Acoustic properties of the film/plate layered structure

摘要

A new propagation medium??a layered structure composed of a film and a plate??is suggested and studied, using c-oriented ZnO and AlN films on (001), {100}-Si plate, as two opposite examples of slow-on-fast and fast-on-slow material combinations. For both structures, the modes belonging to Lamb, quasi-longitudinal (QL), and Anisimkin Jr.?? (AN) families are found. For each family, the velocities vn, displacement profiles, and electromechanical coupling coefficients Kn 2 for 4 electrode configurations are numerically calculated by the matrix method as a function of the mode order n = 0 to 8, plate thickness H/;B; = 0 to 2.0, and film thickness h/;B; = 0.02 to 0.04 (H and h are thicknesses; ;B; is the wavelength). Some highorder modes in the structure have Kn 2 = 0 for any H/;B;, h/;B;, and electrode configuration. Other modes possess variable Kn 2 with a maximum value larger than the coupling coefficient for the Rayleigh SAWs in ZnO and AlN single crystals or layered structures using the same films and semi-infinite silicon substrate. There are also QL-modes having high velocity vn, large Kn 2, and low propagation loss caused by liquid loading. These modes are well suited for liquid sensors.