Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H61/00—Electrothermal relays
  • H01H61/01—Details
  • H01H61/0107—Details making use of shape memory materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
  • H01H2001/0042—Bistable switches, i.e. having two stable positions requiring only actuating energy for switching between them, e.g. with snap membrane or by permanent magnet
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H61/00—Electrothermal relays
  • H01H2061/006—Micromechanical thermal relay

Definitions

• This invention relates in general to micro-switches and, more particularly, to a micro-machined bistable switch using a shape memory alloy.
• a shape memory alloy (“SMA”) is a known material capable of undergoing plastic deformation from a "deformed” shape to a “memory” shape when heated. If the SMA material is then allowed to cool, it will return partially to its deformed shape and can be fully returned to the deformed shape. In other words, the SMA material undergoes a reversible transformation from an austenitic state to a martensitic state with a change in temperature.
• controllable shape deformation material can be used in switching structures.
• conventional electro-mechanical switches have used SMA wires as a rotary actuator and bent SMA sheets as a valve.
• the wire is twisted or torsioned about its longitudinal axis and the ends of the wire are then constrained against movement.
• the sheet actuators are mechanically coupled to one or more movable elements such that the temperature-induced deformation of the actuators exerts a force or generates a motion of the mechanical elements.
• the present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
• the present invention provides a bistable switch.
• the switch includes the following 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 at a second and opposite distal end of the flexible sheet; and at least one heat activated element connected to a first surface of the flexible sheet and between the second distal end and the power source, wherein current from the power source passing through the heat activated element indirectly bends the flexible sheet and shorts the signal contacts on the substrate with a sustainable force.
• Another embodiment of the present invention provides a process for manufacturing a bistable switch for a substrate having signal line contacts and a power source.
• the process comprises providing a flexible sheet; connecting at least one heat activated element between a first distal end of the flexible sheet and the power source; forming a conductive bridge contact at the first distal end of the flexible sheet; and mounting a second and opposite distal end of the flexible sheet to the substrate, wherein current from the power source passing through the heat activated element indirectly bends the flexible sheet and shorts the signal contacts on the substrate.
• the inventive structure provides a relatively simple and inexpensive way to produce bistable switches with performance levels not attainable with current solid state approaches using the standard semiconductor base unit, the transistor.
• This new and innovative micro-machine way of fabricating micro-switches will enable the users to build systems that can carry very high voltage, current, and frequency signals. This becomes possible since the micro-switch is conceptually equivalent to a micro-relay. In fact, this micro-switch is a mechanical micro-structure that moves to connect or disconnect conductive contacts. In addition, this design and method is compatible with standard silicon processing, allowing mass production at a reasonable cost.
• Figure 1 illustrates a perspective view of a bistable switch in accordance with one embodiment of the present invention
• Figure 2 illustrates a general schematic layout of the inventive bistable switch of Figure 1
• Figures 3A and 3B - 5A and 5B illustrate a process for manufacturing the bistable switch of Figure 1;
• Figures 6A and 6B illustrate an alternative process step for manufacturing the bistable switch of Figure 1 to include a crimped arm portion
• Figures 7A and 7B shows the bistable switch of Figure 6A mounted and activated to illustrate a first and a second switch position
• Figure 8 illustrates an alternative embodiment of the bistable switch of Figure 1 to include multiple bridge contacts
• FIGS 9A and 9B illustrate still another embodiment of the inventive bistable switch. While the invention is amenable to various modifications in alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
• the present invention employs the unique properties of a shape memory alloy ("SMA") with recent advances in micro-machining to develop an efficient, effective and highly reliable micro-switch.
• SMA shape memory alloy
• the use of an SMA in micro-switches increases the performance of switches or relays by several orders of magnitude. In particular, this is accomplished because both stress and strain of the shape memory effect can be very large, providing substantial work output per unit volume. Therefore, micro- mechanical switches using SMA as the actuation mechanism can exert stresses of hundreds of megapascals; tolerate strains of more than three percent; work at common TTL voltages that are much lower than electrostatic or PZO requirements; be directly powered with electrical leads on a chip; and survive millions of cycles without fatigue.
• Shape memory alloys undergo a temperature related phase change beginning at temperatures above T A , which can be characterized by the ability of the alloy to recover any initial shape upon heating of the alloy above a temperature T A and below T H , regardless of mechanical deformation imposed on the alloy at temperature below T A .
