kHz, and at temperatures between 35 K and 80 K. All junct
ions tested had bias-dependent noise peaks ranging in amplitude (at 60
kHz) from 0.2 to 5 nV Hz-1/2, which generally increased with decreasi
ng temperature. The noise power spectral density varied with frequency
as 1/f. Higher levels of noise, and a more complex current dependence
, were found for small-area bi-crystal junctions, and for step-edge ju
nctions generally. The results are compared with theory, and the impli
cations for the development of low-noise devices (e.g. SQUID's) are di
scussed.