Chemical phase segregation during the crystallization of Ge-rich GeSbTe alloys

Agati, Marta; Vallet, Maxime; Joulie, Sébastien; Benoît, Daniel; Claverie, A.

doi:10.1039/c9tc02302j

Cited by 46 publications

(61 citation statements)

References 28 publications

(47 reference statements)

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“…For Ge 7 Sb 1 Te 2 , the overall structural similarity to a-Ge is rather high, as expected, at least up to the chosen NNN cutoff. Nevertheless, this phase is still very different from the strongly segregated phase observed in experiments under high annealing temperatures, where stoichiometric GST grains and nanoscale elemental Ge clusters were found 31 .…”

Section: Soap Similarity Analysiscontrasting

confidence: 68%

“…Although not specified, the initial T x of the as-deposited Ge-rich GST thin film is derived to be above 380°C, as compared to the compositions reported in refs. [28][29][30][31] , and the T x drops to 245-275°C after partial segregation of excess Ge 63 .…”

Section: Energetics Of Phase Separationmentioning

confidence: 99%

“…It is well known that the GST alloys along the GeTe-Sb 2 Te 3 pseudo-binary line tend to crystallize into a cubic rocksalt structure with a high amount of atomic vacancies [38][39][40] . Yet, for the Ge-rich GST devices used in practice [28][29][30][31] , the Ge concentration ranges from~35 tõ 45%, exceeding the maximum of a cubic structure by full occupation of the vacant sites, i.e., Ge 1 Sb 2 Te 4 → Ge 1 Sb 1 Te 2 (25%) or Ge 2 Sb 2 Te 5 → Ge 3 Sb 2 Te 5 (30%). In refs.…”

Section: Energetics Of Phase Separationmentioning

confidence: 99%

“…However, phase segregation is a critical issue in these alloys. If Ge atoms segregate and form small clusters, then the remaining switching component reverts to stoichiometric GST phases, e.g., Ge 2 Sb 2 Te 5 , Ge 1 Sb 2 Te 4 , or others 31 , and the amorphous-phase stability in subsequent switching processes would therefore be seriously weakened. A survey of the relevant PCMs in the ternary system, including an indication of their application frontiers, is given in Fig.…”

Section: Introductionmentioning

confidence: 99%

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Ab initio molecular dynamics and materials design for embedded phase-change memory

et al. 2021

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The Ge2Sb2Te5 alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature. However widely used, this composition is not suitable for embedded memories—for example, for automotive applications, which require very high working temperatures above 300 °C. Ge–Sb–Te alloys with higher Ge content, most prominently Ge2Sb1Te2 (‘212’), have been studied as suitable alternatives, but their atomic structures and structure–property relationships have remained widely unexplored. Here, we report comprehensive first-principles simulations that give insight into those emerging materials, located on the compositional tie-line between Ge2Sb1Te2 and elemental Ge, allowing for a direct comparison with the established Ge2Sb2Te5 material. Electronic-structure computations and smooth overlap of atomic positions (SOAP) similarity analyses explain the role of excess Ge content in the amorphous phases. Together with energetic analyses, a compositional threshold is identified for the viability of a homogeneous amorphous phase (‘zero bit’), which is required for memory applications. Based on the acquired knowledge at the atomic scale, we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability, as well as potentially good cycling capability.

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Section: Soap Similarity Analysiscontrasting

confidence: 68%

Section: Energetics Of Phase Separationmentioning

confidence: 99%

Section: Energetics Of Phase Separationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ab initio molecular dynamics and materials design for embedded phase-change memory

et al. 2021

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“…[12][13][14][15][16][17] Recently, the crystallization characteristics and resulting microstructural evolutions of such optimized N-doped Ge-rich GST alloys have been reported in detail. 18 However, the influence of N concentration on these characteristics has not been studied yet. To this end, we report the impact of N concentration on the microstructure, composition, and surface morphologies of N-doped Ge-rich GST alloys during thermal annealing by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).…”

Section: Introductionmentioning

confidence: 99%

Impact of Nitrogen on the Crystallization and Microstructure of Ge‐Rich GeSbTe Alloys

Luong

Wen

Rahier

et al. 2020

Physica Rapid Research Ltrs

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We report the influence of N concentration on the crystallization kinetics, microstructural evolution, and composition of Ge-rich GeSbTe (GST) alloys during thermal annealing by using X-ray diffraction and scanning and transmission electron microscopy. We show that the incorporation of N in Ge-rich GST tends to slow down the phase separation, crystallization, and growth processes during annealing. This can be attributed to the reduced diffusivity of Ge, which interacts and quickly bonds with N. Technological advantages of N doping are also discussed, considering the increased stability of the amorphous phase with respect to its parent crystalline phase, finer microstructure, flatness of the GST films after crystallization, and disappearance of the low-resistivity hexagonal phase at high temperature.

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Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe_1−xTe_x Thin Films

Tomelleri

Hippert

Farjot

et al. 2020

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The electrical, optical, and structural properties of GeSe1−xTex phase‐change materials thin films with 0.16 ≤ x ≤1 prepared by cosputtering of GeSe and GeTe targets are studied. The crystallization temperature of the films increases significantly when the Te content decreases. Se‐rich films show an extremely large electrical contrast between their amorphous and crystalline states. A high polarizability of the crystalline phase is observed in the entire x range and is related to the presence of metavalent bonds. This is explained by the persistence of a rhombohedral crystalline phase, isostructural to GeTe, in the GeSe1−xTex films down to x = 0.16. Hence, the substitution of only 16 at% of the Se atoms by Te atoms transforms the covalent GeSe into a phase‐change material with a huge and unprecedented contrast of resistivity (up to 11 orders of magnitude) and a very high thermal stability (up to 10 years at 272 °C) for an alloy exhibiting no phase separation upon crystallization. This outstanding combination of properties makes Se‐rich GeSe1−xTex thin films extremely promising for integration in memory devices requiring a very high data retention such as automotive and embedded applications.

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Chemical phase segregation during the crystallization of Ge-rich GeSbTe alloys

Abstract: Crystallization of Ge-rich GST leads to phase separation, a characteristic which explains their superior properties for electronic memory devices

Cited by 46 publications

References 28 publications

Ab initio molecular dynamics and materials design for embedded phase-change memory

Ab initio molecular dynamics and materials design for embedded phase-change memory

Impact of Nitrogen on the Crystallization and Microstructure of Ge‐Rich GeSbTe Alloys

Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe_1−xTe_x Thin Films

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Chemical phase segregation during the crystallization of Ge-rich GeSbTe alloys

Abstract: Crystallization of Ge-rich GST leads to phase separation, a characteristic which explains their superior properties for electronic memory devices

Cited by 46 publications

References 28 publications

Ab initio molecular dynamics and materials design for embedded phase-change memory

Ab initio molecular dynamics and materials design for embedded phase-change memory

Impact of Nitrogen on the Crystallization and Microstructure of Ge‐Rich GeSbTe Alloys

Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe1−xTex Thin Films

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Product

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About

Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe_1−xTe_x Thin Films