Microelectromechanical capacitive accelerometer and method of ma

Details Microelectromechanical capacitive accelerometer and method of ma Microelectromechanical capacitive accelerometer and method of ma

1997-09-08

2000-03-14

Williams, Hezron

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

G01P 15125

Patent

active

060357142

ABSTRACT:
A high sensitivity, Z-axis capacitive microaccelerometer having stiff sense/feedback electrodes and a method of its manufacture are provided. The microaccelerometer is manufactured out of a single silicon wafer and has a silicon-wafer-thick proofmass, small and controllable damping, large capacitance variation and can be operated in a force-rebalanced control loop. The multiple stiffened electrodes have embedded therein damping holes to facilitate both force-rebalanced operation of the device and controlling of the damping factor. Using the whole silicon wafer to form the thick large proofmass and using the thin sacrificial layer to form a narrow uniform capacitor air gap over a large area provide large capacitance sensitivity. The structure of the microaccelerometer is symmetric and thus results in low cross-axis sensitivity. In one embodiment, because of its all-silicon structure, the accelerometer exhibits very low temperature sensitivity and good long term stability. The manufacturing process is simple and thus results in low cost and high yield manufacturing. In the one embodiment, the electrodes are formed by thin polysilicon deposition with embedded vertical stiffeners. The vertical stiffeners are formed by refilling vertical trenches in the proofmass and are used to make the electrodes stiff in the sense direction (i.e. Z or input axis). In a second embodiment, the electrodes are metallized and dimensioned so as to be stiff in the sense direction.

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