Helmut Schlaak

Micromechanical Capacitive Acceleration Sensor with Force Compensation

A micromechanical acceleration sensor consisting of a differential capacitor has been developed. The seismic mass is etched in silicon forming simultaneously the middle electrode and is suspended on 8 cantilever beams consisting of highly boron doped silicon. The mass is embedded in a glass-siliconglass-sandwich between the counter electrodes which are placed in 5 μm deep etched grooves in the glass substrates. The complete fabrication including the anodic bonding of glass and silicon is processed on 4″-wafers. The sensor design with smooth cantilever beams (10 μm thickness, 1.3 mm length) provides a high sensitivity. The sensor element operates in an electronic force compensation circuit with electrostatic reset to keep the seismic mass in a virtual idle position. The circuit provides an error compensation. The measurement resolution has been performed within μg-range. The fabrication tolerances of all important dimensions have been evaluated to 1 %. They correspond to the results of sensor characteristics measurements.