Monolithically Integrated RRAM- and CMOS-Based In-Memory Computing Optimizations for Efficient Deep Learning

Resistive RAM (RRAM) has been presented as a promising memory technology toward deep neural network (DNN) hardware design, with nonvolatility, high density, high ON/OFF ratio, and compatibility with logic process. However, prior RRAM works for DNNs have shown limitations on parallelism for in-memory computing, array efficiency with large peripheral circuits, multilevel analog operation, and demonstration of monolithic integration. In this article, we propose circuit-/device-level optimizations to improve the energy and density of RRAM-based in-memory computing architectures. We report experimental results based on prototype chip design of 128 x 64 RRAM arrays and CMOS peripheral circuits, where RRAM devices are monolithically integrated in a commercial 90-nm CMOS technology. We demonstrate the CMOS peripheral circuit optimization using input-splitting scheme and investigate the implication of higher low resistance state on energy efficiency and robustness. Employing the proposed techniques, we demonstrate RRAM-based in-memory computing with up to 116.0 TOPS/W energy efficiency and 84.2% CIFAR-10 accuracy. Furthermore, we investigate four-level programming with single RRAM device, and report the system-level performance and DNN accuracy results using circuit-level benchmark simulator NeuroSim.