Method of making an X-Y axis dual-mass tuning fork gyroscope with vertically integrated electronics and wafer-scale hermetic packaging

• US 7,250,112 B2
• Filed: 07/28/2005
• Issued: 07/31/2007
• Est. Priority Date: 10/20/2003
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Nasiri, Steven S., Flannery, Anthony Francis Jr.
• Primary Examiner(s): Ahmed; Shamim
• Application Number:
  US11/193,127
• Publication Number:
  US 20070012653A1
• Time in Patent Office: 733 Days
• Field of Search: 216/2, 216/67, 216/88, 216/89, 735/040.2
• US Class Current: 216/2
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A method for making an angular velocity sensor having two masses which are laterally disposed in an X-Y plane and indirectly connected to a frame is provided. The two masses are linked together by a linkage such that they necessarily move in opposite directions along Z. Angular velocity of the sensor about the Y axis can be sensed by driving the two masses into Z-directed antiphase oscillation and measuring the angular oscillation amplitude thereby imparted to the frame.

Claims

1. A method for manufacturing a sensor for measuring angular velocity in a sensing plane, the method comprising:

etching a sensing subassembly from a gyroscope wafer, wherein the sensing subassembly includes;

a substantially planar frame parallel to the sensing plane; and

a linkage connected to the frame and comprising a first mass and a second mass laterally disposed in the sensing plane, the linkage mechanically constraining the first mass and the second mass to move in opposite directions perpendicular to the sensing plane,

wherein angular velocity in the sensing plane is measurable based on the movement of the first mass and the second mass in opposite directions.

2. The method of claim 1, further comprising:

providing an actuator for driving a first portion of the sensing subassembly into oscillation at a drive frequency; and

providing a transducer for sensing motion of a second portion of the sensing subassembly responsive to the angular velocity.

3. The method of claim 2, wherein providing an actuator comprises providing an actuator selected from the group consisting of electrostatic actuators, electromagnetic actuators, piezoelectric actuators, and thermal actuators.

4. The method of claim 2, wherein providing a transducer comprises providing a transducer selected from the group consisting of capacitive sensors, electromagnetic sensors, piezoelectric sensors, and piezoresistive sensors.

5. The method of claim 2, wherein the first portion of the sensing subassembly is the linkage and the second portion of the sensing subassembly is the frame.

6. The method of claim 2, wherein the first portion of the sensing subassembly is the frame and the second portion of the sensing subassembly is the linkage.

7. The method of claim 2, wherein etching a sensing subassembly further comprises etching a hole in at least one of the first mass or the second mass to reduce air resistance.

8. The method of claim 2, wherein etching a sensing subassembly comprises high aspect ratio etching.

9. The method of claim 8, wherein the high aspect ratio etching comprises deep reactive ion etching.

10. The method of claim 2, further comprising thinning the gyroscope wafer prior to etching the sensing subassembly.

11. The method of claim 10, wherein thinning the gyroscope wafer comprises grinding and polishing the gyroscope wafer.

12. The method of claim 10, wherein thinning the gyroscope wafer comprises thinning the gyroscope wafer to a thickness of about 40 microns.

13. The method of claim 10, wherein thinning the gyroscope wafer comprises selectively thinning the gyroscope wafer to at least two different thicknesses, such that the first mass and the second mass defined by the etching have the larger of the two different thicknesses.

14. The method of claim 2, further comprising photolithographically patterning the gyroscope wafer to define the sensing subassembly prior to etching the sensing subassembly from the gyroscope wafer.

15. The method of claim 2, further comprising:

etching a substantially planar base from the gyroscope wafer, the base being parallel to and positioned around the frame; and

reference bonding the base to a top surface of a reference wafer;

wherein providing an actuator comprises depositing a plurality of control electrodes on the top surface of the reference wafer, and

wherein providing a transducer comprises depositing a frame electrode connected to the frame and depositing a base electrode connected to the base, wherein the frame electrode and the base electrode comprise a capacitive sensor.

16. The method of claim 15, wherein reference bonding comprises one of Al—

Ge bonding, solder bonding, In—

Au bonding, eutectic alloy bonding, or polymer bonding.

17. The method of claim 15, further comprising fabricating CMOS circuitry within the reference wafer.

18. The method of claim 17, further comprising connecting the CMOS circuitry to the plurality of control electrodes, and connecting the CMOS circuitry to the capacitive sensor, whereby wafer scale integration of the actuator and the transducer is obtained.

19. The method of claim 17, further comprising depositing a sense electrode connected to the CMOS circuitry and positioned on the top surface of the reference wafer for sensing motion of the linkage relative to the reference wafer.

