Vibratory tuning fork based six-degrees of freedom inertial measurement MEMS device

• US 9,003,882 B1
• Filed: 11/03/2011
• Issued: 04/14/2015
• Est. Priority Date: 11/03/2010
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Ayazi, Farrokh, Agrawal, Divyanshu
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US13/288,744
• Time in Patent Office: 1,258 Days
• Field of Search: 735/041.2, 735/041.4, 735/041.6, 735/040.4, 735/143.2, 735/143.8, 735/10, 735/11, 735/040.3
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/574 the devices having two sensing masses in anti-phase motion

Abstract

A high-Q, mode-matched, vibratory tuning fork based MEMS device, capable of sensing rotational and translational motion around three axes, and processes of fabrication are disclosed herein. In one embodiment, a MEMS device has first and second proof masses actuated along a first axis, and a third and fourth proof masses actuated along a second orthogonal axis. Each of the proof masses includes an inner mass mechanically coupled to an outer frame. A plurality of electrodes sense rotational or translational motion along the three orthogonal axes.

Claims

1. A MEMS device comprising:

a first proof mass and a second proof mass that can be actuated along a first axis;

a third proof mass and a fourth proof mass that can be actuated along a second orthogonal axis; and

a plurality of electrodes capable of sensing at least one rotational motion around at least one of three orthogonal axes, and at least one translational motion along at least one of the three orthogonal axes, wherein the proof masses comprise a corresponding inner mass mechanically coupled to an outer frame via a tether, wherein the tether has a cross-shape proximate a point of attachment to the inner mass.

2. The MEMS device of claim 1, wherein the at least one tether is made from a different structural layer than the inner mass.

3. The MEMS device of claim 1, wherein a thickness of the at least one tether is less than a thickness of the inner mass.

4. The MEMS device of claim 3, wherein the tether is anchored to a top surface of the inner mass.

5. The MEMS device of claim 1, wherein the inner mass is separated from the outer frame by a gap such that the inner mass can move relative to the outer frame.

6. The MEMS device of claim 1, wherein an out-of-plane resonance frequency of the inner mass and the tether attached directly thereto is approximately equal to an in-plane resonance frequency of the first proof mass, such that rotation around a corresponding in-plane axis is sensed at the resonance frequency of the inner mass and the tether attached directly thereto.

7. The MEMS device of claim 1, wherein the outer frame of the first proof mass is tethered to at least two fixed structures.

8. The MEMS device of claim 7, wherein the fixed structures are ladder shaped structures.

9. The MEMS device of claim 1, wherein the plurality of electrodes comprises:

a first x-axis sense electrode separated from a corresponding proof mass along the first axis;

a first y-axis sense electrode separated from the corresponding proof mass along the second axis; and

a first z-axis sense electrode separated from the inner mass of the corresponding proof mass along a third axis.

10. The MEMS device of claim 9, wherein the plurality of electrodes further comprises:

a second x-axis sense electrode separated from the corresponding proof mass along the first axis;

a second y-axis sense electrode separated from the corresponding proof mass along the second axis; and

a second z-axis sense electrode separated from the inner mass of the corresponding proof mass along the third axis.

11. The MEMS device of claim 1 further comprising:

circuitry responsive to signals received from the plurality of electrodes for determining a degree of said at least one rotational motion.

12. The MEMS device of claim 1 further comprising:

circuitry responsive to signals received from the plurality of electrodes for determining a degree of said at least one translational motion.

13. The MEMS device of claim 1, wherein the drive electrode comprises:

a comb drive for driving one or more of the proof masses to resonate at a resonating frequency.

14. A MEMS device comprising:

a first plurality of proof masses that can be actuated along a first axis;

a second plurality of proof masses that can be actuated along a second orthogonal axis; and

a plurality of electrodes capable of sensing at least one of rotational motion around and translational motion along at least one of three orthogonal axes, wherein the proof masses comprise a corresponding inner mass mechanically coupled to an outer frame via a tether, wherein the tether attaches to a center point of one of a top and bottom surface of the inner mass.

15. The MEMS device of claim 14, wherein each of one of the first and second plurality of the proof masses comprises an inner mass mechanically coupled to an outer frame.

16. The MEMS device of claim 15, wherein the inner mass is mechanically coupled to the outer frame via at least one tether.

17. The MEMS device of claim 16, wherein the inner mass is separated from the outer frame by a gap such that the inner mass can move relative to the outer frame.

18. The MEMS device of claim 15, wherein the outer frame of the proof masses are tethered to at least two fixed structures.

19. A MEMS device comprising:

a first plurality of proof masses that can be actuated along a first axis;

a second plurality of proof masses that can be actuated along a second axis orthogonal to the first axis; and

a plurality of electrodes capable of sensing at least one of rotational motion around and translational motion along any of three orthogonal axes wherein the proof masses comprise a corresponding inner mass mechanically coupled to an outer frame via a tether, wherein the tether is made from a different structural layer than any of the proof masses.