Josephson arrays for dc and ac metrology

Large series arrays of underdamped SIS tunnel junctions are the basic eleme nt of the primary de voltage standards used at present. The development of versatile quantum voltmeters for de and ac metrology requires the preparati on of large and perfect series arrays of overdamped Josephson junctions. Ov erdamped junctions can be realized by externally shunted SIS junctions or b y internally shunted SNS or SINIS junctions. Arrays of up to 8000 SINIS jun ctions or 30000 SNS junctions were successfully operated at the 1 V de leve l. In addition to being used in large arrays for voltage metrology and oscilla tors, the described junction types may become very useful for the preparati on of highly integrated single-flux-quantum digital devices.