Modeling Computer Memory Based on Ferromagnetic/Superconductor Multilayers

Abstract

A model of superconducting computer memory exploiting the orthogonal spin transfer (OST) in the pseudospin valve (PS) that is controlled by the three-terminal Josephson superconducting-ferromagnetic transistor (SFT) is developed. The building blocks of the memory are hybrid PS and SFT structures. The memory model is formulated in terms of the equation-defined PS and SFT devices integrated into the PS/SFT memory cell (MC) circuit. Logical units "0" and "1" are associated with the two PS states respectively characterized by two different values of resistance. Elementary logical operations comprising the read/write processes occur when a word pulse applied to the SFT's injector coincides with the respective bit pulse acting on MC. Physically, a word pulse triggers SFT to a resistive state, causing the PS switching between the logical "0" and "1" states. Thus, the whole switching dynamics of MC depends on the non-equilibrium and nonstationary properties of PS and SFT. Modeling the single MC as well as the larger MC-based circuits comprising respectively twelve and thirty elements suggest that such the memory cells can undergo ultrafast switching (sub-ns) and low energy consumption per operation (sub-100 fJ). The suggested model allows studying the influence of noises, punch-through effect, crosstalk, parasitic, etc. The obtained results suggest that the hybrid PS/SFT structures are well-suited to superconducting computing circuits as they are built of magnetic and non-magnetic transition metals and therefore have low impedances (1-30 ). c I achieving much better flexibility of control, as compared to a conventional Josephson junction, where the tilt is controlled only by I . (b) The time dependence of the JJ voltage   V  , where J t   is the dimensionless time, J  is the Josephson plasma frequency. Curves 1, 2, 3, and 4 are related respectively to 0.01, 0.03, 0.033 J   and 0.065. We emphasize that in SFT one can readily alter both, J  and J  by merely changing the injector current. I  for 0.05 J   (curve 1), 0.3 J   (curve 2) and 0.6 J   (curve 3). One can see the hysteresis (curve 4) that is larger for smaller J  . , , J J J J J dimensionless time, J  is the Josephson plasma frequency curves 1, 2, 3, and 4 are related respectively to 0.01, 0.03, 0.033 J   and 0.065. In Fig. 3, we show the time-averaged SFT d.c. return current curves   V  versus   I  for 0.05 J   (curve 1), 0.3 J   (curve 2) and 0.6 J   (curve 3). Remarkably, that in SFT one can readily alter both, J  and J  by merely

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