Patent Publication Number: US-2007096860-A1

Title: Compact MEMS thermal device and method of manufacture

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      Not applicable.  
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
      Not applicable.  
     STATEMENT REGARDING MICROFICHE APPENDIX  
      Not applicable.  
     BACKGROUND  
      This invention relates to a compact microelectromechanical systems (MEMS) thermal device, and its method of manufacture. More particularly, this invention relates to a compact MEMS thermal switch for switching electrical signals.  
      Microelectromechanical systems (MEMS) are very small moveable structures made on a substrate using lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. A moveable MEMS switch, for example, may be used to connect one or more input terminals to one or more output terminals, all microfabricated on a substrate. The actuation means for the moveable switch may be thermal, piezoelectric, electrostatic, or magnetic, for example.  
       FIG. 1  shows an example of a prior art thermal switch, such as that described in U.S. Patent Application Publication 2004/0211178 A1. The thermal switch  10  includes two cantilevers,  100  and  200 . Each cantilever  100  and  200  contains a flexor beam  110  and  210 , respectively. A conductive circuit  120  and  220 , is coupled to each flexor beam  110  and  210  by a plurality of dielectric tethers  150  and  250 , respectively. When a voltage is applied between terminals  130  and  140 , a current is driven through conductive circuit  120 . The Joule heating generated by the current causes the circuit  120  to expand relative to the unheated flexor beam  10 . Since the circuit is coupled to the flexor beam  110  by the dielectric tether  150 , the expanding conductive circuit drives the flexor beam in the upward direction  165 .  
      Applying a voltage between terminals  230  and  240  causes heat to be generated in circuit  220 , which drives flexor beam  210  in the direction  265  shown in  FIG. 1 . Therefore, one beam  100  moves in direction  165  and the other beam  200  moves in direction  265 . These movements may be used to open and close a set of contacts located on contact flanges  170  and  270 , each in turn located on tip members  160  and  260 , respectively. The sequence of movement of contact flanges  170  and  270  on tip members  160  and  260  of switch  10  is shown in  FIGS. 2   a - 2   d , to close and open the electrical switch  10 .  
      To begin the closing sequence, in  FIG. 2   a , tip member  160  and contact flange  170  are moved about 10 μm in the direction  165  by the application of a voltage between terminals  130  and  140 . In  FIG. 2   b , tip member  260  and contact flange  270  are moved about 17 μm in the direction  265  by application of a voltage between terminals  230  and  240 . This distance is required to move twice the 5 μm width of the contacts, a 4  82  m initial offset between the contact flanges  170  and  270 , and additional margin for tolerances of 3 μm. In  FIG. 2   c , tip member  160  and contact flange  170  are brought back to their initial position by removing the voltage between terminals  130  and  140 . This stops current from flowing and cools the cantilever  100  and it returns to its original position. In  FIG. 2   d , tip member  260  and contact flange  270  are brought back to nearly their original position by removing the voltage between terminals  230  and  240 . However, in this position, tip member  160  and contact flange  170  prevent tip member  260  and contact flange  270  from moving completely back to their original positions, because of the mechanical interference between contact flanges  170  and  270 . In this position, contact between the faces of contact flanges  170  and  270  provides an electrical connection between cantilevers  100  and  200 , such that in  FIG. 2   d , the electrical switch is closed. Opening the electrical switch is accomplished by reversing the movements in the steps shown in  FIGS. 2   a - 2   d.    
     SUMMARY  
      In general, the larger the size of the switch, the higher the cost because fewer devices may be made on the area of the wafer substrate. Therefore, it is advantageous from a cost perspective to make the switches as small as possible. One drawback of switch  10  shown in  FIG. 1  is the relatively large distance that tip member  260  and contact flange  270  must travel in order to clear tip member  160  and contact flange  170 . Because of this rather large distance, about 17 μm, the cantilever  200  must be made of a size to have sufficient compliance to be able to travel this distance given the temperature change provided by the drive circuit  220 . In particular, cantilever  200  is required to be at least about 400 μm long, in order to have sufficient compliance to move the required distance.  
