Helen Knight, technology reporter
Wireless sensor networks - otherwise known as smart dust - could generate enough energy to run themselves, thanks to the development of solar-powered microchips.
For the first time researchers have built a solar cell directly on top of a chip's microelectronics, allowing it to harvest energy from light without the need for a battery.
A team led by Jurriaan Schmitz at the University of Twente in Enschede in the Netherlands deposited layers of photovoltaic material onto a complementary metal oxide semiconductor (CMOS), of the type commonly used as sensors.
The team used conventional vapour deposition techniques employed widely in the electronics industry to deposit the solar cells. To ensure the microchip was not damaged during manufacturing, they chose amorphous silicon and copper-indium-gallium-selenide (CIGS) solar cells, as these can be processed at temperatures of 400 degrees Celsius or less.
The team found that, when added to the microchips, the photovoltaic materials had efficiencies of 5.2 and 7.1 per cent, respectively. When operating indoors, the cells were able to generate around 1 micro watt of electricity per square millimetre.
That's not enough to power a microchip in a cell phone or computer, but it is enough to power a CMOS chip, and at least double the amount generated by other techniques such as piezoelectrics, says Schmitz. When used in direct sunlight, the solar-powered chips can generate up to 70 micro watts of electricity per square millimetre.
"The chips are likely to be used in ubiquitous computing networks, where you are spreading sensors around," says Schmitz. "If you are going to put a lot of sensors in the field, you don't want to worry about replacing their batteries," he says.
Attaching the solar cells does not affect the operation of the semiconductor itself, he adds.
The team presented their work at the International Electron Devices Meeting in San Francisco last week.