Differential Phase Change Memory (PCM) Cell for Drift-Compensated In-Memory Computing
L. Pistolesi, L. Ravelli, Artem Glukhov, Amadeo de Gracia Herranz, Marisa López‐Vallejo, Marcella Carissimi, M. Pasotti, P.L. Rolandi, Andrea Redaelli, I. Muñoz Martín, S. Bianchi, Andrea Bonfanti, Daniele Ielmini
Abstract
Phase change memory (PCM) is a scalable, reliable, and robust technology for embedded and stand-alone memory device. PCM has also been extensively demonstrated for analog in-memory computing (IMC), which allows energy-efficient acceleration of AI workloads. High-temperature data retention requirements in PCM devices are met by Ge-rich GeSbTe (GST), which allows to satisfy consumer- and automotive-grade reliability specifications. However, Ge-rich GST suffers from set state drift, which affects the stability of the multilevel cell (MLC), hence the accuracy of IMC. This work presents: 1) a novel multilevel programming algorithm from weak reset state to prevent conductance instabilities; 2) a drift compensation scheme through a differential weight approach, validated on matrix-vector multiplication (MVM) after high-temperature annealing; and 3) a detailed study of the impact of PCM variability and weight quantization on hardware implementation of neural networks.