Patent Publication Number: US-6909059-B2

Title: Liquid switch production and assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a divisional of application Ser. No. 10/317,597 filed on Dec. 12, 2002, now U.S. Pat. No. 6,774,324 the entire disclosure of which is incorporated into this application by reference. 

   BACKGROUND 
   Liquid metal micro-switches (LIMMS) have been developed to provide reliable switching capability using compact hardware (e.g., on the order of microns). The small size of LIMMS make them ideal for use in hybrid circuits and other applications where smaller sizes are desirable. Besides their smaller size, advantages of LIMMS over more conventional switching technologies include reliability, the elimination of mechanical fatigue, lower contact resistance, and the ability to switch relatively high power (e.g., about 100 milli-Watts) without overheating, to name just a few. 
   According to one design, LIMMS have a main channel partially filled with a liquid metal. The liquid metal may serve as the conductive switching element. Drive elements provided adjacent the main channel move the liquid metal through the main channel, actuating the switching function. 
   During assembly, the volume of liquid metal must be accurately measured and delivered into the main channel. Failure to accurately measure and/or deliver the proper volume of liquid metal into the main channel could cause the LIMM to fail or malfunction. For example, too much liquid metal in the main channel could cause a short. Not enough liquid metal in the main channel may prevent the switch from making a good connection. 
   The compact size of LIMMS makes it especially difficult to accurately measure and deliver the liquid metal into the main channel. Even variations in the tolerance of the machinery used to deliver the liquid metal may introduce error during the delivery process. Variations in the dimensions of the main channel itself may also introduce volumetric error. 
   SUMMARY OF THE INVENTION 
   In one embodiment, a switch is assembled by depositing a liquid switching element on a substrate. A channel plate is then positioned adjacent the substrate. The channel plate has a main channel and a waste chamber, and the main channel is positioned over the liquid switching element. The channel plate is then moved toward the substrate to cause a portion of the liquid switching element that overfills the main channel to be isolated from the main channel in the waste chamber. 
   In another embodiment, a switch is produced by depositing a liquid switching element on a substrate, with the volume of the liquid switching element being more than needed to fulfill a switching function. The channel plate is then moved toward the substrate such that barriers of the channel plate isolate a portion of the liquid switching element into at least one waste chamber in the channel plate as the barriers contact the liquid switching element. The channel plate is then closed against the substrate. 
   Yet other embodiments are also disclosed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative and presently preferred embodiments of the invention are illustrated in the drawings, in which: 
     FIG.  1 ( a ) is a perspective view of one embodiment of a switch, shown in a first state; 
     FIG.  1 ( b ) is a perspective view of the switch of FIG.  1 ( a ), shown in a second state; 
     FIG.  2 ( a ) is a plan view of a channel plate used to produce the switch according to one embodiment of the invention; 
     FIG.  2 ( b ) is a plan view of a substrate used to produce the switch according to one embodiment of the invention; 
       FIG. 3  is a side view of the channel plate positioned adjacent the substrate, showing a liquid switching element deposited on the substrate; 
       FIG. 4  is a side view of the channel plate and substrate moved toward one another, showing the liquid switching element wet to the channel plate; 
       FIG. 5  is a side view of the channel plate and substrate moved closer to one another, showing the liquid switching element discharging into the waste chambers; 
       FIG. 6  is a side view of the channel plate and substrate, showing the liquid switching element in equilibrium; 
       FIG. 7  is a side view of the channel plate assembled to the substrate, shown in a first state; and 
       FIG. 8  is another side view of the channel plate assembled to the substrate, shown in a second state. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   One embodiment of a switch  100  is shown and described according to the teachings of the invention with respect to FIG.  1 ( a ) and FIG.  1 ( b ). Switch  100  comprises a channel plate  110  defining a portion of a main channel  120 , drive chambers  130 ,  132 , and subchannels  140 ,  142  fluidically connecting the drive chambers  130 ,  132  to the main channel  120 . The channel plate  110  is assembled to a substrate  150 , which further defines the main channel  120 , drive chambers  130 ,  132 , and subchannels  140 ,  142 . 
   In one embodiment, the channel plate  110  is manufactured from glass, although other suitable materials may also be used (e.g., ceramics, plastics, a combination of materials). The substrate  150  may be manufactured from a ceramic material, although other suitable materials may also be used. 
   Channels may be etched into the channel plate  110  (e.g., by sand blasting) and covered by the substrate  150 , thereby defining the main channel  120 , drive chambers  130 ,  132 , and subchannels  140 ,  142 . Other embodiments for manufacturing the channel plate  110  and substrate  150  are also contemplated as being within the scope of the invention. 
   Of course it is understood that the main channel  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  may be defined in any suitable manner. For example, the main channel  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  may be entirely formed within either the channel plate  110  or the substrate  150 . In other embodiments, the switch may comprise additional layers, and the main channel  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  may be partially or entirely formed through these layers. 
