On the negative capacitance in ferroelectric heterostructures

Abstract: Negative capacitance can be used to overcome the lower limit of subthreshold swing (SS) in field effect transistors (FETs), enabling ultralow-power microelectronics, though the concept of ferroelectric negative capacitance remains contentious. In this work, we analyze the negative capacitance in ferroelectric/dielectric heterostructure rigorously using Landau-Denvonshire theory, identifying three (one) critical dielectric thicknesses for first (second) order ferroelectric phase transition upon which the stability of negative capacitance changes. A critical electric window is also identified, beyond which the ferroelectric negative capacitance cannot be maintained. Between the first and second critical thicknesses, meta-stable negative capacitance exists near zero polarization, yet it will be lost and cannot be recovered when the electric window is broken. Between the second and third critical thicknesses, stable negative capacitance always exists near zero polarization within the electric window regardless of initial polar state, resulting in hysteretic double P-E loop. Beyond the third (first) critical thickness of first (second) order phase transition, P-E loop becomes hysteresis free, though the spontaneous polarization can still be induced at sufficient large electric field. Singularities in the effective dielectric constant is also observed at the critical thickness or electric field. The analysis demonstrates that the negative capacitance of ferroelectric can be stabilized by linear dielectric within a critical electric window, and the negative capacitance can be either hysteresis free or hysteretic for first order ferroelectrics, while it is always hysteresis free for the second order ferroelectrics.