Study on Flux Trapping in Superconducting Integrated Circuits and Development of a Method for Eliminating Flux Trapping

本研究的目的是研究超导集成电路中的磁通捕获机理，并开发一种有效的消除磁通捕获的方法。我们按照最初的计划进行了一系列的研究，并成功地达到了目的。研究结果如下：1)Nb薄膜约瑟夫森结阵列的制备和俘获磁通空间分布的测量--我们发展了一种用Nb基电极制作高质量约瑟夫森结的技术，并成功地实现了50个串联结。2)磁通捕获机理的阐明--我们根据实验结果提出了一种可能的磁通捕获机制。研究表明，磁通钉扎有两种机制，即体钉扎和表面钉扎。3)消除磁通捕获实验--我们用He-Ne激光照射光束进行了消除磁通捕获的实验。结果表明，用功率为10~(-100)微米的激光照射可以消除磁通的俘获。4)基于上述方案，我们考虑了消除磁通俘获的有效方法。

The purpose of this research is to study the mechanism of flux trapping in superconducting integrated circuits and to develop an effective method for eliminating the trapped flux. We have conducted a series of study according to the initial plan, and successfully achieved the purpose. The obtained results are as follows:1) Fabrication of Josephson junction arrays on Nb thin film and measurement of spatial distribution of trapped magnetic flux- We have developed a technique for fabricating good-quality Josephson junctions with Nb base electrode, and succeeded in realizing 50 series connected junctions.2) Elucidation of flux-trapping mechanism- We have considered a probable mechanism for the flux trapping based on the experimental results. It has been shown that there are two mechanisms of flux pinning,i.e., bulk pinning and surface pinning.3) Experiment on eliminating flux trapping- We have made an experiment on eliminating the trapped flux by irradiating a light beam from He-Ne laser. It is shown that the trapped flux can be eliminated by the laser irradiation of the power of 10-100<micrn>W.4) We have considered usefull methods for eliminating the flux trapping based on the above scheme.