Patent Publication Number: US-7212091-B2

Title: Micro-electro-mechanical RF switch

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional application of U.S. Ser. No. 10/150,285 filed on May 17, 2002 now U.S. Pat. No. 6,876,282 the disclosure of which is incorporated herein by its reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to RF switches, and more particularly, to single-pole, multi-throw (micro-electro-mechanical) MEMS RF switches. 
   2. Prior Art 
   MEMS switches are called as such because they use electrostatic actuation to create movement of a beam or membrane that results in an ohmic contact (i.e. an RF signal is allowed to pass-through) or by a change in capacitance by which the flow of signal is interrupted and typically grounded. 
   In a wireless transceiver, pin diodes or GaAs MESFET&#39;s are used as switches. However, these have high power consumption rates, high losses (typically 1 dB insertion loss at 2 GHz), and are non-linear devices. MEMS switches on the other hand, have demonstrated insertion loss of less than 0.5 dB, are highly linear, and have very low power consumption since they use a DC voltage for electrostatic actuation. If the actuators are coupled to the RF signal in a series switch, then the DC bias would need to be decoupled from the RF signal. Usually, the DC current for the pin diodes in conventional switches is handled in the same way. Decoupling is never 100% and there are always some losses to the RF signal power either by adding resistive losses or by direct leakage. Another source of losses is capacitive coupling of actuators to the RF signal (especially when a series switch is closed). If high power is fed through the switch, then a voltage drop of about 10V is associated with the RF signal. That voltage is present at the RF electrode of the series switches in the open state. If these electrodes are also part of the closing mechanism (by comprising one of the actuator electrodes) that could cause the switches to close and thus limit the switch linearity (generate harmonics etc.). Usually transistor switches such as CMOS or FET suffer from non-linearity and high losses. 
   U.S. Pat. No. 5,619,061 to Goldsmith et al. has shown designs of MEMS switches comprised of metal and dielectric films for both capacitive coupling and ohmic contact but the metal films and the designs proposed by their invention rely on thin metal films either on top or below a beam made out of a dielectric material. A disadvantage of this type of switch is that unless the beam is made out of a single metal, there is no effective heat dissipation mechanism due to the Joule heating effect generated by the a high power RF signal that may go through. 
   SUMMARY OF THE INVENTION 
   Therefore, it is an object of the present invention to provide a single-pole, multi-throw MEMS RF switch that minimizes losses and improves on switch linearity as compared to the MEMS RF switches of the prior art. 
   It is another object of the present invention to provide a single-pole, multi-throw MEMS RF switch that improves heat dissipation as compared to the MEMS RF switches of the prior art. 
   Accordingly, a microelectromechanical switch is provided. The microelectromechanical switch comprises: at least one pair of actuator electrodes; at least one input electrode and at least one output electrode for input and output, respectively, of a radio frequency signal; and a beam movable by an attraction between the at least one pair of actuator electrodes, the movable beam having at least a portion electrically connected to the at least one input electrode and to the at least one output electrode when moved by the attraction between the at least one pair of actuator electrodes to make an electrical connection between the at least one input and output electrodes; wherein the at least one pair of actuator electrodes are electrically isolated from each of the at least one input and output electrodes. 
   Also provided is a microelectromechanical switch comprising: a first level portion having a first electrode for input or output of a radio frequency signal, at least one first actuator electrode electrically isolated from the first electrode, and a first contact electrically cooperating with the first electrode; and a second level portion having at least a portion separated from the first level portion by an air gap, the second level portion having a deflective beam capable of deflecting into the air gap, the beam having at least one second actuator electrode corresponding to the at least one first actuator electrode, the beam further having a second electrode corresponding to the first electrode for the other of the input or output of the radio frequency signal and a second contact electrically cooperating with the second electrode, the at least one second attractive electrode being electrically isolated from the second electrode; wherein creation of an electrical attraction between the at least one first and second actuator electrodes causes the beam to deflect into the air gap and to provide an electrical connection between the first and second contacts and their respective first and second electrodes for allowing the input radio frequency signal to one of the first and second electrodes to be output to the other of the first and second electrodes. 
