MEMS proof mass with split Z-axis portions

• US 9,599,472 B2
• Filed: 03/16/2015
• Issued: 03/21/2017
• Est. Priority Date: 02/01/2012
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Acar, Cenk
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US14/658,579
• Publication Number:
  US 20150185012A1
• Time in Patent Office: 736 Days
• Field of Search: 735/143.2, 735/143.8
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5733 Structural details or topology
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0811 for one single degree of freedom of movement of the mass
• CPC Class Codes: G01P 2015/082 for two degrees of freedom of movement of a single mass
• CPC Class Codes: G01P 2015/0848 using a plurality of mechanically coupled spring-mass systems, the sensitive direction of each system being different

Abstract

This document discusses among other things apparatus and methods for a proof mass including split z-axis portions. An example proof mass can include a center portion configured to anchor the proof-mass to an adjacent layer, a first z-axis portion configure to rotate about a first axis using a first hinge, the first axis parallel to an x-y plane orthogonal to a z-axis, a second z-axis portion configure to rotate about a second axis using a second hinge, the second axis parallel to the x-y plane, wherein the first z-axis portion is configured to rotate independent of the second z-axis portion.

Claims

1. A proof-mass structure for an accelerometer, the proof mass structure configured to couple to an adjacent layer using a single anchor, the proof mass structure comprising:

a first z-axis portion configured to rotate about a first axis using a first hinge, the first axis parallel to an x-y plane orthogonal to a z-axis;

a second z-axis portion configured to rotate about a second axis using a second hinge, the second axis parallel to the x-y plane;

wherein the first z-axis portion is configured to rotate independent of the second z-axis portion;

a central portion coupled to the first z-axis portion and the second z-axis portion via the first hinge and the second hinge, respectively, the central portion configured to couple with the single anchor and to suspend the first z-axis portion and the second z-axis portion from an adjacent layer of the accelerometer, one or more moveable portions of an electrode coupled to a frame of the central portion;

wherein movement of the one or more moveable portions of the electrode is associated with movement of the frame resulting from either x-axis motion of the proof mass structure or y-axis motion of the proof mass structure;

wherein the first z-axis portion and the second z-axis portion are coupled to the single anchor via the frame.

2. The proof mass of claim 1, wherein the first z-axis portion is configured to rotate in an opposite direction than that of the second z-axis portion in response to an acceleration of the proof mass along the z-axis.

3. The proof mass of claim 1, wherein the first hinge is located opposite the second hinge with respect to the central portion.

4. The proof mass of claim 1, wherein the first hinge is coupled to the first z-axis portion closer to a first end of the first z-axis portion than a second end of the first z-axis portion.

5. The proof mass of claim 1, wherein the second hinge is coupled to the second z-axis portion closer to a first end of the second z-axis portion than a second end of the axis z-axis portion.

6. The proof mass of claim 1, including a third hinge, wherein the first z-axis portion is configured to rotate about the first axis in the x-y plane using the first hinge and the third hinge.

7. The proof mass of claim 1, including a fourth hinge, wherein the second z-axis portion is configured to rotate about the second axis in the x-y plane using the second hinge and the fourth hinge.

8. The proof mass of claim 1, wherein the central portion includes an anchor portion and an x-axis proof mass portion, the x-axis proof mass portion configured to deflect, with respect to the anchor portion, in response to an acceleration of the proof mass along the x-axis.

9. The proof mass of claim 8, wherein the central portion includes a y-axis proof mass portion, the y-axis proof mass portion configured to deflect, with respect to the anchor portion, in response to an acceleration of the proof mass along the y-axis.

10. The proof mass of claim 1 wherein the first z-axis portion and the second z-axis portion substantially envelop the central portion in the x-y-plane.

