Capacitively coupled micromirror

• US 6,906,850 B2
• Filed: 12/21/2001
• Issued: 06/14/2005
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Knipe, Richard L.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): CHOI, WILLIAM C
• Application Number:
  US10/027,873
• Publication Number:
  US 20020122238A1
• Time in Patent Office: 1,271 Days
• Field of Search: 359/223, 359/224, 359290-292, 359/298, 359/295, 345/30, 345/55, 345/84, 345/85
• US Class Current: 359/295
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

A capacitively coupled microelectromechanical device comprising: a semiconductor substrate; a member operable to deflect to either of at least two states; and a switch for selectively connecting the member to a voltage signal. When a logic high signal is stored on memory capacitor, mirror transistor is turned on, grounding the mirror structure. When a logic low signal is stored on the memory capacitor, the mirror transistor is turned off, allowing the mirror to float electrically. Mirrors that are tied to a voltage potential, which typically are grounded, are affected by a reset pulse and rotate away from their landed position. When the mirrors have rotated to the opposite side, a bias signal is applied to hold the repositioned mirror in place in the opposite state. Mirrors that electrically are floating do not experience the forces generated by the reset voltage and remain in their previous state.

Claims

1. A micromechanical device comprising:

at least one member operable to deflect to either of at least two states;

a switch associated with each said at least one member for selectively connecting said member to a ground signal; and

at least one bias electrode associated with each said at least one member operable to apply a reset pulse when said member is connected to said ground signal by said switch.

2. The micromechanical device of claim 1, further comprising:

a memory cell for storing positioning information, said memory cell having an output driving said switch.

3. The micromechanical device of claim 1, further comprising:

a memory cell for storing positioning information, said memory cell comprising a capacitor storing a charge representing said positioning information.

4. The micromechanical device of claim 1, further comprising:

a memory cell for storing positioning information, said memory cell comprising a capacitor storing a charge representing said positioning information and a pass transistor.

5. The micromechanical device of claim 1, said bias electrode comprising:

at least two said bias electrodes, one associated with each said state.

6. The micromechanical device of claim 1, said member operable to deflect about an axis, said bias electrode comprising:

at least two said bias electrodes, one on either side of said axis, said at least two bias electrodes electrically connected.

7. The micromechanical device of claim 1, said switch comprising:

a pass transistor.

8. The micromechanical device of claim 1, wherein said member is a micromirror.

9. The micromechanical device of claim 1, further comprising:

a memory cell for storing positioning information, said memory cell comprising a capacitor storing a charge representing said positioning information and a pass transistor, wherein said switch comprises;

a pass transistor having a gate and two terminals, said gate connected to said memory capacitor, one said terminal connected to said member and a second said terminal connected to said ground connection.

10. The micromechanical device of claim 9, said memory cell operable to turn on said pass transistor when said memory cell capacitor holds a first charge.

11. The micromechanical device of claim 9, said memory cell operable to turn off said pass transistor when said memory cell capacitor holds a second charge.

12. A micromechanical device comprising:

an array of independently deflectable members, each deflectable member supported by a hinge and spaced apart from a substrate;

at least two bias electrodes supported by said substrate, one on each side of an axis of said hinge; and

a means associated with at least one deflectable member of said array for selectively connecting said deflectable member to a ground potential during a period in which said bias electrodes provide a reset signal.

13. The micromechanical device of claim 12, said means for selectively connecting comprising a pass transistor.

14. The micrornechanical device of claim 12, said means for selectively connecting comprising:

a pass transistor; and

a capacitor connected to a gate terminal of said pass transistor.

15. The micromechanical device of claim 12, said means for selectively connecting comprising:

a pass transistor; and

a capacitor, a first terminal of said capacitor connected to a gate terminal of said pass transistor and a second terminal of said capacitor connected to said ground potential.

16. A method of operating a micromechanical device, the method comprising:

grounding a deflectable member;

applying a reset signal to bias electrodes to reposition said selectively grounded deflectable member;

electrically floating said deflectable member such that said reset signal does not reposition said electrically floating deflectable member.

17. The method of claim 16, further comprising:

applying a bias potential to said bias electrodes to hold said repositioned deflectable member in place.

18. The method of claim 16, said deflectable member operable to deflect in one of two directions from a neutral position.

19. The method of claim 16, said selectively grounding a deflectable member comprising:

grounding said deflectable member to cause said deflectable member to be repositioned during by said reset signal, and floating said deflectable member to prevent said deflectable member from being repositioned by said reset signal.

20. The method of claim 16, further comprising:

applying an initialization signal to said bias electrodes to force said deflectable member to a known state.

21. The method of claim 20, said applying an initialization signal to said bias electrodes to force said deflectable member to a known state comprising:

applying a voltage signal to one of said bias electrodes and a ground signal to another one of said bias electrodes.

22. A method of operating an array of micromechanical elements, the method comprising:

grounding a deflectable member of a first group of said micromechanical elements;

allowing a deflectable member of a second group of said micromechanical elements to electrically float; and

applying a reset signal to bias electrodes associated with said micromechanical elements in said first and said second groups.

23. The method of claim 22, said reset signal operable to reposition said deflectable members of said first group.

24. The method of claim 22, said reset signal operable to reposition said deflectable members of said first group and not said deflectable members of said second group.

25. The method of claim 22, further comprising:

applying a bias potential to said bias electrodes to hold said repositioned deflectable members of said first group and said deflectable members of said second group in place.

26. The method of claim 22, said deflectable members operable to deflect in one of two directions from a neutral position.

27. The method of claim 22, further comprising:

applying an initialization signal to said bias electrodes to force said deflectable members of said first and second groups to a known state.

28. The method of claim 27, said applying an initialization signal to said bias electrodes to force said deflectable members of said first and second groups to a known state comprising:

applying a voltage signal to one of said bias electrodes and a ground signal to another one of said bias electrodes.