On the structural origins of ferroelectricity in HfO2 thin films

Sang, Xiahan; Grimley, Everett D.; Schenk, Tony; Schroeder, Uwe; LeBeau, James M.

doi:10.1063/1.4919135

Cited by 532 publications

(381 citation statements)

References 28 publications

(39 reference statements)

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“…In a later theoretical work, Huan et al 18 proposed that two orthorhombic phases with polar space groups of Pca2 1 and Pmn2 1 were possible to be the ferroelectric phases of HfO 2 , because their calculations showed that both Pca2 1 and Pmn2 1 phases had low free energies and small energy barriers for polarization switching. More recently, Sang et al 19 provided supportive evidence for the existence of the Pca2 1 phase as the structural origin of ferroelectricity in Gd:HfO 2 thin films using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in combination with position averaged convergent beam electron diffraction (PACBED (Figs. 2(a) and 2(b)).…”

Section: Origins Of Ferroelectricity In Hfo 2 -Based Materialsmentioning

confidence: 99%

Ferroelectric HfO₂-based materials for next-generation ferroelectric memories

2016

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Ferroelectric random access memory (FeRAM) based on conventional ferroelectric perovskites, such as Pb(Zr,Ti)O 3 and SrBi 2 Ta 2 O 9 , has encountered bottlenecks on memory density and cost, because those conventional perovskites suffer from various issues mainly including poor complementary metal-oxide-semiconductor (CMOS)-compatibility and limited scalability. Nextgeneration cost-efficient, high-density FeRAM shall therefore rely on a material revolution. Since the discovery of ferroelectricity in Si:HfO 2 thin films in 2011, HfO 2 -based materials have aroused widespread interest in the field of FeRAM, because they are CMOScompatible and can exhibit robust ferroelectricity even when the film thickness is scaled down to below 10 nm. A review on this new class of ferroelectric materials is therefore of great interest. In this paper, the most appealing topics about ferroelectric HfO 2 -based materials including origins of ferroelectricity, advantageous material properties, and current and potential applications in FeRAM, are briefly reviewed.

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Section: Origins Of Ferroelectricity In Hfo 2 -Based Materialsmentioning

confidence: 99%

Ferroelectric HfO₂-based materials for next-generation ferroelectric memories

2016

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“…[3][4][5][6][7][8][9][10] Ferroelectric phenomenon in these doped-HfO 2 films deposited by various deposition techniques such as atomic layer deposition, [5][6][7][8][9][10] chemical solution deposition, 11 and sputtering 12 was mainly explained by the existence of noncentrosymmetric orthorhombic phase (space group of Pca2 1 ). 5,6,12 The dopant incorporation into monoclinic HfO 2 matrix results in a transformation to tetragonal/cubic phase with the appearance of an intermediate metastable orthorhombic (Pca2 1 ) phase.…”

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confidence: 99%

Ferroelectricity in Rare-Earth Modified Hafnia Thin Films Deposited by Sequential Pulsed Laser Deposition

Sharma

Barrionuevo

Agarwal

et al. 2015

ECS Solid State Letters

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Room temperature ferroelectricity in pulsed laser deposited rare-earth doped hafnium oxide (HfO 2 ) thin films is discussed. Maximum values of remnant polarizations (P r ) ∼13.5 and 12 μC/cm 2 along with coercive fields (E C ) ∼334 and 384 kV/cm are observed in 6 mol. % of rare-earth (Sm or Gd) doped-HfO 2 thin films (Sm:HfO 2 and Gd:HfO 2 ), respectively. Piezoresponse force microscopy measurements confirmed ferroelectric nature of films by showing phase hysteresis and butterfly amplitude loops. It is noticed that wake-up cycles improved the remnant polarization and found to be necessary for the forming of well saturated hysteresis loops. Our results showed potential toward realization of future highly scaled non-volatile ferroelectric memories. Ferroelectric materials are engendering considerable interest because of a variety of emerging applications including ferroelectric memories which have promising potentials for next generation high integration density and low power nonvolatile memory technology. 1,2The most studied material for ferroelectric memories, Pb[Zr x Ti 1-x ]O 3 (PZT), 1 is facing severe scaling limitations due to its complicated crystal structure which in turn hinders its applicability toward dense integration in the complementary metal oxide semiconductor (CMOS) technology. The lead (Pb) toxicity in PZT is also a snag due to ecological concerns.Recently, experimental as well as theoretical studies showed ferroelectricity in doped hafnia (HfO 2 ) thin films which are compatible with existing CMOS technology.3-10 Ferroelectric phenomenon in these doped-HfO 2 films deposited by various deposition techniques such as atomic layer deposition, 5-10 chemical solution deposition, 11 and sputtering 12 was mainly explained by the existence of noncentrosymmetric orthorhombic phase (space group of Pca2 1 ). 5,6,12 The dopant incorporation into monoclinic HfO 2 matrix results in a transformation to tetragonal/cubic phase with the appearance of an intermediate metastable orthorhombic (Pca2 1 ) phase. On the other hand, in some of the reports, ferroelectric nature in doped-HfO 2 films was attributed to the influence of "wake-up" effect. [11][12][13] In this paper, we report on the ferroelectric properties of rare earth doped Sm:HfO 2 (SHO) and Gd:HfO 2 (GHO) thin films fabricated by the sequential pulsed laser deposition (SPLD) technique. [14][15][16] The deposition was performed by periodic depositions from HfO 2 and Sm 2 O 3 /Gd 2 O 3 ceramic targets. The dopant concentration was obtained by controlling number of Sm 2 O 3 /Gd 2 O 3 ablation pulses relative to that of HfO 2 . To study the ferroelectric properties of the deposited samples, polarization-voltage (P-V), capacitance-voltage (C-V), and piezoresponse force microscopy (PFM) measurements were performed. ExperimentalPolycrystalline thin films of SHO and GHO of ∼60 nm thickness were fabricated on Pt/TiO 2 /SiO 2 /Si substrates by SPLD technique at a fixed temperature of 650• C and in an oxygen ambient partial pressure of ∼0.5 Pa. The KrF excimer laser...