      Attempting to miniaturize the switch shown in  FIG. 1  is not straightforward. A first problem is that the displacement of the cantilevers  100  or  200  does not vary linearly with the beam length, but rather varies rather to a higher power, so the MEMS switch  10  cannot be simply scaled down to reduce its size. Also, if an attempt is made to miniaturize the switch shown in  FIG. 1 , the drive loop will be shorter, and therefore will not generate the heat necessary to move the cantilevers  100  and  200  the required distances. The drive loops  120  and  220  will also not have as much heat capacity, and the thermal transfer rate to the substrate will be greater, resulting in less heat buildup in the drive loops  120  and  220 , and therefore less thermal displacement.  
      A compact MEMS thermal switch is disclosed herein which has substantially reduced size compared to switch  10  shown in  FIG. 1 . Accordingly, the switch described herein may have cost advantages relative to the switch shown in  FIG. 1 . In addition, the switch described here may be more robust during a shock event than the switch illustrated in  FIG. 1 . Finally, the switch described herein may have a simpler activation sequence than that illustrated in  FIGS. 2   a - 2   d.    
      The compact MEMS thermal switch is one embodiment of the more general compact MEMS device. The compact MEMS device comprises a first cantilevered thermal actuator with a first contact and a second cantilevered thermal actuator with a second contact, wherein the first cantilevered thermal actuator is less stiff than the second cantilevered thermal actuator, and wherein the first cantilevered thermal actuator moves a greater distance than the second cantilevered thermal actuator to activate the device by engaging the first contact with the second contact.  
      The MEMS thermal switch embodiment may have two cantilevered beams, with one cantilevered beam being less stiff than the other. Each cantilevered beam may also have a tip member with a contact and a contact surface. In the quiescent state, the contacts on the tip members of the cantilevered beams are directly adjacent to one another. To close the MEMS switch, the second stiffer cantilever swings away to clear the adjacent contact of the tip member of the first cantilever. The first cantilever then deflects into a flexed position, whereupon the second cantilever relaxes to approximately  ⅔ of it stroke causing the two contacts to touch thus closing the switch. The second cantilever then holds the first cantilever in the displaced position, despite the restoring force acting upon the first cantilever, thus the switch is latched. In one exemplary embodiment, frictional forces keep the cantilevers from becoming unlatched. In another exemplary embodiment, the contact surfaces of the cantilevers are angled to prevent unlatching, even in the situation where no friction is present.    
      Because the cantilevered beams are arranged with their contacts adjacent, the cantilevered beams are not required to travel as far, because the second cantilever has only to clear the width of the contact on the first cantilever. Because of the smaller amount of travel required of the first and the second cantilevers, the beams may be made shorter, and thus the entire switch may be made more compact than the switch illustrated in  FIG. 1 .  
      Another advantage of this design is that the two cantilevers may be optimized independently, because their functions and movements are different. That is, the cantilevers may be made with dissimilar mechanical attributes, the first enhancing the travel of the cantilever at the expense of its stiffness, and the second enhancing the stiffness at the expense of reduced travel.  
      Because the second cantilever may be made very stiff, it can hold the first cantilever in the latched position even in the event of shock, and despite the restoring force of the first cantilever tending to unlatch the first cantilever from the second.  
      These and other features and advantages are described in, or are apparent from, the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Various exemplary details are described with reference to the accompanying drawings, which however, should not be taken to limit the invention to the specific embodiments shown but are for explanation and understanding only.  
