Critical Effect of Bottom Electrode on Ferroelectricity of Epitaxial Hf0.5Zr0.5O2 Thin Films

TL;DR

This study demonstrates that the choice and engineering of the bottom electrode, especially La0.67Sr0.33MnO3, critically influence the stabilization of ferroelectric orthorhombic Hf0.5Zr0.5O2 films, with interface quality being a key factor.

Contribution

It reveals the critical role of the electrode interface in stabilizing ferroelectric phases in HZO films, highlighting interface engineering as a new approach.

Findings

LSMO electrodes enable robust ferroelectricity in HZO films.

Other perovskite electrodes show reduced or no ferroelectric phase.

Interface engineering on a monolayer level stabilizes the orthorhombic phase.

Abstract

Epitaxial orthorhombic Hf0.5Zr0.5O2 (HZO) films on La0.67Sr0.33MnO3 (LSMO) electrodes show robust ferroelectricity, with high polarization, endurance and retention. However, no similar results have been achieved using other perovskite electrodes so far. Here, LSMO and other perovskite electrodes are compared. A small amount of orthorhombic phase and low polarization is found in HZO films grown on La-doped BaSnO3 and Nb-doped SrTiO3, while null amounts of orthorhombic phase and polarization are detected in films on LaNiO3 and SrRuO3. The critical effect of the electrode on the stabilized phases is not consequence of differences in the electrode lattice parameter. The interface is critical, and engineering the HZO bottom interface on just a few monolayers of LSMO permits the stabilization of the orthorhombic phase. Furthermore, while the specific divalent ion (Sr or Ca) in the manganite is not relevant, reducing the La content causes a severe reduction of the amount of orthorhombic phase and the ferroelectric polarization in the HZO film.