20. The method of claim 15, further comprising etching two recesses into the top surface of the reference wafer, the two recesses being aligned with the first mass and the second mass to accommodate motion of the first mass and the second mass perpendicular to the sensing plane.

21. The method of claim 15, wherein etching a sensing subassembly further comprises:

etching a center plate connected to the frame and connected to and in between the first mass and the second mass;

etching a first edge plate connected to the frame and to the first mass; and

etching a second edge plate connected to the frame and to the second mass;

wherein the first edge plate and the second edge plate are rotatable about parallel axes of rotation which are also parallel to the sensing plane, and

wherein the linkage further comprises the center plate and the first edge plate and the second edge plates plate.

22. The method of claim 21, wherein etching a sensing subassembly further comprises:

etching a first pair of torsional flexures connecting the center plate to the frame;

etching a second pair of torsional flexures connecting the first edge plate to the frame; and

etching a third pair of torsional flexures connecting the second edge plate to the frame.

23. The method of claim 21, wherein etching a sensing subassembly further comprises etching a hole in at least one of the center plate, the first edge plate, or the second edge plate to reduce air resistance.

24. The method of claim 21, wherein depositing a plurality of control electrodes comprises:

depositing a first edge split electrode positioned beneath the first edge plate on the top surface of the reference wafer and separated from the first edge plate by a predetermined distance d;

depositing a second edge split electrode positioned beneath the second edge plate on the top surface of the reference wafer and separated from the second edge plate by the distance d;

depositing a center split electrode positioned beneath the center plate on the top surface of the reference wafer and separated from the center plate by the distance d.

25. The method of claim 24, further comprising depositing a standoff on the top surface of the reference wafer to define the distance d.

26. The method of claim 24, further comprising etching a standoff on the base to define the distance d.

27. The method of claim 21, wherein etching a center plate further comprises etching a first lever arm connected to the first mass and etching a second lever arm connected to the second mass, whereby motion of the first mass and the second mass perpendicular to the sensing plane responsive to rotation of the center plate is increased.

28. The method of claim 21, wherein etching a first edge plate further comprises etching a lever arm connected to the first mass, whereby motion of the first mass perpendicular to the sensing plane responsive to rotation of the first edge plate is increased.

29. The method of claim 21, wherein etching a second edge plate further comprises etching a lever arm connected to the second mass, whereby motion of the second mass perpendicular to the sensing plane responsive to rotation of the second edge plate is increased.

30. The method of claim 15, further comprising etching a plurality of flexures connecting the base to the frame.

31. The method of claim 30, wherein etching a sensing subassembly further comprises etching a groove in a surface of the frame facing the base, and wherein etching a substantially planar base further comprises etching a tab extending from the base toward the frame and engaged in the groove, the combination of the tab and the groove restricting a range of motion of the frame, thereby protecting the flexures.

32. The method of claim 15, further comprising

etching a plurality of flexures connecting the frame to the reference wafer;

and

etching a plurality of base isolation trenches separating the flexures from the base;

whereby stress in the base is not coupled to the flexures.

33. The method of claim 32, further comprising

etching a plurality of reference isolation trenches separating the flexures from the top surface of the reference wafer,

whereby stress in the top surface of said reference wafer is substantially not coupled to the flexures.

34. The method of claim 15, further comprising cap bonding the base to a bottom surface of a silicon cap wafer.

35. The method of claim 34, wherein cap bonding comprises one of glass bonding, gold eutectic bonding, solder bonding, Si to Si fusion bonding, or Si to SiO₂ fusion bonding.

36. The method of claim 34, wherein cap bonding is performed at an equal or higher temperature than the reference bonding, and wherein the cap bonding is performed prior to the reference bonding.

37. The method of claim 34, further comprising etching a recess into the bottom surface of the silicon cap wafer to accommodate motion of the sensing subassembly.

38. The method of claim 34, wherein cap bonding comprises a first hermetic bonding and wherein the reference bonding comprises a second hermetic bonding, thereby providing a hermetic enclosure surrounding the sensing subassembly.

39. The method of claim 38, further comprising changing a pressure within the hermetic enclosure to be substantially different from atmospheric pressure.

40. The method of claim 38, wherein the first hermetic bonding comprises a first eutectic metal sealing, and the second hermetic bonding comprises a second eutectic metal sealing.

41. The method of claim 34, further comprising:

etching a plurality of flexures connecting the frame to the silicon cap wafer; and

etching a plurality of base isolation trenches separating the flexures from the base;

whereby stress in the base is not coupled to the flexures.

42. The method of claim 41, further comprising

etching a plurality of cap isolation trenches separating the flexures from the bottom surface of the silicon cap wafer,

whereby stress in the bottom surface of the silicon cap wafer is substantially not coupled to the flexures.