Nanotechnology extends battery life in mobile devices

Engineers at the University of Illinois have developed an ultra-low-power digital memory that is faster and uses 100 times less energy than similar memory – which could give portable devices much longer battery life between charges.

Companies have been exploring alternatives to flash memory in mobile devices which stores bits as charges, requiring high voltage and being relatively slow.

The team, led by electrical and computer engineering professor Eric Pop at the Beckman Institute for Advanced Science and Technology at Illinois, looked at faster but higher power phase-change materials (PCM), where a bit is stored in the resistance of the material.

Instead of conventional metal wires, the group used carbon nanotubes just a few nanometres in diameter to store the bits and lower the power per bit to 100 times less than existing PCM.

“The energy consumption is essentially scaled with the volume of the memory bit,” said graduate student Feng Xiong. “By using nanoscale contacts, we are able to achieve much smaller power consumption.”

To create a bit, the researchers placed a small amount of PCM in a nanoscale gap formed in the middle of a carbon nanotube. They could then switch the bit “on” and “off” by passing small currents through the nanotube.

The method has several advantages over metal wires, as nanotubes are much more stable than metal wires and the PCM is immune to accidental erasure from a passing scanner or magnet.

The low-power PCM bits could be used to give mobile devices a significant increase in battery life, and in larger applications could drastically cut the energy consumption and expense of data storage.

“Anytime you’re running an app, or storing MP3s, or streaming videos, it’s draining the battery,” said graduate student Albert Liao.

“The memory and the processor are working hard retrieving data. As people use their phones to place calls less and use them for computing more, improving the data storage and retrieval operations are important.”

Pop said: “I think anyone who is dealing with a lot of chargers and plugging things in every night can relate to wanting a cell phone or laptop whose batteries can last for weeks or months.

“This is also important for anything that has to operate on a battery, such as satellites, telecommunications equipment in remote locations, or any number of scientific and military applications.”

Pop believes that, along with improvements in display technology, the nanotube PCM memory could increase an iPhone’s energy efficiency so it could run for a longer time on a smaller battery, or even to the point where it could run simply by harvesting its own thermal, mechanical or solar energy.

The team is continuing to work to reduce power consumption and increase energy efficiency even beyond the groundbreaking savings they’ve already demonstrated.

“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 paper is available to read online at: http://www.sciencemag.org/content/early/2011/03/09/science.1201938.full.pdf

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