Micromachined silicon gyro using tuned accelerometer

• US 20020104378A1
• Filed: 02/07/2001
• Published: 08/08/2002
• Est. Priority Date: 02/07/2001
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Stewart, Robert E.
• Granted Patent: US 6,595,056 B2
• Time in Patent Office: Days
• US Class Current: 73/514.21
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces

Abstract

A micromachined silicon tuned accelerometer gyro is formed out of silicon wafers, by micromachining. The top and bottom cover which include driver, forcer, tuning and guard ring elements mounted therein are micromachined in arrays on silicon-on-insulator (SOI) wafers. The center (driver and sensing) element between the top and bottom is micromachined in an array of four inch diameter silicon wafers. The driver and sensing structure is a tuned pendulum attached by flexure joints to a vibrating structure which is in then suspended by a parallelogram dither suspension. The pendulum is tuned by adjusting the magnitude of a d.c. signal to match the natural frequency of the pendulum to the natural frequency of the vibrating structure. The dither suspension flexures of the vibrating structure is uniquely defined and easily machined but yet provides a dither suspension that restrains the vibrating structure within its vibrating plane with no harmonic distortion.

Claims

1. An accelerometer gyro for sensing linear acceleration and angular motion having a sensing element formed from a substantially planar monolithic material, the accelerometer gyro sensing element comprising:

a frame portion;

a vibrating structure having a top, bottom and sides disposed within said frame portion and connected to said frame portion by two flexures at about the bottom, and by two flexures at about the top; and

a pendulum disposed within said vibrating structure and connected to said vibrating structure by a flexure.

2. The accelerometer gyro of claim 1 wherein said vibrating structure and suspension have a natural frequency of vibration;

and

the pendulum and its flexure is designed to have a natural frequency of oscillation that is higher than the natural frequency of vibration of the vibrating structure and suspension.

3. The accelerometer gyro of claim 2 wherein the natural frequency of oscillation of the pendulum is up to 2% higher than the natural frequency of vibration of the vibrating structure.

4. The accelerometer gyro of claim 3 wherein the vibrating structure and pendulum are micomachined out of silicon wafers.

5. The accelerometer gyro of claim 1 wherein all four flexures of the vibrating structure each have a long and short axis and are of like size and shape with the long axis of each flexure running parallel with the sides of the pendulum.

6. The accelerometer gyro of claim 1 further comprising a top and bottom cover for the frame portion made from silicon-on-insulator wafers having a handle wafer and a device wafer fusion bonded together with a silicon dioxide dielectric layer in between.

7. The accelerometer gyro of claim 6 wherein the top and bottom covers include drivers, force and tuning electrodes, and ohmic contacts formed in the device wafer.

8. The accelerometer gyro of claim 7 further comprising a silicon dioxide layer on both sides of the frame and around the perimeter of the top and bottom cover, the thickness of the layer chosen to define the spacing between the pendulum and the forcer and tuning electrodes when the top, bottom and frame are joined.

9. The accelerometer gyro of claim 8 wherein said vibrating structure has a natural frequency of vibration;

and

the pendulum and its flexure are designed to have a natural frequency of oscillation that is higher than the natural frequency of vibration of the vibrating structure.

10. The accelerometer gyro of claim 8 wherein the natural frequency of oscillation of the pendulum is up to 2% higher than the natural frequency of vibration of the vibrating structure.

11. The accelerometer gyro of claim 10 wherein the vibrating structure and pendulum are micomachined out of silicon wafers.

12. The accelerometer gyro of claim 2 further comprising a signal generator for applying a d.c. signal of predetermined amplitude to reduce the natural frequency of the pendulum and its flexure to the natural frequency of the vibrating structure.

13. The accelerometer gyro of claim 12 wherein the natural frequency of oscillation of the pendulum is up to 2% higher than the natural frequency of vibration of the vibrating structure.

14. The accelerometer gyro of claim 13 wherein the vibrating structure and pendulum are micomachined out of silicon wafers.

15. The accelerometer gyro of claim 14 wherein the four flexures of the vibrating structure each have a long and short axis and are of like size and shape with the long axis of each flexure running parallel with the sides of the pendulum.

16. The accelerometer gyro of claim 15 further comprising a top and bottom cover for the frame portion made from silicon-on-insulator wafers having a handle wafer and a device wafer fusion bonded together with a silicon dioxide dielectric layer in between.

17. The accelerometer gyro of claim 16 wherein the top and bottom covers include drivers, and force and tuning electrodes, a guard ring and ohmic contacts formed in the device wafer.

18. The accelerometer gyro of claim 17 further comprising a silicon dioxide layer on both sides of the frame and around the perimeter of the top and bottom cover, the thickness of the layer chosen to define the spacing between the pendulum and the forcer and tuning electrodes when the top, bottom and frame are joined.