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Ultrasonic characterization of materials

These research activities focus on new ultrasonic characterization methods for microelectronic or energetic efficiency applications. The studied structures have dimensions lower than the usual ultrasonic wavelength 

Porous silicon characterization

This work is carried out in a collaboration with the porous Si research group (Microelectronic research topic). The studied samples are porous silicon wafers obtained by electrochemical etching.

 

Figure 1 : Sample and micrography schema of studied porous silicon

A ultrasonic measurement technic of the etching depth and the porosity has been developed based on a comparison of theoretical and experimental spectra of the acoustic transmission coefficient through a bilayer stack (crystalline Si and porous Si).

Figure 2 : Theoretical and experimental transmission coefficient for porous silicon samples (a : etching depth of 115 mm porosity 40%, b : etching depth of 119 mm porosity 45%)

The interaction between surface acoustic waves (SAW) and porous silicon layer are also studied, in order to develop innovative surfacic acoustic wave sensors, where the porous silicon play both the role of sensitive and waveguide layers.

Proton membrane characterization

In collaboration with CEA Le Ripault, a technic of characterization of NAFION membranes is developp. The characterization of the thin membranes (typically 25 micrometers) requires a specific instrumentation (use of high ultrasonic frequencies, around 50MHz). In addition, a ‘Matching poursuit’ algorithm is adapted to determine the material properties, despite the strong overlap of the ultrasound echoes due to the small sample thickness in comparison with the wavelength.  


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