MEMS HEMISPHERICAL RESONATOR GYROSCOPE

• US 20130104653A1
• Filed: 10/31/2012
• Published: 05/02/2013
• Est. Priority Date: 10/31/2011
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Bernstein, Jonathan, Sherman, Peter G., Weinberg, Marc Steven, Chaparala, Murali
• Granted Patent: US 9,423,253 B2
• Time in Patent Office: Days
• US Class Current: 73/504.13
• CPC Class Codes: G01C 19/5691 of essentially three-dimensional vibrators, e.g. wine glass-type vibrators
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.

Abstract

A MEMS gyroscope is provided. A substrate can be formed with a substantially planar surface, a substantially hemispherical cavity extending into the surface, an actuation electrode, and a plurality of sensing electrodes. A resonator formed from a substantially hemispherical shell can be suspended within the cavity by a stem coupling the center of the bottom of the cavity to the center of the bottom of the shell. An electronic processor can be configured to cause a voltage to be applied to the actuation electrode, receive signals from the sensing electrodes, and process the received signals to determine rotation of the MEMS gyroscope.

Claims

1. A MEMS gyroscope comprising:

a substrate having a substantially planar surface, a substantially hemispherical cavity extending into the surface, an actuation electrode, and a plurality of sensing electrodes;

a resonator formed from a substantially hemispherical shell suspended within the cavity by a stem coupling the center of the bottom of the cavity to the center of the bottom of the shell; and

an electronic processor configured to;

cause a voltage to be applied to the actuation electrode;

receive signals from the sensing electrodes; and

process the received signals to determine rotation of the MEMS gyroscope.

2. The MEMS gyroscope of claim 1, wherein the resonator comprises a lip extending radially outwards around an edge of the hemispherical shell.

3. The MEMS gyroscope of claim 2, wherein the resonator comprises an electrically conductive material.

4. The MEMS gyroscope of claim 3, wherein the electrically conductive material comprises one of boron doped diamond, doped silicon carbide, and doped silicon.

5. The MEMS gyroscope of claim 3, wherein the actuation and sensing electrodes are positioned on the surface of the substrate beneath the resonator.

6. The MEMS gyroscope of claim 5, wherein the actuation and sensing electrodes are positioned such that a first portion of each electrode is located on the surface of the substrate beneath the lip of the resonator and a second portion of each electrode extends downward on the surface of the hemispherical cavity.

7. The MEMS gyroscope of claim 3, wherein the actuation and sensing electrodes are positioned on the top surface of the substrate surrounding the lip of the resonator.

8. The MEMS gyroscope of claim 1, wherein the actuation and sensing electrodes surround the hemispherical cavity and the number of electrodes is a multiple of eight.

9. The MEMS gyroscope of claim 1, wherein the actuation and sensing electrodes are made from a silicide comprising at least one of chromium, zirconium, platinum, palladium, nickel, cobalt, iron, iridium, rhodium, and ruthenium.

10. The MEMS gyroscope of claim 1, wherein the actuation and sensing electrodes comprise dual metal stacks made from chromium or zirconium and at least one of platinum, palladium, nickel, cobalt, iron, iridium, rhodium, zirconium, vanadium, hafnium and ruthenium.

11. The MEMS gyroscope of claim 1, wherein the resonator is made from a dielectric material.

12. The MEMS gyroscope of claim 11, wherein the dielectric material is one of diamond, SiO₂, Si₃N₄, and SiO₂—

TiO₂.

13. The MEMS gyroscope of claim 2, wherein the actuation electrodes comprise interdigitated electrode pairs located on the surface of the substrate beneath the lip of the resonator such that a voltage applied to the electrodes creates fringing fields that cause the resonator to vibrate.

14. The MEMS gyroscope of claim 1, wherein the substrate is made from an amorphous material.

15. The MEMS gyroscope of claim 14, wherein the amorphous material is selected such that the coefficient of thermal expansion of the substrate matches the coefficient of thermal expansion of the resonator.

16. The MEMS gyroscope of claim 14, wherein the amorphous material comprises Corning 1715 glass.

17. The MEMS gyroscope of claim 14, wherein the coefficients of thermal expansion of the resonator and the substrate are both in the range of about 2 to about 4 parts per million per degree Celsius.

18. The MEMS gyroscope of claim 2, wherein the lip of the resonator is segmented into tabs extending radially outward from the edge of the resonator.

19. The MEMS gyroscope of claim 18, wherein the total number of tabs is a multiple of eight.

20. The MEMS gyroscope of claim 18, further comprising a metal deposited onto the tabs, wherein a mass of the metal differs on at least two of the tabs.

21. The MEMS gyroscope of claim 20, wherein the metal comprises an adhesion layer of chromium, zirconium or titanium and at least one of gold and copper.

