Cryogenic Characterization of Ferroelectric Non-volatile Capacitors

TL;DR

This paper investigates cryogenic temperature effects on ferroelectric non-volatile capacitors, demonstrating improved noise performance and higher effective bits for in-memory computing arrays at low temperatures.

Contribution

It provides the first characterization of nvCaps at cryogenic temperatures and shows how lowering temperature enhances ENOB in capacitive crossbar arrays.

Findings

Memory window remains stable at cryogenic temperatures.

ON state retention improves at lower temperatures.

Higher ENOB (~5 bits) achieved at 77K for 128x128 MAC operations.

Abstract

Ferroelectric-based capacitive crossbar arrays have been proposed for energy-efficient in-memory computing in the charge domain. They combat the challenges like sneak paths and high static power faced by resistive crossbar arrays but are susceptible to thermal noise limiting the effective number of bits (ENOB) for the weighted sum. A direct way to reduce this thermal noise is by lowering the temperature as thermal noise is proportional to temperature. In this work, we first characterize the non-volatile capacitors (nvCaps) on a foundry 28 nm platform at cryogenic temperatures to evaluate the memory window, ON state retention as a function of temperature down to 77K, and then use the calibrated device models to simulate the capacitive crossbar arrays in SPICE at lower temperatures to demonstrate higher ENOB (~5 bits) for 128x128 multiple-and-accumulate (MAC) operations.