Kinetics Features Conducive to Cache-Type Nonvolatile Phase-Change Memory

Chen, Bin; Chen, Yimin; Ding, Keyuan; Li, Kunlong; Jiao, Fangying; Wang, Lei; Zeng, Xierong; Wang, Junqiang; Shen, Xiang; Zhang, Wei; Rao, Feng; Ma, Evan

doi:10.1021/acs.chemmater.9b02598

Cited by 38 publications

(26 citation statements)

References 44 publications

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“…These two traits together prompt a dramatic decrease in the energy barrier for nucleation, reducing the stochasticity and thus shortening the wait time for incubation 11 . We have also elucidated that Sc addition can create an enlarged kinetic contrast inside the supercooled liquid state over a fairly narrow temperature range 23 . This guarantees high atomic mobility at elevated temperatures for rapid crystal growth and suppressed atomic diffusion near room temperature for good data retention.…”

Section: Introductionmentioning

confidence: 83%

“…The viscosity model used in this work is illustrated in the Supplementary information. Since the Sc x Sb 2 Te 3 flakes were only one-side capped, it is appropriate to compare the FDSC results with those of uncapped Ge 2 Sb 2 Te 5 films 13,23 .…”

Section: Flash Differential Scanning Calorimetry (Fdsc) Measurementsmentioning

confidence: 99%

“…This also suggests that a slight doping will not significantly change the melting temperature (T m ) of rocksalt Sc x Sb 2 Te 3 . However, it can still essentially alter the crystallization (including both nucleation and growth) behavior 23 . The DFMD simulation here qualitatively illustrates that numerous subcritical Sc-Te nucleation embryos can survive the melt-quenching process, along with the quenched-in nuclei of larger size, acting as intrinsic (robust) seeds 11,30 to speed up the nucleationdominant crystallization (inset of Fig.…”

Section: Reset Energy and Set Speed Of Pcram Devicesmentioning

confidence: 99%

“…The shift of T p allows for the investigation of the crystallization kinetics at elevated temperatures. Note that the lowest 2 to 3 T p values at each Φ were regarded as the most credible data because they correspond to the best thermal contact between the stripped-off Sc x Sb 2 Te 3 films and chip sensors 14,23 . The crystallization data of Sc x Sb 2 Te 3 obtained via FDSC measurements are portrayed in a Kissinger plot (Fig.…”

Section: Enlarged Kinetic Contrast Through a Fragile-to-strong Crossovermentioning

confidence: 99%

“…If a single-fragility model is employed to describe the viscosity behavior of Sc x Sb 2 Te 3 , then it can only be applicable to the high-temperature regime above~400-500 K, generating rather large fragilities of over~170. Instead, the generalized MYEGA model can nicely fit not only the curved (non-Arrhenius behavior) but also the linear (Arrhenius behavior) parts in the Kissinger plot 14,23 . The high-to-low change in the fragility strongly indicates that an enlarged contrast in the kinetics occurs below and above these inflection temperatures at~400-500 K, manifesting as an apparent fragile-to-strong (FTS) crossover in the deeply supercooled Sc x Sb 2 Te 3 liquid (Fig.…”

Section: Enlarged Kinetic Contrast Through a Fragile-to-strong Crossovermentioning

confidence: 99%

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Recipe for ultrafast and persistent phase-change memory materials

Ding

Chen

et al. 2020

NPG Asia Mater

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The contradictory nature of increasing the crystallization speed while extending the amorphous stability for phase-change materials (PCMs) has long been the bottleneck in pursuing ultrafast yet persistent phase-change random-access memory. Scandium antimony telluride alloy (ScxSb2Te3) represents a feasible route to resolve this issue, as it allows a subnanosecond SET speed but years of reliable retention of the RESET state. To achieve the best device performances, the optimal composition and its underlying working mechanism need to be unraveled. Here, by tuning the doping dose of Sc, we demonstrate that Sc0.3Sb2Te3 has the fastest crystallization speed and fairly improved data nonvolatility. The simultaneous improvement in such ‘conflicting’ features stems from reconciling two dynamics factors. First, promoting heterogeneous nucleation at elevated temperatures requires a higher Sc dose to stabilize more precursors, which also helps suppress atomic diffusion near ambient temperatures to ensure a rather stable amorphous phase. Second, however, enlarging the kinetic contrast through a fragile-to-strong crossover in the supercooled liquid regime should require a moderate Sc content; otherwise, the atomic mobility for crystal growth at elevated temperatures will be considerably suppressed. Our work thus reveals the recipe by tailoring the crystallization kinetics to design superior PCMs for the development of high-performance phase-change working memory technology.

