Abstract:
A switch comprises a first switch element configured to actuate by electrowetting, the first switch element comprising at least two radio frequency contacts and at least two control electrodes. The switch also comprises at least two additional switch elements configured to make and break an electrical connection between the at least two control electrodes of the first switch element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Many different technologies have been developed for fabricating switches and relays for low frequency and high frequency switching applications. Many of these technologies rely on solid, mechanical contacts that are alternatively actuated from one position to another to make and break electrical contact. Unfortunately, mechanical switches that rely on solid-solid contact are prone to wear and are subject to a condition known as “fretting.” Fretting refers to erosion that occurs at the points of contact on surfaces. Fretting of the contacts is likely to occur under load and in the presence of repeated relative surface motion. Fretting typically manifests as pits or grooves on the contact surfaces and results in the formation of debris that may lead to shorting of the switch or relay.  
         [0002]     To minimize mechanical damage imparted to switch and relay contacts, switches and relays have been fabricated using liquid metals to wet the movable mechanical structures to prevent solid to solid contact. Unfortunately, as switches and relays employing movable mechanical structures for actuation are scaled to sub-millimeter sizes, challenges in fabrication, reliability and operation begin to appear. Micromachining fabrication processes exist to build micro-scale liquid metal switches and relays that use the liquid metal to wet the movable mechanical structures, but devices that employ mechanical moving parts can be overly-complicated, thus reducing the yield of devices fabricated using these technologies. A liquid metal switch with no mechanical moving parts is disclosed in U.S. patent application Ser. No. 10/996,823, entitled “Liquid Metal Switch Employing Electrowetting For Actuation And Architectures For Implementing Same,” filed on Nov. 24, 2004, assigned to the assignee of the instant application, and is incorporated herein by reference. In the above-identified application, a liquid metal switch is actuated using what is referred to as “electrowetting.” To actuate a liquid metal switch using electrowetting, an electric field is generated in the vicinity of a droplet of electrically conductive liquid. The electric field causes the droplet to deform and translate across a surface. However, a radio frequency (RF) signal that is being switched by the droplet is susceptible to capacitive coupling into the circuitry that controls the electric field in the vicinity of the droplet. Therefore, it would be desirable to prevent the RF signal from capacitively coupling into the control circuitry of the liquid metal switch.  
       SUMMARY OF THE INVENTION  
       [0003]     In accordance with the invention a switch is provided comprising a first switch element configured to actuate by electrowetting, the first switch element comprising at least two radio frequency contacts and at least two control electrodes. The switch also comprises at least two additional switch elements configured to make and break an electrical connection between the at least two control electrodes of the first switch element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0005]      FIG. 1A  is a schematic diagram illustrating a system including a droplet of conductive liquid residing on a solid surface.  
         [0006]      FIG. 1B  is a schematic diagram illustrating the system of  FIG. 1A  having a different contact angle.  
         [0007]      FIG. 2A  is a schematic diagram illustrating one manner in which electrowetting can alter the contact angle between a droplet of conductive liquid and a surface that it contacts.  
         [0008]      FIG. 2B  is a schematic diagram illustrating the system of  FIG. 2A  under an electrical bias.  
         [0009]      FIG. 3A  is a schematic diagram illustrating an embodiment of an electrical switch employing a conductive liquid droplet.  
         [0010]      FIG. 3B  is a schematic diagram illustrating the movement imparted to a droplet of conductive liquid as a result of the change in contact angle due to electrowetting.  
         [0011]      FIG. 3C  is a schematic diagram illustrating the switch of  FIG. 3A  after the application of an electrical potential.  
         [0012]      FIG. 4A  is a schematic diagram illustrating a cross-section of a liquid metal switch assembly having an electrically isolated control element according to an embodiment of the invention.  
         [0013]      FIG. 4B  is a schematic diagram illustrating a cross-section of the liquid metal switch assembly of  FIG. 4A  and showing the translation of the droplet of the switch.  
         [0014]      FIG. 4C  is a schematic diagram illustrating a cross-section of the liquid metal switch assembly of  FIG. 4B  and showing the completed translation of the droplet of the switch.  
         [0015]      FIG. 5  is a flowchart illustrating an embodiment of the operation of the liquid metal switch of  FIGS. 4A, 4B  and  4 C. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     The switch structure described below can be used in any application where it is desirable to provide fast, reliable switching. While described below as switching a radio frequency (RF) signal, the architecture can be used for other switching applications.  
