Nb/Al/AlOx/Al/AlOx/Al/Nb junctions with critical current densities, jc, up to 38 kA/cm2 were fabricated. A critical voltage of Vc=1.25 mV and small hysteresis (about 6% of the critical current) at 4.2 K were obtained for jc=21 kA/cm2. Also, Nb/Al/AlOx/Al/Nb/Al/NbN junctions with jc=33 kA/cm2 and Vc=0.76 mV were fabricated, where it is suggested that a second tunnel barrier at the Al/NbN interface is present as a result of Al nitridation during NbN deposition.

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