Abstract:
A MEMS thermal switch is disclosed which couples a hot, expanding beam to a cool flexor beam using a slideably engaged tether, and bends the cool, flexor beam by the expansion of the hot beam. A rigidly engaged tether ties the distal ends of the hot, expanding beam and the cool, flexor beam together, whereas the slideably engaged tether allows the hot, expanding beam to elongate with respect to the cool, flexor beam, without loading the slideably engaged tether with a large shear force. As a result, the material of the tether can be made stiffer, and therefore transmit the bending force of the hot, expanding beam more efficiently to the cool, flexor beam.

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 microelectromechanical systems (MEMS) thermal switch and its method of manufacture. More particularly, this invention relates to a MEMS thermal switch having a tether slideably engaged with a hot, expanding beam and rigidly engaged with a cool, passive beam. 
     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, sensors, 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 electrical input terminals to one or more electrical output terminals, all microfabricated on a substrate. The actuation means for the moveable switch may be thermal, piezoelectric, electrostatic, or magnetic, for example. 
     A thermal electrical switch may be formed, for example, by disposing an expanding beam adjacent to a passive cantilever, and causing the expanding beam to expand, thereby deflecting the passive cantilever. In one known embodiment, the expanding beam is a conductive circuit through which a current is driven to heat the conductive circuit. The conductive circuit may be tethered to the passive cantilever, also called herein a flexor beam, by a dielectric tether, such that the current does not flow to the passive cantilever from the conductive circuit. The conductive circuit may heat from Joule heating and expand relative to the passive cantilever, thus bending the passive cantilever to which it is tethered. If the passive cantilever is coupled to an electrical input terminal carrying an electrical signal, energizing the conductive circuit may deflect the passive cantilever to a position in which it is in contact with another electrical output terminal, thereby connecting an input terminal to an output terminal. The conductive circuit and passive cantilever may therefore constitute an electrical switch 
     The dielectric tether may therefore be coupled to both the conductive circuit as well as the passive cantilever. The expansion of the conductive circuit generates a force in the longitudinal direction, which is converted into a lateral, bending force by the rigid attachment of the dielectric tether. The dielectric tether of this thermal switch therefore applies a force in a lateral direction against the passive cantilever, in order to cause the passive cantilever to bend laterally in the desired direction However, because the conductive circuit expands longitudinally, the expanding beam also exerts a shear force on the dielectric tether, in a direction orthogonal to the desired bending direction Accordingly, the dielectric tether may be required to accommodate a substantial amount of shear force while converting the shear force to the desired lateral force. Excessively large shear forces may lead to cracking and delamination of the dielectric tether. 
     Therefore, in order to avoid large stresses, the dielectric tether may be made from a relatively compliant material. The compliance of the material may reduce the efficiency of the device, however, because some amount of the force exerted goes into the deformation of the compliant material, rather than to the deflection of the passive cantilever in the desired direction. Accordingly, using compliant materials reduces the mechanical and thermal efficiency of the device, by requiring higher temperatures to produce the desired amount of deflection in the passive cantilever. 
     SUMMARY 
     Systems and methods are described here which address the above-mentioned problems, and may be particularly applicable to the formation of a MEMS thermal switch The systems and methods include at least one tether which is slideably engaged with a hot, expanding beam, allowing the hot, expanding beam to expand by sliding along and through the tether, thereby avoiding the application of a shear stress to the tether. The slideably engaged tether is then rigidly coupled to a passive cantilever, in order to apply the lateral bending force to the passive cantilever, or flexor beam. 
     The systems and methods described here may therefore include a MEMS thermal device, comprising at least one flexor beam formed over a substrate and at least one expanding beam formed adjacent to the flexor beam and at least one slideably engaged tether rigidly adhered to the at least one flexor beam and slideably engaged with the at least one expanding beam The slideably engaged tether allows a portion of the at least one expanding beam to slide longitudinally relative to the flexor beam, but constrains the expanding beam from moving laterally relative to the flexor beam. 
