Surface morphology effects on polarization switching in nanoscale ferroelectrics

Abstract

The effects of surface morphology on polarization switching in thin ferroelectric films areinvestigated using a real-space, time-dependent Ginzburg–Landau model that incorporateselectrostatic interactions. We consider a two-dimensional uni-axial ferroelectric film with athickness that varies sinusoidally. Polarization switching, starting from a singledomain remnant state, is simulated for several surface modulation amplitudes andwavelengths. We demonstrate that surface heterogeneities produce inhomogeneitiesin the electric field within the film. These inhomogeneities become preferentialsites for easy nucleation of reverse domains. This has a profound effect on theexternal field necessary to switch the polarization. Increasing the surface undulationamplitude significantly reduces the coercive field compared to the ideal flat film,even for very small amplitude modulations in the thickness. Although surfaceroughness decreases the field required to form reverse domains, it also hinderssubsequent domain wall migration. In fact, for very high amplitude and smallwavelength surface morphologies, complete switching to a single domain state becomesimpossible. This is because the domain walls become trapped near the peaks inthe modulated surface. The technological implications of the present results forutilization of surface roughness and for surface morphology design are discussed.