Evaluating Ovonic Threshold Switching Materials with Topological Constraint Theory

Read, J.C.; Stewart, Derek A.; Reiner, J. W.; Terris, B.D.

doi:10.1021/acsami.1c10131

Cited by 7 publications

(7 citation statements)

References 96 publications

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“…Amorphous selenium (a-Se) is a high-resistivity photoconductor that has many applications in X-ray detection, such as medical and industrial imaging, materials science, and threat detection. Amorphous Se is a leading direct-conversion photoconductive layer for thin-film-transistor (TFT) flat panel imagers and complementary metal-oxide semiconductor (CMOS) readouts used in detectors for mammography. − Its high absorption and quantum efficiency (QE) in ultraviolet through blue wavelengths (∼80% at 400 nm and 30 V/μm) also make it well suited as a photodetector, with additional interest for the life sciences, high energy physics, and nuclear radiation detection. − Recent work also suggests its alloys may have promise as memory and selector elements in nonvolatile memory systems. , Its fabrication is a mature technology, and its photogeneration efficiency was extensively studied during the 1960s and 1970s . It is capable of avalanche multiplication at relatively low fields compared to other common avalanche materials, such as amorphous silicon .…”

Section: Introductionmentioning

confidence: 99%

Tuning Amorphous Selenium Composition with Tellurium to Improve Quantum Efficiency at Long Wavelengths and High Applied Fields

Hellier

Stewart

Read

et al. 2023

ACS Appl. Electron. Mater.

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Amorphous selenium (a-Se) is a large-area compatible photoconductor that has received significant attention toward the development of UV and X-ray detectors for a wide range of applications in medical imaging, life science, high-energy physics, and nuclear radiation detection. A subset of applications require detection of photons with spectral coverage from UV to infrared wavelengths. In this work, we present a systematic study utilizing density functional theory simulations and experimental studies to investigate optical and electrical properties of a-Se alloyed with tellurium (Te). We report hole and electron mobilities and conversion efficiencies for a-Se1–x Te x (x = 0, 0.03, 0.05, 0.08) devices as a function of applied field, along with band gaps and comparisons to previous studies. For the first time, these values are reported at high electric field (>10 V/μm), demonstrating recovery of quantum efficiency in Se–Te alloys. A comparison to the Onsager model for a-Se demonstrates the strong field dependence in the thermalization length and expands on the role of defect states in device performance.

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Section: Introductionmentioning

confidence: 99%

Tuning Amorphous Selenium Composition with Tellurium to Improve Quantum Efficiency at Long Wavelengths and High Applied Fields

Hellier

Stewart

Read

et al. 2023

ACS Appl. Electron. Mater.

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“…A 2.4 < MCN < 3.0 is required for OTS chalcogenide glasses to be considered rigid in normal conditions. 60 Our materials are, indeed, rigid-glass-formers by the MCN criterium, which is in the range of 2.7−3.0, as listed in Table 1. Since both MCN and #e are derived from the composition stoichiometry, the two parameters have a reciprocal relationship (see Supplementary Figures S1 and S2).…”

Section: Ots Materials Characteristics 311 Valence Electrons (#E)mentioning

confidence: 73%

“…A simple, but efficient parameter to define the matrix rigidity is the MCN of a material, which is simply derived from the chemical composition by averaging the formal coordination numbers of the atoms, weighted by their concentration in the material. A 2.4 < MCN < 3.0 is required for OTS chalcogenide glasses to be considered rigid in normal conditions . Our materials are, indeed, rigid-glass-formers by the MCN criterium, which is in the range of 2.7–3.0, as listed in Table .…”

Section: Resultsmentioning

confidence: 90%

Ovonic Threshold Switch Chalcogenides: Connecting the First-Principles Electronic Structure to Selector Device Parameters

Clima

Ravsher

Garbin

et al. 2022

ACS Appl. Electron. Mater.

