New 'FeTRAM' is promising computer memory technology

ScienceDaily (Sep. 27, 2011) — Researchers are developing a new type of computer memory that could be faster than the existing commercial memory and use far less power than flash memory devices.

The technology combines silicon nanowires with a "ferroelectric" polymer, a material that switches polarity when electric fields are applied, making possible a new type of ferroelectric transistor.

"It's in a very nascent stage," said doctoral student Saptarshi Das, who is working with Joerg Appenzeller, a professor of electrical and computer engineering and scientific director of nanoelectronics at Purdue's Birck Nanotechnology Center.

The ferroelectric transistor's changing polarity is read as 0 or 1, an operation needed for digital circuits to store information in binary code consisting of sequences of ones and zeroes. The new technology is called FeTRAM, for ferroelectric transistor random access memory.

"We've developed the theory and done the experiment and also showed how it works in a circuit," he said. Findings are detailed in a research paper that appeared this month in Nano Letters, published by the American Chemical Society.

The FeTRAM technology has nonvolatile storage, meaning it stays in memory after the computer is turned off. The devices have the potential to use 99 percent less energy than flash memory, a non-volatile computer storage chip and the predominant form of memory in the commercial market.

"However, our present device consumes more power because it is still not properly scaled," Das said. "For future generations of FeTRAM technologies one of the main objectives will be to reduce the power dissipation. They might also be much faster than another form of computer memory called SRAM."

The FeTRAM technology fulfills the three basic functions of computer memory: to write information, read the information and hold it for a long period of time.

"You want to hold memory as long as possible, 10 to 20 years, and you should be able to read and write as many times as possible," Das said. "It should also be low power to keep your laptop from getting too hot. And it needs to scale, meaning you can pack many devices into a very small area. The use of silicon nanowires along with this ferroelectric polymer has been motivated by these requirements."

The new technology also is compatible with industry manufacturing processes for complementary metal oxide semiconductors, or CMOS, used to produce computer chips. It has the potential to replace conventional memory systems.

A patent application has been filed for the concept.

The FeTRAMs are similar to state-of-the-art ferroelectric random access memories, FeRAMs, which are in commercial use but represent a relatively small part of the overall semiconductor market. Both use ferroelectric material to store information in a nonvolatile fashion, but unlike FeRAMS, the new technology allows for nondestructive readout, meaning information can be read without losing it.

This nondestructive readout is possible by storing information using a ferroelectric transistor instead of a capacitor, which is used in conventional FeRAMs.

This work was supported by the Nanotechnology Research Initiative (NRI) through Purdue's Network for Computational Nanotechnology (NCN), which is supported by National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Purdue University. The original article was written by Emil Venere.

Journal Reference:

Saptarshi Das, Joerg Appenzeller. FETRAM. An Organic Ferroelectric Material Based Novel Random Access Memory Cell. Nano Letters, 2011; 11 (9): 4003 DOI: 10.1021/nl2023993

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Shape memory materials ready for mass production

ScienceDaily (Sep. 27, 2011) — Materials that can remember their shape and switch from one form to another may sound like science fiction, they are actually real and already in use all around us. But the alloy used to produce shape memory materials, based on nickel and titanium is expensive. Some researchers have started looking for cheaper options.

Five years ago, Professor Mirko Gojic, a researcher at the University of Zagreb in Croatia, wondered what his small team of researchers could do to lower the price of 'smart metals': a type of high-tech materials that can remember their original cold-forged shape, returning the pre-deformed shape by heating -- a property that makes them crucial in a series of industries. The idea was there, but problems quickly aroused from lack of money and key equipment. Thanks to the support of EUREKA, the product is now almost finalised and could be rolled out within the next two years. Gojic thinks that this international research project he led could soon turn into commercial production of a cheaper alloy for use in aerospace engineering or electronics.

Shape memory alloys can be produced to many shapes and sizes for various uses. Although not as strong as steel, they are much more elastic and their properties allow them to adopt the needed shape when exposed to high temperatures. They are used in smart phones, robotics and for medical purposes. For example, nickel-titanium alloy balloons that expand and adapt to the shape of a blood vessel when exposed to body temperatures are used in stent grafts and surgery.

