Abstract:
Advantage is taken of the fact that each switching state change (i.e., each throw) of a double throw switch requires a pair of controlled input signals to be applied to the switching element that controls that throw. By sharing input leads among several switches and by arranging the leads with respect to each switch throw element such that for any pair of leads only one switch throw element will activate, it is possible to reduce the total number of leads for the combined switch package. In one embodiment, all of the switches in a switching device are packaged as a single device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is related to commonly assigned U.S. patent application Ser. No. 10/996,823, filed on Nov. 24, 2004, published as 2006/0108209, May 25, 2006, entitled “LIQUID METAL SWITCH EMPLOYING ELECTROWETTING FOR ACTUATION AND ARCHITECTURES FOR IMPLEMENTING SAME”, which application is hereby incorporated by reference herein. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    Microfluidic architectures, are increasingly being used for control purposes. Electrowetting on dielectric (EWOD) technology can be used to construct microfluidic switches as shown in commonly assigned U.S. patent application Ser. No. 10/996,823, filed on Nov. 24, 2004, published as 2006/0108209, May 25, 2006, entitled “LIQUID METAL SWITCH EMPLOYING ELECTROWETTING FOR ACTUATION AND ARCHITECTURES FOR IMPLEMENTING SAME”, which application is hereby incorporated by reference. For example, switching devices are being designed on wafer chips (substrates) where liquid metal within the switch structure opens and closes the switched circuit. Often many such switches are constructed on a single substrate. For example, in the above-referenced application there is shown a single-pole double-throw (SPDT) switch having four control inputs (two for each “throw” position) to control the switched state. In some cases, one of the input controls can be common resulting in three control leads per switch. When multiple switches are constructed on a single substrate the total number of input control leads would be four (or perhaps three) times the number of switches. 
         [0003]    Such a large numbers of control inputs is impractical on a single substrate (especially considering the small size of microfluidic devices) and the problem is compounded when the switching circuit is to be used with RF signals since the large number of switching inputs increases the risk of interference with the RF signals. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    Advantage is taken of the fact that each switching state change (i.e., each throw) of a double throw switch requires a pair of controlled input signals to be applied to the switching element that controls that throw. By sharing input leads among several switches and by arranging the leads with respect to each switch throw element such that for any pair of leads only one switch throw element will activate, it is possible to reduce the total number of leads for the combined switch package. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIGS. 1A ,  1 B and  1 C show, in schematic diagram form, an embodiment of a single-pole double-throw switch; 
           [0006]      FIG. 2  is a representation of the switch shown in  FIGS. 1A through 1C ; 
           [0007]      FIG. 3A  illustrates one embodiment of a switching strategy for three switches of the type discussed above with respect to  FIG. 2 ; 
           [0008]      FIG. 3B  shows a chart of one possible set of paired control lines for operating three separate switches; 
           [0009]      FIG. 4A  illustrates one embodiment of a switching strategy for five switches of the type discussed with respect to  FIG. 2 ; and 
           [0010]      FIG. 4B  shows a chart of which pair of control leads must be made active to cause a particular device to switch. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIGS. 1A ,  1 B and  1 C show, in schematic diagram form, an embodiment of a single-pole double-throw switch, such as switch  100 . In  FIG. 1A , electrically conductive liquid droplet  110  is shown bridging electrical continuity between RFin contact  118  and RFout 1  contact  122  while in  FIG. 1C  droplet  110  has moved from the left throw position to the right throw position and now bridges electrical continuity between RFin contact  118  and RFout 2  contact  124 . For a more complete understanding of the operation of switch  100  reference is made to the above-identified application entitled “LIQUID METAL SWITCH EMPLOYING ELECTROWETTING FOR ACTUATION AND ARCHITECTURES FOR IMPLEMENTING SAME”. 
         [0012]    As shown in  FIG. 1A , switch  100  comprises dielectric  102  having surface  103  forming the floor of the switch, and dielectric  104  having surface  105  that forms the roof of the switch. Droplet  110  of a conductive liquid, such as, for example, mercury (Hg) or a gallium alloy is sandwiched between dielectric  102  and dielectric  104 . 
         [0013]    Dielectric  102  includes electrode  106  and electrode  112 . Dielectric  104  comprises electrode  108  and electrode  114 . Electrodes  106  and  112  are buried within dielectric  102  and electrodes  108  and  114  are buried within dielectric  104 . In this example, and to induce droplet  110  to move right toward electrodes  112  and  114 , electrodes  106  and  108  are coupled to an electrical return path  116  and are electrically isolated from electrodes  112  and  114 , and electrodes  112  and  114  are coupled to voltage source  126 . Alternatively, to induce droplet  110  to move left toward electrodes  106  and  108 , electrodes  112  and  114  can be coupled to an isolated electrical return path and electrodes  106  and  108  can be coupled to a voltage source. 
