Low-Power, High-Speed and High-Density Magnetic Non-Volatile SRAM Design with Voltage-Gated Spin-Orbit Torque

Abstract

This paper proposes two different magnetic nonvolatile SRAM (MNV-SRAM) cell circuits for low-power and fast backup operation with a compact cell area. They employ perpendicular magnetic tunnel junctions (p-MTJs) as non-volatile backup storage elements and explore the spin-orbit torque (SOT) with the assistance of the voltage-controlled magnetic anisotropy effect (VCMA), referred to voltage-gated SOT (VGSOT), to perform the backup operation. Owing to the aid of the VCMA effect, the critical SOT write current for 1-ns backup operation can be significantly reduced, thus resulting in high speed and low power consumption. Moreover, such small write current allows to be driven by the cross-coupled inverters in the SRAM cell, instead of a dedicated write driver, thereby leading to low cell area overhead. By using a commercial CMOS 40 nm design kit and a physics-based VGSOT-MTJ model, we have demonstrated their functionalities and evaluated their performance. Compared to previous MNV-SRAM cell circuits, the proposed MNV-SRAM cell circuits can achieve lower backup energy dissipation, smaller backup delay and less cell area overhead. Additionally, the proposed MNV-SRAM cell circuits can achieve field-free backup operation, thus being suitable for practical applications.