Magnetic Josephson Junctions With Superconducting Interlayer for Cryogenic Memory

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.