A Low-Noise Piezoelectric MEMS Oscillator Based on a Flexural Mode Membrane Resonator Array Toward In-Air Resonant Sensors

Flexural mode MEMS resonators are ideal candidates for resonant microsensors. However, their high motional resistance in air restricts the performance of corresponding oscillators and consequently the sensor performance. In this work, we report a piezoelectric MEMS oscillator based on a flexural mode membrane resonator array for in-air resonant sensors. Array design and piezoelectric transduction of the membrane resonators facilitate a low motional resistance and a high power handling capability. At the resonator level, the electrode pattern is optimized to further reduce the motional resistance, and the nonlinearity of the resonator is analyzed to fully exploit its high power handling for oscillator design. At the oscillator level, transimpedance and Pierce circuits are designed, analyzed and characterized. Theoretical calculations well fit measured results, both for the white and 1/f(2) phase noise of the transimpedance oscillator and for the Allan deviation below an integration time of 0.1 s of the Pierce oscillator. The Pierce oscillator achieves a phase noise of - 119 dBc/Hz at a 1 kHz offset and a -151 dBc/Hz noise floor. The frequency resolution of the Pierce oscillator reaches 0.024 Hz. To the best of our knowledge, the measured phase noise and frequency resolution are the best among reported low-frequency piezoelectric MEMS oscillators for in-air resonant sensors. The proposed solution could be applied for a variety of sensing scenarios, such as mass, pressure, acceleration and strain sensing. A theoretical resolution as low as 15 p epsilon is expected if it is utilized as a strain sensor.