Active lateral force stiction self-recovery for microelectromechanical systems devices

• US 9,213,045 B2
• Filed: 05/23/2013
• Issued: 12/15/2015
• Est. Priority Date: 05/23/2013
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Jia, Kemiao, Jones, Peter T.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US13/901,189
• Publication Number:
  US 20140345380A1
• Time in Patent Office: 936 Days
• Field of Search: 735/143.2, 735/10, 734/93, 735/143.6, 735/143.8
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 3/0016 Arrangements for avoiding sticking of the flexible or moving parts not provided for in groups B81B3/0005 - B81B3/0013
• CPC Class Codes: B81C 1/00968 Methods for breaking the stiction bond
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A mechanism for recovering from stiction-related events in a MEMS device through application of a force orthogonal to the stiction force is provided. A small force applied orthogonal to the vector of a stiction force can release the stuck proof mass easier than a force parallel to the vector of the stiction force. Example embodiments provide a vertical parallel plate or comb-fingered lateral actuator to apply the orthogonal force. Alternate embodiments provide a proof mass of a second transducer to impact a stuck MEMS actuator to release stiction.

Claims

1. A method for recovering from a stiction event in a microelectromechanical systems (MEMS) device, the method comprising:

subjecting the MEMS device to a force sufficient to cause stiction between a moving portion of the MEMS device and a fixed portion of the MEMS device, wherein the MEMS device comprises a teeter-totter accelerometer and the moving portion of the MEMS device is a rotating proof mass;

exerting a release force to the MEMS device sufficient to release the stiction between the moving portion of the MEMS device and the fixed portion of the MEMS device, wherein

the release force comprises a release force vector orthogonal to a stiction force vector associated with the stiction,

said exerting is performed by a component in a package comprising the MEMS device, and

the release force is an electromagnetic force.

2. The method of claim 1 wherein the component in the package comprises:

an electrode formed on a side surface of an end of the rotating proof mass; and

a fixed electrode formed on a fixed surface proximate to the electrode formed on the side surface of the end of the rotating proof mass.

3. The method of claim 2 wherein said exerting comprises:

applying a charge to the fixed electrode wherein the charge is of a sufficient magnitude to cause the electromagnetic force.

7. The method of claim 1 further comprising:

detecting the presence of the stiction event in the MEMS device; and

performing said exerting the release force in response to said detecting.

4. A method for recovering from a stiction event in a microelectromechanical systems (MEMS) device, the method comprising:

subjecting the MEMS device to a force sufficient to cause stiction between a moving portion of the MEMS device and a fixed portion of the MEMS device, wherein the MEMS device comprises a teeter-totter accelerometer and the moving portion of the MEMS device is a rotating proof mass;

exerting a release force to the MEMS device sufficient to release the stiction between the moving portion of the MEMS device and the fixed portion of the MEMS device, wherein

the release force comprises a release force vector orthogonal to a stiction force vector associated with the stiction, and

said exerting is performed by a component in a package comprising the MEMS device, and

said exerting the release force comprises impacting a side surface of the rotating proof mass with a mechanical force, wherein the release force comprises the mechanical force.

5. The method of claim 4, wherein the component comprises a second MEMS device located in proximity to the MEMS device.

6. The method of claim 5, wherein

the second MEMS device comprises a capacitive plate XY-accelerometer, and

the capacitive plate XY-accelerometer comprises an impact feature located in proximity to the MEMS device.

8. A microelectromechanical systems (MEMS) device comprising:

a first proof mass subject to a stiction force between the first proof mass and a fixed portion of the MEMS device;

means for applying a release force to the first proof mass in response to the stiction force, wherein

the release force is sufficient to release the stiction force, and

the release force comprises a release force vector orthogonal to a stiction force vector associated with the stiction force, and

the means for applying the release force comprises a means for applying an electromagnetic force.

9. The MEMS device of claim 8 wherein the means for applying the electromagnetic force comprises:

an electrode formed on a side surface of a portion of the first proof mass; and

a fixed electrode formed on a fixed surface proximate to the electrode formed on the side surface of the portion of the first proof mass, wherein

the portion of the first proof mass comprises a location in contact with the fixed portion of the MEMS device while under application of the stiction force.

10. The MEMS device of claim 9, wherein

the fixed electrode is configured for applying a charge of a sufficient magnitude to generate the electromagnetic force with the electrode on the side surface of the first proof mass.

11. A microelectromechanical systems (MEMS) device comprising:

a first proof mass subject to a stiction force between the first proof mass and a fixed portion of the MEMS device;

means for applying a release force to the first proof mass in response to the stiction force, wherein

the release force is sufficient to release the stiction force, and

the release force comprises a release force vector orthogonal to a stiction force vector associated with the stiction force, and

the means for applying the release force comprises a means for applying a mechanical force.

12. The MEMS device of claim 11 wherein the means for applying the mechanical force comprises:

a second MEMS device located in proximity to the first proof mass, wherein the second MEMS device is configured to impact the first proof mass in response to the stiction force.

13. The MEMS device of claim 12, wherein

a teeter-totter accelerometer comprises the first proof mass,

the first proof mass is a rotating proof mass,

a capacitive plate XY-accelerometer comprises the second MEMS device, and

the capacitive plate XY-accelerometer comprises an impact feature configured to impact the MEMS device.

14. The MEMS device of claim 13 wherein the capacitive plate XY-accelerometer further comprises:

a capacitive plate pair configured to move a second proof mass of the capacitive plate XY-accelerometer to impact the first proof mass in response to the stiction force.

15. The MEMS device of claim 14 wherein the capacitive plate pair is further configured to provide capacitance signals in response to movement in an X or Y axial direction of the capacitive plate XY-accelerometer.

16. A semiconductor device package comprising:

a Z-axis accelerometer comprising a first proof mass, wherein

the Z-axis accelerometer is subject to a stiction force when a portion of the first proof mass contacts a fixed surface; and

a capacitive plate XY-axis accelerometer comprising a second proof mass, wherein

a portion of the second proof mass is configured to impact the portion of the first proof mass in response to the stiction force.

17. The semiconductor device package of claim 16 further comprising:

logic, communicatively coupled to the Z-axis accelerometer and the capacitive plate XY-axis accelerometer, configured to

receive a first signal from the Z-axis accelerometer, wherein the first signal indicates an occurrence of the stiction force,

provide a second signal to the capacitive plate XY-axis accelerometer, in response to the first signal, wherein the portion of the second proof mass impacts the portion of the first proof mass in response to the second signal.