University of Illinois engineers have developed a form of ultra-low-power non-volatile memory could someday provide consumers with hand-held devices that go without recharging for weeks or even months.
The results of the study by a team of engineers, lead by assistant professor Eric Pop, was published late last week in Science Express, which posts selected papers in advance of publication in the print version of Science magazine.
The team has so far been able to store few hundred bits of data, but they hope to scale up production to create arrays of memory bits that can operate together. They also want to create multi-bit memory, not unlike today's multi-level cell (MLC) NAND flash-based solid state drives (SSDs) in order to achieve greater data density.
Phase change memory
The research is based on an existing technology known as phase change random access memory, or just phase change memory (PCM). However, instead of using metal wires as resisters, the research team used carbon nanotubes that are 10,000 times thinner than a human hair and that require far less power than standard PCM.
PCM products are being manufactured by very few companies today, having yet to catch on as a mainstream technology. Among the companies working with PCM are Intel, STMicroelectronics and Numonyx, which shipped its Omneo line of 128-Mbit NOR-compatible PCM products last year. Samsung last year announced a 512Mbit PCM RAM chip for use in mobile handsets.
PCM uses chalcogenide, a glassy substance containing silvery semiconductors, such as sulphur, selenium or tellurium. The semiconductors have a property that allows their physical state, the arrangement of their atoms, to be changed from crystalline to amorphous through the application of a small zap of electricity. The two states have very different electrical resistance properties that can be easily measured, making chalcogenide ideal for data storage.
The University of Illinois engineers said in order to create a bit of data using their new technology they place a small amount of PCM in a nanoscale gap formed in the middle of a carbon nanotube, which is 10 nanometers wide. They can switch the bit "on" and "off" by passing small currents through the nanotube.
They say their technology is faster than typical PCM and uses 100 times less energy, which offers portable devices much longer battery life. The engineers say they are working to further reduce power consumption by further improving energy efficiency.
"Even though we've taken one technology and shown that it can be improved by a factor of 100, we have not yet reached what is physically possible. We have not even tested the limits yet. I think we could lower power by at least another factor of 10," Pop said.
The nanotube PCM could increase a mobile device's energy efficiency to the point where a smartphone could run for a longer time on a smaller battery, or even to the point where it could be powered without a battery by simply by harvesting its own thermal, mechanical or solar energy, Pop said.
"I think anyone who is dealing with a lot of chargers and plugging things in every night can relate to a cell phone or laptop whose batteries can last for weeks or months," said Pop, who is also affiliated with the Beckman Institute for Advanced Science and Technology at Illinois.
The researchers noted that batteries today mostly power the display of a smart phone or ultra-portable laptop, though an increasing percentage is dedicated to memory.
"Anytime you're running an app, or storing MP3s, or streaming videos, it's draining the battery," said graduate student Albert Liao, a co-author of the upcoming report. "The memory and the processor are working hard retrieving data. As people use their phones less to place calls and more for computing, improving data storage and retrieval operations is important."
The team said the nanotube PCM could also be used to reduce power consumption on any device run by a battery, including satellites, remote telecommunications equipment, as well as a number of scientific and military applications.
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