Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-04-26
2001-02-20
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06189381
ABSTRACT:
INTRODUCTION
The present invention relates to an angular rate sensor and specifically one which detects the rate of rotation using the Coriolis effect.
BACKGROUND
Rotational rate sensors based on the Coriolis effect have been commercially produced in the form of a micro-miniature double-ended quartz tuning forks. Such vibrating quartz tuning forks are generally composed of a single wafer of monocrystalline piezoelectric quartz. One use of such a rate sensor is as a yaw sensor in a motor vehicle. Because of the above use in automotive applications it is desired to have a device which is the most economical, miniaturized, and which is compatible with other semiconductive components of the automobile.
Silicon devices have been proposed but as yet have not become commercially available because of processing difficulties compared to the commercial quartz-based device. For example, one type of silicon device is constructed of polycrystalline silicon whose limited thickness is detrimental to sensitivity.
OBJECT AND SUMMARY OF INVENTION
It is therefore the general object of the present invention to provide an improved rate sensor utilizing which is responsive to a Coriolis force.
In accordance with the above object there is provided a method of making an angular rate sensor from a structural wafer of single crystal silicon, the structural wafer having at least one proof mass, which is part of a rotating reference frame, the mass lying substantially in an X-Y plane which is oscillated or driven in the X direction and responds to a Z-axis input rotation to deflect at least partially in the Y direction, where Coriolis acceleration is sensed. The method comprises the steps of providing a silicon wafer handle to implement processing, bonding the handle wafer to the structural wafer and vertically etching through at least the structural wafer to provide sensing and drive means. Both the silicon handle and structural wafers have an identical expansion rate.
From a structural point-of-view, there is provided an angular rate sensor comprised of a structural wafer composed of single crystal silicon and having a pair of proof masses which are part of a rotating reference frame, the masses lying substantially in an X-Y plane orthogonal to a Z input axis of rotation. Interdigitated comb drive means included in the structural wafer drive the masses into oscillation in an X or Y direction. Frame means are included in the structural wafer in the X-Y plane for supporting the masses and allowing opposing Coriolis induced forces to rotate the frame, the rotation of the frame being indicative of the angular rate of the sensor. Parallel plate sensing means located outside of the circular frame also in the X-Y plane sense the rotation of the frame.
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William A. Clark, Rogert T. Howe, and Roberto Horowitz; “Surface Micromachined Z-Axis Vibratory Rate Gyroscope;”Solid-State Senor and Actuator WorkshopJun. 2-6, 1996, pp. 283-287.
Haniff Tariq M.
Huang Yongli
Lim Martin
Yun Weijie
Chapman John E.
Flehr Hohbach Test Albritton & Herbert LLP
Sitek, Inc.
Wright Jerry G.
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