A research group with members from the University of Freiburg (Germany) and semiconductor vendor Micronas AG has integrated a fuel cell array on a chip. The device could power autonomous microsystems, also known as ‘smart dust’.
The chip has 42 microscale fuel cells on a CMOS device plus four cells to power the control circuitry necessary to maintain a constant 3.3-V output voltage. The semiconductor structures were fabricated using a standard CMOS process, while the fuel cell elements, consisting of a palladium layer for H2 storage, a cathode and a membrane, were added in a post-process spin-on, according to Micronas project leader Karl Hoffmann.
Hoffmann said that one of the challenges was to intelligently interconnect the fuel cells in a way that allows the control circuitry to keep the output as stable as possible during the lifetime of the device. With several elements in parallel and in series, it is much easier to keep the voltage and current constant.
With a lifetime of about one year at nominal load in the triple-digit microwatt range, the device could eventually power smart autonomous systems in applications where no conventional power source is available. In Hoffmann’s view, energy harvesting devices and the chip-level fuel cell are not mutually competitive, but can instead be regarded as complimentary technologies, For instance, the fuel cell could be used as a power buffer for periods when energy harvesting methods don't generate enough power.
According to Hoffmann, the technology is suitable for more than just exotic applications. For instance, it could be used for mundane tasks such a building monitoring.
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