Abstract:
An article comprising a support portion that is coupled to an element portion, both of which portions are formed from some of the layers of a multi-layer substrate. In one embodiment, the support portion comprises a torsional member, an actuating plate and a beam, wherein the beam mechanically links the actuating plate and the element portion. At least one torsional member attaches the support portion to the multi-layer substrate and allows the element portion to move independently of the substrate, such as when actuated by an underlying electrode. When actuated, the actuating plate of the support portion is drawn toward the underlying electrode while the element portion rises from a first (unactuated) position within the substrate toward a second (actuated) position outside of the substrate, in see-saw like fashion. The present article is useful in a variety of applications, such as, for example, optical applications where it can be used to form improved chopper switches and optical cross connects.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to micro-electromechanical systems (“MEMS”) devices. More particularly, the present invention relates to a MEMS device that is movable between a first position located within a multi-layer substrate and a second position that is located outside of the substrate. 
     BACKGROUND OF THE INVENTION 
     MEMS technology is becoming ubiquitous. MEMS accelerometers, pressure sensors, and even MEMS-based electrical components have been developed for use in a wide variety of applications. 
     Presently, some of the most important applications for MEMS are in the area of optical communications, wherein MEMS-based optical modulators, switches, attenuators, filters and like devices have been developed. While MEMS technology is very well suited for optical communications applications, integrating MEMS devices into such systems does present certain challenges. In particular, to process an optical signal via a MEMS device, the MEMS device must typically capture or engage the optical signal in a region of space that is “out-of-the-plane” relative to the substrate layer of the MEMS device. In other words, a raised or three-dimensional MEMS component is required to capture the signal. 
     Such components have traditionally been fabricated as “flip-up” structures that incorporate micro-hinges. Flip-up structures are formed by (1) fabricating hinged plates that lie on a base or substrate layer; (2) raising the hinged plates by rotating them about their micro-hinges; and (3) locking the hinged plates into the raised position. See, e.g., U.S. Pat. Nos. 5,923,798 and 5,963,367; Pister et al., “Microfabricated Hinges,” Sensors and Actuators A, vol. 33, pp 249-256 (June 1992); Lee et al., “Surface-Micromachined Free-Space Fiber Optic Switches with Integrated Microactuators for Optical Fiber Communication Sytsems,” Transducers &#39;97, 1997 Int&#39;l. Conf. Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997, pp 85-88, and Reid et al., “Automated Assembly of Flip-Up Micromirrors,” Transducers &#39;97, 1997 Int&#39;l. Conf. Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997, pp 347-350. 
     While flip-up optical MEMS structures represent a tremendous advance over earlier bulk devices having moving parts, they nevertheless suffer from certain drawbacks. 
     For instance, many of the MEMS foundries offer fabrication processes that use alternating layers of oxide and polysilicon to form the various plates and other elements of a MEMS structure. Typically, the polysilicon layers exhibit compressive stress that can cause the fabricated elements to warp. Warped elements can cause assembly and operational problems. Additionally, flip-up structures must be assembled. In some cases, processing steps and structures are required for no reason other than to drive the assembly process. 
     Furthermore, optical applications often have stringent placement tolerances (e.g., for single mode fiber, etc.). Due to the nature of (i.e., the “play” in) micro-hinges, rotating a plate or other hinged element into a precise position is problematic. Moreover, once a hinged element is moved to a desired position, it must be locked in place. The locking mechanism is often realized as an additional notched plate that is rotated into interlocking engagement with the hinged element. Again, the notched plate represents additional fabrication and assembly steps. 
     The art would therefore benefit from an article that offers the functionality of the flip-up structures of the prior art but avoids at least some of their drawbacks. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a MEMS device that avoids some of the drawbacks of the prior art. The present MEMS device, which is fabricated from a multi-layer substrate, comprises a support portion coupled to an element portion. In some embodiments, the MEMS device is configured as an optical switching element, wherein, for example, the element portion is physically adapted to receive and reflect an optical signal. It is to be understood, however, that such embodiments are merely illustrative; in other embodiments, the present MEMS device is suitably used as other than an optical switching element. 
