Cover based adhesion force measurement system for microelectromechanical system (MEMS)

Patent metadata

Field	Value
Publication number	US-10717641-B2
Application number	US-201715846990-A
Country	US
Kind code	B2
Filing date	Dec 19, 2017
Priority date	Aug 30, 2017
Publication date	Jul 21, 2020
Grant date	Jul 21, 2020

Abstract

In some embodiments, a sensor includes a microelectromechanical system (MEMS) structure, a cover, and a bump stop. The MEMS structure is configured to move responsive to electromechanical stimuli. The cover is positioned on the MEMS structure. The cover is configured to mechanically protect the MEMS structure. The bump stop is disposed on a substrate and the bump stop is configured to stop the MEMS structure from moving beyond a certain point. The bump stop is further configured to stop the MEMS structure from making physical contact with the substrate. Moreover, the cover is configured to apply a force to the MEMS structure responsive to a voltage being applied to the cover.

First claim

What is claimed is:

1. A sensor comprising:
a microelectromechanical system (MEMS) structure anchored to a substrate, wherein the MEMS structure is configured to move responsive to electromechanical stimuli;
electrodes on the substrate configured for sensing MEMS structure motion by changing capacitance value in response thereto;
a cover positioned over the MEMS structure, wherein the cover is configured to mechanically protect the MEMS structure; and
a bump stop disposed on the substrate wherein the bump stop is configured to stop the MEMS structure from moving beyond a certain point and further configured to stop the MEMS structure from making physical contact with the substrate, wherein the cover is positioned opposite to the substrate with respect to the MEMS structure
and wherein the cover is configured to apply a force to the MEMS structure responsive to a voltage being applied to the cover, and wherein the MEMS structure is configured to contact the bump stop and wherein the MEMS structure and the cover make no contact; and
a processor configured to measure adhesion force between the MEMS structure and the bump stop when the MEMS structure makes contact with the bump stop and not released, wherein the adhesion force is measured responsive to the voltage being applied and by measuring capacitance value through the electrodes.

2. The sensor as described in claim 1 , wherein the MEMS structure is released from being in contact with the bump stop when a magnitude of the voltage is decreased to overcome the adhesion force or when a polarity of the voltage is reversed.

3. The sensor as described in claim 1 , wherein the applied voltage ranges between 5 V to 75 V.

4. The sensor as described in claim 1 further comprising a wire bond connected to an electrical connection on an exterior of the cover, wherein the voltage is applied to the cover via the wire bond.

5. The sensor as described in claim 4 , wherein the electrical connection is positioned on a horizontal surface of the cover.

6. The sensor as described in claim 4 , wherein the electrical connection is positioned on a vertical surface of the cover.

7. The sensor as described in claim 1 further comprising:
a circuitry disposed on an interior of the cover facing the MEMS structure, wherein the circuitry is configured to apply the voltage.

8. The sensor as described in claim 7 , wherein the circuitry comprises a charge pump.

9. The sensor as described in claim 1 further comprising vias disposed within the cover, wherein the vias are configured to electrically connect the voltage being applied to an exterior of the cover to an electrode within an interior portion of the cover.

10. A sensor comprising:
a microelectromechanical system (MEMS) structure configured to move responsive to electromechanical stimuli;
a cover positioned on the MEMS structure, wherein the cover is configured to mechanically protect the MEMS structure;
a bump stop disposed on a substrate wherein the bump stop is configured to stop the MEMS structure from moving beyond a certain point and further configured to stop the MEMS structure from making physical contact with the substrate, and wherein the cover is configured to apply a force to the MEMS structure; and
a processor configured to measure adhesion force between the MEMS structure and the bump stop when the MEMS structure makes contact with the bump stop and not released, wherein the adhesion force is measured responsive to the force and by measuring output of the sensor.

11. The sensor as described in claim 10 , wherein a magnetic material is disposed over the MEMS structure, and wherein a coil is disposed on the cover, and wherein the cover applies the force to the MEMS structure responsive to electromagnetic field created by the coil.

12. The sensor as described in claim 10 , wherein a mechanical vibration applies the force to the MEMS structure.

13. The sensor as described in claim 10 , wherein the MEMS structure is released from being in contact with the bump stop when the force overcomes the adhesion force.

14. A method comprising:
applying a voltage to an exterior surface of a cover, wherein the cover is positioned on a microelectromechanical system (MEMS) structure, wherein an interior surface of the cover is within a same housing as the MEMS structure, wherein the cover is configured to mechanically protect the MEMS structure, and wherein the applying the voltage to the exterior surface of the cover moves the MEMS structure;
increasing the voltage until the MEMS structure makes physical contact with a bump stop and further until it stays in contact with the bump stop and is not released;
reducing the voltage until the MEMS structure is released from being in physical contact with the bump stop;
measuring output of a sensor comprising the MEMS structure during the application of the voltage, and during the increasing the voltage, and during the reducing of the voltage; and
determining adhesion force between the MEMS structure and the bump stop based on the measurement output of the sensor.

15. The method as described in claim 14 , wherein the MEMS structure is released from being in contact with the bump stop when a magnitude of the voltage is reduced to overcome the adhesion force.

16. The method as described in claim 14 , wherein the applied voltage ranges between 15 V to 75 V.

17. The method as described in claim 14 , wherein the voltage is applied to the exterior surface of the cover via a wire bond connected to an electrical connection on the exterior surface of the cover.

18. The method as described in claim 14 , wherein the cover comprises vias, wherein the vias are configured to electrically establish a connection from the exterior of the cover to an electrode within an interior surface of the cover to move the MEMS structure in response to the voltage being applied.

Assignees

• Invensense Inc

Inventors

• Castro Alexander
• Ahn Chae

Classifications

• B81B3/001 Primary

  Structures having a reduced contact area, e.g. with bumps or with a textured surface · CPC title

• B81C99/0045

  End test of the packaged device · CPC title

• B81B7/008

  MEMS characterised by an electronic circuit specially adapted for controlling or driving the same (B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00) · CPC title

• B81B7/0045

  for reducing stress inside of the package structure · CPC title

• G01L1/10

  by measuring variations of frequency of stressed vibrating elements, e.g. of stressed strings (using resistance strain gauges G01L1/22) · CPC title