One of the key problems with manufacturing such materials is their high price. Gojic and his team embarked on producing a new, cheaper alloy, based on copper, whereas the most-used alloy is built on a half-half mix of titanium and nickel, known under its trade name Nitinol. 'It is also the most expensive alloy, so there is a lot of effort going into finding an economically viable alternative', says Gojic. The research project called RSSMA, for Rapidly Solidified Shape Memory Alloys, lasted three years.

"We are not the only ones to put our efforts into research on copper alloys, we contributed to the extent of the possibilities offered by our infrastructure and benefited greatly from collaborations with international partners." Trans-border cooperation between R&D partners is one of the pre-requisites to receive financial support from EUREKA.

The Croatian team did not have the facilities to produce the new alloy, but the EUREKA grant allowed them to grow an existing collaboration with colleagues from the Faculty of Mechanical Engineering at the University of Maribor, Slovenia who helped to produce the alloys, which were then tested and examined for their characteristics in Croatia. They also collaborated with colleagues from Montanuniversität Leoben in Austria, and the Faculty of Natural Science and Engineering, University of Ljubljana in Slovenia.

'It is difficult to know exactly how much cheaper the final product will be -- it is an important economic parameter to evaluate the success of the project -- and it depends partly on techniques used to produce the alloy, but it would certainly be a cost-effective alternative, as titanium and nickel are far more expensive raw materials than copper and aluminium.' Besides the economic requirements, materials used in the production of alloys also have to comply with a certain level of purity and hold specific properties in order to be worthwhile for the industry. 'Tests so far have shown that we are on the right way and we should be able to enter soon in the production phase', Gojic says.

"We have successfully reached the final stages of the research and testing, notably in setting up a process of 'continuous casting', which is crucial for commercial production," he says. "It is important because it allows you to get an important quantity of semi-product, you can make it without interruptions, allowing for mass production, as it is done with other common metallic materials, such as steel."

The next step will be to pursue research, aiming to have a finalised product within the next one and a half years, followed by the construction of a pilot plant and then finally the take-off of the commercial production. If the next stage of the research goes well it should lead rapidly to the creation of a spin-off pilot firm to manufacture the new alloy. 'This would require more funding and I am considering applying for a further grant that would help us get to the pilot stage, which could then eventually lead to industrial scale manufacturing of the new, cheaper alloy.'

The new alloy has great commercial potential, it would mainly be used in electronics and mechanical industries, since it does not hold the biocompatibility properties of nickel and titanium. It might also find use in the booming market of smartphones and high-tech gadgets. "It would not have been possible for us to improve our knowledge and competencies without EUREKA," Gojic admits.

The grant also allowed the team to put money towards buying new equipment, such as a scanning electronic microscope and equipment for thermal analysis which was important in studying the properties of the alloys developed during the research project. Financing for the new equipment several sources, but the team had to make their own initial investment in order to be granted access to it, and EUREKA allowed them to do so. The team now continues to use this new equipment to develop the project further but also for new research activities in the field of smart materials.

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Note: If no author is given, the source is cited instead.

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New 'FeTRAM' is promising computer memory technology

ScienceDaily (Sep. 27, 2011) — Researchers are developing a new type of computer memory that could be faster than the existing commercial memory and use far less power than flash memory devices.

The technology combines silicon nanowires with a "ferroelectric" polymer, a material that switches polarity when electric fields are applied, making possible a new type of ferroelectric transistor.

"It's in a very nascent stage," said doctoral student Saptarshi Das, who is working with Joerg Appenzeller, a professor of electrical and computer engineering and scientific director of nanoelectronics at Purdue's Birck Nanotechnology Center.

The ferroelectric transistor's changing polarity is read as 0 or 1, an operation needed for digital circuits to store information in binary code consisting of sequences of ones and zeroes. The new technology is called FeTRAM, for ferroelectric transistor random access memory.