     The multi-layer substrate that forms the present MEMS device has at least a first layer, a second layer and an intermediate layer that separates the first and second layers. In accordance with the present teachings, the element portion of the MEMS device is fabricated from the second layer of the multi-layer substrate. Furthermore, it is particularly advantageous if the element portion has a major surface that is defined by the thickness of the second layer of the multi-layer substrate. When formed this fashion, the element portion itself is substantially orthogonal to the major surface of the surrounding multi-layer substrate. 
     In one embodiment, the multi-layer substrate is a silicon-on-insulator wafer. The support portion is advantageously formed from the top, relatively thin silicon layer of the silicon-on-insulator insulator wafer, while the element portion is formed from the bottom, relatively thick silicon layer of the wafer. 
     In some embodiments, the support portion of the MEMS device includes an actuating plate, one or more torsional members and a beam. The beam advantageously rigidly couples the actuating plate to the element portion. The torsional members, which depend from the beam, are coupled to the first layer of the multi-layer substrate (from which the torsional members are formed). The MEMS device is therefore supported, via the torsional members, from the multi-layer substrate. The torsional members are operative to twist, thereby allowing the MEMS device to move (e.g., rotate, etc.) independently of the multi-layer substrate. 
     The actuating plate and the element portion, which depend from the beam, are disposed on opposite sides of an axis of rotation that is aligned with the torsional members (i.e., the axis of rotation of the beam). Furthermore, the actuating plate is advantageously rigidly coupled to the element portion. This configuration functions as a mechanism by which at least some of the element portion formed from the second layer is raised “above” the first layer of the substrate. 
     Specifically, in a first position, the element portion is disposed within the multi-layer substrate. In some embodiments, the first position results when the MEMS device is in an unactuated state (i.e., no potential difference between the actuating plate and the underlying electrode). In an actuated state, a potential difference is created across the actuating plate and the electrode, thereby generating an electrostatic force of attraction therebetween. When the electrostatic force exceeds the restoring force of the torsional members, the actuating plate moves toward the underlying electrode such that the beam rotates about its axis of rotation. As the actuating plate moves downwardly toward the electrode, the element portion moves upwardly out of the multi-layer substrate to a second position in seesaw-like fashion. When the actuating force is removed, the element portion drops back within the multi-layer substrate to the first position. 
     The term “restoring force,” as used herein, is the force of the torsional elements that must be overcome in order to move the element portion from its unactuated state to its actuated state. The term “unactuated state,” or “first position” as used herein, refers to when the element portion is within (i.e., beneath the surface of) the multi-layer substrate. The term “actuated state,” or “second position,” as used herein, refers to when the element portion is outside (i.e., above the surface) of the multi-layer substrate. 
     In the context of an optical switching element, the element portion is used to direct an optical signal. For example, in one embodiment, the two optical fibers are positioned end-to-end, with a gap between the ends, over the multi-layer substrate. The element portion of the present MEMS device is aligned with the gap between the fiber ends. When the MEMS device is in the first position within the multi-layer substrate, the optical signal is able to pass from the first fiber to the second fiber. When, however, the MEMS device is actuated, the optical signal does not pass from the first fiber to the second fiber since the element portion is raised above the surface of the multi-layer substrate and into the path of the optical signal. 