   Preferably, the at least one first actuator electrode comprises two first actuator electrodes each of which are electrically isolated from the first electrode and wherein the at least one second actuator electrode comprises two second actuator electrodes, each of the two first actuator electrodes corresponding to a respective second actuator electrode when the beam is deflected into the air gap. 
   The microelectromechanical switch preferably further comprises at least one bumper arranged on the first level portion adjacent the first contact for urging contact between the first and second contacts when the beam is deflected into the air gap. More preferably, the at least one bumper comprises first and second bumpers, each of which is arranged on the first level portion adjacent the first contact for urging contact between the first and second contacts when the beam is deflected into the air gap. 
   Preferably, the creation of an electrical attraction between the first and second actuator electrodes comprises means for maintaining one of the first and second actuator electrodes at a ground state and the other of the first and second actuator electrodes energized with an applied voltage. 
   The beam preferably further having a plurality of access holes formed therein for facilitating creation of the air gap and for minimizing air damping during switch operation. 
   The first and second level portions preferably have a width and wherein at least one of the first and second electrodes is aligned in the direction of the width and has a first dimension in the direction of the width which is less than the width. More preferably, each of the first and second electrodes are aligned in the direction of the width and each has the first dimension in the direction of the width which is less then the width. In which case, the microelectromechanical switch preferably further comprises at least one dummy conductor disposed in the direction of the width and electrically isolated from a corresponding first and/or second electrode, the dummy conductor having a second dimension in the direction of the width which is less than the difference between the width and the first dimension. 
   Preferably, at least one of the first and second actuator electrodes are rectangular and wherein at least a portion of the first and second actuator electrodes correspond with each other across the air gap. More preferably, each of the first and second actuator electrodes comprises two first and second actuator electrodes, each of which are rectangular and disposed on both sides of their corresponding first and second electrodes. 
   The microelectromechanical switch of claim  1 , wherein at least one of the second actuator electrodes are triangular having a base and an apex and wherein at least a portion of the first and second actuator electrodes correspond with each other across the air gap. Preferably, each of the first and second actuator electrodes comprises two first and second actuator electrodes, disposed on both sides of their corresponding first and second electrodes. More preferably, the base of each of the second actuator electrodes is proximate the second electrode. 
   Preferably, the microelectromechanical switch of claim  1 , further comprising a ground plate electrically connected to one of the first or second actuator electrodes for grounding one of the first or second actuator electrodes. 
   Still provided is a multiple throw microelectromechanical switch comprising two or more single throw microelectromechanical switches. Each of the single throw microelectromechanical switches comprising: a first level portion having a first electrode for input or output of a radio frequency signal, at least one first actuator electrode electrically isolated from the first electrode, and a first contact electrically cooperating with the first electrode; and a second level portion having at least a portion separated from the first level portion by an air gap, the second level portion having a deflective beam capable of deflecting into the air gap, the beam having at least one second actuator electrode corresponding to the at least one first actuator electrode, the beam further having a second electrode corresponding to the first electrode for the other of the input or output of the radio frequency signal and a second contact electrically cooperating with the second electrode, the at least one second attractive electrode being electrically isolated from the second electrode; wherein creation of an electrical attraction between the at least one first and second actuator electrodes causes the beam to deflect into the air gap and to provide an electrical connection between the first and second contacts and their respective first and second electrodes for allowing the input radio frequency signal to one of the first and second electrodes to be output to the other of the first and second electrodes. 
   The multiple throw microelectromechanical switch preferably further comprises a ground plate electrically connected to one of the first or second actuator electrodes for each of the single throw microelectromechanical switches for grounding the one of the first or second actuator electrodes. The multiple throw microelectromechanical switch more preferably further comprises a substrate upon which is disposed one of the first or second level portions for each of the single throw microelectromechanical switches. The ground plate is preferably a continuous solid plate disposed on a lower surface of the substrate. Where the multiple throw microelectromechanical switch further comprises radio frequency input and output lines disposed on the substrate, one of which is connected to one of the first or second electrodes of each of the single throw microelectromechanical switches and the other of which is connected to the other of the first second electrodes of each of the single throw microelectromechanical switches, the ground plate is alternatively disposed on a lower surface of the substrate only in portions corresponding to the single throw microelectromechanical switches and the radio frequency input and output lines. 
