Structural changes during the switching transition of chalcogenide selector devices

Guo, Yuzheng; Li, Huanglong; Zhang, W.; Robertson, John

doi:10.1063/1.5125215

Cited by 14 publications

(9 citation statements)

References 29 publications

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“…For the Ge chain, an additional Ge atom joins the chain by forming bond with a Ge in the chain. Guo et al 49 and Clima et al also observed the formation of new Ge-Ge bonds and over-coordinated Ge under high field and thermal excitation in GeSe, respectively 45 . The lengthened Ge chain and the more connected network by the formation of overcoordinated Ge could eventually lead to conductive local paths.…”

Section: Resultsmentioning

confidence: 93%

Ultrahigh drive current and large selectivity in GeS selector

et al. 2020

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Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm−2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field.

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Section: Resultsmentioning

confidence: 93%

Ultrahigh drive current and large selectivity in GeS selector

et al. 2020

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“…The scientific interest to better understand OTS memory devices is currently directed in understanding the nature of the localized defect structures that contribute to the formation of the MG states. With the Ge–S‐ and Ge–Se‐based OTS memory devices, there is evidence to suggest that the Ge–Ge bonds form chain‐like structures, 148 and these could provide a conductive path. The nature of the defect configurations that populate the high‐resistance amorphous phase and lead to the MG states needs to be reliably ascertained to permit one to better understand how devices can withstand the repeated cycling of 10 8 or greater in the OTS memory devices.…”

Section: Broader Aspectsmentioning

confidence: 99%

Glass transition, topology, and elastic models of Se‐based glasses

et al. 2023

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Features intrinsic to disorder and network aspects are ubiquitous in structural glasses. Among this important class of materials, chalcogenide glasses are special-they are built of short-range covalent forces, making them simpler than silicate glasses that possess mixed ionic and covalent forces. Selenium-based glasses also display complex elastic phase transitions that have been described from various models, including mean-field approaches to molecular simulations. These point to the presence of two sharply defined elastic phase transitions, a rigidity and stress transition that are non-mean-field in character, and separate the three distinct topological phases of flexible, isostatically rigid, and stressedrigid. This article reviews the physics of these glassy networks. The elastic phases and glass transition temperature are explained on a molecular level in terms of topological constraint theory (TCT), connectivity, and the open degrees of freedom. The broader aspects of TCT in relation to phase change materials, high-k dielectrics, and cements are also commented upon.

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“…5b-c. The trap states A, B, C and D in the a-GeSAs models are mainly found to be associated with structural motifs consisting of Ge-Ge bonds/chains 40,41,54,57 , while the trap state E of a-GeSAs 43 is different from the others, and is dominantly associated with As-As bonds/chains. As the major sources of these traps, Ge-Ge bonds/chains therefore play a crucial role in OTS behavior, and As/S atoms also contribute to these in-gap states from the PDOS.…”

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confidence: 94%

“…39 Nonetheless, owing to being surrounded by large numbers of Ge atoms (41.8% of the next-nearest neighbors, Fig. S19), Ge atoms could migrate and form Ge-Ge laments 40,41 triggered by high electric elds in the FF process 17,42,43 , leading to the delocalization of conduction state. Such paths dramatically increase the conductivity, resulting in a sharp increase in I off by more than 140 times in the following switching operations (Fig.…”

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confidence: 99%

The Role of Arsenic in the Operation of Electrical Threshold Switches

Gotoh

et al. 2023

Preprint

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Arsenic is one of the most frequently used elements for doping conventional silicon-based semiconductors and particularly in emerging phase-change-memory (PCM) chips, yet the detailed functional mechanism as well as its experimental demonstration is still lacking in the latter in spite of its wide application. Here, we fabricate chalcogenide-based ovonic threshold switching (OTS) selectors, which are essential units for suppressing sneak currents in 3D PCM arrays, with various As concentrations. We discovered that incorporation of 20 at. % As brings a more than 100 ℃ increase in crystallization temperature, remarkably improving the switching repeatability and prolonging the device lifetime. These benefits arise from strengthened As-S bonds and sluggish atomic migration after As incorporation, as demonstrated by molecular-dynamics simulations. As a result, the addition of As reduces the leakage current by more than an order of magnitude and significantly suppresses the operational voltage drift, ultimately enabling a backend-of-the-line (BEOL)-compatible OTS selector with > 12 MA/cm2 on-current, >104 on/off ratio, ~ 10 ns speed, and a lifetime approaching 1010 cycles after 450 ℃ annealing. These performance enhancements can be explained by an As-induced increase of the band gap and of trap states, as determined by experimental photothermal deflection spectroscopy. Mechanistically, this is due to abundant defect states associated with Ge-Ge chains introduced by As-Ge and As-S bonds. These findings allow the use of precise control of the As concentration in OTS materials for improved-performance high-density 3D PCM applications.

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Structural changes during the switching transition of chalcogenide selector devices

Cited by 14 publications

References 29 publications

Ultrahigh drive current and large selectivity in GeS selector

Ultrahigh drive current and large selectivity in GeS selector

Glass transition, topology, and elastic models of Se‐based glasses

The Role of Arsenic in the Operation of Electrical Threshold Switches

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