   It is also understood that the switch  100  is not limited to any particular configuration. In other embodiments, any suitable number of main channels  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  may be provided and suitably linked to one another. Similarly, the main channels  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  are not limited to any particular geometry. Although according to one embodiment, the main channels  120 , drive chambers  130 ,  132 , and/or subchannels  140 ,  142  have a semi-elliptical cross section, in other embodiments, the cross section may be elliptical, circular, rectangular, or any other suitable geometry. 
   According to the embodiment shown in FIG.  1 ( a ) and FIG.  1 ( b ), switch  100  may also comprise a plurality of electrodes or contact pads  160 ,  162 ,  164  which are exposed to the interior of the main channel  120 . Leads  170 ,  172 , and  174  may be provided through the substrate  150  and may carry electrical current to/from the contact pads  160 ,  162 ,  164  during operation of the switch  100 . 
   Of course the switch  100  may be provided with any number of contact pads, including more or less than shown and described herein. The number of contact pads may depend at least to some extent on the intended use of the switch  100 . 
   The main channel  120  is partially filled with a liquid switching element  180 . In one embodiment, the liquid switching element  180  is a conductive fluid (e.g., mercury (Hg)). As such, the liquid switching element  180  may serve as a conductive path between the contact pads  160 ,  162  or contact pads  162 ,  164 . Alternatively, an opaque fluid may be used for an optical switch (not shown). The opaque fluid is used to block and unblock optical paths, as will be readily understood by one skilled in the art after having become familiar with the teachings of the invention. 
   The subchannels  140 ,  142  may be at least partially filled with a driving fluid  185 . Preferably, the driving fluid  185  is a non-conductive fluid, such as an inert gas or liquid. The driving fluid  185  may be used to move the liquid switching element  180  within the main channel  120 . 
   Drive elements  200 ,  202  (FIG.  2 ( b )) may be provided in drive chambers  130 ,  132 . Drive elements  200 ,  202  may comprise, for example, heat-producing means (e.g., thin-film resistors) which heat the driving fluid  185  and cause it to expand. Other embodiments, now known or later developed, are also contemplated as being within the scope of the invention. For example, drive elements  200 ,  202  may comprise acoustic or pump means, to name only a few. In any event, the drive elements  200 ,  202  can be operated to force the driving fluid  185  (see FIG.  1 ( a ) and FIG.  1 ( b )) into the main chamber  120 , causing the liquid switching element  180  to “part” and move within the main channel  120 . 
   By way of illustration, switch  100  is shown in a first state in FIG.  1 ( a ) wherein the liquid switching element  180  makes a conductive path between contact pads  162  and  164 . Drive element  202  may be operated to effect a change in state of switch  100 , as shown in FIG.  1 ( b ). Operation of the drive element  202  (FIG.  2 ( b )) causes the liquid switching element  180  to move toward the other end of the main channel  120 , wherein the liquid switching element  180  makes a conductive path between contact pads  160  and  162 . Similarly, drive element  200  (FIG.  2 ( b )) can be operated to change the state of the switch  100  back to the first state. 
   Suitable modifications to switch  100  are also contemplated as being within the scope of the invention, as will become readily apparent to one skilled in the art after having become familiar with the teachings of the invention. For example, the present invention is also applicable to optical micro-switches (not shown). Also see, for example, U.S. Pat. No. 6,323,447 of Kondoh et al. entitled “Electrical Contact Breaker Switch, Integrated Electrical Contact Breaker Switch, and Electrical Contact Switching Method”, and U.S. patent application Ser. No. 10/137,691 and filed on May 2, 2002 of Marvin Wong entitled “A Piezoelectrically Actuated Liquid Metal Switch”, each hereby incorporated by reference for all that is disclosed. 
   The foregoing description of one embodiment of switch  100  is provided in order to better understand its operation. It should also be understood that the present invention is applicable to any of a wide range of other types and configurations of switches, now known or that may be developed in the future. 
   Switch  100  may comprise a channel plate  110  and a substrate  150 , as shown in more detail according to one embodiment in FIG.  2 ( a ) and FIG.  2 ( b ), respectively. Note that the channel plate  110  is shown in FIG.  2 ( a ) as it appears from the top looking through the channel plate  110 . Substrate  150  is shown in FIG.  2 ( b ) as it appears from the side (e.g., top) that abuts the channel plate  110 . In addition, the main channel  120 , subchannels  140 ,  142 , waste chambers  210 ,  212 , and heater chambers  130 ,  132  are outlined in FIG.  2 ( b ) to indicate their presence in embodiments where at least a portion of these features are provided in the substrate  150 , as discussed above. 
