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The barrier-layer thickness of cross-type square Pb-PbO-Pb thin-film Josephson junctions has been varied systematically and reproducibly by employing a mask-substrate changer and a low-pressureglow-discharge oxidation technique. A series of junctions has been fabricated in which the ratio of film width w to the Josephson penetration depth AJ is varied from XJ»w to AJ«W while the width of both films is kept constant at 0.3rnm. The magnetic-field dependence of the maximum zero-voltage current in these junctions has been measured as a function of the barrier-layer thickness. For non-negligible self-fields of the tunneling currents, the field dependence follows a Fresnel diffraction pattern rather than a Fraunhofer diffraction pattern. For very thin barrier layers, the maximum zero-voltage current is eventually limited by the critical current of the Pb films. Relatively thick barrier layers, on the other hand, tend to be shorted at the edges, as can be seen from the magnetic-field dependence. The stability of Pb-PbO-Pb Josephson junctions is compared with that of Nb-NbOx-Pb Josephson junctions.

The magnetic field dependence of the maximum dc Josephson current and of the ac Josephson-effect-induced step structure have been measured for sputtered Nb–NbOx–Pb Josephson junctions, and found to be in very good agreement with theoretical predictions; even for junctions made with ``dirty'' Nb thin films. From this agreement it is concluded that the observed anomalies in the I-V characteristics, namely, excess currents for voltages Δ(Pb)<V<Δ(Pb) + Δ(Nb) and a ``knee'' in the I-V curve at voltages just above Δ(Pb) + Δ(Nb), cannot be attributed to nonuniformities in the plane of the junction. It is further shown that these anomalies, especially the ``knee'', can be explained by a proximity-effect model in which the surface of the Nb thin film is assumed to be gapless due to gaseous impurities. The junctions were found to be much more stable with respect to repeated-thermal cycling and storage at room temperature than Pb–PbOx–Pb junctions made under the same conditions.

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