     The slideably engaged tether may be made from a dielectric polymer material such as SU8 photoresist, developed by IBM Corporation of Armonk, N.Y. In one exemplary embodiment, the slideably engaged tether may be manufactured by depositing a sacrificial material over the expanding beam, and then depositing the SU8 photoresist over the sacrificial material to form the dielectric tether. After curing the SU8, the sacrificial layer may be removed, leaving a gap for the sliding contact between the SU8 dielectric tether and the hot, expanding beam. 
     The sliding gap between the tether and the hot, expanding beam may be anywhere between about 200 nm and about 1.5 μm depending on the requirements of the application. Because the slideably engaged tether allows the hot, expanding beam to expand without applying a shear force to the dielectric tether, the tether may be made from relatively stiff material, which allows efficient transmission of the expansion force to the bending of the passive cantilever, or flexor beam. 
     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 following figures, wherein: 
         FIG. 1  is a diagram showing an exemplary MEMS thermal switch using the slideably engaged tether; 
         FIG. 2  is a diagram of the tether used at the distal end of the MEMS thermal switch shown in  FIG. 1 ; 
         FIG. 3  is a diagram of the slideably engaged tether used in medial portion of the MEMS thermal switch of  FIG. 1 ; 
         FIG. 4  is a diagram showing a first exemplary step in the manufacture of the slideably engaged tether; 
         FIG. 5  is a diagram showing a second exemplary step in the manufacture of the slideably engaged tether; 
         FIG. 6  is a diagram showing a third exemplary step in the manufacture of the slideably engaged tether; 
         FIG. 7  is a diagram showing a fourth exemplary step in the manufacture of the slideably engaged tether; and 
         FIG. 8  is a diagram showing a fifth exemplary step in the manufacture of the slideably engaged tether. 
     
    
    
     DETAILED DESCRIPTION 
     The systems and methods described herein may be particularly applicable to a MEMS thermal switch. However, it should be understood that this embodiment is exemplary only, and that the systems and methods disclosed herein may be used in any number of applications requiring structures to move relative to one another. Moreover, the systems and methods are described with regard to a thermal actuator which uses a current-carrying hot beam tethered to a passive flexor beam. However, it should be understood that the systems and methods may be applied to any of a number of other thermal actuators, such as bimorphs, homogeneous, or differential temperature driven actuators. 
     The MEMS thermal device may, in general, include at least one hot, expanding beam disposed adjacent to a cool passive bean The cool, passive beam is also called a “flexor” beam herein, because it is designed to flex in a desired direction, as a result of the force exerted by the hot, expanding beam The ends of the hot, expanding beam are coupled to the ends of the flexor beam, such that the expansion of the hot, expanding beam causes it to bend the flexor beam The bending of the flexor beam is then used to close an electrical switch. In the systems and methods disclosed here, the hot, expanding beam is coupled in its midsection to the flexor beam using a slideably engaged tether. The slideably engaged tether allows at least a portion of the hot, expanding beam to slide along and through the tether, thereby reducing the shear stress on the slideably engaged tether. The hot, expanding beams may be, for example, conductive beams forming an electrical circuit, which, when current is applied, may heat due to the Joule heating of the flowing current within the conductive beams. 
       FIG. 1  shows an example of a MEMS thermal switch  10  which may use the slideably engaged tether. The thermal switch  10  includes two cantilevers,  100  and  200 . Each cantilever  100  and  200  includes a flexor beam  110  and  210 , respectively, and conductive circuits  120   a  and  b  and  220   a  and  b , respectively. The flexor beams may be the cool, passive beams and the conductive beams  120   a  and  b  may be the hot, expanding beams in this embodiment. 
     Each of conductive circuits  120   a  and  b  and  220   a  and  b  is coupled to flexor beams  110  and  210  by a set of at least two dielectric tethers, which transmit the motion of the conductive circuits  120   a  and  b  and  220   a  and  b  to the flexor beams  110  and  210 . A first dielectric tether  150  is a distal dielectric tether, which tethers the distal ends of conductive circuit  120   a  and  b  to flexor beam  110 . A second dielectric tether  152  is a medial dielectric tether, which couples a medial portion of conductive circuit  120   a  and  b  to flexor beam  110 . Similarly, dielectric tether  250  is a distal dielectric tether, which tethers the distal ends of conductive circuit  220   a  and  b  to flexor beam  210 . Another dielectric tether  252  is a medial dielectric tether, which couples a medial portion of conductive circuit  220   a  and  b  to flexor beam  210 . 
