A Mechanically Coupled Piezoelectric MEMS Filter With Tiny Percent Bandwidth and Low Insertion Loss

Mechanical filters implement channel selection in a tiny percent bandwidth and become essential components in wireless communication systems and sensor networks. This paper reports a mechanically coupled piezoelectric microelectromechanical system (MEMS) filter, which consists of two width-extensional (WE) mode resonators mechanically coupled by a straight beam. The coupling beam, located at the plate edges and purposely designed to operate in flexural mode with low dynamic stiffness, enables the filter to achieve a small percent bandwidth. The designed mechanically coupled piezoelectric MEMS filter is fabricated based on a thin-film piezoelectric on silicon (TPoS) platform. Measurement results indicate that under a termination impedance of
$550~\Omega $
, the fabricated piezoelectric MEMS filter has a center frequency of 28.38 MHz, a percent bandwidth of 0.049%, an insertion loss of 2.0 dB, and a stopband rejection of approximately 41 dB outside the desired frequency range. [2023-0141]