KR20020018655A - Bistable micro-switch and method of manufacturing the same - Google Patents

Abstract

The present invention provides a bistable switch using a shape memory alloy, and a manufacturing method thereof. Specifically, the bi-stable switch includes a substrate having at least one power source, a flexible sheet having a first distal end attached to the substrate, a bridge contact formed at an opposite second distal end of the flexible sheet, One or more thermally active elements connected between the second distal end and the power source to the first surface of the flexible sheet. In operation, current from a power source passing through the thermally active element indirectly curves the flexible sheet, shorting the signal contacts on the substrate with a constant force.

Description

Bistable microswitch and its manufacturing method {BISTABLE MICRO-SWITCH AND METHOD OF MANUFACTURING THE SAME}

The first electro-mechanical and solid state micro switches were developed in the late 1940s. Since then, the electronics industry has spurred manufacturing and functional limitations to produce such switches. In particular, current electro-mechanical microswitches are technically inadequate for high frequency applications in size, price, function, durability and connection methods. In addition, the solid state switch is characterized by a high impedance ratio of the off state to the on state, and in various applications, the "contact" resistance value of the on state is not preferable because of the combined capacitance of the off state. Thus, the electronics industry is currently investigating new and innovative ways to fabricate smaller, better reliability and durability, functional and cost effective switches.

In various circuit applications, both now and in the future, there is a need for low cost miniature switching devices that can be mounted on conventional hybrid circuit boards and have bistable performance. In addition, the manufacturing method for such a device must be compatible with solid state methods such as thin film deposition and patterning methods used to form conductive wiring, connection pads and passive circuit elements mounted in such circuits.

Shape memory alloys ("SMA") are materials that are known to be plastically deformed from a "deformation" shape to a "memory" shape when heated. Thereafter, when the SMA material is cooled, the material can be fully restored to the deformed shape after partially recovering the deformed shape. That is, the SMA material is reversibly transformed from an austenitic state to a martensite state upon temperature change.

Research and development companies have only briefly discussed how the surfaces of these adjustable shape-deforming materials can be used in switching structures. For example, conventional electromechanical switches used SMA wires as rotary actuators and SMA seats as valves. The wire was twisted or twisted about its longitudinal axis and restrained from moving the end of the wire. The seat actuator is mechanically connected to one or more movable elements such that deformation of the actuator caused by temperature forces the mechanical element or moves the mechanical element.

The problems with the construction and manufacturing method of these and similar SMA switches are similar to those described above for conventional electromechanical switches. In particular, constraints in size, reliability, durability, functionality and price have limited the utility of prior art switches.

As a result, conventional switches and relays with or without shape memory alloys are often large and bulky, making them too difficult to use for industrial or mass production. Therefore, there is a need to develop a switch or relay that takes advantage of the features of the shape memory alloy and can eliminate the aforementioned problems of current switching methods with or without the shape memory alloy.

The present invention is directed to being able to overcome or at least reduce the effects of one or more of the aforementioned problems.

BACKGROUND OF THE INVENTION The present invention generally relates to microswitches, and more particularly to micromachined bistable switches using shape memory alloys.

1 is a perspective view of a bistable switch according to an embodiment of the present invention.

2 is a schematic diagram showing a general appearance of the bistable switch of the present invention of FIG.

3A and 3B to 5A and 5B illustrate a method of manufacturing the bistable switch of FIG.

6A and 6B show steps of another method of making the bistable switch of FIG. 1 including a crimped arm portion.

7A and 7B show the bistable switch of FIG. 6A mounted and actuated to illustrate the first and second positions of the switch.

8 illustrates another embodiment of the bistable switch of FIG. 1 including multiple bridge contacts.

9A and 9B illustrate another embodiment of the bistable switch of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are described in more detail herein. However, the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is contemplated by all modifications falling within the scope and spirit of the invention as defined by the appended claims. It should be understood that the equivalents and alternative embodiments thereof are included.

