Concurrent Optimization of Electrical and Thermal Performances of Ovonic Threshold Switching Si-Ge-Te-N Selector Device for Neuromorphic Applications

Threshold switching selector is an essential component within the 3D cross-point (X-Point) array that enables stable synaptic operation in neuromorphic devices. The necessity of high-performance selector is especially emphasized in the 3D X-Point due to requirements of low-power operation and drastic switching characteristic for neuromorphic operation, as well as low off-state leakage and device stability for data reliability of integrated circuit. In this respect, research on selector devices with outstanding electrical performances and stability have been conducted. Among various candidates for high-performance and 3D-stackable selector device, Ovonic threshold switching (OTS) device showed excellent properties that can potentially satisfy all the requirements that can be successfully adopted into the 3D X-Point memory.<br/><br/>OTS phenomenon is characterized by a drastic on/off switching operation within the amorphous chalcogenide film. Thanks to its potential for meeting various requirements, OTS selectors are considered strong candidates for neuromorphic and high-density memory applications. However, the demand for improvements in OTS selector has increased due to its poor device characteristics such as on/off ratio, delay time, endurance, and thermal stability. Preceding research had initially endeavored to satisfy the requirements mainly with binary OTS systems but failed to satisfy all the parameters due to limited composition controllability when fabricating the device. Such limitation motivated researchers to proceed to ternary and quaternary material systems where positive results were obtained with arsenic-based quaternary systems, but the toxicity of arsenic remains a major concern. In this research, we first demonstrate arsenic-free quaternary OTS device based on N-Si-Ge-Te chalcogenide system that shows excellent electrical performance such as high on/off ratio with an intrinsic selectivity of 10⁶, delay time of less than 5 nanoseconds while providing thermal stability over 400°C and an endurance of 10⁸ cycles. All of the parameters can be simultaneously achieved by understanding the role of each element in the material system that contribute to device’s overall characteristics, and thereby concurrently optimizing the device performances through precise modification of material composition. We hope that this result will help the development of high performance As-free OTS devices for neuromorphic applications as well as next-generation electronics.<br/><br/>This research was supported by the Ministry of Trade, Industry & Energy (MOITIE)/Korean Evaluation Institute Industrial Technology (KEIT) (Project No. 10080625) and Korea Semiconductor Research Consortium (KSRC) program for the development of the future semiconductor devices, and by Samsung Electronics Co. Ltd. (Project number IO2102021-08356-01).