Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Shiraishi, Takashi; Mimura, Takanori; Kiguchi, Takanori; Shiraishi, Takahisa; Konno, Toyohiko J.; Katsuya, Yoshio; Sakata, Osami; Funakubo, Hiroshi

doi:10.1063/1.5055258

Cited by 87 publications

(84 citation statements)

References 37 publications

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“…This would make an alignment of the long a-axis preferentially in-plane the desired situation for HfO 2 in order to at least partially compensate the stress building up during cool down. A recent study by Shimizu et al [51] suggests a significant fraction of 010-oriented unit cells (nonpolar b-axis plane-normal) of their epitaxial film switched to a 001 configuration (polar c-axis planenormal) after the application of an electric field. Achieving a perfect alignment of a in-plane and b or c (c is of course more desired) out-of-plane by optimizing the stress conditions during cool down could help promoting P r toward the theoretical limits.…”

Section: Discussionmentioning

confidence: 99%

“…The prominent interphase boundaries found by Grimley et al also point toward that conclusion. A recent study by Shimizu et al suggests a significant fraction of 010‐oriented unit cells (nonpolar b ‐axis plane‐normal) of their epitaxial film switched to a 001 configuration (polar c ‐axis plane‐normal) after the application of an electric field.…”

Section: Discussionmentioning

confidence: 99%

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On the Origin of the Large Remanent Polarization in La:HfO₂

Schenk

Fancher

Park

et al. 2019

Adv Elect Materials

102

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extraordinary result. [2][3][4][5][6][7] A physical explanation for these results has remained elusive. The dopant size has been speculated to be a key parameter and larger dopants seem in general favorable compared to dopants with a smaller ionic radius than Hf. [2,8] This trend has been confirmed theoretically by Batra et al., [5] who additionally conclude that trivalent dopants in general are a good choice to favor the polar phase in HfO 2 . Large trivalent dopants, as the lanthanoid series are therefore especially suitable to promote ferroelectricity. In comparison to Gd, as another lanthanoid, La lowers the total energy difference to the monoclinic ground state the most. Also, they derived general trends that a larger ionic radius and a lower electronegativity of a dopant are favorable for the FE phase. Batra et al. [5] did not firmly conclude that La is the most favorable dopant to promote ferroelectricty in hafnia because a clear identification of the relaxed structures was not always possible and assumptions required concerning the distribution of oxygen vacancies and dopants in the high-throughput computational approach. They rather focused on the aforementioned general chemical trends of dopant attributes that promote the FE Pca2 1 phase. Further clarification of this trend could be provided by Materlik et al., [6] who compared La with Al and Y (also trivalent, but different in atomic radius) andThe outstanding remanent polarization of 40 µC cm -2 reported for a 10 nm thin La:HfO 2 film in 2013 has attracted much attention. However, up to now, no explanation for this large remanent polarization has been presented. Density functional theory and X-ray diffraction are used to shine light onto three major aspects that impact the macroscopically observed remanent polarization: phase fraction, spontaneous polarization, and crystallographic texture. Density functional theory calculations show that the spontaneous polarization (P s ) of La:HfO 2 is indeed a bit larger than for other HfO 2 -or ZrO 2 -based compounds; however, the P s is not large enough to explain the observed differences in remanent polarization. While neither phase fractions nor spontaneous polarization nor strain are significantly different from those in other HfO 2 films, a prominent 020/002 texture distinguishes La doped from other HfO 2 -based ferroelectric films. Angulardependent diffraction data provide a pathway to calculate the theoretically expected remanent polarization, which is in agreement with the experimental observations. Finally, an interplay of the in-plane strain and texture is proposed to impact the formation of the ferroelectric phase during annealing. Further aspects of the special role of La as a dopant are collected and discussed to motivate future research.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

On the Origin of the Large Remanent Polarization in La:HfO₂

Schenk

Fancher

Park

et al. 2019

Adv Elect Materials

102

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“…Additionally, it agrees with a stronger pronounced texture in the case of HSO. Furthermore, a [010] out-of-plane texture is supported by an initially pinched P-V loop, which opens during cycling due to ferroelastic switching [8,15]. The stronger textured HSO is further apparent in the very sharp switching peak in the I-V loop after wake-up.…”

