Area and Energy Efficient Magnetic Full Adder based on Differential Spin Hall MRAM

Abstract

The in-memory computing concept has gained significant attraction with the inception of perpendicular magnetic tunnel junction (PMTJ) device, due to its nonvolatility and CMOS compatibility. Recently, several magnetic full-adder (MFA) designs based on spin-transfer torque (STT) and spin- Hall effect (SHE) magnetic random access memories (MRAMs) have been demonstrated. However, they consume higher write energy and occupy larger area. In this work, a novel MFA using differential spin-Hall (DSH) MRAM is proposed. The DSH- MRAM provides simultaneous switching of two PMTJ devices using SHE and generates complementary logic outputs. The single Hall metal (HM) shared by these PMTJ devices offers a very low resistance path for write operation. In this work, an external magnetic field (EMF) is used to assist the SHE current for PMTJ switching that eliminates the need for a STT current. A SPICE-compatible Verilog-A MTJ behaviour model of the proposed MFA is developed. The EMF-assisted DSH-MRAM requires a very short pulse (300 ps) of SHE current to switch both the PMTJs. The proposed MFA exhibits 65% less time, consumes 93% (18%) less write (read) energy, and saves 23% area compared to recent STT/SHE-MTJ based MFA designs.