       FIG. 1  is a schematic view of a prior art MEMS thermal switch;  
       FIGS. 2   a - 2   d  are diagrams illustrating the sequence of movements required to close the switch illustrated in  FIG. 1 ;  
       FIG. 3  is a schematic view of an exemplary MEMS thermal switch;  
       FIGS. 4   a - 4   d  are diagrams illustrating an exemplary sequence of movements;  
       FIG. 5  is a schematic view showing greater detail of an exemplary shape of the angle contact flanges;  
       FIG. 6  is a schematic view showing the functioning of the angled contact flange of FIG.;  
       FIGS. 7   a - 7   d  are diagrams illustrating an exemplary sequence of movements for the angled contact flanges of  FIG. 5 ;  
       FIG. 8  illustrates a second exemplary shape of the angled contact flanges;  
       FIG. 9  illustrates a first step in the fabrication of the compact MEMS switch;  
       FIG. 10  illustrates a second step in the fabrication of the compact MEMS switch;  
       FIG. 11  illustrates a third step in the fabrication of the compact MEMS switch;  
       FIG. 12  illustrates a fourth step in the fabrication of the compact MEMS switch; and  
       FIG. 13  illustrates a fifth step in the fabrication of the compact MEMS switch; 
    
    
     DETAILED DESCRIPTION  
      Although the devices and methods described herein are applied to an electrical switch, it should be understood that this is only one embodiment, and that the device and methods may include any number of devices, such as valves and actuators.  
       FIG. 3  is a schematic view of an exemplary compact MEMS thermal switch  100 . Like the MEMS switch  10  illustrated in  FIG. 1 , the compact MEMS switch  1000  includes two cantilevers. The first cantilever will be hereinafter referred to as the “latch” cantilever  300 , and the second cantilever will be referred to as the “spring” cantilever  400 . The latch cantilever  300  and the spring cantilever  400  both include a cantilevered flexor beam  310  and  410 , respectively, and a drive loop circuit  320  and  420 , respectively. The flexor beams  310  and  410  and the drive loops  320  and  420  each have proximal and distal ends, with the proximal end of the flexor beams  310  and  410  coupled to anchor points  317  and  417 , respectively, and the proximal ends of the drive loops  320  and  420  coupled to terminals  330  and  340 , and  430  and  440 , respectively.  
      In the embodiment depicted in  FIG. 3 , the flexor beams  310  and  410  will carry the signal being switched. Therefore, the flexor beams  310  and  410  may be made of any suitably conductive material. In one exemplary embodiment, nickel is chosen because it is a straightforward material to plate, as will be described below. However, in order to isolate the signal carrying flexor beams  310  and  410  from the drive loop circuits  320  and  420 , the drive loop circuits  320  and  420  will be tethered to the flexor beams  310  and  410  by dielectric tethers  350  and  450 , respectively, which are electrically insulating but mechanically rigid materials. The drive loop circuits  320  and  420  may also be made of nickel, and formed at the same time as the cantilevered flexor beams  310  and  410 .  
      As can be seen in  FIG. 3 , the compact MEMS switch  1000  also includes two tip members  360  and  460 , to which two contacts  370  and  470  are affixed. Like the prior art switch  10 , the tip members  360  and  460  and the two contacts  370  and  470  may be made of different material than cantilevered flexor beams  310  and  410 . The material of tip members  360  and  460  and contacts  370  and  470  may be made of a material which has a low contact resistance relative to the material of cantilevered flexor beams  310  and  410 . In one embodiment, the material of tip members and contacts  360 ,  460 ,  370  and  470  is gold, however, other materials such as gold cobalt alloy, palladium, etc., may be used as well.  
      In contrast to MEMS switch  10 , in the quiescent state, the two contacts  370  and  470  of compact MEMS switch  1000  are located adjacent to each other, rather than one in front of the other as is the case with contact flanges  170  and  270  shown in  FIG. 1 . The initial position of contact  370  relative to contact  470  is shown schematically in  FIG. 4   a . By being “adjacent” to each other, it should be understood that the spring contact  470  and latch contact  370  have one dimension longer than the other, and in a quiescent state, surfaces having the shorter dimension are located a minimum distance apart.  
      Because of the location of contact flanges  370  and  470  adjacent to one another, contact flange  370  does not need to be retracted as was shown in  FIG. 2   a . Instead, the sequence of motion for the compact MEMS switch  1000  is shown in  FIGS. 4   b - 4   d . In  FIG. 4   b , spring drive loop  420  is energized by applying a voltage to terminals  430  and  440 . The resulting current flowing through spring drive loop  420  causes the drive loop  420  to rise in temperature and expand. Because spring drive loop  420  is tethered to spring flexor beam  410  by dielectric tethers  450 , the expansion of spring drive loop  420  causes the spring flexor beam  410  to arc in the direction  465  shown in  FIG. 3 . This moves the spring tip member  460  along with spring contact flange  470  as shown in  FIG. 4   b . However, in contrast to the motion depicted in  FIG. 2   b , the distance that the spring cantilever  400  must move is only the width of the contact  370 , about 5 μm. This has a substantial impact on the mechanical characteristics of the spring beam. Specifically, because the travel distance of spring beam  400  is relatively small, the relative stiffness of spring beam may be made large compared to the stiffness of the latch beam. In one exemplary embodiment, the spring cantilever stiffness is about 140 N/m.  
