 Orlando Auciello uses this unique system, developed at Argonne, to understand ferroelectric thin film growth and interface processes critical to fabrication of smart cards based on ferroelectric random access memories. Individual atoms can be detected as they land on a substrate surface. |
Smaller, lighter computers and an end to worries about electrical failures sending hours of on-screen work into an inaccessible limbo mark the potential result of Argonne research on tiny ferroelectric crystals.
"Tiny" means billionths of a meter, or about 1/500th the width of a human hair. These nanomaterials behave differently than their larger bulk counterparts. Argonne researchers have learned that they are more chemically reactive, exhibit new electronic properties and can be used to create materials that are stronger, tougher and more resistant to friction and wear than bulk materials.
Improved nano-engineered ferroelectric crystals could realize a 50-year-old dream of creating nonvolatile random access memory (NVRAM). The first fruits of it can be seen in Sony's PlayStation 2 and in smart cards now in use in Brazil, China and Japan. A simple wave of a smart card identifies personnel or pays for gas or public transportation.
Computing applications
RAM – random access memory – is used when someone enters information or gives a command to the computer. It can be written to as well as read but - with standard commercial technology - holds its content only while powered by electricity.
Argonne materials scientists have created and are studying nanoscale crystals of ferroelectric materials that can be altered by an electrical field and retain any changes.
Ferroelectric materials – so called, because they behave similarly to ferromagnetic materials even though they don't generally contain iron – consist of crystals whose low symmetry causes spontaneous electrical polarization along one or more of their axes. The application of voltage can change this polarity. Ferroelectric crystals can also change mechanical to electrical energy– the piezoelectric effect – or electrical energy to optical effects.
A strong external electrical field can reverse the plus and minus poles of ferroelectric polarization. The crystals hold their orientation until forced to change by another applied electric field. Thus, they can be coded as binary memory, representing "zero" in one orientation and "one" in the other.
Because the crystals do not revert spontaneously, RAM made with them would not be erased should there be a power failure. Laptop computers would no longer need back-up batteries, permitting them to be made still smaller and lighter. There would be a similar impact on cell phones.
Achieving such permanence is a long-standing dream of the computer industry.
"Companies such as AT&T, Ford, IBM, RCA and Westinghouse Electric made serious efforts to develop non-volatile RAMs in the 1950s, but couldn't achieve commercial use," said Argonne researcher Orlando Auciello. "Back then, NVRAMs were based on expensive ferroelectric single crystals, which required substantial voltage to switch their polarity. This, and cross talk inherent in the then recently devised row matrix address concept, made them impractical.
"Working on the nanoscale changes this," said Auciello. "It means higher density memories with faster speeds and megabyte (the amount of memory needed to store one million characters of information) - or even gigabyte (one billion bytes) - capacity. It's not clear how soon such capacity will be available, but competition is heavy, stakes are high, and some companies claim they will have the first fruits of this research within two years."
Smart cards don't forget
Argonne scientists are using their expertise in ferroelectrics to improve smart cards. These are the size and shape of credit cards but contain ferroelectric memory that can carry substantial information, such as its bearer's medical history for use by doctors, pharmacists and even paramedics in an emergency. Unlike magnetic strips on credit cards, these memories do not come in contact with their readers and will not wear out.
Current smart cards carry about 250 kilobytes of memory. Argonne researchers are collaborating with the Colorado Springs, Colo., Symetrix Corp. to develop a higher capacity card with a more flexible and longer-lasting memory.
Nanomaterials have been studied at Argonne since the 1980s. They are now one of the hottest research topics worldwide. Several nanoscale materials research centers are being planned by the U.S. Department of Energy (DOE), with one likely to be built at Argonne.
Nanomaterials challenge researchers
The effort to understand ultra-small materials is on the frontier where physics, chemistry and biology meet. "Chemists work with atoms and molecules, moving from the smallest particles to larger ones, while physical scientists work from larger materials down," J. Murray Gibson, associate laboratory director for Argonne's Advanced Photon Source, said. "They come together as we approach the nanoscale.
