Abstract:
A heat actuated switch comprises a substrate, a moveable element having at least one electrical contact associated therewith, a permanent magnet in the vicinity of the electrical contact, a ferromagnetic material in the vicinity of the permanent magnet and associated with the at least one electrical contact, and a heater adjacent the ferromagnetic material, whereby actuating the heater alters the magnetic properties of the ferromagnetic material and causes the moveable element to switch the electrical contact.

Description:
BACKGROUND  
       [0001]     Many different technologies have been developed for implementing micro electromechanical systems (MEMS) radio frequency (RF) switches. These technologies include, for example, magnetically driven MEMS RF switches, electrostatically driven MEMS RF switches, thermal expansion MEMS RF switches and liquid metal microswitches. These technologies all have disadvantages. For example, magnetically driven MEMS RF switches require high drive power, on the order of 100-300 milliwatts (mW), electrostatically driven MEMS RF switches require high drive voltage, on the order of 48 volts (V), and produce unwanted RF signal components, thermal expansion MEMS RF switches require high drive power and are unable to latch, and liquid metal microswitches are difficult to manufacture. In addition, existing MEMS microswitches suffer from stiction. Stiction is an informal contraction of the term static friction. Stiction occurs when surface adhesion forces are higher than the mechanical restoring force of the microswitch. Stiction refers to the reluctance of the contacts to separate when switching is desired.  
         [0002]     Therefore, it would be desirable to have a microswitch capable of switching RF signals and that overcomes these deficiencies.  
       SUMMARY OF THE INVENTION  
       [0003]     A heat actuated switch comprises a substrate, a moveable element having at least one electrical contact associated therewith, a permanent magnet in the vicinity of the electrical contact, a ferromagnetic material in the vicinity of the permanent magnet and associated with the at least one electrical contact, and a heater adjacent the ferromagnetic material, whereby actuating the heater alters the magnetic properties of the ferromagnetic material and causes the moveable element to switch the electrical contact.  
         [0004]     A method for operating a heat actuated switch comprises latching a heat actuated switch in a first position, heating a first ferromagnetic material to a temperature at which the first ferromagnetic material becomes non-magnetic, and attracting a second ferromagnetic material using a permanent magnet to cause the switch to latch in a second position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0006]      FIG. 1A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with an embodiment of the invention.  
         [0007]      FIG. 1B  is a schematic diagram of the heat actuated microswitch of  FIG. 1A  after transitioning from a first position to a second position.  
         [0008]      FIG. 2A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with an alternative embodiment of the invention.  
         [0009]      FIG. 2B  is a schematic diagram of the heat actuated microswitch of  FIG. 2A  after transitioning from a first position to a second position.  
         [0010]      FIG. 3A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with another alternative embodiment of the invention.  
         [0011]      FIG. 3B  is a schematic diagram of the heat actuated microswitch of  FIG. 3A  after transitioning from a first position to a second position.  
         [0012]      FIG. 4A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with another alternative embodiment of the invention.  
         [0013]      FIG. 4B  is a schematic diagram of the heat actuated microswitch of  FIG. 4A  after transitioning from a first position to a second position.  
         [0014]      FIG. 5  is a flowchart describing an exemplary method of operating a heat activated microswitch in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Embodiments of the heat actuated magnetic latching microswitch to be described below will be referred to as a heat actuated microswitch. The heat actuated microswitch can be fabricated using micro electromechanical systems technologies known to those skilled in the art. Accordingly, details of the fabrication and assembly of the heat actuated microswitch have been omitted.  
         [0016]     The heat activated microswitch is based on the realization that once a ferromagnetic material reaches its Curie temperature, the ferromagnetic material will no longer be magnetized and will therefore no longer be attracted to a magnet. At a temperature above the Curie temperature, the ferromagnetic material is said to exhibit a paramagnetic characteristic. By controlling the temperature of a ferromagnetic material, the heat actuated microswitch to be described below can be rapidly switched between states.  
         [0017]      FIG. 1A  is a schematic diagram illustrating an embodiment of a heat actuated magnetic latching microswitch in accordance with an embodiment of the invention. The heat actuated microswitch  100  comprises a permanent magnet  102  over which a substrate  104  is attached. The permanent magnet can be, for example, any ferromagnetic material with a sufficiently high Curie temperature that has been permanently magnetized. A sufficiently high Curie temperature is one that will allow the heat actuated magnetic latching microswitch to operate in a particular environment. The substrate  104  can be, for example, silicon for a low frequency RF switch (e.g., operating frequencies from approximately DC to approximately 3 gigahertz (GHz) or a ceramic material for a high frequency RF switch (e.g., operating frequencies from approximately DC to approximately 15 GHz). The substrate  104  can be bonded, glued, or otherwise attached to the permanent magnet  102 .  
