A Robust Fully-Integrated Digital-Output Inductive CMOS-MEMS Accelerometer with Improved Inductor Quality Factor.

Area of Science:

• Micro-electromechanical systems (MEMS)
• Semiconductor device physics
• Sensor technology

Background:

• Capacitive detection schemes are standard for MEMS accelerometers but are prone to stress-induced deformation in CMOS-MEMS.
• Existing systems often require complex analog-to-digital conversion stages.
• Need for robust and simplified MEMS accelerometer designs.

Purpose of the Study:

• To design, fabricate, and characterize an inductive CMOS-MEMS accelerometer.
• To leverage an LC oscillator for on-chip digital frequency readout.
• To mitigate common CMOS-MEMS fabrication issues like structural curling.

Main Methods:

• Utilized an inductive detection scheme instead of capacitive.
• Integrated a high-Q CMOS inductor with a low-Q MEMS sensing inductor.
• Employed an LC oscillator circuit for frequency-based signal processing.

Main Results:

• Achieved an offset frequency of 85.5 MHz.
• Demonstrated a sensitivity of 41.6 kHz/g.
• Reported a noise floor of 8.2 mg/√Hz and bias instability of 0.94 kHz (11 ppm).
• Exhibited nonlinearity of 1.5% full-scale.

Conclusions:

• The inductive CMOS-MEMS accelerometer design is viable and offers advantages over capacitive methods.
• The oscillator-based readout simplifies the system architecture by eliminating the need for ADC.
• The device exhibits competitive performance metrics for MEMS accelerometers.