   Still yet provided is a multiple throw microelectromechanical switch comprising two or more single throw microelectromechanical switches. Each of the single throw microelectromechanical switches comprises: at least one pair of actuator electrodes; at least one input electrode and at least one output electrode for input and output, respectively, of a radio frequency signal; and a beam movable by an attraction between the at least one pair of actuator electrodes, the movable beam having at least a portion electrically connected to the at least one input electrode and to the at least one output electrode when moved by the attraction between the at least one pair of actuator electrodes to make an electrical connection between the at least one input and output electrodes; wherein the at least one pair of actuator electrodes are electrically isolated from each of the at least one input and output electrodes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1   a  illustrates a top view of a preferred single-pole single-throw MEMS RF switch having a single contact. 
       FIG. 1   b  illustrates a sectional view of the switch of  FIG. 1   a  taken along line  1   b — 1   b  thereof. 
       FIG. 1   c  illustrates a sectional view of the switch of  FIG. 1   a  taken along line  1   c — 1   c  thereof. 
       FIG. 2  illustrates a top view of the switch of  FIG. 1   a  showing access holes on the beam thereof. 
       FIGS. 3   a  and  3   b  illustrate a sectional view of a MEMS switch and a graph, respectively, showing the Joule heating results thereof. 
       FIG. 4  illustrates a preferred MEMS RF switch where the RF signal line is partly metal and partly dielectric. 
       FIG. 5  illustrates a preferred MEMS RF switch where the RF signal line is composed of two metal segments with a small thickness dielectric in between. 
       FIG. 6  illustrates another preferred implementation of a RF MEMS switch. 
       FIG. 7  illustrates yet another preferred implementation of a RF MEMS switch. 
       FIG. 8  illustrates a top view of a schematic layout of a single-pole double-throw MEMS RF switch according to a preferred implementation. 
       FIG. 9  illustrates a bottom view of the single-pole double-throw MEMS RF switch of  FIG. 8 . 
       FIG. 10  illustrates an alternative bottom view of the single-pole double-throw MEMS RF switch of  FIG. 8 . 
       FIG. 11   a  illustrates a schematic view of paired single-pole, single-throw torsional switches having a single contact according to a preferred implementation. 
       FIG. 11   b  illustrates paired single-pole, single-throw torsional switches of  FIG. 11   a  in which path C–B is completed. 
       FIG. 11   c  illustrates the paired single-pole, single-throw torsional switches of  FIG. 11   a  in which path A–D is completed. 
       FIG. 11   d  illustrates the structure of the pivot point in greater detail. 
       FIG. 12   a  illustrates a schematic view of the paired single-pole, single-throw torsional switches having v-shaped beams with a single contact according to a preferred implementation. 
       FIG. 12   b  illustrates the paired single-pole, single-throw torsional switch of  FIG. 12   a  in which path C–B is completed. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1   a ,  1   b , and  1   c  there is illustrated a single-contact MEMS, generally referred to by reference numeral  100 . The single contact MEMS  100  is electrostatically activated as will be described below. Although the MEMS switch  100  illustrated in  FIGS. 1   a ,  1   b , and  1   c  is a single-pole, single-throw switch, such is given by way of example only and not to limit the scope or spirit of the present invention. Those skilled in the art will realize that multiple pole and/or multiple-throw configurations are also possible, as described below. 
