Observability of negative capacitance of a ferroelectric film: Theoretical predictions

TL;DR

This paper provides a theoretical analysis of negative capacitance phenomena in ferroelectric films, deriving analytical expressions and exploring the effects of screening charges, which can explain transient negative capacitance observed experimentally.

Contribution

It introduces a comprehensive theoretical framework for understanding steady-state and transient negative capacitance in ferroelectric films, including analytical formulas and the impact of screening charges.

Findings

Analytical expressions for capacitance, polarization, and domain stability are derived.

Transient negative capacitance can occur with slow screening charges and low-frequency conditions.

The study helps interpret experimental observations of negative capacitance in ferroelectric films.

Abstract

We theoretically explore mechanisms that can potentially give rise to the steady-state and transient negative capacitance in a uniaxial ferroelectric film stabilized by a dielectric layer. The analytical expressions for the steady-state capacitance of a single-domain and poly-domain states are derived within Landau-Ginzburg-Devonshire approach and used to study the state stability vs. the domain splitting as a function of dielectric layer thickness. Analytical expressions for the critical thickness of the dielectric layer, polarization amplitude, equilibrium domain period and susceptibility are obtained and corroborated by finite element modelling. We further explore the possible effects of nonlinear screening by two types of screening charges at the ferroelectric-dielectric interface and show that if at least one of the screening charges is very slow, the total polarization dynamics can exhibit complex time- and voltage dependent behaviors that can be interpreted as an observable negative capacitance. In this setting, the transient negative capacitance effect is accompanied by almost zero dielectric susceptibility in a wide voltage range and low frequencies. These results may help to elucidate the observation of the transient negative capacitance in thin ferroelectric films, and identify materials systems that can give rise to the behavior.