In one embodiment, the present invention provides a bistable switch. The switch includes a substrate having at least one power source, a flexible sheet having a first distal end attached to the substrate, a bridge contact formed on an opposite second distal end of the flexible sheet, and the second distal end. And one or more thermally active elements connected to a first surface of the flexible sheet between a power source and a power source, wherein current from the power source passing through the thermally active element indirectly curves the flexible sheet to cause signal contacts on the substrate. Short-circuit with constant force.

Another embodiment of the present invention provides a method of manufacturing a bistable switch for a substrate having a signal line contact and a power supply. In particular, the method includes providing a flexible sheet, connecting one or more thermally active elements between a first distal end of the flexible sheet and a power source, and a conductive bridge in the first distal end of the flexible sheet. Forming a contact; and mounting an opposite second distal end of the flexible sheet to the substrate, wherein a current from a power source passing through the thermally active element indirectly curves the flexible sheet on the substrate. Short the signal contacts.

The configuration of the present invention provides a relatively simple and inexpensive bistable switch fabrication method that performs a level not achievable with current solid state methods using standard semiconductor base units, i.e., transistors. The micromachining method of manufacturing this new and innovative microswitch enables users to create systems that can tolerate very high voltage, current and frequency signals. This is possible because the microswitch is conceptually equivalent to a micro relay. In practice, this micro switch is a mechanical microstructure that moves to connect or short-circuit conductive contacts. In addition, this configuration and method is suitable for standard silicon processing processes and enables mass production of the device at an affordable price.

Other aspects and advantages of the present invention will become apparent upon reading the following detailed description with reference to the drawings.

The present invention adopts a unique characteristic shape memory alloy ("SMA") which has recently advanced to produce an efficient, effective and highly reliable microswitch. Using SMA in a microswitch can increase the performance of a switch or relay by a factor of several. In particular, this is achieved because both the stress and strain of the shape memory effect can be very large to provide a substantial work output per unit volume. Thus, micromechanical switches using SMA as the actuation mechanism can exert stresses of hundreds of megapascals, allow strains greater than 3 percent, operate at typical TTL voltages well below the blackout or PZO requirements, and provide on-chip electrical It is directly excited by the lead and remains fatigue-free even in millions of cycles.

A shape memory alloy is the first random time to heat the alloy to T _A mechanical deformation and no matter T _A or more to a temperature initiating the phase change associated with the temperature at which the temperature T _A to T _H exerted on the alloy at a temperature not higher than the It can be characterized by the ability of the alloy to recover shape. In operation, when the SMA material is at a temperature T _L below the temperature T _A , the SMA has a specific crystal structure that allows the material to be soft and relatively easily deformed into any shape. When heating the SMA to a temperature T _H above the temperature T _A , the crystal structure changes to recover the SMA back to its original undeformed shape, ie to regain the original given shape, thereby showing the onset of the recovery stress. Therefore, the transition temperature range of the shape memory alloy in which the phase transformation occurs is defined to be between T _H and T _A. SMA is optimally deformed from 2 to 8% at temperatures below T _A where the deformation can be fully recovered when heating the SMA to a temperature between T _A and T _H. As an example of modification, 4% is preferred.

These memory materials were produced mainly in bulk in the form of wires, rods and plates. The best conventional shape memory alloy readily available is Nitinol, an alloy of nickel and titanium. However, other SMAs include copper-zinc-aluminum or copper-aluminum-nickel. Even at small temperature changes, such as 18 ° C, nitinol can transform its phase and exert a very large force when applied to resistance to shape change. As mentioned above, conventional switches and relays using shape memory alloys generally operate according to the principle that the shape memory alloy deforms when it is below the phase transformation temperature range. Heating the deformed alloy above the transformation temperature range restores some or all of the deformation and moves the mechanical elements that require movement of this alloy.

