High-frequency and low-resonance-impedance lamb wave resonators utilizing the S1 mode

In this work, a high-frequency (f_s) and low-resonance-impedance (Z_min) Lamb wave resonator utilizing the first-order symmetric (S₁) mode propagating in highly textured aluminum nitride (AlN) plates is presented. In order to achieve the larger electromechanical coupling coefficient and smooth phase velocity dispersion as well as to avoid the negative group velocity in the S₁ Lamb wave mode, the 4-μm-thick AlN layer and 3-μm-wide finger electrodes are employed in the Lamb wave resonator design. The experimental results show that despite the S₁ mode shows a slightly lower quality factor than the lowest-order symmetric (S₀) mode, the S₁ mode presents a Z_min of 94 © at 1.34 GHz, lower than the S₀ mode showing a Z_min equal to 224 © at 878.3 MHz.