• T A temperature
• the SMA material is at a temperature T L , below temperature T A
• the SMA possesses a particular crystal structure whereby the material is ductile and may be deformed into an arbitrary shape with relative ease.
• the crystal structure changes in order to restore the SMA back to an initial, undeformed shape, to resume the originally imparted shape, thereby representing the onset of a restoring stress.
• the transition temperature range of a shape memory alloy, over which the phase transformation occurs is defined as being between T H and T A .
• the SMA is optimally deformed between 2 and 8% at temperatures below T A which deformation can be fully recovered upon heating of the SMA to between T A and T H .
• One preferred deformation is 4%.
• Nitinol an alloy of nickel and titanium.
• SMAs include copper-zinc-aluminum, or copper-aluminum-nickel. With a temperature change of as little as 18°C, Nitinol can go through its phase transformation and exert a very large force when exerted against a resistance to changing its shape.
• conventional switches and relays that use shape memory alloys generally operate on the principle of deforming the shape memory alloy while it is below phase transformation temperature range. Heating the deformed alloy above its transformation temperature range recovers all or part of the deformation, and the motion of the alloy moves the necessary mechanical elements.
• FIG. 1 illustrates a thermally-actuated bistable micro-mechanical switch 10 in accordance with one embodiment of the present invention.
• Actuating arm 12 of switch 10 is micro-machined and secured to an upper substrate surface 14.
• Substrate 14 could include an insulated silicon or gallium- arsonide substrate, a printed circuit board, a flat plate of a ceramic material such as high density alumina (Al 2 O 3 ) or beryllia (BeO), or a glassy material such as fused silica.
• a ceramic material such as high density alumina (Al 2 O 3 ) or beryllia (BeO)
• BeO beryllia
• fused silica fused silica
• Upper surface 14 provides control contacts 16a, 16b and ground contact 18 to securely interconnect the respective control and ground contacts of arm 12.
• upper substrate surface 14 provides signal contacts 20a and 20b to be bridged or shorted by conductive bridge contact 22 of arm 12.
• Signal contacts 20a and 20b may carry or support any electrical signal, including, for example, conventional analog or digital data, or voice signals.
• Top and bottom conductive path elements 24a and 24b couple to arm 12 by a conventional technique, and the two SMA elements 26a and 26b mount between the contact and ground vias on the top and bottom center beam of arm 12.
• SMA elements 26a and 26b are made from a wire of a titanium nickel alloy having a diameter of between about 25 and 125 microns.
• the above inventive switch provides the basic circuit structure as illustrated in Figure 2.
• relay 30a when relay 30a is closed and relay 30b is open, current passing through the top conductive horseshoe-type path, composed of elements 16a, 24a, 26a, and 18, will move arm 12 upward.
• relay 30a when relay 30a is open and relay 30b is closed, current passing through the bottom conductive horseshoe-type path, composed of elements 16b, 24b, 26b, and 18, will move arm 12 downward.
• the force present during the thermal cooling stage is much less than the force present while an SMA element is being heated.
• conductive means transfers the necessary power from either control contact 16a or 16b through conductive path element 24a or 24b and SMA element 26a or 26b, respectively, to ground contact element 18.
• SMA elements 26a and 26b will preferably have a diameter of between about 25 and 125 microns and can be supplied with 40 to 160 milliamps during operation.
• Figures 3A - 3B through 6A - 6B the manufacturing process for fabricating the bistable switch according to the present invention will follow.
• Figure 3 A, 4A, 5 A and 6A illustrate the bottom surface of switch 10
• Figures 3B, 4B, 5B and 6B illustrate the respective side views of the same Figures.
• FIGS 3A and 3B illustrate a stabilizing material 50 coated with a patterned photoresist layer 52.
• stabilizing material 50 is a beryllium copper alloy that is manufactured in rolled sheets having a thickness between about 12 to 50 microns and a width of between about 300 to 1,200 microns.
• other materials may be used that provide the desired elastic or flexible properties and thickness.
• materials selected from the group including polyresin, plastic, wood composites, silicon, silicon resin, and various alloy materials such as a stainless steel alloy may be used.
• a conventional photolithographic technique is used to define the desired pattern onto the surface of stabilizing material 50 (pattern represented by dotted lines).
• patterned photoresist 52 defines a three beam structure having a tail portion 54 and a head portion 56, contact vias 58a and 58c, and two gaps 60a and 60b to define beams 62a, 62b, and 62c.
