The elastic properties of ZnO films deposited by rf magnetron sputtering on Al₂O₃ substrates have been analyzed by means of an acoustic investigation technique. The phase velocities of a spectrum of acoustic modes propagating along the layered structure have been measured and the results exploited for determining the complete set of elastic constants of the film. The effective constants of the film are lower than those of the bulk material by amounts which depend on the elastic constant considered and range from −1.2% for c₃₃ to −24.8% for c₁₁. The values obtained were used for determining the dispersion curves of acoustic modes propagating along ZnO layers deposited on fused quartz and silicon and showed good agreement with experimental results.

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AlN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity - the highest among all piezoelectric materials - together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of AlN films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed AlN films on diamond. SAW propagation on AlN/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted k/sup 2/ = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively comparable to those observed in strongly piezoelectric single crystals such as LiNbO/sub 3/, but with SAW velocities approximately two-fold higher. Experiments performed on AIN/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.