Quantifying non-centrosymmetric orthorhombic phase fraction in 10 nm ferroelectric Hf0.5Zr0.5O2 films

In this Letter, we report the percentage of the ferroelectric phase in a 10-nm-thick Hf0.5Zr0.5O2 (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 orthorhombic phase [Müller 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 (P42/nmc) phase is the most prevalent at 48-60% followed by the polar non-centrosymmetric orthorhombic (Pca21) phase at 35%-40% with the remainder consisting of the monoclinic (P21/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. V.M. acknowledges TEL Technology Center, America, LLC, for funding support. V.M. thanks Dr. Martin McBriarty for detailed discussion regarding the EXAFS analysis procedure. The authors also acknowledge Dr. Bruce Ravel from NIST for the use of XAS end-station at 6-BM, NSLS-II. This work is based on research done at 6-BM, of the NSLS II, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by BNL under Contract No. DE-SC0012704.