Magnetic Josephson Junctions with Superconducting Interlayer for Cryogenic Memory

TL;DR

This paper explores Magnetic Josephson Junctions with a superconducting interlayer, demonstrating their potential for high-density, energy-efficient cryogenic memory compatible with superconducting digital circuits through experimental and theoretical analysis.

Contribution

It introduces a novel SIS'FS magnetic Josephson junction design, fabricates compatible devices, and validates their suitability for cryogenic memory and digital circuits with both experimental and analytical results.

Findings

MJJs show IcRn product ~30% lower than conventional SIS junctions.

Experimental results confirm applicability for superconducting memory.

Analytical models align well with experimental data.

Abstract

We investigate 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 IcRn 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.