Ion migration in crystalline and amorphous HfO<i>X</i>

Schie, Marcel; Müller, Michael; Salinga, Martin; Waser, Rainer; Souza, Roger A. De

doi:10.1063/1.4977453

Cited by 50 publications

(38 citation statements)

References 53 publications

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“…The field at which this occurs can be calculated, given the height of the migration barrier in the field-free case ( E m ). The calculations give E cr m,cub = 2.7 GVm −1 for the cubic structure (with E m = 0.43 eV [67]) and E cr m,mon = 4.1 GVm −1 for the monoclinic structure (with E m = 0.66 eV [67]). The higher migration barrier for oxygen-ion migration in the monoclinic structure allows higher fields to be applied before the structure disintegrates.…”

Section: B Dynamics Of Anti-frenkel Pair Formationmentioning

confidence: 95%

“…We use the set of empirical potentials derived by Lewis and Catlow (see Table I). We have shown previously that these potentials are able to model oxygen-ion transport in cubic and [67,68]. Initial cell vectors and ion positions were taken from Jaffe et al [69] and were relaxed with the GULP [70] code to the minimum cell energy.…”

Section: Computational Methodologymentioning

confidence: 99%

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Field-enhanced route to generating anti-Frenkel pairs in HfO2

Schie

Menzel

Robertson

et al. 2018

Phys. Rev. Materials

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The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic and cubic HfO 2 under an applied electric field is examined. A thermodynamic model is used to derive an expression for the critical field strength required to generate an anti-Frenkel pair. The critical field strength of E cr aF ∼ 10 1 GVm −1 obtained for HfO 2 exceeds substantially the field strengths routinely employed in the forming and switching operations of resistive switching HfO 2 devices, suggesting that field-enhanced defect generation is negligible. Atomistic simulations with molecular static (MS) and molecular dynamic (MD) approaches support this finding. The MS calculations indicated a high formation energy of E aF ≈ 8 eV for the infinitely separated anti-Frenkel pair, and only a decrease to E aF ≈ 6 eV for the adjacent anti-Frenkel pair. The MD simulations showed no defect generation in either phase for E < 3 GVm −1 , and only sporadic defect generation in the monoclinic phase (at E = 3 GVm −1) with fast (t rec < 4 ps) recombination. At even higher E but below E cr aF both monoclinic and cubic structures became unstable as a result of field-induced deformation of the ionic potential wells. Further MD investigations starting with preexisting anti-Frenkel pairs revealed recombination of all pairs within t rec < 1 ps, even for the case of neutral vacancies and charged interstitials, for which formally there is no electrostatic attraction between the defects. In conclusion, we find no physically reasonable route to generating point-defects in HfO 2 by an applied field.

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Section: B Dynamics Of Anti-frenkel Pair Formationmentioning

confidence: 95%

Section: Computational Methodologymentioning

confidence: 99%

Field-enhanced route to generating anti-Frenkel pairs in HfO2

Schie

Menzel

Robertson

et al. 2018

Phys. Rev. Materials

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“…Of all the high dielectric constant materials considered as possible replacements for SiO 2 as a gate dielectric, the transition metal oxide HfO 2 is the material of choice for resistive random-access memory (RAM) applications [ 1 , 2 , 3 ]. HfO 2 can be grown as metastable amorphous phases on a silicon wafer; however, it is not a good glass former, and annealing it leads to crystallization [ 4 ].…”

Section: Introductionmentioning

confidence: 99%

“…While HfO 2 offers good chemical stability, defects in the HfO 2 crystalline bulk can be detrimental to the behavior of the devices, as they can lead to flat-band voltage instabilities [ 3 ]. A number of computer simulations have been performed in the literature to characterize and understand the atomic and electronic structure of amorphous HfO 2 and the associated oxygen diffusion [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. The majority of these simulations form amorphous or glassy phases by quenching from the melt, but there is a lack of experimental data available to benchmark the various approaches.…”

Section: Introductionmentioning

confidence: 99%

The Structure of Liquid and Amorphous Hafnia

et al. 2017

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Understanding the atomic structure of amorphous solids is important in predicting and tuning their macroscopic behavior. Here, we use a combination of high-energy X-ray diffraction, neutron diffraction, and molecular dynamics simulations to benchmark the atomic interactions in the high temperature stable liquid and low-density amorphous solid states of hafnia. The diffraction results reveal an average Hf–O coordination number of ~7 exists in both the liquid and amorphous nanoparticle forms studied. The measured pair distribution functions are compared to those generated from several simulation models in the literature. We have also performed ab initio and classical molecular dynamics simulations that show density has a strong effect on the polyhedral connectivity. The liquid shows a broad distribution of Hf–Hf interactions, while the formation of low-density amorphous nanoclusters can reproduce the sharp split peak in the Hf–Hf partial pair distribution function observed in experiment. The agglomeration of amorphous nanoparticles condensed from the gas phase is associated with the formation of both edge-sharing and corner-sharing HfO6,7 polyhedra resembling that observed in the monoclinic phase.

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“…As such, more stable and reliable resistive switching performance can be expected for multivalue in-memory computing applications. 24,37 Based on this idea, we fabricated a Pt/ZnO/Pt structured device on a commercially available SiO 2 /Si substrate by magnetron sputtering as described above in the Experimental Methods section. The X-ray diffractive pattern and TEM images indicate that the ZnO nanolm is (002)-textured and grew into straight columnar microcrystals ( Fig.…”

Section: Resultsmentioning

confidence: 99%