"Materials behave differently in the range of size below 100 nanometers (billionths of a meter)," Gibson noted. Atomic and molecular clusters at this size may be different colors from the same elements or compounds in bulk. They become more chemically reactive and display new electronic properties. Objects assembled from them can be stronger and tougher than their bulk counterparts. However, the science that is the foundation for the technology is still not understood.
"Nanoscale ferroelectrics allow us to develop better multilayer capacitors, which could be used in even smaller cell phones," added Stephen Streiffer, a colleague of Auciello's. He also sees application in motors to power micro- and nano-electro-mechanical systems.
"Nature likes to put things together in certain ways," Streiffer said. "As we learn more about nanoscience - when we can control construction at the nanoscale - we will be able to engineer the nanoworld differently and create novel combinations. We should find new materials, things we can't even imagine yet."
Argonne's broad program in ferroelectrics includes making and studying the properties of ferroelectrics using a time-of-flight ion scattering and recoil spectroscopy system developed by Auciello and Argonne colleagues A.R. Krauss and D.M. Gruen in conjunction with J.A. Schultz of Ionwerks." Ferroelectrics, he said, are also investigated using state-of-the-art in-situ X-ray scattering techniques at Argonne's Advanced Photon Source, the nation's brightest source of hard X-rays for materials research, by a Materials Science Division team consisting of G.B. Stephenson, J.A. Eastman, C. Thompson (Northern Illinois/Argonne), Streiffer, and Auciello.
It is synergistic with a broader strength in complex oxide materials, including related high-temperature superconductors and thermal barrier coatings and colossal magnetoresistive materials.
Ferroelectrics is just one of the hot new areas in nanomaterials, Gibson said. Argonne's work with ultra-nanocrystalline diamond films for micromachines for medical, transportation, industrial and aerospace uses was featured in logos Vol. 18 No. 1. "Although many novel nanosize effects have been found in ferroelectrics, there are as many or more in magnets, superconductors, metals, etc.," said Gibson. "In addition, there are composite materials, where two or more of the above are combined, introducing proximity effects, which can be dominant on the nanoscale. The possibilities for creating new useful materials through nanotechnology are endless."
Closeness breeds material changes
Such proximity effects – changes in material behavior because the materials are so close – show up in giant magneto-resistance, a phenomenon discovered in 1988 and used in computer hard drives. Tiny magnetic bits are hard to read individually, but interleaved nanolayers of cobalt, copper, iron and chromium show substantial changes in resistance in magnetic fields because the layers are so close together. IBM and the magnetic recording industry have used this to create ultrasensitive hard-drive read mechanisms. "The nano-community looks at a wide range of phenomena," said Sam Bader, Argonne senior physicist and coordinator of a new research initiative in nanomagnetic research that DOE recently approved for funding at a rate of $1.2 million a year. "It includes atoms, molecules and small clusters, and carries forward some existing technologies - such as semiconductors - by understanding bulk materials from a micro-structural view.
"We want to know how properties change at the smaller scales and are finding new effects, some of which are commercially viable. Nanoscience draws some of its importance from how quickly we've been able to turn these into technological applications."
The nanomagnetism initiative provides an interdisciplinary framework to help stage the next advance in complex materials research. It takes a broad approach, working with materials that fall from around one micron (one millionth of a meter) in size to less than 10 nanometers. As the scale decreases, the dominant physics changes, and new materials, properties and applications emerge.
Bader suggested that the computer world might one day be based in magnetic properties instead of electrical. This might make it possible to build computers with architectures that could be restructured depending on the task of the moment. The same machine could be configured like a Macintosh for tasks that a Mac operating system performs best and like a PC when Windows OS is preferable.
Also possible could be magnetic configurations that would not be limited by binary logic, making them more like the human brain. "This is far away, but promising," Bader said.
Studies on the nanoscale could lead to better bulk magnets and more efficient motors with consequent savings in the use of fossil fuels. It may also become possible to incorporate magnetic molecules in polymers, creating plastics that could be used where traditional magnets cannot, for example in certain corrosive environments.
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