A Vertically Coupled MEMS Resonator Pair for Oscillator Applications

This letter presents the design of a micromechanical oscillator based on a vertically coupled (VC) CMOS-microelectromechanical systems (MEMS) resonator pair for phase noise reduction. The prototyped resonator pair consists of two vibrating plates coupled with each other, thus providing enhanced power handling while keeping compact footprint. The proof-of-concept oscillator based on a 6.5-MHz, VC mode resonator achieves a phase noise of -97 dBc/Hz at 1-kHz offset and -118 dBc/Hz at 1-MHz offset from carrier with a resonator size of 30 x 30 mu m(2). Compared with its nonresonance-coupled saddle mode counterpart, the VC-mode-based oscillator features 10-dB phase noise reduction using the same oscillator circuit setup. The design concept of this letter can be extended to three dimensional (3-D) mechanically coupled resonator designs in the future.