Dependence of the scatter of the electrical properties on local non-uniformities of the tunnel barrier in Nb/Al-AlOx/Nb junctions

Abstract

In this paper, we study the effect of the tunnel barrier thickness non-uniformity in Nb/Al-AlO x /Nb tunnel junctions using the measurement results of the junction capacitance (C) and the normal resistance (R n ). The local thickness distribution of the AlO x tunnel barrier in Nb/Al-AlO x /Nb trilayer (R n A $ 30 X lm 2 ) was studied by high resolution transmission electron microscopy. The specific resistance (R n A) values of the measured junctions range from 8.8 to 68 X lm 2 . We observed scatter in both the junction specific resistance and capacitance data, which is considerably higher than the measurement uncertainty. We also observed noticeable scatter in the R n C product, which does not stem from junction area estimation uncertainties. We discuss the possible reasons that contribute to this scatter. We suggest that the local thickness non-uniformity of the tunnel barrier significantly contributes to the scatter in the R n C product. We confirm this conclusion through an illustrative model based on the barrier imaging data, which results in the variation of the R n C data consistent with the measurements in this paper. V C 2016 AIP Publishing LLC.