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Title:
MEMS ACTUATORS AND SWITCHES
Document Type and Number:
WIPO Patent Application WO/2008/101347
Kind Code:
A1
Abstract:
The MEMS actuator comprises a hot beam and a cold beam connected to a substrate. Portions of the hot beam are connected together at a common end. A dielectric tether is attached over the common end of the hot beam portions and a free end of the cold beam. The hot beam is configured to exhibit an asymmetric lengthening. This actuator has a better stress distribution compared to an actuator in which both hot beam portions do not have an asymmetric configuration. It also provides a more efficient actuation mechanism that can reduce stress along the structure and reduce the temperature of the hot beam portions during an actuation.

Inventors:
MENARD STEPHANE (CA)
LU JUN (CA)
GONON NICOLAS (CA)
LASSONDE NORMAND (CA)
Application Number:
PCT/CA2008/000341
Publication Date:
August 28, 2008
Filing Date:
February 21, 2008
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SIMPLER NETWORKS INC (CA)
MENARD STEPHANE (CA)
LU JUN (CA)
GONON NICOLAS (CA)
LASSONDE NORMAND (CA)
International Classes:
B81B3/00; B81B7/02; H01H3/00
Foreign References:
US7043910B22006-05-16
US6691513B12004-02-17
US6983088B22006-01-03
Other References:
See also references of EP 2114819A4
Download PDF:
Claims:

CLAIMS:

1. A Micro-Electromechanical (MEMS) actuator comprising: a hot beam; and a cold beam; characterized in that: the hot beam exhibits an asymmetric lengthening.

2. The MEMS actuator of claim 1 , characterized in that the asymmetric hot beam includes a first portion and a second portion wherein one of the portions is longer than the other portion.

3. The MEMS actuator of claim 2, characterized in that the longer portion also has a width that is narrower than that of the other portion.

4. The MEMS actuator of claim 1 , characterized in that the asymmetric hot beam includes a first portion and a second portion wherein one of the portions is wider than the other portion.

5. The MEMS actuator of claim 1 , characterized in that the actuator further comprises: a substrate upon which a portion of the actuator is anchored; and a second actuator anchored to the substrate at a portion thereof; wherein each of the actuators includes a tip, the tips mechanically contacting one another upon actuation.

6. The MEMS actuator of claim 5, characterized in that each tip includes a flange and where at least one of the flanges includes a bump disposed thereon.

7. The MEMS actuator of claim 5, characterized in that each tip includes a flange at least one of which is angled.

8. The MEMS actuator of claim 7, characterized in that an angle associated with each angled flange is between 45 and 90 degrees.

9. The MEMS actuator of any one of claims 1 to 4, characterized in that the actuator further comprises: means for mechanically latching the actuator to a similar actuator.

10. The MEMS actuator of claim 9, characterized in that the actuator further comprises: means for increasing contact pressure associated with latched actuators.

11. The MEMS actuator of claim 9, characterized in that the actuator further comprises: means for self-wiping the mechanical latch.

12. The MEMS actuator of claim 1 , further characterized in that: the cold beam has a free end and a fixed end wherein the width of the cold beam is wider at a portion thereof nearer the fixed end than the free end.

13. The MEMS actuator of claim 12, further characterized in that:

the cold beam includes a tip at its free end for making mechanical and/or electrical contact with a tip of another actuator.

14. The MEMS actuator of claim 12, further characterized in that: the tip includes means for increasing the contact pressure exerted by the tip on the tip of the other actuator.

15. The MEMS actuator of claim 14, further characterized in that: the tip includes means for latching the other actuator into a deflected position.

16. The MEMS actuator of claim 15, further characterized in that: the tip includes a means for self wiping.

17. A MEMS switch comprising: a substrate; a first actuator anchored to the substrate; and a second actuator anchored to the substrate; wherein at least one of the actuators is an asymmetric actuator and both actuators mechanically contact one another upon the application of an actuating voltage.

18. The MEMS switch of claim 17, characterized in that the switch further comprises means for mechanically latching the two actuators together.

19. The MEMS switch of claim 18, characterized in that the switch further comprises means for increasing the contact pressure between the mechanically latched actuators.

20. The MEMS switch of claim 18 or 19, characterized in that the switch further comprises means for self-wiping the mechanical latching means.

