XNOR-VSH: A Valley-Spin Hall Effect-Based Compact and Energy-Efficient Synaptic Crossbar Array for Binary Neural Networks

Abstract

Binary neural networks (BNNs) have shown an immense promise for resource-constrained edge artificial intelligence (AI) platforms. However, prior designs typically either require two bit-cells to encode signed weights leading to an area overhead, or require complex peripheral circuitry. In this article, we address this issue by proposing a compact and low power in-memory computing (IMC) of XNOR-based dot products featuring signed weight encoding in a single bit-cell. Our approach utilizes valley-spin Hall (VSH) effect in monolayer tungsten di-selenide to design an XNOR bit-cell (named “XNOR-VSH”) with differential storage and access-transistor-less topology. We co-optimize the proposed VSH device and a memory array to enable robust in-memory dot product computations between signed binary inputs and signed binary weights with sense margin (SM) $1 ~\mu \text{A}$ . Our results show that the proposed XNOR-VSH array achieves 4.8%–9.0% and 37%–63% lower IMC latency and energy, respectively, with 49%–64% smaller area compared to spin-transfer-torque (STT)-magnetic random access memory (MRAM) and spin-orbit-torque (SOT)-MRAM based XNOR-arrays. We also present the impact of hardware non-idealities and process variations in XNOR-VSH on system-level accuracy for the trained ResNet-18 BNNs using the CIFAR-10 dataset.