Strain fluctuations unlock ferroelectricity in wurtzites

TL;DR

This paper reveals that local strain fluctuations in wurtzite (Zn,Mg)O materials facilitate ferroelectric switching, offering a pathway to scalable ferroelectric devices through strain engineering.

Contribution

It uncovers the role of strain fluctuations in enabling ferroelectricity in (Zn,Mg)O and demonstrates polarization switching via experimental and computational methods.

Findings

Strain fluctuations reduce local barriers to ferroelectric switching by over 40%.

Experimental evidence of polarization switching in heterostructures with strain gradients.

Computational models support the role of strain in ferroelectricity.

Abstract

Ferroelectrics are of practical interest for non-volatile data storage due to their reorientable, crystallographically defined polarization. Yet efforts to integrate conventional ferroelectrics into ultrathin memories have been frustrated by film-thickness limitations, which impede polarization reversal under low applied voltage. Wurtzite materials, including magnesium-substituted zinc oxide (Zn,Mg)O, have been shown to exhibit scalable ferroelectricity as thin films. In this work, we explain the origins of ferroelectricity in (Zn,Mg)O, showing that large strain fluctuations emerge locally in (Zn,Mg)O and can reduce local barriers to ferroelectric switching by more than 40%. We provide concurrent experimental and computational evidence of these effects by demonstrating polarization switching in ZnO/(Zn,Mg)O/ZnO heterostructures featuring built-in interfacial strain gradients. These results open up an avenue to develop scalable ferroelectrics by controlling strain fluctuations atomistically.