3.8 × 3.8 mm2 PCS-CDMA duplexer incorporating thin film resonator technology

Bulk acoustic wave (BAW) technology based on piezoelectric thin films has recently emerged as a preferred technology for the realization of miniaturized high performance RF filters and duplexers for wireless applications like mobile telephones. We present a duplexer for PCS-CDMA applications with a footprint of 3.8 mm × 3.8 mm and a height of 1.1 mm. The duplexer consists of a transmit (TX) and a receive (RX) filter, both mounted 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 part from the substrate. Duplexer packaging is based on the EPCOS proprietary CSSP technology developed for the miniaturization of chip sized SAW packages including a cavity between the package and the acoustically active filter areas. 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 ohms 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.