Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Penn researchers' study of phase change materials could lead to better computer memory

Abstract:
Memory devices for computers require a large collection of components that can switch between two states, which represent the 1's and 0's of binary language. Engineers hope to make next-generation chips with materials that distinguish between these states by physically rearranging their atoms into different phases. Researchers at the University of Pennsylvania have now provided new insight into how this phase change happens, which could help engineers make memory storage devices faster and more efficient.

Penn researchers' study of phase change materials could lead to better computer memory

Philadelphia, PA | Posted on June 22nd, 2012

The research was conducted by Ritesh Agarwal, associate professor in the Department of Materials Science and Engineering in Penn's School of Engineering and Applied Science, along with members of his research group. A.T. Charlie Johnson, professor in the Department of Physics and Astronomy in the School of Arts and Sciences, and Ju Li, now a professor of nuclear science and engineering at the Massachusetts Institute of Technology, also contributed to the study.

Their research was published in the journal Science.

"For many years there has been a push to find memory storage that is at once scalable, non-volatile and fast," Agarwal said. "Phase change materials could meet all of those criteria, but the problem is that we don't know much about how these materials actually work."

Some kinds of memory, like a computer's RAM, can switch between states very quickly, allowing for the computation necessary to run programs. But this kind of memory is "volatile" in that it needs a constant supply of power to maintain its states. Other kinds of memory, like the kind found on a flash drive, is non-volatile in that it retains its data even after the power is turned off. This kind of memory, however, has low switching speeds. Researchers have long attempted to find a "universal memory" which combines both non-volatility and high switching speeds, along with scalability, the ability to store large amounts of data.

While there are other contenders, phase change materials, or PCMs, are ideal candidates for universal memory. PCM storage devices are now starting to become commercially available, but their efficiency is hindered by the fact that the actual mechanics of their phase change are not well understood.

The phases these PCMs switch between are different arrangements of their internal atomic structure. They begin in a crystalline phase, where their atoms are in an ordered lattice but can switch to a disordered, amorphous phase. The two phases provide much different levels of resistance to electrical current, which is why they are useful for memory storage.

"When you have atoms arranged in a periodic lattice, electrons can flow very easily as they essentially know what to expect," Agarwal said. "But in the amorphous phase, there is no long-range order; there's no way to predict the position of atoms going from one part of the material to the other. This scatters the electrons, leading to very high resistance."

It has been generally believed that the only way to switch between these two states involved heating, which allows the atoms to move out of their lattice positions as the material briefly melts, and rapid cooling, or "quenching," which solidifies the material into the amorphous phase without giving its atoms the chance to re-crystallize.

"Now we have shown that there is a way to achieve this transition without melting the material," Agarwal said. "We show that short electrical pulses of a few hundred nanosecond duration gradually induce disorder in the material until it amorphizes."

Their advance was made possible by fashioning a PCM into thin nanowires, rather than a more bulky counterpart. This enabled the researchers to observe the phase change as it happened using a high-resolution transmission electron microscope. Earlier researchers could only look at cross sections of their bulkier PCMs after the switching process was over.

By looking at the change in "real time," the Penn researchers could see what effect the electrical pulses were having at an atomic level of detail.

"The pulses create 'dislocations,' which are planes of atoms removed from the crystal pattern, disrupting the order locally on an atomic length scale," said Pavan Nukala, a co-author and member of the Agarwal group. "As we apply more and more pulses, the number of these dislocations start to increase."

"Eventually, the dislocations start to move down the nanowire in the direction of the current," Agarwal said. "At certain point, the number and density of dislocations becomes so huge that they jam in one spot."

Like a traffic jam on a highway, the dislocations continue to pile up at that spot as more and more move down the length of the nanowire. At a critical point, the increasing disorder causes the material to amorphize the wire at the location of the jam.

The amorphous region, which always forms at the point of the jam and cuts through the entire cross section of the nanowire, is proof that this dislocation-based mechanism is fundamentally different from the melt-quench mechanism. With melting, the amorphous part should have spread along the surface of the material, rather than cut through its cross section.

"Having the surface amorphize doesn't give us high resistance ratios because current can still travel through the crystalline interior," Agarwal said. "Cutting across the entire nanowire completely blocks the current, making for a much better memory devices.

"With surface melting, you can increase the resistance a few times at most, but our observation that the resistance increased by two or three orders of magnitude is another evidence of the new mechanism."

The PCM that researchers used in their study contained long tellurium-telluriumbonds that can easily slide apart, facilitating the planar dislocations that cause the material to amorphize.

The material, along with a better understanding of the mechanics of its phase change, will provide a starting point for picking the right qualities for future PCMs.

"If people think that melting is the only mechanism for phase change, then all the emphasis will be on making materials with low melting temperatures," Agarwal said. "But we've shown that we need to do something else, which is to also look for materials that can create dislocations easily."

