This paper reports on the design and characterization of a low phase noise MEMS oscillator with ultra-low polarization voltage. An innovative oscillation circuitry is also proposed by a high gain-bandwidth, low-power TIVA (trans-impedance voltage amplifier) which is composed of two stages: the I-to-V stage and voltage gain stage. The TIVA is fabricated using 1P6M 0.18 m CMOS technology and has been demonstrated with gain of 110dBΩ, 3-dB bandwidth of 60MHz, and power consumption of only 5.9mW, achieving the highest figure of merit (FOM) among reported literatures. Moreover, the input referred noise is less than 2.5 pA/√Hz in the 10 kHz to 100 MHz range. In order to reduce the motional impedance of capacitive MEMS resonators, a 50 nm-gap process together with vacuum capping technology is implemented. The TIVA chip is wire-bonded to a 17.6-MHz high-Q (Q unloaded ~ 8,000) silicon-based capacitive MEMS resonator and perform the phase noise of -121 dBc/Hz @1kHz offset and -131 dBc/Hz @10kHz offset, respectively, at polarization voltage of 6.8V. At 2.5V polarization voltage, the phase noise can reach -116 dBc/Hz @1kHz offset and -125 dBc/Hz @10kHz offset, respectively.

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