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

We present a high coupling coefficient, k(eff)(2), micromechanical resonator based on the propagation of SHO 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 degrees from the y-axis, where a fundamental mode SHO Lamb wave resonator with a plate width of 20 mu m and a corresponding resonant frequency of 101 MHz achieves a k(eff)(2) of 12.4%, a quality factor of 1300 and a resonator figure of merit (M) of 185. The k(eff)(2). and M are among the highest reported for micromechanical resonators. (C) 2014 Elsevier B.V. All rights reserved.