Recovery system and methods for MEMS devices

Patent metadata

Field	Value
Publication number	US-9517930-B2
Application number	US-201414047944-A
Country	US
Kind code	B2
Filing date	Jan 29, 2014
Priority date	Jun 28, 2013
Publication date	Dec 13, 2016
Grant date	Dec 13, 2016

Abstract

Various embodiments of the invention reduce stiction in a wide range of MEMS devices and increase device reliability without negatively impacting performance. In certain embodiments, stiction recover is accomplished by applying electrostatic forces to electrodes via optimized voltage signals that generate a restoring force that aids in overcoming stiction forces between electrodes. The voltage signals used within a stiction recovery procedure may be static or a dynamic, and may be applied directly to existing electrodes within a MEMS device, thereby, eliminating the need for additional components. In some embodiments, the voltage is estimated or calibrated and swept through a range of frequencies that contains one or more resonant frequencies of the mechanical structure that comprises the parts to be detached.

First claim

The invention claimed is:

1. A circuit to recover from stiction, the circuit comprising:
a stiction detection circuit coupled to receive a first signal from a MEMS device, the stiction detection circuit detects, based on the first signal, a stiction event between two components of the MEMS device; and
a stiction recovery circuit coupled to the stiction detection circuit, the stiction recovery circuit generates a second signal in response to detecting the stiction event and applies the second signal to at least a mechanical structure of the MEMS device to cause an electrostatic force.

2. The circuit according to claim 1 , wherein the second signal is one of a non-periodic waveform signal having a continuously increasing frequency, a non-periodic waveform signal having a continuously decreasing frequency, and static signal.

3. The circuit according to claim 1 , wherein the stiction recovery circuit comprises a waveform generator capable of sweeping the second signal through a predetermined range of frequencies.

4. The circuit according to claim 1 , wherein the mechanical structure of the MEMS device comprises a mass.

5. The circuit according to claim 4 , wherein the second signal has a spectral content that comprises at least one frequency in common with a resonant frequency of the mass.

6. The circuit according to claim 4 , wherein the electrostatic force is configured to increase a restoring force of the mass.

7. The circuit according to claim 4 , wherein the mechanical structure of the MEMS device comprises an electrode, the electrode is configured to generate the electrostatic force on the mass.

8. The circuit according to claim 7 , wherein the electrode is a sensor readout electrode that is configured to read the first signal.

9. The circuit according to claim 1 , wherein the MEMS device is one of an acceleration sensor and an angular rate sensor.

10. A method to recover from stiction between two components of a MEMS device, the method comprising:
receiving a first signal;
detecting a stiction event based on the first signal;
generating a second signal in response to detecting the stiction event; and
applying the second signal to a mechanical structure to cause an electrostatic force.

11. The method according to claim 10 , wherein applying the second signal comprises sweeping the second signal through a predetermined range of frequencies.

12. The method according to claim 11 , further comprising calibrating the range of frequencies to increase a restoring force of a first mass.

13. The method according to claim 10 , wherein the second signal has a spectral content that comprises at least one frequency in common with a resonant frequency of the mechanical structure comprising a second mass.

14. The method according to claim 10 , wherein detecting the stiction event comprises detecting the presence of a saturation.

15. The method according to claim 10 , wherein detecting the stiction event comprises detecting the presence of an over-threshold signal.

16. The method according to claim 10 , further comprising determining a stiction recovery mode.

17. A system to recover from stiction between two components of a MEMS device, the system comprising:
a MEMS device that generates a first readout signal;
a readout circuit coupled to receive the first readout signal and convert it into a second readout signal;
a stiction detection circuit coupled to the readout circuit, the stiction detection circuit detects a stiction event based on the second readout signal; and
a stiction recovery circuit coupled to the stiction detection circuit, the stiction recovery circuit generates a voltage signal in response to detecting the stiction event and applies the voltage signal to at least one electrode of the MEMS device to cause an electrostatic force.

18. The system according to claim 17 , further comprising a processing circuit coupled to receive and process the second readout signal.

19. The system according to claim 17 , wherein the voltage signal is a bias voltage.

20. The system according to claim 17 , wherein the voltage signal has a non-periodic square wave voltage having a continuously increasing or decreasing frequency.

Assignees

• Maxim Integrated Products
• Hanking Electronics Ltd

Inventors

• Cazzaniga Gabriele
• Coronato Luca
• Simoni Barbara
• Prandi Luciano

Classifications

• B81C1/00968 Primary

  Methods for breaking the stiction bond · CPC title

• B81B3/0056

  Adjusting the distance between two elements, at least one of them being movable, e.g. air-gap tuning · CPC title

• B81B3/001

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

• H01H1/0036

  Switches making use of microelectromechanical systems [MEMS] (for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009) · CPC title

• B81B2201/016

  having a bridge fixed on two ends and connected to one or more dimples · CPC title