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Surface wave propagation in thin silver films under residual stress

: Njeh, A.; Wieder, T.; Schneider, D.; Fuess, H.; Ben Ghozlen, M.H.

Zeitschrift für Naturforschung. A 57 (2002), Nr.1-2, S.58-64
ISSN: 0044-3166
ISSN: 0932-0784
Fraunhofer IWS ()
Laser-Akustik; mechanische Schichtcharakterisierung; Lasermeßtechnik; Ultraschall

Surface acoustic wave (SAW) investigations provide information on the elastic proper-ties of thin films. In the presence of residual stresses the phase velocity of the surface wave is changed. We have calculated this velocity change in deposited Ag films on (001) silicon us-ing the Farnell and Alder model. The change is to small to be observed in thin films. How-ever, since the wave velocity depends on the frequency, dispersion has been observed in the films. A non-linear description of the surface waves propagating along the [110]-direction of the substrate has been developed on the basis of the acoustoelasticity theory. The relative shift Dv/v is linear for large values of the excitation frequency. Experimentally, the dispersion curves were measured using a photoacoustic method. Good agreement has been found be-tween the experimental and calculated dispersion curves.