• a conventional etching technique removes stabilizing material 50 unprotected by pattern photoresist 52 to form the desired three beam structure 12 as illustrated in Figure 4A.
• a nonconductive insulation layer 64 coats the top and bottom surface of structure 12.
• This electrical insulator is preferably a paralene layer.
• insulation material 64 could be selected from the group including silicon dioxide, polyimide, wet oxide, and silicon nitride layer. These alternatives will provide a similar structure having similar operational characteristics. Persons of ordinary skill in the art will appreciate that insulation layer 64 may be eliminated if stabilizing material 50 is a nonconductive material.
• coated structure 12 On each side of coated structure 12, a conductive material, such as gold, is deposited and patterned to create a portion of the desired horseshoe-type path. More specifically, the top surface of coated structure 12 (see Figure 1) provides an L-shaped conductive path 24a coupled between control via 58a and top contact pad. In addition, the same conductive material forms ground via 58c. On the opposite or bottom side of structure 12, as illustrated in Figure 4A, coated structure 12 provides another L-shaped conductive path 24b coupled between control contact 68b and bottom contact pad 58b. In addition, the same material forms control contact 68a, ground contact 70 and bridge contact 22.
• a conductive material such as gold
• conductive material for conductive paths 24a and 24b, control contacts 68a and 68b, ground contact 70, ground and control vias 58a and 58c, top and bottom contact pads 58b, and bridge contact 22 may be selected from the group of gold, copper, palladium-gold alloy, nickel, silver, aluminum, and many other conductive materials available in the art.
• an actuator element 26a and 26b securely couples to the top and bottom surfaces of arm 12 between each contact pad and ground via 58c.
• an adhesive material (not shown) can be used to couple actuator elements 26a and 26b to respective top and bottom arm surfaces.
• the adhesive material could be selected from the group including cement, epoxy, lock on chip tap, solder, embedding, polyimide, and mechanical attachment such as a clip or clamp.
• This connection positions each actuator element 26a and 26b over a central portion of the top and bottom surface of middle beam 62B to complete the conductive horseshoe-type path.
• Actuator elements 26a and 26b are preferably a nickel-titanium SMA provided in a sheet, ribbon, or wire form.
• SMA elements 26a and 26b will preferably have a diameter of between about 25 and 125 microns.
• phase transformation process will typically occur by one of two methods.
• a first phase transformation technique reduces the bulk volume of the actuation material, and as a result, the length of the shape memory alloy will reduce, contracting stabilizing material 12.
• SMA is stretched by a percentage not exceeding 8% before and/or after it is installed to stabilizing structure 12.
• the length of SMA will reduce, going back to its original length before contracting the stabilizing material 12 layer even more, up to 8%.
• the shape memory alloy may or may not be stretched.
• the last steps of the desired process includes crimping and mounting the above structure.
• the above structure can be mounted to a desired substrate to form a reliable micro-machined bistable switch having a cantilever structure as illustrated in Figure 1.
• the switch cannot continuously short the signal contacts unless power is active to generate the necessary current and transformation within the desired SMA element. Consequently, this final coining or crimping step will allow the active device to maintain a contact position, even after the power is deactivated.
• This coining or crimping therefore, provides a snap action function to the arm that maintains the arm in a given position, except when one of the SMA elements flips the arm to the opposite position.
• This snap action structure may be formed using a conventional punch and dye method. More specifically, a central portion of left and right beams 62A and 62C are crimped to form a wave-type deformation or ungulation. To persons skilled in the relevant arts, this crimped area 80A and 80B will create a sustainable force when actuator element 26a or 26b transforms to move arm tip 12a up or down. In turn, crimped areas 80A and 80B will allow bridge contact 22 to maintain contact with or separation from signal contacts 20a and 20b even after the source coupled to switch 10 is deactivated.
• switch 10 will always be positioned up or down unless it is physically moved by the user.
• cantilever switch 10 couples to substrate surface 14 by a conventional bonding method.
• solder or pressure slots of a printed circuit board are used to attach and secure power and ground contacts 16a, 16b, and 18 to substrate surface 14 of switch 10. Consequently, when actuating element 26b is heated by the bottom horseshoe-type conductive path, the resultant structure will bend downwards to couple bridge contact 22 with signal contacts 20a and 20b. In turn, when actuating material 26A is heated by the top horseshoe-type conductive path, the connection between bridge contact 22 and signal contacts 20a and 20b will be broken.
