Characterization of different types of Nb-AlOx based Josephson tunnel junctions

This paper reports on three types of Josephson tunnel junctions, standard Nb/Al,AlOx/Nb, symmetric Nb/Al,AlOx/Al/Nb, and Nb/Al,AlOx/AlOx/Nb containing a double oxide layer investigated by means of temperature dependent I-V measurements, conductance-voltage measurements, noise analysis, and Auger Electron Spectroscopy scanning across the edge of a sputtered crater profile. In standard junctions frequently small leakage currents have been observed as well as resistance fluctuations, leading to telegraph noise. Both effects can be related to the direct contact between the AlOx and the Nb counter electrode. In none of the symmetric junctions leakage currents larger than 0.01% of the theoretical maximum critical current have been observed