Understanding the Selector-Only Memory (SOM) Mechanism of Te-Based Ovonic Threshold Switch

In recent years, Artificial Intelligence (AI) has exponentially evolved, increasing the importance of efficient data processing in computing architecture. Addressing high-density and low-cost requirements, Storage-Class Memory (SCM) has emerged as a promising candidate for utilizing crossbar architecture while meeting the requirements of low latency and power consumption. In general, emerging phase-change or resistive-switching memories are used with selector devices as 1-selector 1-resistor (1S1R) to suppress unavoidable leakage current from half-selected cells. Ovonic Threshold Switch (OTS) selectors are one of the notable candidates for integration with memory in crossbar arrays, offering advantages such as high on/off ratio, endurance, and thermal stability, but an improved method is needed for overcoming scaling limitations and fabrication complexity.<br/>Selector-Only Memory (SOM) was recently introduced to mitigate the scaling issues by utilizing a single selector cell with a programmable threshold voltage (V_th) similar to NAND Flash operations, thereby eliminating the need for multiple stacking. SOM device shows the effect of polarity-induced V_th shift in which, depending on the polarity of the input program pulse (whether positive or negative), V_th can be programmed to high (if negative) or low (if positive) states. To ensure reliable program and read operations, Read Window Margin (RWM) or the difference between high and low V_th states, needs to be sufficiently large.<br/>This work aims to investigate one of the hypotheses, field-driven atomic segregation from preceding research, especially in Te-based OTS materials exhibiting SOM characteristics. The presence or absence of SOM characteristics based on pulse modulation is confirmed to indirectly verify whether a certain amount of time is required for atomic segregation. Additionally, analysis using Atomic Force Microscopy (AFM) reveals that the conductivity changes of confined switching region on the film depend on the applied voltage polarity, which is mainly observed on films with SOM characteristics. These results enhance our understanding and help validate the field-driven atomic segregation hypothesis for SOM characteristics.<br/><br/><b>Acknowledgments</b><br/>This research was supported by Samsung Electronics Co., Ltd. (Project No. IO2102021-08356-01), the BK21 FOUR (Fostering Outstanding Universities for Research) funded by the Ministry of Education (MOE) of Korea and National Research Foundation (NRF) of Korea.