WO2001059504A2

WO2001059504A2 - Stiction release mechanism

Info

Publication number: WO2001059504A2
Application number: PCT/US2001/004687
Authority: WO
Inventors: John S. Berg; Chong Won Byun; Scott Friends; John Ritter; Michael Chung; David Kindler
Original assignee: Zygo Corporation
Priority date: 2000-02-11
Filing date: 2001-02-12
Publication date: 2001-08-16
Also published as: AU2001236992A1; WO2001059504A3

Abstract

An optical switch includes a stiction release mechanism for overcoming stiction between a structure defining a contact surface, and a movable electrode. At least two auxiliary electrodes are provided. A movable electrode is movable between a first position in which the movable electrode is retracted from the contact surface, and a second position in which the movable electrode contacts the contact surface and has at least one portion spaced from the contact surface proximate each of the auxiliary electrodes. When the movable electrode is held in the second position by stiction, the movable electrode can be released from the second position by applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence so that fluid can be forced in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface. Stiction is thereby overcome and the movable electrode is caused to be released from the contact surface. Alternatively, electric fields are applied at a resonant frequency of the movable electrode so that transverse resonant vibrations are excited in the portions of the movable electrode spaced apart from the contact surface. Stiction is thereby progressively overcome, and the movable electrode is caused to be released from the contact surface.

Description

STICTION RELEASE MECHANISM

FIELD OF THE INVENTION The present invention relates generally to mechanisms for overcoming stiction between adhering surfaces, and more particularly to mechanisms for overcoming stiction between adhering surfaces in optical switches.

BACKGROUND OF THE INVENTION

Microelectromechanical systems ("MEMS") are integrated micro systems which combine electrical and mechanical components and which are fabricated using semiconductor integrated circuit (IC) technology. Applications include sensors- scanners, and optical devices, including optical switches and beam steerers. Micromachined optical switches are disclosed for example in U.S. Pat. Nos. 5.233.459. and 5,784,189. U.S. Pat. Nos. 5.233,459 and 5,784,189 disclose optical switches that are formed of a movable electrode which is disposed opposite a fixed electrode and is biased to roll in a preferred direction upon application of an electric field across the electrodes to produce a light valve display.

Micromachined optical devices such as the optical switches described above generally require that two flat surfaces be in intimate contact for a period of time and then be controllably separated from each other. For various reasons, including surface contamination and van der Waals forces, the adhering surfaces can stick together and resist separation. The tendency of a component to stick to another is referred to as its stiction- The long term reliability of the optical switches described above is necessarily limited by the phenomenon of stiction. A mechanism for overcoming or minimizing stiction is therefore necessary in order to prevent device failure and in order to successfully commercialize and implement micromachined optical switches.

It is an object of this invention to provide mechanisms for overcoming stiction between adhering surfaces, thereby providing an increased reliability for devices affected by stiction, including MEMS optical switches. SUMMARY OF THE INVENTION

The present invention relates to a stiction release mechanism for overcoming stiction between a structure defining a contact surface and a movable electrode, wherein the movable electrode is held in contact with the contact surface when stiction occurs. The present invention also relates to optical switches which have a stiction release mechanism for overcoming stiction between a structure defining a contact surface, and a movable electrode.

In one embodiment of the invention, stiction between the movable electrode and the contact surface is overcome by applying electric fields between the movable electrode and at least two auxiliary electrodes in a predetermined sequence so as to force fluid in between the movable electrode and the contact surface. In this embodiment, at least two auxiliary electrodes are provided, and are preferabh^* disposed between the contact surface and the movable electrode. Also, means are provided for applying electric fields between the movable electrode and the auxiliary electrodes. In one embodiment, a principal electrode, which preferably forms a portion of the movable electrode, is provided. In one embodiment, a plurality of corrugations are formed at one end of the movable electrode, the corrugations defining at least two portions of the movable electrode spaced apart from the contact surface.

In one embodiment, the movable electrode includes a valve element formed at one end of the movable electrode and disposed above the auxiliary electrode positioned furthermost from the principal electrode. The valve element is movable between a closed position in which the valve element contacts the contact surface, and an open position in which the valve element is retracted from the contact surface.

