Research of Superconduting Tunnel Junctions for Visible Photon and Molecular Beam

超导隧道结是一种低温探测器，可以在低于1 K的较高温度下工作，是下一代通用辐射探测器的候选者。本项目研究了用于可见光和分子束探测的超导隧道结的制备技术，利用日本理化学研究所（RIKEN）的专用生产线研制出了用于X射线探测的超导隧道结，其结构为在硅和蓝宝石衬底上的氧化铝缓冲层上沉积Nb/Al/AlOx/Al/Nb五层结构。通过改进在氧等离子体下氧化结侧的技术，抑制了穿过隧道势垒的漏电流。因此，泄漏电流被成功地抑制了一个数量级以上，具有良好的再现性。测量了20μm×20μm、100μm×100μm、200μm× 200 μ m、500μm× 500μm不同尺寸的结对5.9keV X射线的响应。在所有情况下都观察到X射线信号，最佳能量分辨率达到41 eV。使用半导体电子学和超导电子学还改进了读出电子学。开发了没有顶部SiO2层的结，以将敏感能量扩展到较低能量。实验结果表明，这种结可以测量低至50 eV的光子能量。本项目研究和发展了实现低能量子（如可见光子和分子束）超导探测器的技术。

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.