In situ TEM observation of void formation and migration in phase change memory devices with confined nanoscale Ge 2 Sb 2 Te 5

• Published in: Nanoscale advances 2020-09, Vol.2 (9), p.3841-3848
• Main Authors: Oh, Sang Ho, Baek, Kyungjoon, Son, Sung Kyu, Song, Kyung, Oh, Jang Won, Jeon, Seung-Joon, Kim, Won, Yoo, Jong Hee, Lee, Kee Jeung
• Format: Article
• Language: English
• ISSN: 2516-0230; 2516-0230
• DOI: 10.1039/D0NA00223B

The reliability of Ge–Sb–Te phase-change memory (PCM) devices has been limited by failure due to void formation and this still remains one of the critical issues affecting their use in storage-class memory applications. To directly observe the void formation processes in real-time, we implemented in situ switching of PCM devices by applying set and reset voltage pulses to a Ge 2 Sb 2 Te 5 (GST) cell inside a transmission electron microscope (TEM). The in situ TEM observations directly show that a void nucleates preferentially near the TiN bottom electrode in the GST cell, where the temperature is the highest. The nucleated void grows gradually until it reaches a certain size while migrating slowly toward the positively biased electrode. The fully grown void then continues migrating toward the positively biased electrode in subsequent set pulses. The observed polarity-dependent void migration can be explained by the field-induced redistribution of the constituent elements, especially by the electromigration of under-coordinated Te − ions which have vacancies around them. When the reset pulse with the same voltage polarity is applied, the voids exhibit a slight volume shrinkage but are not completely eliminated, resulting in a reset-stuck failure. The present in situ TEM observations revealing the nucleation, growth, and polarity-dependent migration of voids will contribute to the fundamental understanding of the failure by void formation in nanoscale GST-based PCM devices and help improving the design of reliable PCM devices.