Scaling Acoustic Filters Towards 5G

This paper presents a micro-electro-mechanical system (MEMS) filter at 10.8 GHz as the first step of scaling electromechanical filters towards fifth-generation (5G) frequencies beyond 6 GHz. The scaling of the center frequency to 10. 8 GHz is made possible by resorting to a higher order asymmetrical lamb wave mode (A3) in lithium niobate (LiNbO3) MEMS resonators. The filter is then constructed using A3 resonator arrays in a ladder configuration. The fabricated resonator has demonstrated an electromechanical coupling $(k_{t}^{\ 2})$ of 3.6% and a quality factor ($Q$) of 337. The $Q$ is among the highest reported for piezoelectric MEMS resonators operating at this frequency range. The fabricated filter at 10.8 GHz has a 3 dB bandwidth of 70 MHz, a minimum insertion loss of 3.7 dB, an in-band ripple less than 0.1 dB, and a compact footprint of $0.7\times 0.5\ \text{mm}^{2}$.