Scalability of Sulfur‐Based Ovonic Threshold Selectors for 3D Stackable Memory Applications

Jia, Shaofeng; Li, Huanglong; Liu, Qi; Zhang, Song; Zhu, Min

doi:10.1002/pssr.202100084

Cited by 9 publications

(7 citation statements)

References 36 publications

(42 reference statements)

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“…S2). The value of I on for GeS in this work differs from the DC results of a previous study 17 , due to the series resistance (1.1 kΩ) employed and the different device structures (TiN/Al top electrode and W bottom electrode in previous work), but is consistent with the I-V curves from subsequent work with the same structure 24 . Since I on is almost size-independent, the current density of GeSAs devices sharply increases to >20 MA/cm 2 as the device size scales down to 60 nm, higher than Ge-Se/Te-based OTSs (Fig.…”

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confidence: 75%

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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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confidence: 75%

“…To reveal the role of As in the performance of OTS selectors, we employed GeS as a prototype material, for which there are already clear device-performance parameters and energy-band data 17,24 . We added x = 0, 20, 25 and 43 at.…”

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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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“…8 c, the detail data of the materials investigated is listed. Three OTS materials, GeTe 6 , GeSe and GeS, exhibit electric field ranging from 75 to 175 V/μm 24 . In addition, the average threshold switching field of six PCM materials, Ge 15 Sb 85 , Ti–Sb–Te (TST), Ag–In–Sb–Te (AIST), Sc–Sb–Te (SST), Sb and Ge 2 Sb 2 Te 5 (GST), is distributed in 8.1–56 V/μm 33 , 44 – 48 .…”

Section: Resultsmentioning

confidence: 99%

“…The OTS device has a sandwich structure, in which the middle layer is chalcogenide glass, called OTS material. Although hundreds of OTS materials have been found since first discovery in 1964 19 , the OTS materials cannot function without Te, Se and S chalcogens 17 , represented by GeTe 6 18 , 20 , GeSe 21 – 23 and GeS 24 , 25 , respectively. Among them, As and Si co-doped GeSe OTS materials are believed to be the ones successfully utilized in commercial 3D PCM 26 , 27 .…”

Section: Introductionmentioning

confidence: 99%

GeSe ovonic threshold switch: the impact of functional layer thickness and device size

Zhao,

Song

et al. 2024

Sci Rep

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Three-dimensional phase change memory (3D PCM), possessing fast-speed, high-density and nonvolatility, has been successfully commercialized as storage class memory. A complete PCM device is composed of a memory cell and an associated ovonic threshold switch (OTS) device, which effectively resolves the leakage current issue in the crossbar array. The OTS materials are chalcogenide glasses consisting of chalcogens such as Te, Se and S as central elements, represented by GeTe6, GeSe and GeS. Among them, GeSe-based OTS materials are widely utilized in commercial 3D PCM, their scalability, however, has not been thoroughly investigated. Here, we explore the miniaturization of GeSe OTS selector, including functional layer thickness scalability and device size scalability. The threshold switching voltage of the GeSe OTS device almost lineally decreases with the thinning of the thickness, whereas it hardly changes with the device size. This indicates that the threshold switching behavior is triggered by the electric field, and the threshold switching field of the GeSe OTS selector is approximately 105 V/μm, regardless of the change in film thickness or device size. Systematically analyzing the threshold switching field of Ge–S and Ge–Te OTSs, we find that the threshold switching field of the OTS device is larger than 75 V/μm, significantly higher than PCM devices (8.1–56 V/μm), such as traditional Ge2Sb2Te5, Ag–In–Sb–Te, etc. Moreover, the required electric field is highly correlated with the optical bandgap. Our findings not only serve to optimize GeSe-based OTS device, but also may pave the approach for exploring OTS materials in chalcogenide alloys.

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“…However, loads of materials with superior performance emerging from the OTS research in full swing contain eco-unfriendly elements such as sulfur [ 8 , 9 , 10 ], arsenic [ 11 , 12 ] etc. ; additionally, most OTS materials are ternary, quaternary or even more [ 13 , 14 ], which means they inevitably suffer from element segregation and inhomogeneous composition.…”

Section: Introductionmentioning

confidence: 99%

Great Potential of Si-Te Ovonic Threshold Selector in Electrical Performance and Scalability

Sun

Zhang

et al. 2023

Nanomaterials

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The selector is an indispensable section of the phase change memory (PCM) chip, where it not only suppresses the crosstalk, but also provides high on-current to melt the incorporated phase change material. In fact, the ovonic threshold switching (OTS) selector is utilized in 3D stacking PCM chips by virtue of its high scalability and driving capability. In this paper, the influence of Si concentration on the electrical properties of Si-Te OTS materials is studied; the threshold voltage and leakage current remain basically unchanged with the decrease in electrode diameter. Meanwhile, the on-current density (Jon) increases significantly as the device is scaling down, and 25 MA/cm2 on-current density is achieved in the 60-nm SiTe device. In addition, we also determine the state of the Si-Te OTS layer and preliminarily obtain the approximate band structure, from which we infer that the conduction mechanism conforms to the Poole-Frenkel (PF) model.

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Scalability of Sulfur‐Based Ovonic Threshold Selectors for 3D Stackable Memory Applications

Cited by 9 publications

References 36 publications

The Role of Arsenic in the Operation of Electrical Threshold Switches

The Role of Arsenic in the Operation of Electrical Threshold Switches

GeSe ovonic threshold switch: the impact of functional layer thickness and device size

Great Potential of Si-Te Ovonic Threshold Selector in Electrical Performance and Scalability

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