ИСТИНА

The report provides an overview of the current state in the development of control units for superconducting memory compatible with logic elements of rapid single fast quantum logic (RSFQ). The interest to this problem is motivated by the recent developments, which clearly demonstrated that the achieved background in this field provides the opportunity for finding solutions for elaboration of superconducting memory cells, which can be integrated with RSFQ logic circuits. These cells are based on heterostructures, which consist of superconducting (S) materials, insulator (I), ferromagnetic (F) and normal (N) metals. The basic physical mechanisms underlying the operation of the control elements with superconducting and ferromagnetic materials are formulated. We start with the brief discussion of peculiarities of proximity effect in SF and SFF multilayers and their manifestation in spin valve devices controlling critical temperature of S film, conductance of one of the F layers or critical current of Josephson junctions. In the latter case a recent status of experimental and theoretical achievements in developing SIsFS and SFFS Josephson devices is discussed. It is shown that the simplest versions of such elements, having two or more ferromagnetic layers in the weak-coupling Josephson junctions have low characteristic voltage Vc, resulting in degradation of their properties and оperating voltage mismatch with RSFQ logic circuits. It is demonstrated that this drawback can be overcame in a class of structures that except F films also contains additional thin superconducting film in the weak coupling region of Josephson devices. This makes it possible not only to increase the Vc to the required level, but also to offer structure, in which switching states are not connected with the processes of magnetization reversal of the ferromagnetic films. Special attention will be given to the effect of formation of domain walls and normal phase inclusions in the F films on the junction critical current. Support by RFBR grants 15-52-10045 KO_a, 15-32-20362-mol_a_ved, Russian President Grant No. МК-5813.2016.2 and Ministry of Education and Science of the Russian Federation (grant No. 14Y26.31.0007) is acknowledged.