         [0018]     Electrodes  106 ,  108  and  112  are formed on the substrate  104 . The electrodes can be a metallic material, such as copper (Cu), gold (Au), aluminum (Al), etc., suitable for making electrical connection with electrical contacts to be described below. The electrode  108  can be referred to as an input electrode and the electrodes  106  and  112  can be referred to as output electrodes. In one example, the heat actuated microswitch  100  is used to switch a radio frequency (RF) input signal from the electrode  108  to either the electrode  106  or the electrode  112 . The electrode  108  includes a portion  144  that extends through the substrate  104  and the permanent magnet  102  so that the electrode  108  can be externally electrically connected to an input signal. Similarly, electrodes  106  and  112  include portions  142  and  146 , respectively, which extend through the substrate  104  and the permanent magnet  102  so that the electrodes  106  and  112  can be externally electrically connected to other signal conductors. It should be mentioned that there are other ways of connecting to the electrodes  106 ,  108  and  112 , and the manner shown here is merely one example.  
         [0019]     The heat actuated microswitch  100  also comprises a support element  116  to which is mounted a cantilever  114 . The support element  116  can be formed over the surface of the electrode  108  as shown, or can be otherwise formed over the substrate  104 . For example, the electrode  108  need not extend under the support element  116 . In this embodiment, the cantilever  114  is pivotally coupled to the support element  116  so that the cantilever  114  may tilt with respect to the support element  116 , while the support element  116  and the length of the cantilever  114  defines the arc through which the cantilever  114  rotates. The cantilever  114  can be fabricated from, for example, silicon, or from a metal, such as copper, aluminum, gold, etc.  
         [0020]     A contact assembly  170  and a contact assembly  180  are located at the ends of the cantilever  114 . The contact assembly  170  comprises a contact  120 , a ferromagnetic material  122  and a heater  124 . The contact assembly  180  comprises a contact  130 , a ferromagnetic material  132  and a heater  134 . The contacts  120  and  130  can be any metallic or semi-metallic material that is capable of providing electrical contact with the electrodes  106 ,  108  and  112 . The ferromagnetic material  122  and  132  can be, for example, chromium dioxide (Cr 2 O), which possesses a Curie temperature of 113 degrees Celsius (C). Chromium dioxide is chosen as the ferromagnetic material in switching applications that will generally not exceed 100 degrees C. If switching applications require operating temperatures in excess of 100 degrees C., then another material, such as yttrium iron garnet (YIG) (Y 3 Fe 5 O 12 ), having a curie temperature of 280 degrees C., or magnesium antimonide (MnSb), having a curie temperature of 310 degrees C., can be used as the ferromagnetic material. Further, other ferromagnetic materials may be used.  
         [0021]     The heaters  124  and  134  can be, for example, a sheet resistive material comprising tantalum nitride (Ta 2 N) with a passivation layer (not shown). The heaters can be on the order of 100 micrometers (μm)×50 μm, and be approximately less than 0.2 μm thick. In this example, an approximately 10 μm thick layer of chromium oxide (Cr 2 O) is deposited, or otherwise formed, on the passivation layer (not shown) and forms the ferromagnetic material  122  and  132 . The contacts  120  and  130  are formed over the ferromagnetic material  122  and  132 , respectively. Alternatively, other heater architectures can be used.  
         [0022]     Power is provided to the heaters  124  and  134  by a power source  138  via connections  140 . Although the connections  140  are shown as extending through the substrate  104 , other connections between the power source  138  and the heaters  124  and  134  are possible. In one example, the power source provides approximately 2 watts (W) to the heaters  124  and  134 . A power source providing 2 W can provide a switching time of less than 50 μs and a cycle time of approximately 0.1 millisecond (ms). Alternatively, a power source providing 0.16 W (5 volts and 32 milliamps (mA)) can provide a switching time of approximately 1 ms. However, the switching and cycle times can be varied based on the drive power. The heat actuated microswitch  100  is covered by an enclosure  136  that forms a seal around the cantilever  114  and electrodes  106 ,  108  and  112 .  
