Patent Publication Number: US-6903493-B2

Title: Inserting-finger liquid metal relay

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to the following co-pending U.S. Patent Applications, being identified by the below enumerated identifiers and arranged in alphanumerical order, which have the same ownership as the present application and to that extent are related to the present application and which are hereby incorporated by reference: 
   Application 10010448-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/137,691; 
   Application 10010529-1, “Bending Mode Latching Relay”, and having the same filing date as the present application; 
   Application 10010531-1, “High Frequency Bending Mode Latching Relay”, and having the same filing date as the present application; 
   Application 10010570-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/142,076; 
   Application 10010571-1, “High-frequency, Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application; 
   Application 10010572-1, “Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application; 
   Application 10010573-1, “Insertion Type Liquid Metal Latching Relay”, and having the same filing date as the present application; 
   Application 10010617-1, “High-frequency, Liquid Metal, Latching Relay Array”, and having the same filing date as the present application; 
   Application 10010618-1, “Insertion Type Liquid Metal Latching Relay Array”, and having the same filing date as the present application; 
   Application 10010634-1, “Liquid Metal Optical Relay”, and having the same filing date as the present application; 
   Application 10010640-1, titled “A Longitudinal Piezoelectric Optical Latching Relay”, filed Oct. 31, 2001 and identified by Ser. No. 09/999,590; 
   Application 10010643-1, “Shear Mode Liquid Metal Switch”, and having the same filing date as the present application; 
   Application 10010644-1, “Bending Mode Liquid Metal Switch”, and having the same filing date as the present application; 
   Application 10010656-1, titled “A Longitudinal Mode Optical Latching Relay”, and having the same filing date as the present application; 
   Application 10010663-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application; 
   Application 10010664-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
   Application 10010790-1, titled “Switch and Production Thereof”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,597; 
   Application 10011055-1, “High Frequency Latching Relay with Bending Switch Bar”, and having the same filing date as the present application; 
   Application 10011056-1, “Latching Relay with Switch Bar”, and having the same filing date as the present application; 
   Application 10011064-1, “High Frequency Push-mode Latching Relay”, and having the same filing date as the present application; 
   Application 10011065-1, “Push-mode Latching Relay”, and having the same filing date as the present application; 
   Application 10011121-1, “Closed Loop Piezoelectric Pump”, and having the same filing date as the present application; 
   Application 10011329-1, titled “Solid Slug Longitudinal Piezoelectric Latching Relay”, filed May 2, 2002 and identified by Ser. No. 10/137,692; 
   Application 10011344-1, “Method and Structure for a Slug Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application; 
   Application 10011345-1, “Method and Structure for a Slug Assisted Longitudinal Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
   Application 10011397-1, “Method and Structure for a Slug Assisted Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
   Application 10011398-1, “Polymeric Liquid Metal Switch”, and having the same filing date as the present application; 
   Application 10011410-1, “Polymeric Liquid Metal Optical Switch”, and having the same filing date as the present application; 
   Application 10011436-1, “Longitudinal Electromagnetic Latching Optical Relay”, and having the same filing date as the present application; 
   Application 10011437-1, “Longitudinal Electromagnetic Latching Relay”, and having the same filing date as the present application; 
   Application 10011458-1, “Damped Longitudinal Mode Optical Latching Relay”, and having the same filing date as the present application; 
   Application 10011459-1, “Damped Longitudinal Mode Latching Relay”, and having the same filing date as the present application; 
   Application 10020013-1, titled “Switch and Method for Producing the Same”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,963; 
   Application 10020027-1, titled “Piezoelectric Optical Relay”, filed Mar. 28, 2002 and identified by Ser. No. 10/109,309; 
   Application 10020071-1, titled “Electrically Isolated Liquid Metal Micro-Switches for Integrally Shielded Microcircuits”, filed Oct. 8, 2002 and identified by Ser. No. 10/266,872; 
   Application 10020073-1, titled “Piezoelectric Optical Demultiplexing Switch”, filed Apr. 10, 2002 and identified by Ser. No. 10/119,503; 
