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Contribution au développement d'une méthode à ondes acoustiques de surface hautes fréquences dédiée à la caractérisation ultrasonore des structures à couches minces et au silicium mésoporeux

Abstract : This work is within the scope of characterization of thin layers, coatings and functional surfaces (thickness, elastic constants, porosity,…). Among the characterization methods, the ultrasonic methods using surface acoustic waves are particularly interesting. Indeed, the propagation of these waves is close to the surface of material and the energy is concentrated within a layer under the surface of about one wavelength thick. In the case of layer-on-substrate structures, SAWs become dispersive. By exploiting this dispersion over a wide frequency band, significant variations in SAW propagation velocity can be obtained and it becomes possible to characterize these structures with interesting precision on the mechanical and dimensional characteristics of the layers. On the other hand, the layers can be fragile, transparent and with a complex morphology. This explains why the choice of using IDT transducers for the generation of SAWs was considered. They have two advantages. Firstly, they are wide band and secondly they are used in the same way as conventional ultrasonic contact transducers. For the optimization of these SAW-IDT, particularly their band-width, it is necessary to study various IDT configurations by varying the number of electrodes, dimensions of the electrodes, their shapes and finger spacings. Finally, to generate SAW over a wide frequency range with sufficient displacement amplitude in order to characterize thin films and coatings, a time-space double chirp technique based on SAWIDT transducers was preferred. We have shown the potentialities of this approach by first characterizing metallic thin film structures with thicknesses of 50 nm and more, then continuous and discontinuous ultra-thin films (islands) with thicknesses of 5 to 20 nm as well as transparent sol-gel coatings. The possibility of characterizing mesoporous silicon layers has also been demonstrated.
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https://hal-uphf.archives-ouvertes.fr/tel-03385665
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Submitted on : Tuesday, October 19, 2021 - 3:29:36 PM
Last modification on : Tuesday, November 23, 2021 - 9:44:56 AM

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  • HAL Id : tel-03385665, version 1

Citation

Tahar Kadi. Contribution au développement d'une méthode à ondes acoustiques de surface hautes fréquences dédiée à la caractérisation ultrasonore des structures à couches minces et au silicium mésoporeux. Acoustique [physics.class-ph]. Université Polytechnique Hauts-de-France; Institut national des sciences appliquées Hauts-de-France, 2021. Français. ⟨NNT : 2021UPHF0023⟩. ⟨tel-03385665⟩

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