An all-silicon single-wafer micro-g accelerometer with a combined surface and bulk micromachining process

Area of Science:

• MEMS (Micro-Electro-Mechanical Systems)
• Solid-State Physics
• Sensor Technology

Background:

• Capacitive accelerometers are crucial for measuring acceleration.
• Achieving micro-g and sub-micro-g resolution requires high sensitivity, low noise, and controllable damping.
• Existing fabrication methods may limit device performance and scalability.

Purpose of the Study:

• To develop and demonstrate an all-silicon, fully symmetrical z-axis micro-g accelerometer.
• To achieve high sensitivity and low noise performance for precise acceleration detection.
• To explore a combined surface and bulk microfabrication process for enhanced device characteristics.

Main Methods:

• Fabrication of a fully symmetrical z-axis micro-g accelerometer on a single silicon wafer.
• Utilizing a combined surface and bulk microfabrication process.
• Employing a large proof mass (whole wafer thickness) and thin sacrificial layer for large sense capacitance.
• Forming sense/feedback electrodes with embedded stiffeners for force rebalancing and damping holes for controlled damping.

Main Results:

• Successful batch fabrication, packaging, and testing of the microaccelerometers.
• Measured sensitivities of 2 pF/g (2-mm x 1-mm proof mass, full bridge) and 19.4 pF/g (4-mm x 1-mm proof mass, cantilever support).
• Calculated noise floors of 0.23 micro g/sqrt(Hz) and 0.16 micro g/sqrt(Hz) at atmospheric pressure.

Conclusions:

• The developed all-silicon accelerometer demonstrates high sensitivity and low noise, suitable for micro-g and sub-micro-g applications.
• The combined fabrication process enables the creation of devices with desirable characteristics like large proof mass and sense capacitance.
• The results validate the potential of this approach for advanced inertial sensing applications.