Physical Origin of Transient Negative Capacitance in a Ferroelectric Capacitor

TL;DR

This paper investigates the physical origin of transient negative capacitance in ferroelectric capacitors, revealing it stems from charge dynamic mismatch driven by negative curvature in the free energy landscape during polarization switching.

Contribution

It analytically links transient negative capacitance to the negative curvature of the ferroelectric free energy profile, providing a physical understanding of the phenomenon.

Findings

Transient NC arises from charge mismatch during polarization switching.

Negative curvature of free energy landscape is essential for transient NC.

External resistance and FE viscosity influence transient NC behavior.

Abstract

Transient negative differential capacitance (NC), the dynamic reversal of transient capacitance in an electrical circuit is of highly technological and scientific interest since it probes the foundation of ferroelectricity. In this letter, we study a resistor-ferroelectric capacitor (R-FeC) network through a series of coupled equations based on Kirchhoff's law, Electrostatics, and Landau theory. We show that transient NC in a R-FeC circuit originates from the mismatch between rate of free charge change on the metal plate and that of bound charge change in a ferroelectric (FE) capacitor during polarization switching. This transient charge dynamic mismatch is driven by the negative curvature of the FE free energy landscape. It is also analytically shown that a free energy profile with the negative curvature is the only physical system that can describe transient NC during the two-state switching in a FE capacitor. Furthermore, this transient charge dynamic mismatch is justified by the dependence of external resistance and intrinsic FE viscosity coefficient. The depolarization effect on FE capacitors also shows the importance of negative curvature to transient NC. The relation between transient NC and negative curvature provides a direct insight into the free energy landscape during the FE switching.