         [0017]     Prior to describing embodiments of the invention, a brief description of the use of electrowetting to move a droplet of conductive liquid will be provided.  FIG. 1A  is a schematic diagram illustrating a system  100  including a droplet of conductive liquid residing on a solid surface. The droplet  104  can be, for example, mercury or a gallium alloy, and resides on a surface  108  of a solid  102 . A contact angle, also referred to as a wetting angle, is formed where the droplet  104  meets the surface  108 . The contact angle is indicated as θ and is measured at the point at which the surface  108 , liquid  104  and gas  106  meet. The gas  106  can be, in this example, air, or another gas that forms the atmosphere surrounding the droplet  104 . A high contact angle, as shown in  FIG. 1A , is formed when the droplet  104  contacts a surface  108  that is referred to as relatively non-wetting, or less wettable. The wettability is generally a function of the material of the surface  108  and the material from which the droplet  104  is formed, and is specifically related to the surface tension of the liquid.  
         [0018]      FIG. 1B  is a schematic diagram  130  illustrating the system  100  of  FIG. 1A  having a different contact angle than the contact angle shown in  FIG. 1A . In  FIG. 1B , the droplet  134  is more wettable with respect to the surface  108  than the droplet  104  with respect to the surface  108 , and therefore forms a lower contact angle, referred to as θ′. As shown in  FIG. 1B , the droplet  134  is flatter and has a lower profile than the droplet  104  of  FIG. 1A .  
         [0019]     The concept of electrowetting, which is defined as a change in contact angle with the application of an electrical potential, relies on the ability to electrically alter the contact angle that a conductive liquid forms with respect to a surface with which the conductive liquid is in contact. In general, the contact angle between a conductive liquid and a surface with which it is in contact ranges between 0° and 180°.  
         [0020]      FIG. 2A  is a schematic diagram  200  illustrating one manner in which electrowetting can alter the contact angle between a droplet of conductive liquid and a surface that the droplet contacts. In  FIG. 2A , a droplet  210  of conductive liquid is sandwiched between dielectric  202  and dielectric  204 . The dielectric can be, for example, tantalum oxide, or another dielectric material. An electrode  206  is buried, or otherwise located, within dielectric  202  and an electrode  208  is buried, or otherwise located, within dielectric  204 . The electrodes  206  and  208  are coupled to a voltage source  212 . In  FIG. 2A , the system is electrically non-biased. Under this non-bias condition, the droplet  210  forms a contact angle, referred to as θ 1 , with respect to the surface  205  of the dielectric  204  that is in contact with the droplet  210 . A similar contact angle exists between the droplet  210  and the surface  203  of the dielectric  202 .  
         [0021]      FIG. 2B  is a schematic diagram  230  illustrating the system  200  of  FIG. 2A  under an electrical bias. The voltage source  212  provides a bias voltage to the electrodes  206  and  208 . The voltage applied to the electrodes  206  and  208  creates an electric field through the conductive liquid droplet causing the droplet to move. The movement of the droplet  210  increases the capacitance of the system, thus increasing the stored energy of the system. In this example, the contact angle of the droplet  240  is altered with respect to the contact angle of the droplet  210 . The new contact angle is referred to as θ 2 , and is a result of the electric field created between the electrodes  206  and  208  and the droplet  240 .  
         [0022]     It is typically desirable to isolate the droplet from the electrodes, and thus allow the droplet to become part of a capacitive circuit. The application of an electrical bias as shown in  FIG. 2B , makes the surface  205  of the dielectric  204  and the surface  203  of the dielectric  202  more wettable with respect to the droplet  240  than the no-bias condition shown in  FIG. 2A . Although the surface tension of the liquid that forms the droplet  240  resists the electrowetting effect, the contact angle changes as a result of the creation of the electric field between the electrodes  206  and  208 . As will be described below, the change in the contact angle alters the curvature of the droplet and leads to translational movement of the droplet.  
         [0023]      FIG. 3A  is a schematic diagram illustrating an embodiment of an electrical switch  300  employing a conductive liquid droplet. The switch  300  includes a dielectric  302  having a surface  303  forming the floor of the switch, and a dielectric  304  having a surface  305  that forms the roof of the switch. A droplet  310  of a conductive liquid is sandwiched between the dielectric  302  and the dielectric  304 .  
