High-Q Resonators using FBAR/SAW Technology and their Applications

This paper describes FBAR and SAW resonators which have high-Q factor using unique technology, and their applications. A new electrode material suitable for AlN-based FBARs have been developed in order to realize high-Q factor for low loss. The necessary conditions for FBAR electrode materials are low resistivity and high acoustic impedance. It is found the properties of ruthenium (Ru) to be suitable for use as electrode materials for AlN-based FBARs. The resonant characteristics of FBAR using Ru electrodes indicates Qr of 1200 and an effective electromechanical coupling coefficient k² of 6.7% at 2 GHz. On the contrary, SAW resonator with narrow finger electrode, which can suppress transverse leakage of SAW, shows Qr of 670 and k² of 7.1%. Furthermore, we applied these resonators to ladder-type FBAR filter for 2-GHz WCDMA and SAW duplexer for US-PCS, respectively, and achieved low-loss and step cut-off filters as a result.