Nb/Al-AlOx/Nb overdamped junctions suitable for voltage standard operation above 4.2 K

Nb/Al-AlOx/Nb Josephson junctions of few micrometers size, derived by the basic hysteretic SIS process, have shown stable overdamped current voltage, I-V, characteristic with Ic of 1-10 mA and Vc of 100-600 mu V at 4.2 K. The moderate dependence on temperature of these parameters has allowed to use them at temperatures above 4.2 K, near the Nb transition temperature, measuring quantized voltage steps several hundreds p A wide on single and 10 junctions arrays at T > 8 K. This paves the way to their use in cryocooler setup of reduced cost and power consumption for a future generation of programmable and AC voltage standard.