Intrinsic ferroelectricity in Y-doped HfO2 thin films

Abstract Ferroelectric HfO2-based materials hold great potential for widespread integration of ferroelectricity into modern electronics due to their robust ferroelectric properties at the nanoscale and compatibility with the existing Si technology. Earlier work indicated that the nanometer crystal grain size was crucial for stabilization of the ferroelectric phase of hafnia. This constraint caused high density of unavoidable structural defects of the HfO2-based ferroelectrics, obscuring the intrinsic ferroelectricity inherited from the crystal space group of bulk HfO2. Here, we demonstrate the intrinsic ferroelectricity in Y-doped HfO2 films of high crystallinity. Contrary to the common expectation, we show that in the 5% Y-doped HfO2 epitaxial thin films, high crystallinity enhances the spontaneous polarization up to a record-high 50 µC/cm2 value at room temperature. The high spontaneous polarization persists at reduced temperature, with polarization values consistent with our theoretical predictions, indicating the dominant contribution from the intrinsic ferroelectricity. The crystal structure of these films reveals the Pca21 orthorhombic phase with a small rhombohedral distortion, underlining the role of the anisotropic stress and strain. These results open a pathway to controlling the intrinsic ferroelectricity in the HfO2-based materials and optimizing their performance in applications.

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Formation of the orthorhombic phase in CeO2-HfO2 solid solution epitaxial thin films and their ferroelectric properties

Applied Physics Letters ◽

10.1063/1.5097980 ◽

2019 ◽

Vol 114 (23) ◽

pp. 232902 ◽

Cited By ~ 2

Author(s):

T. Shiraishi ◽

S. Choi ◽

T. Kiguchi ◽

T. Shimizu ◽

H. Funakubo ◽

...

Keyword(s):

Thin Films ◽

Solid Solution ◽

Ferroelectric Properties ◽

Orthorhombic Phase ◽

Epitaxial Thin Films

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The role of intermediate S-polymorph towards high piezoelectricity in La-doped BiFeO3 epitaxial thin films

Acta Materialia ◽

10.1016/j.actamat.2021.116683 ◽

2021 ◽

Vol 207 ◽

pp. 116683

Author(s):

Jun Young Lee ◽

Gopinathan Anoop ◽

Sanjith Unithrattil ◽

WooJun Seol ◽

Youngki Yeo ◽

...

Keyword(s):

Thin Films ◽

Epitaxial Thin Films ◽

La Doped

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Effect of Cr substitution on ferrimagnetic and ferroelectric properties of GaFeO3 epitaxial thin films

Applied Physics Letters ◽

10.1063/1.5029442 ◽

2018 ◽

Vol 113 (16) ◽

pp. 162901 ◽

Cited By ~ 3

Author(s):

Tsukasa Katayama ◽

Takuya Osakabe ◽

Shintaro Yasui ◽

Yosuke Hamasaki ◽

Badari Narayana Rao ◽

...

Keyword(s):

Thin Films ◽

Ferroelectric Properties ◽

Epitaxial Thin Films ◽

Cr Substitution

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High-sensitivity of initial SrO growth on the residual resistivity in epitaxial thin films of SrRuO$$_3$$ on SrTiO$$_3$$ (001)

Scientific Reports ◽

10.1038/s41598-021-95554-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Uddipta Kar ◽

Akhilesh Kr. Singh ◽

Song Yang ◽

Chun-Yen Lin ◽

Bipul Das ◽

...

Keyword(s):

Volume Fraction ◽

High Sensitivity ◽

Orthorhombic Phase ◽

Residual Resistivity ◽

Epitaxial Thin Films ◽

Residual Resistivity Ratio ◽

Resistivity Ratio ◽

Growth Technique ◽

X Ray ◽

High Crystallinity

AbstractThe growth of SrRuO$$_3$$ 3 (SRO) thin film with high-crystallinity and low residual resistivity (RR) is essential to explore its intrinsic properties. Here, utilizing the adsorption-controlled growth technique, the growth condition of initial SrO layer on TiO$$_2$$ 2 -terminated SrTiO$$_3$$ 3 (STO) (001) substrate was found to be crucial for achieving a low RR in the resulting SRO film grown afterward. The optimized initial SrO layer shows a c(2 $$\times $$ × 2) superstructure that was characterized by electron diffraction, and a series of SRO films with different thicknesses (ts) were then grown. The resulting SRO films exhibit excellent crystallinity with orthorhombic-phase down to $$t \approx $$ t ≈ 4.3 nm, which was confirmed by high resolution X-ray measurements. From X-ray azimuthal scan across SRO orthorhombic (02 ± 1) reflections, we uncover four structural domains with a dominant domain of orthorhombic SRO [001] along cubic STO [010] direction. The dominant domain population depends on t, STO miscut angle ($$\alpha $$ α ), and miscut direction ($$\beta $$ β ), giving a volume fraction of about 92 $$\%$$ % for $$t \approx $$ t ≈ 26.6 nm and $$(\alpha , \beta ) \approx $$ ( α , β ) ≈ (0.14$$^{\mathrm{o}}$$ o , 5$$^{\mathrm{o}}$$ o ). On the other hand, metallic and ferromagnetic properties were well preserved down to t$$\approx $$ ≈ 1.2 nm. Residual resistivity ratio (RRR = $$\rho ({\mathrm{300 K}})$$ ρ ( 300 K ) /$$\rho ({\mathrm{5K}})$$ ρ ( 5 K ) ) reduces from 77.1 for t$$\approx $$ ≈ 28.5 nm to 2.5 for t$$\approx $$ ≈ 1.2 nm, while $$\rho ({\mathrm{5K}})$$ ρ ( 5 K ) increases from 2.5 $$\upmu \Omega $$ μ Ω cm for t$$\approx $$ ≈ 28.5 nm to 131.0 $$\upmu \Omega $$ μ Ω cm for t$$\approx $$ ≈ 1.2 nm. The ferromagnetic onset temperature ($$T'_{\mathrm{c}}$$ T c ′ ) of around 151 K remains nearly unchanged down to t$$\approx $$ ≈ 9.0 nm and decreases to 90 K for t$$\approx $$ ≈ 1.2 nm. Our finding thus provides a practical guideline to achieve high crystallinity and low RR in ultra-thin SRO films by simply adjusting the growth of initial SrO layer.