   Referring to  FIG. 1   a , a top schematic view of the MEMS  100  is shown in which a first level portion  102  of the switch  100  is shown with solid areas while a second level portion  104  is shown with hatched areas. In the preferred implementation of the switch  100 , the first level portion  102  is a lower level, while the second level portion  104  is an upper level portion. However, those skilled in the art will appreciate that the switch  100  can be configured with the first and second level portions  102 ,  104  oriented in any manner. The switch further has radio frequency (RF) input and output lines  106 ,  108 . The RF input line  106  is shown as inputting the upper level portion  104  and the RF output line  108  is shown as being output from the lower level portion  102 . However, those skilled in the art will appreciate that the switch  100  can be configured in the reverse orientation (i.e., the RF input line  108  is inputted into the lower level portion  102  and the RF output line  106  is output from the upper level portion  104 ). 
   Referring now to  FIGS. 1   b  and  1   c  there is illustrated a cross-section of the switch  100  of  FIG. 1   a  as taken along line  1   b — 1   b  and  1   c — 1   c , respectively. The lower level portion  102  consists of at least one, and preferably two lower actuator electrodes  110 . The lower actuator electrodes  110  are typically kept at ground potential. The lower level portion  102  further has a lower electrode  112  which acts to input or output the RF signal from the RF input or output lines  106 ,  108 . As illustrated, the lower electrode  112  is electrically connected to the RF output line  108 . The lower actuator electrodes  110  are completely electrically isolated from the lower electrode  112 . Those skilled in the art will appreciate that the separation of the actuator electrodes  110  from the lower electrode which carries the RF signal results in minimizing losses and improving the switch linearity. 
   A first contact  114  is provided and is electrically connected to the lower electrode  112 . The first contact  114  is raised above the top surface of the lower actuator electrodes  110  and first electrode  112 . At least one bumper and preferably two bumpers  116  are disposed above the top surface of the lower actuator electrodes  110  and first electrode  112  and are not necessarily made out of metal and are electrically isolated from the other electrodes  110 ,  112 . As will be discussed below, the bumpers  116  act to prevent stiction between the upper contact  126  and the lower contact  114 . The above-described elements of the lower level portion  102  are formed on a substrate (not shown) by etching and deposition methods known in the art. 
   The upper level portion  104  includes a movable beam  121 , which in the preferred implementation of  FIGS. 1   a ,  1   b , and  1   c  moves by deflecting or bowing towards the lower level portion  102 . The beam  121  comprises upper actuator electrodes  120  which correspond to the lower actuator electrodes  110  across an air gap  122 . The air gap  122  is represented in  FIG. 1   a  by a dotted line, which is referenced with reference numeral  122 . The upper actuator electrodes  120  are preferably rectangular in shape, as are the lower actuator electrodes  110 , and at least a portion corresponds or overlaps with the lower actuator electrodes  110 . As discussed above with regard to the lower actuator electrodes  110  and lower electrode  112 , the upper actuator electrodes  120  and upper electrode  124  are completely electrically isolated from each other. Thus, for the same reason as discussed above, the separation of the actuator electrodes  120  from the upper electrode  124  which carries the RF signal results in minimizing losses and improving the switch linearity. 
   While the lower actuator electrodes  110  are preferably held at a ground potential, the upper actuator electrodes  120  are preferably and selectively held at contact voltage V 1 , to create an attractive electrostatic force between the beam  121  and the lower actuator electrodes  110  that are at ground. The beam  121  further has a upper electrode  124  for carrying the RF signal, which in the preferred implementation illustrated in  FIGS. 1   a ,  1   b , and  1   c  is the RF input signal from the RF input line  106 . An upper contact  126  is provided which is electrically connected to the upper electrode  124  and is extended into the air gap  122 . 
   The MEMS  100  also includes voltage potential lines  105 ,  107  to create an electrostatic attraction between the first and second actuator electrodes. As discussed above, the lower actuation electrodes  110  are preferably maintained at a ground potential by connecting voltage potential line  105  to a ground while the upper actuator electrodes  120  are selectively held at a contact voltage V 1  by connecting voltage potential line  107  to a power (voltage) source. In operation, when an electrostatic attraction is created between the upper and lower actuator electrodes  110 ,  120 , the beam  121  bends or deflects towards the lower level portion  102  and the upper contact  126  touches the lower contact  114  and allows an RF signal go through from the input line  106  to the output line  108 . The bumpers  116  act to prevent stiction between contacts  124  and  114  and also act to prevent shorting of the beam  100  to actuators  110 . As discussed previously, the configuration of the MEMS  100  illustrated in  FIGS. 1   a ,  1   b , and  1   c  has the actuation DC electrodes  110 ,  120  entirely separated from the AC RF signal electrodes  112 ,  124  resulting in minimizing losses and improving the switch linearity. 
