Nonvolatile memory cell using a superconducting-ferromagnetic π Josephson junction

• Published in: Superconductor science & technology 2022-10, Vol.35 (10), p.105009
• Main Authors: Zeng, Junwen, Chen, Lei, Zhong, Xianghai, Wang, Yue, Pan, Yinping, Zhang, Denghui, Yu, Shujie, Wu, Ling, Zhang, Lu, Peng, Wei, Wang, Zhen
• Format: Article
• Language: English
• Subjects: flux quantum; junction; nonvolatile; SFS junction; superconducting memory
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/1361-6668/ac80d9

Storage of a single magnetic flux quantum in a superconducting loop containing a Josephson junction represents a promising unit cell configuration for construction of a cryogenic memory of superconducting digital circuits. However, application of a DC bias current is required for operation of such a memory cell to maintain trapping of the flux quantum in the storage loop. In this work, we present a superconducting memory cell that uses a superconducting-magnetic π junction. The cell characteristics show flux quantum hysteresis centering at the zero-bias current. We develop a fabrication process that combines superconductor–ferromagnet–superconductor (SFS) junctions with superconductor–normal metal–superconductor (SNS) junctions. The critical current density of the SFS junctions shows a 0– π oscillation as a function of the ferromagnetic layer thickness. The formation of the π junction is confirmed further by the flux modulation curves of a superconducting quantum interference device made from SNS junctions with an additional SFS junction.