         [0024]     The dielectric  302  includes an electrode  306  and an electrode  312 . The dielectric  304  includes an electrode  308  and an electrode  314 . The electrodes  306  and  312  are buried within the dielectric  302  and the electrodes  308  and  314  are buried within the dielectric  304 . In this example, and to induce the droplet  310  to move toward the electrodes  312  and  314 , the electrodes  306  and  308  are coupled to an electrical return path  316  and are electrically isolated from electrodes  312  and  314 , and the electrodes  312  and  314  are coupled to a voltage source  326 . Alternatively, to induce the droplet  310  to move toward the electrodes  306  and  308 , the electrodes  312  and  314  can be coupled to an isolated electrical return path and the electrodes  306  and  308  can be coupled to a voltage source.  
         [0025]     In this example, the switch  300  includes electrical contacts  318 ,  322 , and  324  positioned on the surface  303  of the dielectric  302 . In this example, the contact  318  can be referred to as an input, and the contacts  322  and  324  can be referred to as outputs. As shown in  FIG. 3A , the droplet  310  is in electrical contact with the input contact  318  and the output contact  322 . Further, in this example, the droplet  310  will always be in contact with the input contact  318 .  
         [0026]     As shown in  FIG. 3A  as a cross section, the droplet  310  includes a first radius, r 1 , and a second radius, r 2 . When electrically unbiased, i.e., when there is zero voltage supplied by the voltage source  326 , the curvature of the radius r 1  equals the curvature of the radius r 2  and the droplet is at rest. The radius of curvature, r, of the droplet is defined as  
             r   =     d       cos   ⁢           ⁢     θ   top       +     cos   ⁢           ⁢     θ   bottom                   Eq   .           ⁢   1             
 
 where d is the distance between the surface  303  of the dielectric  302  and the surface  305  of the dielectric  304 , cos θ top  is the contact angle between the droplet  310  and the surface  305 , and cos θ bottom  is the contact angle between the droplet  310  and the surface  303 . Therefore, as shown in  FIG. 3A , the droplet  310  is at rest whereby the radius r 1  equals the radius r 2 , where the curvatures are in opposing directions 
 
         [0027]     Upon application of an electrical potential via the voltage source  326 , a new contact angle between the droplet  310  and the surfaces  303  and  305  is defined. The following equation defines the new contact angle.  
               cos   ⁢           ⁢     θ   ⁡     (   V   )         =       cos   ⁢           ⁢     θ   o       +       ɛ     2   ⁢           ⁢   γ   ⁢           ⁢   t       ⁢     V   2                 Eq   .           ⁢   2             
 
         [0028]     Equation 2 is referred to as Young-Lipmann&#39;s Equation, where the new contact angle, cos θ (V), is determined as a finction of the applied voltage. In equation  2 , ε is the dielectric constant of the dielectrics  302  and  304 , γ is the surface tension of the liquid, t is the dielectric thickness, and V is the voltage applied to the electrode with respect to the conductive liquid. Therefore, to change the contact angle of the droplet  310  with respect to the surfaces  303  and  305  a voltage is applied to electrodes  314  and  312 , thus altering the profile of the droplet  310  so that r 1  is not equal to r 2 . If r 1  is not equal to r 2 , then the pressure, P, on the droplet  310  changes according to the following equation.  
             P   =     γ   ⁡     (       1     r   1       +     1     r   2         )               Eq   .           ⁢   3             
 
         [0029]      FIG. 3B  is a schematic diagram illustrating the movement imparted to a droplet of conductive liquid as a result of the pressure change of the droplet  310  caused by the reduction in contact angle due to electrowetting. When a voltage is applied to the electrodes  314  and  312  by the voltage source  326 , the contact angle of the droplet  310  with respect to the surfaces  303  and  305  in  FIG. 3A  is reduced so that r 1  does not equal r 2 . When the radii r 1  and r 2  differ, a pressure differential is induced across the droplet, thus causing the droplet to translate across the surfaces  303  and  305 .  
         [0030]      FIG. 3C  is a schematic diagram  330  illustrating the switch  300  of  FIG. 3A  after the application of a voltage. As shown in  FIG. 3C , the droplet  310  has moved and now electrically connects the input contact  318  and the output contact  324 . In this manner, electrowetting can be used to induce translational movement in a conductive liquid and can be used to switch electronic signals.  
         [0031]     Additional description of the fabrication of the switch  300  employing a conductive liquid droplet, including tailoring of the contact angle of the droplet, can be found in the above-identified U.S. patent application Ser. No. 10/996,823.  
