GHz frequency ZnO/Si SAW device.

The demand for high-frequency low-loss filters generates intensive research on innovative wave guide solutions. In this work, a GHz SAW device based on a ZnO/Si structure was fabricated using classical UV photolithography. The thickness of the piezoelectric thin film was optimized and a specific interdigital transducer structure was used to generate third and fifth harmonic guided waves at 2.5 GHz and 3.5 GHz, respectively, with an aluminum strip larger than 1 micrometer. Different modes have been measured and theoretically identified thanks to an advanced finite-element/boundary-elementbased model. Good agreement is found between theory and experiments. The high-frequency modes have been fully characterized, allowing for accurate design of SAW devices exploiting such modes.

High-frequency surface acoustic waves excited on thin-oriented LiNbO3 single-crystal layers transferred onto silicon.

The need for high-frequency, wide-band filters has instigated many developments based on combining thin piezoelectric films and high acoustic velocity materials (sapphire, diamond-like carbon, silicon, etc.) to ease the manufacture of devices operating above 2 GHz. In the present work, a technological process has been developed to achieve thin-oriented, single-crystal lithium niobate (LiNbO3) layers deposited on (100) silicon wafers for the fabrication of radio-frequency (RF) surface acoustic wave (SAW) devices. The use of such oriented thin films is expected to favor large coupling coefficients together with a good control of the layer properties, enabling one to chose the best combination of layer orientation to optimize the device. A theoretical analysis of the elastic wave assumed to propagate on such a combination of material is first exposed. Technological aspects then are described briefly. Experimental results are presented and compared to the state of art.

Prediction of the thermal sensitivity of surface acoustic waves excited under a periodic grating of electrodes.

The prediction of the temperature sensitivity of surface acoustic wave (SAW) devices still requires improvement because the nature of the implemented surface modes and the devices' complexity strongly change from the early basic Rayleigh-wave-based devices. To address this problem, a theoretical analysis and a numerical tool have been developed to predict the thermal dispersion of general electro-acoustic devices. The proposed model accounts for the electrode contribution to the frequency-temperature law. The computed thermal sensitivities are compared to experimental results for different kinds of substrates and waves.

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 case an infinite periodic interdigital transducer is located at the interface. Simulation results are commented upon for some usual piezoelectric material cuts and outline a modal selection specific to IAWs as compared with SAWs. The temperature dependence of the resonance frequency is also estimated.

A full 3D plane-wave-expansion model for 1-3 piezoelectric composite structures.

The plane-wave-expansion (PWE) approach dedicated to the simulation of periodic devices has been extended to 1-3 connectivity piezoelectric composite structures. The case of simple but actual piezoelectric composite structures is addressed, taking piezoelectricity, acoustic losses, and electrical excitation conditions rigorously into account. The material distribution is represented by using a bidimensional Fourier series and the electromechanical response is simulated using a Bloch-Floquet expansion together with the Fahmy-Adler formulation of the Christoffel problem. Application of the model to 1-3 connectivity piezoelectric composites is reported and compared to previously published analyses of this problem.