ANGULAR RATE SENSOR

• US 20170343350A1
• Filed: 05/26/2016
• Published: 11/30/2017
• Est. Priority Date: 05/26/2016
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Geisberger, Aaron A.
• Granted Patent: US 10,126,128 B2
• Time in Patent Office: Days
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5755 the devices having a single sensing mass

Abstract

A MEMS sensor for measuring rotational motion about a first axis includes a frame, a base structure under the frame, a drive mass mounted in the frame for rotational movement about a second axis perpendicular to the first axis, and a first drive paddle in the drive mass. A first link includes a first end coupled to a first spring that movably couples the first drive paddle to the drive mass and a second end coupled to a second spring that movably couples the first link to the frame. A drive system includes an electrode aligned to exert electromotive force to pivot the first drive paddle and move the drive mass about the second axis. Deflection of the drive mass is greater than deflection of the first drive paddle when the drive system is operating.

Claims

1. A MEMS sensor for measuring rotational motion about a first axis, comprising:

a frame;

a base structure under the frame;

a drive mass mounted in the frame for rotational movement about a second axis perpendicular to the first axis;

a first drive paddle in the drive mass;

a first link including;

a first end coupled to a first spring, wherein the first spring movably couples the first drive paddle to the drive mass, and

a second end coupled to a second spring, wherein the second spring movably couples the first link to the frame; and

a drive system including an electrode aligned to exert electromotive force to pivot the first drive paddle and move the drive mass about the second axis, and deflection of the drive mass is greater than deflection of the first drive paddle when the drive system is operating.

2. The MEMS sensor of claim 1, further comprising a cavity in the base structure below the drive paddle, wherein a height of the cavity is sufficient to accommodate the deflection of the drive mass.

3. The MEMS sensor of claim 1, further comprising:

a deflection sense system including a first electrode on the base structure, wherein capacitance between the first electrode and the drive mass increases when the deflection of the drive mass decreases.

4. The MEMS sensor of claim 1, further comprising:

a second drive paddle in the drive mass;

a second link including;

a first end coupled to a third spring, wherein the third spring movably couples the second drive paddle to the drive mass, and

a second end coupled to a fourth spring, wherein the fourth spring movably couples the second link to the frame.

5. The MEMS sensor of claim 1, further comprising:

a sense finger adjacent the frame, wherein the sense finger includes;

first and second electrodes anchored to the base structure,

a first movable wall on one side of the first and second electrodes,

a second movable wall on another side of the first and second electrodes,

wherein

capacitance between the first electrode and the first movable wall increases when the MEMS sensor rotates in a first direction about a third axis, and

capacitance between the second electrode and the second movable wall increases when the MEMS sensor rotates in a second direction about the third axis.

6. The MEMS sensor of claim 4, further comprising:

a fifth spring coupled between one side of the frame and the drive mass,

a sixth spring coupled between an opposite side of the frame and the drive mass, wherein the fifth and sixth springs enable the rotational movement of the drive mass about the second axis.

7. The MEMS sensor of claim 1, further comprising:

a first anchor coupled to the frame, wherein the second spring is formed around the first anchor.

8. The MEMS sensor of claim 1, wherein the drive mass and the drive paddle are formed from an electrically conductive material.

9. The MEMS sensor of claim 3, wherein the first electrode is formed from an electrically conductive material.

10. The MEMS sensor of claim 5, wherein the drive mass, the drive paddle, the frame and the sense finger are coplanar when the drive mass and the drive paddle are not being driven, and the sense finger is parallel to the first axis of rotation.

11. A transducer adapted to sense rotation about a first axis comprising:

a drive mass mounted to rotate about a second axis;

a first drive paddle;

a second drive paddle;

a frame around a periphery of the drive mass;

a first link having a first spring coupled to the drive mass and the first drive paddle on one end and having a second spring coupled to the frame on another end, wherein the first drive paddle and the first link are on one side of the second axis;

a second link having a third spring coupled to the drive mass and the second drive paddle on one end and having a fourth spring coupled to the frame on another end, wherein the second drive paddle and the second link are on another side of the second axis.

12. The transducer of claim 11, further comprising:

a base structure under the frame, the drive mass and the first and second drive paddles;

a first cavity in the base structure sized to accommodate deflection of the drive mass on the one side of the second axis;

a second cavity in the base structure sized to accommodate deflection of the drive mass on the other side of the second axis.

13. The transducer of claim 11, further comprising:

a first drive electrode on the base structure, the first drive electrode is configured to exert electromotive force on the first drive paddle;

a second drive electrode on the base structure, the second drive electrode is configured to exert electromotive force on the second drive paddle.

14. The transducer of claim 11, further comprising:

a first measurement electrode configured to measure deflection of the drive mass on the one side of the second axis;

a second measurement electrode configured to measure deflection of the drive mass on the other side of the second axis.

15. The transducer of claim 11, further comprising:

sense fingers including first and second sense electrodes between first and second movable walls, wherein capacitance between the first sense electrode and the first movable wall increases when the transducer rotates in one direction about a third axis, and capacitance between the second sense electrode and the second movable wall increases when the transducer rotates in a direction opposite the one direction.

16. The transducer of claim 11, wherein:

maximum deflection of the first and second drive paddles is less than a maximum deflection of the drive mass.

17. The transducer of claim 11, wherein the first and second drive paddles are in openings in respective areas of the drive mass, and the first and second drive plates are connected on only one edge to the drive mass by the respective first and third springs.

18. The transducer of claim 17 wherein:

the first and second drive paddles are closer to the second axis of rotation than the respective first and third springs.

19. A method of making a transducer adapted to sense rotation about a first axis comprising:

forming a base structure including first and second cavities;

forming a rigid, planar drive mass using a conductive material;

separating first and second drive paddles from the drive mass in respective areas on respective opposite sides of a second axis of rotation of the drive mass;

forming movable links between the first and second drive paddles and edges of the drive mass at the respective areas of the first and second drive paddles;

anchoring the drive mass to the base structure so that one outer edge of the drive mass is in the first cavity when the drive mass rotates in a first direction, and an opposite outer edge of the drive mass is in the second cavity when the drive mass rotates in an opposite direction.

20. The method of claim 19, further comprising:

forming sense fingers adjacent the drive mass, wherein the sense fingers include movable portions and stationary portions so distance between one of the movable portions and one of the stationary portions increases during rotation in a first direction of rotation about a third axis, and distance between a second one of the movable portions and a second one of the stationary portions increases during rotation in a second direction of rotation about the third axis.