Methods for measurement and characterization of interferometric modulators

• US 8,258,800 B2
• Filed: 09/30/2008
• Issued: 09/04/2012
• Est. Priority Date: 02/11/2008
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Govil, Alok
• Primary Examiner(s): Dole, Timothy J
• Application Number:
  US12/242,763
• Publication Number:
  US 20090251157A1
• Time in Patent Office: 1,435 Days
• Field of Search: 324676-679
• US Class Current: 324/713
• 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 systems (MEMS) device, the method comprising:

providing a circuit comprising the MEMS device, the circuit being configured to provide a substantially constant impedance for an applied voltage;

applying a constant voltage to the circuit for a period of time, wherein application of the constant voltage causes a change in the state of the MEMS device, and wherein the impedance of the circuit before the state change of the MEMS device is substantially equal to the impedance of the circuit after the state change;

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

identifying the transition voltage at which the state of the MEMS device changes based upon the measurement of the voltage as a function of time.

2. The method of claim 1, wherein the impedance remains substantially constant independent of the state of the MEMS device.

3. The method of claim 1, wherein the circuit further comprises a resistance in series with the MEMS device, wherein the series resistance is substantially larger than a resistance of the MEMS device.

4. The method of claim 3, wherein the series resistance is at least 1 MΩ

.

5. The method of claim 1, wherein identifying the transition voltage comprises identifying a period wherein the measured voltage remains substantially constant for a period of time.

6. The method of claim 1, wherein the MEMS device comprises a plurality of MEMS devices arranged in parallel.

7. The method of claim 6, wherein the number of MEMS devices is sufficient that parasitic capacitance between the MEMS devices maintains the voltage across the MEMS devices at a substantially constant level during transition of the plurality of MEMS devices from a first state to a second state.

8. The method of claim 7, wherein the number of MEMS devices is greater than 100.

9. The method of claim 1, wherein applying the substantially constant voltage for a period of time comprises applying a periodic voltage which remains substantially constant for the period of time.

10. The method of claim 9, wherein the periodic voltage comprises a square wave.

11. The method of claim 9, wherein the periodic voltage alternates between at least 3 voltage levels.

12. The method of claim 9, wherein the periodic voltage spans at least a predetermined hysteresis window of the MEMS device.

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

14. The method of claim 1, wherein the transition voltage corresponds to one of an actuation voltage or a release voltage of the MEMS device.

15. A method of identifying a transition voltage in an array of electromechanical system (EMS) devices, the method comprising:

applying a driving voltage which remains substantially constant for a period of time to the array of EMS devices arranged in parallel, wherein the driving voltage is applied via a circuit comprising a resistance in series with the array of EMS devices, wherein the resistance in series with the array of EMS devices is substantially larger than the resistance of the array of EMS devices, wherein applying a driving voltage causes a change in the states of the array of EMS devices, and wherein an impedance of the circuit remains substantially constant during application of the driving voltage;

measuring a resultant voltage across the array of EMS devices as a function of time; and

identifying the transition voltage at which the resultant voltage remains substantially constant for a period of time during transition of the EMS devices within the array from a first state to a second state.

16. The method of claim 15, wherein the applied driving voltage comprises a substantially square waveform.

17. The method of claim 15, wherein the EMS devices within the array comprise interferometric modulators.

18. The method of claim 17, wherein the first state corresponds to a relaxed state of the interferometric modulator and the second state corresponds to a collapsed state of the interferometric modulator.

19. The method of claim 17, wherein the first state corresponds to a collapsed state of the interferometric modulator and the second state corresponds to a relaxed state of the interferometric modulator.

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

applying a driving voltage comprising a substantially square waveform to the MEMS device using a circuit configured to provide a substantially constant impedance for an applied voltage, wherein applying a driving voltage causes a change in the state of the MEMS device, and wherein the impedance of the circuit before the change in state of the MEMS device is substantially equal to the impedance of the circuit after the change in state of the MEMS device;

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

determining at least a first transition voltage wherein the voltage across the MEMS device remains substantially constant for a period of time.

21. The method of claim 20, additionally comprising determining a second transition voltage wherein the voltage across the MEMS device remains substantially constant for a period of time, wherein the second transition voltage differs from the first transition voltage.

22. The method of claim 21, wherein the first transition voltage represents an actuation voltage of the MEMS device, and the second transition voltage corresponds to a release voltage of the MEMS device.

23. A device, comprising:

a circuit comprising a microelectromechanical system (MEMS) device, wherein the circuit is configured to provide a substantially constant impedance for an applied voltage; and

circuitry configured to apply a constant voltage to the MEMS device for a period of time, measure a voltage across the MEMS device as a function of time, and identify a transition voltage based upon the measurement of the voltage as a function of time, wherein application of the constant voltage causes the MEMS device to change from a first state to a second state, and wherein the impedance of the circuit remains substantially constant regardless of the state of the MEMS device.

24. The MEMS device of claim 23, wherein the circuitry is configured to identify a transition voltage corresponding to a voltage at which the voltage across the MEMS device remains substantially constant for a period of time.

25. The MEMS device of claim 23, wherein MEMS device comprises an interferometric modulator.

26. The MEMS device of claim 25, wherein the transition voltage comprises an actuation voltage of the interferometric modulator.

27. The MEMS device of claim 25, wherein the transition voltage comprises a release voltage of the interferometric modulator.

28. A device, comprising:

means for maintaining a constant impedance for an applied voltage;

means for applying a voltage to a microelectromechanical system (MEMS) device to induce a state change of the MEMS device, wherein the voltage remains substantially constant for a period of time, and wherein the impedance remains constant regardless of the state change of the MEMS device;

means for measuring a voltage across the MEMS device; and

means for identifying a transition voltage of the MEMS device based on the measured voltage.

29. The device of claim 28, wherein the means for maintaining a constant impedance for an applied voltage comprise a circuit comprising a resistance in series with the MEMS device, wherein the resistance in series with the MEMS device is substantially larger than the resistance of MEMS device.

30. The device of claim 28, wherein the means for identifying the transition voltage comprises circuitry configured to identify a transition voltage corresponding to a voltage at which the measured voltage across the MEMS device remains substantially constant for a period of time.