21. A Micro-Electromechanical (MEMS) actuator disposed upon a substrate, the actuator comprising: a hot beam having an end anchored to the substrate and a movable free end; and a cold beam; characterized in that: the hot beam comprises two spaced-apart portions having asymmetric widths.

22. The MEMS actuator of claim 21 , further characterized in that one hot beam portion exhibits a width w1 at an anchored end and exhibits a width w2 at a free end, wherein w2 > w1.

23. The MEMS actuator of claim 21 , further characterized in that each hot beam portion has a tapered profile.

24. A method of operating a Micro-Electromechanical (MEMS) switch, the switch comprising: a substrate; a first actuator disposed upon the substrate, the first actuator having an anchored end and a free end including a latch; a second actuator disposed upon the substrate, the second actuator having an anchored end and a free end including a latch;

wherein each of the first and second actuators is normally in an undeflected position and may be independently moved to a respective deflected position upon the application of a respective actuating voltage; wherein the movements of the actuators are substantially perpendicular to one another over an actuating distance; the method of operating the MEMS switch comprising the steps of: actuating one of the actuators such that its free end including the latch is deflected towards the free end of the other actuator; actuating the other actuator such that its free end including the latch is deflected towards the free end of the other actuator; and deactuating one of the deflected actuators such that the latches engage one another.

25. The method of claim 24, further comprising the step of deactuating the other deflected actuator.

26. The method of claim 25, characterized in that the latches are angled latches.

27. A MEMS cantilever actuator mounted on a substrate, the actuator comprising: an elongated cold beam, the cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof; an elongated hot beam adjacent to the cold beam, the hot beam having first and second spaced-apart portions, the second portion being

closer to the cold beam than the first portion, each portion being provided at one end with a corresponding anchor pad connected to the substrate, the portions being connected together at a common end that is opposite their anchor pads; and a dielectric tether attached over the common end of the portions of the hot beam and the free end of the cold beam to mechanically couple the hot beam and the cold beam and keep them electrically independent; the MEMS actuator being characterized in that: the first portion of the hot beam has an increased lengthening compared to that of the second portion.

28. The MEMS actuator of claim 27 characterized in that the first portion is longer than the second portion.

29. The MEMS actuator of claim 27 or 28, characterized in that the second portion is wider than the first portion.

30. The MEMS actuator of any one of claims 27 to 29, characterized in that the first portion and the second portion have a tapered profile.

31. The MEMS actuator of claim 30, characterized in that the tapered profile of the first portion is inverted compared to the tapered profile of the second portion.

32. The MEMS actuator of any one of claims 26 to 31 , characterized in that the actuator further comprises a tip having a flange.

33. The MEMS actuator of claim 32, characterized in that the cold beam is electrically connected to the flange.

34. The MEMS actuator of claim 33, characterized in that the flange includes a bump disposed on a mating face.

35. The MEMS actuator of any one of claims 32 to 34, characterized in that the flange defines an angle with reference to a longitudinal direction of the actuator.

36. The MEMS actuator of claim 35, characterized in that the angle of the flange with reference to the longitudinal direction is a negative angle between 45 and less than 90 degrees.

37. The MEMS actuator of any one of claims 27 to 36, characterized in that the cold beam is wider near its anchor pad than near its free end.

38. The MEMS actuator of any one of claims 27 to 37, characterized in that the cold beam has a narrower portion adjacent to its anchor pad.

39. The MEMS actuator of any one of claims 27 to 38, characterized in that each hot beam portion has a length between its anchor pad and the dielectric tether that is longer than a length of the cold beam between its anchor pad and the dielectric tether.

40. The MEMS actuator of any one of claims 27 to 39, characterized in that at least one additional dielectric tether is transversally disposed over the hot beam and the cold beam.

41. The MEMS actuator of any one of claims 27 to 40, characterized in that the hot beam portions are substantially parallel to the cold beam.