     In such embodiments, the element portion is configured and placed to direct the optical signal either back to the input source of the optical signal (i.e., the input fiber or input waveguide) or to a different fiber or waveguide. Thus, the optical switching element is used to either redirect or reflect the optical signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts an n×n array of MEMS devices in accordance with the illustrative embodiment of the invention. 
     FIG. 2 depicts a top view of an illustrative embodiment of one of the MEMS devices of FIG.  1 . 
     FIG. 3 depicts a side cross-sectional view of the MEMS device of FIG. 2, wherein the MEMS device is in an unactuated state. 
     FIG. 4 depicts the side cross-sectional view of FIG. 3, but when the MEMS device in an actuated state. 
     FIG. 5 depicts a flow diagram of a method for making a MEMS device in accordance with the present teachings. 
     FIG. 6 depicts a method for carrying out one of the operations in the method depicted in FIG.  5 . 
     FIG. 7 depicts the processing of the top side of a SOI wafer during the fabrication of a MEMS device in accordance with the present teachings. 
     FIG. 8 depicts the processing of the bottom side of a SOI wafer during the fabrication of a MEMS device in accordance with the present teachings. 
     FIG. 9 depicts dimensional parameters of a MEMS device for use in conjunction with a physical design example. 
     FIG. 10 depicts a plot of reduced actuation voltage versus reduced rotation angle. 
     FIG. 11 depicts a top view of an improved chopper switch in accordance with the present teachings. 
     FIG. 12 depicts a cross-sectional side view of the chopper switch of FIG.  11  through line  1 — 1  of FIG.  11 . 
     FIG. 13 depicts an optical cross connect comprising a n×n array of MEMS devices in accordance with the present teachings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Structure and Operation of the Present MEMS Device 
     FIG. 1 depicts a n×n array of MEMS devices  100  in accordance with the illustrative embodiment of the present invention. For the illustrative array depicted in FIG. 1, n equals 3. That is, there are three columns and three rows of MEMS devices  100 . It will be understood that in other embodiments of the n×n array, n is less than 3, and in still further embodiments, n is greater than 3. As described later in this Specification, the illustrative n×n array of MEMS devices can function as an optical cross connect, among other uses. 
     A first embodiment of a MEMS device  100  is depicted in FIGS. 2-4. FIG. 2 depicts a top view of MEMS device  100 , while FIGS. 3 and 4 depict cross-sectional side views. 
     With reference to FIGS. 1-4, each MEMS device  100  comprises a support portion  102  and element portion  110  (FIG. 1) that are substantially separated from multi-layer substrate  112  by trench  222  (FIG.  2 ). 
     In the illustrative embodiment, support portion  102  comprises torsional members  104 , beam  106  and actuating plate  108 . Torsional members  104  rotatably couple MEMS device  100  to multi-layer substrate  112 . Torsional members  104  depend from beam  106  at a location between actuating plate  108  and element portion  110 . Torsional members  104  create a “pivot point” along beam  106  between actuating plate  108  and element portion  110  about which beam  106  rotates in the manner of a “see-saw” when suitably actuated. 
     In some embodiments, multi-layer substrate  112  comprises three layers, including a bottom, relatively thick layer  114  (also referred to herein as the “second layer”), an intermediate, relatively thin layer  116  disposed on bottom layer  114 , and a top, relatively thin layer  118  (also referred to herein as the “first layer”) disposed on intermediate layer  116 . As described in more detail later in this Specification, MEMS device  100  is advantageously formed from some of the layers comprising multi-layer substrate  112 . 
     MEMS devices  100  are movable between two states or positions that are depicted in FIG.  1 . In particular, in a first position illustrated by MEMS device  100 - 1 , a MEMS device resides substantially within multi-layer substrate  112 . More particularly, the upper surface of MEMS devices  100  (i.e., the upper surfaces of torsional members  104 , actuating plate  108  and beam  106 ) is co-planar with upper surface  120  of multi-layer substrate  112 , while element portion  110  resides within multi-layer substrate  112 . In the second position, which is illustrated by MEMS device  100 - 2 , a portion of the MEMS device, predominantly element portion  110 , is disposed above upper surface  120  of multi-layer substrate  112 . 
     For clarity and for the purposes of exposition, when MEMS device  100  is in the first position, it (and/or element portion  110 ) is referred to herein as being “within” or “in” multi-layer substrate  112 . When MEMS device  100  is in the second position, it (and/or element portion  110 ) is referred to herein as being “outside” of multi-layer substrate  112 . 
