Engineering Ferroelectric Hf_0.5Zr_0.5O₂ Thin Films by Epitaxial Stress

Abstract

The critical impact of epitaxial stress on the stabilization of the ferroelectric orthorhombic phase of hafnia is proved. Epitaxial bilayers of Hf0.5Zr0.5O2 (HZO) andLa0.67Sr0.33MnO3 (LSMO) electrodes were grown on a set of single crystalline oxide (001)oriented (cubic or pseudocubic setting) substrates with lattice parameter in the 3.71 -4.21 Å range. The lattice strain of the LSMO electrode, determined by the lattice mismatch with the substrate, is critical in the stabilization of the orthorhombic phase of HZO. On LSMO electrodes tensile strained most of the HZO film is orthorhombic, whereas the monoclinic phase is favored when LSMO is relaxed or compressively strained. Therefore, the HZO films on TbScO3 and GdScO3 substrates present substantially enhanced ferroelectric polarization in comparison to films on other substrates, including the commonly used SrTiO3. The capability of having epitaxial doped HfO2 films with controlled phase and polarization is of major interest for a better understanding of the ferroelectric properties and paves the way for fabrication of ferroelectric devices based on nanometric HfO2 films.

High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

“…The coercive field could be conditioned by the amount of monoclinic phase, which increases with thickness. However, the recent demonstration 27 of control of the ratio between monoclinic and orthorhombic phases by epitaxial stress (via substrate selection) discards this possibility. In ref.…”

Unraveling Ferroelectric Polarization and Ionic Contributions to Electroresistance in Epitaxial Hf0.5Zr0.5O2 Tunnel Junctions

“…Sample Growth: Epitaxial HZO films with nominal thicknesses 4.6 nm were grown on LSMO (22 nm thick) buffered STO (001), (001)-oriented (pseudocubic indexation) GSO and TSO substrates as described elsewhere. [40] Pt electrodes (20 nm thick) were grown ex-situ, at room substrates has been reported elsewhere. [40] Structural Characterization: X-ray diffraction 2- recorded using Bruker Bruker-AXS D8…”

“…[40] Pt electrodes (20 nm thick) were grown ex-situ, at room substrates has been reported elsewhere. [40] Structural Characterization: X-ray diffraction 2- recorded using Bruker Bruker-AXS D8…”

“…[34] Since the structural mismatch between HZO and the LSMO buffer layer is different for the samples grown on STO and GSO substrates, the formation of monoclinic and orthorhombic phases is different. Indeed, it has been recently reported [40] that the orthorhombic phase is favored with…”

Blocking of Conducting Channels Widens Window for Ferroelectric Resistive Switching in Interface‐Engineered Hf0.5Zr0.5O2 Tunnel Devices

“…It should be expected V GB to be shifted to higher voltages and eventually suppressed (Figure 1b Here, we first report the ER of thin HZO (4.6 nm) films grown on SrTiO 3 and GdScO 3 substrates, which allows controlling the relative abundance of GB-I and GB-II grain boundaries in the films. [42] Then, dielectric AlO x and SrTiO 3 layers of different thickness (1-2 nm range) were grown on HZO and the voltage-dependent ER of the junctions was measured.…”