Referring now to the drawings, FIG. 1 shows a thermally actuated bistable micromechanical switch 10 according to the present invention. The actuating arm 12 of the switch 10 is micromachined and fixed to the upper substrate surface 14. The substrate 14 includes an insulating silicon or gallium arsenide substrate, a printed circuit board, a flat plate of ceramic material such as high density alumina (Al ₂ O ₃ ) or belia (BeO), or a glassy material such as fused silica. However, those skilled in the art should recognize that the switch of the present invention is not limited to this, but can be installed in almost any stable structure to provide a preferred cantilevered bistable switch.

Top surface 14 provides control contacts 16a and 16b and ground contact 18 to firmly interconnect each control and ground contact of arm 12. The upper substrate surface 14 also provides signal contacts 20a and 20b that can be connected or shorted by the conductive bridge contacts 22 of the arm 12. Signal contacts 20a and 20b may transmit or sustain any electrical signal, including, for example, conventional analog data or digital data, or voice signals.

The upper and lower conductive wiring elements 24a and 24b are connected to the arm 12 by a conventional method, and between the contact vias of the center compensation of the upper and lower portions of the arm 12 and the ground vias SMA elements 26a and 26b are provided. In one embodiment, the SMA elements 26a and 26b are made of a wire of titanium nickel alloy having a diameter of about 25 to 125 microns.

In operation, the switch of the present invention provides a basic circuit structure as shown in FIG. In particular, when the relay 30a is closed and the relay 30b is open, the current passing through the horseshoe-shaped upper conductive wiring of the elements 16a, 24a, 26a and 18 moves the arm 12 upward. Conversely, when the relay 30a is opened and the relay 30b is closed, the current passing through the horseshoe-shaped lower conductive wiring of the elements 16b, 24b, 26b and 18 moves the arm 12 downward. The force present during the thermal cooling step is much less than the force present while the SMA element is heating up. That is, the conductive means, which will be described in detail below, transfers the necessary power from one regulating contact 16a or 16b to the grounding element 18 via the conductive wiring element 24a or 24b and the SMA element 26a or 26b, respectively. do. In the following embodiments, it is desirable that the diameters of the SMA elements 26a and 26b be about 25 to 125 microns to supply 40 to 160 milliamps during operation.

Referring now to FIGS. 3A and 3B, a manufacturing method for manufacturing a bistable switch in accordance with the present invention is disclosed. In particular, FIGS. 3A, 4A, 5A and 6A show the bottom surface of the switch 10 and FIGS. 3B, 4B, 5B and 6B show side views of the same figure, respectively.

3A and 3B illustrate stabilizing material 50 applied to patterned photoresist layer 52. In this particular embodiment, the stabilizing material 50 is a beryllium copper alloy made from a rolled sheet that is about 12 to 50 microns thick and about 300 to 1,200 microns wide. However, other materials may be used that provide the desired elastic or flexible properties and thicknesses. For example, a material selected from the group comprising various alloy materials such as polyresin, plastic, wood composite material, silicone, silicone resin and stainless steel alloy can be used.

In a preferred micromachining method, conventional photolithography techniques are used to form a desired pattern (patterned by dashed lines) on the surface of the stabilizing material 50. In particular, the patterned photoresist 52 has a distal end 54 and a head 56, contact vias 58a, 58c and two gaps 60a, to form beams 62a, 62b and 62c. It consists of three beam structures with 60b). The stabilizing material 50, which is not protected by the pattern photoresist 52, is removed by a conventional etching method to form three desired beam structures 12 as shown in FIG. 4A.

Those skilled in the art will appreciate that the desired pattern can also be formed by other conventional methods. For example, if the desired switch size is large enough to avoid the use of micromachining methods, the stabilizing material 50 may be patterned by conventional punching or molding methods.

Next, as shown in FIGS. 4A and 4B, the top and bottom surfaces of the structure 12 are covered with a non-conductive insulating layer 64. This electrical insulator is preferably a paralene layer. In an alternate embodiment, insulating material 64 may be selected from the group comprising silicon dioxide layers, polyimide layers, wet oxide layers, silicon nitride layers. These alternatives provide similar structures with similar operating characteristics. Those skilled in the art will appreciate that the insulating layer 64 may be omitted if the stabilizing material 50 is a non-conductive material.

