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The recent development of three‐dimensional semiconductor integration technology demands a key component—the ovonic threshold switching (OTS) selector to suppress the current leakage in the high‐density memory chips. Yet, the unsatisfactory performance of existing OTS materials becomes the bottleneck of the industrial advancement. The sluggish development of OTS materials, which are usually made from chalcogenide glass, should be largely attributed to the insufficient understanding of the electronic structure in these materials, despite of intensive research in the past decade. Due to the heavy first‐principles computation on disordered systems, a universal theory to explain the origin of mid‐gap states (MGS), which are the key feature leading to the OTS behavior, is still lacking. To avoid the formidable computational tasks, we adopt machine learning method to understand and predict MGS in typical OTS materials. We build hundreds of chalcogenide glass models and collect major structural features from both short‐range order (SRO) and medium‐range order (MRO) of the amorphous cells. After training the artificial neural network using these features, the accuracy has reached ~95% when it recognizes MGS in new glass. By analyzing the synaptic weights of the input structural features, we discover that the bonding and coordination environments from SRO and particularly MRO are closely related to MGS. The trained model could be used in many other OTS chalcogenides after minor modification. The intelligent machine learning allows us to understand the OTS mechanism from vast amount of structural data without heavy computational tasks, providing a new strategy to design functional amorphous materials from first principles. The 3D semiconductor fabrication technology requires an “ovonic threshold switching (OTS)” selector device to control the open and shut of each memory unit. The physics of these materials, however, has not been well understood due to complex structure of chalcogenide glass. The authors focus on the defect states which are responsible for OTS behaviors via machine learning of the large amount of structure data. The physical origin of OTS is revealed and the properties of these materials can be predicted, paving the way for the materials design toward high‐density memory integration.

Ovonic threshold switching (OTS) selectors based on amorphous chalcogenides can revolutionize 3D memory technology owing to their self‐selecting memory (SSM) behavior. However, the complex mechanism governing the memory writing operation limits compositional and device optimization. This study investigates the mechanism behind the polarity‐dependent threshold voltage shift (ΔVTH) through theoretical and experimental analyses. By examining the physical principles of threshold switching and conducting defect state analysis, the ΔVTH as a memory window is confirmed to be attributed to the dynamics of charged defects and their gradient near electrodes, influenced by the nonuniform electric field after threshold switching. This study provides critical insights into the operational mechanism of OTS‐based SSM, known as selector‐only memory, highlighting its advantages for developing high‐density, low‐cost, and energy‐efficient memory technologies in the artificial intelligence era. This study explores the mechanism behind polarity‐dependent threshold voltage shifts (ΔVTH) in ovonic threshold switching selectors using amorphous chalcogenides. Through theoretical and experimental analyses, it reveals that the ΔVTH originates from charged Se and cation dimer defect redistribution near electrodes, influenced by nonuniform electric fields, providing insights for optimizing self‐selecting memory devices in 3D memory technology.

A new architecture has become necessary owing to the power consumption and latency problems of the von Neumann architecture. A neuromorphic memory system is a promising candidate for the new system as it has the potential to process large amounts of digital information. A crossbar array (CA), which consists of a selector and a resistor, is the basic building block for the new system. Despite the excellent prospects of crossbar arrays, the biggest obstacle for them is sneak current, which can cause a misreading between the adjacent memory cells, thus resulting in a misoperation in the arrays. The chalcogenide-based ovonic threshold switch (OTS) is a powerful selector with highly nonlinear I–V characteristics that can be used to address the sneak current problem. In this study, we evaluated the electrical characteristics of an OTS with a TiN/GeTe/TiN structure. This device shows nonlinear DC I–V characteristics, an excellent endurance of up to 109 in the burst read measurement, and a stable threshold voltage below 15 mV/dec. In addition, at temperatures below 300 °C, the device exhibits good thermal stability and retains an amorphous structure, which is a strong indication of the aforementioned electrical characteristics.

