Design and Optimization of SHF Composite FBAR Resonators

We propose an apodization technique-based composite thin-film bulk acoustic wave resonator (c-FBAR) design to enable the displacement and strain energy confinement at the central section of the resonator while in operation at the resonance mode. Sinc-shaped AlN on Silicon on Insulator apodized c-FBARs is designed to attain close to 90% energy localization. In this paper, a single crystal silicon as the mechanical layer and an AlN piezoelectric material as the transducer layer of the resonator implemented by InvenSense Inc.'s AlN MEMS-CMOS platform renders an asymmetric feature to the traditional FBAR resonator. The nature of composite thin-film piezoelectric on substrate FBAR resonators in the super high-frequency (SHF) range is studied in detail. Furthermore, a complete deembedding procedure to extract the resonator parameters from the CMOS + MEMS measured data is also explained meticulously. A complete equivalent circuit modeling for c-FBAR operating in the SHF is provided. Measurement data statistics show that sinc c-FBAR features superior electromechanical coupling coefficient (k
_teff
²
) than that of pentagon c-FBAR. As a result, we successfully demonstrate a sinc c-FBAR resonator operating at 3.264 GHz with an electromechanical coupling coefficient of 2.12%, a loaded quality factor (Q) of 790 and an unloaded Q of 2507.