1998 Fiscal Year Final Research Report Summary
A Study on Josephson Junctions with Controlled Barrier Layrs Operating at 10 K for Integrated Circuit Application
| Project/Area Number |
09305026
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
電子デバイス・機器工学
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| Research Institution | Nagoya University |
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Principal Investigator |
HAYAKAWA Hisao Nagoya Univ., Grad.School of Eng., Professor, 工学研究科, 教授 (60189636)
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| Co-Investigator(Kenkyū-buntansha) |
AKAIKE Hiroyuki Nagoya Univ., Center for Cooperative Research in Advance Science and Technology., 先端技術共同研究センター, 助手 (20273287)
INOUE Masumi Nagoya Univ., Grad.School of Eng., Assist.Professor, 工学研究科, 講師 (00203258)
FUJIMAKI Akira Nagoya Univ., Grad.School of Eng., Assoc.Professor, 工学研究科, 助教授 (20183931)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Superconductor / Josephson Junctions / 10 K Operation / Niobium-nitride / Plasma-nitrided Barriers / Overdamped Junctions / High IcRn Product |
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| Research Abstract |
The purpose of this work is to develop Josephson junctions as basic elements in single flux quantum superconducting integrated circuits operating at 10 K.The junctions are required to have overdamped characteristics and the high IcRn products at 10 K.Here, the Ic and Rn are a critical current and a junction resistance, respectively. In order to attain the purpose, we have proposed NbN Josephson junctions with plasma-nitrided NbNx barriers and investigated the electrical characteristics of the junctions. The results we have obtained are listed as follows.
1. We have obtained overdamped NbN junctions with the IcRn product as large as 0.6 mV at 10K.
2. The Ic uniformity was within the standard deviation, 1-sigma, of 2.9% for a series of 64 junctions in a chip and the run-to-run variation in the critical current density, Jc, was within 1-sigma of 14%. This means that the junctions can be applied to Josephson ICs.
3. The Jc was obtained in the range of a few tens A/cm^2 to a few ten kA/cm^2.
4. The conduction mechanism of the junctions was investigated. It was found that the plasma-nitrided NbNx barrier has localized states in it and that quasi-particles tunnel via localized states between both of the NbN electrodes. It was also found that the junctions behave as a Superconductor-Normal layer-Insulator-Normal layer-Superconductor (SNINS) junction.
5. The junction characteristics depend strongly on the crystallinity of the base NbN layers and the NbNx barrier formation conditions.
6. The control of the localized state density in the NbNx barriers is essential for controlling the junction characteristics.
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