A wide band gap phononic crystal strip for quality factor improvement in a length extensional mode MEMS resonator

A wide bandgap (BG) relates to the performance of the prevention of the elastic wave propagation of the phononic crystal (PnC) structures. The wider the BG, the higher the safety of the wave propagation isolation. For microelectromechanical systems (MEMS) resonators, suppressing anchor energy flow from the resonator body through support tethers into the substrate is a key design requirement to improve their quality factor (Q). To suppress/eliminate the anchor loss, the operating frequency of a MEMS resonator must be within the BG frequency range of the PnC. In this research, a low wide bandgap PnC strip is first proposed to support the length extensional mode MEMS resonator in improving the Q. Secondly, impacts of the geometrical dimensions on the BG of the proposed PnC trip are evaluated. Thirdly, a comparison between the proposed PnC strip and four counterparts is performed to verify the effectiveness of the proposed PnC strip in improving the Q of the resonator. The operating frequency of the resonator is 115.15 MHz. The covering BG of the resonant frequency is 96.34 MHz within 100.34-196.68 MHz. The numerical results show that the lowest BG of the proposed PnC strip is opened within 100.34-196.68 MHz which is much lower than that of the counterparts. The widest BG of the proposed PnC strip over the maximum BG of the counterparts is enhanced 168.61%. The Q of the resonator with proposed PnC strip tethers over the same one with four counterparts are boosted to 4447.21, 3952.99, 4002.62 and 85044.99%. The effectiveness of the proposed PnC strip on suppressing/eliminating anchor loss in the resonator is superior to that of four types of PnC strip counterparts. The finite element analysis (FEA) in COMSOL Multiphysics software (COMSOL) is employed to simulate the band structure and Q scenarios of the PnC strips as well as MEMS resonator.