The suppression of transverse modes in POI-SAW resonators with selective etching method

Piezoelectric-on-insulator surface acoustic wave (POI-SAW) devices are pivotal components in modern mobile communications and a major challenge in these devices is the suppression of transverse modes. This work investigates the suppression of these unwanted modes both theoretically and experimentally in POI SAW devices utilizing a 50°Y--XLiTaO3/SiO2/\,poly-Si/Si substrate with selective etching of the piezoelectric layer across the entire gap region to a certain depth. First, the response of conventional POI SAW resonators is analyzed by the 3D periodic finite element method, and the results show that transverse modes caused by oblique propagation of acoustic wave are obvious. Subsequently, the thickness of the piezoelectric layer within the gap region is regulated to achieve a lower phase of reflection coefficient at the boundary by the traveling wave excitation source (TWES) method, and the theoretical simulation results show that this method can achieve the effective suppression of transverse modes in POI SAW devices. Finally, a series of SAW resonators incorporating the proposed design were fabricated, and the results show a dramatic mitigation of transverse modes and the enhancement of Q factor. Thus, we contend that this method is effective for the suppression of transverse modes and energy leakage in POI SAW resonators.