     The tethers  150 ,  152  and  250 ,  252  may be made from a dielectric material, so that the current does not flow from the conductive circuit  120   a  and  b  or  220   a  and  b  to the flexor beam  110  or  210 , respectively. When a voltage is applied between terminals  130  and  140 , a current is driven through conductive circuit  120   a  and  b . The Joule heating generated by the current causes the circuit  120   a  and  b  to expand relative to the unheated flexor beam  110 . Since the conductive circuit  120   a  and  b  is coupled to the flexor beam  110  by the dielectric tethers  150  and  152 , the expanding conductive circuit  120   a  and  b  drives the flexor beam in the upward direction  165 . Similarly, since the conductive circuit  220   a  and  b  is coupled to flexor beam  210  by the dielectric tethers  250  and  252 , the expanding conductive circuit  220   a  and  b  drives the flexor beam  210  in the rightward direction  265 , when a current is applied between terminals  230  and  240 . 
     The switch is closed when the contact members  160 ,  170 ,  260  and  270  are placed into electrical contact by the movement of cantilevers  100  and  200 . In particular, cantilever  100  is moved in direction  165  by application of a current to terminals  130  and  140 , after which cantilever  200  is moved in direction  265  by application of current to terminals  230  and  240 . Thereafter, cantilever  100  is allowed to relax, followed by cantilever  200 . However, cantilever  200  is prevented from returning to its original position by mechanical interference from contact member  170 , so that contact member  270  rests against contact member  170 , establishing an electrical connection between flexor beam  110  and flexor beam  210 , thereby closing the electrical switch. If an input electrical signal is applied to terminal  255 , it appears at output terminal  155  by flowing through the contacts  170  and  270  of the switch in the closed position. 
     Because conductive circuits  120   a  and  b  and  220   a  and  b  expand relative to flexor beams  110  and  210 , a component of the force from the expansion goes into a shear force in direction  162  and  262  along beams  100  and  200 , respectively. This shear force is accommodated by the compliance of distal dielectric tethers  150  and  250 . Distal dielectric tethers  150  and  250  are disposed at the distal ends of cantilevered beams  100  and  200 , and translate the shear expansion force into a deflection force, by coupling the ends of the conductive circuits  120   a  and  b  and  220   a  and  b  rigidly to flexor beams  110  and  210 . The term “rigidly coupled” should be understood to mean that the surfaces of the distal dielectric tether are adhered mechanically to the surfs of conductive circuits  120   a  and  b  and  220   a  and  b , and to the surfaces of flexor beams  110  and  210 . Because of the rigid coupling of the conductive circuits  120   a  and  b  and  220   a  and  b  to flexor beams  110  and  210  at the distal ends, the longer length of the conductive circuits  120   a  and  b  and  220   a  and  b  relative to flexor beams  110  and  210  is accommodated by the bowing of the conductive circuits  120   a  and  b  and  220   a  and  b  and flexor beams  110  and  210  in the directions  165  and  265 , respectively. Distal dielectric tethers  150  and  250  which rigidly couple the conductive circuits  120   a  and  b  and  220   a  and  b  to flexor beams  110  and  210 , respectively, are shown in  FIG. 2 . The tether material  122  may be, for example, cured SU8 photoresist. 
