Josephson arrays for dc and ac metrology

Large series arrays of underdamped SIS tunnel junctions are the basic element of the primary dc voltage standards used at present. The development of versatile quantum voltmeters for dc and ac metrology requires the preparation of large and perfect series arrays of overdamped Josephson junctions. Overdamped junctions can be realized by externally shunted SIS junctions or by internally shunted SNS or SINIS junctions. Arrays of up to 8000 SINIS junctions or 30000 SNS junctions were successfully operated at the 1 V dc level. In addition to being used in large arrays for voltage metrology and oscillators, the described junction types may become very useful for the preparation of highly integrated single-flux-quantum digital devices. (author)