Design flow and methodology on the design of BAW components

Bulk acoustic wave (BAW) technology based on the sputtering of piezoelectric thin films on high resistive silicon has recently emerged as one of the preferred technologies for the realization of miniaturized high performance RF filters and duplexers for wireless CDMA-based applications like mobile phones. We present the performance improvements within the development of a duplexer for US-PCS-CDMA applications with a footprint of 3.8mm × 3.8mm and a height of 1.1mm. The duplexer consists of a transmit (TX) and a receive (RX) filter, which are flip-chipped as bare dies on a low temperature co-fired ceramic (LTCC) multilayer substrate incorporating additional matching elements. The filters are realized using solidly mounted resonator (SMR) technology, where an acoustic mirror separates the active resonator from the substrate. Duplexer packaging is based on the EPCOS´ proprietary CSSP technology, originally developed to further shrink the size of SAW devices. This technology includes a cavity between the package and the acoustically active filter areas and therefore keeps the surface of the active device protected from environmental influences. The front-end technology for realizing the RF filters uses standard 200 mm CMOS technology and the deposition of AlN piezoelectric thin films with high thickness uniformity over the wafer. The duplexer is fully matched to 50 ohm with low insertion attenuation in the pass band, a superior stop band characteristic up to 10 GHz, and a temperature coefficient of frequency (TCF) of -20 ppm/K.