MEMS Bandpass Filters Based on Cyclic Coupling Architectures

Resonant microelectromechanical systems (MEMS) offer distinct utility in signal processing and wireless communications applications due to their comparatively-high quality factors, low power consumption, and ease of integration with existing integrated circuit (IC) technologies. While a number of efforts have previously demonstrated the use of mechanically-coupled microresonators in bandpass signal filtering applications, the vast majority of these works have emphasized the use of resonator chains coupled in an open configuration, wherein the terminating (end) elements in the array are coupled to only a single resonator and the interior resonators are coupled solely to their nearest neighbors. While this configuration suffices for many MEMS-based filter designs, it is not guaranteed to be an optimal coupling architecture. The present work explores an alternative class of MEMS bandpass filters based on cyclically-coupled, closed-chain resonator configurations and specifically examines the pertinent performance metrics (effective quality factor, shape factor, bandwidth, ripple, and maximum transmission) associated with each architecture. By varying coupling strength and the quality factor of individual resonators over wide, yet realistic, parameter ranges, regions of superior performance for both open- and closed-chain filter architectures have been observed. Of particular interest here, is the fact that preliminary results indicate that cyclically-coupled resonator configurations exhibit improved ripple metrics, reduced frequency dependence within the passband, and, generally speaking, more robustness to process-induced variations than their open-chain counterparts. As such, cyclically-coupled filter designs, with further refinement, may ultimately lead to an improved MEMS bandpass filter capability.