  Over the past few years, microelectromechanical system (MEMS) based on-chip
resonators have shown significant potential for sensing and high frequency
signal processing applications. This is due to their excellent features like
small size, large frequency-quality factor product, low power consumption, low
cost batch fabrication, and integrability with CMOS IC technology. Radio
frequency communication circuits like reference oscillators, filters, and
mixers based on such MEMS resonators can be utilized for meeting the increasing
count of RF components likely to be demanded by the next generation
multi-band/multi-mode wireless devices. MEMS resonators can provide a feasible
alternative to the present day well established quartz crystal technology that
is riddled with major drawbacks like relatively large size, high cost, and low
compatibility with IC chips. This article presents a survey of the developments
in this field of resonant MEMS structures with detailed enumeration on the
various micromechanical resonator types, modes of vibration, equivalent
mechanical and electrical models, materials and technologies used for
fabrication, and the application of the resonators for implementing oscillators
and filters. These are followed by a discussion on the challenges for RF MEMS
technology in comparison to quartz crystal technology; like high precision,
stability, reliability, need for hermetic packaging etc. which remain to be
addressed for enabling the inclusion of micromechanical resonators into
tomorrow's highly integrated communication systems.

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