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Researchers harness solar energy for sensor nodes

Posted: 04 Sep 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Fraunhofer IMS? sensor? SOLCHIP? solar energy? ASIC?

"We use special process steps to place a mini solar cell straight on sensor modules' silicon chips," noted Andreas Goehlich, who heads up the project for Fraunhofer IMS. This might sound easy at first, but it actually isn't. For one thing, the application specific integrated circuits (ASICs) on the silicon chip cannot be disturbed in any way by later steps in the process. ASICs could be termed the brain of the sensor module, facilitating its specific functions. They are manufactured on a piece of silicon in the course of several processing steps, including ion implantation, oxidisation or metal deposition. "The structures of ASICs are extremely sensitive, which makes subsequent processing extremely tricky," said Goehlich. "That's why we use a specially developed 'soft' processing technology that has already proved itself on a variety of different ASICs."

In opting for mini solar cells, the researchers from Duisburg are turning to a method that is becoming more and more established in the low-power sector in particular. Energy harvesting, as it is known, is about exploiting resources in the immediate vicinity to generate small amounts of power. This means that the sensor modules are their own mini power stations, independent of external sources of electricity. Potential energy resources include harnessing vibrations or differences in temperature. Goehlich, however, believes that solar cells have a few advantages over these solutions: "Light is almost always available over long periods of time. What's more, it is not subject to such great fluctuations in supply as other resources." Then there is the advantage that solar energy can be converted into electricity relatively easily.

Development work is focusing primarily on agricultural applications. For instance, wireless, energy-autonomous sensor networks known as smart dust could be distributed over large areas of farmland. Goehlich added: "You can picture it as simply scattering the sensor nodes over the field." These miniature smart helpers would then measure details such as the moisture in the soil or the level of sunlight and relay the data to a central interface. The farmer could then use the measurements to regulate the amount of watering or even to predict the expected crop yield. The technology is ready to be implemented and SOLCHIP Ltd is now taking care of marketing its first product.

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