Atomic-Level Mechanisms of Phase-Change Memory Materials Revealed

Apr 15, 2008 by Laura Mgrdichian feature
Atomic-Level Mechanisms of Phase-Change Memory Materials Revealed
A model of an amorphous form of the memory material Ge2Sb2Te5, showing the square molecular rings that nucleate the crystallization process.

Scientists from the University of Cambridge in the UK have uncovered the atomic-level interactions that occur when a class of “phase-change” memory materials stores information. Their work, reported in the March 23 online edition of Nature Materials, may open up new avenues for research into these fascinating materials, possibly leading to a new generation of “super” memory materials for electronic devices.

The materials studied are each composed of the elements germanium, antimony, and tellurium (Ge, Sb, and Te). They are used in devices that can retain information even when powered off, such as rewritable optical DVDs and a new type of electrical random-access memory intended to be a replacement for Flash memory, which is used in memory sticks, digital cameras, cell phones, and other portable devices.

The materials work by undergoing changes in their atomic structure. To store information, the structure rapidly switches from amorphous (disordered) to crystalline (ordered) in response to either an optical or electrical pulse. When the information is erased, the structured becomes amorphous again.

Despite many theoretical and experimental studies to understand the phase-change mechanism, the microscopic interactions have remained a mystery. This is due in part because the phase changes occurs so quickly, over only about one nanosecond, and the dimensions of the materials in the active regions on the devices are so small, only about 10 nanometers.

“For the first time, we have determined what goes on at the atomic level when one of these materials, Ge2Sb2Te5, stores information,” said University of Cambridge researcher Stephen Elliott to “We have gained deep and valuable insight into this process.”

Elliott and co-researcher Jozsef Hegedüs set out to answer some basic questions about phase-change memory materials, including why the crystallization process occurs so quickly, taking only about one nanosecond, and why the process is so readily reversible.

They carried out a series of molecular dynamics simulations using computer software and were able to reproduce the entire Ge2Sb2Te5 read-write phase-change cycle. They modeled what would happen as the material was heated and then cooled rapidly or slowly, changing from a liquid to either an amorphous phase or a crystal, and then from amorphous to crystal upon reheating.

They found that, as the liquefied Ge2Sb2Te5 cools, very high densities of square-shaped molecular rings form, which persist even into the amorphous phase. The rings form the backbone of the crystal phase, serving as nucleation points for its growth.

“The significance is that this is the first time that the entire phase change cycle has been simulated by accurate molecular dynamics simulations, and that the role of the square rings in the crystallization process has been established,” said Elliott.

“Our approach may lead to the design of superior phase-change materials in the future, if we can find compositions, for example, that nucleate at much shorter times or at lower temperatures, and by investigating the effects of doping, such as with nitrogen. These properties could allow better memory devices to be manufactured, and more rapidly.”

Citation: J. Hegedüs and S. R. Elliott Nature advance online publication, 23 March 2008 (DOI 10.1038/nmat2157)

Copyright 2008
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of

Explore further: Pseudoparticles travel through photoactive material

Related Stories

Beyond human: Exploring transhumanism

Nov 25, 2014

What do pacemakers, prosthetic limbs, Iron Man and flu vaccines all have in common? They are examples of an old idea that's been gaining in significance in the last several decades: transhumanism. The word ...

New research lights the way to super-fast computers

Nov 07, 2014

New research published today in the journal Nature Communications, has demonstrated how glass can be manipulated to create a material that will allow computers to transfer information using light. This development could ...

'Smart' medical material aims to unfurl at 98.6 degrees

Nov 22, 2013

( —Mechanical Engineering Professor Lih-Sheng (Tom) Turng has a simple office demonstration of how shape-memory polymers work. He takes the material, which is formed into a compact flower bud, ...

Recommended for you

Pseudoparticles travel through photoactive material

Apr 23, 2015

Researchers of Karlsruhe Institute of Technology (KIT) have unveiled an important step in the conversion of light into storable energy: Together with scientists of the Fritz Haber Institute in Berlin and ...

From metal to insulator and back again

Apr 22, 2015

New work from Carnegie's Russell Hemley and Ivan Naumov hones in on the physics underlying the recently discovered fact that some metals stop being metallic under pressure. Their work is published in Physical Re ...

Electron spin brings order to high entropy alloys

Apr 22, 2015

Researchers from North Carolina State University have discovered that electron spin brings a previously unknown degree of order to the high entropy alloy nickel iron chromium cobalt (NiFeCrCo) - and may play ...

Expanding the reach of metallic glass

Apr 22, 2015

Metallic glass, a class of materials that offers both pliability and strength, is poised for a friendly takeover of the chemical landscape.

Electrons move like light in three-dimensional solid

Apr 22, 2015

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional ...

Quantum model helps solve mysteries of water

Apr 20, 2015

Water is one of the most common and extensively studied substances on earth. It is vital for all known forms of life but its unique behaviour has yet to be explained in terms of the properties of individual ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Apr 17, 2008
From Colossal Storage Website:

Most all Blu-Ray / DVD Phase Change media uses ferroelectric Chalcogenide Ge2Sb2Te5 material.

The IC DVD/CD/MO/Blu-Ray Phase Change companies didn't know the media they were using was ferroelectric but only knew if they heated it up and cooled it down something happened to the surface of the chalcogenide material.

Colossal Storage will be the only drive in the world that will be able to read any Chalcogenide phase change disk with the capability of overwriting or infinitely rewriting data to any phase change disk by changing the internal molecular structure of the polarized atom dipole geometry without heat and cooling.

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.