Inhomogeneities of the current density distribution of Nb–NbOx–Pb‐Josephson tunnel junctions are caused by contaminations from boundary materials during the sputter cleaning process of the Nb‐surface. The variations of the current density distributions of various junction types during storage in dry air or in open air are dependent on the kind of the impurity. Window type junctions show a smaller influence on the current density at the edges of the barrier area by penetrating water than crossed type junctions. The reason is that the edges are covered by the SiO‐window mask. Furthermore, with a high spatial resolution the current density distribution shows a fine structure independent of junction preparation.
The most frequently given even-symmetric current density distributions can be directly calculated from the I c ( H ) characteristic by Fourier transformation. The calculated current density distributions of crossed-type 10 x 10 pm2 Nb-Nb0,-Pb tunnel junctions are presented and reasons of the smaller barrier permeability at the edges of the strip lines are discussed. The small odd-symmetric parts of the distributions are estimated.Symmetrische Stromdichteverteilungen, welche fast ausschlieDlich vorliegen, lassen sich direkt aus der I,(H)-Charakteristi mittels Fouriertransformation berechnen. Die berechneten Stromdichteverteilungen von gekreuzten 10 x 10 pm2 Nb-Nb0,-Pb-Tunnelelementen werden vorgestellt und die Ursachen der geringeren Barrierendurchlassigkeiten an den Randern der Streifenleiter werden diskutiert. Die auftretenden geringen Unsymmetrien werden abgeschatzt.
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