   Application 10020162-1, titled “Volume Adjustment Apparatus and Method for Use”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,293; 
   Application 10020241-1, “Method and Apparatus for Maintaining a Liquid Metal Switch in a Ready-to-Switch Condition”, and having the same filing date as the present application; 
   Application 10020242-1, titled “A Longitudinal Mode Solid Slug Optical Latching Relay”, and having the same filing date as the present application; 
   Application 10020473-1, titled “Reflecting Wedge Optical Wavelength Multiplexer/Demultiplexer”, and having the same filing date as the present application; 
   Application 10020540-1, “Method and Structure for a Solid Slug Caterpillar Piezoelectric Relay”, and having the same filing date as the present application; 
   Application 10020541-1, titled “Method and Structure for a Solid Slug Caterpillar Piezoelectric Optical Relay”, and having the same filing date as the present application; 
   Application 10030440-1, “Wetting Finger Liquid Metal Latching Relay”, and having the same filing date as the present application; 
   Application 10030521-1, “Pressure Actuated Optical Latching Relay”, and having the same filing date as the present application; 
   Application 10030522-1, “Pressure Actuated Solid Slug Optical Latching Relay”, and having the same filing date as the present application; and 
   Application 10030546-1, “Method and Structure for a Slug Caterpillar Piezoelectric Reflective Optical Relay”, and having the same filing date as the present application. 

   FIELD OF THE INVENTION 
   The invention relates to the field of micro-electromechanical systems (MEMS) for electrical switching, and in particular to an actuated liquid metal relay. 
   BACKGROUND 
   Liquid metals, such as mercury, have been used in electrical switches to provide an electrical path between two conductors. An example is a mercury thermostat switch, in which a bimetal strip coil reacts to temperature and alters the angle of an elongated cavity containing mercury. The mercury in the cavity forms a single droplet due to high surface tension. Gravity moves the mercury droplet to the end of the cavity containing electrical contacts or to the other end, depending upon the angle of the cavity. In a manual liquid metal switch, a permanent magnet is used to move a mercury droplet in a cavity. 
   Liquid metal is also used in relays. A liquid metal droplet can be moved by a variety of techniques, including electrostatic forces, variable geometry due to thermal expansion/contraction and magneto-hydrodynamic forces. 
   Rapid switching of high currents is used in a large variety of devices, but provides a problem for solid-contact based relays because of arcing when current flow is disrupted. The arcing causes damage to the contacts and degrades their conductivity due to pitting of the electrode surfaces. 
   Micro-switches have been developed that use liquid metal as the switching element and the expansion of a gas when heated to move the liquid metal and actuate the switching function. Liquid metal has some advantages over other micro-machined technologies, such as the ability to switch relatively high powers (about 100 mW) using metal-to-metal contacts without micro-welding or overheating the switch mechanism. However, the use of heated gas has several disadvantages. It requires a relatively large amount of energy to change the state of the switch, and the heat generated by switching must be dissipated effectively if the switching duty cycle is high. In addition, the actuation rate is relatively slow, the maximum rate being limited to a few hundred Hertz. 
   SUMMARY 
   An electrical relay array is disclosed that uses a conducting liquid in the switching mechanism. The relay uses a piezoelectric element to cause a switch finger to prevent or permit the formation of a conducting liquid bridge between two fixed electrical contacts. The relay array is amenable to manufacture by micro-machining techniques. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the claims. The invention itself, however, as well as the preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawing(s), wherein: 
       FIG. 1  is a side view of a relay in accordance with certain embodiments of the present invention. 
       FIG. 2  is a top view of a relay in accordance with certain embodiments of the present invention. 
       FIG. 3  is a sectional view of a relay in accordance with certain embodiments of the present invention. 
       FIG. 4  is a sectional view of a relay in accordance with certain embodiments of the present invention in a closed state. 
       FIG. 5  is a top view of a relay in a closed state in accordance with certain embodiments of the present invention. 
       FIG. 6  is a top view of a relay in an open state in accordance with certain embodiments of the present invention. 
