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

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them November 24th, 2017

NanoSummit in Luxembourg: single wall carbon nanotubes have entered our lives as we approach a nanoaugmented future November 23rd, 2017

JPK reports on the exciting research in the School of Medicine at Sungkyunkwan University (SKKU), Suwon, South Korea using the NanoWizard® ULTRA Speed AFM to understand the binding of transcription factor Sox2 with super enhancers November 23rd, 2017

Precision NanoSystems to host nanomedicines roundtable November 23rd, 2017

Govt.-Legislation/Regulation/Funding/Policy

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them November 24th, 2017

EC Project Aims at Creating and Commercializing Cyber-Physical-System Solutions November 14th, 2017

Nanobiotix presented new clinical and pre-clinical data confirming NBTXR3’s significant potential role in Immuno-Oncology at SITC Annual Meeting November 14th, 2017

Leti Joins DARPA-Funded Project to Develop Implantable Device for Restoring Vision November 9th, 2017

Chip Technology

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them November 24th, 2017

Quantum optics allows us to abandon expensive lasers in spectroscopy: Lomonosov Moscow State University scientists have invented a new method of spectroscopy November 21st, 2017

Nano Global, Arm Collaborate on Artificial Intelligence Chip to Drive Health Revolution by Capturing and Analyzing Molecular Data in Real Time November 21st, 2017

ICN2 researchers compute unprecedented values for spin lifetime anisotropy in graphene November 17th, 2017

Memory Technology

Injecting electrons jolts 2-D structure into new atomic pattern: Berkeley Lab study is first to show potential of energy-efficient next-gen electronic memory October 13th, 2017

First on-chip nanoscale optical quantum memory developed: Smallest-yet optical quantum memory device is a storage medium for optical quantum networks with the potential to be scaled up for commercial use September 11th, 2017

High-speed quantum memory for photons September 9th, 2017

Fast magnetic writing of data September 7th, 2017

Nanoelectronics

GLOBALFOUNDRIES, Fudan Team to Deliver Next Generation Dual Interface Smart Card November 14th, 2017

Leti Will Present 11 Papers and Host More-than-Moore Technologies Workshop November 14th, 2017

The next generation of power electronics? Gallium nitride doped with beryllium: How to cut down energy loss in power electronics? The right kind of doping November 9th, 2017

Researchers bring optical communication onto silicon chips: Ultrathin films of a semiconductor that emits and detects light can be stacked on top of silicon wafers October 23rd, 2017

Discoveries

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them November 24th, 2017

Fine felted nanotubes : Research team of Kiel University develops new composite material made of carbon nanotubes November 22nd, 2017

Quantum optics allows us to abandon expensive lasers in spectroscopy: Lomonosov Moscow State University scientists have invented a new method of spectroscopy November 21st, 2017

Nano-watch has steady hands November 21st, 2017

Announcements

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them November 24th, 2017

NanoSummit in Luxembourg: single wall carbon nanotubes have entered our lives as we approach a nanoaugmented future November 23rd, 2017

JPK reports on the exciting research in the School of Medicine at Sungkyunkwan University (SKKU), Suwon, South Korea using the NanoWizard® ULTRA Speed AFM to understand the binding of transcription factor Sox2 with super enhancers November 23rd, 2017

Precision NanoSystems to host nanomedicines roundtable November 23rd, 2017

Military

Math gets real in strong, lightweight structures: Rice University researchers use 3-D printers to turn century-old theory into complex schwarzites November 16th, 2017

Promising sensors for submarines, mines and spacecraft: MSU scientists are developing nanostructured gas sensors that would work at room temperature November 10th, 2017

Leti Joins DARPA-Funded Project to Develop Implantable Device for Restoring Vision November 9th, 2017

Nanoshells could deliver more chemo with fewer side effects: In vitro study verifies method for remotely triggering release of cancer drugs November 8th, 2017

Research partnerships

Nano Global, Arm Collaborate on Artificial Intelligence Chip to Drive Health Revolution by Capturing and Analyzing Molecular Data in Real Time November 21st, 2017

EC Project Aims at Creating and Commercializing Cyber-Physical-System Solutions November 14th, 2017

Leti Joins DARPA-Funded Project to Develop Implantable Device for Restoring Vision November 9th, 2017

Nanoshells could deliver more chemo with fewer side effects: In vitro study verifies method for remotely triggering release of cancer drugs November 8th, 2017

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



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project