CAPACITIVE MEMS DEVICE WITH PROGRAMMABLE OFFSET VOLTAGE CONTROL

• US 20090122384A1
• Filed: 11/12/2007
• Published: 05/14/2009
• Est. Priority Date: 11/12/2007
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm, Inc.
• Inventors: Gousev, Evgeni, Felnhofer, Daniel
• Granted Patent: US 7,729,036 B2
• Time in Patent Office: Days
• US Class Current: 359/290
• CPC Class Codes: B81B 2201/045 Optical switches
• CPC Class Codes: B81B 3/0086 Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage
• 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: G11C 23/00 Digital stores characterised by movement of mechanical parts to effect storage, e.g. using balls; Storage elements therefor

Abstract

A capacitive MEMS device is formed having a material between electrodes that traps and retains charges. The material can be realized in several configurations. It can be a multilayer dielectric stack with regions of different band gap energies or band energy levels. The dielectric materials can be trappy itself, i.e. when defects or trap sites are pre-fabricated in the material. Another configuration involves a thin layer of a conductive material with the energy level in the forbidden gap of the dielectric layer. The device may be programmed (i.e. offset and threshold voltages pre-set) by a method making advantageous use of charge storage in the material, wherein the interferometric modulator is pre-charged in such a way that the hysteresis curve shifts, and the actuation voltage threshold of the modulator is significantly lowered. During programming phase, charge transfer between the electrodes and the materials can be performed by applying voltage to the electrodes (i.e. applying electrical field across the material) or by UV-illumination and injection of electrical charges over the energy barrier. The interferometric modulator may then be retained in an actuated state with a significantly lower actuation voltage, thereby saving power.

Claims

1. A device comprising:

an electrode;

a movable layer extending over the electrode and forming a cavity therebetween; and

a material coupled to one or both the electrode and the movable layer, the material being effective at trapping charge due to intrinsic electronic energy band structure and/or extrinsic defects;

wherein the movable layer is configured to move in response to an electrical potential between the electrode and at least a portion of the movable layer, the electrical potential being greater than an actuation threshold voltage, and wherein charge is transferred to or from the material to change the actuation threshold voltage in response to actuation of the device.

2. The device of claim 1, wherein the material is configured to maintain enough transferred charge to change the actuation threshold voltage for a period of time exceeding 100 ms.

3. The device of claim 1, wherein the material comprises a first material and at least one other material having an electron energy band gap that is less than the electron energy band gap of the first material.

4. The device of claim 3, wherein the first material comprises at least one of silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide, or transition metal oxide or silicate.

5. The device of claim 3, wherein the at least one other material comprises at least one of the following:

a metal, a semi-conductor, and a dielectric material.

6. The device of claim 1, wherein the device comprises an interferometric light modulator.

7. The device of claim 6, wherein said device is configured to be connected to additional interferometric light modulators of an array.

8. The device of claim 7, wherein the array is configured to display an image.

9. The device of claim 1, wherein the material comprises regions of different electron energy band gaps.

10. The device of claim 1, wherein the device is a memory device.

11. The device of claim 1, wherein the material comprises SiN_x, and x is an integer greater than zero.

12. The device of claim 1, wherein the material is a dielectric layer with process induced defects throughout the layer.

13. The device of claim 1, wherein the material is a dielectric layer with charge trapping sites introduced at a particular depth.

14. The device of claim 13, wherein the charge trapping sites are formed by implanted dopant atoms.

15. The device of claim 1, wherein the material is coupled to the movable layer.

16. The device of claim 1, wherein the material is coupled to the electrode.

17. The device of claim 1, wherein the material comprises:

a dielectric layer; and

a layer of conductive material with the energy level in the forbidden gap of the dielectric layer.

18. The device of claim 1, wherein the device is a microelectromechanical (MEMS) device.

19. The device of claim 1, wherein the actuation threshold voltage is tunable approximately within one of the following ranges:

0 to 15 volts, 4 to 10 volts, 3 to 15 volts, 0 to 2 volts, wherein the actuation threshold voltage is either negative or positive.