   Channel plate  110  has a main channel  120  and waste chambers  210 ,  212  formed therein. Substrate  150  has contact pads  160 ,  162 ,  164 . Contact pads  160 ,  162 ,  164  may be made of a wettable material. Where the contact pads  160 ,  162 ,  164  serve to make electrical connections, contact pads  160 ,  162 ,  164  are made of a conductive material, such as metal. 
   Contact pads  160 ,  162 ,  164  are spaced apart from one another. Preferably, subchannels  140 ,  142  open to the main chamber  120  in the space provided between the contact pads  160 ,  162 ,  164 . Such an arrangement serves to enhance separation of the liquid switching element  180  during switching operations. 
   A liquid switching element  180  may be deposited on the contact pads  160 ,  162 ,  164 , as shown according to one embodiment in FIG.  3 . Preferably, the liquid switching element  180  is more than needed to fulfill a switching function. An excess portion of the liquid switching element discharges from the main channel  120  into the waste chambers  210 ,  212  when the channel plate  110  is assembled to the substrate  150 , as will be discussed in more detail below. 
   The main channel  120  may be isolated from the waste chambers  210 ,  212  by dams or barriers  300 ,  302  on the channel plate  110 . Barriers  300 ,  302  serve to isolate the liquid switching element  180  into the main channel  120  and the waste chambers  210 ,  212  during assembly. See for example, the illustration of FIG.  4  through  FIG. 7  discussed below. Barriers  300 ,  302  also serve to isolate the excess liquid switching element  180  in the waste chambers  210 ,  212  after assembly (e.g., during operation of the switch  100 ). Accordingly, the waste chambers  210 ,  212  do not need to be separately sealed, but may be if so desired. 
   Seal belts  220 ,  222 ,  224  may be provided on the channel plate  110  to promote wetting of the liquid switching element  180  to the channel plate  110 . Seal belts  220 ,  222 ,  224  are illustrated in FIG.  2 ( a ) in outline form to better show their position relative to main channel  120  and waste chambers  210 ,  212  (i.e., overlaying the channels). 
   Seal belts  220 ,  222 ,  224  are preferably made of a wettable material. Suitable materials may include metal, metal alloys, to name only a few. In one embodiment, seal belts  220 ,  222 ,  224  are made of one or more layers of thin-film metal. For example, the seal belts  220 ,  222 ,  224  may comprise a thin layer (e.g., about 1000 Å) of chromium (Cr), a thin layer (e.g., about 5000 Å) of platinum (Pt), and a thin layer (e.g., about 1000 Å) of gold (Au). The outermost layer of gold quickly dissolves when it comes into contact with a mercury (Hg) liquid switching element  180 , and the mercury forms an alloy with the layer of platinum. Accordingly the liquid switching element  180  readily wets to the seal belts  220 ,  222 ,  224 . 
   It is noted that one of the seal belts (e.g.,  220 ) preferably extends across one of the barriers (e.g.,  300 ) into the adjacent waste chamber (e.g.,  210 ). Therefore, the liquid switching element  180  wets to the barrier  300  and excess liquid switching element  180  is readily discharged into the waste chamber  210  during assembly (see FIG.  4 ). 
   It is also noted that one of the seal belts (e.g.,  224 ) preferably does not extend across one of the barriers (e.g.,  302 ) into the adjacent waste chamber (e.g.,  212 ). The liquid switching element  180  does not readily wet to the barrier  302  without a seal belt. Accordingly, at least a portion of the liquid switching element  180  is forced into the main channel  120  toward contact pad  162  during assembly (see FIG.  5 ). 
   Following assembly, the desired amount of liquid switching element  180  remains in the main channel  120  as shown in FIG.  7  and FIG.  8 . The liquid switching element  180  remaining in the main channel  120  can be used to effect a change of state in the switch  100 , as described above. Excess of the liquid switching element  180  is isolated from the main channel  120  in the waste chambers  210 ,  212 . 
   Preferably, waste chambers  210 ,  212  are isolated from the main channel  120  by barriers  300 ,  302 . Waste chambers may also be sealed (e.g., around the outer perimeter of the switch  100 ). For example, seals  310 ,  312  (e.g., made of CYTOP®, commercially available from Asahi Glass Company, Ltd (Tokyo, Japan)) may be provided on the outer perimeter of the channel plate  110  and/or substrate  150 . Excess liquid switching element  180  therefore remains in the waste chambers  210 ,  212 . Alternatively, excess liquid switching element  180  may be removed from the waste chambers  210 ,  212 , as desired. 
   Switch  100  may be produced according to one embodiment of the invention as follows. Liquid switching element  180  is deposited on the substrate  150 , as illustrated in FIG.  3 . In one embodiment, liquid switching element  180  is deposited on each of the contact pads  160 ,  162 ,  164 . Although liquid switching element  180  need not be accurately measured, suitable volumes of deposited liquid switching element  180  may form “swells” on the contact pads  160 ,  162 ,  164 , but preferably does not run over the sides of the contact pads  160 ,  162 ,  164  onto the substrate  150 . 
