Mystery of phase change in sub-nanosecond-octahedra structure motif

July 9, 2018, Science China Press

Phase change random access memory (PCRAM) has been successfully applied in the computer storage architecture, as storage class memory, to bridge the performance gap between DRAM and Flash-based solid-state drive due to its good scalability, 3-D integration ability, fast operation speed and compatible with CMOS technology. Focusing on phase change materials and PCRAM for decades, we have successfully developed 128 Mb embedded PCRAM chips, which can meet the requirements of most embedded systems.

3-D Xpoint (3-D PCRAM), invented by Intel and Micron, has been regarded as a new breakthrough in the last 25 years since the application of NAND in 1989, which represents state-of-the-art memory technology. This technology has some remarkable features, such as the confined device structure with 20 nm size, the metal crossbar electrodes to reduce the resistance variations in PCRAM arrays, and the ovonic threshold switching selector that can provide a high drive current and a low leakage current. A good understanding of phase change mechanism is of great help to design new with fast operation speed, low power consumption and long-lifetime.

In a recent paper published in SCIENCE CHINA Information Sciences, researchers reviewed the development of PCRAM and different understandings on phase change mechanisms in recent years, and have proposed a new view on the mechanism, which is based on the octahedral structure motifs and vacancies.

Octahedral structure motifs are generally found in both amorphous and crystalline materials. They are considered to be the basic units during phase transition, which are severely defective in the amorphous phase. These configurations turn into more ordered ones after minor local rearrangements, the growth of which results in the crystallization of rocksalt (RS) phase with a large amount of vacancies in the cation sites. Further driven by thermodynamic driving force, these vacancies move and layer along certain directions; consequently, the metastable RS structure transforms into the stable hexagonal (HEX) . Based on the results, the researchers found that the reversible phase transition between the amorphous phase and the RS phase, without further changing into the HEX phase, would greatly decrease the required power consumption. Robust octahedra and plenty of vacancies in both the amorphous and the RS , respectively avoiding large atomic rearrangement and providing necessary space, are crucial to achieve the nanosecond or even sub-nanosecond operation of PCRAM.

Explore further: Ultralow power consumption for data recording

More information: Zhitang Song et al, From octahedral structure motif to sub-nanosecond phase transitions in phase change materials for data storage, Science China Information Sciences (2018). DOI: 10.1007/s11432-018-9404-2

Related Stories

Ultralow power consumption for data recording

January 25, 2018

A team of researchers at Tohoku University, in collaboration with the National Institute of Advanced Industrial Science and Technology (AIST) and Hanyang University, has developed new phase change material with electrical ...

The '50-50' chip: Memory device of the future?

September 13, 2013

A new, environmentally-friendly electronic alloy consisting of 50 aluminum atoms bound to 50 atoms of antimony may be promising for building next-generation "phase-change" memory devices, which may be the data-storage technology ...

Recommended for you

Complete world map of tree diversity

February 21, 2019

Biodiversity is one of Earth's most precious resources. However, for most places in the world, scientists only have a tiny picture of what this diversity actually is. Researchers at the German Centre for Integrative Biodiversity ...

'Butterfly-shaped' palladium subnano cluster built in 3-D

February 21, 2019

Miniaturization is the watchword of progress. Nanoscience, studying structures on the scale of a few atoms, has been at the forefront of chemistry for some time now. Recently, researchers at the University of Tokyo developed ...

Water is more homogeneous than expected

February 21, 2019

In order to explain the known anomalies in water, some researchers assume that water consists of a mixture of two phases, even under ambient conditions. However, new X-ray spectroscopic analyses at BESSY II, ESRF and Swiss ...

Squid could provide an eco-friendly alternative to plastics

February 21, 2019

The remarkable properties of a recently-discovered squid protein could revolutionize materials in a way that would be unattainable with conventional plastic, finds a review published in Frontiers in Chemistry. Originating ...

Female golden snub-nosed monkeys share nursing of young

February 21, 2019

An international team of researchers including The University of Western Australia and China's Central South University of Forestry and Technology has discovered that female golden snub-nosed monkeys in China are happy to ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.