The movable electrode is movable between a first position wherein the movable electrode is retracted from the contact surface, and a second position wherein the movable electrode contacts the contact surface adjacent the principal electrode and has at least one portion spaced from the contact surface proximate each of the auxiliary electrodes. When the movable electrode is held in the second position by stiction. the movable electrode can be released from the second position by applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence. This forces fluid in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface- In one embodiment, forcing fluid in between the movable electrode and the contact surface increases fluid pressure between the movable electrode and the contact surface, thereby generating and amplifying a separation force between the movable electrode and the contact surface. Stiction is thereby progressively overcome, and the movable electrode and the principal electrode are caused to be released from the contact surface. In another embodiment of the invention, stiction between the movable electrode and the contact surface is overcome by exciting transverse resonant vibrations in the movable electrode. In this embodiment, a plurality of corrugations are formed on the movable electrode. The corrugations define at least two portions of the movable electrode spaced apart from the contact surface, and corresponding contact points at which the movable electrode contacts the contact surface. The spaced apart portions of the movable electrode are characterized by a resonant frequency. A spring electrode is formed at one end of the movable electrode, and is adapted to resonate at substantially the same resonant frequency as the spaced apart portions.

A succession of electric fields are applied between the movable electrode and the contact surface at the resonant frequency of the portions of the movable electrode spaced apart from the contact surface. Because the electric fields are applied at the resonant frequency, the vibrational motion of the spaced apart portions is progressively amplified, ultimately overcoming stiction and causing release of the movable electrode from the contact surface. The present invention also relates to a method for overcoming stiction between a structure defining a contact surface and a movable electrode. The method includes forming a plurality of corrugations in the movable electrode so as to define at least two portions of the movable electrode spaced apart from the contact surface. At least two auxiliary electrodes are provided on the contact surface proximate the spaced apart portions of the movable electrode. Electric fields are applied between the movable electrode and the auxiliary electrodes in a predetermined sequence so as to force fluid in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface. The predetermined sequence is repeated until fluid pressure between the movable electrode and the contact surface is increased in an amount sufficient to overcome stiction and to cause release of the movable electrode from the contact surface.

Another method for overcoming stiction between a structure defining a contact surface and a movable electrode includes providing at one end of the movable electrode a spring electrode characterized by a resonant frequency substantially equal to the resonant frequency of the portions of the movable electrode spaced apart from the contact surface. Electric fields are applied at the resonant frequency between the spring electrode and the contact surface so as to excite transverse resonant vibrations in the spaced apart portions of the movable electrode while the movable electrode is in contact with the contact surface. Stiction is progressively overcome, and the movable electrode is caused to be released from the contact surface.

BRIEF DESCRIPION OF THE DRAWINGS

FIGs. 1 (a) and 1 (b) are perspective views of an optical switch having a stiction release mechanism in accordance with the present invention.

FIG. 2 illustrates one embodiment of a stiction release mechanism in accordance with the present invention, in which fluid is pumped at increasing pressure between a movable electrode and a contact surface.

FIG. 3 illustrates one embodiment of a stiction release mechanism in accordance with the present invention, in which transverse resonances are excited in non-adhering portions of the movable electrode at a mechanical resonant frequency of the movable electrode.

DETAILED DESCRIPTION

FIGs. 1 (a) and 1 (b) are perspective views of an optical switch 10 having a stiction release mechanism 102 in accordance with the present invention. The optical switch 10 may, by way of example, be a bistable electrostatic light valve display. The optical switch 10 includes a movable electrode 11 disposed on a structure 16 defining a contact surface 18. The structure 16 may be a substrate 15. A fixed electrode 17 may be formed by coating the substrate 15 with a thin conductive layer 12. and etching the layer 12 using photoresist as a mask. The movable electrode 1 1 is biased to move in a preferred direction, and to unroll upon application of an electric field across the electrodes 14 and 17, to produce a light valve. Stiction can cause the movable electrode 11 to stick, however, to the contact surface 18, preventing the movable electrode 1 1 from rolling back, and thereby seriously undermining the reliability of the optical switch 10. Stiction is a major impediment toward the commercialization of the optical switch 10. The present invention discloses stiction release mechanisms 102 and 103 for overcoming stiction between the movable electrode 1 1 and the fixed electrode 17 of the optical switch 10. In accordance with the stiction release mechanism 102 illustrated in FIGs. 1 and 2, fluid is pumped at increasing pressure between the movable electrode 1 1 and the contact surface 18. so as to overcome stiction and release the movable electrode 1 1 from the contact surface 18. In accordance with another stiction release mechanism 103 illustrated in FIG. 3. transverse resonant vibrations are excited in the movable electrode 1 1 at the mechanical resonant frequency of the movable electrode 1 1. so as to overcome stiction and release the movable electrode 1 1 from the contact surface 18.