42. A MEMS switch mounted on a substrate, the switch comprising: a first cantilever actuator comprising:

- a first elongated cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof;

- a first elongated hot beam adjacent to the first cold beam, the first hot beam having first and second spaced-apart portions, the second portion being closer to the first cold beam than the first portion, each portion being provided at one end with a corresponding anchor pad connected to the substrate, the portions being connected together at a common end that is opposite their anchor pads; and

- a first dielectric tether attached over the common end of the portions of the first hot beam and the free end of the first cold beam to mechanically couple the first hot beam and the first cold beam and keep them electrically independent; and a second cantilever actuator comprising:

- a second elongated cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof;

- a second elongated hot beam adjacent to the second cold beam, the second hot beam having first and second spaced-apart portions, the second portion of the second hot beam being closer

to the second cold beam than the first portion of the second hot beam, each portion of the second hot beam being provided at one end with a corresponding anchor pad connected to the substrate, the portions of the second hot beam being connected together at a common end that is opposite their anchor pads; and - a second dielectric tether attached over the common end of the portions of the second hot beam and the free end of the second cold beam to mechanically couple the second hot beam and the second cold beam and keep them electrically independent; wherein the first actuator and the second actuator are configured and disposed so that the switch is selectively movable between a closed position and an open position; the MEMS switch being characterized in that: the first portion of the hot beam of at least one of the actuators has an increased lengthening compared to that of the second portion of the corresponding hot beam.

43. The MEMS switch of claim 42, characterized in that each first portion having an increased lengthening is longer than the second portion of the corresponding hot beam.

44. The MEMS switch of claim 42 or 43, characterized in that each first portion having an increased lengthening has a width that is narrower than that of the second portion of the corresponding hot beam.

45. The MEMS switch of any one of claims 42 to 44, characterized in that the first portion and the second portion of the hot beam of at least one of the actuators have a tapered profile.

46. The MEMS switch of claim 45, characterized in that the tapered profile of the first portion is inverted compared to the tapered profile of the second portion of the corresponding hot beam.

47. The MEMS switch of any one of claims 42 to 46, characterized in that each actuator further comprises a tip having a flange, the flanges of the actuators latching together in the closed position of the switch.

48. The MEMS switch of claim 47, characterized in that the cold beam of each actuator is electrically connected to the corresponding flange.

49. The MEMS switch of claim 48, characterized in that each flange includes a bump disposed on a mating face.

50. The MEMS switch of any one of claims 47 to 49, characterized in that each flange defines an angle with reference to a longitudinal direction of the corresponding actuator.

51. The MEMS switch of claim 50, characterized in that the angle of each flange with reference to the longitudinal direction of the corresponding actuator is a negative angle between 45 and less than 90 degrees.

52. The MEMS switch of any one of claims 42 to 51 , characterized in that the cold beam of at least one of the MEMS actuators is wider near its anchor pad than near its free end.

53. The MEMS switch of any one of claims 42 to 52, characterized in that the cold beam of at least one of the actuators has a narrower portion adjacent to its anchor pad.

54. The MEMS switch of any one of claims 42 to 53, characterized in that each hot beam portion has a length between its anchor pad and the corresponding dielectric tether that is longer than a length of the corresponding cold beam between its anchor pad and the corresponding dielectric tether.

55. The MEMS switch of any one of claims 42 to 54, characterized in that at least one additional dielectric tether is transversally disposed over the hot beam and the cold beam of at least one of the actuators.

56. The MEMS switch of any one of claims 42 to 55, characterized in that the hot beam portions are substantially parallel to the corresponding cold beam.

57. The MEMS switch of any one of claims 42 to 56, characterized in that the first and the second actuators are substantially perpendicular to one another.

Description:

MEMS ACTUATORS AND SWITCHES

The technical field of the present document relates generally to Micro- Electromechanical Systems (MEMS) and in particular to actuators for chip level MEMS devices.

MEMS devices are small movable mechanical structures constructed using semiconductor processing methods. MEMS devices are often used as actuators and have proven quite useful in a wide variety of applications.

A MEMS actuator is often configured and disposed in a cantilever fashion. Accordingly, it thus has an end attached to a substrate and an opposite free end that is movable between at least two positions, one being a neutral position and the other(s) being deflected positions.

Common actuation mechanisms used in MEMS actuators include electrostatic, magnetic, piezo and thermal, the last of which is the primary focus of the actuation mechanism presented herein. The deflection of a thermal MEMS actuator results from a potential being applied between a pair of terminals, hereafter called "anchor pads", which potential causes a current flow, thereby elevating the temperature of the structure. This in turn causes a part thereof to either elongate or contract, depending upon the particular material(s) used.

MEMS actuators can be configured as switches. Such MEMS switches offer numerous advantages over alternatives. In particular, they are extremely small, relatively inexpensive, consume little power and exhibit short response times. MEMS actuators can also be useful in applications other than switches.