A conductive material such as gold may be deposited and patterned on each side of the coated structure 12 to form a portion of a desired horseshoe-shaped wiring. Specifically, the coated structure 12 (see FIG. 1) provides an L-shaped conductive wiring 24a connected between the regulating via 58a and the upper contact pad. In addition, the same conductive material forms the ground via 58c. As shown in FIG. 4A, on the opposite or lower side of the structure 12, the coated structure 12 is another L-shaped conductive wire 24b connected between the regulating contact 68b and the lower contact pad 58b. To provide. In addition, the same material forms regulating contact 68a, ground contact 70 and bridge contact 22. Those skilled in the art will appreciate conductive wiring 24a, 24b, regulating contacts 68a, 68b, ground contact 70, ground via and regulating vias 58a, 58c, upper and lower contact pads 58b and bridge contacts ( It will be appreciated that the conductive material for 22) may be selected from the group consisting of gold, copper, palladium-gold alloys, nickel, silver, aluminum and various other conductive materials available in the art.

5A and 5B, actuator elements 26a and 26b are firmly connected to the top and bottom surfaces of arm 12 between each contact pad and ground via 58c. If desired, adhesive materials may be used to couple actuator elements 26a and 26b to each of the top and bottom surfaces. The adhesive material may be selected from the group comprising mechanical attachments such as cement, epoxy, lock on chip taps, solder, embedding, polyimide and clips or clamps. This connection places each actuator element 26a, 26b on the center of the upper and lower surfaces of the intermediate beam 62b to complete the horseshoe-shaped conductive wiring. The actuator elements 26a, 26b are preferably nickel-titanium SMAs provided in the form of sheets, ribbons or wires. In this embodiment, the diameters of the SMA elements 26a and 26b are preferably about 25 to 125 microns.

As described above, the SMA elements 26a and 26b expand or contract after the current through the material reaches a preset phase transformation temperature. In this particular embodiment, the phase transformation process occurs by one of the following two methods. The first phase transformation reduces the bulk of the actuator material and consequently reduces the length of the shape memory alloy to shrink the stabilizing material 12. In the second phase transformation method, the SMA is stretched at a rate of 8% or less before and / or after mounting the SMA to the stabilizing structure 12. Upon phase transformation, the length of the SMA decreases and shrinks the layer of stabilizing material 12 by 8% after returning to the original length. Depending on the arrangement of the head portion 12a, the contact force, the number of cycles and the requirements for the manufacturing method, the shape memory alloy may or may not be stretched.

The final step of the desired method involves crimping and mounting the structure. The structure can be mounted on a desired substrate without crimping to form a bistable switch that has a cantilevered structure as shown in FIG. 1 and that is reliably micromachined. Also, unless power is excited to generate the necessary currents and transformations in the desired SMA element, the switch cannot continuously short the signal contacts. Thus, this final stamping or crimping step allows the active element to maintain the contact position even after power is cut off. Thus, such stamping or crimping gives the arm a snap actuation function that keeps the arm in position except when one of the SMA elements moves the arm to the opposite position.

6A and 6B, the desired stamped or crimped elements 80 and 80b are shown. Such snap actuation structures may be formed using conventional punching and dyeing methods. Specifically, the center portion of the left and right beams 62a and 62c can be crimped to form a waveform deformation or horseshoe shape. Those skilled in the art will appreciate that these crimped areas 80a, 80b produce a constant force when the actuator element 26a or 26b is deformed to move the arm tip 12a up or down. In addition, the crimped areas 80a and 80b maintain the bridge contact 22 in contact with the signal contacts 20a and 20b or separate from the signal contacts 20a and 20b even after the power supply connected to the switch 10 is cut off. To keep it going. In other words, by forming the crimps 80a and 80b, once the arm 12 is positioned upward or downward, current must pass through the appropriate SMA element in order to bend the arm 12 into another position, either downward or upward, respectively. . In addition, the switch 10 will always be positioned up or down unless the user physically moves the switch.

