Engineers develop new energy-efficient computer memory using magnetic materials

Dec. 14, 2012 — By using electric voltage instead of a flowing electric current, researchers from UCLA's Henry Samueli School of Engineering and Applied Science have made major improvements to an ultra-fast, high-capacity class of computer memory known as magnetoresistive random access memory, or MRAM.

The UCLA team's improved memory, which they call MeRAM for magnetoelectric random access memory, has great potential to be used in future memory chips for almost all electronic applications, including smart-phones, tablets, computers and microprocessors, as well as for data storage, like the solid-state disks used in computers and large data centers.

MeRAM's key advantage over existing technologies is that it combines extraordinary low energy with very high density, high-speed reading and writing times, and non-volatility -- the ability to retain data when no power is applied, similar to hard disk drives and flash memory sticks, but MeRAM is much faster.

Currently, magnetic memory is based on a technology called spin-transfer torque (STT), which uses the magnetic property of electrons -- referred to as spin -- in addition to their charge. STT utilizes an electric current to move electrons to write data into the memory.

Yet while STT is superior in many respects to competing memory technologies, its electric current-based write mechanism still requires a certain amount of power, which means that it generates heat when data is written into it. In addition, its memory capacity is limited by how close to each other bits of data can be physically placed, a process which itself is limited by the currents required to write information. The low bit capacity, in turn, translates into a relatively large cost per bit, limiting STT's range of applications.

With MeRAM, the UCLA team has replaced STT's electric current with voltage to write data into the memory. This eliminates the need to move large numbers of electrons through wires and instead uses voltage -- the difference in electrical potential -- to switch the magnetic bits and write information into the memory. This has resulted in computer memory that generates much less heat, making it 10 to 1,000 times more energy-efficient. And the memory can be more than five-times as dense, with more bits of information stored in the same physical area, which also brings down the cost per bit.

The research team was led by principal investigator Kang L. Wang, UCLA's Raytheon Professor of Electrical Engineering, and included lead author Juan G. Alzate, an electrical engineering graduate student, and Pedram Khalili, a research associate in electrical engineering and project manager for the UCLA-DARPA research programs in non-volatile logic.

"The ability to switch nanoscale magnets using voltages is an exciting and fast-growing area of research in magnetism," Khalili said. "This work presents new insights into questions such as how to control the switching direction using voltage pulses, how to ensure that devices will work without needing external magnetic fields, and how to integrate them into high-density memory arrays.

"Once developed into a product," he added, "MeRAM's advantage over competing technologies will not be limited to its lower power dissipation, but equally importantly, it may allow for extremely dense MRAM. This can open up new application areas where low cost and high capacity are the main constraints."

Said Alzate: "The recent announcement of the first commercial chips for STT-RAM also opens the door for MeRAM, since our devices share a very similar set of materials and fabrication processes, maintaining compatibility with the current logic circuit technology of STT-RAM while alleviating the constrains on power and density."

The research was presented Dec. 12 in a paper called "Voltage-Induced Switching of Nanoscale Magnetic Tunnel Junctions" at the 2012 IEEE International Electron Devices Meeting in San Francisco, the semiconductor industry's "pre-eminent forum for reporting technological breakthroughs in the areas of semiconductor and electronic device technology."

MeRAM uses nanoscale structures called voltage-controlled magnet-insulator junctions, which have several layers stacked on top of each other, including two composed of magnetic materials. However, while one layer's magnetic direction is fixed, the other can be manipulated via an electric field. The devices are specially designed to be sensitive to electric fields. When the electric field is applied, it results in voltage -- a difference in electric potential between the two magnetic layers. This voltage accumulates or depletes the electrons at the surface of these layers, writing bits of information into the memory.

"Ultra-low-power spintronic devices such as this one have potential implications beyond the memory industry," Wang said. They can enable new instant-on electronic systems, where memory is integrated with logic and computing, thereby completely eliminating standby power and greatly enhancing their functionality."

The work was supported by the Defense Advanced Research Projects Agency (DARPA) NV Logic Program. Other authors included researchers from the UCLA Department of Electrical Engineering; UC Irvine's Department of Physics and Astronomy; Hitachi Global Storage Technologies (a Western Digital Company); and Singulus Technologies, of Germany.

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The above story is reprinted from materials provided by University of California - Los Angeles. The original article was written by Matthew Chin.

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Smartphones might soon develop emotional intelligence: Algorithm for speech-based emotion classification developed

Dec. 4, 2012 — If you think having your phone identify the nearest bus stop is cool, wait until it identifies your mood. New research by a team of engineers at the University of Rochester may soon make that possible. At the IEEE Workshop on Spoken Language Technology on Dec. 5, the researchers will describe a new computer program that gauges human feelings through speech, with substantially greater accuracy than existing approaches.

Surprisingly, the program doesn't look at the meaning of the words. "We actually used recordings of actors reading out the date of the month -- it really doesn't matter what they say, it's how they're saying it that we're interested in," said Wendi Heinzelman, professor of electrical and computer engineering.

Heinzelman explained that the program analyzes 12 features of speech, such as pitch and volume, to identify one of six emotions from a sound recording. And it achieves 81 percent accuracy -- a significant improvement on earlier studies that achieved only about 55 percent accuracy.

The research has already been used to develop a prototype of an app. The app displays either a happy or sad face after it records and analyzes the user's voice. It was built by one of Heinzelman's graduate students, Na Yang, during a summer internship at Microsoft Research. "The research is still in its early days," Heinzelman added, "but it is easy to envision a more complex app that could use this technology for everything from adjusting the colors displayed on your mobile to playing music fitting to how you're feeling after recording your voice."

