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IMEC Reports 40 Micro-Watt Energy Harvester from Micromachined Piezoelectric Material

June 21, 2007 by Jeff Shepard

IMEC announced that it has fabricated an energy harvester to generate energy from mechanical vibrations by using micromachining technology. Output power as high as 40µW was obtained, thereby achieving the range of required power for wireless sensor applications. The harvester comes with a model that can be used to optimize the device during design.

IMEC claims that energy harvesters, which transform ambient energy into electrical energy, are of great value for situations where batteries cannot be easily replaced. A typical example is autonomous sensor networks that are spread over large areas or placed in locations that are difficult to access. Vibration harvesters in general make use of electromagnetic, electrostatic or piezoelectric conversion to generate electrical power. IMEC and IMEC-NL developed, modeled and characterized a miniaturized vibration harvester based on a piezoelectric transducer.

For an input vibration with a resonance frequency of 1.8kHz and an amplitude of 180nm, a maximum experimental output power of 40µW was measured. This comes well in range of the amounts of power needed by wireless sensor applications, such as the pulse-oxymeter developed earlier by IMEC, operating from the Holst Centre in Eindhoven, the Netherlands.

"After demonstrating a battery-less pulse-oxymeter fully powered by a thermal scavenger, this is another encouraging result that brings us closer to seeing miniaturized scavengers in real-life applications," said Bert Gyselinckx, Program Director IMEC-NL at the Holst Centre. "We believe that first of such devices will see market introduction about 5 years from now and will become mainstream by the end of next decade."

The device consists of a piezoelectric capacitor formed by a Pt electrode, a PZT layer and a top Al electrode. This capacitor is fabricated on a cantilever that supports a mass on its tip. As the harvester is subjected to oscillations, the mass causes the piezoelectric layer to be stretched. By doing so, it induces an electrical power when an electrical load is connected to the device.

To optimize the proposed device concept, a model was generated to estimate the output power for a given design. The output power of the fabricated devices can be maximized by maximizing the quality factor Q (through a low parasitic dissipation) and the coupling between the electrical and mechanical part (GEMC – generalized electromechanical coupling factor). IMEC is seeking industrial partners for further joint research on the development and application of energy harvesters for wireless sensor nodes.