     In the illustrative embodiments, the movement of element portion  110  between the first and second positions results from the combined action of torsional members  104 , actuating plate  108  and electrode  326  (see FIG. 3) that is disposed on electrode layer  124  that abuts bottom multi-layer substrate layer  114 . 
     In particular, in the absence of an actuating force, element portion  110  remains in the first position within multi-layer substrate  112 . This state is illustrated, via a cross-sectional view, in FIG.  3 . When a potential difference is created across electrode  326  of electrode layer  124  and actuating plate  108 , an electrostatic force is generated therebetween. This force draws actuating plate  108  toward electrode  326 . As this occurs, and in response thereto, element portion  110  rises above upper surface  120  of multi-layer substrate  112 , as is depicted in FIG.  4 . 
     In the embodiment depicted in FIGS. 1-4, torsional members  104  twist to allow the MEMS device  100  to rotate relative to multi-layer substrate  112  allowing actuating plate  108  to move toward electrode  326 . In other embodiments, other support arrangements (i.e., other than torsional members) for movably coupling MEMS device  100  to multi-layer substrate  112  may suitably be used. 
     Illustrative Fabrication Method 
     As indicated above, the present MEMS devices are advantageously formed from substrate  112 , itself. To this end, substrate  112  comprises several layers, such as layers  114 ,  116  and  118  that are depicted in FIGS. 1-4. 
     The present MEMS devices can of course be fabricated in a wide variety of configurations to satisfy the requirements of a particular application. It will be appreciated that, as a function of MEMS device configuration, the thickness of the layers of the multi-layer substrate, and even the arrangement of the layers, might vary from the guidelines provided below for the illustrative configuration. It is within the capabilities of those skilled in the art to modify the nominal thicknesses and the arrangement of the various layers of the multi-layer substrate as is necessary or desirable to satisfy the requirements of any particular application. 
     For the MEMS devices described herein, suitable multi-layer substrates advantageously comprise at least three layers, including a first layer (e.g., top, relatively thin layer  118 ), a second layer (e.g., bottom, relatively thick layer  114 ), and an intermediate, relatively thin layer (e.g., layer  116 ) that is sandwiched between the first and second layers. The first (top) layer and intermediate layer each have a thickness that is in the range of about 1 to 2 microns. The second layer has a thickness in the range of about 300 to 700 microns. 
     In accordance with the present teachings, the second layer, which in the illustrative embodiments is the bottom, relatively thick layer, is used to form element portion  110 . The “height” (from the perspective of FIGS. 3 and 4) of a major surface of element portion  110  (i.e., the surface that is depicted in the cross sectional views of FIGS. 3 and 4) is advantageously defined by the thickness of the bottom layer (e.g., layer  114 ) of the multi-layer substrate. For simplicity of description, this major surface is referred to herein as the “working surface” of element portion  110 . 
     The relatively first layer, which in the illustrative embodiments is the top, relatively thin layer, is used to form support portion  102  of MEMS device  100 , including actuating plate  108 , torsional members  104  and beam  106 . The intermediate layer serves as an etch/milling stop between the two layers. While it is possible to fabricate a MEMS device without the use of an etch-stop (ie., the intermediate layer), it is substantially more difficult to control the extent of the etching/milling step without it. 
     The top and bottom layers of multi-layer substrate  112  comprise, without limitation, silicon or polysilicon. Since the intermediate layer functions as a “stop-etch” layer, it must therefore comprise a material that resists being etched by processes that will readily etch the top and bottom layers. For instance, if silicon or polysilicon is used for the top and bottom layers, silicon oxide is advantageously used for the intermediate layer. 
     In one particularly advantageous embodiment, multi-layer substrate  112  comprises a silicon-on-insulator (“SOI”) wafer. Such wafers typically comprise a bottom bulk or “thick” silicon layer (about 500 to 700 microns in thickness as a function of wafer diameter), an oxide layer (about 0.2 to 3 microns in thickness) disposed thereon, and a “thin” silicon layer (about 0.1 to 10 microns) that is disposed on top of the oxide layer. The arrangement and thickness of such layers are consistent with the nominal ranges for layer thickness that have been previously provided. SOI wafers are commercially available from SOITEC USA, Inc. of Peabody, Mass. and others. 
