Micro hemispheric resonator gyro

• US 20090031831A1
• Filed: 07/31/2007
• Published: 02/05/2009
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: Litton Systems Incorporated
• Original Assignee: Litton Systems Incorporated
• Inventors: Stewart, Robert E.
• Granted Patent: US 8,109,145 B2
• Time in Patent Office: Days
• US Class Current: 74/5.60D
• CPC Class Codes: G01C 19/5691 of essentially three-dimensional vibrators, e.g. wine glass-type vibrators
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: Y10T 74/1275 Electrical

Abstract

One embodiment is a micro hemispheric resonator gyro having: a plurality of pickoff and forcer electrodes; a hemispheric resonator; a guard ring having first and second opposed sides, the guard ring containing the plurality of pickoff and forcer electrodes, and the hemispheric resonator; a top cover operatively coupled to the first side of the guard ring; and a bottom cover operatively coupled to the second side of the guard ring; wherein the plurality of pickoff and forcer electrodes, the hemispheric resonator, the guard ring, the top cover and the bottom cover form a micro hemispheric resonator gyro.

Claims

1. An apparatus, comprising:

a plurality of pickoff and forcer electrodes;

a hemispheric resonator;

a guard ring having first and second opposed sides, the guard ring encompassing the plurality of pickoff and forcer electrodes, and the hemispheric resonator;

a top cover operatively coupled to the first side of the guard ring; and

a bottom cover operatively coupled to the second side of the guard ring;

wherein the plurality of pickoff and forcer electrodes, the hemispheric resonator, the guard ring, the top cover and the bottom cover form a micro hemispheric resonator gyro.

2. The apparatus according to claim 1, wherein the plurality of pickoff and forcer electrodes comprises eight pickoff and forcer electrodes.

3. The apparatus according to claim 1, wherein the plurality of pickoff and forcer electrodes surround the hemispheric resonator.

4. The apparatus according to claim 1, wherein the plurality of pickoff and forcer electrodes, the guard ring, the top cover and the bottom cover may be formed from single crystal silicon.

5. The apparatus according to claim 1, wherein the micro hemispheric resonator gyro is formed from a high Q material.

6. The apparatus according to claim 5, wherein the high Q material is low stress silicon nitride.

7. The apparatus according to claim 1, wherein the micro hemispheric resonator gyro is composed of first, second and third silicon layers.

8. The apparatus according to claim 7, wherein the first layer is a top layer that contains the cover and a getter.

9. The apparatus according to claim 7, wherein the second layer is a center layer that contains the guard ring, the eight pickoff and forcer electrodes and the hemispheric resonator.

10. The apparatus according to claim 7, wherein the third layer is a bottom layer that contains the bottom cover with vias for electrical contact to the electrodes and the resonator.

11. A micro hemispheric resonator gyro, comprising:

at least first, second and third silicon layers;

the first layer having a top cover;

the second silicon layer having a plurality of pickoff and forcer electrodes, a hemispheric resonator and a guard ring having first and second opposed sides, the guard ring containing the plurality of pickoff and forcer electrodes, and the hemispheric resonator;

the third layer having a bottom cover;

the top cover operatively coupled to the first side of the guard ring;

the bottom cover operatively coupled to the second side of the guard ring;

the plurality of pickoff and forcer electrodes, the guard ring, the top cover and the bottom cover being formed from single crystal silicon.

12. The apparatus according to claim 11, wherein the plurality of pickoff and forcer electrodes comprises eight pickoff and forcer electrodes.

13. The apparatus according to claim 11, wherein the plurality of pickoff and forcer electrodes surround the hemispheric resonator.

14. The apparatus according to claim 11, wherein the micro hemispheric resonator gyro is formed from a high Q material.

15. The apparatus according to claim 14, wherein the high Q material is low stress silicon nitride.

16. The apparatus according to claim 11, wherein the cover has a getter.

17. The apparatus according to claim 11, wherein the bottom cover has vias for electrical contact to the electrodes and the resonator.

18. A method, comprising:

applying and patterning resist on a first side of a center silicon wafer followed by isotropic etching to form hemispherical cavities;

patterning and etching a second side of the center silicon wafer using deep reactive ion etching (DRIE) to form cylindrical holes that intersect the hemispherical cavities;

growing over the entire center silicon wafer a conformal l;

m thick layer of sacrificial silicon dioxide;

removing the silicon dioxide from both the first and second sides of the center silicon wafer using chemical mechanical polishing (GMP);

coating the entire center wafer with low stress PECVD silicon nitride;

depositing a thin layer of titanium and gold over the entire silicon wafer;

patterning with a mask the titanium and gold coated silicon nitride on the second side of the center silicon wafer to thereby define the eight pickoff and forcer electrodes and the silicon nitride;

removing the silicon nitride, titanium and gold film from the first side of the center silicon wafer by chemical mechanical polishing (CMP);

bonding a top cover wafer with patterned getters to the first side of the center silicon wafer using gold eutectic bonding;

etching the electrode pattern established on the second side of the center silicon wafer using DRIE;

bonding a bottom cover wafer with silicon dioxide to the second side of the center silicon wafer using low temperature direct wafer fusion bonding;

etching vias in the bottom cover, through the silicon dioxide and silicon nitride layers to expose contact areas on the eight pickoff and forcer electrodes and guard ring;

etching another via through the bottom cover and silicon dioxide layer to expose a contact area on the titanium and gold film on the surface of the silicon nitride layer; and

depositing aluminum, using a shadow mask, on contact areas for ohmic contacts.

19. The method according to claim 18, wherein fabrication of the micro hemispheric resonator gyro is performed at a wafer level using standard MEMS processes.

20. The method according to claim 18, wherein each of the top cover wafer, the center silicon wafer, and the bottom cover wafer is approximately 3 mm thick.

21. The method according to claim 18, wherein the entire center silicon wafer is coated with 3:

m of low stress PECVD silicon nitride.

22. The method according to claim 18, wherein a thickness of the titanium and gold film is limited to only what is necessary for electrical conductive in order to minimize damping that would lower a Q of the hemispheric resonator.

23. The method according to claim 18, wherein the bottom cover wafer is bonded with 1:

m of silicon dioxide to the second side of the center wafer.