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Chalcogenides are attractive materials for microelectronics applications due to their ability to change physical, optical, and electrical properties under applied electric stimulus. One of the most recent interest in chalcogenides is their use to enable the development of a two-terminal selector device, which is a fast, volatile, resistance switching device. The electrical signature of Ovonic threshold switching (OTS) chalcogenide materials is well suited for such applications. While there are numerous known OTS materials, most of them contain toxic elements. There is hence a need to find environment-friendly OTS materials. For this to happen, we strive to predict electrical device parameters only from atomistic first-principles simulations of the chalcogenide materials, as this can be a faster and less expensive route to screen the performances of chalcogenide candidates. By mapping the experimentally measured set of electrical OTS materials into atomistic models and computing their electronic properties, we were able to identify correlations between computed properties such as the theoretical trap/mobility gaps, the local atomic coordination environments of the elements adopted in the material, and the experimentally measured first-fire/threshold/hold voltages, hold/leakage currents, or extracted trap density. These findings can guide in identifying OTS materials with predefined electronic properties, tailored to the requirements of specific microelectronics applications with only first-principles simulations.

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“…TEM analysis revealed regions of crystalline TiSe 2 in the OTS layer near the interface with TiN. Adding a thin carbon layer was found to improve the endurance from 10 6 to 10 9 . Evidence for segregation and crystallization has also been reported in Ge-rich Ge x Se 1−x OTS layers after 1 M cycles, although the authors did not characterize the crystallized regions.…”

Section: Introductionmentioning

confidence: 95%

“…The electronic transformation observed in OTS materials may also precede the phase transformation observed in phase change materials like Ge 2 Sb 2 Te 5 . For OTS with sufficiently high OFF state resistance, this volatile switching has made these amorphous chalcogenide alloys leading candidates for selectors to prevent sneak current paths in memory arrays. − Given the high temperatures and applied fields experienced by these thin chalcogenide alloy films, the long-term stability of the material composition is critical for device operation. Interactions between the chalcogenide layer and neighboring electrodes can have direct effects on the device switching characteristics and the overall device endurance.…”

Section: Introductionmentioning

confidence: 99%

Using Machine Learning Potentials to Explore Interdiffusion at Metal–Chalcogenide Interfaces

Achar

Schneider²,

Stewart

2022

ACS Appl. Mater. Interfaces

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Chalcogenide alloys are key materials for selector and memory elements used in next-generation nonvolatile memory cells. However, the high electric fields and Joule heating experienced during operation can promote interdiffusion at the interfaces that degrade device performance over time. A clear atomic scale understanding of how chalcogenide alloys interact with electrodes could aid in identifying ways to improve long-term device endurance. In this work, we develop a robust set of moment tensor potentials (MTPs) to examine interactions between Ge−Se alloys and Ti electrodes. Previous works have shown evidence of strong interactions between Ti and chalcogenide alloys. This system offers an important first test in the use of ML empirical potentials to understand the role of interfaces in endurance in memory elements and broader nanoscale devices. The empirical potentials are constructed using an active learning moment tensor potential framework that leverages a broad data set of first-principles calculations for Ti, Ge, and Se compounds. Long-term simulations (>1 ns) show significant interdiffusion at the Ti|Ge−Se interface with Ti and Se both actively moving across the original interface. The strong chemical affinity of Ti and Se leads to a well-defined Ti−Se region and a severely Se-depleted central Ge−Se region with unfavorable selector characteristics. The evolution of the Ti−Se layer can be described using a self-limited growth model. By comparing effective Ti−Se diffusion constants for simulations at different temperatures, we find a low activation energy of 0.1 eV for Ti−Se layer interdiffusion.

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Evaluating Ovonic Threshold Switching Materials with Topological Constraint Theory

Cited by 7 publications

References 96 publications

Tuning Amorphous Selenium Composition with Tellurium to Improve Quantum Efficiency at Long Wavelengths and High Applied Fields

Tuning Amorphous Selenium Composition with Tellurium to Improve Quantum Efficiency at Long Wavelengths and High Applied Fields

Ovonic Threshold Switch Chalcogenides: Connecting the First-Principles Electronic Structure to Selector Device Parameters

Using Machine Learning Potentials to Explore Interdiffusion at Metal–Chalcogenide Interfaces

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