Dispersion characteristics of high-order lamb wave modes in an AlN/3C-SiC layered plate

A new propagation layered media composed of a piezoelectric thin film and a substrate plate is studied in this work. The displacement profiles, phase velocities, and electromechanical coupling coefficients of Lamb wave modes are theoretically investigated for the c-axis oriented AlN films on cubic silicon carbide (3C-SiC) plates. Due to the different material properties of the AlN and 3C-SiC layers, the displacement profiles of Lamb wave modes are not simply antisymmetric or symmetric with respect to the neutral axis. According to the displacement profiles, the plate acoustic wave modes in the layered plate are classified as quasi-Lamb wave modes. Some high-order quasi-Lamb wave modes in the layered plate have larger electromechanical couplings than the corresponding Lamb wave modes in an AlN thin plate. In addition, the third quasi-symmetric (QS₃) Lamb wave mode exhibits a low motional impedance (R_m) of 91 ohm and a high quality factor (Q) up to 5510 at a frequency (f_s) of 2.92 GHz, resulting in the highest f_s·Q product, 1.61×10¹³ Hz, among suspended piezoelectric thin film resonators reported to date.