"We've developed the theory and done the experiment and also showed how it works in a circuit," he said. Findings are detailed in a research paper that appeared this month in Nano Letters, published by the American Chemical Society.

The FeTRAM technology has nonvolatile storage, meaning it stays in memory after the computer is turned off. The devices have the potential to use 99 percent less energy than flash memory, a non-volatile computer storage chip and the predominant form of memory in the commercial market.

"However, our present device consumes more power because it is still not properly scaled," Das said. "For future generations of FeTRAM technologies one of the main objectives will be to reduce the power dissipation. They might also be much faster than another form of computer memory called SRAM."

The FeTRAM technology fulfills the three basic functions of computer memory: to write information, read the information and hold it for a long period of time.

"You want to hold memory as long as possible, 10 to 20 years, and you should be able to read and write as many times as possible," Das said. "It should also be low power to keep your laptop from getting too hot. And it needs to scale, meaning you can pack many devices into a very small area. The use of silicon nanowires along with this ferroelectric polymer has been motivated by these requirements."

The new technology also is compatible with industry manufacturing processes for complementary metal oxide semiconductors, or CMOS, used to produce computer chips. It has the potential to replace conventional memory systems.

A patent application has been filed for the concept.

The FeTRAMs are similar to state-of-the-art ferroelectric random access memories, FeRAMs, which are in commercial use but represent a relatively small part of the overall semiconductor market. Both use ferroelectric material to store information in a nonvolatile fashion, but unlike FeRAMS, the new technology allows for nondestructive readout, meaning information can be read without losing it.

This nondestructive readout is possible by storing information using a ferroelectric transistor instead of a capacitor, which is used in conventional FeRAMs.

This work was supported by the Nanotechnology Research Initiative (NRI) through Purdue's Network for Computational Nanotechnology (NCN), which is supported by National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Purdue University. The original article was written by Emil Venere.

Journal Reference:

Saptarshi Das, Joerg Appenzeller. FETRAM. An Organic Ferroelectric Material Based Novel Random Access Memory Cell. Nano Letters, 2011; 11 (9): 4003 DOI: 10.1021/nl2023993

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Shape memory materials ready for mass production

ScienceDaily (Sep. 27, 2011) — Materials that can remember their shape and switch from one form to another may sound like science fiction, they are actually real and already in use all around us. But the alloy used to produce shape memory materials, based on nickel and titanium is expensive. Some researchers have started looking for cheaper options.

Five years ago, Professor Mirko Gojic, a researcher at the University of Zagreb in Croatia, wondered what his small team of researchers could do to lower the price of 'smart metals': a type of high-tech materials that can remember their original cold-forged shape, returning the pre-deformed shape by heating -- a property that makes them crucial in a series of industries. The idea was there, but problems quickly aroused from lack of money and key equipment. Thanks to the support of EUREKA, the product is now almost finalised and could be rolled out within the next two years. Gojic thinks that this international research project he led could soon turn into commercial production of a cheaper alloy for use in aerospace engineering or electronics.

Shape memory alloys can be produced to many shapes and sizes for various uses. Although not as strong as steel, they are much more elastic and their properties allow them to adopt the needed shape when exposed to high temperatures. They are used in smart phones, robotics and for medical purposes. For example, nickel-titanium alloy balloons that expand and adapt to the shape of a blood vessel when exposed to body temperatures are used in stent grafts and surgery.

One of the key problems with manufacturing such materials is their high price. Gojic and his team embarked on producing a new, cheaper alloy, based on copper, whereas the most-used alloy is built on a half-half mix of titanium and nickel, known under its trade name Nitinol. 'It is also the most expensive alloy, so there is a lot of effort going into finding an economically viable alternative', says Gojic. The research project called RSSMA, for Rapidly Solidified Shape Memory Alloys, lasted three years.

"We are not the only ones to put our efforts into research on copper alloys, we contributed to the extent of the possibilities offered by our infrastructure and benefited greatly from collaborations with international partners." Trans-border cooperation between R&D partners is one of the pre-requisites to receive financial support from EUREKA.

