Reduction of 1/f-noise in HTS-SQUIDs by artificial defects

We report on the detection of matching effects between antidot and vortex lattices in rf SQUIDs that clearly demonstrate, that antidots can strongly reduce the low-frequency 1/f noise in active superconducting devices. Square lattices of holes (antidots) with diameters of 0.25-2 /spl mu/m and lattice parameters ranging from 0.5 to 50 /spl mu/m are patterned into optimized sputtered YBa/sub 2/Cu/sub 2/O/sub 7-/spl delta// thin films without deterioration of superconducting properties. First, a special experimental set-up consisting of an antidot lattice in flip-chip configuration with a bicrystal rf-SQUID is used for the demonstration of the principle of noise reduction by antidots. Matching effects between vortex and antidot lattice in form of minima in the noise spectra are observed, indicating that thermally activated hopping of vortices can strongly be reduced by antidots. Second, antidots are directly patterned into step-edge rf-SQUIDs. For large antidot lattice parameters (50 /spl mu/m) no degradation of the SQUID parameters can be measured. However, matching effects and noise reduction due to the presence of the antidots can not be observed in this first attempt. The results are discussed in terms of multiquanta, possible solutions and suggestions for improvements are given.