U.S. Patent No. 7,036,312 issued on 2 May 2006 to Simpler Networks Inc. shows examples of MEMS actuators and switches, each having a hot beam and a cold beam mechanically coupled together by a dielectric tether.

Given the importance of MEMS actuators, new configurations that enhance their performance, reliability and/or manufacturability always represent a significant advance in the art.

In one aspect, there is provided a Micro-Electromechanical (MEMS) actuator comprising: a hot beam; and a cold beam; characterized in that the hot beam exhibits an asymmetric lengthening.

In another aspect, there is provided a MEMS switch comprising: a substrate; a first actuator anchored to the substrate; and a second actuator anchored to the substrate; wherein at least one of the actuators is an asymmetric actuator and both actuators mechanically contact one another upon the application of an actuating voltage.

In another aspect, there is provided a Micro-Electromechanical (MEMS) actuator disposed upon a substrate, the actuator comprising: a hot beam having an end anchored to the substrate and a movable free end; and a cold beam; characterized in that the hot beam comprises two spaced-apart portions having asymmetric widths.

In another aspect, there is provided a method of operating a Micro- Electromechanical (MEMS) switch, the switch comprising: a substrate; a first actuator disposed upon the substrate, the first actuator having an anchored end and a free end including a latch; a second actuator disposed upon the substrate,

the second actuator having an anchored end and a free end including a latch; wherein each of the first and second actuators are normally in an undeflected position and may be independently moved to a respective deflected position upon the application of a respective actuating voltage; wherein the movements of the actuators are substantially perpendicular to one another over an actuating distance; the method of operating the MEMS switch comprising the steps of: actuating one of the actuators such that its free end including the latch is deflected towards the free end of the other actuator; actuating the other actuator such that its free end including the latch is deflected towards the free end of the other actuator; and deactuating one of the deflected actuators such that the latches engage one another.

In another aspect, there is provided a MEMS cantilever actuator mounted on a substrate, the actuator comprising: an elongated cold beam, the cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof; an elongated hot beam adjacent to the cold beam, the hot beam having first and second spaced-apart portions, the second portion being closer to the cold beam than the first portion, each portion being provided at one end with a corresponding anchor pad connected to the substrate, the portions being connected together at a common end that is opposite their anchor pads; and a dielectric tether attached over the common end of the portions of the hot beam and the free end of the cold beam to mechanically couple the hot beam and the cold beam and keep them electrically independent; the MEMS actuator being characterized in that the first portion of the hot beam has an increased lengthening compared to that of the second portion.

In another aspect, there is provided a MEMS switch mounted on a substrate, the switch comprising: a first cantilever actuator comprising: a first elongated cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof; a first elongated hot beam adjacent to the first cold beam, the first hot beam having first and second spaced-apart portions, the second portion being closer to the first cold beam than the first portion, each portion being provided at one end with a corresponding anchor pad connected to the substrate, the portions being connected together at a common end that is opposite their anchor pads; and a first dielectric tether attached over the common end of the portions of the first hot beam and the free end of the first cold beam to mechanically couple the first hot beam and the first cold beam and keep them electrically independent; and a second cantilever actuator comprising: a second elongated cold beam having at one end an anchor pad connected to the substrate, and a free end that is opposite the anchor pad thereof; a second elongated hot beam adjacent to the second cold beam, the second hot beam having first and second spaced-apart portions, the second portion of the second hot beam being closer to the second cold beam than the first portion of the second hot beam, each portion of the second hot beam being provided at one end with a corresponding anchor pad connected to the substrate, the portions of the second hot beam being connected together at a common end that is opposite their anchor pads; and a second dielectric tether attached over the common end of the portions of the second hot beam and the free end of the second cold beam to mechanically couple the second hot beam and the second cold beam and keep them electrically independent; wherein the first aGtuator and the second actuator are

configured and disposed so that the switch is selectively movable between a closed position and an open position; the MEMS switch being characterized in that the first portion of the hot beam of at least one of the actuators has an increased lengthening compared to that of the second portion of the corresponding hot beam.

Further aspects and features of what is presented herein will become apparent upon review of the following detailed description made in conjunction with the appended figures.

