Aging mechanisms in amorphous phase-change materials

Raty, Jean Yves; Zhang, Wei; Luckas, Jennifer; Chen, Chao; Mazzarello, Riccardo; Bichara, Christophe; Wuttig, Matthias

doi:10.1038/ncomms8467

Cited by 235 publications

(265 citation statements)

References 56 publications

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“…[44][45][46] Most crystalline chalcogenides contain some degrees of PD, and pairs of collinear short-long bonds indicative of PD occur in liquid and amorphous PCMs as well. [47,48] In general, the stronger the PD is, the larger the bandgap is expected to be. [48] In Figure 4, we plot the length distributions of near-collinear bonds (bond angles are chosen between 160° and 180° and the distance cutoff is 4.6 Å).…”

Section: Aimd Results and Discussionmentioning

confidence: 99%

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Wang

et al. 2015

Adv Elect Materials

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Phase‐change memory devices distinguish “1” and “0” states by the electrical contrast between the amorphous and the crystalline phases. Under ambient conditions, the amorphous phase normally exhibits a higher resistivity, exceeding its crystalline counterpart by 2–5 orders of magnitude. Here, however, it is demonstrated that such pronounced resistivity contrast is remarkably reduced and even reversed with increasing hydrostatic‐like pressure in the prototypical phase‐change material GeSb2Te4 (GST). This anomalous resistivity reversal originates from the differences in the pressure‐induced atomic rearrangement of these two phases, as revealed by ab initio molecular dynamics simulations. Specifically, a low to medium pressure (<7 GPa) primarily compresses the bonds in crystalline GST without significantly displacing the atoms and vacancies off the lattice sites. As a result, only relatively small changes in the band structure are induced. In contrast, in amorphous GST, the fraction of voids changes drastically with pressure and the Peierls‐like distortion is greatly reduced, yet the average bond length remains almost constant. These effects eventually turn the semiconducting glass into a metallic one. Our work reveals distinct behaviors of amorphous and crystalline phase‐change materials under stress, shedding light on the mechanisms of electronic transport in different phases, and thus may have important implications on the design of phase‐change memory devices.

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Section: Aimd Results and Discussionmentioning

confidence: 99%

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Wang

et al. 2015

Adv Elect Materials

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“…Evolution of the average number of constraints during aging in amorphous GeTe. 5,12 The reference energy is taken as the lowest energy among models. A variety of amorphous GeTe models were analyzed, showing the direct correlation between fraction of homopolar Ge-Ge bonds (top panel), fraction of tetrahedral Ge, and energy (not shown here).…”

Section: To Publish In Mrs Bulletinmentioning

confidence: 99%

Phase-change materials and rigidity

2017

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“…[ 28,29 ] The as-sputtered a -GST is found to have more tetrahedral Ge than the melt-quenched one. [29][30][31] The high-pressure a -GST at ≈15 GPa is also dominated by the octahedral arrangement, yet the voids are largely squeezed out by pressure. [ 32,33 ] c-GST : Metastable cubic GST bears a rocksalt-like structure.…”

Section: Structure Of Gst Polymorphsmentioning

confidence: 99%

Disorder Control in Crystalline GeSb₂Te₄ Using High Pressure

Zhang

Mazzarello

et al. 2015

Advanced Science

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disordered as possible. However, usually such chemical disorder is discouraged by the concomitant enthalpy rise, caused by the formation of homopolar bonds. Disorder can induce localization of electronic wavefunctions (e.g., Anderson localization [ 1 ] and thus can be crucial for the electronic properties of materials. [2][3][4][5][6][7] The current applications of phasechange materials (PCMs) take advantage of the fast transformations and large property contrast between the amorphous and the crystalline states. [8][9][10][11] Such binary memory devices, however, may fail to meet the increasingly demanding requirements of data storage. A possible solution to this issue is to record data on each memory cell with multiple states of electrical resistivity, in addition to "on" and "off" switches. This may be achieved by tuning disorder in PCMs. Therefore, it is important to understand and control disorder in these materials. The development of a multistate memory device would signifi cantly increase the data density and could change the way electronic devices work. [ 12,13 ] To manipulate the disorder in data storage media, Siegrist et al. have modifi ed the atomic arrangement in crystalline PCMs such as Ge-Sb-Te (GST), a prototype of PCMs, by annealing. [ 2 ] At low annealing temperatures, these GST samples form metastable cubic rocksalt phases ( c -GST) with different levels of electrical resistivity. In this phase, one sublattice contains Te atoms, whereas Ge, Sb, and vacancies occupy the sites of the second sublattice in a random fashion. High annealing temperatures induce the ordering of the vacancies in c -GST, which gradually evolves into a metallic hexagonal phase ( h -GST) with all vacancies diffusing into layers. Ab initio simulations [ 3 ] show that such multiple resistive states are indeed due to the different degrees of vacancy ordering. In particular, strong disorder results in the localization of electron wave functions at the Fermi energy.In this article, we report that the compositional disorder in PCMs can also be tuned by pressure in lieu of the thermal treatment. Large-scale ab initio molecular dynamics (AIMD) simulations reveal that pressure can expedite the antisite hopping in the vacancy-ridden c -GST by lowering the migration barrier. Accumulation of these antisites leads to severe atomic distortions. The resulting strong misalignment of bonds may trigger the loss of the long-range order in the crystal [ 14 ] and contributes to the amorphization of c -GST under high pressure, as observed in experiments at 15 GPa. [ 15,16 ] Our simulations identify a new disorder-triggered mechanism of the amorphization Electronic phase-change memory devices take advantage of the different resistivity of two states, amorphous and crystalline, and the swift transitions between them in active phase-change materials (PCMs). In addition to these two distinct phases, multiple resistive states can be obtained by tuning the atomic disorder in the crystalline phase with heat treatment, because the disorder can lead to...

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Aging mechanisms in amorphous phase-change materials

Cited by 235 publications

References 56 publications

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Phase-change materials and rigidity

Disorder Control in Crystalline GeSb₂Te₄ Using High Pressure

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Aging mechanisms in amorphous phase-change materials

Cited by 235 publications

References 56 publications

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb2Te4 Using High Pressure

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb2Te4 Using High Pressure

Phase-change materials and rigidity

Disorder Control in Crystalline GeSb2Te4 Using High Pressure

Contact Info

Product

Resources

About

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Reversing the Resistivity Contrast in the Phase‐Change Memory Material GeSb₂Te₄ Using High Pressure

Disorder Control in Crystalline GeSb₂Te₄ Using High Pressure