Surface morphology effects on polarization switching in nanoscale ferroelectrics

Abstract

The effects of surface morphology on polarization switching in thin ferroelectric films are investigated using a real-space, time-dependent Ginzburg-Landau model that incorporates electrostatic interactions. We consider a two-dimensional uni-axial ferroelectric film with a thickness that varies sinusoidally. Polarization switching, starting from a single domain remnant state, is simulated for several surface modulation amplitudes and wavelengths. We demonstrate that surface heterogeneities produce inhomogeneities in the electric field within the film. These inhomogeneities become preferential sites for easy nucleation of reverse domains. This has a profound effect on the external field necessary to switch the polarization. Increasing the surface undulation amplitude significantly reduces the coercive field compared to the ideal flat film, even for very small amplitude modulations in the thickness. Although surface roughness decreases the field required to form reverse domains, it also hinders subsequent domain wall migration. In fact, for very high amplitude and small wavelength surface morphologies, complete switching to a single domain state becomes impossible. This is because the domain walls become trapped near the peaks in the modulated surface. The technological implications of the present results for utilization of surface roughness and for surface morphology design are discussed.

Suppression of creep-regime dynamics in epitaxial ferroelectric BiFeO3 films

“…3c,d) which indicate that the height variation of the BFO/SRO film is considerably smaller than that for the BFO/LMSO film. Since domain wall pinning is more likely to occur for the film with larger surface roughness3839, these topography images suggest that the BFO/LSMO film has a higher density of stronger pinning sites.…”

Surface Morphology Induced Localized Electric Field and Piezoresponse Enhancement in Nanostructured Thin Films

“…When a potential difference is applied across such films, the nonplanar surface morphology results in an inhomogeneous distribution of the electric field within the material. Recently, it has been shown that such electric field inhomogeneity can significantly reduce the applied electric field required to initiate polarization switching process in ferroelectric thin films . In this work, we investigate the influence of such inhomogeneous electric fields on the piezoresponse of such films using experimental measurements, finite element modeling, and phase field simulations.…”

“…The phase field method has emerged as a powerful technique to simulate ferroelectric domains and polarization switching . Recently, this method was used to simulate the polarization switching behavior in thin films with a nonplanar morphology . We use this framework here to understand the enhancement of piezoresponse due to the nonplanar surface.…”

Ferroelectric switching in ferroelastic materials with rough surfaces

“…This barrier is reduced to ~0.35 eV once the surface contains steps. The surface roughness effectively reduces the barriers for domain nucleation at free surfaces driven by external electric fields, as that shown in ferroelectrics 30 . We also calculate the barrier for kink propagation inside twin boundaries.…”