In the figures:

FIG. 1 is a top plan view of an example of a MEMS switch constructed with a pair of MEMS actuators having hot beam portions with asymmetric lengths;

FIG. 2 is a side view showing one of the MEMS actuators in FIG. 1 and a generic example of a substrate to which the MEMS actuators can be attached;

FIGS. 3A to 3E illustrate an example of the movement of the actuator tips for the MEMS switch of FIG. 1 ;

FIG. 4 is an enlarged view of the anchor pads of one of the MEMS actuators of FIG. 1 ;

FIG. 5 is a top plan view of an example of a MEMS switch constructed with a pair of MEMS actuators having hot beam portions with asymmetric widths;

FIG. 6 is an enlarged view of the hot beam portions of one of the MEMS actuators of FIG. 5;

FIG. 7 is a top plan view of an example of a MEMS switch constructed with a pair of MEMS actuators having hot beam portions with asymmetric widths and tapered profiles;

FIGS. 8A and 8B are enlarged views of ends of one of the tapered hot beam portions of one of the MEMS actuators in FIG. 7;

FIGS. 9A to 9D show different examples of configurations for the actuator tips of a MEMS switch;

FIG. 10 is a top plan view of an example of a MEMS switch constructed with a pair of MEMS actuators having hot beam portions with asymmetric lengths and also a tapered cold beam;

FIG. 11 is an enlarged view of the tapered cold beam of FIG. 10;

FIG. 12 is an enlarged view of the actuator tips in the MEMS switch of FIG. 10, which actuator tips have flanges with an angled contact configuration; and

FIGS. 13A to 13D illustrate an example of the movement of the actuator tips shown in FIG. 12.

FIGS. 1 and 2 show an example of a MEMS switch 100 comprising two substantially similar MEMS cantilever actuators 10, 10' disposed perpendicularly. FIG. 2 is a side view of the first actuator 10 (shown at the left in FIG. 1) and shows that it is attached to a substrate 12 at one end. The second actuator 10' is attached to the substrate 12 the same way. The following description of the first actuator 10 also applies to the second actuator

10' as they are both substantially similar in the illustrated example. It should be noted, however, that they may be constructed differently to one another.

The actuator 10 comprises an elongated hot beam 20 having two spaced-apart portions 22a, 22b, each being provided at one end with a corresponding anchor pad 24a, 24b connected to the substrate 12. The portions 22a, 22b are substantially parallel and are connected together at a common end 26 that is opposite the anchor pads 24a, 24b and overlying the substrate 12, as shown in FIG. 2. The actuator 10 also comprises an elongated cold beam 30 adjacent and substantially parallel to the hot beam 20. The cold beam 30 has at one end an anchor pad 32 connected to the substrate 12, and a free end 34 that is opposite the anchor pad 32. The free end 34 is overlying the substrate 12. Although the illustrated example shows substantially parallel beams 20, 30, it should be noted that various other configurations are possible.

A dielectric tether 40 is attached over the common end 26 of the portions 22a, 22b of the hot beam 20 and the free end 34 of the cold beam 30. The dielectric tether 40 is used to mechanically couple the hot beam 20 and the cold beam 30 and keep them electrically independent, thereby maintaining them in a spaced- apart relationship with a minimum spacing so as to avoid a direct contact or a short circuit in normal operation as well as to maintain the required withstand voltage, which voltage is somewhat proportional to the spacing between the beams 20, 30. The dielectric tether 40 can be molded directly in place at the desired location and attached by direct adhesion. Direct molding can allow having a small quantity of material entering the space between the parts before solidifying. It should be noted that the dielectric tether 40 can be attached to the

hot beam 20 and the cold beam 30 in a different manner than the one shown in FIG. 1.

As can be appreciated, the dielectric tether 40 is located over the actuator 10, namely on the opposite side with reference to the substrate 12. The dielectric tether 40 can be made entirely of a photoresist material, using for instance the material known in the trade as "SU-8". The SU-8 is a negative, epoxy-type, near-UV photo resist based on EPON SU-8 epoxy resin (from Shell Chemical) that has been originally developed by IBM. It should be noted that other photoresist do exist and can be used as well, depending on the design requirements. Other possible suitable materials include polyimide, spin on glass or other polymers. Moreover, combining different materials is also possible.