Referring to FIGs. 1 (a) and 1 (b), the substrate 15 may be made of glass. Other substrate materials may include, but are not limited to, fused quartz, single crystal silicon, or metals. The thin conductive layer 12 may be made of indium tin oxide (ITO). Ultra-thin transparent layers of metals, such as gold, platinum, or silver may be used in place of ITO. The thin conductive layer 12 may be overcoated with a photoresist, which is patterned using conventional photolithography techniques. The patterned ITO layer 12 is preferably covered with a high resistance insulative layer 14. such as a silicon dioxide layer. Because of the insulative layer that is disposed on the fixed electrode 17 and beneath the movable electrode 1 1 , when the movable electrode is moved toward the fixed electrode by application of an electric field, no metal-to- metal or metal-to-insulator contact occurs. As illustrated in FIG. 1 (a), the movable electrode 1 1 is a coilable electrode restrained at one end 20. The movable electrode 1 1 rolls up and coils about the restrained end 20 in a preferential roll direction, as illustrated in FIG. 1 (a). In one embodiment, the bias is achieved by inducing anisotropic stress or anisotropic stiffness. The anisotropic stress causes the electrode to move in a preferential direction, namely perpendicular to the direction of stiffening.

In the configuration shown in FIG. 1 (b), the coiled movable electrode 1 1 is caused to unroll, upon application of an electric field between the electrodes- The coiled electrode 14 thus acts as a light shutter. As part of the stiction release mechanism 102, described in detail below with regard to FIG. 2. a plurality of corrugations 22 are introduced at an unrestrained end 24 of the movable electrode 1 1. FIG. 2 illustrates one embodiment of a stiction release mechanism 102 for the optical switch 10, in accordance with the present invention. FIG. 2 provides an exploded view of the unrestrained end 24 of the movable electrode 1 1 , showing the plurality of corrugations 22 formed thereon. When stiction occurs, the movable electrode is held in contact with the contact surface 18 at a sticking region 28.

As illustrated in FIG. 2, a principal electrode 30 and at least two auxiliary electrodes 32 and 33 are provided on the contact surface 18. In a preferred embodiment, the principal electrode 30 forms a part of the movable electrode 1 1. The movable electrode 1 1 contacts the contact surface 18 at the sticking region 28 that is adjacent the principal electrode 30. In the illustrated embodiment, three auxiliary electrodes 32, 33, and 34 are provided. The auxiliary electrodes 32, 33. and 34 may be conductive plates which can each be independently energized ^*with an electric voltage. The auxiliary electrodes are preferably encapsulated with a dielectric, so that the surface of the electrodes are nonconducting. The principal electrode 30 is also a similarly encapsulated conductive plate.

The plurality of corrugations 22 define, above the auxiliary electrodes, a corresponding plurality of portions of the movable electrode 1 1 that are spaced apart from the contact surface 18. In the embodiment illustrated in FIG. 2, in which three auxiliary electrodes are provided, the plurality of corrugations 22 define three portions 36, 37, and 38 of the movable electrode 1 1 that are spaced apart from the contact surface 18, and that are proximate to and disposed above the corresponding auxiliary electrodes 32, 33, and 34. The corrugations 22 also define contact points 40 and 41 in between the portions 36. 37, and 38 of the movable electrode 1 1. The movable electrode 1 1 contacts the contact surface at the contact points 40 and 41. Actual surface contact area is thereby minimized.

