Coupling of electrical and mechanical switching in nanoscale ferroelectrics

Abstract

While electric field induced ferroelectric switching has been extensively studied and broadly utilized, pure mechanical switching via flexoelectric effect has recently opened up an alternative method for domain writing due to their highly localized, electrically erasable and electric damage free characteristics. Thus far, few studies have been made on the coupling effect of electro-mechanical switching in ferroelectric materials, likely due to the experimental difficulty in the accurate definition of the tip-surface contact area and in the identification of mechanical contribution from electrical effect. Here, we employed self-consistent phase-field modeling to investigate the bi-polar switching behavior of (001) oriented Pb(Zr 0.2 Ti 0.8)O 3 thin film under concurrent electric and strain field created via a piezoresponse force microscope probe. By separating the effects from electric field, homogeneous strain and strain gradient, we revealed that the homogeneous strain suppresses the spontaneous polarization and accordingly increases the coercive field, and the strain gradient favors unipolar switching and inhibit it in the reverse direction, thus causing lateral offset of the hysteresis loop. The uncertainty of flexoelectric coefficients and the influence of flexocoupling coefficients on switching have also been discussed. Our study could necessitate further understanding of the electric, piezoelectric, and flexoelectric contribution to the switching behavior in nanoscale ferroelectric oxides.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…Combined with relatively large (10-100 pm/V) piezoelectric constants, this made PFM the leading technique for almost two decades and enabled the rapid development of this field. An important component of this progress was the emergence of effective phase-field models that allowed simulation of ferroelectric domain dynamics as a function of global (temperature, pressure) [171][172][173]394 and local (tip bias, tip pressure) 164,172,358,359,395 parameters and hence provide insight into local switching mechanisms. 306,396,397 Recent emergence of phase field models for combined ferroelectric-semiconductor and ferroelectric-surface electrochemical behaviors offers numerous future opportunities.…”

Surface charged species and electrochemistry of ferroelectric thin films

“…19,20 Moreover, surface chemistry is not only important for the stabilization of ferroelectric surfaces, 21 but in fact polarization switching kinetics are intrinsically coupled to surface electrochemical phenomena. [22][23][24][25][26][27] Finally, not only the surface but also the bulk chemical composition is susceptible to the polarization direction and switching. 28 Exploring the coupling between electrochemistry and ferroelectricity is made particularly challenging by not only the spatial but also chemical resolution required, lacking in any one single technique.…”

Quantification of flexoelectricity in PbTiO3/SrTiO3 superlattice polar vortices using machine learning and phase-field modeling

“…Theoretically, a systematic range of structural and dynamical behaviors of materials can be modulated by flexoelectricity, including phonon softening and associated structural instabilities 10 – 13 , polarization switching 14 – 16 , domain wall formation 17 , 18 , and as charge carrier transport 19 . Experimental observations based on scanning probe, scattering, and bulk measurement techniques have provided compelling evidence of these flexocoupling effects 6 , 11 – 13 , 19 .…”