Resonating sensor with mechanical constraints

• US 8,631,700 B2
• Filed: 11/05/2010
• Issued: 01/21/2014
• Est. Priority Date: 11/05/2010
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Sammoura, Firas N., Sawyer, William D.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US12/940,354
• Publication Number:
  US 20120111112A1
• Time in Patent Office: 1,173 Days
• Field of Search: 735/040.1, 735/040.2, 735/041.2, 735/041.3
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5698 using acoustic waves, e.g. surface acoustic wave gyros

Abstract

A method and apparatus for sensing movement resonates a primary member in a flexure mode at a given frequency, thus causing the primary member to have top and bottom portions that resonate at substantially about zero Hertz. The method also secures the bottom portion to a first substrate, and mechanically constrains the top portion while resonating in the flexure mode to substantially eliminate vibrations in the top portion. Finally, the method generates a changing capacitance signal in response to movement of the primary member. When generating this changing capacitance signal, the primary member resonates in a bulk mode at a given frequency.

Claims

1. A bulk acoustic wave sensor comprising:

a primary member having a top side and a bottom side;

at least one bottom electrode for actuating the primary member in an out-of-plane flexure mode;

at least one side electrode for detecting an in-plane bulk mode of the primary member when the sensor is rotated about an axis in the plane of the primary member;

a bottom substrate; and

a top substrate,

the primary member being between the bottom substrate and the top substrate,

the bottom substrate having a bottom support portion securing the bottom substrate to the bottom side of the primary member,

the top substrate having a top support portion securing the top substrate to the top side of the primary member.

2. The bulk resonating sensor as defined by claim 1 wherein the primary member is configured to resonate in a flexure mode to cause a given top portion of the top surface to form a stationary node, the top support portion being secured to the given top portion.

3. The bulk resonating sensor as defined by claim 1 wherein the primary member is configured to resonate in a flexure mode to cause a given bottom portion of the bottom surface to form a stationary node, the bottom support portion being secured to the given bottom portion.

4. The bulk resonating sensor as defined by claim 1 wherein the bottom substrate and top substrate form a hermetically sealed chamber to hermetically seal the primary member.

5. The bulk resonating sensor as defined by claim 4 further comprising a plurality of electrodes within the chamber to electrostatically actuate the primary member, the sensor also comprising a plurality of pads electrically connected with the plurality of electrodes, the plurality of pads being outside of the chamber.

6. The bulk resonating sensor as defined by claim 1 wherein the top substrate is formed from a top material, the bottom substrate is formed from a bottom material, the top support being formed from the top material, the bottom support being formed from bottom material.

7. The bulk resonating sensor as defined by claim 1 wherein the sensor comprises a gyroscope.

8. The bulk resonating sensor as defined by claim 1 wherein the bottom substrate comprises a plurality of bottom support portions that are symmetrically arranged with respect to the primary member.

9. A MEMS bulk resonating gyroscope comprising:

a primary member having a top side and a bottom side;

at least one bottom electrode for actuating the primary member in an out-of-plane flexure mode;

at least one side electrode for detecting an in-plane bulk mode of the primary member when the sensor is rotated about an axis in the plane of the primary member;

a bottom substrate secured to the primary member; and

a bottom support portion securing the bottom substrate to the bottom side of the primary member,

the top side of the primary member having a constrained portion that is mechanically constrained to form a stationary node when resonating in the flexure mode and in the bulk mode.

10. The sensor as defined by claim 9 further comprising a top substrate secured to the constrained portion on the top side of the primary member.

11. The sensor as defined by claim 10 further comprising a top support portion securing the top substrate to the constrained portion of the primary member.

12. The sensor as defined by claim 9 wherein the bottom substrate in part forms a chamber for hermetically sealing the primary member.

13. The sensor as defined by claim 12 wherein a top substrate secured to the constrained portion in part forms the chamber.

14. The bulk resonating sensor as defined by claim 12 further comprising a plurality of electrodes within the chamber to actuate the primary member, the sensor also comprising a plurality of pads electrically connected with the plurality of electrodes, the plurality of pads being outside of the chamber.

15. A method of sensing movement, the method comprising:

resonating a primary member in an out-of-plane flexure mode, resonating causing the primary member to have top and bottom portions that form stationary nodes;

securing the bottom portion to a first substrate;

mechanically constraining the top portion while resonating in the flexure mode to substantially eliminate vibrations in the top portion; and

generating a changing capacitance signal in response to movement of the primary member, generating comprising the primary member resonating in an in-plane bulk mode at a given frequency.

16. The method as defined by claim 15 wherein the given frequency is the resonant frequency of the primary member.

17. The method as defined by claim 15 wherein mechanically constraining comprises securing a second substrate to the top portion.

18. The method as defined by claim 15 further comprising reading the changing capacitance signal at a pad that is mechanically secured to the first substrate.

19. The method as defined by claim 15 wherein the primary member is hermetically sealed in a chamber.

20. The method as defined by claim 15 wherein the changing capacitance signal indicates a movement change in at least 2 dimensions.