METHODS FOR MEASUREMENT AND CHARACTERIZATION OF INTERFEROMETRIC MODULATORS

• US 20090201008A1
• Filed: 09/30/2008
• Published: 08/13/2009
• Est. Priority Date: 02/11/2008
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chou, Chen-Jean, Govil, Alok
• Granted Patent: US 8,115,471 B2
• Time in Patent Office: Days
• US Class Current: 324/76.110
• CPC Class Codes: G01R 31/2637 for testing other individual devices G01R31/2608 - G01R31/2632, G01R31/27 take precedence
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3466 based on interferometric effect

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 identifying a transition voltage in a microelectromechanical system (MEMS) device, the method comprising:

applying a substantially constant source current to the MEMS device;

measuring a voltage across the MEMS device as a function of time;

determining the rate of change of the measured voltage; and

identifying a discontinuity in the rate of change of the measured voltage, wherein the voltage at which the discontinuity occurs corresponds to a transition voltage of the MEMS device.

2. The method of claim 1, wherein the MEMS device comprises a movable electrode and a fixed electrode.

3. The method of claim 2, wherein the transition voltage corresponds to an actuation voltage wherein the movable electrode collapses towards the fixed electrode.

4. The method of claim 2, wherein the transition voltage corresponds to a release voltage wherein the movable electrode relaxes from a position in which the movable electrode is collapsed relative to the fixed electrode to a position in which the movable electrode is spaced apart from the fixed electrode.

5. A method of identifying a transition voltage in a microelectromechanical system (MEMS) device, the method comprising:

applying a substantially constant source current to the MEMS device;

measuring a voltage across the MEMS device as a function of time; and

identifying a beginning or end of a transition period in the measured voltage, wherein a voltage at which the transition period begins or ends corresponds to a transition voltage of the MEMS device.

6. The method of claim 5, additionally comprising determining a value for the source current based upon at least one property of the device to be tested.

7. The method of claim 6, wherein the determined value for the source current depends on a desired measurement speed of the method

8. The method of claim 6, wherein the determined value for the source current depends on an internal capacitance of the MEMS device to be measured and an area to be measured.

9. The method of claim 5, wherein the MEMS device comprises a plurality of MEMS structures.

10. The method of claim 5, wherein the MEMS device comprises at least one interferometric modulator.

11. The method of claim 5, wherein the variance in the magnitude of the source current during the transition period is less than 20% of the magnitude of the source current.

12. The method of claim 10, wherein the transition voltage corresponds to an actuation voltage at which the interferometric modulator collapses to an actuated state.

13. The method of claim 10, wherein the transition voltage corresponds to a release voltage at which the interferometric modulator releases from an actuated state.

14. The method of claim 5, additionally comprising determining a transition time corresponding to a length of the transition period.

15. The method of claim 14, wherein the transition voltage comprises an actuation voltage, and wherein the transition time corresponds to a period of time between the beginning of the transition period and a point in time where the measured voltage increases beyond the actuation voltage to a higher voltage without decreasing below the actuation voltage.

16. The method of claim 14, wherein the transition voltage comprises a release voltage, and wherein the transition time corresponds to a period of time between the beginning of the transition period and a point in time where the measured voltage decreases below the release voltage to a lower voltage without increasing above the release voltage.

17. A method of determining a transition voltage of an interferometric modulator, the interferometric modulator comprising a movable electrode, a fixed electrode, and an optical stack, the method comprising:

applying a source current to the interferometric modulator;

measuring a voltage across the interferometric modulator as a function of time; and

identifying a discontinuity in a rate of change of the measured voltage, wherein a voltage at which the discontinuity occurs corresponds to a transition voltage of the interferometric modulator.

18. The method of claim 18, wherein the interferometric modulator is in a relaxed position without application of the constant source current, and the transition voltage corresponds to an actuation voltage of the interferometric modulator.

19. The method of claim 18, wherein the interferometric modulator is in a collapsed state without application of the constant source current, and the transition voltage corresponds to a release voltage of the interferometric modulator.

20. A device, comprising:

a microelectromechanical system (MEMS) device, and

circuitry configured to apply a current to the MEMS device, measure a voltage across the MEMS device, identify a discontinuity in a rate of change of the measured voltage, and determine a transition voltage of the MEMS device based upon the identified discontinuity in the measured voltage.

21. The MEMS device of claim 20, wherein MEMS device comprises an interferometric modulator.

22. The MEMS device of claim 21, wherein the transition voltage comprises an actuation voltage of the interferometric modulator.

23. The MEMS device of claim 21, wherein the transition voltage comprises a release voltage of the interferometric modulator.

24. The MEMS device of claim 20, wherein the magnitude of the applied current varies by no more than 20% during the transition period.

25. The MEMS device of claim 24, wherein the magnitude of the applied current varies by no more than 10% during the transition period.

26. The MEMS device of claim 20, wherein the magnitude of the applied current remains substantially constant during the transition period.

27. A device, comprising:

means for applying a source current to a microelectromechanical (MEMS) device;

means for measuring a voltage across the MEMS device; and

means for determining a transition voltage of the MEMS device based upon an identified discontinuity in the rate of change of the measured voltage.