The figure depicts a micromachined silicon vibratory gyroscope that senses rotation about its z axis. The rotation-sensitive vibratory element is a post oriented (when at equilibrium) along the z axis and suspended at its base by thin, flexible silicon bands oriented along the x and y axes, respectively. Unlike in the vibratory microgyroscopes described in the immediately preceding article ["Cloverleaf Vibratory Microgyroscope With Integrated Post" (NPO-20688)] and other previous articles in NASA Tech Briefs, the rotation-sensitive vibratory element does not include a cloverleaf-shaped structure that lies (when at equilibrium) in the x-y plane.
As in the cases of the previously reported vibratory microgyroscopes, vibrations of the rotation-sensitive vibratory element are excited electrostatically, the vibrations are measured by use of capacitive proximity sensors, and the rate of rotation along the axis of sensitivity is deduced from the effect of the Coriolis force upon the vibrations. To create electrodes for electrostatic excitation and capacitive sensing of vibrations, portions of the facing surfaces of the post and of the four stationary members that surround the post are rendered electrically conductive; this can be accomplished by either depositing metal films or else doping the silicon in the affected areas.
In this case, the vibrations in question are those associated with motion of the outer ends of the post in the x-y plane, and the axis of sensitivity is the z axis. The post is initially driven to oscillation of its outer (free) ends along, say, the x axis. Under rotation about the z axis, the Coriolis force causes the outer ends of the post to oscillate along the y axis also. The rotation-rate sensitivity of the microgyroscope is proportional to the rate of rotation about the z axis, the drive amplitude, and the resonance quality factor (Q) of the vibratory element.
Like the vibratory microgyroscope described in the immediately preceding article, this one is fabricated as two micromachined silicon components, which are then bonded together. In this case, the four flexible suspension bands and half of the post are made from one silicon wafer, while the other half of the post is made from another silicon wafer.
This work was done by Tony K. Tang and Roman Gutierrez of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Mechanics category.
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Refer to NPO-20690, volume and number of this NASA Tech Briefs issue, and the page number.