The Croatian team did not have the facilities to produce the new alloy, but the EUREKA grant allowed them to grow an existing collaboration with colleagues from the Faculty of Mechanical Engineering at the University of Maribor, Slovenia who helped to produce the alloys, which were then tested and examined for their characteristics in Croatia. They also collaborated with colleagues from Montanuniversität Leoben in Austria, and the Faculty of Natural Science and Engineering, University of Ljubljana in Slovenia.

'It is difficult to know exactly how much cheaper the final product will be -- it is an important economic parameter to evaluate the success of the project -- and it depends partly on techniques used to produce the alloy, but it would certainly be a cost-effective alternative, as titanium and nickel are far more expensive raw materials than copper and aluminium.' Besides the economic requirements, materials used in the production of alloys also have to comply with a certain level of purity and hold specific properties in order to be worthwhile for the industry. 'Tests so far have shown that we are on the right way and we should be able to enter soon in the production phase', Gojic says.

"We have successfully reached the final stages of the research and testing, notably in setting up a process of 'continuous casting', which is crucial for commercial production," he says. "It is important because it allows you to get an important quantity of semi-product, you can make it without interruptions, allowing for mass production, as it is done with other common metallic materials, such as steel."

The next step will be to pursue research, aiming to have a finalised product within the next one and a half years, followed by the construction of a pilot plant and then finally the take-off of the commercial production. If the next stage of the research goes well it should lead rapidly to the creation of a spin-off pilot firm to manufacture the new alloy. 'This would require more funding and I am considering applying for a further grant that would help us get to the pilot stage, which could then eventually lead to industrial scale manufacturing of the new, cheaper alloy.'

The new alloy has great commercial potential, it would mainly be used in electronics and mechanical industries, since it does not hold the biocompatibility properties of nickel and titanium. It might also find use in the booming market of smartphones and high-tech gadgets. "It would not have been possible for us to improve our knowledge and competencies without EUREKA," Gojic admits.

The grant also allowed the team to put money towards buying new equipment, such as a scanning electronic microscope and equipment for thermal analysis which was important in studying the properties of the alloys developed during the research project. Financing for the new equipment several sources, but the team had to make their own initial investment in order to be granted access to it, and EUREKA allowed them to do so. The team now continues to use this new equipment to develop the project further but also for new research activities in the field of smart materials.

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Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Subatomic quantum memory in diamond demonstrated

ScienceDaily (June 28, 2011) — Physicists working at the University of California, Santa Barbara and the University of Konstanz in Germany have developed a breakthrough in the use of diamond in quantum physics, marking an important step toward quantum computing. The results are reported in this week's online edition of Nature Physics.

The physicists were able to coax the fragile quantum information contained within a single electron in diamond to move into an adjacent single nitrogen nucleus, and then back again using on-chip wiring.

"This ability is potentially useful to create an atomic-scale memory element in a quantum computer based on diamond, since the subatomic nuclear states are more isolated from destructive interactions with the outside world," said David Awschalom, senior author. Awschalom is director of UCSB's Center for Spintronics & Quantum Computation, professor of physics, electrical and computer engineering, and the Peter J. Clarke director of the California NanoSystems Institute.

Awschalom said the discovery shows the high-fidelity operation of a quantum mechanical gate at the atomic level, enabling the transfer of full quantum information to and from one electron spin and a single nuclear spin at room temperature. The process is scalable, and opens the door to new solid-state quantum device development.

Scientists have recently shown that it is possible to synthesize thousands of these single electron states with beams of nitrogen atoms, intentionally creating defects to trap the single electrons. "What makes this demonstration particularly exciting is that a nitrogen atom is a part of the defect itself, meaning that these sub-atomic memory elements automatically scale with the number of logical bits in the quantum computer," said lead author Greg Fuchs, a postdoctoral fellow at UCSB.

Rather than using logical elements like transistors to manipulate digital states like "0" or "1," a quantum computer needs logical elements capable of manipulating quantum states that may be "0" and "1" at the same time. Even at ambient temperature, these defects in diamond can do exactly that, and have recently become a leading candidate to form a quantum version of a transistor.