         [0032]      FIG. 4A  is a schematic diagram illustrating a cross-section of a liquid metal switch assembly having an electrically isolated control element according to an embodiment of the invention. The switch assembly  400  comprises a switch  300  and, in this embodiment, four isolation switches  410 ,  420 ,  430  and  440  located on a dielectric  402 . In this example, the switch  300  is a single pole double throw (SPDT) switch and is sometimes referred to as an RF switch because it can be used to switch RF signals. The switches  410 ,  420 ,  430  and  440  are single pole single throw (SPST) switches and are referred to as “isolation” switches because they electrically isolate the control lines that supply the signal which causes the switch  300  to actuate from the electrical contacts  318 ,  322  and  324  associated with the switch  300 . The dielectric  402  is similar to the dielectrics described above. However, in this embodiment, the dielectric  402  is illustrated as a single dielectric in which the switch  300  and the isolation switches  410 ,  420 ,  430  and  440  are located.  
         [0033]     The switch  300  includes electrodes  306 ,  308 ,  312  and  314  as described above and a cavity  315 , through which a droplet  310  of conductive liquid translates. The isolation switch  410  includes electrodes  411 ,  412 ,  413  and  414 ; the isolation switch  420  includes electrodes  421 ,  422 ,  423  and  424 ; the isolation switch  430  includes electrodes  431 ,  432 ,  433  and  434 ; and the isolation switch  440  includes electrodes  441 ,  442 ,  443  and  444 . The control lines associated with the electrodes of isolation switches  410 ,  420 ,  430  and  440  are omitted for simplicity. The isolation switch  410  includes a cavity  450  through which a droplet  419  of conductive liquid translates. The isolation switch  420  includes a cavity  460  through which a droplet  429  of conductive liquid translates; the isolation switch  430  includes a cavity  470  through which a droplet  439  of conductive liquid translates; and the isolation switch  440  includes a cavity  480  through which a droplet  449  of conductive liquid translates. The isolation switches  410 ,  420 ,  430  and  440  operate in similar manner to the switch  300  described above. Alternatively, the isolation switches  410 ,  420 ,  430  and  440  may be actuated in a manner that does not use the electrowetting effect. For example, the isolation switches  410 ,  420 ,  430  and  440  may be actuated using heating elements that cause a confined gas to expand and cause the droplet of conductive liquid to move.  
         [0034]     Electrode  308  is coupled to control line  417 ; electrode  306  is coupled to control line  427 ; electrode  314  is coupled to control line  437  and electrode  312  is coupled to control line  447 . The control line  417  is terminated in the chamber  418  of the isolation switch  410  in a manner such that when the droplet  419  translates through the cavity  450  to occupy the chamber  418 , the droplet  419  will be in electrical contact with the control line  417 . A control line  416  is also terminated in the chamber  418  of the isolation switch  410  in a manner such that when the droplet  419  translates through the cavity  450  to occupy the chamber  418 , the droplet will be in electrical contact with the control line  416 . In this manner, when the droplet occupies the chamber  418 , the droplet  419  completes an electrical connection between the control lines  416  and  417 . Similarly, the control line  427  is terminated in the chamber  428  of the isolation switch  420  in a manner such that when the droplet  429  translates through the cavity  460  to occupy the chamber  428 , the droplet  429  will be in electrical contact with the control line  427 . A control line  426  is also terminated in the chamber  428  of the isolation switch  420  in a manner such that when the droplet  429  translates through the cavity  460  to occupy the chamber  428 , the droplet  429  will be in electrical contact with the control line  426 . In this manner, the droplet  429  completes an electrical connection between the control lines  426  and  427 . The electrodes  312  and  314  are similarly coupled to isolation switches  430  and  440 .  
         [0035]     The control lines  416  and  426 ; and the control lines  436  and  446  can be coupled to a voltage source, such as the voltage source  326  described above. In this embodiment, the voltage source  326  can also be referred to as a control circuit, or control circuitry, that causes the droplet  310  to translate in the cavity  315  when the droplets  419  and  429 ; and the droplets  439  and  449  couple the voltage source  326  to the electrodes  306  and  308 , or electrodes  312  and  314 .  
         [0036]     In accordance with an embodiment of the invention, when the droplets  419 ,  429 ,  439  and  449  are located as shown in  FIG. 4A , the control signals that are coupled to control lines  416 ,  426 ,  436  and  446  are electrically isolated from the electrical contacts  318 ,  322  and  324  associated with switch  300 . In this manner, capacitive coupling between the electrical contacts  318 ,  322  and  324  and the electrodes  306 ,  308 ,  312  and  314  is minimized, and substantially eliminated.  
