Are ferroelectric multilayers capacitors in series?

Abstract

We show that ferroelectric multilayers are not simple capacitors in series (CIS) and treating these as CIS may lead to misinterpretation of experimental results and to erroneous conclusions. Here, we present a theoretical model of ferroelectric bilayers using basic thermodynamics taking into account the appropriate electrical boundary conditions and electrostatic fields. The spontaneous polarization mismatch in ferroelectric/ferroelectric (FE/FE), FE/paraelectric (FE/PE), and FE/dielectric (FE/DE) bilayers results in a non-linear electrostatic coupling which produces significant deviations in the overall dielectric response if it is computed using the simple capacitor-inseries (CIS) model. Our results show that the CIS approach is a good approximation only for DE/DE multilayers and for FE heterostructures if the individual layers are electrostatically screened from each other.

Ferroelectric Polarization Switching of Hafnium Zirconium Oxide in a Ferroelectric/Dielectric Stack

“…All these facts are extremely important to understand and interpret the experimental observation related to Fe-FETs and NC-FETs. The so-called interfacial coupling effect or capacitance enhancement was observed in the previous reports 19,[27][28][29][30] . This interfacial coupling effect can improve the equivalent oxide thickness of FE/DE gate stack, which is also observed in the HZO/Al2O3 FE/DE stack as shown in supplementary section 2.…”

Ferroelectric negative capacitance

“…The role of domains has been explicitly addressed for PbTiO 3 /SrTiO 3 and Pb 0.5 Sr 0.5 TiO 3 /SrTiO 3 superlattices 32 . Modelling these structures as capacitors in series is complicated owing to the strong electrostatic interactions between the dielec tric and ferroelectric layers 70 . However, by carefully designing the superlattices to ensure sufficient electro static decoupling between the ferroelectric layers, the series capacitor model can be applied, and the permit tivities of the ferroelectric and dielectric layers can be separated.…”

Polarization coupling transition inBaTiO3/PbZr0.2Ti0.8Salev1, Mahayni2, Grigoriev3 2016Phys. Rev. B13250View full textAdd to dashboardCite

“…3). Even in the thickest modeled bilayer the BTO layer retains a noticeable polarization up to the PZT transition temperature of 681 K that is just slightly lower than the Ferroelectric layers of the BTO/PZT bilayer system can be considered as capacitors in series because of weak coupling and large interface free charge density [35]. Using the calculated magnitudes of the internal electric field and polarization in the middle of ferroelectric layers, we could obtain, as a coarse estimate, the relative dielectric permittivities of 149, 129, and 103 for 500-nm, 100-nm, and 20-nm bilayers, respectively.…”