However, there are still major challenges to building a diamond-based quantum computer. One of these is finding a method to store quantum information in a scalable way. Unlike a conventional computer, where the memory and the processor are in two different physical locations, in this case they are integrated together, bit-for-bit.

"We knew that the nitrogen nuclear spin would be a good choice for a scalable quantum memory -- it was already there," said Fuchs. "The hard part was to transfer the state quickly, before it is lost to decoherence."

Awschalom explained: "A key breakthrough was to use a unique property of quantum physics -- that two quantum objects can, under special conditions, become mixed to form a new composite object." By mixing the quantum spin state of the electrons in the defect with the spin state of the nitrogen nucleus for a brief time -- less than 100 billionths of a second -- information that was originally encoded in the electrons is passed to the nucleus.

"The result is an extremely fast transfer of the quantum information to the long-lived nuclear spin, which could further enhance our capabilities to correct for errors during a quantum computation," said co-author Guido Burkard, a theoretical physicist at the University of Konstanz, who developed a model to understand the storage process.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Barbara, via EurekAlert!, a service of AAAS.

Journal Reference:

G. D. Fuchs, G. Burkard, P. V. Klimov, D. D. Awschalom. A quantum memory intrinsic to single nitrogen–vacancy centres in diamond. Nature Physics, 2011; DOI: 10.1038/nphys2026

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With an Artificial Memory Chip, Rats Can Remember and Forget At the Touch of a Button

Dr. Theodore Berger PR NEWSWIRE

A new brain implant tested on rats restored lost memories at the flick of a switch, heralding a possible treatment method for patients with Alzheimer’s disease, stroke or amnesia. Such a “neural prosthesis” could someday be used to facilitate the memory-forming process and help patients remember.

The device can mimic the brain’s own neural signals, thereby serving as a surrogate for a piece of the brain associated with forming memories. If there is sufficient neural activity to trace, the device can restore memories after they have been lost. If it’s used with a normal, functioning hippocampus, the device can even enhance memory.

In the study, scientists at Wake Forest University and the University of Southern California trained rats to learn a task, pressing one lever after another to receive water. In a series of tests, the rats pressed one lever and were then distracted. They had to remember which one they’d already pressed and therefore which lever to press next, left or right, in order to receive their reward.

The team attached electrodes to the rats’ brains, connected to two areas in the hippocampus, called CA1 and CA3. Prior research has shown that the hippocampus converts short-term memory into long-term memory. The team recorded the signals between these regions as the rats performed their tasks, and then they drugged the rats so that the hippocampus regions could not communicate. The rats forgot which lever to press next, said Theodore Berger, a biomedical engineering professor at USC and lead author of the study, which is published in the Journal of Neural Engineering.

“The rats still showed that they knew ‘when you press left first, then press right next time, and vice-versa,’” Berger said. “And they still knew in general to press levers for water, but they could only remember whether they had pressed left or right for 5-10 seconds.”

Then, the team made an artificial hippocampus, which could duplicate the normal neural signals between the CA1 and CA3 regions. They turned it on, and replayed the previously recorded signal from CA1 — like a recorded message from the brain. The rats remembered.

“Flip the switch on, and the rats remember. Flip it off, and the rats forget,” Berger said.

Although this is a long way from being tested in humans, the research shows that if there’s enough information about the neural coding of memories, the signal patterns can be recorded and duplicated, and restored later through a neural implant. This could be difficult to do in patients with severely limited memory, as the New York Times points out — there needs to be a memory trace that can be recorded and amplified. But for patients with dementia, enhancing the memory-formation process can be useful — remembering where you put the keys, for instance, or where the bathroom is located. Simple memories like those could keep people independent for longer periods.

The researchers want to test the device in monkeys next, according to USC.

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Hardware encryption developed for new computer memory technology

ScienceDaily (May 18, 2011) — Security concerns are one of the key obstacles to the adoption of new non-volatile main memory (NVMM) technology in next-generation computers, which would improve computer start times and boost memory capacity. But now researchers from North Carolina State University have developed new encryption hardware for use with NVMM to protect personal information and other data.