   Referring now to  FIG. 2 , there is shown a top view of the MEMS  100 , and in particular beam  121  having access holes  128  to facilitate easier removal of a sacrificial layer in order to create the air gap  121 . The access holes  128  are preferably 2×2 micron insulator plugs, having 1×1 micron etch holes  130  which are cut within the 2×2 um plugs. Access slots  132  are also provided and used for etching the sacrificial material. 
   Referring now to  FIGS. 3   a  and  3   b , there is described results of a Joule heating model. When 1–4 Watts of RF power are passed through the MEMS switch  100  at the upper electrode  124 , there is a lot of heat generated that needs to be dissipated to the surrounding substrate  135 , which is preferably Si. Although only shown with regard to the upper level portion  104 , the upper actuator electrodes  120 , and upper electrode  124 , a similar analysis is applicable to the lower level portion  102 , the lower actuator electrodes  110  and lower electrode  112 . The model shown in  FIG. 3   a  assumes that the second electrode  124  (or first electrode  112 ) is copper and that its width (w) is 20 microns. The graph shown in  FIG. 3   b  shows the temperature rise as a function of the insulator width (w i ) for the case of a copper second electrode  124  and for two different insulator  134  materials, namely silicon dioxide and silicon nitride. It is apparent from the model that the insulator width (w i ) needs to be kept below 6 microns, and preferably at about 5 microns for effective heat dissipation. Although either silicon nitride or silicon dioxide can be used, it is apparent that silicon nitride is more effective than silicon dioxide to dissipate the released heat. 
   Referring now to  FIG. 4 , there are shown typical dimensions of a composite metal-insulator-metal beam  121 , the dimensions being by way of example only and not to limit the scope or spirit of the present invention. Etch holes  136  are provided within the center part of the beam  121  to make the beam  121  lighter thereby resulting in faster switching times and at the same time will provide better access for etching away the sacrificial material and releasing the beam  121 . The upper conductor  124  in this design spans only a portion of the beam length. In other words, upper and lower level portions  104 ,  102  have a width W and the second electrode  124  (and/or first electrode  112 ) is aligned in the direction of W and has a first dimension L 1  in the direction of W which is less than W. An improved design of the beam  121  is shown in  FIG. 5  in which a dummy conductor  138  is used to improve heat dissipation. The dummy conductor is preferably not electrically connected to the upper electrode  124  and upper actuator electrodes  120  and is preferably aligned in the same direction as W and has a length L 2 , which is smaller than L 1 . Preferably, there is a slight gap L 3 , such as 1 micron, between the dummy conductor  138  and the second electrode  124 . The dummy conductor  138  provides effective heat dissipation and also provides symmetry in terms of materials for improved mechanical performance. 
   Referring now to  FIG. 6 , there is shown an alternative design for the beam  121 , referred to therein as  121   a , in which similar reference numerals denote similar features as that shown in the previous FIGS. The beam  121   a  is fixed at both ends through the center dummy conductor  138  and RF signal output line  124 . The RF signal comes in through line  106  that is at a lower level than the beam  121   a . When the beam  121   a  is actuated electrostatically through actuator electrodes  120 , then it bends down and makes contact through the RF contact  126  and the signal passes through the beam  121   a  and line  108 . The area designated by reference numeral  132  in  FIG. 6  is the area surrounding the beam  121   a  where the sacrificial material has been etched away and the beam  121   a  is free. The lower level portion  102  is similar to that previously described with regard to  FIGS. 1   a ,  1   b , and  1   c . This alternative design will offer a lower actuation voltage along with the advantages of the previous designs due to a less stiff anchoring scheme. 