      The dielectric tethers  350  and  450  may be made of any convenient, non-conducting material which couples the drive loops  320  and  420  to cantilevered flexor beams  310  and  410  mechanically, but not electrically. In one embodiment, dielectric tethers  350  and  450  may be made from an epoxy based photoresist such as SU-8, a negative photoresist developed by IBM of Armonk, N.Y.  
      After the spring beam has moved 5 μm, the latch drive loop  320  is energized by applying a voltage to terminals  330  and  340 . This resulting current flowing through latch drive loop  320  causes the latch drive loop to rise in temperature and expand. Because the latch drive loop  320  is tethered to the latch flexor beam  310  by dielectric tethers  350 , the expansion of latch drive loop  320  causes the latch flexor beam  310  to arc in the direction  365  shown in  FIG. 3 . This moves the latch tip member  360  along with latch contact flange  370  as shown in  FIG. 4   c , a total distance of about 8 μm. Because the latch cantilever  300  moves a larger distance than the spring cantilever  400 , it may be made relatively flexible. Several features contribute to the greater displacement capability of the latch cantilever  300 , compared to spring cantilever  400 .  
      First, the latch beam  310  may be made with a narrower hinge portion  315  in the area where it is anchored to the substrate. This may make the latch flexor beam  310  less rigid, and therefore it may have a greater displacement as a function of temperature. Secondly, the drive loop may be made with an outer portion  322  and an inner portion  324 , with the outer portion  322  located further away from the cantilevered flexor beam  310  than the inner portion  324 . The outer portion  322  of the latch drive loop  320  may. then be formed with a serpentine shape, as shown in  FIG. 3 . As the latch flexor beam  310  bends during actuation, it forms an arc. In order for the latch flexor beam  310  to take the shape of an arc, with minimum stress, the outer portion  322  of the drive loop  320  will need to be elongated more along the longitudinal axis of the flexor beam  310  than an inner portion  324  of the drive loop, because it is farther away from the axis of curvature. The serpentine shape allows the outer portion  322  of drive loop  320  to expand more easily than the inner portion  324  of the drive loop, and therefore reducing the binding between the inner portion  324  and outer portion  322  of the drive loop  320 , and thus enhances the thermal displacement created by the drive loop  320 . The addition of these serpentines will also reduce the bending stiffness of the latch cantilever beam structure  300 . Rear serpentines  325  in both the outer portion  322  and inner portion  324  of the drive loop  320  again decrease the stiffness of the latch cantilever  300  at its base. Each of these features is designed to increase the displacement of the latch cantilever for a given temperature, at the expense of latch stiffness. However, as will be described further below, the latch beam is not required to have much stiffness, as the contact force for the contact flanges  370  and  470  will be provided by the spring cantilever  400 , rather than the latch cantilever.  
      One drawback to the compact MEMS switch  1000  is that the longitudinal length of the drive loops are shorter, thus having lower electrical resistance which will reduce the maximum temperature the drive loops will achieve with the same voltage applied. Increasing the voltage is not a good solution due to the increased costs of controlling CMOS chips that can operate at higher currents. Therefore, an additional advantage of the rear latch drive loop serpentine  325  is that it adds length to the drive loop without adding length to the flexor beam  310 . This additional length may increase the temperature achieved by the latch drive loop  320 , thus increasing its displacement during actuation. In fact, the presence of the serpentine shape may increase the peak temperature achieved by the drive loop  320  by about  200  degrees centigrade. The displacement of the cantilevered flexor beam  310  can be further increased by forming the outer portion  322  of the drive loop  320 , narrower than the inner portion  324 . In one embodiment, the width of the outer portion  322  of the drive loop  320  is 4.5 μm whereas the width of the inner portion  324  of the drive loop  320  is 5.0 μm. This will cause the outer portion  322  of drive loop  320  to generate more heat than the inner portion  324 , and therefore encourage bending in direction  365 .  
