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Microstructure-Dependent DC Set Switching Behaviors of Ge–Sb–Te-Based Phase-Change Random Access Memory Devices Accessed by in Situ TEM

Investigation of DC set switching of Ge–Sb–Te-based vertical PCRAM cells

Nature, Asia Materials has published an article written by Kyungjoon Baek, Kyung Song, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea, Sung Kyu Son, Jang Won Oh, Seung-Joon Jeon, Won Kim, Ho Joung Kim, Analysis Team, R&D Division, SK Hynix Semiconductor Inc., Icheon, Republic of Korea, and Sang Ho Oh, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea.

Cross-sectional transmission electron microscope
sample of a vertical phase-change random access memory cell
prepared for
in situ switching.
The W plug connected to the TiN heater (highlighted in red) is grounded through attachment to the Cu support grid. A Pt–Ir tip makes electrical contact with the W top electrode contact, constructing an electrical circuit for the application of DC voltage.
The TiN heater is surrounded by a thermal/electrical insulator
(Si3N4, highlighted in yellow).
The active switching volume (hemispherical volume)
is outlined by a white dotted line.

PCRAM_am201549f1

 

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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