Quantifying non-centrosymmetric orthorhombic phase fraction in 10 nm ferroelectric Hf_(0.5)Zr_(0.5)O_2 films

摘要

In this Letter, we report the percentage of the ferroelectric phase in a 10-nm-thick Hf_(0.5)Zr_(0.5)O_2 (HZO) film deposited in a metal-insulator-metal stack by atomic layer deposition. The ferroelectric behavior was confirmed by polarization measurements and piezoresponse force microscopy. Ferroelectric behavior in this material has been attributed most likely to the formation of the polar non-centrosymmetric ortho-rhombic phase [Muller et al, Appl. Phys. Lett. 99, 102903 (2011)], which is difficult to distinguish from the tetragonal phase in x-ray diffraction due to peak overlap. Using a model for each of the crystal phases of hafnia-zirconia, the phase percentages were estimated using a Rietveld refinement method applied to grazing incidence x-ray diffraction data and a linear combination fit analysis procedure [McBriarty et al, Phys. Status Solidi 257, 1900285 (2020)] applied to grazing incidence extended x-ray absorption fine structure data. Using these methods, it was found that the tetragonal (P4_2/nmc) phase is the most prevalent at 48-60% followed by the polar non-centrosymmetric ortho-rhombic (Pca2_1) phase at 35%-40% with the remainder consisting of the monoclinic (P2_1/c) phase. Understanding the details of the effect of the phase structure on the electrical properties of these materials is extremely important for device engineering of HZO for logic and emerging nonvolatile memory applications.