         [0023]     The heat actuated microswitch shown in  FIG. 1A  is shown as being latched in a first position, which is arbitrary. In the position shown in  FIG. 1A , under ambient temperature conditions, the permanent magnet  102  attracts the ferromagnetic material  122  so that the contact  120  is drawn to and comes into electrical contact with the electrode  108  and the electrode  112 . The permanent magnet  102  has sufficient magnetic attraction to the ferromagnetic material  122  to overcome the inertia of the cantilever  114  and the distance separating the permanent magnet  102  and the ferromagnetic material  122 . In this first position, the contact  120  causes an electrical connection to be established between the electrodes  108  and  112 .  
         [0024]      FIG. 1B  is a schematic diagram of the heat actuated microswitch of  FIG. 1A  after transitioning from a first position to a second position. By activating the power source  138  the temperature of the heater  124  and the ferromagnetic material  122  begins to increase. When the temperature of the ferromagnetic material  122  reaches its Curie temperature, it is no longer attracted to the permanent magnet  102 . When the ferromagnetic material  122  is no longer attracted by the permanent magnet  102 , the magnetic attraction between the ferromagnetic material  132  and the permanent magnet  102  overcomes the inertia of the cantilever  114  and the cantilever  114  begins to tilt. The ferromagnetic material  132  is attracted by the permanent magnet  102  as long as its temperature is lower than its Curie temperature. The magnetic attraction between the ferromagnetic material  132  and the permanent magnet  102  causes the cantilever  114  to tilt and bring the contact  130  into electrical contact with the electrodes  106  and  108 . In this manner, an input signal supplied to the electrode  108  can be switched between a first output (electrode  112 ) and a second output (electrode  106 ). Once the cantilever  114  begins moving the contact  130  toward the electrodes  106  and  108  as a result of the magnetic attraction between the ferromagnetic material  132  and the permanent magnet  102 , the power source  138  is switched off. When power is removed from the heater  124 , the ferromagnetic material  122  begins to cool and will fall below the Curie temperature. However, the magnetic attraction between the ferromagnetic material  132  and the permanent magnet  102  will keep the heat activated microswitch latched in the second position, shown in  FIG. 1B .  
         [0025]     By actuating the power source  138  to supply power to the heater  134 , the magnetic attraction between the ferromagnetic material  132  and the permanent magnet  102  can be reduced to cause the cantilever  114  to transition in the opposite direction.  
         [0026]      FIG. 2A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with an alternative embodiment of the invention. The heat actuated microswitch  200  comprises a substrate  204  that is similar to the substrate  104  of  FIG. 1A .  
         [0027]     Electrodes  206 ,  208  and  212  are formed on the substrate  204 . The electrodes can be a metallic material, such as copper (Cu), gold (Au), aluminum (Al), etc., suitable for making electrical connection with electrical contacts to be described below. The electrode  208  can be referred to as an input electrode and the electrodes  206  and  212  can be referred to as output electrodes. In one example, the heat actuated microswitch  200  is used to switch a radio frequency (RF) input signal from the electrode  208  to either the electrode  206  or the electrode  212 . The electrode  208  includes a portion  244  that extends through the substrate  204  so that the electrode  208  can be externally electrically connected to an input signal. Similarly, electrodes  206  and  212  include portions  242  and  246 , respectively, which extend through the substrate  204  so that the electrodes  206  and  212  can be externally electrically connected to other signal conductors. It should be mentioned that there are other ways of connecting to the electrodes  206 ,  208  and  212 , and the manner shown here is merely one example.  
         [0028]     In this embodiment, heaters  224  and  234  are formed over the substrate  204  in the region between the electrodes. The heater  224  is formed on the substrate  204  in the region between the electrodes  208  and  212 , and the heater  234  is formed in the region between the electrodes  206  and  208 . The heaters  224  and  234  are similar to the heaters  124  and  134  described above. The heaters  224  and  234  are coupled to a power source  238  via connections  240 . The connections  240  are similar to the connections  140  described above. The power source  238  is similar to the power source  138  described above.  
         [0029]     A portion of ferromagnetic material  222  is located over the heater  224  between the electrodes  208  and  212 . Similarly, a portion of ferromagnetic material  232  is located over the heater  234  between the electrodes  206  and  208 . The portions of ferromagnetic material  222  and  232  are similar in characteristics to the ferromagnetic material  122  and  132  described above.  
