DISTRIBUTED MICROWAVE DAMPING FILTERS FOR SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES

We describe a distributed thin-film filter for the broad-band damping of microwave resonances in thin-film superconducting strip lines and c oils used in Nb-Al/AlOx-Nb superconducting quantum interference device s (SQUIDs). The filter consists of an array of 14 mu m diameter thin-f ilm Au-Cu dots which are insulated from the strip lines or coils by an SiO2 layer. Damping occurs via eddy current induced in the dots. Our measurements show that the filter removes resonance steps from the cur rent-voltage curves of SQUIDs which are coupled to the coils and reduc es white noise associated with the resonances. (C) 1997 American Insti tute of Physics.