The movable electrode 1 1 is movable between a first position in which the movable electrode 11 (except for its restrained end 20) is fully retracted from the contact surface, and a second position in which the movable electrode 1 1 contacts the contact surface 18 at the sticking region 28 adjacent the principal electrode 30 and at the contact points 40 and 41. The movable electrode 1 1 can be held in the second position by stiction, thereby preventing the optical switch 10 from properly functioning as a light shutter.

In accordance with the stiction release mechanism 102 of the present invention- means (not shown) are provided for applying electric fields between the movable electrode 1 1 and the auxiliary electrodes 32, 33, and 34. The movable electrode 1 1 can be released from the second position by applying electric fields between the movable electrode 1 1 and the auxiliary electrodes 32, 33, and 34 in a predetermined sequence so that fluid can be forced in between the movable electrode 1 1 and the contact surface 18 while the movable electrode 1 1 is in contact with the contact surface 18. In one embodiment, the fluid may include air. In another embodiment, the fluid may be a gaseous fluid, including but not limited to nitrogen and/or hydrogen. In this embodiment, the optical switch 10 may be disposed in a hermetically sealed environment, and may be provided with an appropriate gas. such as nitrogen or hydrogen. The fluid pressure alternately acts on the regions in which the movable electrode 1 1 adheres to the contact surface 18 and gradually forces separation of the movable electrode 11 from the contact surface 18, starting from the least adhered contact points 40 and 41, and moving onto the sticking region 28. When the movable electrode 1 1 is forced apart from the contact surface 18 at one of the contact points, for example at contact point 40, fluid pressure on the remaining adhering regions 41 and 28 is increased. The increased fluid pressure between the movable electrode 1 1 and the contact surface at the contact point 41 and the sticking region 28 progressively overcomes stiction, first at 41 and then at 28. Ultimately, the movable electrode 1 1 and the principal electrode 30 are caused to be released completely from the contact surface 18.

In one embodiment, the movable electrode 1 1 terminates in its unrestrained end 24 in a flap valve 44. The flap valve 44 is preferably located above and proximate the outermost one of the auxiliary electrodes, namely auxiliary electrode 32. In one embodiment, the predetermined sequence includes first applying opposite electric fields between the principal electrode 30 (held to the sticking region 28 by stiction) and the outermost auxiliary electrode 32. Energizing the auxiliary electrode 32 and the principal electrode 30 with opposite voltages attracts together the surfaces of the movable 14 and the fixed 17 electrodes- The flap valve 44 is attracted to the contact surface 18 and contacts the contact surface 18. so that the flap valve 44 is closed. Closure of the flap valve 44 entraps the fluid under the portion 38 and above the portion of the contact surface 18 between the closed valve 44 and the contact point 40. The spaced apart portion 38 of the movable electrode 1 1. while not contacting the contact surface 18. is attracted toward the contact surface 18, thereby compressing the entrapped fluid. The compression of the entrapped fluid increases the fluid pressure between the movable electrode 1 1 and the contact surface 19 at the contact point 40, forcing fluid in between the movable electrode 1 1 and the contact surface 18 at the contact point 40. The fluid pressure between the movable electrode 1 1 and the contact surface 18 at the contact point 40 is increased until the movable electrode 1 1 is lifted from the contact surface 18 at the contact point 40. and fluid is forced in the drum of the spaced apart portion 37 located above and proximate the auxiliary electrode 33.

Next, auxiliary electrodes 32 and 33 are energized, while keeping the flap valve 44 closed. Fluid is thereby forced in between the movable electrode 1 1 and the contact surface 18 at the contact point 41. Fluid is also forced under the drum of the portion 36 located above the auxiliary electrode 32 adjacent the electrode 33. Finally, auxiliary electrode 34 is energized, compressing the fluid entrapped under the portion 36 and above the part of contact surface 18 between the contact point 41 and the sticking region 28.

