Study on elastic energy distribution in layered structures for application to surface acoustic wave devices

The relative fraction r of the elastic energy of an acoustic mode localized in a supported film is shown to play an important role in some applications of layered structures such as electroelastic effect, gas sensing and acoustic characterization. Computer simulation of the parameter r as a function of the film thickness normalized to the acoustic wavelength is performed for different possible material combinations in accordance with Farnell-Adler's scheme. Some general features of the parameter r are discussed. Measurements of acoustic attenuation and temperature coefficient of delay, are shown to correlate with the behavior of this parameter for Rayleigh and Sezawa modes and for both conditions of slow film on fast substrate and fast film on slow substrate. The analysis and experiments have been carried out on layered structures made of AlN and ZnO films on glass, fused quartz, and Si substrates.