       FIG. 7  is a sectional view of a relay in an open state in accordance with certain embodiments of the present invention. 
       FIG. 8  is a top view of a circuit substrate of a relay in accordance with certain embodiments of the present invention. 
       FIG. 9  is a side view of a circuit substrate of a relay in accordance with certain embodiments of the present invention. 
       FIG. 10  is a top view of a relay in a closed state in accordance with certain embodiments of the present invention. 
       FIG. 11  is a sectional view of a relay in accordance with certain embodiments of the present invention. 
       FIG. 12  is a top view of a relay in an open state in accordance with certain embodiments of the present invention. 
       FIG. 13  is a top view of a circuit substrate of a relay in accordance with certain embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings. 
   The present invention relates to an electrical relay is which the formation of a conducting liquid bridge between two fixed contacts is prevented or permitted by action of a non-conducting, non-wettable finger. The conducting liquid may be a liquid metal, such as mercury. The finger is attached to one end of a beam, the other end of the beam is fixed to the substrate of the relay. The beam and the attached finger are moved by the action of one or more piezoelectric elements acting on the beam. The piezoelectric elements may operate in bending or extensional modes. Magnetorestrictive actuators, such as Terenol-D, that deform in the presence of a magnetic field may be used as an alternative to piezoelectric actuators. In the sequel, piezoelectric actuators and magnetorestrictive actuators will be collectively referred to as “piezoelectric actuators”. 
     FIG. 1  is a side view of an exemplary embodiment of a relay of the present invention. The relay has three layers: a cap layer  102 , a piezoelectric layer  104  and a substrate layer  106 . The substrate layer  106  supports electrical connections  108  to the switch, electrical connections  110  to the piezoelectric actuator and the associated circuitry. These three layers form a relay housing. 
     FIG. 2  is a top view of the relay in FIG.  1 . The broken lines indicate hidden structure including the moveable beam  112  and the switch finger  114  that is attached to the free end of the beam  112 . These elements are positioned within a switching cavity  116  in the piezoelectric layer of the relay. Also shown are two electrical contacts  118  and  120  that have wettable surfaces supporting droplets of conducting liquid. The sections  3 — 3  and  4 — 4  will be described below with reference to FIG.  3  and  FIG. 4  respectively. 
     FIG. 3  is a sectional view through the section  3 - 3  in FIG.  2 . The moveable beam  112  is fixed at one end to the substrate of the piezoelectric layer  104 . The free end of the beam supports the switch finger  114 . These elements are positioned within the switching cavity  116 . The contact  120  is attached via a non-wettable pad  124  to the substrate  106 . The other contact ( 118  in  FIG. 2 ) is attached via a non-wettable pad  122  to the substrate  106 . The electrical contacts are positioned within a recess in the switching cavity. The contacts have a wettable surface that supports a volume of conducting liquid  126 . The volume of the conducting liquid is chosen such that the liquid forms a bridge between the contacts, the bridge being maintained by surface tension in the liquid. The contacts are electrically connected to the connectors  108  that allow signal to be routed through the relay. The beam  112  is moved by action of a piezoelectric actuator. Control signals are coupled to the actuator via connectors  110  that are electrically coupled to contact pads  128  in the switching cavity. 
     FIG. 4  is a sectional view through the section  4 - 4  in FIG.  2 . The switch finger  114  is attached to the free end of the moveable beam  112  and is partially inserted into the conducting liquid volume  126 . The conducting liquid  126  fills the gap between the two electrical contacts, but does not wet the non-wettable pad  124 . In this embodiment, the beam  112  is moved by action of a piezoelectric element  130  attached to the side of the beam and operable to bend the beam. 
     FIG. 5  is a top view of a relay with the cap layer  102  removed. The switch is in a closed state, since the liquid metal bridges the gap between the electrical contacts. In this embodiment, the moveable beam  112  is acted upon by one or two piezoelectric elements  130  and  132  attached to the sides of the beam. Extension of the piezoelectric element  130  along the length of the beam or contraction of the piezoelectric element  132  along the length of the beam will cause the beam to bend such that the free end of the beam, and the attached switch finger, moves in the direction indicated by the arrow  134 . The piezoelectric elements may be used alone or in concert. Control signals to the piezoelectric elements are provided via contact pads  128 . 
