Domain Wall-Magnetic Tunnel Junction Analog Content Addressable Memory Using Current and Projected Data

TL;DR

This paper proposes a magnetic tunnel junction-based analog content-addressable memory (ACAM) using domain wall-MTJs, demonstrating multi-bit storage, ternary search capability, and optimized device-circuit co-design for efficient in-memory computing.

Contribution

It introduces a novel DW-MTJ based ACAM circuit with multi-bit and ternary functions, along with design guidelines and material analysis for optimized performance.

Findings

Achieved 8-10 bits of weight storage in DW-MTJ ACAM.

Demonstrated ternary CAM function with prototype simulation.

Identified platinum as the optimal material for maximum search bounds.

Abstract

With the rise in in-memory computing architectures to reduce the compute-memory bottleneck, a new bottleneck is present between analog and digital conversion. Analog content-addressable memories (ACAM) are being recently studied for in-memory computing to efficiently convert between analog and digital signals. Magnetic memory elements such as magnetic tunnel junctions (MTJs) could be useful for ACAM due to their low read/write energy and high endurance, but MTJs are usually restricted to digital values. The spin orbit torque-driven domain wall-magnetic tunnel junction (DW-MTJ) has been recently shown to have multi-bit function. Here, an ACAM circuit is studied that uses two domain wall-magnetic tunnel junctions (DW-MTJs) as the analog storage elements. Prototype DW-MTJ data is input into the magnetic ACAM (MACAM) circuit simulation, showing ternary CAM function. Device-circuit co-design is carried out, showing that 8-10 weight bits are achievable, and that designing asymmetrical spacing of the available DW positions in the device leads to evenly spaced ACAM search bounds. Analyzing available spin orbit torque materials shows platinum provides the largest MACAM search bound while still allowing spin orbit torque domain wall motion, and that the circuit is optimized with minimized MTJ resistance, minimized spin orbit torque material resistance, and maximized tunnel magnetoresistance. These results show the feasibility of using DW-MTJs for MACAM and provide design parameters.