Optimal and robust design method for two-chip out-of-plane microaccelerometers.

Area of Science:

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

Background:

• MEMS accelerometers are crucial for motion sensing.
• Fabrication variations and parasitic effects challenge MEMS accelerometer performance and uniformity.
• Robust design methodologies are needed to overcome these limitations.

Purpose of the Study:

• To present an optimal and robust design for a two-chip out-of-plane microaccelerometer system.
• To minimize fundamental noise levels and enhance robustness against fabrication variations.
• To improve die-to-die uniformity of the packaged microsystem.

Main Methods:

• An optimized design method for MEMS sensing element dimensions (thickness, sacrificial gap, vertical gap length).
• A digitally trimmable architecture with an 11-bit capacitor array in the CMOS readout circuit to cancel offset and gain variations.
• Integration of MEMS sensing chip and CMOS signal processing chip.

Main Results:

• Achieved scale factor of 372 mV/g–389 mV/g and output nonlinearity of 0.43%–0.60% FSO.
• Bias instability ranged from 122 μg–229 μg with signal-to-noise ratio of 74.00 dB–75.23 dB.
• Low in-plane cross-axis sensitivities (1.1%–1.9% and 0.3%–0.7%).

Conclusions:

• The optimal and robust design method enhances MEMS sensing element performance.
• The highly trimmable CMOS capacitive readout circuit ensures die-to-die uniformity.
• The proposed two-chip microaccelerometer system achieves high performance without compromising uniformity.