Clockwise from left: Rice professors Douglas Natelson and Lin Zhong, graduate students Zhengzong Sun and Jun Yao, and Professor James Tour.
“I’ve been told by industry professionals that if you’re not in the 3-D memory business in four years, you’re not going to be in the memory business. This is perfectly suited for that.” —James Tour
Breaking a Barrier
If you can’t accept a physical limitation, then push its boundaries.
The limitation, in this case, is the physical limits of miniaturization possible for today’s electronics. If Moore’s Law, which states the number of devices on a circuit doubles every 18 to 24 months, continues to hold true, our electronic devices will reach their smallest — and fastest — state in the very near future.
Graphic: Jun Yao
a charge. “Flash memory is going to hit a brick wall at about 20 nanometers,” Tour said. “But our technique is perfectly suited for sub10-nanometer circuits.” It also means layers of silicon-oxide memory can be stacked in tiny but capacious three-dimensional arrays. “I’ve been told by industry professionals that if you’re not in the 3-D memory business in four years, you’re not going to be in the memory business,” Tour said. Now, however, Rice University scientists have created the first two“This is perfectly suited for that.” terminal memory chips that use only silicon, one of the most common Silicon-oxide memory also is compatible with conventional transubstances on the planet, in a way that should be easily adaptable to sistor manufacturing technology. The circuits feature high on-off nanoelectronic manufacturing techniques and promises to extend the ratios, excellent endurance and fast switching — below 100 nanolimits of miniaturization. seconds — and they will be resistant to raLast year, researchers in the lab of Rice diation, which should make them suitable Professor James Tour showed how elecfor military and NASA applications. trical current could repeatedly break and Yao had a hard time convincing his reconnect 10-nanometer strips of graphite colleagues that silicon oxide alone could to create a robust, reliable memory “bit.” make a circuit even though it is, according At the time, they didn’t fully understand to Tour, the most-studied material in huwhy it worked so well, but that recently man history. “In research, if everyone nods changed thanks to a new collaboration by their heads, then it’s probably not that big,” the Rice labs of professors Tour, Douglas Yao said. “But if you do something and evNatelson and Lin Zhong, and it turns out eryone shakes their heads, and then you that you don’t need the carbon at all. prove it, it could be big.” Jun Yao, a graduate student in Tour’s Austin tech design company PrivaTran lab and primary author of a paper that A silicon-oxide memory chip in which silicon nanowire forms is testing a silicon-oxide chip with 1,000 appeared in the online edition of Nano when a charge is sent through the silicon oxide, creating a memory elements that was built in colLetters, confirmed his breakthrough idea laboration with the Tour lab. The company two-terminal resistive switch. when he sandwiched a layer of silicon oxis using the technology in several projects ide, an insulator, between semiconducting supported by the Army Research Office, National Science Foundation, sheets of polycrystalline silicon that served as the top and bottom Air Force Office of Scientific Research, and Navy Space and Naval electrodes. Applying a charge to the electrodes created a conductive Warfare Systems Command Small Business Innovation Research pathway and formed a chain of nanosized silicon crystals. The chain (SBIR) and Small Business Technology Transfer programs. can be repeatedly broken and reconnected by applying a pulse of Yao’s co-authors on the paper were Tour; Natelson, a Rice profesvarying voltage. The nanocrystal wires are as small as 5 nanometers sor of physics and astronomy; Zhong, assistant professor of electri(billionths of a meter) wide, far smaller than circuitry in even the most cal and computer engineering; and Zhengzong Sun, then a graduadvanced computers and electronic devices. ate student in Tour’s lab. The David and Lucile Packard Foundation, “The beauty is its simplicity,” said Tour, Rice’s T.T. and W.F. Chao the Texas Instruments Leadership University Program, the National Professor of Chemistry as well as a professor of mechanical engineerScience Foundation, PrivaTran and the Army Research Office SBIR ing and materials science and of computer science. That simplicity is Program supported the research. key to the technology’s scalability. Silicon oxide switches or memory locations require only two terminals, not three — as in flash memory —Mike Williams — because the physical process doesn’t require the device to hold Read the paper: ›› › ricemagazine.info/67 4
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