TY - JOUR
T1 - Reducing Coercive-Field Scaling in Ferroelectric Thin Films via Orientation Control
AU - Xu, Ruijuan
AU - Gao, Ran
AU - Reyes-Lillo, Sebastian E.
AU - Saremi, Sahar
AU - Dong, Yongqi
AU - Lu, Hongling
AU - Chen, Zuhuang
AU - Lu, Xiaoyan
AU - Qi, Yajun
AU - Hsu, Shang Lin
AU - Damodaran, Anoop R.
AU - Zhou, Hua
AU - Neaton, Jeffrey B.
AU - Martin, Lane W.
N1 - Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/5/22
Y1 - 2018/5/22
N2 - The desire for low-power/voltage operation of devices is driving renewed interest in understanding scaling effects in ferroelectric thin films. As the dimensions of ferroelectrics are reduced, the properties can vary dramatically, including the robust scaling relationship between coercive field (Ec) and thickness (d), also referred to as the Janovec-Kay-Dunn (JKD) law, wherein Ec ? d-2/3. Here, we report that whereas (001)-oriented heterostructures follow JKD scaling across the thicknesses range of 20-330 nm, (111)-oriented heterostructures of the canonical tetragonal ferroelectric PbZr0.2Ti0.8O3 exhibit a deviation from JKD scaling wherein a smaller scaling exponent for the evolution of Ec is observed in films of thickness ≤ 165 nm. X-ray diffraction reveals that whereas (001)-oriented heterostructures remain tetragonal for all thicknesses, (111)-oriented heterostructures exhibit a transition from tetragonal-to-monoclinic symmetry in films of thickness ≤ 165 nm as a result of the compressive strain. First-principles calculations suggest that this symmetry change contributes to the deviation from the expected scaling, as the monoclinic phase has a lower energy barrier for switching. This structural evolution also gives rise to changes in the c/a lattice parameter ratio, wherein this ratio increases and decreases in (001)- and (111)-oriented heterostructures, respectively, as the films are made thinner. In (111)-oriented heterostructures, this reduced tetragonality drives a reduction of the remanent polarization and, therefore, a reduction of the domain-wall energy and overall energy barrier to switching, which further exacerbates the deviation from the expected scaling. Overall, this work demonstrates a route toward reducing coercive fields in ferroelectric thin films and provides a possible mechanism to understand the deviation from JKD scaling.
AB - The desire for low-power/voltage operation of devices is driving renewed interest in understanding scaling effects in ferroelectric thin films. As the dimensions of ferroelectrics are reduced, the properties can vary dramatically, including the robust scaling relationship between coercive field (Ec) and thickness (d), also referred to as the Janovec-Kay-Dunn (JKD) law, wherein Ec ? d-2/3. Here, we report that whereas (001)-oriented heterostructures follow JKD scaling across the thicknesses range of 20-330 nm, (111)-oriented heterostructures of the canonical tetragonal ferroelectric PbZr0.2Ti0.8O3 exhibit a deviation from JKD scaling wherein a smaller scaling exponent for the evolution of Ec is observed in films of thickness ≤ 165 nm. X-ray diffraction reveals that whereas (001)-oriented heterostructures remain tetragonal for all thicknesses, (111)-oriented heterostructures exhibit a transition from tetragonal-to-monoclinic symmetry in films of thickness ≤ 165 nm as a result of the compressive strain. First-principles calculations suggest that this symmetry change contributes to the deviation from the expected scaling, as the monoclinic phase has a lower energy barrier for switching. This structural evolution also gives rise to changes in the c/a lattice parameter ratio, wherein this ratio increases and decreases in (001)- and (111)-oriented heterostructures, respectively, as the films are made thinner. In (111)-oriented heterostructures, this reduced tetragonality drives a reduction of the remanent polarization and, therefore, a reduction of the domain-wall energy and overall energy barrier to switching, which further exacerbates the deviation from the expected scaling. Overall, this work demonstrates a route toward reducing coercive fields in ferroelectric thin films and provides a possible mechanism to understand the deviation from JKD scaling.
KW - X-ray diffraction
KW - coercive-field scaling
KW - ferroelectric
KW - size effects
KW - thin film
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U2 - 10.1021/acsnano.8b01399
DO - 10.1021/acsnano.8b01399
M3 - Article
C2 - 29641177
AN - SCOPUS:85047615045
SN - 1936-0851
VL - 12
SP - 4736
EP - 4743
JO - ACS nano
JF - ACS nano
IS - 5
ER -