     FIG. 6  is a top view of a relay with the cap layer  102  removed. The switch is in an open state. The beam  112  has been bent by action of the piezoelectric elements  130  and  132 , causing the switch finger  114  to insert into the conducting liquid volume  126 and to separate the volume into two parts. This breaks the electrical connection between the two electrical contacts and opens the circuit. The switch finger is non-wettable and non-conductive. 
     FIG. 7  is sectional view through the section  7 — 7  in FIG.  6 . The free end of the beam  112  has been displaced vertically in the figure relative to its position in FIG.  4 . The switch finger  114  has been fully inserted into the conducting liquid volume  126 , separating the volume into two parts and breaking the electrical connection. 
   In this embodiment of the invention, the circuit between the electrical contacts is complete unless the actuator is energized. In a further embodiment of the invention, the switch finger separates the conducting liquid volume when the piezoelectric actuator in not energized, and is partially withdrawn when the actuator is energized to complete the electrical circuit. In this further embodiment, the circuit between the electrical contacts is broken unless the actuator is energized. 
     FIG. 8  is a top view of a substrate layer  106  of a relay. Two electrical contacts  118  and  120  are fixed to non-wettable pads that are in turn fixed to the substrate  106 . Electrical pads  128  provide electrical connections to the piezoelectric elements. The pads and contacts may be formed on the substrate using known micro-machining techniques. 
   A side view of the circuit substrate is shown in FIG.  9 . The electrical contacts  118  and  120  are fixed to non-wettable pads  122  and  124 , respectively, which are in turn fixed to the substrate  106 . The electrical contacts  118  and  120  are electrically coupled to connectors  108  on the external surface of the substrate. Alternatively, the electrical connectors may be connected, via traces on the top of the substrate, to connectors on the edge of the substrate. The electrical pads  128  provide electrical connections to the piezoelectric elements and are electrically coupled to the connectors  110  on the external surface of the substrate. 
     FIG. 10  is a top view of an alternative embodiment of the relay with the cap layer  102  removed. The switch is in a closed state. In this embodiment, the moveable beam  112  is acted upon by a piezoelectric actuator  140  attached to a side of the switching channel  116 . Extension of the piezoelectric element  140  in the plane of the layer and perpendicular to the beam moves the beam in the direction indicated by the arrow  134 . In this embodiment, the piezoelectric actuator is positioned closer to the fixed end of the beam than to the free end. In this configuration, the beam amplifies the motion of the piezoelectric element, thereby producing a larger displacement of the switch finger  114 . Other forms of mechanical amplification may be used. Control signals are supplied to the piezoelectric element via the pads  128  and the contacts  142  and  144 . The piezoelectric actuator  140  may comprise a single piezoelectric element or a stack of piezoelectric elements. 
     FIG. 11  is a sectional view through the section  11 - 11  in FIG.  10 . The piezoelectric element  140  is coupled via the contact  142  to the substrate  104 , and via the contact  144  to the beam  112 . When a voltage is applied across the piezoelectric element it deforms in an extensional mode (the vertical direction in the figure) and acts laterally on the beam  112 . This, in turn, moves the switch finger  114 . 
     FIG. 12  is a top view of the relay in  FIG. 10  showing the switch is in an open state. The piezoelectric element  140  has been energized and displaces the beam  112  laterally. This has moved the switch finger  114  into to volume of conducting fluid  126 , separating it into two volumes and breaking the electrical circuit between the electrical contacts. 
     FIG. 13  is a top view of a substrate layer  106  of the relay shown in  FIGS. 10 ,  11  and  12 . Two electrical contacts  118  and  120  are fixed to non-wettable pads that are in turn fixed to the substrate  106 . Electrical pads  128  provide electrical connections to the two ends of the piezoelectric element. The pads and contacts may be formed on the substrate using known micro-machining techniques. 
   While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.