         [0037]      FIG. 4B  is a schematic diagram illustrating a cross-section of the liquid metal switch assembly  400  and showing the translation of the droplet  310  of the switch  300 . The droplet  419  of the isolation switch  410  and the droplet  429  of the isolation switch  420  have translated through their respective cavities  450  and  460  and latched. By selecting the material of the droplet, the shape of the cavity in which the droplet translates and the material applied to surfaces of the cavity in which the droplet translates, it is possible to tailor the initial contact angle to ensure latching of the droplets, as more fully described in the above-identified U.S. patent application Ser. No. 10/996,823.  
         [0038]     When the droplet  419  translates through the cavity  450 , the droplet  419  completes an electrical connection between the control line  416  and the control line  417 . In this manner, an electrical control signal is delivered to the electrode  308  of the RF switch  300 . The electrical control signals and control lines that cause the droplet  419  to translate through the cavity  450  are omitted for simplicity. The droplet  419  is caused to move as described above with respect to  FIGS. 2A , and  2 B; and  FIGS. 3A, 3B  and  3 C. After the droplet  419  latches, the control signal that caused the droplet to translate may be removed. By latches is meant that once the droplet translates through the cavity  450  it remains there until it is caused to translate in the opposite direction.  
         [0039]     Similarly, when the droplet  429  translates through the cavity  460 , the droplet  429  completes an electrical connection between the control line  426  and the control line  427 . In this manner, an electrical control signal is delivered to the electrode  312  of the switch  300 . The electrical control signals and control lines that cause the droplet  429  to translate through the cavity  460  are omitted for simplicity. The droplet  429  is caused to move as described above with respect to  FIGS. 2A , and  2 B; and  FIGS. 3A, 3B  and  3 C. When the control signal is delivered to the electrodes  308  and  312  of the switch  300 , the droplet  310  is caused to translate through the cavity  315  as illustrated by the arrow  317 . When the droplet  310  translates through the cavity  315 , an RF signal supplied to electrical contact  318  can be switched from output electrical contact  324  to output electrical contact  322 . In this example, only the isolation switches  410  and  420  are actuated. If it is desired to translate the droplet  310  in the opposite direction, then isolation switches  430  and  440  are actuated in a similar manner to that described with respect to isolation switches  410  and  420 .  
         [0040]      FIG. 4C  is a schematic diagram illustrating a cross-section of the liquid metal switch assembly  400  and showing the completed translation of the droplet  310  of the switch  300 . After the droplet  310  has translated through the cavity  315  and has switched the RF signal from output electrical contact  324  to output electrical contact  322 , the isolation switches  410  and  420  are again actuated. The isolation switch  410  is actuated to translate the droplet  419  back to its position as shown in  FIG. 4A . In this manner, the electrical circuit coupling the electrode  308  to the control line  416  is broken, thus presenting a high impedance and electrically isolating the control line  417  and preventing electrical coupling of the RF signal from the electrical contacts  318  or  322  into the control line  416 . Similarly, the isolation switch  420  is actuated to translate the droplet  429  back to its position as shown in  FIG. 4A . In this manner, the electrical circuit coupling the electrode  306  to the control line  426  is broken, thus presenting a high impedance and electrically isolating the control line  427  and preventing electrical coupling of the RF signal from the electrical contacts  318  or  322  into the control line  426 .  
         [0041]     The isolation switches  430  and  440  can be actuated as described above with respect to isolation switches  410  and  420  to cause the RF switch  300  to again actuate and translate the droplet  310  in the opposite direction.  
         [0042]      FIG. 5  is a flowchart  500  illustrating an embodiment of the operation of the liquid metal switch of  FIGS. 4A, 4B  and  4 C. In block  502 , the isolation switches  410  and  420  are actuated to connect the electrodes  306  and  308  of the switch  300  to control lines  426  and  416 , respectively. In block  504 , the control circuit causes the switch  300  to change state by translating through the cavity  315 .  
         [0043]     In block  506 , the isolation switches  410  and  420  are actuated to electrically disconnect the electrodes  306  and  308  of the switch  300  from the control lines  426  and  416 , respectively. In block  508 , the electrical contacts  318 ,  322  and  324  of the switch  300  are electrically isolated from the control lines  416  and  426  because the electrodes  306  and  308  no longer have an electrical connection path to the control lines  426  and  416 , respectively.  
         [0044]     This disclosure describes the invention in detail using illustrative embodiments. However, it is to be understood that the invention defined by the appended claims is not limited to the precise embodiments described.