Sol Chip – integrated solar energy harvesting for sensor nodes

Increased interest for sensor networks in various applications are forcing research groups to come up with ways to power the individual sensor modules remains a sticking point in these sorts of applications. While wiring and batteries can be viable solutions for small-scale projects, researchers at the Fraunhofer Institute came up with tiny solar cells that can directly be applied onto silicon chip sensors to reliably power wireless sensors networks.

Application Specific Integrated Circuits (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, oxidization or metal deposition. That makes the structures of ASICs extremely sensitive, thus increasing difficulty of subsequent processing.

ASICs on the silicon chip cannot be disturbed in any way by later steps in the process, but the researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems (Fraunhofer IMS) used a specially developed ‘soft’ processing technology that has already proved itself on a variety of different ASICs.

By opting for mini solar cells, the Fraunhofer researchers are turning to a method that is becoming more and more established in the low-power sector in particular. While there are other potential energy generating resources such as vibrations or differences in temperature, involved Fraunhofer researchers believe 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”, said Dr. Andreas Goehlich, who heads up the project for Fraunhofer IMS. “Then there is the advantage that solar energy can be converted into electricity relatively easily.”

Sensor networks made up of individual sensor modules that communicate wirelessly with one another have the capacity to measure local parameters over large areas, and then to pass these data on among sensor modules to a central station. This makes sensor networks suitable for a wide range of applications, whether for fire prevention or monitoring large areas of farmland.

The team is currently focusing on development of energy-autonomous sensor networks for agricultural applications, where it could be used to 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 Sol Chip Ltd. is going to place it as a product on the market.