         [0030]     The heat actuated microswitch  200  also comprises a support element  216  to which is mounted a cantilever  214 . The support element  216  can be formed over the surface of the electrode  208  as shown, or can be otherwise formed over the substrate  204 . For example, the electrode  208  need not extend under the support element  216 . In this embodiment, the cantilever  214  is pivotally coupled to the support element  216  so that the cantilever  214  may tilt with respect to the support element  216 , while the support element  216  and the length of the cantilever  214  defines the arc through which the cantilever  214  rotates. The cantilever  214  can be fabricated from, for example, silicon, or from a metal, such as copper, aluminum, gold, etc.  
         [0031]     A contact assembly  270  and a contact assembly  280  are located at the ends of the cantilever  214 . The contact assembly  270  comprises a contact  220  a permanent magnet  202 . The contact assembly  280  comprises a contact  230  and a permanent magnet  252 . The contacts  220  and  230  are similar to the contact  120  and  130  described above. The permanent magnets  202  and  252  have similar characteristics as the permanent magnet  102  described above.  
         [0032]     Power is provided to the heaters  224  and  234  by a power source  238  via connections  240 . Although the connections  240  are shown as extending through the substrate  204 , other connections between the power source  238  and the heaters  224  and  234  are possible. In one example, the power source  238  provides approximately 2 watts (W) to the heaters  224  and  234 . A power source providing 2 W can provide a switching time of less than 50 μs and a cycle time of approximately 0.1 millisecond (ms). However, as mentioned above, the switching and cycle times can be varied based on the drive power. The heat actuated microswitch  200  is covered by an enclosure  236  that forms a seal around the cantilever  214  and electrodes  206 ,  208  and  212 .  
         [0033]     The heat actuated microswitch  200  shown in  FIG. 2A  is shown as being latched in a first position, which is arbitrary. In the position shown in  FIG. 2A , under ambient temperature conditions, the permanent magnet  202  attracts the ferromagnetic material  222  so that the contact  220  is drawn to and comes into electrical contact with the electrode  208  and the electrode  212 . The permanent magnet  202  has sufficient magnetic attraction to the ferromagnetic material  222  to overcome the inertia of the cantilever  214  and the distance separating the permanent magnet  202  and the ferromagnetic material  222 . In this first position, the contact  220  causes an electrical connection to be established between the electrodes  208  and  212 .  
         [0034]      FIG. 2B  is a schematic diagram of the heat actuated microswitch of  FIG. 2A  after transitioning from a first position to a second position. By activating the power source  238  the temperature of the heater  224  and the ferromagnetic material  222  begins to increase. When the temperature of the ferromagnetic material  222  reaches its Curie temperature, it is no longer attracted to the permanent magnet  202 . When the ferromagnetic material  222  is no longer attracted by the permanent magnet  202 , the magnetic attraction between the ferromagnetic material  232  and the permanent magnet  252  overcomes the inertia of the cantilever  214  and the cantilever  214  begins to tilt. The ferromagnetic material  232  is attracted by the permanent magnet  252  as long as its temperature is lower than its Curie temperature. The magnetic attraction between the ferromagnetic material  232  and the permanent magnet  252  causes the cantilever  214  to tilt and bring the contact  230  into electrical contact with the electrodes  206  and  208 . In this manner, an input signal supplied to the electrode  208  can be switched between a first output (electrode  212 ) and a second output (electrode  206 ). Once the cantilever  214  begins moving the contact  230  toward the electrodes  206  and  208  as a result of the magnetic attraction between the ferromagnetic material  232  and the permanent magnet  252 , the power source  238  is switched off. When power is removed from the heater  224 , the ferromagnetic material  222  begins to cool and will fall below the Curie temperature. However, the magnetic attraction between the ferromagnetic material  232  and the permanent magnet  252  will keep the heat activated microswitch latched in the second position, shown in  FIG. 2B .  
         [0035]     By actuating the power source  238  to supply power to the heater  234 , the magnetic attraction between the ferromagnetic material  232  and the permanent magnet  252  can be reduced to cause the cantilever  214  to transition in the opposite direction.  
         [0036]      FIG. 3A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with another alternative embodiment of the invention. The heat actuated microswitch  300  comprises a substrate  304  that is similar to the substrate  104  of  FIG. 1A .  