As shown in FIGS. 7A and 7B or 1, with or without crimp elements formed on the first and third beams 62a, 62c, the resulting structure must be secured to the substrate 14. In particular, the cantilever switch 10 is coupled to the substrate surface 14 by conventional attachment methods. In particular, solder or pressure slots on the printed circuit board are used to attach and secure the power and ground contacts 16a, 16b and 18 to the substrate surface 14 of the switch 10. Thus, when the actuator element 26b is heated by the horseshoe-shaped lower conductive wiring, the resulting structure is bent downward to couple the bridge contact 22 with the signal contacts 20a and 20b. In addition, when the actuator material 26a is heated by the horseshoe-shaped upper conductive wiring, the connection between the bridge contact 22 and the signal contacts 20a and 20b is short-circuited.

Another embodiment of the present invention includes an additional bridge contact 22 'disposed on the top surface of tip 12a for shorting complementary signal contacts 20a', 20b 'on a multilayer substrate. In this embodiment as shown in FIG. 8, when the upper SMA element 26a is heated by a current passing through the upper conductive wiring in the form of a horseshoe, the structure moves upwards to raise the upper bridge contact 22 '. It is connected to the signal contacts 20a 'and 20b'. On the other hand, when the actuator element 26b is heated by a current passing through the lower conductive wirings 24b and 26b in the horseshoe shape, the structure moves downward to connect the bridge contacts 22 to the signal contacts 20a and 20b. . In this particular embodiment, arm 12 is not crimped. Accordingly, bridge contact 22 or 22 'continues signal contact 20a, 20b or 20a', 20b 'only while each SMA element 26a or 26b is heated to move tip 12a up or down. You can short circuit. However, those skilled in the art will appreciate that crimping may be used to keep the arm 12 in contact with one or the other of the contacts 20a and 20b or 20a 'and 20b'.

9A and 9B show another embodiment of the switch of the present invention. In this embodiment, the sheet 50 is patterned and then etched or punched to form the desired arm 12 as described above with reference to FIG. 3B and the bridge contact 22 arm (as described above). It is formed on the tip portion 12a. Next, the center portion of the actuator element is annular over the arm 12 at a position adjacent the tip portion 12a or attached to the arm 12 to be electrically separated from the bridge contact 22. Finally, the distal end 54 of the arm 12 is attached to the substrate surface 14 and the ends 62a and 62b of the actuator element 60 and extends in a horizontally opposite direction close to the length of the arm 12 so as to extend the substrate surface. It is connected to the power supply 64 adjacent to (14). That is, the L-shaped conductive wires and contacts previously disposed on the arm 12 are moved to the off position of the switch arm 12 to provide the current required to excite the SMA element (see FIG. 1) to provide power ( 64).

Referring to FIG. 9B, during operation, the current supplied to the SMA 60 by the power source 62 causes the SMA 60 to contract and move the arm 12 downward so that the signal contacts 20a and 20b are bridge contacts. Short with (22). As described above, if the power source 62 is not excited, the SMA 60 is restored to a position for separating the bridge contact 22 from the signal contacts 20a and 20b. One skilled in the art may attach another SMA (not shown) to the arm 23 on the opposite side to the SMA 60 and supply current by a similar power source in a similar manner. In addition, the arm 12 can be crimped to form a means to function as described above with reference to FIGS. 7A and 7B, and the arm 12 can be patterned with or without multiple parallel beams. In this particular embodiment, a single press or complete surface crimping may be used if no beam is present on the arm 12 and additional SMA elements are attached or wound on the other side of the arm 12.

