Inhomogeneities in arrays of Josephson junctions: Their imaging by low-temperature scanning electron microscopy

The first application of low-temperature scanning electron microscopy for investigating the homogeneity of an array of Josephson tunnel junctions is reported. The experiments were performed on a series configuration of 166 junctions. The junction fabrication process was identical to that developed recently for the fabrication of a frequency-based Josephson voltage standard. The shorted junctions of the array could be easily detected. The quasiparticle imaging method, used previously for investigating spatial structures within individual tunnel junctions, can be extended in a straightforward way also to junction arrays.