EXCESS LOW-FREQUENCY NOISE IN YBCO THIN-FILM DEVICES

Excess low-frequency noise degrades the performance of many of the hig h T-c superconducting devices that have been proposed or demonstrated, We report measurements of noise in grain-boundary junctions and nux-f low amplifier devices that have been fabricated in several different l aboratories, The system is calibrated in terms of absolute noise tempe rature, and its voltage noise sensitivity is below 0.1 nVHz(-1/2). Dev ice characteristics and noise have been measured as a function of junc tion area, critical current, temperature, bias current and magnetic fi eld, Noise levels in a fixed frequency band of 40-60 kHz are reported, as well as the frequency dependence between 0.1 Hz and 60 kHz. Noise temperatures exceeding the device physical temperature at certain leve ls of bias current are attributed to fluctuations in critical current and normal tunnelling resistance. Noise due to magnetic nw motion is a lso seen, We compare results with available theory and other relevant data in the literature, and assess the practical effects of noise on t he performance of high T-c devices such as SQUIDs, nux flow amplifiers and bolometers.