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A Study on Josephson Junctions with Controlled Barrier Layrs Operating at 10 K for Integrated Circuit Application

集成电路应用中工作温度为 10 K 的可控势垒层约瑟夫森结的研究

基本信息

批准号：
09305026
负责人：
HAYAKAWA Hisao
金额：
$ 23.3万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

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.

这项工作的目的是开发约瑟夫森结作为工作温度为 10 K 的单通量量子超导集成电路的基本元件。该结需要具有过阻尼特性和在 10 K 下的高 IcRn 乘积。这里，Ic 和 Rn 分别是临界电流和结电阻。为了实现这一目的，我们提出了具有等离子体氮化NbNx势垒的NbN约瑟夫森结，并研究了该结的电特性。我们得到的结果如下： 1．我们获得了过阻尼 NbN 结，在 10K.2 时 IcRn 乘积高达 0.6 mV。对于芯片中一系列 64 个结点，Ic 均匀性在 2.9% 的标准偏差 1-sigma 范围内，并且临界电流密度 Jc 的运行间变化在 14% 的 1-sigma 范围内。这意味着该结可以应用于约瑟夫森ICs.3。获得的Jc在几十A/cm^2到几十kA/cm^2.4的范围内。研究了结的传导机制。研究发现，等离子体氮化的 NbNx 势垒中具有局域态，并且准粒子通过两个 NbN 电极之间的局域态隧道。还发现该结表现为超导体-普通层-绝缘体-普通层-超导体(SNINS)结。5．结特性很大程度上取决于基底 NbN 层的结晶度和 NbNx 势垒形成条件。 6． NbNx 势垒中局域态密度的控制对于控制结特性至关重要。