NVMM technologies, such as phase-change memory, hold great promise to replace conventional dynamic random access memory (DRAM) in the main memory of computers. NVMM would allow computers to start instantly, and can fit more memory into the same amount of space used by existing technologies. However, NVMM poses a security risk.

Conventional DRAM main memory does not store data once the computer is turned off. That means, for example, that it doesn't store your credit card number and password after an online shopping spree. NVMM, on the other hand, retains all user data in main memory even years after the computer is turned off. This feature could give criminals access to your personal information or other data if your laptop or smart phone were stolen. And, because the data in the NVMM is stored in main memory, it cannot be encrypted using software. Software cannot manage main memory functions, because software itself operates in main memory.

NC State researchers have developed a solution using a hardware encryption system called i-NVMM.

"We could use hardware to encrypt everything," explains Dr. Yan Solihin, associate professor of electrical and computer engineering at NC State and co-author of a paper describing i-NVMM, "but then the system would run very slowly -- because it would constantly be encrypting and decrypting data.

"Instead, we developed an algorithm to detect data that is likely not needed by the processor. This allows us to keep 78 percent of main memory encrypted during typical operation, and only slows the system's performance by 3.7 percent."

The i-NVMM tool has two additional benefits as well. First, its algorithm also detects idleness. That means any data not currently in use -- such as your credit card number -- is automatically encrypted. This makes i-NVMM even more secure than DRAM. Second, while 78 percent of the main memory is encrypted when the computer is in use, the remaining 22 percent is encrypted when the computer is powered down.

"Basically, unless someone accesses your computer while you're using it, all of your data is protected," Solihin says.

i-NVMM relies on a self-contained encryption engine that is incorporated into a computer's memory module -- and does not require changes to the computer's processors. That means it can be used with different processors and different systems.

"We're now seeking industry partners who are interested in this technology," Solihin says.

The paper, "i-NVMM: A Secure Non-Volatile Main Memory System with Incremental Encryption," will be presented June 6 at the International Symposium on Computer Architecture (ISCA) in San Jose, Calif. The paper was co-authored by Dr. Siddhartha Chhabra, a former Ph.D. student at NC State. The research was supported, in part, by the National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by North Carolina State University.

Note: If no author is given, the source is cited instead.

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View the original article here

Hardware encryption developed for new computer memory technology

ScienceDaily (May 18, 2011) — Security concerns are one of the key obstacles to the adoption of new non-volatile main memory (NVMM) technology in next-generation computers, which would improve computer start times and boost memory capacity. But now researchers from North Carolina State University have developed new encryption hardware for use with NVMM to protect personal information and other data.

NVMM technologies, such as phase-change memory, hold great promise to replace conventional dynamic random access memory (DRAM) in the main memory of computers. NVMM would allow computers to start instantly, and can fit more memory into the same amount of space used by existing technologies. However, NVMM poses a security risk.

Conventional DRAM main memory does not store data once the computer is turned off. That means, for example, that it doesn't store your credit card number and password after an online shopping spree. NVMM, on the other hand, retains all user data in main memory even years after the computer is turned off. This feature could give criminals access to your personal information or other data if your laptop or smart phone were stolen. And, because the data in the NVMM is stored in main memory, it cannot be encrypted using software. Software cannot manage main memory functions, because software itself operates in main memory.

NC State researchers have developed a solution using a hardware encryption system called i-NVMM.

"We could use hardware to encrypt everything," explains Dr. Yan Solihin, associate professor of electrical and computer engineering at NC State and co-author of a paper describing i-NVMM, "but then the system would run very slowly -- because it would constantly be encrypting and decrypting data.

"Instead, we developed an algorithm to detect data that is likely not needed by the processor. This allows us to keep 78 percent of main memory encrypted during typical operation, and only slows the system's performance by 3.7 percent."

The i-NVMM tool has two additional benefits as well. First, its algorithm also detects idleness. That means any data not currently in use -- such as your credit card number -- is automatically encrypted. This makes i-NVMM even more secure than DRAM. Second, while 78 percent of the main memory is encrypted when the computer is in use, the remaining 22 percent is encrypted when the computer is powered down.