The outermost auxiliary electrodes are then sequentially de-energized, namely the electric fields between the auxiliary electrodes and the movable electrode 1 1 are sequentially removed. The electric field between the outermost auxiliary electrode 32 and the movable electrode 1 1 is removed first. This opens the flap valve 44. and also allows the portion 38 of the movable electrode 1 1 to retract from the contact surface 18, so that fluid is allowed under the drum of the portion 38. Next, the electric field between the auxiliary electrode 33 and the movable electrode 1 1 is removed, allowing the portion 37 of the movable electrode 1 1 to also retract from the contact surface 18. The flap valve 44 is closed again, by applying once more an electric field between outermost auxiliary electrode 32 and the movable electrode 1 1. Fluid is thereby pumped into the space under the drum of the portion 37 of the movable electrode 11. With the flap valve 44 still closed, the electric field between the auxiliary electrode 34 and the movable electrode 1 1 is removed, allowing fluid under the drum of the portion 36 of the movable electrode 1 1. An electric field is applied again between the auxiliary electrode 33 and the portion 37 of the movable electrode 11. thereby forcing fluid in between the movable electrode 1 1 and the contact surface 18 at the contact point 41. With sufficiently increased fluid pressure, the movable electrode 1 1 is released from the contact surface 18 at the contact point 41, allowing fluid under the drum of portion 36, and increasing fluid pressure on the remaining adhering region, namely the sticking region 28. An electric field is finally applied between the auxiliary electrode 34 and the portion 36, thereby increasing fluid pressure and forcing fluid between the movable electrode 11 and the contact surface 18 at the sticking region 28. The above described procedure is repeated for as many number of times as is needed, each time increasing fluid pressure between the adhering portions of the movable electrode 11 and the contact surface 18, until stiction is progressively overcome and the movable electrode 1 1 is ultimately caused to be released from the contact surface 18 at the sticking region 28. as well as at the contact points 40 and 41. The above described mechanism can be used generally as a mechanism for moving and compressing fluid at very small scales. The mechanism illustrated in FIG. 2 may thus be used as a miniature fluid compressor pump for purposes other than stiction release, such as cooling, localized cooling or sampling gaseous fluids.

FIG. 3 illustrates one embodiment of another stiction release mechanism 103 in accordance with the present invention, in which transverse resonances are excited at a resonant frequency of the movable electrode in order to overcome stiction between the movable electrode and the contract surface. As in FIG. 2. FIG.3 provides an exploded view of the unrestrained end 24 of the movable electrode 1 1. and the plurality of corrugations 22 formed thereon. The plurality of corrugations 22 define a corresponding plurality of portions of the movable electrode 1 1 that are spaced apart from the contact surface 18. In the embodiment illustrated in FIG. 3, the plurality of corrugations 22 define three portions 36, 37, and 38 of the movable electrode 1 1 that are spaced apart from the contact surface 18. The corrugations 22 also define contact points 41, 40. and 43 at which the movable electrode 11 contacts the contact surface 18.

The movable electrode 11 is movable between a first position in which the movable electrode 11 (except for its restrained end 20) is fully retracted from the contact surface, and a second position in which the movable electrode 1 1 contacts the contact surface 18 at the sticking region 28 and at the contact points 41 , 40. and 43. In the second position, the movable electrode 1 1 has portions 36. 37, and 38 spaced apart from the contact surface 18. As explained before, the movable electrode 11 can be held in the second position by stiction. In order to excite resonant vibrations in the portions 36. 37, and 38 of the movable electrode 1 1 , the stiffness and mass of portions are chosen so that the portions have a mechanical resonant frequency v at:

v = 1 / 2π sqrt(k / m)

where m = mass of the portion and k = stiffness (spring constant) of the portion.

The stiffness k is a function of the width of the portion, the thickness of the electrode 14 at the portion, and the modulus of elasticity E of the material which makes up the portion. Each spaced apart portion thus functions as a spring with a drum resonance. The unrestrained end 24 of the movable electrode terminates in a spring element 50. which preferably is a leaf spring. The leaf spring 50 is designed to resonate at substantially the same frequencies as the portions 36, 37, and 38.

In operation, transverse resonant vibrations are generated in the spaced apart portions 36, 37, and 38 by applying electric fields between the movable electrode 1 1 and the contact surface 18 at a mechanical resonant frequency of each portion. In other words, the portions 36. 37, and 38 each function as springs having drum resonances, which vibrate in the transverse direction indicated in FIG. 3. When an electric field is applied at the resonant frequency of a portion, the portion begins to vibrate at a significantly higher amplitude than it would have if the electric field had been applied at a non-resonant frequency. Successive applications of the electric field at the resonant frequency progressively amplifies the vibrational motion of the portion, and amplifies a separation force between the movable electrode 1 1 and the contact surface 18 at a contact region adjacent the vibrating portion. An analogy can be made to a motorist who is stuck in a rut and rocks the car back and forth to drive enough force to drive the car out of the rut.