20. The device of claim 1, wherein the actuation threshold voltage is tunable between about 20 and 50 volts, wherein the actuation threshold voltage is either negative or positive.

21. A device comprising:

an electrode;

a multi-layer material comprising a first material and at least one other material with an electron energy band gap that is less than the electron energy band gap of the first material; and

a movable layer extending over the surface of the multi-layer material so as to form a cavity therebetween, the movable layer being configured to contact the multi-layer material in response to an electrical potential between the electrode and at least a portion of the movable layer that is greater than an actuation threshold voltage, wherein when the movable layer contacts the multi-layer material, charge is transferred between the movable layer and the multi-layer material to change the actuation threshold voltage.

22. The device of claim 21, wherein the multi-layer material is configured to maintain enough transferred charge to change the actuation threshold voltage for a period of time exceeding 100 ms after contact between the movable layer and the material is broken.

23. The device of claim 21, wherein the first material comprises a dielectric or insulator material.

24. The device of claim 21, wherein the at least one other material comprises a metal.

25. The device of claim 21, wherein the at least one other material comprises a semi-conductor.

26. The device of claim 21, wherein the at least one other material comprises a dielectric material.

27. The device of claim 21, wherein the device comprises an interferometric light modulator.

28. The device of claim 27, wherein said multi-layer material comprises a first dielectric layer, a second dielectric layer and an additional material layer, and wherein the additional material layer has a conduction band that is offset from the conduction band of the first and/or second dielectric layers.

29. The device of claim 28, wherein the additional material layer is situated between the first and second dielectric layers, the first and second dielectric layers having a thickness of about 50 to 10000 Angstroms and the additional material layer having a thickness of about 2 to 200 Angstroms;

30. The device of claim 27, further configured to be connected to additional interferometric light modulators of an array.

31. The device of claim 28, wherein the array is configured to display an image.

32. The device of claim 31, further comprising:

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

a memory device in electrical communication with said processor.

33. The device of claim 31, further comprising:

a first controller configured to send at least one signal to said array; and

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

34. The device of claim 32, further comprising:

an image source module configured to send said image data to said processor.

35. The device of claim 24, wherein said image source module comprises at least one of a receiver, transceiver, and transmitter.

36. The device of claim 32, further comprising:

an input device configured to receive input data and to communicate said input data to said processor

37. The device of claim 21, wherein the device is a microelectromechanical (MEMS) device.

38. The device of claim 21, wherein the actuation threshold voltage is tunable approximately within one of the following ranges:

0 to 15 volts, 4 to 10 volts, 3 to 15 volts, 0 to 2 volts, wherein the actuation threshold voltage is either negative or positive.

39. The device of claim 21, wherein the actuation threshold voltage is tunable between about 20 and 50 volts, wherein the actuation threshold voltage is either negative or positive.

40. A device comprising:

means for trapping charge in a portion of the device;

means for altering a state of the device, the state being based on an actuation threshold voltage; and

means for altering the actuation threshold voltage.

41. The device of claim 40, wherein the threshold altering means comprises:

an electrode; and

a movable layer extending over the surface of the material so as to form a cavity therebetween, the movable layer being configured to contact the material if an electrical potential between the electrode and at least a portion of the movable layer is greater than the actuation threshold voltage.

42. The device of claim 41, wherein the means for trapping charge is configured to maintain enough transferred charge to change the actuation threshold voltage for a period of time exceeding 100 ms after contact between the movable layer and the material is broken.

43. The device of claim 41, wherein the means for trapping charge comprises a first material and at least one other material having an electron energy band gap that is less than the electron energy band gap of the first material.

