We investigate a Magnetic Josephson Junction (MJJ) -a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energyefficient single flux quantum (SFQ) circuits. The superconductorinsulator-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.Index Terms-Energy efficient, memory devices, proximity effect, RAM, single flux quantum, superconducting logic elements.

The predictions of Moore’s law are considered by experts to be valid until 2020 giving rise to “post-Moore’s” technologies afterwards. Energy efficiency is one of the major challenges in high-performance computing that should be answered. Superconductor digital technology is a promising post-Moore’s alternative for the development of supercomputers. In this paper, we consider operation principles of an energy-efficient superconductor logic and memory circuits with a short retrospective review of their evolution. We analyze their shortcomings in respect to computer circuits design. Possible ways of further research are outlined.

Motivated by recent progress in development of cryogenic memory compatible with single flux quantum (SFQ) circuits we have performed a theoretical study of magnetic SIsFS Josephson junctions, where 'S' is a bulk superconductor, 's' is a thin superconducting film, 'F' is a metallic ferromagnet and 'I' is an insulator. We calculate the Josephson current as a function of s and F layers thickness, temperature and exchange energy of F film. We outline several modes of operation of these junctions and demonstrate their unique ability to have large product of a critical current I C and a normal-state resistance R N in the π state, comparable to that in SIS tunnel junctions commonly used in SFQ circuits. We develop a model describing switching of the Josephson critical current in these devices by external magnetic field. The results are in good agreement with the experimental data for Nb-Al/AlO x -Nb-Pd 0.99 Fe 0.01 -Nb junctions.

We present a study of magnetic structures with controllable effective exchange energy for Josephson switches and memory applications. As a basis for a weak link we propose to use a periodic structure composed of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on the Usadel equations show that switching from parallel (P) to antiparallel (AP) alignment of neighboring F layers can lead to a significant enhancement of the critical current through the junction. To control the magnetic alignment we propose to use a periodic system whose unit cell is a pseudo spin valve of structure F1/s/F2/s where F1 and F2 are two magnetic layers having different coercive fields. In order to check the feasibility of controllable switching between AP and P states through the whole periodic structure, we prepared a superlattice [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)]6 between two superconducting layers of Nb(25 nm). Neutron scattering and magnetometry data showed that parallel and antiparallel alignment can be controlled with a magnetic field of only several tens of Oersted.

We present the results of theoretical study of surface state properties in a two-dimensional model for triplet p-wave superconductors. We derive boundary conditions for Eilenberger equations at rough interfaces and develop the approach for self-consistent solution for the spatial dependence of px and px + i py -wave pair potentials. In the px case we demonstrate the robustness of the zero-energy peak in the density of states (DoS) with respect to surface roughness, in contrast to the suppression of such a peak in the case of dxy symmetry. This effect is due to stability of oddfrequency pairing state at the surface with respect to disorder. In the case of the chiral px + i py state we demonstrate the appearance of a complex multi-peak subgap structure in the spectrum with increasing surface roughness.