Section: Discussionmentioning

confidence: 99%

“…Ferroelectric properties in HfO 2 , which have been reported to originate from the orthorhombic phase of the space group Pca2 1 [6], have already been demonstrated in polycrystalline films doped with various elements such as Y, Sr, Al, Si, or Zr [5] as well as in undoped films [7]. Furthermore, epitaxially grown films of ferroelectric HfO 2 have been recently reported [8,9].…”

Section: Introductionmentioning

confidence: 94%

Structural and Electrical Comparison of Si and Zr Doped Hafnium Oxide Thin Films and Integrated FeFETs Utilizing Transmission Kikuchi Diffraction

et al. 2020

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The microstructure of ferroelectric hafnium oxide plays a vital role for its application, e.g., non-volatile memories. In this study, transmission Kikuchi diffraction and scanning transmission electron microscopy STEM techniques are used to compare the crystallographic phase and orientation of Si and Zr doped HfO2 thin films as well as integrated in a 22 nm fully-depleted silicon-on-insulator (FDSOI) ferroelectric field effect transistor (FeFET). Both HfO2 films showed a predominately orthorhombic phase in accordance with electrical measurements and X-ray diffraction XRD data. Furthermore, a stronger texture is found for the microstructure of the Si doped HfO2 (HSO) thin film, which is attributed to stress conditions inside the film stack during crystallization. For the HSO thin film fabricated in a metal-oxide-semiconductor (MOS) like structure, a different microstructure, with no apparent texture as well as a different fraction of orthorhombic phase is observed. The 22 nm FDSOI FeFET showed an orthorhombic phase for the HSO layer, as well as an out-of-plane texture of the [111]-axis, which is preferable for the application as non-volatile memory.

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“…The direct experimental evidence of the ferroelectric Pca2 1 phase was provided by scanning transmission electron microscopy [26]. These findings stimulated significant efforts in studying relevant properties of ferroelectric HfO 2 films [27][28][29][30][31][32], showing their applicability as a functional gate oxide in nanoscale FeFET memory devices [33,34] and ferroelectric tunnel junctions [35][36][37].…”

Section: Introductionmentioning

confidence: 99%

Magnetoelectric Effect at the Ni/HfO2 Interface Induced by Ferroelectric Polarization

et al. 2019

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Driven by the technological importance of the recently discovered ferroelectric HfO 2 , we explore a magnetoelectric effect at the HfO 2-based ferroelectric-ferromagnetic interface. Using density-functionaltheory calculations of the Ni/HfO 2 /Ni (001) heterostructure as a model system, we predict a stable and sizable ferroelectric polarization in a few-nm-thick HfO 2 layer. For the Ni/HfO 2 interface with opposite polarization directions (pointing to or away from the interface), we find a sizable difference in the interfacial Ni-O bonding, resulting in dissimilar degrees of depletion of the electron density around the interface. The latter affects the relative population of the exchange-split majority and minority spin bands at the interface and thus the interfacial magnetic moments. The sizable change in the interface magnetization with ferroelectric polarization reversal of HfO 2 manifests a significant ferroelectrically induced magnetoelectric effect at the Ni/HfO 2 interface. Our results reveal promising prospects of ferroelectric-ferromagnetic composite multiferroics based on HfO 2-based ferroelectric materials.

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Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Cited by 87 publications

References 37 publications

On the Origin of the Large Remanent Polarization in La:HfO₂

On the Origin of the Large Remanent Polarization in La:HfO₂

Structural and Electrical Comparison of Si and Zr Doped Hafnium Oxide Thin Films and Integrated FeFETs Utilizing Transmission Kikuchi Diffraction

Magnetoelectric Effect at the Ni/HfO2 Interface Induced by Ferroelectric Polarization

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Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Cited by 87 publications

References 37 publications

On the Origin of the Large Remanent Polarization in La:HfO2

On the Origin of the Large Remanent Polarization in La:HfO2

Structural and Electrical Comparison of Si and Zr Doped Hafnium Oxide Thin Films and Integrated FeFETs Utilizing Transmission Kikuchi Diffraction

Magnetoelectric Effect at the Ni/HfO2 Interface Induced by Ferroelectric Polarization

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On the Origin of the Large Remanent Polarization in La:HfO₂

On the Origin of the Large Remanent Polarization in La:HfO₂