     The second, medial dielectric tether  152  is disposed in the medial region between proximal anchor points  130 ,  140  and  155  of the cantilevered beams  110  and  120   a  and  b  and the distal ends. Similarly, medial dielectric tether  252  is disposed in the medial region between the anchor points  230 ,  240  and  255  of the cantilevered beams  210  and  220   a  and  b  and the distal ends. Medial dielectric tethers  152  and  252  inhibit the buckling of the conductive circuit  120   a  and  b  away from the flexor beam  110  in its midsection. There is no requirement for medial dielectric tether  152  or  252  to be rigidly coupled to the conductive circuit  120  or  220   a  and  b , respectively, and therefore medial dielectric tethers  152  and  252  may be slideably engaged with conductive circuits  120   a  and  b  and  220   a  and  b . The term “slideably engaged” should be understood to mean that the dielectric tether is not rigidly, mechanically coupled to the conductive circuit, but rather that the surfaces of the conductive circuit are allowed to slide relative to the surfaces of the dielectric tether. Accordingly, the slideably engaged tethers  152  and  252  allow the expanding beams  120   a  and  b  or  220   a  and  b  to slide longitudinally (along their long axes) relative to flexor beam  110  or  210 , respectively, but constrains the expanding beams  120   a  and  b  or  220   a  and  b  from moving laterally (perpendicularly to their long axes) relive to flexor beam  110  or  210 . As a result, relatively little shear force is exerted on medial dielectric tethers  152  and  252 , while also eliminating the possibility of column failure or buckling of the expanding beams. 
     While the MEMS thermal switch  10  is shown having a single medial slideably engaged dielectric tether  152  and  252  on each conductive circuit  120   a  and  b  and  220   a  and  b , respectively, it should be understood that this embodiment is exemplary only, and in other exemplary embodiments, the MEMS thermal switch may have ay number of additional medial slideably engaged dielectric tethers, depending on the requirements of the application. 
     In order to allow the slideable contact, medial dielectric tethers  152  and  252  may be constructed as shown in  FIG. 3 .  FIG. 3  is a cross section of the slideable contact, medial dielectric tether  152  taken along, for example, the dashed line  151  shown in  FIG. 1 . In order to allow the slideable engagement, one or more gaps  124  may be left between the surfaces of the conductive circuits  120   a, b  and  220   a, b  and the tether material  122 . The dimension  126  of the gap may be between about 200 nm and about 1.5 μm, depending on the application The gap may be of constant dimension in the orthogonal direction (into the page of  FIG. 3 ) along the entire length of the dielectric tether, which may be between about 10 μm to about 50 μm long. The dimension  126  of the gap  124  may be made large enough to accommodate the maximum bending of the conductive circuits  120   a, b  and  220   a, b  without binding, but small enough to transmit most of the motion of the conductive circuit  120   a  and  b  to the flexor beam  110 . As the size of gap  124  directly reduces the amount of deflection delivered to the flexor beam  110 , it may, in general, be made as small as practical while still ensuring a sliding engagement. The maximum bending to be accommodated may be estimated using, for example, a finite element model of conductive circuits  120   a, b  and  220   a, b  and modeling the flow of current through the conductive circuits  120   a, b  and  220   a, b  and the consequential build up of heat. 
     The gap  124  may, in general, be filled only with ambient air. Alternatively, a lubricating material may also be disposed in the gap  124 , such as a thin fluorocarbon film, for example, approximately 10 to 20 Angstroms thick, and with some bonding affinity for the dielectric surface. Examples of the fluorocarbon materials include AM2001 or Z-Dol, common lubricants sold by Dupont Corp. (Wilmington, Del.). The inclusion of the lubricating material may discourage the binding of the slideably engaged dielectric tether with the conductive circuits  120   a, b  or  220   a, b .However, it should be understood that the inclusion of the lubricating material is optional, and may depend on other design considerations. 
     An exemplary method for fabricating the MEMS switch  10  with slideably engaged dielectric tethers will be described next, with reference to  FIGS. 4-8 . Particular attention will be given to the slideably engaged dielectric tether portion  152  and  252  of the MEMS switch  10 , as was shown in  FIG. 3 . The cross sections shown in  FIGS. 4-8  may be taken along the dashed line  151  shown in  FIG. 1 . Because in  FIGS. 4-8 , a portion of compact MEMS switch  10  is shown in cross section along the dashed line  151 , only one set of cantilevered beams,  110  and  120   a  and  b , of the two sets  100  and  200  of cantilevered beams of the MEMS thermal switch  10  is shown. However, it should be understood that the second set of cantilevered beams  220   a, b  and  210  may be formed at the same time as, and using similar or identical processes to those used to form the first set  120   a, b  and  110  of cantilevered beams which are depicted in the figures. Furthermore, in order to avoid complicating the figures, the contact members  160  and  170  are not shown, however, they should be understood to be formed at the distal end of flexor beam  110 . 
