When it comes to filtering, MEMS fabrication technology has been exploited for two main purposes : (1) the micromaching of structures (e.g., cavities) so small that their fabrication utilizing conventional machining techniques would be prohibitively expensive or virtually impossible due to tolerance limitations, and (2) the creation of micromechanical resonatorbased filters, typically utilizing polysilicon beam resonators.
As examples of the former, which is typically applied to millimeter-wave frequencies, the works of Brown and Rebeiz  and of Kim et al.  may be cited. As examples of the latter, which so far has only been applied to frequencies lower than 200 MHz, the works of Bannon, Clark, and Nguyen  and of Wang and Nguyen  may be cited. In what follows, we present two case studies: one being an example of a tunable micromachined filter, and the other an example of a micromechanical MEMS filter.