Research and Development of Superconduting Tunnel Junctions for X-ray Astronomy

超导隧道结是一种低温探测器，可以在IK以下相对较高的温度下工作。它是下一代通用辐射探测器的候选者。本课题研究了高质量、高再现性的超导隧道结的制造技术，并开发了读出电路，将低温隧道结的电信号传输到室温下的数据采集系统。利用日本理化学研究所的一条特殊加工生产线，研制出了用于x射线探测的超导隧道结。结的层状结构是在硅和蓝宝石衬底的氧化铝缓冲层上沉积Nb/Al/AlOx/Al/Nb五层。改进了在氧等离子体作用下氧化结侧的技术，抑制了隧道阻挡层上的漏电流。因此，泄漏电流被成功地抑制了一个数量级以上，并具有良好的再现性。测量了不同尺寸的20μm×20μm， 100μm×100μm, 200μm×200μm， 500μm×500μm结对5.9 keV x射线的响应。所有病例均观察到x射线信号，最佳能量分辨率达到41 eV。读出电子学也改进了半导体电子学和超导电子学。本课题对超导x射线探测系统的实现技术进行了研究和开发。

The superconduting tunnel junction is a low temperature detector which can be operated at relatively higher temperatures below IK. It is a candidate of general purpose radiation detector of the next generation. In this project, the fabrication technique of the superconduting tunnel junctions with a good quality and reproducibility is studied together with the development of readout circuits which transmit electric signals from the junctions located at low temperatures to data acquisition system at room temperature.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 techniques to realize superconducting X-ray detection system were studied and developed in this project.