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

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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.