   Referring now to  FIG. 7 , there is shown yet another alternative design for the beam  121 , referred to therein by reference numeral  121   b , in which similar reference numerals denote similar features as that shown in the previous Figures.  FIG. 7  shows a seesaw movable beam  121   b  upper actuator electrodes  120   a ,  120   b ,  120   c , and  120   d . Also provided are RF contacts  126   a ,  126   b  on either side of the anchored beam  121   b . The beam  121   b  is anchored on through RF inputs  106   a ,  106   b  that run in the center but which are long enough allowing free bending of the beam on either side either of RF contact  126   a  or on the side of contact  126   b . When a voltage with respect to ground is applied on actuators  120   a  and  120   b , then the beam  121   b  bends toward contact  126   a . Contact  126   a  bends down and contacts RF output line  108   a , thereby allowing the RF signal to pass from beam  121   b  into line  108   a . When a voltage with respect to ground is applied on actuators  120   c  and  120   d , then the beam  121   b  bends toward contact  126   b  and the RF signal goes out through output line  126   b . The lower level portion  102  is similar to that previously described with regard to  FIGS. 1   a ,  1   b , and  1   c . This alternative configuration, as is the alternative configuration shown in  FIG. 6 , is also a single contact configuration with a full separation of the DC and RF parts of the signal on the movable part of the switch. The seesaw configuration allows the use of DC actuation voltages of less than 10V to electrostatically bend the beam either toward  126   a / 108   a  or  126   b / 108   b.    
   Referring now to  FIG. 8  there is shown a schematic layout of the electrical connections necessary to achieve a single-pole double-throw or multi-throw switch using any of the switch designs previously described, the single-pole double-throw switch being generally referred to by reference numeral  200 . Although switch  200  is shown with 2 single-pole single-throw switches  100 , such is shown by way of example only and not to limit the scope or spirit of the present invention. Those skilled in the art will appreciate that a multiple-throw switch can be configured by using multiple single-pole single-throw switches  100  arranged on a substrate  201 . Switch  200  has one RF in probe pad  202  connected to RF input lines  106 , which input both single-pole single-throw switches  100 . Switch  200  also has two DC bias pads  204 ,  206  each connected to voltage potential lines  107  to actuate separately each single-pole single-throw switch  100 . Two RF out pads  208 ,  210  are provided, each of which are connected to RF output lines  108 . Furthermore, two separate ground pads  212 ,  214  are provided, each of which are connected to voltage potential lines  105 . Those skilled in the art will appreciate that by selectively creating an attraction between the upper and lower actuator electrodes  110 ,  120 , preferably by holding the lower actuator electrodes  110  at ground and the upper actuator electrodes  120  at a constant voltage V 1 , a single-pole, double-throw switch is realized. As discussed above, a multiple-throw switch can be realized by using multiple single-pole single-throw switches  100 . 
   Referring now to  FIG. 9 , there is shown a bottom view of the switch  200  of  FIG. 8 , in which the position of the single-pole single-throw switches  100  are shown as broken lines. A ground plane  216  is provided on a lower surface of the substrate  201 , preferably 3 to 4 microns below the single-pole single-throw switches  100 . The ground plane  216  terminates the electromagnetic field and allows the single-pole single-throw switches  100  to yield low losses on the order of less than −0.5 dB at @2 GHz.  FIG. 10  shows an alternative embodiment for the design of the ground plane  216  for the switch  200  of  FIG. 8 . In the alternative embodiment, the ground plane  216  is present as a solid block of metal only below each throw of the single-pole single-throw switches  100  and below the RF signal lines. Each solid metal piece is connected to a subsequent metal piece with a set of parallel wires  218 . 
