Ferroelectricity in epitaxially strained rhombohedral ZrO2 thin films

TL;DR

This study reports a novel ferroelectric rhombohedral phase of ZrO2 thin films grown on Nb:SrTiO3 substrates, exhibiting switchable polarization without the need for a wake-up cycle, promising for nanoscale ferroelectric devices.

Contribution

The paper demonstrates the synthesis of a new ferroelectric phase of ZrO2 in epitaxially strained thin films without requiring a wake-up cycle, unlike conventional phases.

Findings

Achieved a switchable ferroelectric polarization of about 20.2 μC/cm².

Epitaxial compressive strain stabilizes the rhombohedral ferroelectric phase.

Ferroelectric behavior observed without wake-up cycling, advantageous for device applications.

Abstract

Zirconia and hafnia based thin films have attracted tremendous attention in the last decade due to their unexpected ferroelectric behavior at the nanoscale, which facilitates the downscaling of ferroelectric devices. The present work reports a novel ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown on (111)- Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal that the (111)-oriented ZrO2 films are under epitaxial compressive strain and display a switchable ferroelectric polarization of about 20.2 {\mu}C/cm2 with a coercive field of 1.5 MV/cm. Moreover, the time dependent polarization reversal characteristics of Nb:STO/ZrO2/Au film capacitors exhibit bell-shape curves, a typical feature of ferroelectric films associated with domains reversal. The estimated activation field is comparable to the coercive field obtained from polarization-electric field hysteresis loops. Interestingly, the studied films show ferroelectric behavior per se, i.e., there is no need to apply the wake-up cycle that is essential to induce ferroelectricity in the conventional (orthorhombic) ferroelectric phase of ZrO2. Therefore, the present films have a technologically advantage over the previously studied ferroelectric ZrO2 films, and may be attractive for nanoscale ferroelectric devices.