     When fabricating MEMS devices  100  using a SOI wafer, torsional members  104 , beam  106  and actuating plate  108  are advantageously formed from the thin silicon layer and element portion  110  is advantageously formed from the thick silicon layer. In some embodiments, a SOI wafer (in particular, the thick silicon layer) having a &lt;110&gt; crystal orientation is used. In such embodiments, the wafer can be oriented so that the working surface of element portion  110  is an atomically flat &lt;111&gt; surface. Since each element portion  110  comprises a section of the same single crystal silicon, the working surface of the element portion of each MEMS device  100  in an array of such devices are parallel to one another to a high degree of accuracy. 
     The ability to precisely align the element portions and provide exceedingly smooth, flat surfaces is particularly advantageous for optical applications, a few of which are described later in this Specification. 
     A method for making a MEMS device is now described in conjunction with FIGS. 5-8. The illustrative fabrication method utilizes standard patterning and etching techniques (e.g., photolithographic processing, etc.) Since these techniques are commonplace in the art, they will be referenced without explanation. 
     In accordance with operation  502  of method  500  depicted in FIG. 5, support portion  102  is defined in a multi-layer substrate  112 . In one embodiment, operation  502  is carried out via steps  604  and  606  depicted in FIG.  6 . In particular, support portion  102  is defined by appropriately patterning and etching the top layer (i.e., layer  118 ) of the multi-layer substrate (step  604 ), and by appropriately patterning and etching the bottom layer (i.e., layer  114 ) of the multi-layer substrate (step  606 ). 
     FIG. 7 depicts a view of top layer  118  after etching and patterning in accordance with step  604 . After patterning, top layer  118  is etched (e.g., via reactive ion etching, etc.) such that trench  222 , which substantially encompasses or surrounds support portion  102 , extends “down” to intermediate layer  116 . Trench  222  defines the shape of actuating plate  108 , torsional members  104  and beam  106 . 
     FIG. 8 depicts a view of bottom layer  114  after etching and patterning in accordance with step  606 . After patterning, bottom layer  114  is etched (e.g., via DRIE, laser milling, etc.) “up” to intermediate layer  116 . A thin “slice” of layer  114  is masked such that it remains after etching. That slice becomes, in the illustrative embodiment, element portion  110 . And the thickness of layer  114  defines the “height” (from the perspective of FIGS. 3 and 4) of the working surface of element portion  110 . 
     Bottom layer  114  advantageously comprises silicon having a &lt;110&gt; crystal orientation, which can be oriented so that the working surface (i.e., the vertical face) of element portion  110  comprises &lt;111&gt; facets. After etching, element portion  110  is washed (e.g., KOH, etc.) to clean the &lt;111&gt; facets. 
     After defining the MEMS device  100  as per operation  502 , it is released, as per operation  508 . In the illustrative embodiment of the present method, release is effected by removing the portions of intermediate layer  116  that are exposed due to the previous etching steps. Bottom layer  114  of multi-layer substrate  112  is then bonded, in operation  510 , to a second substrate (e.g., substrate  124  of FIGS. 1,  3 ,  4 ) that is patterned with electrodes. Top layer  118  and bottom layer  114  of multi-layer substrate  112 , and the portions of MEMS device  100  formed from those layers, are electrically grounded. 
     Physical Design Example 
     A MEMS device  100  is to be fabricated from a SOI wafer comprising a thin silicon layer having a thickness t and a thick silicon layer having a thickness t 0 . With reference to FIG. 9, other length parameters include length L of actuating plate  108 , the length L t  of torsional members  104 , the width w of torsional members  104 , the distance d between the center of torsional members  104  and the leading edge of actuating plate  108 , the distance D 1  between the center of torsional members  104  and the trailing edge of actuating plate  108  and the distance D 2  between the center of torsional members  104  and the end of beam  106  or element portion  110 . 
     Assuming further that d/D 1 &lt;0.2, L=2D 1  and that w=t, then the voltage V c  and the corresponding rotation angle θ c  at which snap down (i.e., electrostatic instability) occurs are given by: 
     