      The dielectric tethers  350  are placed in the serpentine portion of drive loop  320  as shown in  FIG. 3 . The placement of dielectric tethers  350  is chosen to transmit as much of the thermal displacement of drive loop  320  to cantilevered flexor beam  310  as possible, without increasing the overall stiffness of cantilever  300  to bending about the anchor point  317 . To achieve this purpose, no dielectric tethers are placed over the rear latch serpentine  325 , that is, the area closest to the anchor point  317 , such that this area is free to bend. The overall dimensions of the dielectric tethers  350  and  450  are generally made as small as practical without sacrificing mechanical strength, in order to reduce heat transfer to the cantilevered flexor beams  310  and  410 , which would otherwise reduce the bending displacement generated by the drive loops  320  and  420 . Exemplary dimensions of dielectric tethers are about 10 μm by 25 μm.  
      The latch cantilever made according to the design shown in  FIG. 3  may have a cantilever stiffness of about 14 N/m, compared to the spring cantilever stiffness of about 140 N/m as set forth above. Accordingly, the latch beam generates about   1/10 of the force of the spring beam. In one exemplary embodiment, in the latched position, the latch beam may generate a force of about  60 μN, whereas the spring beam may generate a force of about 500 μN.  
      Because the travel distances are small, the total length of the spring cantilever  400  and latch cantilever  300  may be made substantially smaller than the prior art switch shown in  FIG. 1 . In fact, one embodiment of the compact MEMS thermal switch  1000  has a cantilever length of only 230 μm, compared to a cantilever length of 440 μm for the prior art switch shown in  FIG. 1 . This may shrink the area required for the entire switch package to an area of only about 66% of the switch package required for the prior art MEMS thermal switch, including overhead areas such as bond pad regions, etc. As described above, the total area of substrate required by the compact MEMS switch package directly impacts the cost of manufacturing the switch, and therefore compact MEMS switch  1000  may be expected to be substantially cheaper to manufacture than prior art MEMS switch  10 .  
      For a spring cantilever  400  made according to the design shown in  FIG. 3 , the displacement of the contact  470  is about 5 μm for a drive current of 180 mA. For a latch cantilever  300  made according to the design shown in  FIG. 3 , including the drive loop serpentine features and narrowed hinge portion  315 , the displacement of the latch contact  370  of the latch cantilever  300  is about 10.5 μm for a 180 mA drive current. This corresponds to an angular deflection of between about 1 and 3 degrees for cantilevers  300  and  400 .  
      In  FIG. 4   d , the switch is closed by allowing the spring cantilever  400  to relax to 80 percent of its initial displacement. This is achieved by removing the voltage applied to terminals  430  and  440 . As the current ceases to flow, the spring drive loop  420  cools, and shrinks, pulling the spring flexor beam  410  back to nearly it original position. However, the presence of the latch contact  370  prevents the spring contact  470  from moving further than the position shown in  FIG. 4   d , in which it is resting against, and engaged with, the latch contact. In this position, the latch contact and the spring contact form an electrical connection, such that an electrical signal is allowed to pass from the latch cantilever  300  to the spring cantilever  400 , thereby closing the switch. Opening the MEMS switch  1000  is accomplished by energizing the spring cantilever  400 , which releases the latch cantilever  300 . The latch cantilever  300  then returns to its initial position shown in  FIG. 4   a , because of the restoring force of the latch cantilevered flexor beam  310 .  
      A comparison of the sequence of motion for the compact MEMS switch  1000  shown in  FIGS. 4   b - 4   d  with the sequence of motion for the prior art MEMS switch  10  shown in  FIGS. 2   a - 2   d  reveals that the sequence of motion is one step shorter for the compact MEMS switch  1000  than for the prior art MEMS switch  10 . This is because the first retraction step shown in  FIG. 2   a  is absent in the sequence for the compact MEMS switch  1000 . Therefore, the control algorithm for the compact MEMS switch  1000  is somewhat simpler than that for the prior art MEMS switch  10 . Simplifying the control algorithm may have the advantage of decreasing the cost of the mating electrical componets for the device.  
