A ferroelectric–memristor memory for both training and inference

Abstract

Developing artificial intelligence systems that are capable of learning at the edge of a network requires both energy-efficient inference and learning. However, current memory technology cannot provide the necessary combination of high endurance, low programming energy and non-destructive read processes. Here we report a unified memory stack that functions as a memristor as well as a ferroelectric capacitor. Memristors are ideal for inference but have limited endurance and high programming energy; ferroelectric capacitors are ideal for learning, but their destructive read process makes them unsuitable for inference. Our memory stack uses a silicon-doped hafnium oxide and titanium scavenging layer that are integrated into the back end of line of a complementary metal–oxide–semiconductor process. With this approach, we fabricate an 18,432-device hybrid array (consisting of 16,384 ferroelectric capacitors and 2,048 memristors) with on-chip complementary metal–oxide–semiconductor periphery circuits. Each weight is associated with an analogue value stored as conductance levels in the memristors and a high-precision hidden value stored as a signed integer in the ferroelectric capacitors. Weight transfers between the different memory technologies occur without a formal digital-to-analogue converter. We use the array to validate an on-chip learning solution that, without batching, performs competitively with floating-point-precision software models across several benchmarks.