Low Power and Scalable Digital Skyrmion Logic Circuits Based on Synthetic Antiferromagnetically Coupled Skyrmions

Skyrmion-based logic gates and circuits provide an advantageous combination of non-volatility and high-density operations compared to standard CMOS-based logic device technologies. Skyrmions are magnetic nanoscale structures that are protected by topology in various ferromagnetic (FM) systems. Nevertheless, in these systems, skyrmions are negatively impacted by the transverse motion resulting from the skyrmion Hall effect (SkHE). This motion hinders their performance in longitudinal nano tracks and prevents their application in cascadable logic circuits. Building upon our previous research on scalable FM skyrmion logic gates [1], we present a study focused on low-energy logic gates that utilize skyrmions in ferromagnetic interfaces. These interfaces are synthetic antiferromagnetically (SAF) coupled, which helps to stabilize the skyrmions and remove the SkHE (Skyrmion Hall Effect). The work employs micromagnetic models to create and showcase SAF skyrmion logic gates and circuits that rely on interactions between current-driven skyrmions and skyrmion-domain walls. Skyrmions have undergone thorough investigation and have been successfully stabilized in SAF layers, exhibiting dynamics free from SkHE. We first present the SAF skyrmion logic inverter gate's operation and show that it performs better than its FM skyrmion gate counterpart [1]. We maintained a switching time of 7 ns that was comparable to that of the FM counterpart while operating the inverter block with lower current density magnitudes. Subsequently, this is evident in the Joule heating, which is substantially reduced from approximately 10^-14 J in the FM case to approximately 10^-18 J. Next, we employ the inverter gate block to construct logic circuits, which include NOR, OR, AND, and NAND. We compare and evaluate the energy consumption and performance of SAF skyrmion logic gates at various stages with those of FM logic gates. We have shown that the SAF gates can operate at lower current densities, which is expected to result in a significant decrease in Joule heating costs. Ultimately, these gates demonstrate scalability, cascadability, and stability in the absence of SkHE, even when utilizing a more intricate design, such as the multiplexer circuit. The SAF skyrmion circuits can achieve higher performance metrics, reduced energy consumption, and low drive current densities with high skyrmion velocity in comparison to the FM skyrmion circuits. Our results have the potential to facilitate the development of spintronic computing devices that are both energy-efficient and fast, and that employ nanoscale skyrmions as information carriers.

References:
1- Arash Mousavi Cheghabouri, M.C.O. Domain Wall-Gated, Cascaded and Low-Power Skyrmion Logic Gates with Robust Operation. in 2022 Joint MMM-INTERMAG. 2022. Underline Science Inc.
2- Yagan, R., A.M. Cheghabouri, and M.C. Onbasli, Stabilization and adiabatic control of antiferromagnetically coupled skyrmions without the topological Hall effect. Nanoscale Advances, 2023. 5(17): p. 4470-4479.