DRIVE METHOD FOR MEMS DEVICES

• US 20110096056A1
• Filed: 01/05/2011
• Published: 04/28/2011
• Est. Priority Date: 08/27/2004
• Status: Abandoned Application

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chui, Clarence, Mignard, Marc, Sampsell, Jeffrey B., Kothari, Manish, Mathew, Mithran C.
• Application Number:
  US12/985,228
• Publication Number:
  US 20110096056A1
• Time in Patent Office: Days
• US Class Current: 345/211
• 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
• CPC Class Codes: G09G 2300/0473 Use of light emitting or modulating elements having two or more stable states when no power is applied
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2310/0267 Details of drivers for scan electrodes, other than drivers for liquid crystal, plasma or OLED displays
• CPC Class Codes: G09G 2310/0275 Details of drivers for data electrodes, other than drivers for liquid crystal, plasma or OLED displays, not related to handling digital grey scale data or to communication of data to the pixels by means of a current
• CPC Class Codes: G09G 2310/0278 Details of driving circuits arranged to drive both scan and data electrodes
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 3/3466 based on interferometric effect
• CPC Class Codes: G09G 3/3618 with automatic refresh of the display panel using sense/write circuits

Abstract

Embodiments of exemplary MEMS interferometric modulators are arranged at intersections of rows and columns of electrodes. In certain embodiments, the column electrode has a lower electrical resistance than the row electrode. A driving circuit applies a potential difference of a first polarity across electrodes during a first phase and then quickly transition to applying a bias voltage having a polarity opposite to the first polarity during a second phase. In certain embodiments, an absolute value of the difference between the voltages applied to the row electrode is less than an absolute value of the difference between the voltages applied to the column electrode during the first and second phases.

Claims

1. An array of light modulators arranged at intersections of rows and columns of electrodes, the array comprising:

a substrate;

at least one first electrode having a first electrical resistance;

at least one second electrode having a second electrical resistance and crossing the at least one first electrode to form at least one light modulator at the intersection(s) of the at least one first electrode and the at least one second electrode, wherein the second electrical resistance is less than the first electrical resistance; and

a driving circuit having outputs connected to the at least one first electrode and to the at least one second electrode and being configured to apply a potential difference of a first polarity across at least one light modulator during a first phase and then quickly transition to applying a bias voltage having a polarity opposite to the first polarity across at least one light modulator during a second phase, and

wherein the driving circuit applies a first voltage to the at least one first electrode during the first phase and a second voltage to the at least one first electrode during the second phase, and applies a third voltage to the at least one second electrode during the first phase and a fourth voltage to the at least one second electrode during the second phase, and wherein an absolute value of the difference between the first voltage and the second voltage is less than an absolute value of the difference between the third voltage and the fourth voltage.

2. The array of claim 1, wherein the first electrode and second electrode comprise at least partially reflective metal surfaces.

3. The array of claim 1, wherein the first electrode and second electrode form a cavity at the intersection(s) of the first and second electrodes, the cavity being configured to reflect or absorb electromagnetic radiation.

4. The array of claim 1, wherein the first voltage is substantially equal to the second voltage, and wherein the first voltage is between the third voltage and the fourth voltage.

5. The array of claim 4, wherein the first voltage is approximately zero.

6. The array of claim 1, wherein the third voltage is approximately equal to and has an opposite polarity to the fourth voltage.

7. The array of claim 1, wherein two times the bias voltage is substantially equal to the absolute value of the difference between the third voltage and the fourth voltage.

8. The array of claim 1, wherein the first and second voltages are approximately zero, and the third voltage and the fourth voltage are positive and negative, respectively.

9. The array of claim 1, wherein the bias voltage falls within a predetermined hysteresis window.

10. The array of claim 1, wherein the at least one first electrode comprises indium-tin-oxide.

11. The array of claim 1, wherein the at least one first electrode comprises chromium.

12. The array of claim 1, wherein the at least one second electrode comprises aluminum.

13. The array of claim 1, wherein the at least one second electrode is orthogonal to the at least one first electrode.

14. An array of light modulators arranged at intersections of rows and columns of electrodes, the array comprising:

a substrate;

at least one first electrode having a first electrical resistance;

at least one second electrode having a second electrical resistance and crossing the at least one first electrode to form at least one light modulator at the intersection(s) of the at least one first electrode and the at least one second electrode, wherein the second electrical resistance is less than the first electrical resistance; and

a driving circuit configured to apply a first voltage to the at least one first electrode during a first phase and apply a second voltage to the at least one first electrode during a second phase, and configured to apply a third voltage to the at least one second electrode during the first phase and apply a fourth voltage to the at least one second electrode during the second phase, and

wherein an absolute value of the difference between the first voltage and the second voltage is less than the absolute value of the difference between the third voltage and the fourth voltage, and wherein the first voltage and the third voltage form an electric field between the at least one first electrode and the at least one second electrode pointing in a first direction, and wherein the second voltage and the fourth voltage form an electric field between the at least one first electrode and the at least one second electrode pointing in a direction opposite to the first direction.