         [0014]    In this example, switch  100  includes electrical contacts  118 ,  122 , and  124  positioned on surface  103  of dielectric  102 . In this example, contact  118  can be referred to as an input, and contacts  122  and  124  can be referred to as outputs. As shown in  FIG. 1A , droplet  110  is in electrical contact with input contact  118  and output contact  122 . Further, in this example, droplet  110  will always be in contact with input contact  118 . 
         [0015]    As shown in  FIG. 1A  as a cross section, droplet  110  includes a first radius, r 1 , and a second radius, r 2 . When electrically unbiased, i.e., when there is zero voltage supplied by voltage source  126 , the magnitude curvature of the radius r 1  equals the magnitude curvature of the radius r 2  and the droplet is at rest. 
         [0016]    Upon application of an electrical potential via voltage source  126 , a new contact angle between droplet  110  and surfaces  103  and  105  is defined thus altering the profile of droplet  110  so that r 1  is not equal to r 2 . If r 1  is not equal to r 2 , then the pressure, P, on droplet  110  changes and movement is imparted to the droplet causing the droplet to translate across surfaces  103  and  105 . 
         [0017]      FIG. 1C  is a schematic diagram  130  illustrating switch  100  of  FIG. 1A  after the application of a voltage. As shown in  FIG. 1C , droplet  110  has moved and now electrically connects input contact  118  and output contact  124 . In this manner, electrowetting can be used to induce translational movement in a conductive liquid and can be used to switch electronic signals. 
         [0018]      FIG. 2  is a representation of the switch shown in  FIGS. 1A , through  1 C, except that the electrodes are now only in the floor, and not in the roof. Conductive droplet  110   a  represents the switch thrown to the left position (between RFin and RFout 1  and droplet  110   b  represents the switch thrown to the right position (between RFin and RFout 2 ). Note that each throw requires a pair of input lines numbered  1  and  2  for the left throw and  3  and  4  for the right throw. These lines are the lines that apply control signals, such as plus and minus voltages (or other signals) to electrodes  108 ,  106 ,  114 , and  112 , respectively, s shown in  FIGS. 1A-1C . 
         [0019]      FIG. 3A  illustrates one embodiment of a switching strategy for three switches of the type discussed above with respect to  FIG. 2 . In an embodiment, these can be stacked one on top of the other or they can be constructed on a single substrate side by side, or interleaved or constructed in any other manner desired. The key factor being that the input lines that control the various throw positions are interconnected so that signals on any pair of input leads will operate only one switch throw. Thus, all line  1   s  are electrically common; all line  2   s  are electrically common; all line  3   s  are electrically common and all line  4   s  are electrically common such that an electrical signal on line  1 , for example, would be delivered to line  1  of all devices A, B and C. In some situations, sets of control line pairs can control multiple switches that operate in parallel if so desired. 
         [0020]    In operation, all control lines leading to the electrode pairs are driven by off-chip drivers, and these drivers should be tri-state devices, with the drivers in the high impedance state when the liquid metal is not being toggled, as this will minimize RF leakage through the control line. Also, each control line should have a high sheet resistance on the die, also to minimize RF leakage. However, it should be ensured that the RC time constant of the control line should be much shorter in duration than the overall switching time, such that the RC time constant is not a significant contributor to the switching time. 
         [0021]    To toggle a SPDT device from state A to state B, the electrode pair that is mostly not covered by the liquid metal is activated, with the other pair left floating (tied to high impedance with, for example, a tri-state driver). The active pair (for device A in  FIG. 3A  that would be input lines  1  and  2 ) can be put at some voltage +V and −V: if the voltages are of equal magnitude and opposite polarity, and the electrode areas are approximately the same, this will keep the DC potential of the liquid metal near zero during switching. Provided the liquid is close enough to the active electrode pair to sense the electric field, the liquid will move over the electrode pair, so as to maximize the capacitance in the system. The device has then “switched.” To move the liquid metal to its initial state, one need only change applied bias to the other electrode pair (for device A in  FIG. 3A  that would be input lines  3  and  4 ). 
