Abstract:
In accordance with the invention, a multiple throw switching device can be achieved on a single substrate by organizing a micro-fluidic switch into spokes radiating outward from the center of a wafer such that each spoke (switch throw) controls a switched output and each switch throw, in turn, is controlled by an individual stimulus.

Description:
BACKGROUND  
       [0001]     Single substrate single pole double throw micro-fluidic switching devices have been designed using liquid metal actuation to provide switching. These switches can use a single switching stage for achieving the open or closed state between two outputs. In one embodiment, high frequency signals can be switched from an input to an output by applying a stimulus, for example, pressure to the liquid within the switch body. The applied pressure (which is generated by a number of methods) causes the liquid (usually liquid metal) to move to one of two bi-stable states. Currently, when more than two throws are required, a plurality of these single stage switches must be used. A four-throw switch (having four possible outputs) would require three distinct switches, where the outputs of the switch of the first stage would become the inputs for two switches of the second stage. Separate switches, in addition to taking up valuable space on a wafer substrate, require complex circuitry to operate.  
       SUMMARY  
       [0002]     In accordance with the invention, a multiple throw switching device can be achieved on a single substrate by organizing a micro-fluidic switch into spokes radiating outward from the center of a wafer such that each spoke (switch throw) controls a switched output and each switch throw, in turn, is controlled by an individual stimulus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]      FIG. 1  is an overhead view of one embodiment of a single pole multi-throw device in accordance with the invention;  
         [0004]      FIGS. 2A-2D  are perspective views of one embodiment illustrating the switching operation of a multi-throw device in accordance with the invention; and  
         [0005]      FIGS. 3A-3D  are simplified diagrams illustrating the switching mechanism of one embodiment of a multi-throw device in accordance with the invention. 
     
    
     DETAILED DESCRIPTION  
       [0006]      FIG. 1  is an overhead view of one embodiment  10  of a single pole multi-throw device in accordance with the invention. Device  10  is manufactured on a substrate using micromachining and thin film fabrication techniques and can be made of any suitable material using any suitable process.  
         [0007]     Device  10  comprises four single pole single throw switches sharing a single switch pole (manifold)  17  creating a multiple throw switch. The switches are comprised of throw contacts  12 - 1  to  12 - 4 , contact cavities  13 - 1  to  13 - 4 , heaters  14 - 1  to  14 - 4 , heated gas channels  15 - 1  to  15 - 4 , liquid reservoir  16 , switch pole  17 , vents  18 - 1  to  18 - 5 , electrical (high frequency) connections  19 - 1  to  19 - 5 ; The shaded areas indicate conductive liquid. The conductive liquid may be any liquid that conducts electrical signals including, but not limited to liquid metals, such as mercury, gallium alloys, and indium alloys. While the present embodiment illustrates a single pole four throw switch, alternative embodiments may use any number of throws.  
         [0008]     It is noted that while the embodiment of  FIG. 1  has switch elements placed radially about a central manifold, alternative embodiments may have an enlarged manifold allowing for switch elements to be placed parallel to each other, for example, a rectangular manifold with switch elements placed in parallel with respect to each other and perpendicular to the manifold.  
         [0009]     Throw contacts  12 - 1  to  12 - 4 , switch pole  17  are cavities formed between a flat surface of a substrate, and the etched surface of another substrate with the two substrates bonded together. The cavities store the liquid and have wetted electrically conductive surfaces attracting the liquid. Throw contacts  12 - 1  to  12 - 4  are electrically connected to connections  19 - 1  to  19 - 4 , respectively, and pole  17  is electrically connected to connection  19 - 5 . Contact cavities  13 - 1  to  13 - 4  separate pole contact  17  from throw contacts  12 - 1  to  12 - 4 , respectively, and have nonwetted surfaces. These portions of the cavities are not electrically conductive, such that when a given contact cavity is empty (i.e., no metallic liquid therein) switch pole  17  is electrically isolated from the contact associated with that cavity. For example, if cavity  13 - 1  is empty of liquid there is electrical isolation between contact  12 - 1  and pole contact  17  switch pole  17  and the given contact cavity&#39;s throw contact are not electrically connected. In order to electrically connect pole  17  with a particular cavity switch of device  10 , liquid must bridge the gap from pole  17  to the switch.  
