Josephson voltage standard microwave circuits fabricated in a modified all-niobium technology for operation at low drive frequencies

A resonant type of cryoelectronic microwave circuit for the generation of frequency-scaled Josephson voltages is presented. The circuits consist of superconducting microstripline resonators with series arrays of Josephson tunnel junctions located on the microwave current antinodes. This microwave design was chosen to obtain highly accurate Josephson voltages at low microwave power levels and low drive frequencies. The resonator circuits have been fabricated in both niobium-lead and all-niobium technology. At present, we have observed long-term stable Josephson voltages up to 0.75 V for niobium-lead circuits with 1320 junctions and 0.66 V for all-niobium circuits with 1456 junctions, respectively.