Size driven thermodynamic crossovers in phase stability in zirconia and hafnia

Sharma, Geetu; Ushakov, Sergey V.; Navrotsky, Alexandra

doi:10.1111/jace.15200

Cited by 29 publications

(29 citation statements)

References 30 publications

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“…[ 2 ] These transition temperatures can be substantially altered by doping, mechanical stress, or surface manipulation and the high‐temperature phases are practically achieved in HfO 2 thin films at room temperature (RT). [ 3–14 ] A non‐centrosymmetric polar orthorhombic phase (Pca2 1 , o‐phase) is believed to be the structural origin of ferroelectricity in HfO 2 ‐based thin films. [ 2,15 ] Pca2 1 is extremely close in free energy (< k B T /5, where k B is the Boltzmann constant) to the equilibrium nonpolar phases.…”

Section: Introductionmentioning

confidence: 99%

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Kashir

Hwang

2020

Adv Eng Mater

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Wake‐up effect is still an obstacle in the commercialization of hafnia‐based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf0.5Zr0.5O2 (HZO) films is investigated. A nearly wake‐up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken‐up Pr at the pristine state whereas that grown below 5 s ozone pulse time shows a pinched hysteresis loop, that underwent a large wake‐up effect. This behavior is attributed to the increase in oxygen vacancy and carbon concentration in the films deposited at insufficient O3 dosage, which is confirmed by X‐ray photoelectron spectroscopy (XPS). The X‐ray diffraction (XRD) scan shows that the increase in ozone pulse time yields the reduction of tetragonal phase; therefore, the dielectric constant reduces. The I–V measurements reveal the increase in current density as the ozone dosage decreases, which might be due to the generation of oxygen vacancies in the deposited film. Finally, the dynamics of wake‐up effect is investigated, and it appears to be explained well by the Johnson–Mehl–Avrami–Kolmogoroff model, which is based on structural phase transformation.

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Section: Introductionmentioning

confidence: 99%

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Kashir

Hwang

2020

Adv Eng Mater

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“…While the monoclinic (P2 1 /c, m-) phase is the bulk ground state, other low-volume metastable polymorphs such as the tetragonal (t-), cubic (c-) or orthorhombic (o-) phases are responsible for the various functionalities in these materials [19,20]. These are high temperature, high pressure phases in the bulk, which can be stabilized at ambient conditions via nanostructuring [21], doping [1,10,[22][23][24][25], oxygen-vacancy engineering [26,27], thermal stresses [28,29] and epitaxial strain [22,25,[30][31][32][33][34][35][36][37], all of which can be suitably factored into thin film geometries. In particular, ferroelectric behavior results from the metastable polar phases.…”

Section: Introductionmentioning

confidence: 99%

Guidelines for the stabilization of a polar rhombohedral phase in epitaxial Hf_0.5Zr_0.5O₂ thin films

et al. 2020

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The unconventional Si-compatible ferroelectricity in hafnia-based systems, which becomes robust only at nanoscopic sizes, has attracted a lot of interest. While a metastable polar orthorhombic (o-) phase ( Pca21) is widely regarded as the responsible phase for ferroelectricity, a higher energy polar rhombohedral (r-) phase is recently reported on epitaxial HfZrO4 (HZO) films grown on (001) SrTiO3 (R3m or R3), (0001) GaN (R3), and Si (111). Armed with results on these systems, here we report a systematic study leading towards identifying comprehensive global trends for stabilizing r-phase polymorphs in epitaxially grown HZO thin films (6 nm) on various substrates (perovskites, hexagonal and Si).

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“…The phase evolution in HZO is largely affected by its composition, film thickness, and other thin‐film processing parameters, and therefore, the region of multiphase formation is influenced by the fabrication conditions. [ 21–33 ] In contrast to other high‐

ϵ_{normalr}

dielectrics, where the

ϵ_{normalr}

value decreases with decreasing film thickness, these films show increasing

ϵ_{normalr}

values with decreasing film thicknesses in the ≈5−20 nm range by adjusting the MPB region, [ 18 ] which is highly promising for future dynamic random access memories. Therefore, this approach emerges as an alternative method for engineering an extremely thin equivalent oxide thickness (EOT).…”

Section: Introductionmentioning

confidence: 99%

Ferroelectric and Dielectric Properties of Hf_0.5Zr_0.5O₂ Thin Film Near Morphotropic Phase Boundary

Kashir

Hwang

2021

Physica Status Solidi (a)

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Since the discovery of ferroelectric (FE) properties in HfO 2 -based materials, [1] numerous advantages, such as simple structures, strong binding energy between oxygen and transition metal ions, large bandgap (%5.3-5.7 eV), and compatibility with current complementary metal-oxide semiconductor technologies, led to extensive research that focused on potential diverse applications, such as FE memory, ferroelectric field-effect transistors (Fe-FETs), pyroelectric sensors, and energy harvesters. Meanwhile, from the material survey of FEs, it is conventional that the structural phase transition induced by a compositional change plays a special role in obtaining excellent piezoelectric and dielectric properties. [2][3][4][5][6][7][8][9] The phase boundary known as morphotropic phase boundary (MPB) separates regions of different symmetries by varying their composition in FEs. [2][3][4][5][6][7][8][9] In fact, when different structural phases are almost degenerated near the MPB, rotations of polarization occur in response to external electric fields instead of a change in the magnitude of polarization. [5] Consequently, materials exhibit maximum piezoelectric and dielectric responses near the MPB, as several phases coexist, and there is nearly no energy barrier separating them. The MPB has garnered significant practical interest, because the variable that drives the transition (i.e., compositions) is inherent. Therefore, it provides an alternative approach to boost the dielectric constant ϵ r without degrading the bandgap. MPB ceramics are the basis of a wide range of piezoelectric and dielectric technologies, such as high-k materials, sensors, actuators, smart systems, ultrasound generation, and sensing and underwater acoustics. These applications motivated researchers to investigate the existence of MPB in the novel promising ceramic compounds, e.g., PbHfO 3 -PbTiO 3 -Pb(Mg 1/3 Nb 2/3 )O 3 , [10,11] lead-free BiFeO 3 -BaTiO 3 , [12,13] Pb(In 1/

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Size driven thermodynamic crossovers in phase stability in zirconia and hafnia

Cited by 29 publications

References 30 publications

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Guidelines for the stabilization of a polar rhombohedral phase in epitaxial Hf_0.5Zr_0.5O₂ thin films

Ferroelectric and Dielectric Properties of Hf_0.5Zr_0.5O₂ Thin Film Near Morphotropic Phase Boundary

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Size driven thermodynamic crossovers in phase stability in zirconia and hafnia

Cited by 29 publications

References 30 publications

Defect Engineering to Achieve Wake‐up Free HfO2‐Based Ferroelectrics

Defect Engineering to Achieve Wake‐up Free HfO2‐Based Ferroelectrics

Guidelines for the stabilization of a polar rhombohedral phase in epitaxial Hf0.5Zr0.5O2 thin films

Ferroelectric and Dielectric Properties of Hf0.5Zr0.5O2 Thin Film Near Morphotropic Phase Boundary

Contact Info

Product

Resources

About

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Defect Engineering to Achieve Wake‐up Free HfO₂‐Based Ferroelectrics

Guidelines for the stabilization of a polar rhombohedral phase in epitaxial Hf_0.5Zr_0.5O₂ thin films

Ferroelectric and Dielectric Properties of Hf_0.5Zr_0.5O₂ Thin Film Near Morphotropic Phase Boundary