The effects of tight capacitive coupling on phase noise performance: A Lamé-mode MEMS oscillator study

Abstract

In this work, we realize low-polarization-voltage (VP) capacitive MEMS oscillators implementing vacuum packaged 50 nm-gap Lame-mode silicon micromechanical resonators and investigate their phase noise (PN) performance. Two different oscillator configurations are studied; these are here referred to as differential-in-differential-out (DIDO) and single-in-differential-out (SIDO). Clear disparities in their respective PN profiles could be observed. The DIDO outperforms the SIDO with an improved close-to-carrier PN by more than 25 dB. This 17.6 MHz oscillator achieves a PN of -127 dBc/Hz at 1 kHz offset and -132 dBc/Hz far-from-carrier PN performance, which is competitive with state-of-the-art capacitive MEMS oscillators but with lowest VP in this work. The measured PN is found to be dependent on VP for our oscillators, which is probably due to the nonlinear effects augmented by the tight electromechanical coupling.