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Phase change memory is an emerging nonvolatile memory technology, recently becoming the center of attention to bridge the speed gap between fast dynamic random access memory and slow flash-based solid-state drives. Lately, CrGeTe3 has been investigated as a special phase change material with an inverse resistance and density change. This material has excellent properties such as good thermal stability, ultralow-energy glass formation process and almost zero mass-density change upon crystallization. Here, we analyzed the amorphous structure of this abnormal material in detail through ab initio simulations and discovered that the metallic-like tight atomic packing is the origin of the high carrier concentration and high mass density in the amorphous phase. Furthermore, the bonding analysis confirms that it is the short Cr–Cr bonds that lead to high packing efficiency in the amorphous local order. Our results discovered the material gene of the amorphous CrGeTe3, paving the way for the design of high-performance memory devices based on this material. [ABSTRACT FROM AUTHOR]

The thermal stability of the amorphous phase is a key property of phase-change memory, which limits the data retention time and device reliability. The high thermal stability of memory devices enables their applications in harsh environments and under extreme conditions. Here, we discovered that the alloying of C, Si and Ge significantly improves the stability of amorphous Sb by adding “alien” tetrahedral seeds to the octahedral matrix. This doping strategy impedes the crystallization at elevated temperatures so that the crystallization temperature of Sb is increased by 170–220 °C. The mechanism is systematically investigated by ab initio molecular dynamics simulations and classical crystal growth theory. We confirm that the alien tetrahedral bonds increase the activation energy of atomic migration upon crystallization. Our results demonstrate an effective alloying strategy to improve the thermal stability of phase change memory, paving the way for the design of durable memory devices. [ABSTRACT FROM AUTHOR]

Abstract: Phase‐change memory (PCM) is a promising candidate for next‐generation memory technology due to the fast switching and large property contrast between the crystalline and amorphous phases. However, the large difference of mass density between these two phases is one of the major factors that lead to the failure of PCM devices. In this work, it is discovered that the carbon alloying remarkably reduces the density change of GeSb film (GeSbC), a chalcogen‐free material with high stability and good switching properties, from ≈6% to ≈3%. In particular, it is focused on the mechanism how carbon affects the structure of GeSbC alloys through X‐ray photoelectron spectroscopy and ab initio calculations, demonstrating that this dopant has increased the packing efficiency by forming small tetrahedral clusters in the bonding region of the glass. The results have important implications on the design of durable phase‐change memory materials. [ABSTRACT FROM AUTHOR]

Phase‐change materials (PCMs) used in data storage devices have unique structural features and transition properties by thermal heating. Pressure, as another important thermodynamic tool, can also induce a series of interesting phase transitions in PCMs, accompanied by the altering of bonding nature and physical properties. Here, the structure transition as well as property change of prototypical phase‐change material Ge–Sb–Te (GST) under hydrostatic pressure has been reviewed. The high‐pressure behavior of some other relevant chalcogenides such as GeTe, Sb2Te3, and GeSe, is also discussed. The revealing of structure and property changes due to high pressure sheds light on the underlying physics of many fascinating properties of PCMs, and therefore it will have profound implications on various applications of phase change materials in memory and other fields. The recent progress in studying the high‐pressure behavior of phase‐change materials (PCMs) has been reviewed in this article. The unique structure and property transitions of these materials, which are widely used in data storage and other electronic devices, reveal rich physics under high pressure, allowing researchers to fully understand the transition mechanism of PCMs. [ABSTRACT FROM AUTHOR]