The role of lattice dynamics in ferroelectric switching

Qiwu Shi,Ramamoorthy Ramesh,Xue Chang,Lane W Martin,Dmitri Nikonov,David Pesquera,Xiaoxing Cheng,Sujit Das,Long-Qing Chen,Hongrui Zhang,Xiaoxi Huang,Alexander Qualls,Ian Young,Eric Parsonnet,Natalya Fedorova,Abel Fernandez,Yen-Lin Huang,Ren-Ci Peng,Jorge Íñiguez

doi:10.1038/s41467-022-28622-z

Abstract

Reducing the switching energy of ferroelectric thin films remains an important goal in the pursuit of ultralow-power ferroelectric memory and logic devices. Here, we elucidate the fundamental role of lattice dynamics in ferroelectric switching by studying both freestanding bismuth ferrite (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 in freestanding films. By removing the constraints imposed by mechanical clamping from the substrate, we can realize a ~40% reduction of the switching voltage and a consequent ~60% improvement in the switching speed. Our findings highlight the importance of a dynamic clamping process occurring during switching, which impacts strain, ferroelectric, and ferrodistortive order parameters and plays a critical role in setting the energetics and dynamics of ferroelectric switching.

Highlights

Reducing the switching energy of ferroelectric thin films remains an important goal in the pursuit of ultralow-power ferroelectric memory and logic devices
We devise a tractable set of theoretical calculations and experiments that aims to answer a question that addresses how lattice dynamics influence polarization reversal, namely, what is the role of the substrate in influencing ferroelectric switching? We begin by considering the clamping effect, or resistance to structural deformation, which imposes an additional energy barrier that must be overcome to induce switching in films constrained to a substrate
While there have been a large number of studies of quasi-static switching behavior and equilibrium properties of thin films[19–23], there have been fewer studies of the limits and timescales of fast switching[24–28], and even fewer on the role of substrate-clamping effects in influencing ferroelectric switching below 1 μs[18]

Summary

Introduction

Reducing the switching energy of ferroelectric thin films remains an important goal in the pursuit of ultralow-power ferroelectric memory and logic devices. Freestanding ferroelectric membranes have recently emerged as an exciting platform to study the role of mechanical constraints in ferroelectric systems[29], and here, we attempt to quantitatively address the effect of mechanical clamping by using a combination of thermodynamic calculations, phase-field simulations, piezoresponse force microscopy, and quasi-static and dynamic switching measurements on epitaxial, substrate-attached, and freestanding versions of the same thin films (Fig. 1a).

Results

Conclusion