We have fabricated Nb/Al-AlO_x/Nb Josephson junctions and have measured their current-voltage characteristics and the two-dimensional magnetic field dependence of the Josephson current. When the external magnetic fields (H_x, H_y) parallel to the junction plane are applied to the Josephson junction from two directions, two Fraunhofer diffraction patterns are observed in the (H_x, H_y) plane. In this study, we have fabricated several Nb/Al-AlO_x/Nb Josephson junctions with different thicknesses of Al layer and have investigated the effect of the Al layer thicknesses on the two-dimensional magnetic field dependence of the Josephson current. The thicknesses of the Al layers in the Josephson junctions we fabricated are 5 nm, 25 nm, 50 nm, 100 nm and 200 nm. When the Al layer thickness was 5 nm and 25 nm thick, a subpeak of the Fraunhofer diffraction pattern was clearly observed. However, the subpeak of the Fraunhofer diffraction pattern was not obviously observed as the Al layer got thicker. In particular, when the Al layer was 200 nm thick, the subpeak of the Fraunhofer diffraction pattern was not observed at all.

我们制造了Nb / Al-AlO _x / Nb约瑟夫森结，并测量了它们的电流-电压特性以及约瑟夫森电流的二维磁场依赖性。当平行于结平面的外部磁场（H _x，H _y）从两个方向施加到约瑟夫森结时，在（H _x，H _y）平面上观察到两个弗劳恩霍夫衍射图。在这项研究中，我们制造了几种Nb / Al-AlO _x/ Nb具有不同厚度的铝层的约瑟夫森结，并研究了铝层厚度对约瑟夫森电流的二维磁场依赖性的影响。我们制造的约瑟夫森结中的Al层厚度为5 nm，25 nm，50 nm，100 nm和200 nm。当Al层厚度为5nm和25nm厚时，清楚地观察到弗劳恩霍夫衍射图的亚峰。但是，由于Al层变厚，因此没有明显观察到Fraunhofer衍射图的亚峰。特别地，当Al层为200nm厚时，根本未观察到弗劳恩霍夫衍射图的亚峰。