Moving Tunable Filters Forward: A \"Heterointegration\" Research Project for Tunable Filters Combining MEMS and RF SAW\/BAW Technologies

This article discusses the possibility of tunable RF surface-acoustic-wave (SAW) and bulkacoustic-wave (BAW) filters using varactors (VCs) integrated by the skillful use of micro-electromechanical system (MEMS) technologies. First, the reasons that RF tunable filters are in demand for current wireless communications are explored, and various RF tunable filters are surveyed and compared. Next comes a discussion of tunable RF SAW/BAW filters combined with MEMS technologies, showing that high performance can be expected, provided that some key technologies are developed. Finally, the article introduces tunable SAW filters, which the authors developed in a research project called "heterointegration" to demonstrate what is possible by combining MEMS technologies with RF SAW/BAW technologies.