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Section: Introductionmentioning

confidence: 83%

Section: Flash Differential Scanning Calorimetry (Fdsc) Measurementsmentioning

confidence: 99%

Section: Reset Energy and Set Speed Of Pcram Devicesmentioning

confidence: 99%

Section: Enlarged Kinetic Contrast Through a Fragile-to-strong Crossovermentioning

confidence: 99%

Section: Enlarged Kinetic Contrast Through a Fragile-to-strong Crossovermentioning

confidence: 99%

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Recipe for ultrafast and persistent phase-change memory materials

Ding

Chen

et al. 2020

NPG Asia Mater

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Insights into the Heterogeneous Nuclei of an Ultrafast‐Crystallizing Glassy Solid

Chen,

Li,

Wang

et al. 2024

Adv Funct Materials

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Crystallization determines the programming speed of phase‐change memory devices; while, the nucleation phenomenon of many phase‐change materials (PCMs) is not entirely understood, especially concerning the atomic structures and dynamic behaviors of the subcritical nuclei. This is undoubtedly an insurmountable challenge for scandium antimony telluride (ScxSb2Te3) PCM as its subnanosecond‐crystallization nature impedes the real‐time observation of the transient nucleation process. To solve the puzzle, atomic probe tomography and transmission electron microscopy are employed to circumvent the technical difficulties; for the first time, the atomistic information of the heterogeneous nuclei in ScxSb2Te3 is unveiled, such as enriched Sc ≈ 25 at% in core composition, ≈1.0 nm in geometric size, and ≈1023–1024 m−3 in spatial density. The unique nanoscale chemical inhomogeneity ensures the unusual stabilities and dynamics of the early‐stage nuclei, reinforcing them to survive the melt‐quenching action and greatly suppressing the nucleating randomness, thereby facilitating simultaneous and prompt crystal growth throughout the amorphous phase to achieve ultrafast crystallization. The present study offers a new insight into the nonclassical pathways, which will improve understanding and promote better regulation of the nucleation phenomenon in functional materials.

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Unraveling Crystallization Mechanisms and Electronic Structure of Phase‐Change Materials by Large‐Scale Ab Initio Simulations

Zhou

Wang

et al. 2022

Advanced Materials

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cutting-edge 3D cross-point memory technology. [20,21] Crystallization of GST at elevated temperatures (500-700 K) occurs via rapid formation and growth of crystallites. In PCRAM cells, the amorphous PCM region is typically surrounded by a crystalline PCM matrix, for example, in the form of a "mushroom head"; therefore, crystal growth at the amorphous-crystalline boundaries is another important ingredient for memory programming.Since full crystallization occurs on the nanosecond time scale for nanometer-sized amorphous marks, the simulation of this process is within reach of ab initio molecular dynamics (AIMD) methods based on density functional theory (DFT). Indeed, quite a few first-principles studies have focused on the crystallization kinetics of Ge 2 Sb 2 Te 5 . [22][23][24][25][26][27][28][29][30][31][32] The system sizes ranged from several tens of atoms up to 900 atoms. In some of these simulations, crystallization was facilitated by constructing 2D crystalline templates, [23] by manually inserting a crystalline seed inside the amorphous network, [26] or by using the metadynamics [33] method. [29,30] These works have shed light on the microscopic mechanisms responsible for the fast crystallization, which proved to be crucial for designing a novel PCM, Sc 0.2 Sb 2 Te 3 , with subnanosecond writing speed. [34][35][36][37][38][39] Furthermore, AIMD simulations indicated that the growth velocity of Ge 2 Sb 2 Te 5 is of the order of a meter per second at ≈600 K, [29,30] in fair agreement with experimental data. [40] The electronic structure of the recrystallized phase is of high interest, since it determines the properties of the SET state of memory cells. The stable crystalline phase of GST is trigonal and consists of layers of Ge, Sb, and Te atoms. [41][42][43] However, upon fast crystallization of amorphous GST, a metastable cubic rocksalt-like phase is obtained: Te atoms occupy one sublattice, whereas Ge, Sb, and vacancies appear to be arranged in a random fashion on the second sublattice. [44][45][46][47][48] AIMD crystallization simulations have corroborated this picture. [24][25][26][27][28][29][30] The large amount of disorder in the rocksalt-like phase has a substantial impact on the electronic states-and thus on transport properties. At room temperature, GST shows relatively high p-type conductivity, due to self-doping. However, low-temperature transport measurements revealed that GST and related chalcogenide crystals are in fact Anderson insulators and that an insulator-metal transition can be induced by thermal annealing. [49][50][51][52] Our previous DFT simulations of GST crystals indicated that vacancy clusters induce localization of the electronic states near the edge of the valence band, and that the ordering of vacancies into layers reduces the total energy of the system and drives both a rocksalt-to-trigonal structural transition and an insulatorto-metal phase transition. [53][54][55] In these computational works, models of disordered GST were created using a quasi-random number generator an...

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Kinetics Features Conducive to Cache-Type Nonvolatile Phase-Change Memory

Cited by 38 publications

References 44 publications

Recipe for ultrafast and persistent phase-change memory materials

Recipe for ultrafast and persistent phase-change memory materials

Insights into the Heterogeneous Nuclei of an Ultrafast‐Crystallizing Glassy Solid

Unraveling Crystallization Mechanisms and Electronic Structure of Phase‐Change Materials by Large‐Scale Ab Initio Simulations

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