Critical effect of the bottom electrode on the ferroelectricity of epitaxial Hf0.5Zr0.5O2 thin films

Abstract

Epitaxial orthorhombic Hf_0.5Zr_0.5O₂ (HZO) films on La_0.67Sr_0.33MnO₃ (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 are 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 a consequence of the 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.