         [0037]     Electrodes  308  and  312  are formed on the substrate  304 . Electrodes  354  and  358  are formed on a surface  362  of the enclosure  336 . The enclosure  336  is similar to the enclosure  136  described above. However, the surface  362  of the enclosure  336  is treated, or has otherwise applied to it, a material over which the electrodes  354  and  358  can be formed, deposited, or otherwise applied. As described above, the electrodes can be a metallic material, such as copper (Cu), gold (Au), aluminum (Al), etc., suitable for making electrical connection with electrical contacts to be described below.  
         [0038]     The electrode  308  and the electrode  354  can be referred to as input electrodes and the electrodes  312  and  358  can be referred to as output electrodes. In one example, the heat actuated microswitch  300  is used to switch a radio frequency (RF) input signal from the electrode  308  to the electrode  312  and from the electrode  354  to the electrode  358 . The electrode  308  includes a portion  344  that extends through the substrate  304  so that the electrode  308  can be externally electrically connected to an input signal. Similarly, the electrode  312  includes a portion  342  that extends through the substrate  304  so that the electrode  312  can be externally electrically connected to other signal conductors. The electrode  354  includes a portion  348  that extends through the enclosure  336  so that the electrode  354  can be externally electrically connected to an input signal. Similarly, the electrode  358  includes a portion  346  that extends through the enclosure  336  so that the electrode  358  can be externally electrically connected to other signal conductors. It should be mentioned that there are other ways of connecting to the electrodes  308 ,  312 ,  354  and  358 , and the manner shown here is merely one example.  
         [0039]     In this embodiment, a heater  324  is formed over the substrate  304  in the region between the electrodes  308  and  312 . A heater  334  is formed on the surface  362  in the region between the electrodes  354  and  358 . The heaters  324  and  334  are similar to the heaters  124  and  134  described above. The heaters  324  and  334  are coupled to a power source  338  via connections  340 . The connections  340  are similar to the connections  140  described above. The power source  338  is similar to the power source  138  described above.  
         [0040]     A portion of ferromagnetic material  322  is located over the heater  224  between the electrodes  308  and  312 ; Similarly a portion of ferromagnetic material  332  is located over the heater  334  between the electrodes  354  and  358 . The portions of ferromagnetic material  322  and  332  are similar in characteristics to the ferromagnetic material  122  and  132  described above.  
         [0041]     The heat actuated microswitch  300  also comprises a support element  356  to which is mounted a cantilever  314 . The support element  316  can be formed over the substrate  304  as shown, can be formed on the surface  364  of the enclosure  336 , or can be otherwise formed to support the cantilever  314 . In this embodiment, the cantilever  314  is rigidly coupled to the support element  356 , but is fabricated of a flexible material so that the cantilever  314  may deflect with respect to the support element  356 . The support element  356 , the length of the cantilever  314  and the material from which the cantilever  314  is fabricated defines the arc through which the cantilever  314  moves. The cantilever  314  can be fabricated from, for example, silicon, or from a metal, such as copper, aluminum, gold, etc.  
         [0042]     A contact assembly  370  and a contact assembly  380  are located on opposite sides of the cantilever  314  approximately as shown. The contact assembly  370  comprises a contact  320  a permanent magnet  302 . The contact assembly  380  comprises a contact  330  and a permanent magnet  352 . The contacts  320  and  330  are similar to the contact  120  and  130  described above. The permanent magnets  302  and  352  have similar characteristics as the permanent magnet  102  described above.  
         [0043]     Power is provided to the heaters  324  and  334  by a power source  338  via connections  340 . Although the connections  340  are shown as extending through the substrate  304  and the enclosure  336 , other connections between the power source  338  and the heaters  324  and  334  are possible. In one example, the power source  338  provides approximately 2 watts (W) to the heaters  324  and  334 . A power source providing 2 W can provide a switching time of less than 50 μs and a cycle time of approximately 0.1 millisecond (ms). However, as mentioned above, the switching and cycle times can be varied based on the drive power. The enclosure  336  forms a seal around the cantilever  314  and electrodes  308 ,  312 ,  354  and  358 .  
         [0044]     The heat actuated microswitch  300  shown in  FIG. 3A  is shown as being unlatched. However, under normal ambient temperature conditions, the heat actuated microswitch  300  would be latched in either the upper position, in which the permanent magnet  352  is attracted to the ferromagnetic material  332 , or in the lower position, in which the permanent magnet  302  is attracted to the ferromagnetic material  322 .  