         [0010]     As illustrated in  FIG. 1 , contact cavities  13 - 1 ,  13 - 3 , and  13 - 4  are empty and the liquid of pole  17  is separated from the liquid of throw contacts  12 - 1 ,  12 - 3 , and  12 - 4 , such that pole  17  is not electrically connected to throw contacts  12 - 1 ,  12 - 3 , and  12 - 4 . However, contact cavity  13 - 2  is full, and thus, the liquid of pole  17  is continuous with the liquid of throw contact  12 - 2 , such that pole  17  is electrically connected to throw contact  12 - 2 . Accordingly, input  19 - 5  is in electrical contact with output  19 - 2 . It is noted that, as with conventional switches, the direction of electrical signals is not constrained by device  10 , such that any of connections  19 - 1  to  19 - 5  may be configured as electrical signal inputs or outputs, depending, at least in part, upon the desired use of device  10 .  
         [0011]     Heat connecting channels  15 - 1  to  15 - 4  have nonwetted surfaces and serve to connect contact cavities  13 - 1  to  13 - 4  with heaters  14 - 1  to  14 - 4 , respectively. These heaters could be, for example, joule heaters. As will be discussed, heaters  14 - 1  to  14 - 4  operate to control the movement of the liquid within device  10  to make connections between throw contacts  12 - 1  to  12 - 4  and contact  17 . Heaters  14 - 1  to  14 - 4  operate by heating gases, which gases are passed through channels  15 - 1  to  15 - 4  thereby causing the liquid within the associated chamber of device  10  to move in a desired direction, as will be discussed.  
         [0012]     Electrical connectors  19 - 1  to  19 - 5  allow other electrical devices to be connected to device  10 . Vents  18 - 1  to  18 - 5  are cavities in substrate  11  serving to allow trapped gases to escape, which is particularly important during liquid loading of the switch, once microfabrication has been completed. These vents have nonwetted surfaces to repel and prevent the escape of liquid from throw contacts  12 - 1  to  12 - 4  (for vents  18 - 1  to  18 - 4 ) and pole  17  (for vent  18 - 5 ). Reservoir cavity  16  also has nonwetted surfaces which allow for the storage of excess amounts of liquid that may temporarily overflow from pole  17  during the operation of device  10 . The reservoir is also used in the loading of liquid metal into the device.  
         [0013]      FIGS. 2A-2D  are perspective views of one embodiment illustrating the switching operation of a multi-throw device in accordance with the invention. As illustrated in  FIG. 2A , contact cavity  13 - 2  is the only contact cavity that is full of liquid (as shown by the diagonal lines). (Note that cavities  13 - 1 ,  13 - 3 , and  13 - 4  are empty of liquid.) The fact that contact cavity  13 - 2  is full of liquid means that electrical continuity exists between connector  19 - 2 , through cavities  12 - 2  and  13 - 2  to contact  17 . Contact cavities  13 - 1 ,  13 - 3 , and  13 - 4  are empty such that electrical continuity does not exist between connectors  19 - 1 ,  19 - 3 , and  19 - 4  and contact  17 . Since connector  19 - 5  is electrically connected to contact  17 , then if follows that electrical continuity exists between connectors  19 - 5  and  19 - 2 .  
         [0014]     Note that reservoir cavity  16  is also empty, at this time.  
         [0015]     Assume now that it is desired to change the switch so post-electrical continuity exists between connectors  19 - 5  and  19 - 3 . Referring to  FIG. 2B , heaters  14 - 1 ,  14 - 2 , and  14 - 4  (shown in  FIG. 1  and represented in  FIGS. 2A-2D  with arrows) are turned on and heater  14 - 3  (represented by a light arrow) remains in its state. Heater  14 - 2  being turned on causes the liquid in contact chamber  13 - 2  to move out of that chamber and into contact  17  chamber. Heaters  14 - 1  and  14 - 4  being on keep the liquid from flowing into contact cavities  13 - 1  and  13 - 4 . The combination of pressures from heaters  14 - 1 ,  14 - 2 , and  14 - 4  operate to cause liquid from chamber  17  to flow into both channel  160  and into contact cavity  13 - 3 . This follows since cavity  13 - 3  is at a lower pressure than the other cavities since heat is not being applied by heater  14 - 3  to cavity  13 - 3 .  