     It should be understood that the method depicted in  FIGS. 4-8  is exemplary only, and that any number of alternative methods may be envisioned for the manufacture of the slideably engaged tether  152  and  252 . Furthermore, although  FIGS. 4-8  are directed to the manufacture of slideably engaged dielectric tether  152 , it should be understood that slideably engaged tether  252  may be manufactured using a similar, or identical process. 
       FIG. 4  is a diagram illustrating a first exemplary step in a method for manufacturing the MEMS switch  10  with slideable tether of  FIG. 3 . As shown in FIG.  4 , a sacrificial layer  114  is first deposited on the surface of a substrate  112 . The substrate material may be any convenient choice, for example silicon, silicon-on-insulator (SOI), glass, or the like. The sacrificial layer  114  may be, for example copper which is electroplated onto the substrate surface  112 . The deposition of the sacrificial layer may have been preceded by the formation of a seed layer (not shown), to seed the formation of the electrochemically deposited sacrificial layer  114 . The seed layer may be chromium (Cr) and/or 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, and patterned by exposure through a mask. A sacrificial layer  114 , such as copper, may then be electroplated over certain portions of the seed layer. In  FIG. 4 , the sacrificial layer  114  is electroplated over the entire surface of the substrate  112 . 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  114 . The photoresist may then be stripped from the substrate  112 . 
     Photoresist may once again e deposited over the substrate  112 , and patterned according to the features in a mask which correspond to the locations of the conductive circuit  120   a  and  b  and the flexor beam  110 . The exposed portions of the photoresist are then dissolved as before, exposing the appropriate areas of the sacrificial layer. The exposed sacrificial layer may then be electroplated with nickel to form the flexor beams  110  and conductive circuit  120   a, b  of the compact MEMS switch  10 . The flexor beam  110  and the conductive circuit  120   a, b  may have the relatively tall aspect ratio shown in  FIG. 4 , with a height of about 13 μm and a width of about 5 μm The length of the flexor beam  110  and conductive circuit  120   a  and  b  may be between about 200 and about 500 μm long. Accordingly, the means for forming the flexor beans  110  and conductive circuit  120   a , may be a patterned photoresist film in combination with an electrochemical plating bath. The plating bath may be any standard commercially available or in-house formulated nickel plating bath, and plating conditions may be particular to the manufacturer&#39;s guidelines. Although nickel is chosen in this example, it should be understood that any other conductive material, such as a nickel alloy, that can be electroplated may also be used. In addition, deposition processes other than plating may be used to form conductive members  110  and  120 . The photoresist may then be stripped from the substrate  112 . 
     Although not shown specifically in  FIG. 4 , the process may also include photolithographic steps for the formation of the contact tips  160 ,  170 ,  260  and  270 . These features may be made from electroplated gold, in order to reduce the contact resistance of the switch The electroplating of the gold features  160  and  170  on the sacrificial layer  114  may precede or be followed by the electroplating of the nickel features  120   a, b , and  110 , as described above. The gold contact members  160  may adhere to the nickel flexor beam  110  by the natural adhesion of gold to nickel, after deposition. Furthermore, although not shown in  FIG. 4 , it should be understood that the flexor beam  110  and conductive circuits  120   a  and  b  are anchored at anchor point  155 ,  130  and  140  to the substrate, through the sacrificial layer  114 . Thus the anchor points and contacts may be formed by first electroplating the features on or through the sacrificial layer  114 , prior to electroplating the flexor beam  110  and conductive circuits  120   a  and  b  over the sacrificial layer  114 . The anchor points  155 ,  130  and  140  may also be formed concurrently with the flexor and expanding beams by appropriately patterning the sacrificial layer on top of the seed layer. 
