Utilizing Valley-Spin Hall Effect in Monolayer WSe2 for Designing Low Power Nonvolatile Spintronic Devices and Flip-Flops

• Published in: IEEE transactions on electron devices Vol. 69; no. 4; pp. 1667 - 1676
• Main Authors: Cho, Karam, Liu, Xiangkai, Chen, Zhihong, Gupta, Sumeet Kumar
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Converters; Coupling; Design; Devices; Electrical junctions; Electromagnetism; Exchange coupling; Exchanging; Flip-flops; Hall effect; Magnetic anisotropy; Magnetic devices; Magnetic separation; Magnetic switching; Magnetic tunneling; Magnets; Misalignment; Monolayers; nonvolatile flip-flops (NVFFs); Perpendicular magnetic anisotropy; perpendicular magnetic anisotropy (PMA); Power management; Selenides; Switches; Transistors; Tungsten compounds; Tunnel junctions; valley–spin Hall effect (VSHE)
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3135475

In this article, we propose low power nonvolatile flip-flops (NVFFs) utilizing valley-spin Hall effect (VSHE) in monolayer tungsten diselenide (WSe 2 ). The proposed designs are based on nonvolatile spintronic devices comprising of WSe 2 -based charge-to-spin converter coupled with magnetic tunnel junctions. The proposed devices have an integrated back-gate to control the flow of charge and spin currents. VSHE leads to the flow of opposite spins in divergent directions perpendicular to the WSe 2 layer with valley/spin Hall angle ~1. This enables encoding true and complementary bits in a single device utilizing magnets with perpendicular magnetic anisotropy (PMA). By introducing exchange coupling between PMA magnets mediated by Ta and FeCo-oxide layers, we electrically isolate but magnetically couple the PMA free layers, which enable the design of backup/restore module of NVFFs with minimal number of transistors. Using object-oriented micromagnetic framework (OOMMF) simulation, we establish the robustness of the exchange-coupled PMA systems and show that the misalignment and reduction in exchange coupling strength, induced by process variations, have a minimal impact on their functionality. Exploiting the unique features of the proposed devices, we design two flavors of VSHE-based NVFFs (VSHE-NVFFs) and carry out their energy-delay characterization, including an extensive variation analysis. The proposed VSHE-NVFFs achieve 74%-75% lower backup energy and 55%-59% lower restore energy than the existing NVFFs based on giant spin Hall effect (GSHE).