• Another embodiment of the present invention would include the placement of an additional bridging contact 22' on the top surface of tip 12a for shorting complementary signal contacts 20a', 20b' on a multiple layer substrate.
• an additional bridging contact 22' on the top surface of tip 12a for shorting complementary signal contacts 20a', 20b' on a multiple layer substrate.
• the structure will move up to couple top bridging contact 22' with top signal contacts 20a' and 20b'.
• actuator element 26B is heated by an electrical current passing through bottom horseshoe-type conductive path 24b and 26b, the structure will move down to couple bridging contact 22 with signal contacts 20a and 20b.
• arm 12 is not crimped.
• FIGS 9 A and 9B illustrate another embodiment of the above inventive switch.
• sheet 50 is patterned and etched or punched to form the desired arm 12 as described above with reference to Figure 3B, and bridge contact 22 is formed (as described above) on arm tip 12a.
• actuator element 60 is looped over or attached to arm 12 at a location adjacent to tip 12a and electrically separated from bridge contact 22.
• tail portion 54 of arm 12 is attached to substrate surface 14 and ends 62a and 62b of actuator element 60 are extended in a horizontally opposed direction adjacent the length of arm 12 to connect with a power source 64 adjacent substrate surface 14.
• the conductive L-shaped path and contacts formerly located on arm 12 to provide the necessary circuit to activate SMA element has been moved to a location off of switch arm 12, to provide power source 64.
• a current supplied to SMA 60 by source 62 contracts SMA 60 to move arm 12 down and short signal contacts 20a and 20b with bridge contact 22.
• SMA 60 will return to a position that will separate bridge contact 22 from signal contact 20a and 20b.
• another SMA (not shown) may be attached in a similar way to arm 12, but on an opposite side to SMA 60, and supplied current by a similar power source.
• arm 12 can be crimped to form a device that will function as described above with reference to Figures 7A and 7B, and arm 12 can be patterned with or without multiple parallel beams.
• a single coining or a complete surface crimp may be used if there are no beams on arm 12 and an additional SMA element is attached to or wrapped around the other side of arm 12.
• arm 12 can be patterned to form a structure having as many beams as necessary to hold any desired SMA element(s).
• arm 12 could be patterned to form only a rectangular structure having no beams.
• the thickness and number of SMA elements 26a and 26b can increase or decrease to accommodate the desired arm structure and force necessary to move the same when heated.
• the number of crimps formed on flexible arm 12 will depend on the shape and functional characteristics of the resultant switch.
• this invention provide a relatively simple and inexpensive way to produce micro-switches and relays.
• This new and innovative micro-machine way of fabricating micro-switch and relays will enable a user to build systems that can carry very high voltage, current, and frequency signals.
• this inventive process can conceptually be designed to be compatible with standard silicon processing and allow mass production of the device at very reasonable cost. Consequently, the inventive structure provides a miniature bistable snap action electro-mechanical switch that can be activated by a shape memory alloy which possess a unique capability for increase speed actuation and forces relative to any prior art switching mechanism.
• this structure can be produced to have a length similar to between about 500 - 3,000 microns, a width between about 200 - 1,200 and between about 25 -35 microns thick, which is smaller than any competing bistable switches on the market today.
• this dimensions may change to obtain the desired size and functional characteristics for the inventive switch.
• the illustrative embodiments described herein employ SMA elements 26a and 26b as part of the conductive path for heating the SMA elements to accomplish the same end.
• the SMA elements could be coupled to a separate electrically conductive element, or they could be coupled to an entirely different sort of heating element (e.g., non-electrical).

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• Thermally Actuated Switches (AREA)
• Semiconductor Memories (AREA)

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• 1999
  • 1999-03-26 AU AU31142/99A patent/AU3114299A/en not_active Abandoned
  • 1999-03-26 EP EP99912877A patent/EP1166298A1/de not_active Withdrawn
  • 1999-03-26 BR BR9917232-1A patent/BR9917232A/pt not_active IP Right Cessation
  • 1999-03-26 CA CA002363386A patent/CA2363386A1/en not_active Abandoned
  • 1999-03-26 KR KR1020017012183A patent/KR20020018655A/ko not_active Application Discontinuation
  • 1999-03-26 WO PCT/US1999/006450 patent/WO2000058980A1/en not_active Application Discontinuation
  • 1999-03-26 CN CN99816529A patent/CN1348597A/zh active Pending

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