Alternative explanation for the steep subthreshold slope in Ferroelectric FETs

TL;DR

This paper proposes a new physical model based on domain wall motion and non-equilibrium behavior to explain the steep subthreshold slope in ferroelectric FETs, challenging the negative capacitance explanation.

Contribution

It introduces an alternative model for steep subthreshold slopes in ferroelectric FETs based on nucleation and propagation, avoiding the unphysical negative capacitance concept.

Findings

Steep subthreshold slope explained by domain wall motion

A two-step switching process accounts for experimental observations

Mathematical model supports the proposed mechanism

Abstract

Since many years, sub-60mV/decade switching has been reported in ferroelectric FETs. However, thus far these reports have lacked full physical explanation since they typically use a negative capacitance in the ferroelectric layer to be able to explain the experimental observations. Because negative capacitance as such is not a physical concept, we propose an alternative model that relies on the non-linear and non-equilibrium behavior of the ferroelectric layer. It is shown that a steep subthreshold slope can be obtained by a 2-step switching process, referred to as nucleation and propagation. Making use of the concept of domain wall motion as known also from fracture dynamics, we are able to explain the steep slope effect. A simple mathematical model is added to further describe this phenomenon, and to further investigate its eventual benefit for obtaining steep slope transistors in the sub-10nm era.