The voltage noise levels of high-Tc based YBa2Cu3Oy bicrystal SQUIDs and SQUID voltmeters were measured to investigate their noise characteristics. The SQUIDs are of washer type with outer dimension of 90 μm × 90 μm and inner dimension of 20 urn x 20 um. The SQUIDs have a normal inductance of about 60 pH. The integrated modulation and input coils were circular in shape. The modulation coil has a radius of r2 = 80 u.m and r, = 60 [im while the input coil for voltage measurement has radius r, = 50 urn and r, =30 (im. Using a dc bias and standard flux locked loop, the spectral density of the voltage noise, Sv, was observed to behave as I/fat low frequencies and the root mean square flux noise, S2, is white and has a value of ~15 nO0/Hz2 at l kHz. The flux noise levels were reduced to ~ 4 ii-4yHz2 using the ac bias reversing technique. These data suggest that the dominant 1/f voltage noise was caused by critical current fluctuations. We further demonstrate that the 1/f can be induced by flux motion. The voltage noise levels of the SQUID voltmeters are also reported.
|頁（從 - 到）||4412-4415|
|期刊||IEEE Transactions on Applied Superconductivity|
|發行號||2 PART 3|
|出版狀態||已發佈 - 1999|
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