       
           V   c ≈2.6×10 4 [( tt   0   1.5 )/( L   t   0.5   D   1   2 )]  [1] 
       
     
     
       
         θ c ≈25.2 t   0   /D   1   [2] 
       
     
     where: length/distance is measured in microns and angle is measured in degrees. 
     Given: 
     thin silicon layer thickness t=2 microns; 
     thick silicon layer thickness t 0 =200 microns; and 
     the distance D 1 =400 microns, then: 
     
       
           V   c =1810 /L   t   0.5 ; and  [3] 
       
     
     
       
         θ c =12.6°.  [4] 
       
     
     So, if L t =200 microns, then: 
     
       
           V   c =128 volts.  [5] 
       
     
     Assuming that the maximum working voltage V mw  would be ninety percent of V c , then: 
     
       
           V   mw =115 volts.  [6] 
       
     
     It is seen from FIG. 10, which is a plot of θ/θ c , that when V/V c =0.9, then: 
     
       
         θ/θ c ≈0.55.  [7] 
       
     
     Therefore, for a maximum working voltage of 0.9V c , the maximum working rotation angle θ mw  is: 
     
       
         θ c =7°.  [8] 
       
     
     If the distance D 2 =800 microns, then the outside edge of element portion  110  is raised a distance of 800 tan 7° or 100 microns above surface  120  of multi-layer substrate  112 . 
     Illustrative Optical Applications 
     As previously indicated, the present MEMS device is well suited for optical applications, among other uses. Two of such optical applications are described below. 
     1. Chopper Switch 
     In a very simple optical application, an on/off switch is created by positioning a movable plate such that it can be moved into or removed from the path of an optical signal that is traveling between two waveguides. See, e.g., U.S. Pat. No. 5,923,798. Such switches are often referred to as “chopper” switches. An improved version of a chopper switch in accordance with the present invention is depicted in FIGS. 11-12. 
     FIG. 11 depicts a top view of improved chopper switch  700 . In accordance with the present teachings, chopper switch  700  includes two optical waveguides (e.g., fibers, etc.)  728  and  730  that are disposed end-to-end and separated by gap  736 . Chopper switch  700  also includes MEMS device  100  that is arranged so that the portion of trench  222  that houses element portion  110  is disposed beneath gap  736 . The working surface of element portion  110  is advantageously highly reflective. 
     FIG. 11 depicts the cross state of switch  700  wherein optical signal  734  travels from waveguide  728 , across gap  736 , to waveguide  730 . In the cross state, element portion  110  is within multi-layer substrate  112  and, therefore, does not impinge upon the path of optical signal  734 . 
     FIG. 12 depicts, via a side cross-sectional view through axis  1 — 1  of FIG. 11, the bar state of switch  700 , wherein optical signal  734  does not cross (i.e., is “barred” from crossing) switch  700 . In the bar state, the working surface of element portion  110  intercepts optical signal  734 , thereby preventing it from entering waveguide  730 . Switch  700  is placed in the bar state by actuating MEMS device  100 , such as by applying a potential difference across electrode  326  and actuating plate  108 , so that element portion  110  moves out of multi-layer substrate  112  and between waveguides  728  and  730 . 
     The embodiment of MEMS device  100  depicted in FIGS. 11I and 12 (hereinafter “configuration B”) for use in chopper switch  700  has a different configuration than MEMS device  100  illustrated in FIGS. 2-4 and  6 - 7  (hereinafter “configuration A”). In particular, in configuration A, bean  106  extends over element portion  110  (see, e.g., FIG.  4 ), while in configuration B, beam  106  does not extend over element portion  110  (see, e.g., FIG.  12 ). 
     The reason for this difference is that for a chopper switch it is usually advantageous to keep the size of gap  736  as small as possible. In this context, observe that beam  106  is wider than element portion  110 . Consequently a relatively wider-sized gap would be required to accommodate the relatively greater width of beam  106  for a MEMS device having configuration A than for a MEMS device having configuration B. 
