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Surface and grain boundary energy as the key enabler to ferroelectricity in nanoscale hafnia-zirconia: comparison of model and experiment

Abstract

The unexpected ferroelectric properties in nanoscale hafnia-zirconia are considered to be promising for a wealth of applications including ferroelectric memory, field effect transistors, and energy-related applications. However, the reason why the unexpected ferroelectric Pca21 phase can be stabilized has not been clearly understood although numerous extensive theoretical and experimental results have been reported recently. The ferroelectric orthorhombic phase is not a stable phase at processing condition from the view point of bulk free energy. Although the possible stabilization of the ferroelectric phase due to the surface energy effect has been theoretically suggested, such theoretical model has not been systematically compared with the actual experimental results. In this study, the experimental observations on polymorphism in nanoscale HfO2-ZrO2 solid solution thin films, in a wide range of film composition and thickness, are comprehensively related to the theoretical predictions based on the thermodynamic surface energy model. The theoretical model can semi-quantitatively explain the experimental results on the phase-evolution, but there was non-negligible discrepancies between the two results. To understand these discrepancies, various factors such as film stress, role of a TiN capping layer, and the kinetics of crystallization are systematically studied. The work also reports on the evolution of electrical properties of the film, i.e. dielectric, ferroelectric, anti-ferroelectric, and morphotropic phase change, as a function of the film composition and the thickness. The in-depth analyses of the phase change are expected to provide an important guideline for subsequent studies.

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Publication details

The article was received on 25 Mar 2017, accepted on 12 Jun 2017 and first published on 14 Jun 2017


Article type: Paper
DOI: 10.1039/C7NR02121F
Citation: Nanoscale, 2017, Accepted Manuscript
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    Surface and grain boundary energy as the key enabler to ferroelectricity in nanoscale hafnia-zirconia: comparison of model and experiment

    M. H. Park, Y. H. Lee, H. J. Kim, T. Schenk, W. Lee, K. D. Kim, F. Fengler, T. Mikolajick, U. Schroeder and C. S. Hwang, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR02121F

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