Original Article

Citation: NPG Asia Materials (2015) 7, e194; doi:10.1038/am.2015.49
Published online 26 June 2015

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM
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Kyungjoon Baek1, Kyung Song1, Sung Kyu Son2, Jang Won Oh2, Seung-Joon Jeon2, Won Kim2, Ho Joung Kim2 and Sang Ho Oh1

  1. 1Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
  2. 2Analysis Team, R&D Division, SK Hynix Semiconductor Inc., Icheon, Republic of Korea

Correspondence: Professor SH Oh, Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang 790-784, Republic of Korea. E-mail: shoh@postech.ac.kr

Received 26 July 2014; Revised 26 February 2015; Accepted 14 April 2015

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Abstract

Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for high-density applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge–Sb–Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polarity-dependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM.

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