Multilevel polarization switching in ferroelectric thin films

Abstract

Ferroic order is characterized by hystereses with two remanent states and therefore inherently binary. The increasing interest in materials showing non-discrete responses, however, calls for a paradigm shift towards continuously tunable remanent ferroic states. Device integration for oxide nanoelectronics furthermore requires this tunability at the nanoscale. Here we demonstrate that we can arbitrarily set the remanent ferroelectric polarization at nanometric dimensions. We accomplish this in ultrathin epitaxial PbZr0.52Ti0.48O3 films featuring a dense pattern of decoupled nanometric 180° domains with a broad coercive-field distribution. This multilevel switching is achieved by driving the system towards the instability at the morphotropic phase boundary. The phase competition near this boundary in combination with epitaxial strain increases the responsiveness to external stimuli and unlocks new degrees of freedom to nano-control the polarization. We highlight the technological benefits of non-binary switching by demonstrating a quasi-continuous tunability of the non-linear optical response and of tunnel electroresistance.

Domain Structure in Ferroelectric Thin Films

“…where K(κ) is the Elliptic integral of the first order. Interstingly enough, in connection with the inherent periodicity of the domain-wall solution obtained in (18) and which emerges in Fig. 1, the authors can postulate that the constraint of a finite size favours periodic structures.…”

“…In crystals, elastic interactions between atoms can be modified by pressure or mechanical stress which affect the cohesion of the crystal lattice thus inducing a piezoelectric effect. For about two decades, the physics of ferroelectric materials has attracted a steady attention from both the experimental [1,14,18,15,16] and theoretical points of view [19,17]. The earliest theory of ferroelectricity is the so-called Mean-Field approach based on the Ginzburg-Landau functional in which an order parameter P was introduced to describe the polarization [1,15,16,20,21].…”

Ferroelectric Thin Films for Oxide Electronics

“…In addition, controlling the B-site occupancy in the Pb[Zr 1−x Ti x ]O 3 family can trigger a structural competition at the so-called morphotropic phase boundary (MPB), where the flattened energy landscape can give rise to domain configurations with unconventional switching pathways and high susceptibility to the electric field. 84 Surprisingly little efforts have been devoted to studying the combined effect in strain-engineered MPB thin films, and only a few reports deal with MPB ferroelectric epitaxial thin films. 84,94 Using ISHG, the investigation of the polarization of PbZr 0.52 Ti 0.48 O 3 films at the morphotropic composition during the growth on various substrates revealed the capacity to design films with unprecedented ferroelectric switching behavior.…”

Wireless Multiferroic Memristor with Coupled Giant Impedance and Artificial Synapse Application

“…[8] Such multilevel polarization switching was also observed in the ultrathin epitaxial PbZr 0.52 Ti 0.48 O 3 (PZT) films by driving the system toward the instability at the morphotropic phase boundary. [30] And Ferroelectric domain switching of Ag/PZT/Nb:SrTiO 3 ferroelectric tunnel junction (FTJ) [31] and Ni/PZT/Nb-doped SrTiO 3 heterojunction [32] were also explored for the high-precision and liner weight updates of neuro-inspired computing application. However, coupling electrically modulated GMI of magnetostrictive material with impedance of piezoelectric layer for the memristor application has not been reported yet.…”

“…The other one is to utilize the multilevel polarization switching of ultrathin piezoelectric film. [30,31] Additionally other multiferroic memristors based on FTJ [32] and resistive switching [39] have been also investigated recently.…”