Design, fabrication and characterization of wideband piezoelectric energy harvesters

Abstract

International audienceThere is nowadays a huge interest for piezoelectric vibration energy harvesters, in order to power wireless sensor networks’ nodes in industrial or natural environment. However, there are still several issues for these devices. First, as these scavengers are resonant, their resonance frequency has to match the dominant frequency in the surroundings to be efficient. As a consequence, an energy harvesting device with adaptable resonance frequency is needed to make this energy scavenging method more efficient [1]. Then, another problem of these scavengers is micro-fabrication: the ultimate goal is to have a system on chip with the sensors, the RF transceiver, the energy harvesters, low power electronics and a microcontroller. To be able to obtain such a chip, the fabrication process of the harvesters has to be CMOS compatible, to allow integration and batch fabrication of the harvesters and electronics.In this work, an innovative passive way of resonance frequency automatic tracking will be presented. We propose a new approach using mechanical non-linear behaviour of the system, so that the nonlinear system tracks the vibration frequency peak [2]. An experimentally verified frequency adaptability of over 36% for a clamped-clamped beam device at 2g (1g=9.81m.s-2) input acceleration is reported. We believe that the proposed solution is perfectly suited for piezoelectric energy harvesters.Moreover, new results of fabrication and characterization of piezoelectric micro- harvesters designed for a frequency of 200Hz and low input accelerations will be presented. We developed a process fully CMOS compatible for AlN (Aluminum Nitride) piezoelectric harvesters. A device of 3 mm3, fabricated with this process, harvests 620nW at 214 Hz for a low input acceleration of 0,17g. Under vacuum the figure of merit of this device is the best figure of merit published up to now. We are now waiting to characterize nonlinear devices fabricated with this process