         [0045]     For illustration, assume that the heat actuated microswitch is latched in the upper position, in which the attraction between the permanent magnet  352  and the ferromagnetic material  332  causes the contact  330  to come into electrical contact with the electrodes  354  and  358 . The permanent magnet  352  has sufficient magnetic attraction to the ferromagnetic material  332  to overcome the inertia of the cantilever  314  and the distance separating the permanent magnet  352  and the ferromagnetic material  332 . In this first position, the contact  330  causes an electrical connection to be established between the electrodes  354  and  358 .  
         [0046]      FIG. 3B  is a schematic diagram of the heat actuated microswitch of  FIG. 3A  after transitioning from a first position to a second position. By activating the power source  338  the temperature of the heater  334  and the ferromagnetic material  332  begins to increase. When the temperature of the ferromagnetic material  332  reaches its Curie temperature, it is no longer attracted to the permanent magnet  352 . When the ferromagnetic material  332  is no longer attracted by the permanent magnet  352 , the force of the cantilever  314  acts to separate the contact  330  from the electrodes  354  and  358 , and the magnetic attraction between the permanent magnet  302  and the ferromagnetic material  322  overcomes the inertia of the cantilever  314 . The ferromagnetic material  322  is attracted by the permanent magnet  302  as long as its temperature is lower than its Curie temperature. The magnetic attraction between the ferromagnetic material  322  and the permanent magnet  302  causes the cantilever  314  to deflect and bring the contact  320  into electrical contact with the electrodes  308  and  312 . In this manner, an input signal supplied to the electrode  354  is decoupled from the electrode  358  and an input signal supplied to the electrode  308  is coupled to the electrode  312 . Once the cantilever  314  begins moving the contact  320  toward the electrodes  308  and  312  as a result of the magnetic attraction between the ferromagnetic material  322  and the permanent magnet  302 , the power source  338  is switched off. When power is removed from the heater  334 , the ferromagnetic material  332  begins to cool and fall below the Curie temperature. However, the magnetic attraction between the ferromagnetic material  322  and the permanent magnet  302  will keep the heat activated microswitch  300  latched in the second position, shown in  FIG. 3B .  
         [0047]     By actuating the power source  338  to supply power to the heater  324 , the magnetic attraction between the ferromagnetic material  322  and the permanent magnet  302  can be reduced to cause the cantilever  314  to transition in the opposite direction.  
         [0048]      FIG. 4A  is a schematic diagram illustrating a heat actuated magnetic latching microswitch in accordance with another alternative embodiment of the invention. The heat actuated microswitch  400  is referred to as a so-called Reed switch. The heat actuated microswitch  400  comprises a substrate  404  that is similar to the substrate  104  of  FIG. 1A .  
         [0049]     A first electrode  408  is formed on an end of the cantilever  414 . The cantilever  414  is similar to the cantilever  314  described above. A second electrode  412  is formed on an end of a contact support  472 . The contact support  472  also locates the contact  420 , which is similar to the contact  120  described above. Electrodes  308  and  312  are formed on the substrate  304 .  
         [0050]     In this embodiment, a heater  424  is formed over the substrate  404  approximately as shown. A heater  434  is formed on the surface  462  of the enclosure  436 . The enclosure  436  is similar to the enclosure  136  described above. However, the surface  462  of the enclosure  436  is treated, or has otherwise applied to it, a material over which the heater  434  can be formed, deposited, or otherwise applied.  
         [0051]     The heaters  424  and  434  are similar to the heaters  124  and  134  described above. The heaters  424  and  434  are coupled to a power source  438  via connections  440 . The connections  440  are similar to the connections  140  described above. The power source  438  is similar to the power source  138  described above.  
         [0052]     A portion of ferromagnetic material  422  is located over the heater  424 . Similarly a portion of ferromagnetic material  432  is located over the heater  434 . The portions of ferromagnetic material  422  and  432  are similar in characteristics to the ferromagnetic material  122  and  132  described above.  
         [0053]     The cantilever  414  is coupled through and supported by the wall  466  of the enclosure  436 . In this embodiment, the cantilever  414  is rigidly coupled to the wall  466 , but is fabricated of a flexible material so that the cantilever  414  may deflect with respect to the wall  466 . The length of the cantilever  414  and the material from which the cantilever  414  is fabricated defines the arc through which the cantilever  414  moves. The cantilever  414  can be fabricated from silicon, or from a metal, such as copper, aluminum, gold, etc.  
