LTS slotted SQUIDs for reduction of 1/f noise

We have developed Nb/Al dc SQUIDs with differently structured washers (including slots and/or holes, a moat surrounding the washer and a zipper slit) to study the reduction of 1/f noise owing to hopping of flux vortices, trapped in the SQUID body during the cool-down process. A gradual reduction of the 1/f noise (measured down to 0.2 Hz) was measured for SQUIDs with increasing number of slots. Holes proved to be less effective than slots in reducing the flicker noise. The 1/f noise of the SQUIDs with a moat and zipper slit was smaller than that of a bold SQUID, but the reduction of noise was on the average less significant than for the slotted SQUIDs.