A microscopic "toy" model of ferroelectric negative capacitance

The continued miniaturization of nanoelectronic devices approaches its fundamental physical limits due to power dissipation. Negative capacitance field-effect transistors using ferroelectric gate insulators are promising to overcome these limits, which would allow further device scaling. However, the microscopic details of negative capacitance are not well understood so far, since mainly Landau based mean-field theories are used to model these phenomena. Here we use an educational and simplified approach to better understand the basic microscopic origin of ferroelectric negative capacitance. Our "toy" model shows that negative capacitance originates from the thermodynamic instability of the ferroelectric polarization and is bounded by the saturation of microscopic dipole polarizability. This shows that negative capacitance is strongly connected to the origin of ferroelectricity itself. Furthermore, our microscopic model results in the same qualitative behavior as mean-field Landau based approaches.