22. The MEMS gyroscope of claim 20, wherein the resonator has a first resonant frequency associated with a first vibratory mode and a second resonant frequency associated with a second vibratory mode, and wherein the mass of metal on each tab is selected to increase a degree of matching between the first resonant frequency and the second resonant frequency.

23. The MEMS gyroscope of claim 1, wherein the stem extends into the substrate below the bottom of the cavity.

24. The MEMS gyroscope of claim 1, further comprising a thin film battery located on the substrate and coupled to the electronic processor.

25. The MEMS gyroscope of claim 1, further comprising at least one resistor located between at least one of the electrodes and electrical or virtual ground or a drive circuit.

26. The MEMS gyroscope of claim 25, wherein the resonator has a first Q value associated with a first vibratory mode and a second Q value associated with a second vibratory mode, and wherein a value of the at least one resistor is selected to increase a degree of matching between the first Q value and the second Q value.

27. The MEMS gyroscope of claim 1, wherein the stem is hollow.

28. The MEMS gyroscope of claim 1, wherein the resonator includes a corrugated region at its center.

29. The MEMS gyroscope of claim 1, wherein the resonator has a thickness in the range of about 0.5 microns to about 20 microns.

30. The MEMS gyroscope of claim 1, wherein the resonator has a diameter in the range of about 0.2 mm to about 10 mm.

31. A method for manufacturing a MEMS gyroscope comprising:

patterning a hemispherical cavity into a surface of a substrate layer;

depositing a sacrificial layer on top of the conductive layer;

patterning the sacrificial layer to provide a central base for a substantially hemispherical resonator;

depositing a resonator layer on top of the sacrificial layer;

patterning the resonator layer to form the substantially hemispherical resonator and electrodes; and

removing the sacrificial layer from beneath the resonator.

32. The method of claim 31, wherein patterning the resonator layer further comprises patterning a continuous actuation electrode to surround an edge of the resonator.

33. The method of claim 31, wherein patterning the resonator layer further comprises patterning a lip coupled to and surrounding an edge of the resonator.

34. The method of claim 33, wherein patterning the resonator layer further comprises patterning tabs extending radially outward from the lip.

35. The method of claim 34, further comprising:

depositing a metal onto each of the tabs; and

selectively removing portions of the metal such that a mass of the metal differs on at least two tabs.

36. The method of claim 35, wherein depositing the metal onto each of the tabs comprises depositing gold.

37. The method of claim 31, further comprising patterning a plurality of channels into a bottom portion of the hemispherical cavity or the sacrificial layer.

38. The method of claim 37, wherein depositing the resonator layer comprises partially filling the channels, resulting in corrugations at a base of the hemispherical resonator.

39. The method of claim 31, further comprising placing resistors between at least one of the electrodes and electrical or virtual ground or a drive circuit, wherein a value of at least one resistor is selected to increase a degree of Q matching between at least two vibratory modes of the resonator.

40. The method of claim 31, further comprising depositing metal bond pads onto the electrodes.

41. A method for manufacturing a MEMS gyroscope comprising:

patterning a hemispherical cavity into a surface of a substrate layer;

depositing a conductive layer on top of the surface;

patterning the conductive layer;

depositing a sacrificial layer on top of the conductive layer;

patterning the sacrificial layer to provide a central base for a substantially hemispherical resonator;

depositing a resonator layer on top of the sacrificial layer;

patterning the resonator layer to form the substantially hemispherical resonator and electrodes; and

removing the sacrificial layer from beneath the resonator.

42. The method of claim 41, wherein patterning the resonator layer further comprises patterning a continuous actuation electrode to surround an edge of the resonator.

43. The method of claim 41, wherein patterning the resonator layer further comprises patterning a lip coupled to and surrounding an edge of the resonator.

44. The method of claim 43, further comprising patterning tabs extending radially outward from the lip.

45. The method of claim 44, further comprising depositing a metal onto each of the tabs, wherein a mass of the metal differs on at least two tabs.

46. The method of claim 45, wherein depositing the metal onto each of the tabs comprises depositing gold.

47. The method of claim 46, further comprising patterning a plurality of channels into a bottom portion of the hemispherical cavity or the sacrificial layer.

48. The method of claim 47, wherein depositing the resonator layer comprises partially filling the channels, resulting in corrugations at a base of the hemispherical resonator.

49. The method of claim 41, further comprising placing resistors between at least one of the electrodes and electrical or virtual ground or a drive circuit, wherein a value of at least one resistor is selected to increase a degree of Q matching between at least two vibratory modes of the resonator.

50. The method of claim 41, further comprising depositing metal bond pads onto the electrodes.