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Integration of P(VDF–TrFE) films into strain-based microsystem designs
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2011 Smart Mater. Struct. 20 087001
(http://iopscience.iop.org/0964-1726/20/8/087001)
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IOP PUBLISHING |
SMART MATERIALS AND STRUCTURES |
Smart Mater. Struct. 20 (2011) 087001 (8pp) |
doi:10.1088/0964-1726/20/8/087001 |
TECHNICAL NOTE
Integration of P(VDF–TrFE) films into strain-based microsystem designs
Mark Roscher,¨ Johannes Scheeren, Benedikt Funke
and Ulrich Bottger¨1
Institute of Materials in Electrical Engineering and Information Technology, RWTH Aachen
University, D-52074 Aachen, Germany
E-mail: boettger@iwe.rwth-aachen.de
Received 13 December 2010, in final form 13 May 2011
Published 28 June 2011
Online at stacks.iop.org/SMS/20/087001
Abstract
The eligibility of poly(vinylidene fluoride–trifluoroethylene) films for microsystem integration has been investigated with respect to strongly strain-reliant device designs such as for example vibration-based piezoelectric energy harvesting devices. Due to their ability to withstand extraordinary elongations, the integration of polymeric materials into appropriately designed devices is exceptionally promising and has been accordingly assessed. However, polymeric films often suffer from an immense sensitivity to many of the processing steps used during microfabrication like lithography. This contribution will show that this is not necessarily so. Functional films have been prepared and comprehensively characterized providing a benchmark for processing induced material deterioration. Further, the damage potential emanating from consecutive processing and lithographical pattern transfer steps was focused on. The inferred course of action was finally applied to the fabrication and vibrational proof of concept of a microsystem based on the polymeric material system poly(vinylidene fluoride–trifluoroethylene).
(Some figures in this article are in colour only in the electronic version)
1. Introduction
Research on new technologies thrives which may be used to harvest energy from ambient sources. One of the most auspicious is the conversion of ubiquitous mechanical vibrations into electrical energy by a perpetually driven piezoelectric transducer. In the past, several publications dealt with or reviewed the respective theoretical and microsystem design questions [1–5]. Until now, the development of piezoelectric energy harvesting devices has largely evolved from first generation large-scale demonstrators and will be further propelled by the possibility for onchip integration [6–9]. However, several unresolved matters remain. Of specific importance is the adjustment of the device’s natural frequency toward the regime of about one hundred Hertz under reduced spatial dimensions as well as the adaptation to randomly fluctuating input vibrations. While
1 Author to whom any correspondence should be addressed.
the former point can be addressed by simply scaling the moving mass, the latter may render nonlinear broad-bandwidth resonance devices desirable. Several publications focus on using nonlinear vibrations. For example, designs that work with stochastic excitations [10, 11] or deliberately incorporate nonlinear behavior [8, 12–14] have been presented. An intriguing characteristic of some of the presented designs is the fact that for comparatively low vibration amplitudes the typical beam bending loading is replaced by a homogeneous stretching of the suspending beams. However, ceramic piezoelectric materials such as for example lead-zirconate-titanate which are almost exclusively used to date are very prone to tension induced material failure thus limiting the obtainable vibration amplitudes. As this is a pivotal design criterion we propose using P(VDF–TrFE) as one of the most promising polymeric substances known to exhibit piezoelectricity.
P(VDF–TrFE) is easy to deposit and well known in the literature [15, 16]. While the intensity of the electromechanical coupling is significantly weaker than
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