This review provides a comprehensive overview of ovonic threshold switch (OTS) materials and their applications in 3D memory and emerging technologies. OTS devices, which utilize chalcogenide films, have gained significant attention due to their high drive current, nanosecond speed, low leakage current, and excellent scalability. The OTS phenomenon was first observed in 1964 by Northover and Pearson, and later described by Ovshinsky in 1968. The OTS device operates by switching between an on-state and an off-state under specific voltage conditions, with the threshold voltage (Vth) playing a crucial role in the switching process. OTS materials are primarily composed of chalcogenides, including selenium (Se), tellurium (Te), and sulfur (S). These materials exhibit distinct electrical properties, such as high drive current, low leakage current, and high endurance. The development of OTS materials has been driven by the need for high-performance memory technologies that can store large volumes of data in shorter time frames. OTS devices are particularly useful in 3D memory, self-selecting memory, and neuromorphic computing due to their ability to suppress leakage current and provide high selectivity. The key electrical parameters of OTS devices include on-state current (Ion), off-state leakage current (Ioff), on/off ratio, endurance, thermal stability, threshold voltage/field (Vth/Eth), and switching speed (ton/toff). These parameters are critical for the performance of OTS devices in various applications. The development of OTS materials has involved extensive research into doping and compositional optimization to enhance their performance. For example, doping with elements such as nitrogen (N), carbon (C), and boron (B) has been shown to improve the thermal stability and reduce leakage current of OTS materials. The application of OTS devices in 3D memory has been successful, with commercial products such as Intel's 3D Xpoint memory. OTS materials have also shown promise in other emerging applications, including self-selecting memory and neuromorphic computing. The future of OTS technology lies in further optimizing the materials and device structures to achieve higher performance, lower power consumption, and greater scalability. The ongoing research in OTS materials and devices is expected to lead to significant advancements in memory technologies for the coming years.This review provides a comprehensive overview of ovonic threshold switch (OTS) materials and their applications in 3D memory and emerging technologies. OTS devices, which utilize chalcogenide films, have gained significant attention due to their high drive current, nanosecond speed, low leakage current, and excellent scalability. The OTS phenomenon was first observed in 1964 by Northover and Pearson, and later described by Ovshinsky in 1968. The OTS device operates by switching between an on-state and an off-state under specific voltage conditions, with the threshold voltage (Vth) playing a crucial role in the switching process. OTS materials are primarily composed of chalcogenides, including selenium (Se), tellurium (Te), and sulfur (S). These materials exhibit distinct electrical properties, such as high drive current, low leakage current, and high endurance. The development of OTS materials has been driven by the need for high-performance memory technologies that can store large volumes of data in shorter time frames. OTS devices are particularly useful in 3D memory, self-selecting memory, and neuromorphic computing due to their ability to suppress leakage current and provide high selectivity. The key electrical parameters of OTS devices include on-state current (Ion), off-state leakage current (Ioff), on/off ratio, endurance, thermal stability, threshold voltage/field (Vth/Eth), and switching speed (ton/toff). These parameters are critical for the performance of OTS devices in various applications. The development of OTS materials has involved extensive research into doping and compositional optimization to enhance their performance. For example, doping with elements such as nitrogen (N), carbon (C), and boron (B) has been shown to improve the thermal stability and reduce leakage current of OTS materials. The application of OTS devices in 3D memory has been successful, with commercial products such as Intel's 3D Xpoint memory. OTS materials have also shown promise in other emerging applications, including self-selecting memory and neuromorphic computing. The future of OTS technology lies in further optimizing the materials and device structures to achieve higher performance, lower power consumption, and greater scalability. The ongoing research in OTS materials and devices is expected to lead to significant advancements in memory technologies for the coming years.