Read Disturbances in Cross-Point Phase-Change Memory Arrays-Part I: Physical Modeling With Phase-Change Dynamics

• Published in: IEEE transactions on electron devices Vol. 70; no. 2; pp. 514 - 520
• Main Authors: Kim, Donguk, Jang, Jun Tae, Kim, Changwook, Kim, Hyun Wook, Hong, Eunryeong, Ban, Sanghyun, Shin, Minchul, Lee, Hanwool, Lee, Hyung Dong, Mo, Hyun-Sun, Woo, Jiyong, Kim, Dae Hwan
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amorphization; Arrays; Chatbots; Crystallization; Disturbances; Electric potential; Electron traps; Mathematical models; Microprocessors; Phase change materials; Phase transitions; Phase-change memory (PCM); read disturbance; Resistance; selector; storage class memory (SCM); Switches; Voltage
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2022.3231818

Phase-change memory (PCM) connected to an additional selector has been implemented in cross-point arrays for storage class memory applications. In the one-PCM and one-selector (1S-1R) configuration, the selector should be turned on first to read the resistance state of the PCM. This requires a large read voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{read} </tex-math></inline-formula>), and a high read current from the PCM is instantly produced, which causes read disturbances. To understand the underlying mechanism of the disturbance, in this study, we developed a physics-based Verilog-A model to describe the measured electrical behavior of the 1S-1R cell in HSPICE by considering thermally induced crystallization and melting dynamics. Based on <inline-formula> <tex-math notation="LaTeX">{V}_{TH} </tex-math></inline-formula>, which is the voltage induced when the selector is on, the crystalline and amorphous phases of the PCM can be identified indirectly. Based on the measured data, when the pristine amorphous state of the PCM is programmed by a higher SET current (<inline-formula> <tex-math notation="LaTeX">{I}_{SET} </tex-math></inline-formula>), <inline-formula> <tex-math notation="LaTeX">{V}_{TH} </tex-math></inline-formula> decreases owing to enhanced crystallization, leading to a low-resistance state. However, <inline-formula> <tex-math notation="LaTeX">{V}_{TH} </tex-math></inline-formula> subsequently begins to increase with respect to <inline-formula> <tex-math notation="LaTeX">{I}_{SET} </tex-math></inline-formula>, which results in a U-shaped <inline-formula> <tex-math notation="LaTeX">{V}_{TH} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{I}_{SET} </tex-math></inline-formula> curve. It is inferred that melting is preferred at temperatures above 900 K induced by the high-read current. The <inline-formula> <tex-math notation="LaTeX">{V}_{TH} </tex-math></inline-formula> increase induced by the amorphization can be explained by transient simulations. The simulation results are in good agreement with the experimental data and reveal that the temperature generated from the 1S-1R cell plays an important role in triggering the unwanted phase transition of the GeSbTe layer during the read operation.