44. The device of claim 43, wherein the at least one dielectric material comprises silicon nitride.

45. The device of claim 43, wherein the at least one dielectric material comprises silicon dioxide.

46. The device of claim 43, wherein the at least one dielectric material comprises a metal oxide.

47. The device of claim 43, wherein the at least one dielectric material comprises a silicate.

48. The device of claim 43, wherein the at least one other material comprises a metal.

49. The device of claim 43, wherein the at least one other material comprises a semi-conductor.

50. The device of claim 43, wherein the at least one other material comprises a dielectric material.

51. The device of claim 40, wherein the state altering means comprises a driving circuit.

52. The device of claim 40, further comprising means for modulating light.

53. The device of claim 52, wherein the modulating means comprises an interferometric cavity.

54. The device of claim 52, further comprising means for connecting the device to additional light modulating means of an array.

55. The device of claim 54, wherein the connecting means comprises row and column electrodes.

56. The device of claim 54, wherein the device is configured to display an image.

57. The device of claim 40, wherein the device is a microelectromechanical (MEMS) device.

58. The device of claim 40, wherein the actuation threshold voltage is tunable approximately within one of the following ranges:

0 to 15 volts, 4 to 10 volts, 3 to 15 volts, 0 to 2 volts, wherein the actuation threshold voltage is either negative or positive.

59. The device of claim 40, wherein the actuation threshold voltage is tunable between about 20 and 50 volts, wherein the actuation threshold voltage is either negative or positive.

60. A method of addressing a microelectromechanical (MEMS) element that includes a movable layer and a material comprising regions of different electron energy band gaps, the method comprising:

transferring charge to a region of low electron energy levels in the material.

61. The method of claim 60, wherein said MEMS element exhibits hysteresis, and wherein said transferred charge is sufficient to shift a center of said hysteresis to a desirable position.

62. The method of claim 60, wherein the desirable position is near zero volts.

63. The method of claim 60, further comprising actuating said MEMS element to move said movable layer toward said material

64. The method of claim 60, wherein the charge is transferred by an electrostatic method.

65. The method of claim 60, wherein the charge is transferred by exciting electrons using ultraviolet illumination.

66. The method of claim 60, wherein the charge is transferred such that an initial offset voltage of the MEMS element is set to a desired value.

67. The method of claim 60, wherein the charge is transferred such that an offset voltage of the MEMS element is set to a desired value during operation.

68. A method of manufacturing a microelectromechanical (MEMS) device, the method comprising:

forming an electrode;

forming a movable layer extending over the electrode and forming a cavity therebetween; and

forming a material coupled to one or both the electrode and the movable layer, the material being effective at trapping charge due to intrinsic electronic energy band structure and/or extrinsic defects;

wherein the movable layer is configured to move in response to an electrical potential between the electrode and at least a portion of the movable layer that is greater than an actuation threshold voltage.

69. The method of claim 68, wherein forming the movable layer comprises forming an interferometric cavity.

70. The method of claim 68, wherein forming the material comprises forming a layer of dielectric material and at least one other layer of material having an electron energy band gap that is less than the electron energy band gap of the at least one dielectric material.

71. The method of claim 70, wherein forming the layer of dielectric material comprises forming the dielectric material to comprise silicon nitride.

72. The method of claim 70, wherein forming the layer of dielectric material comprises forming the dielectric material to comprise silicon dioxide.

73. The method of claim 70, wherein forming the layer of dielectric material comprises forming the dielectric material to comprise a metal oxide.

74. The method of claim 70, wherein forming the layer of dielectric material comprises forming the dielectric material to comprise a silicate.

75. The method of claim 70, wherein forming the at least one other layer of material comprises forming the at least one other layer of material to comprise a metal.

76. The method of claim 70, wherein forming the at least one other layer of material comprises forming the at least one other layer of material to comprise a semi-conductor.

77. The method of claim 70, wherein forming the at least one other layer of material comprises forming the at least one other layer of material to comprise a dielectric material.

78. The method of claim 70, wherein the material is coupled to the movable layer.

79. The method of claim 70, wherein the material is coupled to the electrode.

80. A MEMS device manufactured by the method of claim 68.