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“…This discovery is of great interest to the semiconductor industry and has led to intensive experimental [3][4][5][6][7][8][9][10][11][12][13][14] and theoretical [9,[15][16][17][18][19][20][21][22] research, because these materials are believed to avoid the problems typical for the traditional ferroelectric materials (such as lead zirconate titanate) during integration into microelectronic devices. However, precise identification of the phase(s) in these films is problematic due to experimental limitations such as the broadness of the thin-film diffraction spectra, unknown film texture and strain fields, and possible presence of multiple phases within a single film.…”

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confidence: 99%

“…It is easy to see that this formulation of the "non-clashing" criterion actually implies that an entire "row" of atoms with given β, γ components (β, γ = α) has to have the sameα component of the displacement; thus, rather than enumerating the displacements of individual oxygen ions, only the displacements ofx,ŷ, andẑ rows of oxygen ions need be enumerated. 5 This reduces the number of the "non-clashing" "initial" configurations to the manageable ∼ 5.3 × 10 5 , starting from a cubic fluorite cell. We implemented our enumeration procedure as an atkpython script within Virtual NanoLab (VNL) [36].…”

mentioning

confidence: 99%

“…The "initial" atomic configurations are generated from a single cubic (12-atom) fluorite cell by independently displacing each of thex,ŷ andẑ rows of oxygen ions by − 0.5Å, 0Å, or + 0.5Å. Coulomb (Madelung) energies of the generated "initial" configurations are calculated within VNL, and structures 5 Our simple formulation of the "non-clashing" criterion may appear excessively stringent: For example, the decoration of the Pbcm lattice shown in Fig. 2d as leading to the monoclinic lattice has some displacement components not satisfying our simple formulation of the "non-clashing" criterion.…”

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confidence: 99%

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Prediction of new metastable $$\hbox {HfO}_{2}$$ HfO 2 phases: toward understanding ferro- and antiferroelectric films

Barabash

2017

J Comput Electron

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From first principles, we predict several yetunknown, low-energy, dynamically stable phases of HfO 2 . One of the predicted metastable phases has a finite ferroelectric polarization and could be potentially responsible for the ferroelectric and/or antiferroelectric behavior recently reported in thin (Hf,Zr)O 2 -based films. Other phases predicted here may potentially form as competing nonferroelectric phases in thin films, and the possibility of their formation should be taken into account during analysis of experimental thin-film characterization data. These predictions are made possible by an explicit enumeration approach, designed for the case at hand. Our approach outperforms existing theoretical structure prediction methods, including evolutionary algorithms, which have been previously applied to the same problem yet have not identified most of the possible metastable phases found in this study. This suggests that structure enumeration techniques may be indispensable for practical structure prediction problems that seek to identify all low-energy metastable phases rather the single stable (lowest energy) phase.Keywords Ferroelectricity · Antiferroelectricity · Hafnia · HfO 2 · Zirconia · Structure prediction · Density functional theory

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On the structural origins of ferroelectricity in HfO2 thin films

Cited by 532 publications

References 28 publications

Ferroelectric HfO₂-based materials for next-generation ferroelectric memories

Ferroelectric HfO₂-based materials for next-generation ferroelectric memories

Ferroelectricity in Rare-Earth Modified Hafnia Thin Films Deposited by Sequential Pulsed Laser Deposition

Prediction of new metastable $$\hbox {HfO}_{2}$$ HfO 2 phases: toward understanding ferro- and antiferroelectric films

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On the structural origins of ferroelectricity in HfO2 thin films

Cited by 532 publications

References 28 publications

Ferroelectric HfO2-based materials for next-generation ferroelectric memories

Ferroelectric HfO2-based materials for next-generation ferroelectric memories

Ferroelectricity in Rare-Earth Modified Hafnia Thin Films Deposited by Sequential Pulsed Laser Deposition

Prediction of new metastable $$\hbox {HfO}_{2}$$ HfO 2 phases: toward understanding ferro- and antiferroelectric films

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Ferroelectric HfO₂-based materials for next-generation ferroelectric memories

Ferroelectric HfO₂-based materials for next-generation ferroelectric memories