2x Size And Cost Reduction Of Film Bulk Acoustic Resonator (Fbar) Chips With Tungsten Electrodes For Pcs/Gps/800 Mhz Multiplexers

It is well known that using tungsten electrodes can boost the effective coupling coefficient, hence bandwidth, of Film Bulk Acoustic Resonator (FBAR) filters relative to lower acoustic impedance electrode materials [1]. This effect is strongest for FBARs with much less AIN than would be used to achieve the maximum coupling. In the case of 800 MHz (cellband) duplexers, although the performance has been excellent[2-3], the cost of FBAR solutions has been too high due to large resonator and die size (1.8 mm(2)), even in the PCS/GPS/800 MHz multiplexer applications. A combination of the high effective coupling coefficient of tungsten electrode FBARs, a better duplexer design, tighter design rules, and a higher quality factor (Q) have contributed to a die size reduction to about 1 mm(2). Performance is competitive with the best surface acoustic wave (SAW) devices we have seen. These parts, when used in a PCS/GPS/800 MHz multiplexer provide a high-performance and cost-competitive RF front end filtering solution for CDMA handsets.