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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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A fully-differential CMOS-MEMS ring resonator integrated with a differential-type transimpedance amplifier (TIA) has been demonstrated using a commercially available CMOS process with 30-dB feedthrough suppression as compared to its singled-ended counterparts. To achieve such performance, the flexural-mode ring resonator with a desired mode shape features an inherent differential mode of mechanical operation, therefore not only enabling feedthrough (i.e., common-mode) signal cancellation to attain a clean frequency characteristic of the motional signal but attaining high Q due to its symmetrical structure and nodal support design. The nodal locations of the ring can be precisely accessed by the supporting beams due to its geometrical symmetry by which the process variation would not affect the motionless positions of the ring, therefore assuring low vibration energy loss and high Q. In addition, the on-chip differential TIA provides both the signal gain and impedance matching to further enhance the transmission of the motional current for future single-chip oscillator implementations. As a result, such a CMOS-MEMS ring resonator together with its on-chip circuitry offers a potential benefit from capacitive feedthrough cancelation by means of differential signaling scheme. Theoretical predications and simulations are in good agreement with the experimental demonstration.