Microelectromechanical device and method utilizing a porous surface

• US 7,564,613 B2
• Filed: 10/09/2007
• Issued: 07/21/2009
• Est. Priority Date: 04/19/2006
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Kogut, Lior, Sasagawa, Teruo
• Primary Examiner(s): Tra; Tuyen Q
• Application Number:
  US11/869,467
• Publication Number:
  US 20080030825A1
• Time in Patent Office: 651 Days
• Field of Search: 359/290, 359/291, 359/292, 359/245, 359/247, 359/248, 359/250, 359/295, 359/577, 359/578, 359/580, 359/581, 359/582, 359/584, 359/585
• US Class Current: 359/290
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 3/001 Structures having a reduced contact area, e.g. with bumps or with a textured surface
• CPC Class Codes: B81C 2201/0115 Porous silicon
• 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

A microelectromechanical device (MEMS) utilizing a porous electrode surface for reducing stiction is disclosed. In one embodiment, a microelectromechanical device is an interferometric modulator that includes a transparent electrode having a first surface; and a movable reflective electrode with a second surface facing the first surface. The movable reflective electrode is movable between a relaxed and actuated (collapsed) position. An aluminum layer is provided on either the first or second surface. The aluminum layer is then anodized to provide an aluminum oxide layer which has a porous surface. The porous surface, in the actuated position, decreases contact area between the electrodes, thus reducing stiction.

Claims

1. A microelectromechanical systems (MEMS) device, comprising:

a first electrode having a first surface; and

a second electrode having a second surface facing the first surface, the second electrode movable in a gap between a first position and a second position, the first position being a first distance from the first electrode, the second position being a second distance from the first electrode, the second distance being greater than the first distance,

wherein at least one of the electrodes comprises a porous layer having a porous surface facing the other of the electrodes, and wherein the porous surface is substantially continuous while including a plurality of pores formed therethrough.

2. The MEMS device of claim 1, wherein the MEMS device serves as an interferometric modulator.

3. A display system, comprising:

the MEMS device of claim 2;

a display;

a processor that is in electrical communication with the display, the processor being configured to process image data; and

a memory device in electrical communication with the processor.

4. The display system of claim 3, further comprising:

a first controller configured to send at least one signal to the display; and

a second controller configured to send at least a portion of the image data to the first controller.

5. The MEMS device of claim 1, wherein the porous layer comprises an anodized layer.

6. The MEMS device of claim 1, wherein the porous layer comprises Al₂O₃.

7. The MEMS device of claim 1, wherein the porous layer has a hexagonal array structure.

8. The MEMS device of claim 1, wherein the first electrode comprises the porous layer.

9. The MEMS device of claim 1, wherein the second electrode comprises the porous layer.

10. The MEMS device of claim 9, wherein the second electrode comprises an aluminum reflective layer, and wherein the porous layer is formed directly on the reflective layer such that the porous layer faces the first electrode.

11. The MEMS device of claim 9, further comprising a sacrificial layer between the first electrode and the porous layer.

12. The MEMS device of claim 1, wherein the porous surface has pores having an average diameter between about 50 Å

and about 3,000 Å

.

13. The MEMS device of claim 1, wherein the porous layer has a pore density of between about 10¹² m⁻

2 and about 10¹⁵ m<sup>−

2</sup>.

14. The MEMS device of claim 1, wherein the porous layer has a thickness of between about 30 Å

and about 1,500 Å

.

15. The MEMS device of claim 1, wherein the at least one of the electrodes further comprises an aluminum layer, and wherein the porous layer comprises anodized porous alumina formed directly on the aluminum layer.

16. The MEMS device of claim 15, wherein the aluminum layer has a thickness of between about 30 Å

and about 50 Å

.

17. The MEMS device of claim 15, wherein the aluminum layer has a reflectance of between about 33% and 37%.

18. The MEMS device of claim 1, wherein the first electrode comprises an indium tin oxide (ITO) layer.

19. The MEMS device of claim 18, wherein the first electrode further comprises a chromium layer between the ITO layer and the porous layer.

20. The MEMS device of claim 19, wherein the first electrode further comprises a dielectric layer between the chromium layer and the porous layer.

21. The MEMS device of claim 20, wherein the dielectric layer comprises at least one selected from the group consisting of silicon dioxide and aluminum oxide.

22. The MEMS device of claim 21, wherein the dielectric layer comprises a silicon dioxide layer and an aluminum oxide layer stacked over each other, and wherein the aluminum oxide layer is interposed between the porous layer and the silicon dioxide layer.

23. The MEMS device of claim 1, further comprising a deformable layer, wherein the second electrode is suspended from the deformable layer.

24. An interferometric modulator, comprising:

transmissive means for at least partially transmitting incident light, the transmissive means having a first surface;

reflective means for substantially reflecting incident light, the reflective means having a second surface facing the first surface; and

moving means for moving the reflective means relative to the transmissive means between a driven position and an undriven position, the driven position being closer to the transmissive means than is the undriven position,

wherein at least one of the transmissive and reflective means comprises a porous surface facing the other of the transmissive and reflective means, and wherein the porous surface is substantially continuous while including a plurality of pores formed therethrough.

25. The interferometric modulator of claim 24, wherein the means for moving comprises a deformable layer.

26. The interferometric modulator of claim 24, wherein the transmissive means comprises a transparent conductive layer.

27. The interferometric modulator of claim 26, wherein the transmissive means further comprises an absorber layer.

28. The interferometric modulator of claim 24, wherein the reflective means comprises a reflective layer.

29. The interferometric modulator of claim 24, wherein the porous surface is defined by an anodized layer.

30. The interferometric modulator of claim 24, wherein the porous surface is defined by a layer comprising Al₂O₃.

31. The interferometric modulator of claim 24, wherein the porous surface has a hexagonal array structure.

32. The interferometric modulator of claim 24, wherein the porous surface has pores having an average diameter between about 50 Å

and about 3,000 Å

.

33. The interferometric modulator of claim 24, wherein the porous surface has a pore density of between about 10¹²m⁻

2 and about 10¹⁵ m<sup>−

2</sup>.

34. The interferometric modulator of claim 24, wherein the transmissive means comprises the porous surface.

35. The interferometric modulator of claim 24, wherein the reflective means comprises the porous surface.