Flexible piezoelectric AlN transducers buckled through package-induced preloading for mechanical energy harvesting

M Mariello,M De Vittorio,T.W.A Blad,F Guido,N Tolou,F Madaro,V.M Mastronardi,U Staufer

doi:10.1016/j.nanoen.2021.105986

Abstract

There is a high demand for novel flexible micro-devices for energy harvesting from low-frequency and random mechanical sources. The research of new functional designs is required to strategically enhance the performances and to increase the control on mechanical flexibility. In this work we report the fabrication and characterization of bi-stable and statically balanced thin-film piezoelectric transducers based on Aluminum Nitride (AlN). The device consists of a piezoelectric layer sandwiched between two thin Molybdenum electrodes that were deposited on a Kapton substrate by reactive sputtering and patterned by UV lithography. In order to improve the out-of-plane flexibility, the mechanical design is distinguished by a post-buckled flexure that introduces a negative stiffness to compensate the otherwise positive stiffness of the system. The buckling was introduced by a new method, called Package-Induced Preloading (PIP) where the mechanisms are laminated over a package with a geometry extending out-of-plane. The induced buckling resulted in bi-stable and statically balanced mechanisms which demonstrated an enhanced voltage output during a triggered snapping step. A preliminary study shows potential for the statically balanced designs and the PIP method for wind energy harvesting, revealing prospective applications and future improvements for the development of energy harvesters.

Highlights

Mechanical energy harvesting is a promising field that, in the last decades, has led to the development of novel micro-devices for scav enging energy from unexploited sources, such as ambient vibrations, tiny motions of the human body or low-speed fluid flows
In this work we report the fabrication and characterization of bi-stable and statically balanced thin-film piezoelectric transducers based on Aluminum Nitride (AlN)
The buckling was introduced by a new method, called Package-Induced Preloading (PIP) where the mechanisms are laminated over a package with a geometry extending out-of-plane

Summary

Introduction

Mechanical energy harvesting is a promising field that, in the last decades, has led to the development of novel micro-devices for scav enging energy from unexploited sources, such as ambient vibrations, tiny motions of the human body or low-speed fluid flows. Among well-known piezoelectric thin films (Lead-Zirconium-Titanate, Pb(ZrxTi1−x)O3, [PZT], Zink-Oxide [ZnO], Poly(vinylidene fluoride) [PVDF], Lithium Niobite [LiNbO3]), Aluminium Nitride [AlN] is a suitable candidate for the development of energy harvesters for low-frequency mechanical sources due to its CMOS-fabrication compatibility, the good piezoelectric properties [12,13,14,15], and the ability to be deposited as very thin film (~1 μm) onto soft/flexible [16,17,18,19,20,21] substrates by relatively low-temperature processes such as reactive sputtering [22]. For low-frequency high- amplitude motion, resonance may not be optimal for the highest efficiency due to the limited available space [25,28]

Methods

Results

Conclusion