"Basically, unless someone accesses your computer while you're using it, all of your data is protected," Solihin says.

i-NVMM relies on a self-contained encryption engine that is incorporated into a computer's memory module -- and does not require changes to the computer's processors. That means it can be used with different processors and different systems.

"We're now seeking industry partners who are interested in this technology," Solihin says.

The paper, "i-NVMM: A Secure Non-Volatile Main Memory System with Incremental Encryption," will be presented June 6 at the International Symposium on Computer Architecture (ISCA) in San Jose, Calif. The paper was co-authored by Dr. Siddhartha Chhabra, a former Ph.D. student at NC State. The research was supported, in part, by the National Science Foundation.

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Conducting ferroelectrics may be key to new electronic memory

ScienceDaily (Apr. 25, 2011) — Novel properties of ferroelectric materials discovered at the Department of Energy's Oak Ridge National Laboratory are moving scientists one step closer to realizing a new paradigm of electronic memory storage.

A new study led by ORNL's Peter Maksymovych and published in the American Chemical Society's Nano Letters revealed that contrary to previous assumptions, domain walls in ferroelectric materials act as dynamic conductors instead of static ones.

Domain walls, the separation zones only a few atoms wide between opposing states of polarization in ferroelectric materials, are known to be conducting, but the origin of the conductivity has remained unclear.

"Our measurements identified that subtle and microscopically reversible distortions or kinks in the domain wall are at the heart of the dynamic conductivity," Maksymovych said. "The domain wall in its equilibrium state is not a true conductor like a rigid piece of copper wire. When you start to distort it by applying an electric field, it becomes a much better conductor."

Ferroelectrics, a unique class of materials that respond to the application of an electric field by microscopically switching their polarization, are already used in applications including sonar, medical imaging, fuel injectors and many types of sensors.

Now, researchers want to push the boundaries of ferroelectrics by making use of the materials' properties in areas such as memory storage and nanoelectronics. Gaining a detailed understanding of electrical conductance in domain walls is seen as a crucial step toward these next generation applications.

"This study shows for the first time that the dynamics of these defects -- the domain walls -- are a much richer source of memory functionality," Maksymovych said. "It turns out you can dial in the level of the conductivity in the domain wall, making it a tunable, metastable, dynamic memory element."

The domain wall's tunable nature refers to its delayed response to changes in conductivity, where shutting off an electric field does not produce an immediate drop in conductance. Instead, the domain wall "remembers" the last level of conductance for a given period of time and then relaxes to its original state, a phenomenon known as memristance. This type of behavior is unlike traditional electronics, which rely on silicon transistors that act as on-off switches when electric fields are applied.

"Finding functionality intrinsic to nanoscale systems that can be controlled in a novel way is not a path to compete with silicon, but it suggests a viable alternative to silicon for a new paradigm in electronics," Maksymovych said.

The ORNL-led team focused on bismuth ferrite samples, but researchers expect that the observed properties of domain walls will hold true for similar materials.

"The resulting memristive-like behavior is likely to be general to ferroelectric domain walls in semiconducting ferroelectric and multiferroic materials," said ORNL co-author Sergei Kalinin.

The samples used in the study were provided by the University of California at Berkeley. Other authors are ORNL's Arthur Baddorf, Jan Seidel and Ramamoorthy Ramesh of Lawrence Berkeley National Laboratory and UC Berkeley, and Pennsylvania State University's Pingping Wu and Long-Qing Chen.

Part of this work was supported by the Center for Nanophase Materials Sciences at ORNL. 

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Peter Maksymovych, Jan Seidel, Ying Hao Chu, Pingping Wu, Arthur P. Baddorf, Long-Qing Chen, Sergei V. Kalinin, Ramamoorthy Ramesh. Dynamic Conductivity of Ferroelectric Domain Walls in BiFeO3. Nano Letters, 2011; : 110412163353015 DOI: 10.1021/nl104363x

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View the original article here