Serge Camou

Interface acoustic waves properties in some common crystal cuts

Interface acoustic waves (IAWs), also termed boundary waves, propagate at the interface between two solids. We present two IAW numerical analysis tools, inspired from well established surface acoustic wave (SAW) methods. First, the interface effective permittivity is derived for arbitrary piezoelectric solids and is used to estimate some basic parameters of IAWs. The harmonic admittance for an interface excitation is then derived from the interface effective permittivity, in much the same way the harmonic admittance for surface excitation is obtained from the (surface) effective permittivity. The finite electrode thickness is neglected in this problem analysis. The harmonic admittance is used to model propagation in the case when an infinite periodic interdigital transducer is located at the interface. Simulation results are commented upon for some usual piezoelectric material cuts and the paper outlines a modal selection specific to IAWs as compared with SAWs. The temperature dependence of the resonance frequency is also estimated.

Epitaxy of AIN and GaN thin films on silicon or sapphire for the development of high frequency saw devices

Abstract The increase in operating frequencies of telecommunication systems requires to use Surface Acoustic Wave (SAW) devices for filtering applications that propagate on “high velocity” subtrates like sapphire or even silicon. The excitation of SAW on such materials requires using thin piezoelectric layers deposited on their top surface, like AIN or GaN. This paper is devoted to the theoretical and experimental study of such material combinations. The theoretical models for multimaterial substrates are first presented. Experimental results are then reported, allowing to define the application field of AIN or GaN thin-film based devices.

A mixed FEM/BEM model to characterize surface waves on multilayer substrate

Propagation of elastic waves in piezoelectric films deposited on a given substrate is addressed in this paper. Realistic boundary conditions are applied using a mixed FEM/BEM representation of the problem. Data are extracted from this calculation to compute a elementary P-matrix, allowing to estimate theoretically the electrical response of a given transducer deposited on such substrates.

Theoretical calculations of Boundary Waves using effective permittivity and harmonic admittance approaches on various combination of materials

A theoretical analysis of Boundary Waves assuming infinitely thin excitation electrodes is presented in this paper. First results are shown using standard crystal cuts often used in acoustic wave devices. A comparison between Boundary Waves and Surface Acoustic Waves (without any mechanical effect of the metal strips) is performed, pointing out completely different acoustic wave properties in terms of reflexion coefficient, attenuation and phase velocity and electromechanical coupling factor. A special configuration [001]Si<110>/175 YX LiNbO/sub 3/ is studied, exhibiting a non-leaky boundary wave with a coupling factor close to 11% and a reflexion coefficient of 1.3%.