      As can be seen in  FIGS. 4   a - 4   d , the spring cantilever, and not the latch cantilever, provides the force necessary to close the switch. Furthermore, in the closed state, the latch cantilever is held in the deflected position, under tension, by the spring cantilever. In fact, with the design shown in  FIGS. 4   a - 4   d , the only force keeping the switch closed is friction between the latch contact flange  370  and the spring contact flange  470 . For many situations, this may provide a satisfactory and reliable switch.  
      However, an alternative embodiment for the latch contact  370  and the spring contact  470  which does not rely on friction is the angled latch contact  570  and angled spring contact  670 . Like the embodiment illustrated in  FIGS. 4   a - 4   d , the angled contacts  570  and  670  start in the initial position shown in  FIG. 5 , in which the angled contacts  570  and  670  are in an adjacent arrangement.  
      In the closed position, the spring contact  670  holds the latch contact  570  in the deflected position. However, when the switch is closed, the angled contacts form a contact surface  580 , which is disposed at an angle with respect to the tip members  560  and  660 . The angled contact surface  580  may retain the engagement of the tip members  560  and  660 , without relying on friction.  
      In particular, the normal line to the contact surface  580  is the line designated by reference numeral  590  in  FIG. 6 . This line  590  defines the angles alpha and beta, which are the angles at which the spring force F s , and latch force, F l , respectively are applied to the contact surface  580 . In general, alpha=90−beta, where alpha is the latch angle. Inspection of  FIG. 5  reveals that the larger the latch angle, the more firmly engaged the spring contact  670  with the latch contact  570 , however, the farther the spring beam  600  must travel to clear the latch contact  570 . In fact, no friction is required to maintain the latched condition as long as F s , and F l , satisfy
 
 F   l /cos(beta)&lt; F   s  sin(alpha)  (1)
 
 and the components of F l  and F s  normal to the contact surface are equal, such that the switch is stationary. 
 
      One embodiment of the angled compact MEMS thermal switch  2000  uses a latch angle of about 18 degrees, however, it should be understood that the selection of a latch angle will depend on other details of the design, such as the radius of rotation of the tip members  560  and  660  defined by the length of the cantilevers  500  and  600 , and their displacement. It should also be understood that designs with a latch angle of less than about 3 degrees will be relying largely on friction to keep the contacts  570  and  670  engaged, although this limit will also depend on the lengths and displacements required of latch cantilever  500  and spring cantilever  600 .  
      The switch will not become unlatched unless the restoring force (or force due to a shock) F l  applied by the latch spring meets:
 
 F   l *cos(beta)&gt; F   s *cos(alpha)  (2)
 
 At this point, the component of the latch force in the normal direction exceeds the component of the spring force in the normal direction, and the latch cantilever is able to move free of the spring cantilever. Since the mass of the latch cantilever is very low, the switch may undergo shocks in excess of 145,000 g before the switch becomes unlatched. This performance may exceed the performance of MEMS switch  10  shown in  FIG. 1 , because for MEMS switch  10 , the switch stays closed under shock only because of friction between the contact flanges  170  and  270 . However, the normal force provided by spring beam  210  in MEMS switch  10  is limited, because the spring beam must also travel a relatively long distance, 17 μm, and therefore its stiffness must remain fairly low. 
 
      The sequence of motion for the angled compact MEMS switch  2000  is shown in  FIGS. 7   a - 7   d . As before with the compact MEMS switch  1000 , the angled compact MEMS switch  2000  may lack the first retraction step of the prior art MEMS switch  10 . Instead, the first motion, shown in  FIG. 7   b  is the movement of the spring cantilever  600  about 5 μm to clear the latch contact. Since the spring contact  670  is mounted on a cantilever beam, the actual movement of the spring cantilever is in an arc, as indicated by some rotation of the spring tip member  660 .  