       FIG. 5  is a diagram illustrating a second exemplary step in the manufacture of the slideably engaged dielectric tether  152 . As shown in  FIG. 5 , a photoresist mold  116  may be deposited on the sacrificial layer  114  and over conductive circuit  110  and flexor beam  120 . The photoresist mold may be used to provide a structure for deposition of additional sacrificial layers which will define the gap  124  between the conductive circuit  120   a, b  and the slideably engaged dielectric tether  152 . The photoresist mold may be formed by exposing photoresist through a lithographic mask, and developing and removing the photoresist in areas which will contain the additional sacrificial layers. 
       FIG. 6  is a diagram illustrating a third exemplary step in the manufacture of the slideably engaged dielectric tether  152 . As shown in  FIG. 6 , the additional sacrificial layer  118  is deposited in the photoresist mold  116  shown in  FIG. 5 , and the photoresist mold  116  is removed. The additional sacrificial layer  118  may be any convenient material which is easy to deposit, for example a metal or a polymer material In one exemplary embodiment, the additional sacrificial layer  118  may be electroplated copper. The additional sacrificial layer  118  may be formed using similar equipment as was used for forming the sacrificial layer  114 , which may be a standard copper plating bath. The thickness of the additional sacrificial layer  118  may define the thickness of the air gap  124 , and may be, for example, about 200 nm to about 1.5 μm thick. 
       FIG. 7  is a diagram illustrating a fourth exemplary step in the manufacture of the slideably engaged dielectric tether  152 . As shown in  FIG. 7 , the dielectric material  122  is deposited over the substrate, conductive circuits  120   a, b ,  220   a, b  and flexor beams  110  and  210  and the additional sacrificial layer  118 . In one exemplary embodiment, the dielectric material  122  may be a polymeric, non-conducting material such as SU8 photoresist, developed by IBM Corporation of Armonk, NY. The photoresist may be cross-linked by exposure to UV light, and developed to form dielectric tethers  150 ,  152 ,  250  and  252 . Upon development, the unexposed portions of the dielectric tether material may be removed. The remaining dielectric material  122  may then be cured to obtain advantageous mechanical properties as set forth in U.S. application Ser. No. 11/364,334, incorporated by reference in its entirety. 
       FIG. 8  is a diagram illustrating a fifth exemplary step in the manufacture of the slideably engaged dielectric tether  152 . As shown in  FIG. 8 , the sacrificial layers  114  and  118  may be removed by, for example, immersing the substrate  112  and overlying structures, including sacrificial layers  114  and  118  in an etching solution. Etching of the sacrificial layers  114  and  118  releases the conductive circuit  110   a  and  b , as well as flexor beam  120 , allowing them to move in response to the expansion of conductive circuit  110   a  and  b . Suitable etchants may include, for example, an isotropic etch using a persulfate-based Cu etchant. The Cr and Au seed layer may then also be 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  112 . The substrate  112  and MEMS switch  10  may then be rinsed and dried. 
     It should be understood that the process illustrated in  FIGS. 4-8  is only one example of a process that may be used to form the additional sacrificial layer  118  and slideably engaged dielectric tether  152 . One alternative to the process shown is to make the additional sacrificial layer  118  from a material which is, itself, photopatternable. For example, photoresist may be deposited over the surface of the substrate, conductive circuit  120   a , and  b  and flexor beam  110 , exposed and then removed in all areas except those corresponding to the additional sacrificial layer  118 . The slideably engaged dielectric tether material  122  may then be deposited over the photoresist additional sacrificial layer  118 . The photoresist additional sacrificial layer  118  may then be removed by applying the usual solvents to the photoresist, to remove it from the slideably engaged dielectric tether  152  or  252 , as shown in  FIG. 8 . 
     The resulting MEMS device  10  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, incorporated by reference herein in its entirety. 
     While various details have been described m 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 electrical 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. In addition, which a MEMS thermal switch is described having a single slideable tether, it should be understood that the MEMS thermal switch may have any number of additional slideable tethers. Moreover, a MEMS thermal switch is described wherein the expanding beam is a conductive circuit, however the expanding beam may be any beam which expands upon actuation Furthermore, details related to the specific design features and dimensions of the MEMS thermal 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 liming.