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This paper focuses on the improvement of a relaxor ferroelectric terpolymer, i.e., poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)], filled with a bis(2-ethylhexyl) phthalate (DEHP). The developed material gave rise to a significantly increased longitudinal electrostrictive strain, as well as an increased mechanical energy density under a relatively low electric field. These features were attributed to the considerably enhanced dielectric permittivity and a decreased Young modulus as a result of the introduction of only small DEHP plasticizer molecules. In addition, the plasticizer-filled terpolymer only exhibited a slight decrease of the dielectric breakdown strength, which was a great advantage with respect to the traditional polymer-based electrostrictive composites. More importantly, the approach proposed herein is promising for the future development and scale-up of new high-performance electrostrictive dielectrics under low applied electrical fields through modification simply by blending with a low-cost plasticizer. An experimental demonstration based on a flexible micro-fluidic application is described at the end of this paper, confirming the attractive characteristics of the proposed materials as well as the feasibility of integrating them as micro-actuators in small-scale devices.

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International audienceThe aim of this work is to compare several methods for the determination of very thin films Young's modulus and stress state: the nanoindentation test, the bulge test and the point-deflection method. The tested structures were silicon nitride and silicon nitride/silicon oxide bilayer membranes with different shapes (square or rectangular) and dimensions (from 1 mm to 3 mm). We report new experimental results on submicron thick dielectric membranes with thicknesses down to 100 nm. A Young's modulus of 217 14 GPa have been found for silicon nitride membranes with a residual stress of 411 30 MPa using the bulge test. Using nanoindentation experiments, a Young's modulus higher than 190 GPa has been estimated. The bulge test is still valid for the studied high dimension to thickness ratio membranes and more appropriate to determine the Young's modulus. A mixture law was shown to be possibly applied for SiN/SiO bilayer membranes for the Young's modulus and stress determination. The point deflection method is limited by the very low stiffness of these structures and only the residual stress can be accurately extracted. As the Young's modulus and membrane geometry have no significant influence on the stress determination by means of the point deflection method for the studied membranes (with a high lateral dimension to thickness ratio), more reliable results have been obtained such as 487 40 MPa using an AFM cantilever for load-deflection experiments, for SiN thin films

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