         [0016]     Referring to  FIG. 2C , heaters  14 - 1 ,  14 - 2 , and  14 - 4  have been on long enough to break the connection between pole contact  17  and formally closed throw contact  12 - 2  by emptying contact cavity  13 - 2 . Since liquid has now moved into cavity  13 - 3 , there is electrical continuity between connectors  19 - 5  and  19 - 3  and no electrical contact between connectors  19 - 5  and  19 - 2 . Note that the excess amounts of liquid that cannot be held by pole  17  is pushed primarily into channel  160  which acts as a temporary overflow buffer for liquid flowing within the device. Also note that a small amount of liquid is pushed into heat connecting channel  15 - 3 , which can also act as an overflow buffer.  
         [0017]     Referring to  FIG. 2D , heaters  14 - 1 ,  14 - 2 , and  14 - 4  have been turned off, and the excess liquid that was in reservoir cavity  16  and heat cavity  15 - 2  has settled back into pole cavity  17 . Contact cavity  13 - 2  has been emptied and contact cavity  13 - 3  has been filled, thus changing the electrical connection that existed between terminals  19 - 5  and  19 - 2  to a new connection between  19 - 5  and  19 - 3 .  
         [0018]     A controlling factor in how many poles can be closed at any one time is that the switch must have enough liquid to fill all the cavities that are to be “closed.” However, if too much liquid is added, then the liquid would have no place to go and some switch throws would remain closed even when heat (pressure) is applied. Reservoir  16  is primarily used during loading, where it is filled and then expelled into the various channels. However, during switching come liquid metal could temporarily move into the reservoir. In most situations, the liquid moving between channels during switching would most likely only make it as far as the connection between the switch and the reservoir. Alternative embodiments may make electrical connections with more than one throw contact. For example, if in the previous discussion with respect to  FIGS. 2B and 2C , heater  14 - 4  had been left off, both contact cavities  13 - 3  and  13 - 4  would have been filled, thereby electrically connecting connector  19 - 5  with both connectors  19 - 3  and  19 - 4  in situations where a proper amount of liquid has been loaded into the device.  
         [0019]     Further, alternative embodiments may have switch throws for each electrical connection. For example, if electrical connection  19 - 5  were to be removed, or not used, any one or more terminals  19 - 1  to  19 - 4  could be selectively connected to any one or more other terminals  19 - 1  to  19 - 4 .  
         [0020]     Alternative embodiments may have the contact cavities of multiple poles connected to a single heater, thus creating a multi-pole switch.  
         [0021]     It is noted that while gas pressure is used to move the liquid within device  10 , alternative embodiments may use any other suitable means to move the liquid, such as electrowetting on dielectric or micro-electro-mechanical pumps and motors and combinations of the above.  
         [0022]      FIGS. 3A-3D  are simplified diagrams illustrating the switching mechanism of one embodiment  30  of a multi-throw device having a single pole and two throws in accordance with the invention. Referring to  FIG. 3A , both heaters  34 - 1  and  34 - 2  are off. The left side of switch  30  (between element  38  and element  38 - 1 ) is closed (containing liquid), and the right side (between element  38  and element  38 - 2 ) is open (no liquid). To open the left side of switch  30  and close the right side, heater  34 - 1  is turned on as shown in  FIG. 3B . Heater  34 - 1  increases the gas pressure on the liquid in cavity  32 - 1  via cavity  37 , thereby causing the liquid in left side cavity  32 - 1  to begin to move into right side cavity  32 - 2  as shown beginning to happen in  FIG. 3C .  
         [0023]     As shown in  FIG. 3D , after enough liquid has been pushed from cavity  32 - 1  into cavity  32 - 2 , the left side opens between element  38 - 1  and element  38 , and the right side closes between element  38  and element  38 - 2 . Heater  34 - 1  is then turned off.  
         [0024]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.