Design of novel mechanical coupling for contour mode piezoelectric RF MEMS filters

Abstract

Two novel mechanical coupling methods for synthesizing highly-integrated contour mode piezoelectric aluminum nitride (AlN) filters are introduced. While the underlying resonator technology remains the most viable candidate for realizing arrays of post-CMOS compatible filters at arbitrary frequencies with on-chip matching to 50 Ω, previously demonstrated mechanical coupling topologies do not scale well beyond 100 MHz. The current work focuses on design and fabrication techniques intended to extend the numerous inherent advantages of the AlN contour mode resonator technology to filters that are capable of higher center frequencies. The first design involves a series of alternating high and low acoustic impedance quarter wavelength sections that regulate the strength of the elastic coupling between resonators. The second approach relies on elastic coupling elements that are defined in the relatively compliant bottom metal electrode layer rather than the structural AlN film used by the actual resonators.