In connection with the above embodiments, one skilled in the art will recognize that the arm 12 can be patterned to form a structure having as many beams as necessary to hold any desired SMA element (s). In addition, the arm 12 can be patterned to form only a rectangular structure having no beams. Similarly, the thickness and number of SMA elements 26a and 26b can be increased or decreased to accommodate the desired arm structure and the force required to move the arm structure when heated. The number of crimps formed on the flexible arm 12 also depends on the shape of the resulting switch and the nature of the function.

In summary, the present invention provides a relatively simple low cost method of producing micro switches and relays. The micromachining method of manufacturing these new and innovative micro switches and relays allows users to create systems that can handle very high voltage, current and frequency signals. In addition, the method of the present invention can be conceptually designed to be suitable for standard silicon processing processes and to enable mass production of devices at very reasonable prices. Thus, the structure of the present invention provides a compact bistable snap action electromechanical switch that has the unique ability to increase operating speed and can be excited by a shape memory alloy superior to prior art switching mechanisms. In addition, due to advances in micromachining, these structures can be produced to have a length similar to about 500 to 3,000 microns, a width of about 200 to 1,200 microns and a thickness of about 25 to 35 microns, which structures are currently on the market. Smaller than any competing bistable switch. Those skilled in the art will appreciate that these dimensions may be varied to obtain the desired size and functionality for the switches of the present invention.

Other variations of construction that fall within the inventive concept claimed herein will be apparent to those skilled in the art. For example, the embodiments described herein use SMA elements 26a and 26b as part of the conductive wiring that heats the SMA elements to achieve the same results. For example, the SMA element may be coupled to a separate electrically conductive element, or may be coupled to a completely different type of heating element (eg, non-electric heating element).

Embodiments of the present invention have been described above. In the interest of clarity, not all features of an actual implementation are described in this specification. Of course, it will be appreciated that in the development of any practical embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as suitability for constraints related to systems and projects that vary with each implementation. Moreover, although such development efforts may be complex and time consuming, it will be appreciated that this disclosure is routine to the skilled person.

Claims (32)