When the force and amplitude of the transverse vibrations have been increased to a sufficient level, the movable electrode 1 1 is released from the contact surface 18, first at the contact regions 41, 40, and 43, and ultimately at the sticking region 28. As one region after another becomes released, the force generated from the transverse resonant vibrations of the spaced apart portions 36, 37, and 38 acts on significantly less surface area, so that the release force acting on the adhered surfaces of the remaining adhering regions continues to increase, ultimately exceeding the force bonding the surfaces. Stiction is thereby progressively overcome, and the movable electrode 1 1 is caused to be completely released from the contact surface at the contact regions 41 , 40. and 43. and at the sticking region 28.

The stiction release mechanisms 102 and 103 illustrated in FIG. 2 and FIG.3 can be used in a continuous manner on a part of a device, such as a portion of the movable electrode 1 1 of the optical switch 10. In this way, the part is prevented from ever sticking during the operation of the device, since the part is never allowed to be at rest and in contact with the contact surface 18. In the case of the stiction release mechanism 102 (fluid compression method), the portion of the movable electrode on which the mechanism 102 is applied is continuously separated from the contact surface 18 by a film of fluid. In the case of the stiction release mechanism 103 (resonant vibration method), a lubricant may be used to minimize wear on the parts as transverse resonant vibrations are continuously generated. The lubricant may be either a solid, or a permanently bonded liquid. While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

What is claimed is:

1. An optical switch comprising:

(a) a structure defining a contact surface;

(b) a principal electrode and at least two auxiliary electrodes; and

(c) a movable electrode movable between a first position wherein the movable electrode is retracted from the contact surface and a second position wherein the movable electrode contacts the contact surface adjacent the principal electrode and has at least one portion spaced from the contact surface proximate each of the auxiliary electrodes such that when the movable electrode is held in the second position by stiction. the movable electrode can be released from the second position by applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence so that fluid can be forced in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface so as to progressively overcome stiction and cause release of the movable electrode and the principal electrode from the contact surface.

2. An optical switch according to claim 1 wherein the fluid comprises air.

3. An optical switch according to claim 1 wherein the fluid comprises a gas.

4. An optical switch according to claim 3 wherein the gas is selected from the group consisting of nitrogen and hydrogen.

5. An optical switch according to claim 1 wherein forcing fluid in between the movable electrode and the contact surface increases fluid pressure between the movable electrode and the contact surface, thereby generating and amplifying a separation force between the movable electrode and the contact surface.

6. An optical switch according to claim 1 wherein said auxiliary electrodes are disposed between said contact surface and said movable electrode.

ι:

7. An optical switch according to claim 1 wherein the principal electrode forms a portion of the movable electrode.

8. An optical switch according to claim 1 wherein the movable electrode comprises a valve element formed at one end of the movable electrode and disposed above an auxiliary electrode positioned furthermost from the principal electrode, the valve element being movable between a closed position in which the valve element contacts the contact surface, and an open position in which the valve element is retracted from the contact surface.

9. An optical switch according to claim 8 wherein the valve element when in contact with the contact surface compresses fluid entrapped between one of said at least one portion of the movable electrode positioned proximate said furthermost auxiliary electrode and a portion of the contact surface, thereby forcing fluid in between the movable electrode and the contact surface.

10. An optical switch according to claim 9, wherein electric fields are first applied to the principal electrode and said furthermost auxiliary electrode.

1 1. An optical switch comprising:

(a) a structure defining a contact surface;

(b) at least two auxiliary electrodes; and

(c) a movable electrode movable between a first position wherein the movable electrode is retracted from the contact surface and a second position wherein the movable electrode contacts the contact surface and has at least a portion spaced from the contact surface proximate each of the auxiliary electrodes such that when the movable electrode is held in the second position by stiction, the movable electrode can be released from the second position by applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence so that fluid can be forced in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface so as to overcome stiction and cause release of the movable electrode from the contact surface.

