Design and characterization of mechanically coupled CMOS-MEMS filters for channel-select applications

The CMOS-MEMS mechanically coupled filters fabricated using a mature CMOS-MEMS platform together with simple post-CMOS release processes are proposed in this work for the low-loss and channel-select applications at intermediate frequency (IF) region to enable the MEMS/IC integration in wireless transceivers. For the capacitive transducers implemented in the proposed CMOS-MEMS filters, the combination of the pull-in gap reduction and high-velocity arrayed coupling scheme is adopted in our metal-rich design to reduce the motional impedance (Rm). On the other hand, due to the high electromechanical coupling (ηe) and low material loss (high-Q), the SiO2 structure (i.e., oxide-rich design) is also developed in this work to attain better filter performance as compared to the metal-rich counterpart. As a result, by the use of the extraction technique (i.e., removal of feedthrough effects) and proper termination resistance (i.e., impedance matching), the flattened and properly terminated transmission with filter bandwidth less than 0.72% and stopband rejection greater than 25 dB is successfully demonstrated.