In use, when a control voltage is applied at the anchor pads 24a, 24b of the hot beam 20, a current travels between the first portion 22a and the second portion 22b. In the illustrated example, the material used for making the hot beam 20 is selected so that it increases in length as it is heated. The cold beam 30, however, does not have such lengthening since no current is initially passing through it. The result is that the free end of the actuator 10 is deflected sideward (toward the right in FIG. 1 ) because of the asymmetrical configuration of the hot beam 20 with reference to the cold beam 30, thereby moving the actuator 10 from a neutral position to a deflected position. Conversely, taking away the control voltage allows cooling the hot beam 20 and moving it to its original position. Both movements occur very rapidly.

In the illustrated example, the cold beam 30 comprises a transversally narrower section 36 adjacent to its anchor pad 32 in order to facilitate the movement between the deflected position and the neutral position. The narrower section 36 has a smaller width compared to a main section 38 of the cold beam 30 and is more flexible. The width can decrease sharply, as shown, but other shapes are possible. For instance, the narrower section 36 can also be parabolic or otherwise rounded. It is also possible to omit the narrower section in some designs.

The actuator 10 illustrated in FIG. 1 includes a set of two spaced-apart additional dielectric tethers 50. These additional dielectric tethers 50 are transversally disposed over the portions 22a, 22b of the hot beam 20 and over the cold beam 30. They adhere to these parts. Using at least one of these additional dielectric tethers 50 on the actuator 10 can provide additional strength to the hot beam 20 by reducing its effective length so as to prevent its distortion over time. Since the gap between parts is extremely small, the additional tethers 50 can reduce the risks of a short circuit between the two portions 22a, 22b of the hot beam 20 or between the second portion 22b of the hot beam 20, which is the closest to the cold beam 30, and the cold beam 30 itself by keeping them in a spaced-apart configuration. Moreover, since the cold beam 30 can be used to carry high voltage signals, the second portion 22b of the hot beam 20 can potentially deform, thus moving towards the cold beam 30 due to the electrostatic force between them created by the high voltage signal. If the second portion 22b of the hot beam 20 gets too close to the cold beam 30, a voltage breakdown may occur and destroy the MEMS switch 100. Additionally, since the two portions 22a, 22b of the hot beam 20 are often

relatively long, they may possibly distort when heated, thereby decreasing the effective stroke of the actuator 10. Using one, two or more additional dielectric tethers 50 can increase the rigidity of the portions 22a, 22b of the hot beam 20, increase the stroke of the actuator 10, decrease the risks of short circuits between the portions 22a, 22b of the hot beam 20 and increase the breakdown voltage between the cold beam 30 and hot beams 20. The additional dielectric tethers 50 can be made of a material identical or similar to that of the main dielectric tether 40. Small quantities of materials can be allowed to flow between the parts before solidifying in order to improve the adhesion. Yet, one or more holes can be provided in the cold beam 30 to receive a small quantity of material before it solidifies. It should be noted that it is nevertheless possible to omit the additional dielectric tethers 50 from one or both actuators 10, 10', depending on the design.

FIG. 1 further shows that the illustrated actuator 10 comprises a tip 60 attached to the free end of the cold beam 30. The tip 60 is designed for mechanically latching with the tip 60' of the second actuator 10'. It may also provide an electrical contact between the cold beams 30, 30' of the two actuators 10, 10'.

In this case, the cold beams 30, 30' and their corresponding tips 60, 60' are electrically connected together. If desired, the surface of the tip 60 can provide a lower contact resistance when the mating face of tips 60, 60' makes contact with each other. This can be obtained, for instance, by using a tip 60 made of gold, either entirely made of gold or gold-over plated. Other possible materials include a gold-cobalt alloy, palladium, etc. Generally, all that is required for such materials is that they provide a lower electrical resistance as compared to the material for the cold beam 30, for instance compared to nickel or an alloy

thereof, which are possible materials for the cold beam 30. The hot beam 20 can also be made of nickel or an alloy thereof. Still, other materials can be used for the hot beam 20 and the cold beam 30.

FIG. 2 shows that the tip 60 in the illustrated actuator 10 is attached under the free end 34 of the cold beam 30. It can be attached using the natural adhesion of the materials when plated over each other, although other means can be used as well.

Referring back to FIG. 1 , one can see that the illustrated tips 60, 60' comprise a corresponding lateral contact flange 62, 62'. The flanges 62, 62' can be useful for the latching of the two substantially-perpendicular actuators 10, 10'. Other arrangements are also possible.