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The role of nanoporosity on the local piezo and ferroelectric properties of lead titanate thin films

Journal of Materials Chemistry C ◽

10.1039/c4tc02378a ◽

2015 ◽

Vol 3 (5) ◽

pp. 1035-1043 ◽

Cited By ~ 15

Author(s):

Alichandra Castro ◽

Paula Ferreira ◽

Brian J. Rodriguez ◽

Paula M. Vilarinho

Keyword(s):

Thin Films ◽

Coercive Field ◽

Lead Titanate ◽

Ferroelectric Properties ◽

Ferroelectric Thin Films ◽

Piezoelectric Response ◽

Nanoporous Films ◽

Switching Behaviour ◽

Dense Films

Nanoporous PbTiO3 films present enhanced tetragonality at lower temperatures than respective dense films. Moreover, the porosity present in the nanoporous films allows an increase of the local piezoelectric response and a decrease of the local coercive field. As a result, these nanoporous films might be used to improve the switching behaviour of ferroelectric thin films.

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The Role of Bi 2 O 3 Interfacial Layer in Improvement of Ferroelectric Properties of SrBi 2 Ta 2 O 9 Thin Films Deposited by Liquid-Delivery MOCVD

Integrated Ferroelectrics ◽

10.1080/713718233 ◽

2002 ◽

Vol 46 (1) ◽

pp. 205-214 ◽

Cited By ~ 1

Author(s):

Nak-Jin Seong ◽

Woong-Chul Shin ◽

Eun-Suck Choi ◽

Sung-Nam Ryoo ◽

Soon-Gil Yoon

Keyword(s):

Thin Films ◽

Interfacial Layer ◽

Ferroelectric Properties ◽

Liquid Delivery

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Role of Oxygen Vacancies on the Ferroelectric Properties of Pzt Thin Films

MRS Proceedings ◽

10.1557/proc-243-393 ◽

1991 ◽

Vol 243 ◽

Cited By ~ 17

Author(s):

Chi Kong Kwok ◽

Seshu B. Desu

Keyword(s):

Thin Films ◽

Oxygen Partial Pressure ◽

Partial Pressure ◽

Vacancy Concentration ◽

Ferroelectric Properties ◽

Sol Gel ◽

Low Oxygen ◽

Partial Pressures ◽

Pzt Films

AbstractThe properties of ferroelectric thin films can be significantly influenced by the presence of point defects. The concentration of vacancies presented in these thin films is known to be one of the key parameters causing the degradation of these films when these films are subjected to polarization reversals.To study the effects of the vacancy concentration on the ferroelectric properties, sol gel PZT films and powders were annealed in different oxygen partial pressures. For the PZT films, the reduction of oxides to pure metals was not observed even with films annealed at 2×10−5 atmosphere of oxygen partial pressure. Samples annealed at low oxygen partial pressure (for instance, 10−3 and 2×10−5 atmosphere), which has more Pb and O2 depletions and consequently has more Pb and O2 vacancies, cannot be switched easily. The ratios of coercive field after and before fatigue increase as the defect concentrations of the annealed samples increase.

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The role of excess Pb and PbO overpressure on the microstructural development in polycrystalline PZT thin films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170645 ◽

1994 ◽

Vol 52 ◽

pp. 582-583

Author(s):

M. J. Lefevre ◽

D. B. Dimos ◽

J. S. Speck

Keyword(s):

Thin Films ◽

Data Storage ◽

Perovskite Phase ◽

Ferroelectric Properties ◽

Sol Gel ◽

Pyrochlore Phase ◽

Optical Data Storage ◽

Optical Data ◽

Microstructural Development

Ferroelectric thin films have recently received considerable attention because of their potential in a range of device applications including both volatile and non-volatile memories, optical data storage, and other electrooptic applications (e.g. waveguides, switches, and modulators). The Pb-based perovskites, such as Pb(Zr,Ti)O3, have many properties that make them attractive for such applications because of their high switchable remanant polarization. In addition, many applications require integration of the ferroelectric with semiconductors. In our work we are studying the crystallization sequence of PZT 40/60 (PbZr0.40Ti0.60O3) grown on platinized silicon substrates, with an overall structure given as PZT/Pt/Ti/SiO2Si. The Ti and Pt are sequentially evaporated onto the oxidized Si substrate. Alkoxide-derived films are spun onto these substrates to form a dry amorphous gel2. The crystallization of the sol-gel film proceeds upon heating to temperatures in the range of 400-700°C. Lead volatility is one of the critical issues in the crystallization of Pb-based perovskite thin films. We have carried out a systematic study on the role of a lead atmosphere in crystallization for PZT (40/60). When heat treated the film forms a transitory pyrochlore phase at intermediate temperatures before transforming to the perovskite phase. This non-ferroelectric pyrochlore phase may stabilize if lead stoichiometry is not maintained, leading to poor optical and ferroelectric properties in the thin films.

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