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Critical effect of the bottom electrode on the ferroelectricity of epitaxial Hf_0.5Zr_0.5O_2 thin films

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2021-03-14
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Royal Society of Chemistry
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Epitaxial orthorhombic Hf_(0.5)Zr_(0.5)O_2 (HZO) films on La_(0.67)Sr_(0.33)MnO_3 (LSMO) electrodes show robust ferroelectricity with high polarization, endurance and retention. However, no similar results have been achieved using other perovskite electrodes so far. Here, LSMO and other perovskite electrodes are compared. A small amount of orthorhombic phase and low polarization are found in HZO films grown on La-doped BaSnO_3 and Nb-doped SrTiO_3, while null amounts of orthorhombic phase and polarization are detected in films on LaNiO3 and SrRuO_3. The critical effect of the electrode on the stabilized phases is not a consequence of the differences in the electrode lattice parameter. The interface is critical, and engineering the HZO bottom interface on just a few monolayers of LSMO permits the stabilization of the orthorhombic phase. Furthermore, while the specific divalent ion (Sr or Ca) in the manganite is not relevant, reducing the La content causes a severe reduction of the amount of orthorhombic phase and the ferroelectric polarization in the HZO film.
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©2021 Royal Society of Chemistry The financial support from the Spanish Ministry of Science and Innovation through the Severo Ochoa FUNFUTURE (CEX2019-000917-S), MAT2017-85232-R (AEI/FEDER, EU), and PID2019-107727RB-I00 (AEI/FEDER, EU) projects and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. IF and JG acknowledge Ramon y Cajal contracts RYC-2017-22531 and RYC-2012-11709, respectively. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation and by CSIC through the i-LINK program (LINKA20338). SE acknowledges the Spanish Ministry of Economy, Competitiveness and Universities for his PhD contract (SEV-2015-0496-16-3) and its cofunding by the ESF. SE's work has been done as a part of his PhD program in Materials Science at Universitat Autnoma de Barcelona. The electron microscopy observations carried out at the Centro Nacional de Microscopia Electronica at UCM (MV) were supported by MICINN grant# RTI2018-097895-B-C43. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).
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