5V Electrostatic Actuator Design for MEMS Gyroscope Application

Joe Seeger
(Professor Bernhard E. Boser)
(DARPA) F30602-97-2-0266

A typical MEMS gyroscope measures rotation rate by sensing the Coriolis acceleration of a vibrating proof-mass. The gyroscope design can be divided roughly into three parts: the proof-mass, the actuator for vibrating the proof-mass, and the sensor for detecting the Coriolis acceleration of the proof-mass. This research focuses on the design of 5V CMOS electronics and the mechanics of the actuator to increase sensitivity to rotation and reduce sensitivity to process variation and temperature.

Gyroscope sensitivity depends on the velocity of the proof-mass, which is affected by the size of the actuator, the mechanical spring, and the mechanical damping. Increasing the sensitivity requires more actuation, vibration at the mechanical resonance, and reduced damping. Reducing the sensitivity to process variation and temperature requires position sensing and feedback control to electronically adjust the spring constant and maintain a constant sinusoidal velocity.

The actuator design will use capacitive position sensing and electrostatic forces, which are easy to integrate but tend to be nonlinear for large motion of the proof-mass. The design will use parallel-plate actuators, which can generate significantly larger forces than the more common lateral comb drive and can generate an electrostatic negative spring that adjusts the mechanical spring constant. CMOS circuits will be designed to measure the position, stabilize the parallel-plate actuator over large motions, and reduce the nonlinearity of the negative spring effect. Additionally, the mechanical design of the actuator will minimize damping and maximize stiffness of undesired mechanical modes.

The actuator design will be demonstrated first in a z-axis gyroscope and later in a six-degree-of-freedom inertial measurement unit (6 DOF IMU), which includes three gyroscopes and three accelerometers. The actuator design will be applicable to other MEMS such as scanning mirror displays and micropositioners.

Send mail to the author : (seeger@eecs.berkeley.edu)

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