      The next motion, illustrated by  FIG. 7   c , is the movement of the latch cantilever into the closed position. As with the spring cantilever, this motion is on an arc rather than rectilinear, and is therefore accompanied by some rotation of the latch tip member  760 , as shown in  FIG. 7   c.    
      Finally, the angled compact MEMS switch  2000  is closed by allowing the spring cantilever to relax into a position in which it is latched by the presence of the latch contact  570 . In this position, the spring cantilever makes electrical contact with the latch cantilever, so that an electrical signal can travel from the spring cantilever to the latch cantilever, or vice versa.  
      In another embodiment of the spring contact  870  and latch contact  770 , one side of the spring contact  870  and latch contact  770  is rounded, to discourage arcing from the spring cantilever  600  to the latch cantilever  500 , or vice versa. Such a shape is not generally desired in the prior art MEMS switch  10 , because it increases the distance that the cantilevers  100  and  200  must move. However, in this design, because the spring contact and the latch contact start out adjacent to one another, there is no penalty associated with shaping the backsides of the contacts in a more advantageous way, such as that shown in  FIG. 8 .  
      Another advantage of compact MEMS switch  1000  and  2000  may be the motion of the one contact  370  or  570  against the other contact  470  or  670 . In compact MEMS switch  1000  or  2000 , there is a lateral component of motion of the contacts against each other as the switch closes. In the prior art MEMS switch  10 , the only motion of the switch upon closure is perpendicular to the contact surfaces  170  and  270 . The lateral motion in contact MEMS switch  1000  or  2000  accomplishes a scrubbing action, which may lower the contact resistance between the surfaces. Accomplishing a scrubbing action in prior art MEMS switch  10  requires additional motion which be must be added to the basic motion of closing the switch, by programming the software controlling the switch accordingly. In compact MEMS thermal switch  1000  or  2000 , this scrubbing action is an inherent feature of the switch closure motion.  
      An exemplary method for fabricating the compact MEMS switch  1000  or  2000  will be described next. The compact MEMS switch  1000  or  2000  may be fabricated on any convenient substrate  620 , for example silicon, silicon on insulator (SOI), glass, or the like. Because in  FIGS. 9-13 , the compact MEMS switch is shown in cross section, only one of the two cantilevered beams of the compact MEMS thermal switch is shown. However, it should be understood that the second cantilever  500  may be formed at the same time as, and using identical processes to those used to form the first cantilever  400  which is depicted in the figures.  
       FIG. 9  illustrates a first exemplary step in the fabrication of the compact MEMS switch  1000  or  2000 . The process begins with the deposition of a seed layer  630  for later plating of the MEMS switch cantilever  400 , over the substrate  620 . The seed layer  630  may be chromium (Cr) and gold (Au), deposited by chemical vapor deposition (CVD) or sputter deposition to a thickness of 100-200 nm. Photoresist may then be deposited over the seed layer  630 , and patterned by exposure through a mask. A sacrificial layer  680 , such as copper, may then be electroplated over the seed layer. The plating solution may be any standard commercially available or in house formulated copper plating bath. Plating conditions are particular to the manufacturer&#39;s guidelines. However, any other sacrificial material that can be electroplated may also be used. In addition, deposition processes other than plating may be used to form sacrificial layer  680 . The photoresist may then be stripped from the substrate  620 .  
      A second exemplary step in fabricating the compact MEMS switch  1000  or  2000  is illustrated in  FIG. 10 . In  FIG. 10 , the substrate  620  is again covered with photoresist, which is exposed through a mask with features corresponding to gold pads  640  and  645  and a gold tip member  460 . Gold may be used for the tip members  360 ,  460 ,  560 ,  660 ,  760  and  860  because it may have lower contact resistance than the material that will form the cantilever  600 . Although not shown in this view, it should be understood that the features for contacts  370 ,  470 ,  570 ,  670  or  770  may also be formed in this step. The features  460  and  640  will subsequently be plated in the appropriate areas. The gold features  640 ,  645  may include a bonding ring, which will eventually form a portion of a hermetic seal which may bond a cap layer over the substrate  620  and switch  1000  or  2000 . One of the gold features  645  may also be an external access pad that will provide access to the compact MEMS switch  1000  or  2000  electrically, from outside the hermetically sealed structure.  
