A 0.35-μm CMOS-MEMS Oscillator for High-Resolution Distributed Mass Detection

Area of Science:

• Microelectromechanical Systems (MEMS)
• Sensor Technology
• Integrated Circuits

Background:

• Resonator-based sensors offer high sensitivity for mass detection.
• On-chip integration of sensing elements is crucial for miniaturization and cost reduction.
• Complementary Metal-Oxide-Semiconductor (CMOS) processes enable mass production of MEMS devices.

Purpose of the Study:

• To design, fabricate, and characterize a novel electrostatically actuated and capacitive sensed 2-MHz plate resonator.
• To integrate the resonator into a Pierce oscillator for a quasi-digital output sensor.
• To evaluate the mass sensitivity and noise floor of the developed CMOS-MEMS device.

Main Methods:

• Fabrication of a monolithic CMOS-MEMS resonator using a 0.35-μm 2-poly-4-metal CMOS process.
• Electrical characterization of the resonator's performance, including mass sensitivity and frequency stability.
• Integration with an on-chip Pierce oscillator for signal readout.

Main Results:

• Achieved a predicted mass sensitivity of approximately 250 pg·cm^-2·Hz^-1.
• Demonstrated a short-term frequency stability of 1.2 Hz (0.63 ppm) in air.
• Obtained an equivalent mass noise floor as low as 300 pg·cm^-2.
• Utilized a commercial CMOS process for low-cost, batch fabrication.

Conclusions:

• The developed CMOS-MEMS plate resonator is a cost-effective, high-performance mass sensor.
• The device offers unprecedented mass resolution for its class, suitable for distributed sensing applications.
• The monolithic integration and quasi-digital output simplify sensor system design and implementation.