On the Quasi-static Negative Capacitance in HfO₂-based Ferroelectrics

Negative capacitance stabilized in HfO₂-based ferroelectric films offers a promising solution for low power-dissipation nanoscale electronics, however, its physical picture is still under intensive debate. Herein, the ferroelectric HfO₂/dielectric double layer system was modeled based on the Landau-Devonshire and Landau-Khalatnikov equations. Results show that the conventional quasi-static negative capacitance theory, which is rooted in the zero-field Gibbs free energy landscape and the quasi-static polarization-voltage curve, cannot capture the true polarization-voltage trajectory during the dynamic switching process. The negative capacitance observed in the ferroelectric HfO₂/dielectric system depends strongly on the evolution of the voltage dived by the dielectric layer and has a transient nature, which is at odds with the prediction of the quasi-static negative capacitance theory. Moreover, the emergence of hysteresis is ascribed to the thermal dissipation related to the damping parameter in the Landau-Khalatnikov equation, and it cannot be fully suppressed by the capacitance matching scenario. The thermal dissipation induced by the damping parameter is hugely enhanced with increasing frequency, which makes the high-frequency application of negative capacitance field-effect transistor rather impossible. This study provides an in-depth understanding on the underlying mechanism of the negative capacitance effect found in the HfO₂-related materials.