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

Journal article, 2016

In this paper, we study the effect of the tunnel barrier thickness non-uniformity in Nb/Al-AlOx/Nb tunnel junctions using the measurement results of the junctioncapacitance (C) and the normal resistance (Rn). The local thickness distribution of the AlOx tunnel barrier in Nb/Al-AlOx/Nb trilayer (RnA ∼ 30 Ω μm2) was studied by high resolution transmission electron microscopy. The specific resistance (RnA) values of the measured junctions range from 8.8 to 68 Ω μm2. 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 RnC 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 RnC product. We confirm this conclusion through an illustrative model based on the barrier imaging data, which results in the variation of the RnC data consistent with the measurements in this paper.