The role of lattice dynamics in ferroelectric switching

Abstract

Reducing the switching energy of ferroelectric thin films remains an important goal in the pursuit of ultralow power ferroelectric memories and magnetoelectric spin-orbit logic devices. Here, we elucidate the fundamental role of lattice dynamics in ferroelectric switching by combining thermodynamic calculations, experiments, and phase-field simulations on both freestanding BiFeO3 membranes and films clamped to a substrate. We observe a distinct evolution of the ferroelectric domain pattern, from striped, 71° ferroelastic domains (spacing of ~100 nm) in clamped BiFeO3 films, to large (10’s of micrometers) 180° domains or even single domain structures, in freestanding films. Through the use of piezoresponse force microscopy, X-ray diffraction, polarization-electric field hysteresis loops, and high-speed pulsed ferroelectric switching experiments, it is found that removing the constraints imposed by the requirement of macroscopic continuity of deformation (also known as the von Mises criterion in the deformation of solids)[1]–[3] to the substrate, we can realize a ~40% reduction of the switching voltage and a consequent ~60% gain in the switching speed. The work highlights the critical role of mechanics and the clamping effect from the substrate in setting the energetics and dynamics of switching in ferroelectrics.