   The channel plate  110  may be positioned adjacent the substrate  150 . Although channel plate  110  may be positioned adjacent the substrate  150  prior to depositing the liquid switching element  180 , the invention is not limited to this sequence. The channel plate  110  may then be moved toward the substrate  150 . 
   As the channel plate  110  is moved toward substrate  150 , the liquid switching element  180  on contact pads  160 ,  164  comes into contact with barriers  300 ,  302  on the channel plate  110 , as shown in FIG.  4 . In one embodiment, liquid switching element  180  on contact pad  160  wets to the seal belt  220  extending across the barrier  300  from the main channel  120  into the waste chamber  210 . Accordingly, excess liquid switching element  180  is discharged into waste chamber  210  and is not forced into the main channel  120 . 
   Also according to this embodiment, the liquid switching element  180  on contact pad  164  does not wet to barrier  302 , as it is not provided with a seal belt  220  extending into the waste chamber  212 . Instead, the hydrostatic pressure of the liquid switching element  180  increases as barrier  302  is moved against it, forcing liquid switching element  180  into the main channel  120  and into contact with the liquid switching element  180  on contact pad  162 , as shown in FIG.  4  and  FIG. 5. A  portion of the liquid switching element  180  (i.e., excess) may also be discharged into the waste chamber  212 . 
   Preferably, the assembly process comprises pausing or slowing movement of the channel plate  110  toward the substrate  150  for a time sufficient to allow liquid switching element  180  to equilibrate. The surface tension of the liquid switching element  180  causes the liquid switching element  180  to flow toward an area having a greater cross-sectional area (i.e., the waste chambers  210 ,  212 ). Movement of the liquid switching element  180  is enhanced by wettable areas (i.e., the contact pads  160 ,  164  and seal belts  220 ,  224 ). 
   The liquid switching element  180  is shown in equilibrium between the waste chambers  210 ,  212  and main channel  120  in FIG.  6 . According to this embodiment, the liquid switching element  180  on contact pad  160  extends substantially perpendicular to the substrate  150  and is aligned between the edge of contact pad  160  and the edge of seal belt  220 . Liquid switching element  180  on contact pad  164  has merged with liquid switching element  180  on contact pad  162 . The liquid switching element  180  wets to the contact pads  162 ,  164  and seal belts  222 ,  224 , and has “pulled away” from the channel plate  110  and substrate  150  between the contact pads  162 ,  164  and seal belts  222 ,  224 . Excess liquid switching element  180  is discharged or otherwise removed into the waste chambers  210 ,  212 . 
   The channel plate  110  may then be closed against the substrate  150 , as shown in FIG.  7 . Liquid switching element  180  may be forced out from under the barriers  300 ,  302  and into the main channel  120  and waste chamber  210 ,  212 . The volume of liquid switching element  180  forced out from under barriers  300 ,  302  may bulge toward the air space between the liquid switching element in main channel  120  (as illustrated in FIG.  7 ), but is not forced so far into the main channel  120  that the switch is shorted. 
   The channel plate  110  may be connected to the substrate  150  in any suitable manner. In one embodiment, an adhesive is used to connect the channel plate  110  to the substrate  150 . In another embodiment, screws or other suitable fasteners may be used. Barriers  300 ,  302  serve to isolate the main channel  120  from the waste chambers  210 ,  212 . 
   The switch  100  may be operated as described above. By way of brief illustration, switch  100  is shown in a first state in  FIG. 7  wherein the liquid switching element  180  makes a conductive path between contact pads  162  and  164 . Drive element  202  (FIG.  2 ( b )) may be operated to effect a change in state of switch  100 , as discussed above. Operation of the drive element  202  causes the liquid switching element  180  to move toward the other end of the main channel  120 , wherein the liquid switching element  180  makes a conductive path between contact pads  160  and  162 , as shown in FIG.  8 . Drive element  200  (FIG.  2 ( b )) can be operated to change the state of the switch  100  back to the first state (FIG.  7 ). 
   It is readily apparent that switch  100  and production thereof according to the teachings of the present invention represents an important development in the field. The present invention allows for variance in the volume of liquid metal that is measured and delivered into the main channel  120 . Excess liquid switching element  180  is removed into the waste chamber(s)  210 ,  212 . Accordingly, the present invention corrects for volumetric errors that may be introduced during assembly of compact switching devices (e.g., LIMMS). For example, the present invention corrects volumetric errors resulting from the tolerance of the delivery tools. The present invention also corrects for volumetric errors resulting from variations in the dimensions of the main channel  120  itself. 
   Having herein set forth preferred embodiments of the present invention, it is anticipated that suitable modifications can be made thereto which will nonetheless remain within the scope of the present invention.