Investigation of 1/f noise in tunnel junction DC SQUIDS

We describe two methods of measuring the 1/f noise in a dc SQUID. One is sensitive only to 1/f noise in the critical currents of the junctions, and the other is sensitive only to 1/f flux noise that is not associated with critical current fluctuations. From measurements on a planar thin-film dc SQUID incorporating Josephson tunnel junctions we conclude that the predominant source of 1/f noise is not noise in the crititcal currents, but rather an apparent flux noise of unknown origin.