         [0054]     A contact  430  is located on the cantilever  414  approximately as shown. A permanent magnet  402  is located on the opposite side of the cantilever  414  from the contact  430  and is located in the vicinity of the ferromagnetic material  422  and  432 , approximately as shown. The permanent magnet  402  has similar characteristics as the permanent magnet  102  described above.  
         [0055]     Power is provided to the heaters  424  and  434  by a power source  438  via connections  440 . Although the connections  440  are shown as extending through the substrate  404  and the enclosure  436 , other connections between the power source  438  and the heaters  424  and  434  are possible. In one example, the power source  438  provides approximately 2 watts (W) to the heaters  424  and  434 . A power source providing 2 W can provide a switching time of less than 50 μs and a cycle time of approximately 0.1 millisecond (ms). However, as mentioned above, the switching and cycle times can be varied based on the drive power. The enclosure  436  forms a seal around the cantilever  414  and the contacts  420  and  430 .  
         [0056]     The heat actuated microswitch  400  shown in  FIG. 4A  is shown as being open. However, under normal ambient temperature conditions, the heat actuated microswitch  400  would be latched in either the upper position, in which the permanent magnet  402  is attracted to the ferromagnetic material  432 , or in the lower position, in which the permanent magnet  402  is attracted to the ferromagnetic material  422 .  
         [0057]     For illustration, assume that the heat actuated microswitch is latched in the upper position, in which the attraction between the permanent magnet  402  and the ferromagnetic material  432  causes the contact  430  to be separated from the contact  420 . The permanent magnet  402  has sufficient magnetic attraction to the ferromagnetic material  432  to overcome the inertia of the cantilever  414  and the distance separating the permanent magnet  402  and the ferromagnetic material  432 . In this first position, the separation of the contacts  420  and  430  causes an open electrical connection between the electrodes  408  and  412 .  
         [0058]      FIG. 4B  is a schematic diagram of the heat actuated microswitch of  FIG. 4A  after transitioning from a first position to a second position. By activating the power source  438  the temperature of the heater  434  and the ferromagnetic material  432  begins to increase. When the temperature of the ferromagnetic material  432  reaches its Curie temperature, it is no longer attracted to the permanent magnet  402 . When the ferromagnetic material  432  is no longer attracted by the permanent magnet  402 , the force of the cantilever  414  acts to move the contact  430  toward the contact  420 . Simultaneously, the magnetic attraction between the permanent magnet  402  and the ferromagnetic material  422  overcomes the inertia of the cantilever  414 . The ferromagnetic material  422  is attracted by the permanent magnet  402  as long as its temperature is lower than its Curie temperature. The magnetic attraction between the ferromagnetic material  422  and the permanent magnet  402  causes the cantilever  414  to deflect and bring the contact  430  into electrical contact with the contact  420 . In this manner, an input signal supplied to the electrode  408  is coupled to the electrode  412 . Once the cantilever  414  begins moving the contact  430  toward the contact  420  as a result of the magnetic attraction between the ferromagnetic material  422  and the permanent magnet  402 , the power source  438  is switched off. When power is removed from the heater  434 , the ferromagnetic material  432  begins to cool and fall below the Curie temperature. However, the magnetic attraction between the ferromagnetic material  422  and the permanent magnet  402  will keep the heat activated microswitch  400  latched in the second position, shown in  FIG. 4B .  
         [0059]     By actuating the power source  438  to supply power to the heater  424 , the magnetic attraction between the ferromagnetic material  422  and the permanent magnet  402  can be reduced to cause the cantilever  414  to transition in the opposite direction and separate the contacts  420  and  430 , thus opening the heat activated microswitch  400 .  
         [0060]      FIG. 5  is a flowchart  500  describing an exemplary method of operating a heat activated microswitch in accordance with an embodiment of the invention. In block  502 , it is assumed that a heat actuated microswitch is latched in a first position. A heater in the vicinity of ferromagnetic material is activated to heat the ferromagnetic material to its Curie temperature. In block  504 , the ferromagnetic material loses its magnetic attraction after reaching its Curie temperature.  
         [0061]     In block  506 , the switch actuates to cause electrical contact to be switched. In block  508 , the heat activated microswitch latches in a second position.  
         [0062]     This disclosure describes the invention in detail using illustrative embodiments. However, it is to be understood that the invention defined by the appended claims is not limited to the precise embodiments described.