Aluminum thickness dependence of spatial profile in niobium-based superconducting tunnel junctions

Spatial profiles of low-temperature detectors can be measured with Low-Temperature Scanning Synchrotron Microscopy directly. The dependence of the spatial profiles on the bias current, the magnetic field strength, and the size of junctions have been already studied in previous reports. In this study, we fabricated Nb-based junctions having Al layers of different thicknesses, which are located at the both sides of the tunneling barrier, by using a lift-off technique. It has been found that the spatial uniformity is improved by increasing the Al thickness. Therefore, it is demonstrated that the Al layers play a important role more than quasiparticle trapping.