Guided Lamb Wave Electroacoustic Devices on Micromachined AlN/Al Plates

An electroacoustic micro-device based on the propagation of guided acoustic Lamb waves in AlN/Al plate is described. The AlN thin film is deposited by sputtering technique, optimized to achieve a high degree of orientation (rocking curve full-width at half-maximum approximate to 3.5 degrees) of the c-axis perpendicular to the plate surface. The AlN plate is micromachined using anisotropic reactive ion etching (RIE), followed by isotropic RIE to remove the silicon underlayer. Simulation results for the dispersion phase velocity curves and the electromechanical coupling coefficient (K-2) are obtained by the matrix method and by the finite element method and compared with experimental data. A delay line is implemented on the structure and tested for the propagation of the first symmetrical Lamb mode (s(0)) at the frequency of 1.22 GHz. Measurements have shown that the structure is suitable for implementation of arrays of electroacoustic devices on a single chip for application to both sensing devices and signal processing systems.