MEMS in RF-filter applications: thin film bulk-acoustic-wave technology

RF-filters based on MEMS technology have started to substitute conventional filters in mobile phones as they offer clear performance and size advantages. Bulk acoustic wave (BAW) and FBAR technologies today dominate the market for US-PCS duplexers and transmit filters which are needed between the power amplifier and antenna in mobile phone applications. No other RF-MEMS component has yet emerged in mobile phone applications. The working principle and fundamentals of RF-MEMS filters - and in particular thin film bulk-acoustic-wave (BAW) filters - are summarized in a comprehensive form. Requirements and key performance parameters for filters in next generation mobile phone applications are reviewed in detail. The presentation includes an outlook on future RF architectures and consolidates the demand for filters. BAW and FBAR technologies in wafer-level-packaging enable the building of complete "system-in-package" (SiP) RF-modules using cheap substrates and established assembly methods as are reviewed in detail. The state-of-the-art in BAW filters and future technology trends are presented. Supplementary information covers manufacturing and commercialization issues.