Publication Date:July 3, 2019https://doi.org/10.1021/acsaelm.9b00256

The critical impact of epitaxial stress on the stabilization of the ferroelectric orthorhombic phase of hafnia is proved. Epitaxial bilayers of Hf_0.5Zr_0.5O₂ (HZO) and La_0.67Sr_0.33MnO₃(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.

Engineering Ferroelectric Hf0.5Zr0.5O2 Thin Films by Epitaxial Stress