Electro-optical measurement of hysteresis in interferometric modulators

• US 20060066863A1
• Filed: 03/04/2005
• Published: 03/30/2006
• Est. Priority Date: 09/27/2004
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: IDC, LLC
• Inventors: Cummings, William J., Gally, Brian
• Granted Patent: US 7,359,066 B2
• Time in Patent Office: Days
• US Class Current: 356/450
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26

Abstract

Disclosed herein are methods and apparatus for testing interferometric modulators. The interferometric modulators may be tested by applying a time-varying voltage stimulus and measuring the resulting reflectivity from the modulators.

Claims

1. A method of testing a plurality of interferometric modulators, comprising:

applying a triangular voltage waveform to the interferometric modulators; and

detecting reflectivity of light from the interferometric modulators.

2. The method of claim 1, wherein the step of applying a triangular waveform causes the interferometric modulators to vary between an actuated and a non-actuated state.

3. The method of claim 1, wherein the triangular waveform has a frequency of less than about 20 Hz.

4. The method of claim 3, wherein the triangular waveform has a frequency from about 1 Hz to about 15 Hz.

5. The method of claim 1, wherein the amplitude of the triangular waveform is greater than the voltage necessary to cause a positive or negative going actuation of the interferometric modulators.

6. The method of claim 5, wherein the amplitude of the triangular waveform is less than about 1.5 times the voltage necessary to cause a positive or negative going actuation of the interferometric modulators.

7. The method of claim 1, wherein the triangular voltage waveform is simultaneously applied to all interferometric modulators in a reflective display.

8. The method of claim 1, wherein the detecting step includes detecting reflectivity from less than all interferometric modulators in a reflective display.

9. The method of claim 1, wherein the detecting step includes measuring reflectivity with a photodetector.

10. The method of claim 1, wherein the detecting step includes measuring reflectivity through a diffuser positioned in front of the interferometric modulators.

11. The method of claim 1, wherein the detecting step includes measuring reflectivity at an angle that is substantially perpendicular to the interferometric modulators.

12. A method of determining electrical parameters for driving a plurality of inteferometric modulators, comprising:

applying a time-varying voltage stimulus to the interferometric modulators;

detecting reflectivity of light from the interferometric modulators; and

determining one or more electrical parameters from said reflectivity of light in response to said time-varying voltage stimulus, the electrical parameters indicative of electrical parameters sufficient to cause a change in state of the interferometric modulators.

13. The method of claim 12, wherein the determining step includes determining a voltage necessary to cause the interferometric modulators to change from a non-actuated to an actuated state.

14. The method of claim 12, wherein the determining step includes determining a voltage necessary to cause the interferometric modulators to change from an actuated state to a non-actuated.

15. The method of claim 12, wherein the determining step includes determining amplitude of a bias voltage in the interferometric modulators.

16. The method of claim 12, wherein the determining step includes determining amplitude of an offset voltage in the interferometric modulators.

17. The method of claim 12, wherein the determining step includes determining amplitude of a memory window in the interferometric modulators.

18. The method of claim 12, wherein the determining step includes:

normalizing the reflectivity to one or more pre-determined values; and

determining potentials where the normalized reflectivity crosses zero.

19. A method of testing a plurality of interferometric modulator structures, comprising:

applying a time-varying voltage waveform to the interferometric modulators;

detecting reflectivity of light from the interferometric modulators;

determining reflectivity of light as a function of voltage; and

identifying the plurality of interferometric modulators as of sufficient quality for use in a display based on said determining.

20. The method of claim 19, wherein the interferometric modulators are identified as of sufficient quality for use in the display if said reflectivity of light as a function of voltage displays a predefined hysteresis characteristic.

21. The method of claim 19, wherein the interferometric modulators are identified as of sufficient quality for use in the display if said reflectivity of light as a function of voltage indicates an amplitude of a memory window of the interferometric modulators is within a predefined threshold window.

22. The method of claim 19, wherein the interferometric modulators are identified as of sufficient quality for use in the display if said reflectivity of light as a function of voltage indicates an amplitude of a bias voltage of the interferometric modulators is within a predefined threshold window.

23. A system for testing a plurality of interferometric modulators, comprising:

an illumination source adapted to provide incident light to a plurality of interferometric modulators;

a voltage source adapted to apply enough voltage to the interferometric modulators so as to change their state; and

an optical detector adapted to detect light reflected from the plurality of interferometric modulators.

24. The system of claim 23, wherein the illumination source provides incident light at an angle that is substantially perpendicular to the interferometric modulators.

25. The system of claim 23, wherein the voltage source is simultaneously electrically connected to all interferometric modulators in a reflective display.

26. The system of claim 23, wherein the voltage source is adapted to apply a time-varying voltage waveform.

27. The system of claim 26, wherein the voltage source is adapted to apply a triangular voltage waveform.

28. The system of claim 23, wherein the optical detector is a photo detector.

29. The system of claim 23, wherein the optical detector is adapted to detect light from less than all interferometric modulators in a reflective display.

30. The system of claim 23, wherein the optical detector is adapted to detect light at an angle that is substantially perpendicular to the interferometric modulators.

31. The system of claim 23, wherein the optical detector is adapted to detect light through a diffuser.

32. The system of claim 23, further including a filter disposed in front of the optical detector.

33. A method of testing a plurality of inteferometric modulators, comprising:

applying a time-varying voltage waveform to the interferometric modulators;

detecting reflectivity of light from the interferometric modulators;

repeating said applying and detecting steps one or more times;

averaging at least a portion of the detected reflectivity; and

determining one or more electrical parameters from said averaged reflectivity.

34. A method of testing a color interferometric modulator display, the display comprising a plurality of sub-pixel types, each sub-pixel type corresponding to a different color, the method comprising:

applying a time-varying voltage waveform to one sub-pixel type;

detecting reflectivity of light from said sub-pixel type;

determining one or more electrical parameters from said detecting; and

repeating said applying, detecting, and determining steps for another sub-pixel type.

35. A method of testing a plurality of interferometric modulators, comprising:

a means for applying a time-varying voltage waveform to the interferometric modulators;

a means for detecting reflectivity of light from the interferometric modulators; and

a means for determining one or more parameters based on said detected reflectivity.

36. The method of claim 35, wherein the means for applying a time-varying voltage waveform is a voltage source.

37. The method of claim 35, wherein the means for detecting reflectivity is a photo detector.

38. The method of claim 35, wherein the means for determining one or more parameters is a computer.