PhD Thesis

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« Development of new polymer materials for vibration micro-sensors ».

Author: A. Kachroudi
Advisor: S. Basrour
Co-advisor: F. Jomni
President of jury: A. Sylvestre
thesis reviewer(s): E. Defaÿ, F. Najar,
thesis examinator(s): M. Lallart,
These de Doctorat Université Grenoble Alpes
Speciality: Nanoélectronique et Nanotechnologies
Defense: December 14 2016
ISBN: 978-2-11-129221-5


The use of piezoelectric materials in mechanical vibration micro-sensors have been a promising alternative to have access to certain physical quantities (acceleration, force, displacement...etc). However, the rigidity of ceramics and semiconductors constitute a limit to their integration in the micro-sensors working at low frequencies or subjected to high deformations at low frequencies. The aim of this thesis is to develop new type of exible piezoelectric materials referred as piezo-electret based on polydimethylsiloxane (PDMS). First, a design based on analytical simulations steps were used to determine the geometric parameters of the structures allowing us to optimize the micro-sensors - gure of merit. This phase is followed by micro-fabrication step based on the molding process. The resulting structures are electrically charged by direct contact in order to implement the charges in micro-cavities and ensure the piezoelectric behavior. The second step concerns the piezoelectric characterizations of the obtained materials. The piezo-electret based on PDMS present high longitudinal piezoelectric c÷‑cients which are of 350pC/N in the inverse piezoelectric mode and of 430pC/N for the direct piezoelectric mode. We have shown that these materials maintain their piezoelectricity over a wide range of temperature [−25C,85C]. Finally, we have designed a sensor prototype incorporating these piezo-electrets. It provided a constant sensitivity of 385mV/g covering frequencies from 5Hz to 200Hz at 0.1g of acceleration. This prototype can be used as an energy harvester, it provided a constant power density of 1.3nW/mm3 for the same frequency range.

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