Ultra High Frequency Piezoelectric Resonators: Suspension and Elastic Coupling

In this research project, the suspension and elastic coupling of Film Bulk AcousticResonators (FBAR) has been investigated. Individual resonators and small arrays of AlN FBARs have been designed and fabricated in a post-CMOS compatible process. Suspensions based on networks of thin beams did not perform well, but membrane suspensions enabled strong device performance. Single resonators achieved Q values of 1050 at 2.98 GHz and 1312 at 2.45 GHz, with series motional resistance on the order of 10 Ω. Arrays of two FBARS elastically coupled by their bottom electrode displayed frequency response with two close but distinct resonant peaks. Under applied DC bias voltages, these systems displayed filter-like behavior at 1.97 GHz, with bandwidth of 6 MHz and insertion loss of -30 dB. These results verify the feasibility of mechanically coupled resonator arrays in the UHF range.