A high electromechanical coupling coefficient SH0 Lamb wave lithium niobate micromechanical resonator and a method for fabrication

Abstract

We present a high coupling coefficient, keff2, micromechanical resonator based on the propagation of SH0 Lamb waves in thin, suspended plates of single crystal X-cut lithium niobate (LiNbO3). The thin plates are fabricated using ion implantation of He to create a damaged layer of LiNbO3 below the wafer surface. This damaged layer is selectively wet etched in a hydrofluoric (HF) acid based chemistry to form thin, suspended plates of LiNbO3 without the wafer bonding, layer fracturing and chemical mechanical polishing in previously reported LiNbO3 microfabrication approaches. The highest coupling coefficient is found for resonators with acoustic propagation rotated 170° from the y-axis, where a fundamental mode SH0 Lamb wave resonator with a plate width of 20μm and a corresponding resonant frequency of 101MHz achieves a keff2 of 12.4%, a quality factor of 1300 and a resonator figure of merit (M) of 185. The keff2 and M are among the highest reported for micromechanical resonators.