Inversion Charge-boost and Transient Steep-slope induced by Free charge-polarization Mismatch in a Ferroelectric-metal-oxide-semiconductor Capacitor

TL;DR

This paper presents a theoretical analysis of ferroelectric MOS capacitors, revealing how free charge-polarization mismatch induces a significant inversion charge-boost and transient steep subthreshold swing, with implications for high-speed, low-power transistors.

Contribution

It establishes a theoretical framework explaining the physical origin of inversion charge-boost and highlights the importance of depolarization effects over steep SS in ferroelectric MOS capacitors.

Findings

Inversion charge-boost is driven by free charge-polarization mismatch.

Steep transient SS depends on the viscosity coefficient under Landau theory.

Depolarization effect primarily enhances inversion charge rather than steady-state SS.

Abstract

In this letter, the transient behavior of a ferroelectric (FE) metal-oxide-semiconductor (MOS) capacitor is theoretically investigated with a series resistor. It is shown that compared to a conventional high-k dielectric MOS capacitor, a significant inversion charge-boost can be achieved by a FE MOS capacitor due to a steep transient subthreshold swing (SS) driven by the free charge-polarization mismatch. It is also shown that the observation of steep transient SS significantly depends on the viscosity coefficient under Landau's mean field theory, in general representing the average FE time response associated with domain nucleation and propagation. Therefore, this letter not only establishes a theoretical framework that describes the physical origin behind the inversion charge-boost in a FE MOS capacitor, but also shows that the key feature of depolarization effect on a FE MOS capacitor should be the inversion-charge boost, rather than the steep SS (e.g., sub-60mV/dec at room temperature), which cannot be experimentally observed as the measurement time is much longer than the FE response. Finally, we outlines the required material targets for the FE response in field-effect transistors to be applicable for next-generation high-speed and low-power digital switches.