         [0022]    With the appropriate microfluidic architecture, and choice of applied bias, only the application of bias +V and −V on either the left pair or right pair will lead to actuation. That is, no matter the state if the fluid, if the applied bias is across one of the electrodes on the right (say input line  3 ), and one of the electrodes on the left (say input line  1  or input line  2 ), actuation (switching) will not occur. The liquid metal slug may deform somewhat in response to the applied voltages, but the existing input to output connection will not be broken, and a new connection will not occur. 
         [0023]      FIG. 3B  shows a chart of one possible set of paired control lines for operating three separate switches shown in  FIG. 3A  as device A, device B and device C. 
         [0024]    Four control lines can control three individual EWOD devices (devices A, B, and C shown in  FIG. 3A ). There are six unique combinations of the control lines, and each device has two combinations. 
         [0025]    As an example, if the droplet were to be at the right in device A ( FIG. 3A ) the input would be electrically connected to output  2 . Then, if input pair  1 , 2  were to be made active, device A would switch. However, on device B, since lines  1  and  2  are on different throws, the metallic droplet will not move from its existing position whether it be on the right or on the left. The same goes for device C where inputs  1  and  2  are connected to different throws. 
         [0026]    Assume now that device C has its input connected to output  1  (droplet to the left) and it is desired to switch device C. Then input leads  2  and  3  would be activated. Only device C would switch because in devices A and B activation of the  2 ,  3  inputs applies bias to opposite throw positions. 
         [0027]    The mathematical formula relating the number of individually controllable switches N, to the number of control lines n, is just the possible pair combinations of n control liens, divided by two (two pairs are required for each device). That is: 
         [0000]    
       
         
           
             
               
                 
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                               n 
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                   Equation 
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         [0000]    where N is the number of controllable devices, and n is the number of control lines. A chart of this expression in terms of the devices shown in  FIG. 3A  is shown in  FIG. 3B . As can be seen, the reduction of control lines is appreciable, particularly for large number of devices on the same die. 
         [0028]    One possible drawback: the sharing of control lines between devices may lead to RF coupling between devices, and may be particularly problematic at high frequencies, even with a high sheet resistance used for the control lines. If ultimate RF performance is required, control lines may not be sharable. This is not an issue for low frequency devices. 
         [0029]    Another possible drawback: if the number of control lines is reduced using the expression above, the devices can only be switched sequentially; groups of switches cannot be switched simultaneously. This will slow the reconfiguration of switching networks. It may be that some intermediate reduction of control lines is employed, providing some degree of simultaneous switching of multiple devices. In some applications, devices will always switch together—the tip and ring in a telephone copper pair, for example. In this case independence is not required. The choice of the level of reduction of control lines will be application specific. 
         [0030]    It should be noted that other physical electrode configurations are possible, but that still can be seen as electrode pairs, with a left pair and a right pair, with each electrode in a pair have about the same area. 
         [0031]      FIG. 4A  illustrates one embodiment of a switching strategy for five switches (device A through device E) of the type discussed with respect to  FIG. 2 . 
         [0032]      FIG. 4B  is a chart showing which pair of control leads of the devices shown in  FIG. 4A  must be made active to cause a particular device to switch. Thus, in the example shown, in order to move the droplet of device E from right to left, (switch the input of device E to output  1  from output  2 ) control lines  2  and  3  must be active and all other control lines must be inactive. To move the droplet of device E from left to right, control lines  4  and  5  must become active and all other control lines must be inactive. 
         [0033]    Note that while not shown in  FIG. 3A  or  4 A, the similarly numbered control lines from each device are electrically common and only one physical lead need extend from the combined device package for each numbered control line. Thus, in  FIG. 3A  only four control lines need exit the package while in  FIG. 4A  five lines will extend from the package. Note also that each device has an input and two outputs. The connections to these inputs and outputs (not shown) are separately brought out of the package so that external connection can be made thereto. Thus, for example, in the embodiment of  FIG. 4A , five input RF leads and ten output RF leads would extend from the package. 
         [0034]    This sort of control strategy can work with other switching architectures (e.g., SP3T, SP4T, etc.), provided the correct microfluidic architecture is chosen, along with the appropriate bias voltages and the appropriate formulas relating the number of switches to the minimum number of control lines. 
         [0035]    The electrode pairs are situated side-by-side in the floor of the microfluidic channel, but this disclosure is also relevant to electrode pairs configured top and bottom (in the roof and floor of the microfluidic channel, as seen in other electrowetting devices. This disclosure is also relevant to electrowetting structures where the liquid is in direct electrical contact with one of the electrodes in a pair, with the other electrode buried under a dielectric. Other electrode configurations are possible, as are other multi-throw switches. 
         [0036]    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.