Mechanically Coupled Contour Mode Piezoelectric Aluminum Nitride MEMS Filters

Abstract

A new class of mechanically coupled contour mode MEMS filters is demonstrated using a thin film piezoelectric aluminum nitride (AlN) process. The use of contour modes, whose frequencies are set by lithographically defined dimensions, permits the co-fabrication of multiple filters at arbitrary frequencies on the same chip. The stronger electromechnical coupling of the thin film piezoelectric structural material vis-a-vis electrostatically transduced devices results in lower insertion losses (as low as 1.5 dB) with termination values of 1 to 2.5 kΩ. Finally, filters synthesized using mechanically coupled resonators are fundamentally capable of wider bandwidths than electrically coupled ladder filters without requiring external tuning elements. Two designs for bandpass filters are analyzed, fabricated, and tested. The filters have center frequencies of 40 and 100 MHz.