Record power from harvester

IMEC in Europe claims to have achieved a new record for micromachined piezoelectric energy harvesters, now delivering an output of 60 µW.

The harvester can be made with a low-cost CMOS-compatible production process by using aluminium nitride (AIN) as the piezoelectric material.

The low resonance frequency of 500 Hz makes the device widely applicable. The output of 60 µW is sufficient to drive simple wireless sensors that intermittently transfer sensor readings to a master.

Potential applications include pressure monitoring systems or monitoring industrial equipment.

Energy harvesters convert ambient energy — light, heat or vibrations — into electricity. They are indispensable in situations where batteries cannot be replaced easily.

Examples are autonomous sensor networks that are distributed over large areas and in locations that are difficult to access.

This latest device is micromachined, converting vibration through a piezeoelectric transducer.

It can be used to generate energy for sensors in, for example, planes, vehicles or vibrating industrial equipment.

The output was measured with an input acceleration of 2 g at a resonant frequency of 500 Hz. It consists of a piezoelectric capacitor formed by a Pt electrode, an AIN piezoelectric layer and a top AI electrode.

The capacitor is fabricated on a cantilever which has a mass on its tip. When the harvester vibrates, the mass on the cantilever causes the piezoelectric layer to be stretched, inducing an electric current.

The use of AIN as piezoelectric material makes the device compatible with CMOS processes, allowing production at low cost.