      The gold features  640 ,  645  and  460  may then be electroplated in the areas exposed by the photoresist, to form gold features  640 ,  645  and  460  and any other gold structures needed. The photoresist is then stripped from the substrate  620 . The thickness of the gold features  640 ,  645  and  460  may be, for example, 1 μm.  
       FIG. 11  illustrates a third step in fabricating the compact MEMS switch  1000  or  2000 . In  FIG. 11 , photoresist is once again deposited over the substrate  620 , and patterned according to the features in a mask. The exposed portions of the photoresist are then dissolved as before, exposing the appropriate areas of the seed layer  630 . The exposed seed layer  630  may then be electroplated with nickel to form the flexor beam  410  and drive loop  420  of the cantilever  400  of the compact MEMS switch  1000 . The tip member  460  will be affixed to the cantilevered flexor beam  410  by the natural adhesion of the gold to the nickel, after deposition. Although nickel is chosen in this example, it should be understood that any other conductive material that can be electroplated may also be used. In addition, deposition processes other than plating may be used to form conductive cantilever  400 . The photoresist may then be stripped from the substrate  620 .  
       FIG. 12  illustrates a fourth step in the fabrication of the compact MEMS switch  1000  or  2000 . In  FIG. 12 , a polymeric, nonconducting material such as the photoresist SU-8 is deposited over the substrate  620 , flexor beam  410  and drive loop  420 . The photoresist is then cross-linked, by for example, exposure to UV light. The unexposed resist is then dissolved and removed from the substrate  620  and structure  400  in all areas that the dielectric tether is absent. This step forms the dielectric tether  450 , that tethers drive loop  420  to cantilevered flexor beam and  410 . The photoresist may then be cured by, for example, baking.  
      Although not shown, it should be understood that dielectric tether  350 , flexor beam  310  and drive loop  320  are formed in a manner similar to that described above for dielectric tether  450 , flexor beam  410  and drive loop  420 .  
       FIG. 13  illustrates a fifth step in the fabrication of the compact MEMS switch  1000  or  2000 . In this step, the cantilever  400  may be released by etching the sacrificial copper layer  680 . Suitable etchants may include, for example, an isotropic etch using an ammonia-based Cu etchant. The Cr and Au seed layer  630  is then also etched using, for example, a wet etchant such as iodine/iodide for the Au and permanganate for the Cr, to expose the SiO 2  surface of the substrate  620 . The substrate  620  and MEMS switch  1000  or  2000  may then be rinsed and dried.  
      The resulting compact MEMS device  1000  or  2000  may then be encapsulated in a protective lid or cap wafer. Details relating to the fabrication of a cap layer may be found in co-pending U.S. patent application Ser. No. 11/211,625, (Attorney Docket No. IMT-Interconnect) incorporated by reference herein in its entirety.  
      It should be understood that one gold feature  645  may be used as an external access pad for electrical access to the compact MEMS switch  1000  or  2000 , such as to supply a signal to the compact MEMS switch  1000  or  2000 , or to supply a voltage the terminals  430  or  440  in order to energize the drive loops of the switch, for example. The external access pad  645  may be located outside the bond line which will be formed upon the bonding of a cap layer to the substrate  620 . Alternatively, electrical connections to compact MEMS switch  1000  or  2000  may be made using through-wafer vias, such as those disclosed in co-pending U.S. patent application Ser. No. 11/211,624 (Attorney Docket No. IMT-Blind Trench), incorporated herein by reference in its entirety.  
      While various details have been described in conjunction with the exemplary implementations outlined above, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that are or may be presently unforeseen, may become apparent upon reviewing the foregoing disclosure. While the embodiment described above relates to a microelectromechanical switch, it should be understood that the techniques and designs described above may be applied to any of a number of other microelectromechanical devices, such as valves and actuators. Furthermore, details related to the specific design features and dimensions of the compact MEMS switch are intended to be illustrative only, and the invention is not limited to such embodiments. Accordingly, the exemplary implementations set forth above, are intended to be illustrative, not limiting.