Chalcogenide glass has a unique volatile transition between high‐ and low‐resistance states under an electric field, a phenomenon termed ovonic threshold switching (OTS). This characteristic is extensively utilized in various electronic memory and computational devices, particularly as selectors for cross‐point memory architectures. Despite its advantages, the material is susceptible to glass relaxation, which can result in substantial drifts in threshold voltage and a decline in off‐current performance over successive operational cycles or long storage time. In this study, we introduce an OTS device made from stoichiometric Sb2Se3 glass, which retains an octahedral local structure within its amorphous matrix. This innovative material exhibits outstanding OTS capabilities, maintaining minimal degradation despite undergoing over 107 operating cycles. Via comprehensive first‐principles calculations, our findings indicate that the mid‐gap states in amorphous Sb2Se3 predominantly stem from the atomic chains characterized by heteropolar Sb‐Se bonds. These bonds exhibit remarkable stability, showing minimal alteration over time, thereby contributing to the overall durability and consistent performance of the material. Our findings not only shed light on the complex physical origins that govern the OTS behavior but also lay the groundwork for creating or optimizing innovative electrical switching materials. The performance degradation upon electrical operations often leads to significant read/write errors in the memory array. In this paper, the authors present a simple selector utilizing stoichiometric Sb2Se3, demonstrating exceptional endurance with minimal drift. The underlying mechanism accountable for its robust performance is elucidated through systematic first‐principles calculations.

HighlightsThe development history and key milestones of ovonic threshold switch (OTS) materials were comprehensively summarized. Combined with the latest advancements of OTS research, the mainstream OTS material systems were systematically introduced.A thorough overview of the prevailing viewpoints regarding the OTS switching mechanisms was presented.Recent progress in OTS devices for applications in 3D memory, self-selecting memory, and neuromorphic computing was summarized.Today’s explosion of data urgently requires memory technologies capable of storing large volumes of data in shorter time frames, a feat unattainable with Flash or DRAM. Intel Optane, commonly referred to as three-dimensional phase change memory, stands out as one of the most promising candidates. The Optane with cross-point architecture is constructed through layering a storage element and a selector known as the ovonic threshold switch (OTS). The OTS device, which employs chalcogenide film, has thereby gathered increased attention in recent years. In this paper, we begin by providing a brief introduction to the discovery process of the OTS phenomenon. Subsequently, we summarize the key electrical parameters of OTS devices and delve into recent explorations of OTS materials, which are categorized as Se-based, Te-based, and S-based material systems. Furthermore, we discuss various models for the OTS switching mechanism, including field-induced nucleation model, as well as several carrier injection models. Additionally, we review the progress and innovations in OTS mechanism research. Finally, we highlight the successful application of OTS devices in three-dimensional high-density memory and offer insights into their promising performance and extensive prospects in emerging applications, such as self-selecting memory and neuromorphic computing.

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 GeTe 6 , 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 Ge 2 Sb 2 Te 5 , 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.

Hyper-field effect transistors (hyper-FETs) are crucial in the development of low-power logic devices. With the increasing significance of power consumption and energy efficiency, conventional logic devices can no longer achieve the required performance and low-power operation. Next-generation logic devices are designed based on complementary metal-oxide-semiconductor circuits, and the subthreshold swing of existing metal-oxide semiconductor field effect transistors (MOSFETs) cannot be reduced below 60 mV/dec at room temperature owing to the thermionic carrier injection mechanism in the source region. Therefore, new devices must be developed to overcome these limitations. In this study, we present a novel threshold switch (TS) material, which can be applied to logic devices by employing ovonic threshold switch (OTS) materials, failure control of insulator–metal transition materials, and structural optimization. The proposed TS material is connected to a FET device to evaluate its performance. The results demonstrate that commercial transistors connected in series with GeSeTe-based OTS devices exhibit significantly lower subthreshold swing values, high on/off current ratios, and high durability of up to 108.