The MEMS switch 100 has two positions, namely a closed position where the first actuator 10 and the second actuator 10' are mechanically (and electrically) engaged, and an open position where they are independent, thus where there is no contact between them. FIG. 3A shows the open position of the MEMS switch 100. To move from the open position to the closed position, the actuators 10, 10' are operated in sequence. As shown in FIG. 3B, the tip 60' of the second actuator 10' is deflected upward. Then, as shown in FIG. 3C, the tip 60 of the first actuator 10 is deflected to its right. The control voltage is released in the hot beam 20' of the second actuator 10', which causes its flange 62' to move next to the back side of the flange 62 of the first actuator 10 as it returns towards its neutral position, as shown in FIG. 3D. The control voltage in the hot beam 20 of the first actuator 10 is subsequently released, thereby allowing a stable engagement between both tips 60, 60', as shown in FIG. 3E.

A signal or a current can then be transmitted between the anchor pads 32, 32' of the cold beams 30, 30' in the illustrated example. The closing of the MEMS switch 100 is very rapid, all this possibly occurring within a few milliseconds. Setting the MEMS switch 100 back to the open position can be done by reversing the above-mentioned operations.

FIG. 1 shows " that the actuators 10, 10' have hot beam portions with an asymmetric configuration, in this case having portions with asymmetric lengths. More particularly, one of the portions of the hot beam 20, 20' is longer than the other portion by a length δL, as shown in FIG. 4. FIG. 4 is an enlarged view of the anchor pads 24a, 24b, 32 of the first actuator 10. In the illustrated example, it is the second portion 22b (i.e. the one closer to the cold beam 30) that is shorter by the amount δL. By making the first portion 24a longer, the lengthening of the first portion 24a when an electrical current circulates in the hot beam 20 will be more than that of the second portion 24b. This way, the actuator 10 can exhibit better stress distribution over an actuator in which both hot beam portions do not have an asymmetric configuration. It also provides a more efficient actuation mechanism that can reduce stress along the structure and reduce the temperature (i.e. the current) required for actuation between the latched and unlatched positions.

FIG. 5 shows yet another example of a MEMS switch 200 having an asymmetric configuration of the hot beam in at least one of its MEMS actuators. In this example, the two portions 22a, 22b of the hot beam 20 of each actuator 10, 10' do not exhibit the same width (i.e. the width transversal with reference to the longitudinal direction). In particular, the first portion 22a is shown having a

width w1 , while the second portion 22b is shown having a width w2 where w1 ≠ w2, as shown in FIG. 6. Narrowing the first portion 22a can produce an effect similar to increasing its length since the temperature of the first portion 22a will be higher than in the second portion 22b when the hot beam 20 is activated.

It should be noted at this point that it is possible to construct an actuator and a switch in which one or both actuators have the combined characteristics of what is shown in FIGS. 1 and 5, namely asymmetric lengths and asymmetric widths at the same time.

FIG. 7 shows another example of a MEMS switch 300 that is a variant of the MEMS switch 200 shown in FIGS. 5 and 6. In this example, one end of the first portion 22a of the hot beam 300 is transversally wider than the other end of that same portion 22a. As shown in FIGS. 8A and 8B, the first portion 22a has a width w2 near the common end 26 and a width w1 near its anchor pad 24a where w1 < w2. The taper profile serves as a "choke" to the electrical energy. As a result, the temperature of the first portion 22a so configured can exhibit more uniform temperature distribution across its length and therefore a lower peak temperature for a given displacement. The second portion 22b also have a tapered profile, which can have a tapered profile that is opposite the one of the first portion (i.e. the width near the common end 26 is narrower then the width near its anchor pad 24b. Once again, the particular materials chosen and the application will dictate the taper characteristics and which of the hot beam portions 22a, 22b will have the taper. Other shapes besides a tapered shape are also possible.

FIGS. 9A to 9D show different configurations for the flanges 62, 62' of the tips 60, 60'. FIG. 9A shows a one-bump configuration. The flange 62 has a "bump" 64 of material, for instance gold, which can improve contact resistance between the flanges 62, 62' since it has a much smaller surface area and therefore a higher contact pressure is exhibited. In the illustrated example, the bump 64 has a substantially hemispherical geometry.

