Steady-state negative capacitance in SrTiO3/BaTiO3 trilayers and superlattices

Abstract

Negative capacitance (NC) of ferroelectric materials offers a promising route to realize low-power microelectronics. By introducing an imperfect charge screening medium, the spontaneous polarization of a ferroelectric can be suppressed to achieve a stable NC state, yet experimental evidence of such NC at the material level remains elusive. In this work, we fabricate SrTiO3/BaTiO3 (STO/BTO) heterostructures, including STO/BTO/STO trilayers and [STO10/BTO10]5 superlattices, and we investigate their NC states systematically. Anomalous enhancements in the effective relative permittivity of the trilayer (30%) and superlattice (111%) are observed, far exceeding the theoretical upper bound, which can only be rationalized by the negative permittivity of the constituent BTO. This is supported by second harmonic generation characterizations demonstrating a drastic suppression in spontaneous polarization of heterostructures, resulting in intensity reductions of 69% in trilayer and 89% in superlattice. As a result, the transient voltage drop typically observed during polarization switching of ferroelectrics disappears in these heterostructures, confirming the stable NC state in their BTO constituent. Together, these findings provide conclusive evidence for a steady NC state in dielectric/ferroelectric heterostructures, offering guidance for the regulation of the NC state through structural stacking.