In addition to Agarwal, Li, Johnson and Nukala, the research was conducted by Sung-Wook Nam, Hee-Suk Chung, Yu Chieh Lo, Liang Qi, Ye Lu and Yeonwoong Jung, all of the Department of Materials Science and Engineering in Penn Engineering.

The research was supported by Penn's Nano/Bio Interface Center, the National Science Foundation, the Office of Naval Research and MIT's Materials Structures and Devices Center.

####

For more information, please click here

Contacts:
Evan Lerner

215-573-6604

Copyright © University of Pennsylvania

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Getting electrons to move in a semiconductor: Gallium oxide shows high electron mobility, making it promising for better and cheaper devices April 24th, 2018

JPK reports on research of the Mestroni Lab at the University of Colorado Denver which use the JPK NanoWizardŽ AFM to help in the characterization of cardiomyopathies April 24th, 2018

Organic solar cells reach record efficiency, benchmark for commercialization April 23rd, 2018

Remote-control shoots laser at nano-gold to turn on cancer-killing immune cells April 20th, 2018

Govt.-Legislation/Regulation/Funding/Policy

Organic solar cells reach record efficiency, benchmark for commercialization April 23rd, 2018

Remote-control shoots laser at nano-gold to turn on cancer-killing immune cells April 20th, 2018

Salt boosts creation of 2-D materials: Rice University scientists show how salt lowers reaction temperatures to make novel materials April 18th, 2018

Quantum shift shows itself in coupled light and matter: Rice University scientists corral, quantify subtle movement in condensed matter system April 16th, 2018

Chip Technology

Getting electrons to move in a semiconductor: Gallium oxide shows high electron mobility, making it promising for better and cheaper devices April 24th, 2018

New qubit now works without breaks: A universal design for superconducting qubits has been created April 19th, 2018

Salt boosts creation of 2-D materials: Rice University scientists show how salt lowers reaction temperatures to make novel materials April 18th, 2018

When superconductivity disappears in the core of a quantum tube: By replacing the electrons with ultra-cold atoms, a group of physicists has created a perfectly clean material, unveiling new states of matter at the quantum level April 16th, 2018

Memory Technology

Researchers develop nanoparticle films for high-density data storage: April 3rd, 2018

Design approach developed for important new catalysts for energy conversion and storage: New method could aid in design of pharmaceuticals and optical and data storage materials March 21st, 2018

Unexpected effect could lead to lower-power memory, computing devices March 17th, 2018

The fine-tuning of two-dimensional materials March 1st, 2018

Nanoelectronics

Getting electrons to move in a semiconductor: Gallium oxide shows high electron mobility, making it promising for better and cheaper devices April 24th, 2018

New qubit now works without breaks: A universal design for superconducting qubits has been created April 19th, 2018

Non-toxic filamentous virus helps quickly dissipate heat generated by electronic devices April 4th, 2018

Ancient paper art, kirigami, poised to improve smart clothing: New research shows how paper-cutting can make ultra strong, stretchable electronics April 3rd, 2018

Discoveries

Getting electrons to move in a semiconductor: Gallium oxide shows high electron mobility, making it promising for better and cheaper devices April 24th, 2018

JPK reports on research of the Mestroni Lab at the University of Colorado Denver which use the JPK NanoWizardŽ AFM to help in the characterization of cardiomyopathies April 24th, 2018

Organic solar cells reach record efficiency, benchmark for commercialization April 23rd, 2018

Remote-control shoots laser at nano-gold to turn on cancer-killing immune cells April 20th, 2018

Announcements

Getting electrons to move in a semiconductor: Gallium oxide shows high electron mobility, making it promising for better and cheaper devices April 24th, 2018

JPK reports on research of the Mestroni Lab at the University of Colorado Denver which use the JPK NanoWizardŽ AFM to help in the characterization of cardiomyopathies April 24th, 2018

Organic solar cells reach record efficiency, benchmark for commercialization April 23rd, 2018

Remote-control shoots laser at nano-gold to turn on cancer-killing immune cells April 20th, 2018

Military

Organic solar cells reach record efficiency, benchmark for commercialization April 23rd, 2018

Quantum shift shows itself in coupled light and matter: Rice University scientists corral, quantify subtle movement in condensed matter system April 16th, 2018

New 4-D printer could reshape the world we live in March 20th, 2018

Imaging technique pulls plasmon data together: Rice University scientists' hyperspectral method analyzes many plasmonic nanoparticles in an instant March 16th, 2018

Research partnerships

New qubit now works without breaks: A universal design for superconducting qubits has been created April 19th, 2018

Salt boosts creation of 2-D materials: Rice University scientists show how salt lowers reaction temperatures to make novel materials April 18th, 2018

Psst! A whispering gallery for light boosts solar cells April 14th, 2018

Artificial intelligence accelerates discovery of metallic glass: Machine learning algorithms pinpoint new materials 200 times faster than previously possible April 13th, 2018

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project