Heinzelman and her team are collaborating with Rochester psychologists Melissa Sturge-Apple and Patrick Davies, who are currently studying the interactions between teenagers and their parents. "A reliable way of categorizing emotions could be very useful in our research,." Sturge-Apple said. "It would mean that a researcher doesn't have to listen to the conversations and manually input the emotion of different people at different stages."

Teaching a computer to understand emotions begins with recognizing how humans do so.

"You might hear someone speak and think 'oh, he sounds angry!' But what is it that makes you think that?" asks Sturge-Apple. She explained that emotion affects the way people speak by altering the volume, pitch and even the harmonics of their speech. "We don't pay attention to these features individually, we have just come to learn what angry sounds like -- particularly for people we know," she adds.

But for a computer to categorize emotion it needs to work with measurable quantities. So the researchers established 12 specific features in speech that were measured in each recording at short intervals. The researchers then categorized each of the recordings and used them to teach the computer program what "sad," "happy," "fearful," "disgusted," or "neutral" sound like.

The system then analyzed new recordings and tried to determine whether the voice in the recording portrayed any of the known emotions. If the computer program was unable to decide between two or more emotions, it just left that recording unclassified.

"We want to be confident that when the computer thinks the recorded speech reflects a particular emotion, it is very likely it is indeed portraying this emotion," Heinzelman explained.

Previous research has shown that emotion classification systems are highly speaker dependent; they work much better if the system is trained by the same voice it will analyze. "This is not ideal for a situation where you want to be able to just run an experiment on a group of people talking and interacting, like the parents and teenagers we work with," Sturge-Apple explained.

Their new results also confirm this finding. If the speech-based emotion classification is used on a voice different from the one that trained the system, the accuracy dropped from 81 percent to about 30 percent. The researchers are now looking at ways of minimizing this effect, for example, by training the system with a voice in the same age group and of the same gender. As Heinzelman said, "there are still challenges to be resolved if we want to use this system in an environment resembling a real-life situation, but we do know that the algorithm we developed is more effective than previous attempts."

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Scientists develop indium-free organic light-emitting diodes

Dec. 3, 2012 — Scientists at the U.S. Department of Energy's (DOE) Ames Laboratory have discovered new ways of using a well-known polymer in organic light emitting diodes (OLEDs), which could eliminate the need for an increasingly problematic and breakable metal-oxide used in screen displays in computers, televisions, and cell phones.

The metal-oxide, indium tin oxide (ITO), is a transparent conductor used as the anode for flat screen displays, and has been the standard for decades. Due to indium's limited supply, increasing cost and the increasing demand for its use in screen and lighting technologies, the U.S. Department of Energy has designated indium as "near-critical" in its assessment of materials vital to clean energy technology. Scientists have been working to find an energy efficient, cost effective substitute.

"There are not many materials that are both transparent and electrically conductive," said Joseph Shinar, an Ames Laboratory Senior Scientist. "One hundred percent of commercial display devices in the world use ITO as the transparent conducting electrode. There's been a big push for many years to find alternatives."

"Everybody is trying to find a replacement for ITO, many working with zinc oxide, another metal oxide. But here we are working towards something different, developing ways to use a conducting polymer," said Min Cai, a post-doctoral research scientist in the Ames Laboratory and the Dept. of Physics and Astronomy at Iowa State University.

The polymer's name is a mouthful of a word: poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate), known as PEDOT:PSS for short, and has been around for about 15 years. Until recently, the material wasn't sufficiently conductive or transparent enough to be a viable ITO substitute, Shinar said. But by using a multi-layering technique and special treatments, Cai and his fellow scientists were able to fabricate PEDOT:PSS OLEDs with vastly improved properties.

"Compared to an ITO anode device, the PEDOT:PSS device is at least 44 percent more efficient," said Cai. According to Joe Shinar, that gain in efficiency over ITO-based technology is the highest yet recorded.

The researchers used computer simulations to show that the enhanced performance is largely an effect of the difference in the optical properties between the polymer- and ITO-based devices.

Another key property of PEDOT:PSS is flexibility; using ITO in OLEDs defeats one of OLED's big pluses compared to conventional LED technology.

"OLEDs can be made on a flexible substrate, which is one of their principal advantages over LEDs. But ITO is ceramic in nature; it is brittle rather than flexible," said Ruth Shinar, a Senior Scientist at Iowa State University's Microelectronics Research Center.

The findings, co-authored by Joseph Shinar and Ruth Shinar along with Min Cai, Zhuo Ye, Teng Xiao, Rui Liu, Ying Chen, Robert W. Mayer, Rana Biswas, and Kai-Ming Ho, were recently published in Advanced Materials, one of the most prominent journals in materials science and engineering.

The research builds on continuing work to find more affordable and efficient manufacturing materials and processes for OLED manufacturing. An earlier paper published in Advanced Materials by Joseph Shinar and Ruth Shinar along with Min Cai , Teng Xiao , Emily Hellerich , and Ying Chendemonstrated the use of solution processing for small molecule-based OLEDs, which are typically constructed using a more expensive thermal evaporation deposition process.

The scientists' ongoing investigations into better materials and processes pave the way to more cost-efficient manufacturing and making OLED technology more widely available to consumers.

Joseph Shinar said that OLED televisions were already available to a limited high-end consumer, and that prices would come down as major manufacturers perfected their production processes. Both Samsung and LG exhibited a 55-inch OLED TV as a highlight feature of the 2012 Consumer Electronics Show in Las Vegas in January.

"We are already getting there with OLED televisions. Consumers will see them getting more affordable and more widely available in the very near future," said Joseph Shinar.

Shinar said the technology was also beginning to be used in lighting, in applications where diffuse light is preferred instead of point source lighting, and in architectural and art design.

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