12. A stiction release mechanism for overcoming stiction between a structure defining a contact surface and a movable electrode, wherein the movable electrode is held in contact with the contact surface when stiction occurs, the stiction release mechanism comprising:

(a) a principal electrode disposed adjacent a part of the contact surface that is held in contact with the movable electrode when stiction occurs;

(b) a plurality of corrugations formed at one end of the movable electrode, the corrugations defining at least two portions of the movable electrode spaced apart from the contact surface;

(c) at least two auxiliary electrodes disposed on the contact surface and proximate said at least two portions of the movable electrode; and

(d) means for applying electric fields between the movable electrode and the auxiliary electrodes; wherein when the movable electrode is held in contact with the contact surface by stiction, the movable electrode can be released from the contact surface by applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence so that fluid can be forced in between the movable electrode and the contact surface while the movable electrode is in contact with the contact surface so as to overcome stiction and cause release of the movable electrode and the principal electrode from the contact surface.

13. A stiction release mechanism according to claim 12. wherein the principal electrode forms a portion of the movable electrode.

14. An optical switch comprising:

(a) a structure defining a contact surface; (b) a movable electrode movable between a first position wherein the movable electrode is retracted from the contact surface and a second position wherein the movable electrode contacts the contact surface;

(c) a plurality of corrugations formed on the movable electrode, the corrugations defining at least two portions of the movable electrode spaced apart from the contact surface, the at least two portions being characterized by a resonant frequency; and

(d) a spring element forming one end of the movable electrode, the spring element being adapted to resonate substantially said resonant frequency wherein when the movable electrode is held in the second position by stiction, the movable electrode can be released from the second position by applying a succession of electric fields between the movable electrode and the contact surface at the resonant frequency so that transverse resonant vibrations can be excited in said at least two portions of the movable electrode while the movable electrode is in contact with the contact surface so as to progressively overcome stiction and cause release of the movable electrode from the contact surface.

15. A stiction release mechanism for overcoming stiction between a structure defining a contact surface and a movable electrode wherein the movable electrode is held in contact with the contact surface when stiction occurs, the stiction release mechanism comprising:

(a) a plurality of corrugations formed on the movable electrode, the corrugations defining at least two portions of the movable electrode space apart from the contact surface, the at least two portions being characterized by a resonant frequency: and (b) a spring element forming one end of the movable electrode, the spring element being adapted to resonate at substantially said resonant frequency; wherein when the movable electrode is held in the second position by stiction. the movable electrode can be released from the second position by applying a succession of electric fields between the movable electrode and the contact surface at the resonant frequency so as to excite transverse resonant vibrations in said at least two portions of the movable electrode while the movable electrode is in contact with the contact surface, thereby progressively overcoming stiction and causing release of the movable electrode from the contact surface.

16. A method for overcoming stiction between a structure defining a contact surface and a movable electrode, wherein the movable electrode is held in contact with the contact surface when stiction occurs, the method comprising:

(a) forming a plurality of corrugations in the movable electrode so as to define at least two portions of the movable electrode spaced apart from the contact surface;

(b) providing at least two auxiliary electrodes on the contact surface proximate said at least two portions of the movable electrode:

(c) applying electric fields between the movable electrode and the auxiliary electrodes in a predetermined sequence so as to force fluid in between the movable electrode and the contact surface while the movable electrode is in contact with the fixed element; (d) repeating said predetermined sequence until fluid pressure between the movable electrode and the contact surface is increased in an amount sufficient to overcome stiction and to cause release of the movable electrode from the contact surface.

17- A method for overcoming stiction between a structure defining a contact surface and a movable electrode wherein the movable electrode is held in contact with the contact surface when stiction occurs, the method comprising:

(a) forming a plurality of corrugations in the movable electrode so as to define at least two portions of the movable electrode that are spaced apart from the contact surface and that are characterized by a resonant frequency;

(b) providing at one end of the movable electrode a spring element that is adapted to resonate at substantially said resonant frequency;

(c) applying electric fields between movable electrode and the contact surface so as to excite transverse resonant vibrations at the resonant frequency in said at least two portions of the movable electrode while the movable electrode is in contact with the contact surface so as to progressively overcome stiction and cause release of the movable electrode from the contact surface.