X-ray and optical photon counting detector using superconducting tunnel junctions

• Published in: IEEE transactions on applied superconductivity Vol. 11; no. 1; pp. 824 - 827
• Main Authors: Delaet, B., Feautrier, P., Villegier, J.-C., Benoit, A.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.03.2001; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Astronomy; Electronics; Exact sciences and technology; Fabrication; Josephson junctions; Niobium; Optical detectors; Optical sensors; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Superconducting devices; Superconducting epitaxial layers; Superconducting photodetectors; Telescopes; X-ray detection; X-ray detectors
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/77.919471

The properties of Superconducting Tunnel Junctions (STJ) make them very suitable for low light level astronomical observations. STJ detectors could be used to improve the sensitivity of such a system to be implemented on ground based telescopes. We have developed a modified version of the "SNEP" fabrication process for making Nb/Al-AlO/sub x/-Al/Nb and Ta/Al-AlO/sub x/-Al/Ta/Nb STJ's. These junctions show a very low sub-gap leakage current at 0.1 K. They use a double thin aluminum trapping layer and a Nb or Ta absorber grown epitaxially on a R-plane sapphire substrate. A new experimental set-up has been completed to achieve photon counting performances for the X-ray and for optical-near infrared wavelengths. An original, room temperature, charge sensitive preamplifier has been built for this purpose and tested with a /sup 55/Fe X-ray source. The 6 keV peak of this source can be observed in the measured spectrum. Photon counting ability in the near infrared at 0.78 /spl mu/m is also demonstrated.