FIG. 9B shows a "double bump" configuration, wherein each flange 62, 62' has a bump 64, 64', respectively. As can be appreciated, when so configured and properly aligned, this can minimize the surface area over which the flanges 62, 62' contact one another. Additionally, it should be noted that while only a single bump 64 is shown in FIG. 9A and one bump 64, 64' is shown on each flange 62, 62' in FIG. 9B, one or more bumps may be disposed upon a given flange as an application requires. Such configurations affect the "wiping" or cleaning of the flanges 62, 62' as they become engaged/disengaged. As a result, the contact effectiveness and lifetime can be improved. Additional "self-wiping" configurations are also possible.

FIG. 9C shows yet an alternative tip configuration wherein one of the flanges 62, 62' exhibits a "positive" angle. The positive angle is characterized by an angle that is greater than 90 degrees between the inner flange face and the longitudinal direction of the actuator. This positive angle configuration may be combined with a bump configuration, such as the single bump 64 shown previously wherein the bump 64 is disposed on the inner face of the mating flange 62. Such angular flanges may increase the amount of friction between

the moving flanges 62, 62'. As a result, a more forceful, self-wiping action can be produced, thereby enhancing its operational characteristics.

FIG. 9D shows a configuration having a "negative" angle. The negative angle is characterized by an angle that is less than 90 degrees between the inner flange face and the longitudinal direction of the actuator. This negative angle configuration may be combined with other bump configurations, such as the single bump configuration or, as shown, a plated section 66'.

FIG. 10 shows an example of a MEMS switch 400 with asymmetric hot beam lengths and also with a cold beam exhibiting a tapered profile. In this configuration, as shown in FIG. 11 , the cold beam 30 closest to the anchor pad 34 has a width w1 that is larger than the width of that cold beam 30 near its free end. This tapered cold beam profile distributes more uniformly any stresses introduced into the cold beam 30. It can be used in combination with other kinds of asymmetric hot beam configurations.

FIG. 10 also shows that the MEMS actuators 10, 10' can have mating actuator tips 60, 60' configured with a negative angle producing an angled contact. When configured in this manner, the MEMS switch 400 can have a smaller stroke. FIG. 12 is an enlarged view of these tips 60, 60'. It shows a distance W that is substantially the width of a given flange and any associated bump(s) 64 disposed thereon. The bump 64 and/or the entire flange 62, 62' may be made from gold or other suitable materials. A minimal actuator stroke will produce lower stresses in the actuators 10, 10'. It also permits a lower temperature to actuate, thus smaller deformations. The negative angle may be of a variety, depending upon the application. More particularly, negative angles of between

10 and 45 degrees can be particularly useful. In other words, the negative angle (the angle between the flange 62, 62' and its respective tip 60, 60') can be substantially from 45 degrees to 80 degrees. The angled geometry provides a more positive latch while requiring fewer movements which may provide a longer, less stressful operating lifetime.

The lower stroke is shown in FIGS. 13A to 13D, which depict the actuation latching of MEMS actuators having flanges 62, 62' with a negative angle. FIG. 13A corresponds to the position shown in FIG. 12. When compared to FIGS. 3A to 3E, it can be seen that fewer movements are required to engage the tips 60, 60' of the angled configuration, and the displacement or stroke through which it moves is less as well. While straight flanges 62, 62' first move apart, the angled flanges 60, 62' may first move towards one another, as shown in FIG. 13B. Because they do not have to move apart to engage, fewer movements are required as well. FIG. 13C shows the actuator 10' being deflected and FIG. 13D shows the actuator 10 being released. The actuator 10' can be released thereafter or shortly after the release of the actuator 10.

While some specific examples were used in the present description, those skilled in the art will recognize that the teachings are not so limited. In particular, various permutations of the individual aspects, for example angled geometry, bumps, tapered beams, etc, may be used alone or in any useful combinations. The MEMS actuators presented herein are not limited for use in or as switches. One may use a single MEMS actuator as described herein for a given purpose, whether for use as or in a switch or not. More than two MEMS actuators can also be used. Still, the MEMS actuators of a same device, for instance forming

a switch or another device, do not necessarily need to be similar. It is possible to construct only a single one with a hot beam having an asymmetric configuration. Some MEMS actuators may also have more than one hot beam, for instance one hot beam on each side of the cold beam. In these cases, less than all hot beams can have an asymmetric configuration. It is possible to use the MEMS actuators in a switch without electrically engaging the cold beams and their corresponding tip. For instance, the cold beam of one actuator can hold a lateral conductive member engageable over a pair of electrodes to electrically connect them together when the switch is in a latched position. Other arrangements are also possible.