If you can reduce the power needed to maintain memory on digital devices, you could extend the life of your battery. This is the promise offered by a team of electrical engineers at the University of Illinois.

The team has a form of ultra low power digital memory that is not only faster, but they say uses 100 times less energy. Eric Pop, an electrical and computer engineering professor, and graduate students David Estrada, Albert Liao, and Feng Xiong, lowered the power per bit by concentrating on size. Flash memory used in mobile devices stores bits as charge, which requires high programming voltages. As a faster alternative, higher power phase-change materials (PCM) come into play. PCM memory stores a bit in the resistance of the material, which is switchable.

Four Bits in On-Off StatesThe University group?s approach is an improvement over the existing PCM memory. They used carbon nanotubes, tiny tubes only a few nanometers in diameter, instead of standard-of-the industry metal wires. If you can imagine, the new material is 10,000 times smaller than a human hair. They show a schematic of four bits in various on/off states. The bit is made up of phase-change material with a size of about 10 nanometers with carbon nanotube electrodes.

"Carbon nanotubes are the smallest known electronic conductors," Pop said. Xiong explained: "They are better than any metal at delivering a little jolt of electricity to zap the PCM bit .The energy consumption is essentially scaled with the volume of the memory bit. By using nanoscale contacts, we are able to achieve much smaller power consumption."

Currently, for example, smart phones use about a watt of energy, whereas a laptop runs takes more than 25 watts. The display accounts for some of it, but more and more is being used for memory. The nanotube PCM memory could increase energy efficiency possibly to the point where it could use its own thermal, mechanical or solar energy without a battery.

University of Illinois Electrical Engineering Team. Clockwise: prof. Eric Pop, David Estrada, Albert Liao and Feng XiongLiao, one of the four co-authors of the article in Science Express says that when we use features beyond making calls, a phone?s memory and processor are very busy retrieving data. As people use their phones more for computing functions, improving the data storage and retrieval operations will become more important.

Beyond our mobile devices, the technology might be applied to reducing energy consumption in data storage or supercomputing centers. The question of how to accomplish three dimensional integration, the stacking of chips, just might be answered by low power memory.

Although testing has involved only a few hundred bits, the team wants to create arrays of memory bits that operate together. They also are striving for greater data density so that each physical PCM bit can program two data bits, or multi-bit memory.

Pop said: "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."