11. A method comprising:

suspending a proof mass structure of an accelerometer from an adjacent layer of an accelerometer using a single anchor and a central portion of the proof mass structure, the proof mass structure including a first z-axis portion and a second z-axis portion, wherein the first z-axis portion of the proof mass structure and the second z-axis portion of the proof mass structure are coupled to the central portion, wherein the suspending the proof mass structure includes suspending one or more additional proof mass portions of the proof mass structure and wherein the one or more additional proof mass portions include a moveable portion of an electrode coupled to a frame of the central portion, wherein movement of the one or more moveable portions of the electrode is associated with movement of the frame resulting from either x-axis motion of the proof mass structure or y-axis motion of the proof mass structure;

accelerating the proof mass structure along a z-axis direction;

rotating the first z-axis portion of the proof mass in a first rotational direction about a first axis lying in an x-y-plane using a first hinge, the rotation of the first z-axis portion of the proof mass responsive to the acceleration of the proof mass in the z-axis direction; and

rotating the second z-axis portion of the proof mass in a second rotational direct about a second axis lying in an x-y-plane using a second hinge, the rotation of the second z-axis portion of the proof mass responsive to the acceleration of the proof mass in the z-axis direction; and

wherein the first rotational direction is opposite the second rotational direction using a point of reference outside a perimeter of the proof mass.

12. An apparatus comprising:

a single proof mass accelerometer;

the single proof mass accelerometer including;

a single accelerometer proof mass formed in the x-y plane of a device layer, the single proof mass including;

a central portion including a frame and a single, central anchor configured to suspend the single proof-mass from an adjacent layer of the apparatus;

a first z-axis portion configured to rotate about a first axis in the x-y plane using a first hinge, the first hinge coupled to the central portion;

a second z-axis portion configure to rotate about a second axis in the x-y plane using a second hinge, the second hinge coupled to the central portion; and

one or more moveable portions of an electrode coupled to the frame of the central portion, wherein movement of the one or more moveable portions of the electrode is associated with movement of the frame resulting from either x-axis motion of the proof mass structure or y-axis motion of the proof mass structure; and

wherein the first z-axis portion is configured to rotate independent of the second z-axis portion.

13. The apparatus of claim 12, wherein the central portion includes in-plane x and y-axis accelerometer sense electrodes symmetrical about the single, central anchor.

14. The apparatus of claim 12, wherein the single proof mass includes:

a first portion of first and second out-of-plane z-axis accelerometer sense electrodes coupled to the first z-axis portion, and a first portion of third and fourth out-of-plane z-axis sense electrodes coupled to the second z-axis portion.

15. The apparatus of claim 14, including:

a cap wafer bonded to a first surface of the device layer; and

a via wafer bonded to a second surface of the device layer, wherein the cap wafer and the via wafer are configured to encapsulate the single proof mass accelerometer in a cavity.

16. The apparatus of claim 15, wherein the via wafer includes:

a second portion of the first and second out-of-plane z-axis accelerometer sense electrodes, and a second portion of the third and fourth out-of-plane z-axis sense electrodes.

17. The apparatus of claim 16, including a first portion of x-axis accelerometer electrodes coupled to the device layer, and wherein the central portion of the single proof mass includes a second portion of the x-axis accelerometer electrodes, the second portion of the x-axis accelerometer electrodes coupled to the single central anchor using x flexure bearings.

18. The apparatus of claim 16, including a first portion of y-axis accelerometer electrodes coupled to the device layer, and wherein the central portion of the single proof mass includes a second portion of the y-axis accelerometer electrodes, the second portion of the y-axis accelerometer electrodes coupled to the single central anchor using y flexure bearings.

19. The apparatus of claim 15, including a multiple-axis gyroscope within the cavity and adjacent the single proof mass accelerometer;

the multiple-axis gyroscope including;

a single gyroscope proof-mass formed in the x-y plane of the device layer, the second single proof-mass including;

a main proof-mass section suspended about a second single, central anchor, the main proof-mass section extending outward towards an edge of the multiple-axis gyroscope;

a central suspension system configured to suspend the single gyroscope proof mass from the single, central anchor; and

a drive electrode including a moving portion and a stationary portion, the moving portion including a first set of fingers interdigitated with a second set of fingers of the stationary portion, wherein the drive electrode and the central suspension system are configured to oscillate the single proof mass about the z-axis normal to the x-y plane at a drive frequency.

20. The apparatus of claim 19, wherein the single gyroscope proof mass includes symmetrical x-axis proof-mass sections configured to move anti-phase along the x-axis in response to z-axis angular motion.