Preparing a flexible sheet, Patterning the sheet to form a beam structure having a leading end region, a distal end region, a front surface and a back surface; Forming a first control contact adjacent the distal region of the flexible sheet; A connecting step of connecting an actuator element to the front of the beam; Forming a conductive wiring between the regulating contact and the first end of the actuator element adjacent the tip region of the flexible sheet; Forming a second regulating contact at a second end of an actuator element adjacent the distal region of the flexible sheet, Forming a bridge contact at the distal end of the leading end region of the flexible sheet, A mounting step of attaching a portion of the distal end of the flexible sheet to a substrate to connect the first and second regulating contacts to a power source of the substrate; And the bridge contact is disposed with a space adjacent to at least one signal contact. The method of claim 1, further comprising crimping the beam structure such that the bridge contact can be statically deflected to maintain the position of the bridge contact relative to the one or more signal contacts. . The method of claim 1, wherein the connecting step further comprises adhering a first end and a second end of the actuator element between the first control contact and the second control contact. The method of claim 1, further comprising applying an insulating layer on the flexible sheet after the patterning step. The method of claim 4, wherein the insulating layer is selected from the group consisting of polyimide, silicon dioxide, silicon nitride, wet oxide, and paralene. The method of claim 1, wherein the flexible sheet is selected from the group comprising polyresin, plastic, wood composites, silicone, silicone resin, stainless steel, and beryllium copper. The method of claim 1, wherein the patterning step, Adding a photolithographic mask to the sheet; Etching the masked sheet to form the multi-parallel beam structure Method for producing a bistable switch that further comprises. 8. The method of claim 7, wherein the etching processing step further comprises etching the flexible sheet to form a via in a center portion of the control contact and the ground contact. The method of claim 1, wherein the patterning step further comprises punching or molding the flexible sheet to form the multi-parallel beam structure. The method of claim 1, wherein said connecting step further comprises depositing an adhesive material between said actuator element and a sheet. The method of claim 10, wherein the adhesive material is selected from the group comprising polyimide, tabs fastened on the chip, cement, solder, epoxy, and mechanical attachment. The method of claim 1, wherein the actuator material is a shape memory alloy. The method of claim 12, wherein the shape memory alloy is selected from the group comprising nickel-titanium, copper-zinc-aluminum, and copper-aluminum-nickel. The method of claim 1, wherein the conductive wiring, the bridge contact, and the control contact are formed of a material selected from the group consisting of gold, copper, palladium-gold alloy, nickel, silver, and aluminum. 13. The method of claim 12, wherein the shape memory alloy is a wire having a diameter between about 25 and 125 microns. The method of claim 1, wherein the mounting step forms a cantilever bistable switch structure. The method of claim 1, further comprising: forming additional control contacts on the back side of the beam structure; Coupling a second actuator element to the back of the beam; Forming a conductive line between the additional control contact on the back of the complement and the second actuator element Method for producing a bistable switch that further comprises. 18. The method of claim 17, further comprising forming one or more vias that electrically connect corresponding control contacts on opposite sides of the patterned flexible sheet. The substrate of claim 1, wherein the substrate is made of an insulating silicon or gallium arsenide substrate, a printed circuit board, a plate of a ceramic material such as high density alumina (Al ₂ O ₃ ), beryl, or glass material such as fused silica. A method for producing a bistable switch comprising a structure selected from the group comprising. A method of manufacturing a bistable switch for a substrate having a single contact and a power source, Preparing a flexible sheet, Connecting one or more thermally active elements between the first distal end of the flexible sheet and a power source; Forming a conductive bridge contact on the first distal end of the flexible sheet; Mounting opposite second distal portions of the flexible sheet to a substrate Wherein the current from the power source passing through the thermally active element indirectly curves the flexible sheet to short-circuit the signal contacts on the substrate. 21. The bistable switch of claim 20, wherein providing the flexible sheet further comprises forming three or more parallel beams in the flexible sheet surrounded by the bridge contact and the second distal end. Method of preparation. 22. The method of claim 21, further comprising the step of crimping said flexible sheet to form first and second gaps between said bridge contacts and a power source. 22. The method of claim 21, further comprising forming contact pads on the flexible sheet laterally spaced adjacent said bridge contacts for connecting said one or more thermally active elements. . A substrate having at least one power source, A flexible sheet having a first distal end attached to the substrate; A bridge contact formed on the second distal end portion of the flexible sheet, One or more thermally active elements connected between the second distal end and the power source to the first surface of the flexible sheet And a current from a power source passing through the thermally active element indirectly curves the flexible sheet to short-circuit the signal contacts on the substrate with a constant force. 25. The bistable switch of claim 24, wherein said power source supplies a current of about 40 to 160 milliamps. 25. The bistable switch of claim 24, further comprising a crimp disposed in the central region of said flexible sheet. 27. The bistable switch of claim 26 wherein said crimp enables said sustained force to be maintained even after alternating current from said power source is interrupted. The bistable switch of claim 24, wherein the thickness of the flexible sheet is about 12 to 50 microns. 25. The device of claim 24, further comprising a second thermally active element connected between the second distal end and the second power source to an opposite second surface of the flexible sheet, And a current from a power source passing through the thermally active element indirectly curves the flexible sheet to short-circuit the signal contacts on the substrate with a constant force. 25. The bistable switch of claim 24, further comprising a crimp disposed in the central region of said flexible sheet. 31. The bistable switch of claim 30 wherein said crimp enables said sustained force to be maintained even after alternating current from said power source is lost, i.e., until said second thermally active element is excited. Preparing a flexible sheet, Forming one or more regulating contacts adjacent the first distal portion of the sheet; Forming bridge contacts adjacent opposite second distal portions of the sheet; Forming fixed contacts spaced laterally adjacent to the second distal end portion; Coupling an actuator material between said at least one regulating contact and said fixed element; Mounting the first distal end on a substrate having a power supply and a signal contact; And a bridge contact spaced laterally adjacent said signal contact.