Magnetic Josephson Junctions With Superconducting Interlayer for Cryogenic Memory

• Published in: IEEE transactions on applied superconductivity Vol. 23; no. 3; p. 1701208
• Main Authors: Vernik, I. V., Bol'ginov, V. V., Bakurskiy, S. V., Golubov, A. A., Kupriyanov, M. Y., Ryazanov, V. V., Mukhanov, O. A.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2013; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Energy efficient; Integrated circuits; Josephson junctions; Junctions; Magnetic fields; memory devices; proximity effect; RAM; Random access memory; single flux quantum; Superconducting epitaxial layers; superconducting logic elements
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2012.2233270

We investigate a Magnetic Josephson Junction (MJJ) - a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energy-efficient single flux quantum (SFQ) circuits. The superconductor-insulator-superconductor-ferromagnet-superconductor (SIS ' FS) MJJs are analyzed both experimentally and theoretically. We found that the properties of SIS ' FS junctions fall into two distinct classes based on the thickness of S ' layer. We fabricate Nb-Al/AlOx-Nb-PdFe-Nb SIS ' FS MJJs using a co-processing approach with a combination of HYPRES and ISSP fabrication processes. The resultant SIS ' FS structure with thin superconducting S ' -layer is substantially affected by the ferromagnetic layer as a whole. We fabricate these type of junctions to reach the device compatibility with conventional SIS junctions used for superconducting SFQ electronics to ensure a seamless integration of MJJ-based circuits and SIS JJ-based ultra-fast digital SFQ circuits. We report experimental results for MJJs, demonstrating their applicability for superconducting memory and digital circuits. These MJJs exhibit I c R n product only ~ 30% lower than that of conventional SIS junctions co-produced in the same fabrication. Analytical calculations for these SIS ' FS structures are in a good agreement with the experiment. We discuss application of MJJ devices for memory and programmable logic circuits.