Polarization coupling transition inBaTiO3/PbZr0.2Ti0.8

Abstract

Electrostatic interactions between thin films of two different ferroelectric materials lead to a layer of free charges localized at the interface between ferroelectrics according to a computational analysis presented in this work. The free charges at the interface between BaTiO 3 and PbZr 0.2 Ti 0.8 O 3 reduce polarization coupling strength significantly. This helps the layers to retain most of their single-layer polarizations and enables a layer-by-layer polarization switching, which has been observed in recent experimental studies. The sheet carrier density at the interface decreases by at least 8 orders of magnitude when the film thickness is reduced from 30 nm to 10 nm. This drop in the carrier density is accompanied by a strong increase of polarization coupling between ferroelectric layers. This polarization coupling transition can explain the difference between strong coupling in thin ferroelectric superlattices and weak coupling in thicker multilayer films.

Anomalous Polarization Switching Characteristics in a Ferroelectric Heterostructure

“…Furthermore, as the thickness of the system decreases, the lag of the hysteresis loop is more serious. It is implied that the ferroelectric coupling is stronger in a thinner ferroelectric heterostructure, which is consistent with the experiment phenomenon observed by Salev et al The remanent polarization and coercive field augment with decreasing the thickness of the ferroelectric heterostructure, that is different from the case in Figure a. Similarly, in Figure c, the hysteresis loop of system also shows the serious lag appearance for a larger parameter β .…”

Stepwise internal potential jumps caused by multiple-domain polarization flips in metal/ferroelectric/metal/paraelectric/metal stack

“…In addition, in the case of multiple-domain system, there will be a difference between the cases w/ and w/o internal electrode. In the latter case, the charge flow at FE/PE interface, the local effect of domain switching and the coupling effects between FE and PE layer should be taken into consideration 11,[25][26][27] . It is very interesting to further study these issues.…”

“…However, physical understanding of NC effects is still under intensive debate [25][26][27][28][29][30][31][32][33][34][35][36] . Experimentally observed NC effects are different from each other, and also from the concepts initially proposed.…”

“…Alternative explanations for the capacitance enhancement and transient NC effects in FE/PE stacks have been also proposed [25][26][27][28][29][30][31] . For example, a feasibility of capacitance enhancement is explainable from a strong coupling between FE and PE layers [25][26][27] , while the transient NC is understandable from the viewpoints of overshoot in voltage supply or slower speed of charge compensation relative to polarization switching in FE-CAP [28][29][30][31] . In fact, it has been argued that NC region of FE material is intrinsically unstable or even impossible 32,33 .…”

On the validity and applicability of models of negative capacitance and implications for MOS applications

“…where λ (>0) is the interface polarization coupling parameter describing the strength of the coupling 27,28 . Polarization coupling in epitaxial perovskite superlattices may be attributed to electrostatic contributions, mechanical effects, strain, interface chemistry and interface structure 29,30 . This expression has a minimum at P F E = 0 = P DE , if the following conditions are met:…”