Journal of Low Temperature Physics

, Volume 176, Issue 3–4, pp 465–469 | Cite as

Current Sensitivity Enhancement of a Quasi-One-Junction SQUID Comparator as an Input Circuit of SFQ Readout Circuit for a Superconducting Detector

  • S. Miyajima
  • K. Ito
  • Y. Kita
  • T. Ishida
  • A. Fujimaki


We evaluated the current sensitivity of a quasi-one-junction SQUID (QOS) comparator with an input transformer at 4.2 K. A comparator based on a QOS is promising for constructing the single flux quantum (SFQ) readout circuits of an array system of multiple superconducting detectors.The QOS comparator is made of three Nb/AlO\(_x\)/Nb Josephson junctions, senses an output signal of a superconductor detector, and generates the SFQ pulses.There are strong demands for enhancing the current sensitivity of the QOS comparator because an output current from superconducting detector typically remains at the magnitude of a few \(\upmu \)A. We fabricated the QOS comparator with an input transformer using AIST Standard Process 2, where the critical current density of the Josephson junctions is chosen as high as 2.5 kA/cm\(^{2}\). We designed the input transformer to enhance the current sensitivity under the conditions of 200 \(\upmu \)\(\times \) 200 \(\upmu \)m in size and 20:1 in turn ratio. Consequently, we succeeded in reducing a gray zone width of the comparator, and achieved the current sensitivity of 400 nA at 4.2 K in the low frequency range.


Single flux quantum circuit Quasi-one-junction SQUID Current sensitivity 



This development was supported Grant-in-Aid for Scientific Research (S) (No. 23226019) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.The CONNECT cell library and tools are used for the demonstration. The authors would like to thank all the CONNECT members consisting of SRL-ISTEC, NICT, Nagoya University, and Yokohama National University. The circuits were fabricated in the clean room for analog–digital superconductivity (CRAVITY) of National Institute of Advanced Industrial Science and Technology (AIST) with the standard process 2 (STP2). The AIST-STP2 is based on the Nb circuit fabrication process developed in International Superconductivity Technology Center (ISTEC).


  1. 1.
    K.D. Irwin, G.C. Hilton, D.A. Wollman, J.M. Martinis, Appl. Phys. Lett. 69, 1945 (1996)ADSCrossRefGoogle Scholar
  2. 2.
    P.K. Day, H.G. Leduc, A. Goldin, T. Vayonakis, B.A. Mazin, S. Kumar, J. Gao, J. Zmuidzinas, Nucl. Instrum. Methods Phys. Res. Sect. A 559, 561 (2006)ADSCrossRefGoogle Scholar
  3. 3.
    M. Ohkubo, H. Pressler, D. Fukuda, T. Inou, H. Takahashi, M. Nakazawa, IEEE Trans. Appl. Supercond. 13, 634 (2003)CrossRefGoogle Scholar
  4. 4.
    A. Bozbey, S. Miyajima, H. Akaike, A. Fujimaki, IEEE Trans. Appl. Supercond. 19, 509 (2009)ADSCrossRefGoogle Scholar
  5. 5.
    A. Fujimaki, I. Nakanishi, S. Miyajima, K. Arai, Y. Akita, and T. Ishida, IEICE Trans. Electron. E94-C, 254 (2011)Google Scholar
  6. 6.
    K. Takahashi, S. Miki, K. Satoh, K. Moriwaki, K. Fukuda, T. Yotsuya, H. Shimakage, Z. Wang, S. Okayasu, M. Katagiri, Y. Morii, K. Hojou, N. Niimura, T. Ishida, Phys. C 426–431, 1597 (2004)CrossRefGoogle Scholar
  7. 7.
    T. Ishida, M. Nishikawa, Y. Fujita, S. Okayasu, M. Katagiri, K. Satoh, T. Yotsuya, H. Shimakage, S. Miki, Z. Wang, M. Machida, T. Kano, M. Kato, J. Low Temp. Phys. 151, 1074 (2008)ADSCrossRefGoogle Scholar
  8. 8.
    S. Miyajima, T. Kusumoto, K. Ito, Y. Akita, I. Yagi, N. Yoshioka, T. Ishida, S. Miki, Z. Wang, A. Fujimaki, IEEE Trans. Appl. Supercond. 23, 1800505 (2013)CrossRefGoogle Scholar
  9. 9.
    S. Miyajima, T. Ortlepp, T. Hannes, A. Bozbey, A. Fujimaki, Jpn. J. Appl. Phys. 52, 0331101 (2013)ADSCrossRefGoogle Scholar
  10. 10.
    N. Zen, H. Takahashi, R.M.T. Damayanthi, F. Mori, K. Fujita, D. Fukuda, M. Ohkubo, IEEE Trans. Appl. Supercond. 17, 318 (2007)ADSCrossRefGoogle Scholar
  11. 11.
    C. Otani, T. Taino, R. Nakano, K. Hoshino, T. Shibuya, H. Myoren, S. Ariyoshi, H. Sato, H.M. Shimizu, S. Takada, K. Kawase, IEEE Trans. Appl. Supercond. 15, 591 (2005)CrossRefGoogle Scholar
  12. 12.
    T. Taino, R. Nakano, S. Yoshimura, H. Myoren, S. Takada, C. Otani, S. Ariyoshi, T. Shibuya, K. Kawase, H. Sato, H.M. Shimizu, Nucl. Instrum. Methods Phys. Res. A 559, 751 (2006)ADSCrossRefGoogle Scholar
  13. 13.
    K.K. Likharev, V.K. Semenov, IEEE Trans. Appl. Supercond. 1, 3 (1991)ADSCrossRefGoogle Scholar
  14. 14.
    S. Yorozu, Y. Kameda, H. Terai, A. Fujimaki, T. Yamada, S. Tahara, Phys. C 378–381, 1471 (2002)CrossRefGoogle Scholar
  15. 15.
    S. Nagasawa, Y. Hashimoto, H. Numata, S. Tahara, IEEE Trans. Appl. Supercond. 5, 2447 (1995)CrossRefGoogle Scholar
  16. 16.
    T.V. Filippov, V.K. Kornev, IEEE Trans. Appl. Supercond. 27, 2452 (1991)Google Scholar
  17. 17.
    V.K. Semenov, T.V. Fillippov, YuA Polyakov, K.K. Likharev, IEEE Trans. Appl. Supercond. 7, 3617 (1997)CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • S. Miyajima
    • 1
    • 2
  • K. Ito
    • 2
  • Y. Kita
    • 2
  • T. Ishida
    • 1
  • A. Fujimaki
    • 2
  1. 1.Department of Physics and ElectronicsOsaka Prefecture UniversitySakaiJapan
  2. 2.Department of Quantum EngineeringNagoya UniversityNagoyaJapan

Personalised recommendations