Combined electrical and mechanical coupling for mode-reconfigurable CMOS-MEMS filters

This work presents a novel filter scheme which combines both electrical and mechanical coupling mechanisms implemented in a CMOS-MEMS filter to simultaneously attain small percent bandwidth through weakly mechanical link and decent stopband rejection via differentially electrical configuration. As compared to the traditional parallel-class (i.e., electrically-coupled) filters and mechanically-coupled filters, the proposed oxide-rich filter structure features flexible electrical routing and non-conductive mechanical filter couplers, hence enabling common-mode to differential (CIDO) and differential to common-mode (DICO) reconfigurable modes all within a single device. The proposed 8.6-MHz CMOS-MEMS filter has been successfully demonstrated with a narrow passband of 35 kHz (0.41% bandwidth) and stopband rejection more than 20 dB under proper termination.