   Referring now to  FIGS. 11   a ,  11   b ,  11   c , and  12   a  and  12   b , there is shown alternative designs of a lateral switch with a single contact and a full separation of the DC actuators from the RF signal on the movable part of the beam. The switches of  FIGS. 11   a ,  11   b ,  11   c , and  12   a  and  12   b  are configured as a pair of single-pole, single-throw switches, by way of example only, with the restriction that they cannot both be closed at the same time. Referring only to  FIGS. 11   a ,  11   b , and  11   c , there is shown switch  300  having RF input lines  316   c ,  316   d  where the RF signal comes in and runs on a movable beam  304 , which instead of being movable by way of deflecting, is movable by way of rotation. The beam has an electrode  306  for carrying the RF signal and contacts  308   a ,  308   b ,  308   c , and  308   d  electrically connected to the electrode  306 . The beam  304  further has an insulator  310  disposed about the electrode  306 . The bean further has at least one set, and preferably two sets of first actuator electrodes  312   a ,  312   b ,  312   c , and  312   d , which are preferably maintained at ground. The switch  300  further has second actuator electrodes  314   a ,  314   b ,  314   c , and  314   d , separated by respective air gap  315 , which are selectively held at a constant voltage V 1 . RF input/output lines  316   a ,  316   b ,  316   c , and  316   d  are also provided. 
   As shown in  FIG. 11   b , when the second actuator electrodes  314   b  and  314   c  are biased with a DC voltage, the beam rotates such that contacts  308   b  and  308   c  make contact with RF lines  316   b  and  316   c  such that the signal runs from RF line  316   c  to RF line  316   b . Similarly, as shown in  FIG. 11   c , when the second actuator electrodes  314   a  and  314   d  are biased with a DC voltage, the beam rotates such that contacts  308   a  and  308   d  make contact with RF lines  316   a  and  316   d  such that the signal runs from RF line  316   d  to RF line  316   a .  FIG. 11   d  illustrates a pivot point  302  which is used to supply a DC voltage. It is constructed to wrap around below the beam surface to supply voltage to electrodes  312   c – 312   b  or  312   a – 312   d.    
     FIGS. 12   a  and  12   b , show a similar switch, referred to by reference numeral  400  in which similar reference numeral from  FIGS. 11   a ,  11   b , and  11   c  denote similar features. Switch  400  uses a V-shaped beam  402  with a single contact.  FIG. 12   b  shows a signal path from RF line  316   c  to RF line  316   b  when the second actuator electrodes  314   b  and  314   c  are biased with a voltage V 1 . 
   Therefore, to minimize losses and improve on a MEMS switch linearity, the switches  100 ,  200 ,  300 ,  400  disclosed herein separate entirely the RF signal electrodes from the DC actuators. Another reason for separating the DC actuators of the switch beam from the RF signal beam electrode is the need to design single-pole-multiple-throw switches for transmit/receive or frequency selection wireless applications. Integrating two or N number of switches in parallel provides a multiple throw switch with N number of throws. 
   Furthermore, the switches of the present invention solve the Joule heating dissipation problem of the prior art switches by using a composite metal-dielectric beam comprised of a metal actuator electrode, a thin layer of dieletric, a metal RF signal electrode and a second metal actuator electrode. A preferred metal is copper but other metals such as aluminum, nickel and their alloys can be used to fabricate the MEMS switch. Another advantage is the presence of a single contact for the RF signal. The RF signal is fed at an upper electrode of a fixed upper beam which, when actuated, is moved, such as by bending down to contact a lower electrode. A single RF contact with the use of appropriate contact materials give a lower contact resistance for the same contact force than a dual-contact metal-to-metal switch for the same contact force. Still another advantage of the switches of the present invention is the ability to fabricate very small gaps between the beam and the lower electrodes. Gaps between 0.1–0.5 microns typically yield actuation voltages of less than 10V. Finally, the switches of the present invention provide for a multi-throw MEMS switch for consumer wireless applications. The multi-throw design has typically one RF signal input and four to five RF signal output for selection of different frequencies and bands in GSM or UMTS system. The design of the multi-throw switch includes design of a ground plane to effectively terminate the electromagnetic field and to minimize RF signal losses within the silicon substrate. 
   While it has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. 
   It is, therefore, intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.