15. The array of claim 14, wherein the first electrode and second electrode comprise at least partially reflective metal surfaces.

16. The array of claim 14, wherein the first electrode and second electrode form a cavity at the intersection(s) of the first and second electrodes, the cavity being configured to reflect or absorb electromagnetic radiation.

17. The array of claim 14, wherein the first voltage is substantially equal to the second voltage, and wherein the first voltage is between the third voltage and the fourth voltage.

18. The array of claim 14, wherein the third voltage is substantially equal to and has an opposite polarity to the fourth voltage.

19. The array of claim 14, wherein the at least one first electrode comprises indium-tin-oxide.

20. The array of claim 14, wherein the at least one second electrode is orthogonal to the at least one first electrode.

21. A method of driving an array of light modulators arranged at intersections of rows of electrodes and columns of electrodes, the method comprising:

actuating a light modulator by applying a first potential difference having a first polarity across at least one light modulator during a first phase, wherein the first potential is greater than a bias voltage;

maintaining the at least one light modulator in the actuated state by applying a second potential difference having the first polarity across the at least one light modulator during a second phase, wherein the second potential is substantially equal to the bias voltage; and

applying a third potential difference opposite to the first polarity across the at least one light modulator during a third phase,

wherein one of the columns of electrodes or the rows of electrodes forming the at least one light modulator has a higher conductivity and experiences a larger voltage shift between the first and third phases than the other one of the columns of electrodes and the rows of electrodes.

22. A system for writing data to a MEMS display element of an array, the system comprising:

a first set of electrodes characterized by a first resistivity;

a second set of electrodes characterized by a second resistivity and crossing the first set of electrodes; and

a driver circuit having outputs for applying voltages to the first and second sets of crossing and intersecting electrodes,

wherein the driver circuitry is configured to periodically actuate at least one element of the array with a potential difference having a first polarity, and maintain the at least one element in an actuated state when transitioning to a bias voltage having an opposite polarity, wherein an absolute value of the difference between voltages applied to the row electrode before and after the transition is less than an absolute value of the difference between voltages applied to the column electrode before and after the transition.

23. The system of claim 22, wherein the second set of electrodes is orthogonal to the first set of electrodes.

24. A display system comprising:

an array of microelectromechanical pixels;

row and column driver circuitry configured to apply electrical signals to said pixels;

a sensor, configured to sense a capacitance dependent response to at least some of said electrical signals.

25. The display system of claim 24, wherein a plurality of sensors substantially simultaneously sense a capacitance dependent response of a plurality of microelectromechanical pixels.

26. The display system of claim 25, wherein said sensors comprise current sensors.

27. The system of claim 24, additionally comprising isolating buffers between said row and column driver circuitry and said array.

28. The system of claim 24, wherein at least one column of said array comprises a set of test pixels.

29. The system of claim 24, wherein at least some of said pixels comprise interferometric modulators.

30. The system of claim 24, wherein said sensor comprises a comparator.

31. The system of claim 24, additionally comprising circuit components coupled to either or both said row and column driver circuitry and configured to modulate the response of said array to electrical signals.

32. A method of detecting a state of a microelectromechanical device, the method comprising:

applying a selected voltage to an electrode coupled to at least one device;

measuring a voltage across said device; and

determining, based at least in part on said measured voltage, a state of said device.

33. The method of claim 32, wherein said determining comprises determining whether the measured voltage is greater than a threshold.

34. A system for detecting a state of at least one display pixel, the system comprising:

driver circuits coupled to said display; and

means for measuring a voltage across a display pixel.

35. The system of claim 34, additionally comprising means for determining, based upon the measured voltage, a state of said pixel.

36. The system of claim 35, wherein said means for determining comprises a comparator for determining whether the measured voltage is greater than a threshold.

37. A method of writing data to a portion of an array of microelectromechanical elements, said method comprising:

applying a set of data signals to a series of column electrodes of the array;

applying at least one write waveform to a row electrode;

determining an actuation state of at least one element along said row;

applying at least one additional write waveform to said row electrode if it is determined that an actuation state of at least one element along said row is not consistent with said data signals.

38. The method of claim 37, wherein determining an actuation state of at least one element along said row comprises:

applying an electrical signal to said row electrode;

detecting at least one capacitance dependent response of said row electrode;

determining, based at least in part on said response, an operational state of at least one element along said row.