Search for: All records

While negative capacitance (NC) has been demonstrated in ferroelectric-dielectric (FE-DE) heterostructures in the form of capacitance enhancement, all experimental evidence, to date, suggests the existence of domains therein. Here, we address the question: what are the conditions to achieve ideal, domain-free NC in FE-DE heterostructures? Our main claim is that for given thicknesses of the ferroelectric and the dielectric layers, there is a critical value of domain wall energy parameter— above which the system would be stabilized in an ideal and robust domain-free NC state and would be robust against domain formation. Our analyses suggest that to achieve ideal NC, efforts should lie in understanding the means to control the domain wall energy on all fronts, both theory and experiments via high throughput design, discovery, and engineering of ferroelectrics. 

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. 

Abstract Crystalline materials with broken inversion symmetry can exhibit a spontaneous electric polarization, which originates from a microscopic electric dipole moment. Long-range polar or anti-polar order of such permanent dipoles gives rise to ferroelectricity or antiferroelectricity, respectively. However, the recently discovered antiferroelectrics of fluorite structure (HfO₂and ZrO₂) are different: A non-polar phase transforms into a polar phase by spontaneous inversion symmetry breaking upon the application of an electric field. Here, we show that this structural transition in antiferroelectric ZrO₂gives rise to a negative capacitance, which is promising for overcoming the fundamental limits of energy efficiency in electronics. Our findings provide insight into the thermodynamically forbidden region of the antiferroelectric transition in ZrO₂and extend the concept of negative capacitance beyond ferroelectricity. This shows that negative capacitance is a more general phenomenon than previously thought and can be expected in a much broader range of materials exhibiting structural phase transitions.