     A second difference between configuration A and configuration B of MEMS device  100  is the presence of, in configuration B, stabilization region  838 . Stabilization region  838 , which flares outwardly with increasing distance from element portion  110 , provides additional rigidity to MEMS device  100 . There is nothing unique to the chopper switch application that demands the presence of stabilization region  838 ; this feature is suitably incorporated into the present MEMS devices for use in a wide variety of applications. 
     Optical Cross Connect 
     FIG. 13 depicts optical cross connect  900  in accordance with the present invention. Optical cross connect  900  comprises a n×n array of MEMS devices  100 . In the embodiment depicted in FIG. 13, n=3, such that there are three columns of MEMS devices  100  (labeled columns  1 ,  2  and  3 ) and three rows of MEMS devices  100  (labeled A, B, C). It will be understood that in other embodiments of cross connect  900 , n is less than 3, and in still further embodiments of cross connect  900 , n is greater than 3. 
     An optical signal  948  is delivered to cross connect  900  by a first 1×n array of input waveguides  940 -i, i=1, n. A second 1×n array of output waveguides  946 -i, i=1, n, receives optical signal  948  from cross connect  900 . In the embodiment depicted in FIG. 13, n=3 such that there are three input waveguides  940 - 1 ,  940 - 2  and  940 - 3 , and three output waveguides  946 - 1 ,  946 - 2  and  946 - 3 . 
     In the illustrative embodiment, a first 1×n array of lenses  942 -i, i=1, n, is disposed between input waveguides  940 -i and columns  1 ,  2  and  3  of MEMS devices  100 . More particularly, one lens (e.g.,  942 - 1 ) is disposed between each input waveguide (ie., waveguide  940 - 2 ) and the optically aligned column (ie., column  2 ) of MEMS devices  100 . Similarly, a second 1×n array of lenses  944 -i, i=1, n, is disposed between rows A, B and C of MEMS devices  100  and output waveguides  946 -i. Lenses  942 -i collimate the optical signal as it leaves the input waveguides  940 -i, and lenses  944 -i focus the optical signal into output waveguides  946 -i. 
     By selectively actuating an appropriate MEMS device  100 , optical cross connect  900  is operable to route an optical signal, which can be delivered via any one of the n input waveguides  940 -i, to any one of the n output waveguides  946 i. For example, in FIG. 13, optical signal  948 , which is delivered by input waveguide  940 - 2 , is routed to output waveguide  946 - 2  by actuating MEMS device (B,  2 ). If the signal were instead to be routed to output waveguide  946 - 3 , then MEMS device (C,  2 ) must be actuated. 
     The MEMS devices  100  of cross connect  900  are actuated in the manner previously described by electrodes (not depicted in FIG. 13) that underlie the MEMS devices on an electrode wafer. Typically, each electrode will be individually connected, via a wire trace, to electrical contact pads that are disposed at the edge of electrode wafer. Such contact pads will be in electrical contact with a controlled voltage source that is operable to selectively apply voltage to an appropriate pad to actuate a desired electrode. 
     In cross connect  900 , element portion  110  is oriented at 45 degrees with respect to sides  950  and  952 . This is a consequence of the orientation (orthogonal) of the input and output waveguides relative to each other and of the orientation (orthogonal) of the waveguides with respect to sides  950  and  952 . 
     The individual MEMS devices  100  of cross connect  900  have a structural configuration that is different than configurations A or B previously depicted and described. In particular, while MEMS devices  100  that are depicted in FIG. 13 possess the same elements as in the previous embodiments (i.e., torsional members  104 , beam  106 , actuating plate  108 , element portion  110  and stabilization region  838 ), the shape of the MEMS device is different. More particularly, actuating plate  108  of the MEMS devices depicted in cross connect  900  has a shape that (1) facilitates close packing of MEMS devices and (2) prevents shorting if electrostatic snap-down occurs. In further detail, notch  954  in actuating plate  108  allows for closer packing, and points  956  contact electrode layer  124  rather than electrode  326  if snap-down occurs (see FIG.  4 ). 
     It is to be understood that the above-described embodiments are merely illustrative of the invention and that many variations may be devised by those skilled in the art without departing from the scope of the invention and from the principles disclosed herein. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.