Controlling electromechanical behavior of structures within a microelectromechanical systems device

• US 20040058532A1
• Filed: 09/20/2002
• Published: 03/25/2004
• Est. Priority Date: 09/20/2002
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chui, Clarence, Miles, Mark W., Kothari, Manish, Batey, John
• Granted Patent: US 7,550,794 B2
• Time in Patent Office: Days
• US Class Current: 438/689
• CPC Class Codes: B81B 3/0035 Constitution or structural means for controlling the movement of the flexible or deformable elements
• 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

In one embodiment, the invention provides a method for fabricating a microelectromechanical systems device. The method comprises fabricating a first layer comprising a film having a characteristic electromechanical response, and a characteristic optical response, wherein the characteristic optical response is desirable and the characteristic electromechanical response is undesirable; and modifying the characteristic electromechanical response of the first layer by at least reducing charge build up thereon during activation of the microelectromechanical systems device.

Claims

1. A method for fabricating a microelectromechanical systems device, the method comprising:

fabricating a first layer comprising at least one film having a characteristic electromechanical response, and a characteristic optical response, wherein the characteristic optical response is desirable and the characteristic electromechanical response is undesirable; and

modifying the characteristic electromechanical response of the first layer by at controlling charge buildup thereon during activation of the microelectromechanical systems device.

2. The method of claim 1, wherein controlling charge buildup comprises fabricating at least one second layer on or adjacent the first layer, the second layer being of a material that traps charge.

3. The method of claim 2, wherein fabricating the at least one second layer comprises fabricating two second layers such that the first layer is sandwiched between the two second layers.

4. The method of claim 1, wherein the first layer comprises SiO₂ and the second layer comprises Al₂O₃.

5. The method of claim 1, further comprising fabricating a displaceable layer which is electrostatically displaceable from an undriven condition in which it is spaced from the first layer by a gap to a driven condition in which the gap is at least partially reduced, wherein an activation voltage required to displace the displaceable layer to its driven condition is greater than a bias voltage required to keep the displaceable layer in its driven condition.

6. A microelectromechanical systems device, comprising:

a first layer; and

at least one second layer on or adjacent the first layer, wherein each second layer is of a material having a charge trapping density to manipulate charge buildup on the first layer.

7. The microelectromechanical systems device of claim 6 wherein the charge trapping density of each second layer is such that it acts as a charge trap to at least reduce charge buildup on the first layer.

8. The microelectromechanical systems device of claim 6, comprising two second layers disposed so as to sandwich the first layer therebetween.

9. The microelectromechanical systems device of claim 6, wherein the first layer comprises SiO₂ and the second layers comprise Al₂O₃.

10. The microelectromechanical systems device of claim 9, wherein the first and second layers define a film stack, and the device further comprises a displaceable layer which is electrostatically displaceable from an undriven condition, in which it is spaced from the film stack by a gap, to a driven condition in which the gap is at least partially reduced, wherein an actuation voltage required to displace the displaceable layer to its driven condition is greater than a bias voltage required to keep the displaceable layer in its driven condition.

11. The microelectromechanical systems device of claim 10, wherein the film stack and the displaceable layer define components within a interference modulator.

12. The microelectromechanical sytems device of claim 6, wherein the at least one second layer acts as a barrier to protect the first layer from damage due to etchants.

13. A microelectomechanical systems device comprising:

a layer including SiO₂; and

at least one layer comprising Al₂O₃ on or adjacent the layer comprising SiO₂.

14. The microelectromechanical systems device of claim 13, comprising two layers of Al₂O₃ disposed so as to sandwich the layer of SiO₂ therebetween.

15. A microelectromechanical systems device comprising:

a plurality of elements, each having a component that is electrostatically displaceable between an undriven and a driven condition; and

a driving mechanism to apply an actuation voltage to each element to displace its respective component from its undriven condition to its driven condition, and to apply a bias voltage to each element to keep its respective component in the driven condition, wherein the actuation voltage is greater than the bias voltage.

16. The microelectromechanical systems device of claim 15, wherein each of the elements comprises a hysteresis window of at least 20% defined as [V_actuation−

V_release.]×

100, wherein V_actuation is the actuation voltage, and V_release is a release at which the displaceable layer returns to its undriven condition.

17. The microelectromechanical systems device of claim 15, wherein the plurality of elements each define an interference modulator operable to reflect light of a certain wavelength.

18. A microelectromechanical systems device comprising:

a plurality of interference modulators, each comprising a reflective layer and a transparent layer which is normally spaced from the reflective layer by a gap corresponding to an undriven condition of the interference modulator, the reflective layer being electrostatically drivable towards the transparent layer to at least reduce a height of the gap, corresponding to a driven condition of the interference modulator; and

a driving mechanism to drive each interference modulator to its driven condition wherein an actuation voltage required to drive each transparent layer to its driven condition is greater than a bias voltage required to keep each transparent layer in its driven condition.

19. The microelectromechanical systems device of claim 18, wherein each interference modulator comprises a charge trapping layer disposed between the transparent and reflective layers.

20. The microelectromechanical systems device of claim 18, wherein each intereference modulator comprises two charge trapping layers disposed so as to sandwich the reflective layer therebetween.

21. The interference modulator of claim 18, wherein the transparent layer comprises SiO₂ and the charge trapping layer comprises Al₂O₃.