METHODS FOR MEASUREMENT AND CHARACTERIZATION OF INTERFEROMETRIC MODULATORS

• US 20100039695A1
• Filed: 02/06/2009
• Published: 02/18/2010
• Est. Priority Date: 02/11/2008
• Status: Abandoned Application

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Khazeni, Kasra, Govil, Alok
• Application Number:
  US12/367,428
• Publication Number:
  US 20100039695A1
• Time in Patent Office: Days
• US Class Current: 359/290
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81C 99/0045 End test of the packaged device
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01R 31/2829 Testing of circuits in sensor or actuator systems testing of apparatus for measuring electric or magnetic variables G01R35/00; testing of indicating or recording apparatus G01D; in airbag systems B60R21/0173; checking gas analysers G01N33/007; monitoring or fail-safe circuits for electromagnets H01F7/1844
• CPC Class Codes: G01R 31/2837 Characterising or performance testing, e.g. of frequency response transient response G01R27/28

Abstract

Various methods are described to characterize interferometric modulators or similar devices. Measured voltages across interferometric modulators may be used to characterize transition voltages of the interferometric modulators. Measured currents may be analyzed by integration of measured current to provide an indication of a dynamic response of the interferometric modulator. Frequency analysis may be used to provide an indication of a hysteresis window of the interferometric modulator or mechanical properties of the interferometric modulator. Capacitance may be determined through signal correlation, and spread-spectrum analysis may be used to minimize the effect of noise or interference on measurements of various interferometric modulator parameters.

Claims

1. A method of determining a restoring force of a movable layer of a microelectromechanical system (MEMS) device, the method including:

applying a driving signal to the MEMS device, the MEMS device comprising a movable electrode and a fixed electrode, wherein the driving signal induces movement of the movable electrode relative to the fixed electrode;

measuring a current through the MEMS device during movement of the movable electrode;

identifying frequency components of the measured current; and

utilizing the frequency components of the measured current to determine the restoring force acting on the movable electrode.

2. The method of claim 1, wherein the driving signal is sufficient to induce movement of the movable electrode without collapsing the movable electrode against the fixed electrode.

3. The method of claim 1, wherein identifying the frequency components of the measured current comprises determining a frequency at which the mechanical layer oscillates.

4. The method of claim 1, wherein identifying the frequency components of the measured current comprises performing a Fourier transform on the measured current.

5. The method of claim 1, wherein the MEMS device is located in an environment in which the air pressure is less than one atmosphere.

6. The method of claim 5, wherein the MEMS device is located in a vacuum chamber.

7. The method of claim 1, wherein the MEMS device comprises an interferometric modulator.

8. A method of characterizing mechanical characteristics of a microelectromechanical system (MEMS) device comprising a movable layer, the method comprising:

placing the MEMS device in a low-pressure environment;

applying a driving signal to the MEMS device to induce movement of the movable layer;

measuring a current through the MEMS device during movement of the movable layer; and

determining a frequency at which the movable layer oscillates.

9. The method of claim 8, further comprising calculating a restoring force of the movable layer using the determined frequency.

10. The method of claim 8, wherein determining the frequency at which the movable layer oscillates comprises performing a Fourier transform of the measured current.

11. The method of claim 8, wherein placing the MEMS device in a low-pressure environment comprising placing the MEMS device in a vacuum chamber.

12. A device, comprising:

a microelectromechanical system (MEMS) device comprising a movable layer;

circuitry configured to apply a driving signal to the MEMS device to induce movement of the movable layer, measure a current through the MEMS device, determine a frequency at which the movable layer oscillates, and determine a restoring force acting on the movable layer.

13. The device of claim 12, wherein the circuitry is further configured to perform a Fourier transform of the measured current to determine the frequency at which the movable layer oscillates.

14. The device of claim 12, wherein the driving signal has a maximum voltage less than an actuation voltage of the MEMS device.

15. A device, comprising

means for inducing movement of a movable layer of a microelectromechanical system (MEMS) device;

means for measuring a current through the MEMS device;

means for determining a frequency at which the movable layer oscillates; and

means for determining a restoring force acting on the movable layer.

16. The device of claim 15, wherein the means for inducing movement of the movable layer comprises circuitry configured to apply a driving voltage to the movable layer.

17. The device of claim 15, wherein the means for determining the frequency at which the movable layer oscillates comprises circuitry configured to perform a Fourier transform on the measured current.

18. A display module, comprising:

a display comprising a plurality of microelectromechanical system (MEMS) devices, wherein the MEMS devices each include a movable electrode and a fixed electrode;

driver circuitry configured to drive the MEMS-based display; and

monitoring circuitry configured to;

apply a driving signal to at least one of the plurality of MEMS devices, wherein the driving signal induces movement of the movable electrode relative to the fixed electrode;

measure a current through the at least one of the plurality of MEMS devices;

determine a frequency at which the movable layer oscillates; and

determine a restoring force acting on the movable layer.

19. The display of claim 18, wherein the plurality of MEMS-based devices comprise interferometric modulators.

20. The display of claim 18, wherein the driving signal is sufficient to induce movement of the movable electrode without collapsing the movable electrode against the fixed electrode.

21. The display of claim 18, wherein determining the frequency at which the movable layer oscillates comprises performing a Fourier transform on the measured current.