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Causes of ferroelectricity in HfO2-based thin films: An ab initio perspective

Abstract

We present a comprehensive first principles study of doped hafnia in order to understand the for- mation of the ferroelectric orthorhombic[001] grains. Assuming that tetragonal grains are present during the early stages of growth, matching plane analysis shows that tetragonal[100] grains can transform into orthorhombic[001] during thermal annealing, when they are laterally confined by other grains. We show that among 0%, 2% and %4 Si doping, 4% doping provides the best conditions for the tetragonal[100] → orthorhombic[001] transformation. This also holds for Al dop- ing. We also show that for HfxZr1−xO2, where we have studied x = 1.00, 0.75, 0.50, 0.25, 0.00, the value x = 0.50 provides the most favorable conditions for the desired transformation. In order for this transformation to be preferred over the tetragonal [100] → monoclinic [100] transformation, out-of-plane confinement also needs to be present, as supplied by a top electrode. Our findings illuminate the mechanism that causes ferroelectricity in hafnia-based films and provide an expla- nation for common experimental observations for the optimal ranges of doping in Si:HfO2, Al:HfO2 and HfxZr1−xO2. We also present model thin film heterostructure computations of Ir/HfO2/Ir stacks in order to isolate the interface effects, which we show to be significant.

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Publication details

The article was received on 03 Apr 2019, accepted on 15 May 2019 and first published on 15 May 2019


Article type: Paper
DOI: 10.1039/C9CP01880H
Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Causes of ferroelectricity in HfO2-based thin films: An ab initio perspective

    M. Dogan, N. Gong, T. P. Ma and S. Ismail-Beigi, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP01880H

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