MEMS accelerometer with Z axis anchor tracking

• US 10,203,351 B2
• Filed: 10/03/2014
• Issued: 02/12/2019
• Est. Priority Date: 10/03/2014
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Zhang, Xin
• Primary Examiner(s): Shah, Manish S
• Assistant Examiner(s): Morello, Jean
• Application Number:
  US14/505,928
• Publication Number:
  US 20160097791A1
• Time in Patent Office: 1,593 Days
• Field of Search: 7351432, 7351417, 73497, 73 5432
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/058 Rotation out of a plane parallel to the substrate
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: B81B 3/0054 For holding or placing an element in a given position
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

In some exemplary embodiments, a MEMS accelerometer includes a device wafer having a proof mass and a plurality of tracking anchor points attached to a substrate. Each tracking anchor is configured to deflect in response to asymmetrical deformation in the substrate, and transfer mechanical forces generated in response to the deflection to tilt the proof mass in a direction of the deformation.

Claims

1. A microelectromechanical systems (MEMS) accelerometer comprising:

a device substrate,

a suspended proof mass,

a proof mass support positioned on an axis of rotation of the MEMS accelerometer and movably coupling the suspended proof mass to the device substrate,

torsional springs that are coupled to the suspended proof mass and proof mass support, and

a plurality of tracking anchors coupled to the device substrate and a plurality of beams that are coupled to intermediate points on the torsional springs and configured in combination to tilt the suspended proof mass in a direction of asymmetrical deformation of the device substrate.

2. The MEMS accelerometer of claim 1, wherein a ratio of tilt of the suspended proof mass to deflection of at least one of the plurality of tracking anchors in response to the asymmetrical deformation of the device substrate is about 0.5.

3. The MEMS accelerometer of claim 1, wherein a ratio of tilt of the suspended proof mass to deflection of at least one of the plurality of tracking anchors in response to the asymmetrical deformation of the device substrate is between about 0.5 and about 0.603.

4. The MEMS accelerometer of claim 1, wherein a ratio of tilt of the suspended proof mass to deflection of at least one of the plurality of tracking anchors in response to the asymmetrical deformation of the device substrate is between about 0.4784 and about 0.5.

5. The MEMS accelerometer of claim 1, wherein

at least one of the plurality of tracking anchors is configured to transfer mechanical forces generated in response to the asymmetrical deformation of the device substrate to at least one of the plurality of beams;

the at least one of the plurality of beams transfers the mechanical forces that it receives to at least one of the torsional springs; and

the at least one of the torsional springs apply a torque to the suspended proof mass to tilt the suspended proof mass in the direction of the asymmetrical deformation of the device substrate.

6. The MEMS accelerometer of claim 1, further comprising a frame comprising at least one of the plurality of beams, each tracking anchor having a beam of the plurality of beams directly connecting it to the frame, wherein

each tracking anchor of the plurality of tracking anchors transfers mechanical forces generated in response to the asymmetrical deformation of the device substrate to its respective beam of the plurality of beams;

each beam of the plurality of beams transfers the mechanical forces that it receives to the frame;

the frame transfers the mechanical forces that it receives to the torsional springs; and

the torsional springs apply a torque to tilt the suspended proof mass in a direction of the asymmetrical deformation of the device substrate.

7. The MEMS accelerometer of claim 1, wherein the suspended proof mass is a teeter totter proof mass or a tilt mode proof mass.

8. The MEMS accelerometer of claim 1, wherein:

(1) each tracking anchor of the plurality of tracking anchors is positioned an equal distance from a center axis of the MEMS accelerometer; and

/or

(2) the plurality of tracking anchors are positioned symmetrically across a center axis of the MEMS accelerometer; and

/or

(3) the distance from any given tracking anchor to a center axis of the MEMS accelerometer is defined by the formula

9. The MEMS accelerometer of claim 1, wherein the proof mass support includes at least one anchor attached to the substrate.

10. The MEMS accelerometer of claim 9, wherein the at least one anchor supports the suspended proof mass by the torsional springs.

11. The MEMS accelerometer of claim 1, further comprising circuitry configured to output a signal representative of a position of the suspended proof mass relative to the device substrate, wherein the MEMS accelerometer is configured such that tilting of the suspended proof mass in the direction of the asymmetrical deformation of the device substrate reduces zero-g bias offset introduced by the asymmetrical deformation of the device substrate.

12. The MEMS accelerometer of claim 1, wherein the plurality of beams are symmetrical across a center axis of the MEMS accelerometer.

13. A microelectromechanical systems (MEMS) accelerometer comprising:

a substrate;

a support anchor on the substrate;

a proof mass attached to the substrate by the support anchor and configured to rotate about the support anchor;

torsional springs that couple the proof mass to the support anchor;

a frame connected to intermediate points on the torsional springs;

a first tracking anchor coupled to the substrate;

a second tracking anchor coupled to the substrate;

a first beam connected to the frame and having a first end connected to the first tracking anchor; and

a second beam connected to the frame and having a second end connected to the second tracking anchor.

14. The MEMS accelerometer of claim 13, wherein the first and second tracking anchors are configured to deflect in response to asymmetrical deformation of the substrate and transfer mechanical forces through the frame, first and second beams, and torsional springs to tilt the proof mass in a direction of the asymmetrical deformation of the substrate.

15. The MEMS accelerometer of claim 13, wherein:

(1) the proof mass is a teeter totter proof mass or a tilt mode proof mass; and

/or

(2) each tracking anchor of the first and second tracking anchors is positioned an equal distance from a center axis of the MEMS accelerometer; and

/or

(3) the first and second tracking anchors are positioned symmetrically across a center axis of the MEMS accelerometer; and

/or

(4) a distance from any given tracking anchor to a center axis of the MEMS accelerometer is defined by the formula

16. The MEMS accelerometer of claim 13, further comprising circuitry configured to output a signal representative of a position of the proof mass relative to the substrate, wherein the MEMS accelerometer is configured such that tilt of the proof mass in a direction of asymmetrical deformation of the substrate reduces zero-g bias offset introduced by the asymmetrical deformation of the substrate.

17. A microelectromechanical systems (MEMS) accelerometer comprising:

a proof mass on a substrate;

first means for supporting the proof mass;

torsional springs that are coupled to the proof mass and the first means; and

second means, separate from the first means and attached to the substrate and a plurality of beams that are coupled to intermediate points on the torsional springs, for deflecting in response to asymmetrical deformation of the substrate, and transferring mechanical forces generated in response to the deflection to tilt the proof mass in a direction of the asymmetrical deformation of the substrate.

18. The MEMS accelerometer of claim 17, wherein:

the second means include a first tracking anchor and a second tracking anchor; and

a ratio of tilt of the proof mass to the deflection of at least one of the first and second tracking anchors is between about 0.4784 and about 0.603.

19. The MEMS accelerometer of claim 17, wherein:

(1) the proof mass is a teeter totter proof mass or a tilt mode proof mass; and

/or

(2) the second means include a first tracking anchor and a second tracking anchor, each tracking anchor of the first and second tracking anchors positioned an equal distance from a center axis of the MEMS accelerometer; and

/or

(3) the second means are positioned symmetrically across a center axis of the MEMS accelerometer; and

/or

(4) a distance from any given tracking anchor to a center axis of the MEMS accelerometer is defined by the formula

20. The MEMS accelerometer of claim 17, further comprising circuitry configured to output a signal representative of a position of the proof mass relative to the substrate, wherein the MEMS accelerometer is configured such that tilt of the proof mass in the direction of the asymmetrical deformation of the substrate reduces zero-g bias offset introduced by the asymmetrical deformation of the substrate.