Inversion Charge Boost and Transient Steep-Slope Induced by Free-Charge-Polarization Mismatch in a Ferroelectric-Metal–Oxide–Semiconductor Capacitor

Abstract

In this paper, the transient behavior of a ferroelectric (FE)-metal–oxide–semiconductor (MOS) capacitor is theoretically investigated with a series resistor. It is shown that compared with a conventional high-k dielectric MOS capacitor, a significant inversion charge boost can be achieved by an FE MOS capacitor due to a transient steep subthreshold swing (SS) driven by the free-charge-polarization mismatch. It is also shown that the observation of transient steep SS in the experiment significantly depends not only on the measurement time but also on the viscosity coefficient under Landau’s mean field theory, which in general represents the average FE time response associated with the domain nucleation and propagation. Therefore, this paper not only establishes a theoretical framework that describes the physical origin behind the inversion charge-boost in an FE MOS capacitor but also shows that the key feature of depolarization effect on an FE MOS capacitor in the steady state should be the inversion charge boost, rather than the steep SS (e.g., sub-60 mV/decade at room temperature), which cannot be experimentally observed as the measurement time is much longer than the intrinsic FE response. Finally, from the effect of viscosity coefficient on inversion charge boost, we outline 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.

Keywords

• Ferroelectric (FE) transistor
• negative capacitance
• polarization