Pure polyurethane and nanocomposite carbon black (CB) polyurethane solutions were deposited by spin-coating on a silicon substrate using gold as the adhesion layer and electrode. Different test structures were achieved for electrical and mechanical characterizations. The incorporation of CB nanoparticles in the polyurethane matrix has a significant influence on the dielectric permittivity of the material with an increase of about one third of its value. The Young's modulus of PU and nanocomposite PU films was determined by different characterization methods. Nanoindentation experiments have pointed out a Young's modulus gradient through the film thickness. By performing mechanical tests (tensile, bulge, point deflection) on freestanding films, an average Young's modulus value of about 30 MPa was found as well as a residual stress value of about 0.4 MPa. However, no influence of the presence of the nanoparticles was found. Finally, several MEMS actuators were realized and characterized. At their fundamental resonance frequency, the actuation of the nanocomposite membranes is more efficient than that of pure polyurethane. However, the time constant of the material seems to provide a major barrier for the development of high-frequency PU-based micro-actuators.

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Abstract. Mechanical properties of freestanding electroplated gold thin films were studied in relationship to their geometrical and microstructural properties. Three different techniques of characterization were used: nanoindentation, bulge tests and microtensile tests. Results were compared to literature and also discussed according to physical phenomena related to the elaboration process of the specimens like seed layer exodiffusion or internal stress state. The observed plasticity and failure mechanisms were found to be in good agreement with the literature and are consistent with the microstructure. The measured Young's modulus is slightly higher than expected, and SIMS analysis is exploited to explain such a high value.