Thomas Metzger

Selection of micro-acoustic technologies for the realization of single-ended / balanced WCDMA duplexers

With the increasing number of frequency bands for WCDMA applications, also the need for miniaturized duplexer solutions increases in order to realize multi-band, multi-mode mobile phones. With SAW and BAW, two well established micro-acoustic technologies are available. For the realization of competitive CDMA duplexers like for the US-PCS band, so far the focus has been mainly on the provision of resonators with high quality factors and reduced temperature coefficient of frequency to realize filters with highest guaranteed steepness of filter skirts. With the large variety of duplexer requirements in the new WCDMA bands and the trend towards single-ended / balanced operation in the RX path, the constraints for technology selection have somewhat changed. Only when considering all critical parameters like center frequency, TX-RX bandgap, filter bandwidth, and insertion attenuation requirements, individual technology solutions for the different WCDMA frequency bands can be identified in order to provide superior duplexer solutions with respect to cost, size, quality, and performance.

3.8 /spl times/ 3.8 mm/sup 2/ 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 /spl times/ 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.

Baw components for PCS-CDMA applications

Bulk Acoustic Wave (BAW) technology is highly investigated due to its silicon-based technology for further integration in the RF part of e.g. mobile phones. This paper shows the current performance of various components suitable for the US PCS-CDMA band. In particular, new results of a duplexer are presented as well as new designs for a transmit filter and a receive filter. Besides the transfer functions, measurements of the temperature coefficient for left and right skirts are shown as well. The presented results show clearly our improvements within solidly-mounted-resonator (SMR) -BAW technology. Our process flow using a 200 mm manufacturing line uses only the minimum required process steps by still keeping a high yield in combination with high process stability and high process robustness.

Multiplexers: A necessary extension for 4G/5G systems

Carrier Aggregation is one prominent method to increase the data throughput in mobile communication. Dependent on the band combination to be realized (about 270 different band combinations are currently under discussion) either diplexers or multiplexers need to be used to realize suitable hardware. Whereas already today diplexers are applied for single-feed antenna concepts to separate e.g. the 1GHz from 2GHz bands, multiplexers are required for all those cases where filters and/or duplexers of bands close to each other need to be combined. Besides the pure electrical aspects like low insertion loss, high isolation to all active Rx-bands, steep skirts, high linearity, just to name a few, also mechanical aspects like area consumption and height need to be considered in order to address customer demands. All three items will be discussed shortly and underline the need for continuous improvement not only at the acoustic but also packaging side.