Overdamped Nb∕Al–AlOx∕Nb Josephson junctions

Paola Barbara, G. Costabile, J. Mygind +1 more

Masaaki Maezawa, Akira Shoji

We present characteristics of overdamped Josephson junctions consisting of Nb/AlOx/Al/ AlOx/Nb structures. The junctions were fabricated using a well-developed Nb/AlOx/Nb-junction technology and showed well-defined Josephson characteristics at 4.2 K. The characteristic voltage Vc [the product of the critical current Ic and the effective normal resistance Rn(eff)] of junctions, which determines high-frequency performance of the junction, was in the range of 0.1–0.5 mV, and the critical current density Jc in the range of 102–104 A/cm2. Maximum-to-minimum variations in Ic over a wafer were ±4% for junctions with Vc=0.15 mV and ±13% for junctions with Vc=0.5 mV.

Pascal Febvre, Natascia De Leo, Matteo Fretto +4 more

Takao Iwai, Takashi Aoyama, Ryutaro Oke +3 more

We have fabricated overdamped NbN Josephson junctions based on Nb/AlO x /Nb trilayer technology. The junctions have the structure of NbN/Nb/AlO x /Nb/NbN, where Nb/AlO x /Nb acts as a junction barrier. The overdamped junctions showed a critical current density J c and characteristic voltage as high as 0.44 kA/cm2 and 160 µV at 10 K, respectively. The junction characteristics at 4.2 K were investigated from the viewpoint of their dependence on the film thickness of the Nb layers. The junction uniformity was also evaluated. The standard deviation, 1-σ, was 2.1% for a series of 64 5×5 µm2 junctions at 4.2 K.

V. Lacquaniti, Natascia De Leo, Matteo Fretto +1 more

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 μV 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 μA 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.