Specific capacitance of Nb/AlOx/Nb Josephson junctions with critical current densities in the range of 0.1–18 kA/cm2

Abstract

The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1–18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction.

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

“…5(b)). The results of this analysis show that the nonuniformity of the tunnel barrier thickness is not negligible and presenting it as a continuously variablethickness 28 model is an oversimplification. The tunnel barrier thickness distribution of the 35 nm wide cross-section image was extracted using 0.7 nm wide sampling windows and presented with black bars in Fig.…”

“…5(a), shows that the AlO x layer is amorphous and the concept of monolayers is probably not applicable in the case of amorphous films. 28 Hence, the one-step 29 model of the tunnel barrier is not suitable. In this paper, the thickness of the AlO x amorphous layer is extracted using the image intensity profile (see Fig.…”

“…Previously, continuously variable-thickness model 28 (uniform thickness increasing continuously) or the one-step model 29 (the junction area is divided into two portions with n and n þ 1 monolayers) of the SIS junction tunnel barrier was suggested to illustrate the tunnel barrier thickness distribution. These models were used for fitting the relation between the measured specific capacitance and the specific resistance data.…”

“…These models were used for fitting the relation between the measured specific capacitance and the specific resistance data. Using the continuously variable-thickness model, 28 it was attempted to extract the tunnel barrier height and the dielectric constant. However, in this approach, the barrier height shape was assumed to be rectangular with the same value for all the junctions with various transparencies.…”

High performance Nb Josephson devices for petaflops computing

“…The RSJ model can be adapted to incorporate the nonlinear IVCs of superconducting TJs, but this approach has limited utility because it neglects the frequency dependence of the supercurrent Because TJ electrodes are separated by -1 nm, C' is large. The capacitance of Nb-AI2O3-Nb junctions was measured as a function of J, by Maezawa et al [37]. Their data are summarized by the fit:…”