Research of Superconduting Tunnel Junctions for Visible Photon and Molecular Beam

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The superconduting tunnel junction is a low temperature detector which can be operated at relatively higher temperatures below 1K.It is a candidate of general purpose radiation detector of the next generation. In this project, the fabrication technique of the superconduting tunnel junctions for the detection of visible photons and molecular beam.The superconduting tunnel junctions for X-ray detection have been developed using a special processing line of RIKEN.The layer structure of the junctions was a pentalayer of Nb/Al/AlOx/Al/Nb deposited on an aluminum-oxide buffer layer on silicon and sapphire substrates. The leak current across the tunnel barrier was suppressed by improving the technique to oxidize the side of the junction under oxygen plasma. Consequently, the leak current was successfully suppressed more than one order of magnitude with a good reproducibility. The response of the junction to 5.9 keV X-rays was measured for various dimensions of junctions of 20μm×20μm, 100μm×100μm, 200μm×200μm, 500μm×500μm. X-ray signals were observed in all cases and the best energy resolution reached 41 eV.The readout electronics was also improved using semiconductor electronics and superconducting electronics. The junctions without the top SiO2 layer was developed to extend the sensitive energy to lower energies. We have experimentally shown the junctions can measure the photon energy down to about 50 eV.The techniques to realize superconducting detector for low energy quanta such as visible photon and molecular beam were studied and developed in this project.