Patent Publication Number: US-11640891-B2

Title: Mems switch with multiple pull-down electrodes between terminal electrodes

Description:
FIELD OF THE DISCLOSURE 
     The present invention relates to a microelectromechanical system (MEMS) switch, systems, and devices. In particular, the present invention relates to a MEMS switch with multiple pull-down electrodes between terminal electrodes to limit off-state capacitance. 
     BACKGROUND 
     Microelectromechanical system (MEMS) switches provide high-performance relays that operate across a wide variety of frequency ranges. Unwanted or parasitic capacitance may occur in MEMS switches, such as between the input terminal electrode and the output terminal electrode. Such parasitic capacitance is undesirable as it results in on-state electrical loss and off-state electrical coupling. Reducing this off-state capacitance is desirable, such as to enable more advanced relay applications as tuning elements. 
     SUMMARY 
     Embodiments of the disclosure are directed to microelectromechanical system (MEMS) switches with multiple pull-down electrodes between terminal electrodes to limit off-state capacitance. In exemplary aspects disclosed herein, a plurality of pull-down electrodes are positioned between the input terminal electrode and the output terminal electrode. The plurality of pull-down electrodes are offset from each other to limit off-state capacitance between the input terminal electrode and the output terminal electrode. The separation between the pull-down electrodes disrupts the off-state capacitive path between the input terminal electrode and the output terminal electrode, thereby further insulating the contacts from each other. Limiting off-state capacitance reduces on-state electrical loss and increases off-state electrical isolation for improved performance. 
     One embodiment of the disclosure relates to a microelectromechanical system (MEMS) switch including an input terminal electrode, an output terminal electrode, a plurality of pull-down electrodes positioned between the input terminal electrode and the output terminal electrode, and a beam element. The beam element is configured to move between an on-state adjacent to the plurality of pull-down electrodes to electrically couple the input terminal electrode and the output terminal electrode to the beam element and an off-state away from the plurality of pull-down electrodes to electrically isolate the input terminal electrode and the output terminal electrode from the beam element. The plurality of pull-down electrodes are offset from each other to limit off-state capacitance between the input terminal electrode and the output terminal electrode. 
     An additional embodiment of the disclosure relates to a microelectromechanical system (MEMS), including a plurality of MEMS switches. Each switch includes an input terminal electrode, an output terminal electrode, a plurality of pull-down electrodes positioned between the input terminal electrode and the output terminal electrode, and a beam element. The beam element is configured to move between an on-state adjacent to the plurality of pull-down electrodes to electrically couple the input terminal electrode and the output terminal electrode to the beam element and an off-state away from the plurality of pull-down electrodes to electrically isolate the input terminal electrode and the output terminal electrode from the beam element. The plurality of pull-down electrodes are offset from each other to limit off-state capacitance between the input terminal electrode and the output terminal electrode. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure. 
         FIG.  1 A  is a schematic diagram of microelectromechanical system (MEMS) switch in an off-state, including a pull-up electrode and a single pull-down electrode between terminal electrodes; 
         FIG.  1 B  is a schematic diagram of the MEMS switch of  FIG.  1 A  in an on-state; 
         FIG.  1 C  is a circuit diagram of the MEMS switch of  FIGS.  1 A- 1 B  illustrating off-state capacitances, including a capacitance between the terminal electrodes through the pull-down electrode; 
         FIG.  2 A  is a schematic diagram cross-sectional side view of a MEMS switch in an off-state including a pull-up electrode and a plurality of pull-down electrodes between terminal electrodes; 
         FIG.  2 B  is a schematic diagram of the MEMS switch of  FIG.  2 A  in an on-state; 
         FIG.  2 C  is a circuit diagram of the MEMS switch of  FIGS.  2 A- 2 B  illustrating off-state capacitances, including a capacitance between the terminal electrodes through the plurality of pull-down electrodes; 
         FIG.  3 A  is a cross-sectional side view of one embodiment of the MEMS switch of  FIGS.  2 A- 2 B  in an off-state; 
         FIG.  3 B  is a cross-sectional side view of the MEMS switch of  FIG.  3 A  in an on-state; 
         FIG.  4    is a graph illustrating a ratio of off-state capacitance relative to the amount of coupling to down electrodes; 
         FIG.  5 A  is a schematic diagram of a MEMS switch in an off-state including a plurality of the pull-down electrodes between the terminal electrodes and devoid of a pull-up electrode; 
         FIG.  5 B  is a schematic diagram of the MEMS switch of  FIG.  5 A  in an on-state; 
         FIG.  6 A  is a cross-sectional side view of one embodiment of the MEMS switch of  FIGS.  3 A- 3 B  in an off-state; 
         FIG.  6 B  is a cross-sectional side view of the MEMS switch of  FIG.  6 A  in an on-state; 
         FIG.  7 A  is a schematic diagram of a MEMS switch in an off-state including a plurality of proximal pull-down electrodes between the terminal electrodes, distal pull-down electrodes, and a pull-up electrode; 
         FIG.  7 B  is a schematic diagram of the MEMS switch of  FIG.  7 A  in an on-state; 
         FIG.  8 A  is a cross-sectional side view of one embodiment of the MEMS switch of  FIGS.  7 A- 7 B  in an off-state; 
         FIG.  8 B  is a cross-sectional side view of the MEMS switch of  FIG.  8 A  in an on-state; 
         FIG.  9 A  is a schematic diagram of a MEMS switch in an off-state including a plurality of proximal pull-down electrodes between the terminal electrodes, distal pull-down electrodes, and devoid of a pull-up electrode; 
         FIG.  9 B  is a schematic cross-sectional side view of the MEMS switch of  FIG.  9 A  in an on-state; 
         FIG.  10 A  is a cross-sectional side view of one embodiment of the MEMS switch of  FIGS.  9 A- 9 B  in an off-state; 
         FIG.  10 B  is a cross-sectional side view of the MEMS switch of  FIG.  10 A  in an on-state; and 
         FIG.  11    is a schematic top view of a switch cell  1100  containing a number of MEMS switches  300 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     It should be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It should also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     It should be understood that, although the terms “upper,” “lower,” “bottom,” “intermediate,” “middle,” “top,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed an “upper” element, and, similarly, a second element could be termed an “upper” element depending on the relative orientations of these elements, without departing from the scope of the present disclosure. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having meanings that are consistent with their meanings in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIGS.  1 A- 1 C  are diagrams of a microelectromechanical system (MEMS) switch  100  with a pull-up electrode  102  and a single pull-down electrode  104  between terminal electrodes  106 ,  108 . In particular, terminal electrodes  106 ,  108  include an input terminal electrode  106  (may also be referred to as a first terminal electrode, input electrode, first RF electrode, etc.), and an output terminal electrode  108  (may also be referred to as a second terminal electrode, output electrode, second RF electrode, etc.). The MEMS switch  100  further includes a power source  110  coupled to the first terminal electrode  106  (via a power source circuit), a voltage up coupling (Vup)  112  coupled to a pull-up electrode  102 , and a voltage down coupling (Vdn)  114  coupled to the pull-down electrode  104 . 
     The MEMS switch  100  (may also be referred to herein as a MEMS relay, MEMS ohmic switch, etc.) further includes a moveable beam  116  (may also be referred to as a floating beam) mechanically anchored at both ends by flexible anchors  117  (e.g., springs). In this way, the moveable beam  116  is configured to move between a first position (off-state) and a second position (on-state) for up and down electrostatic actuation. The moveable beam  116  is connected to a ground connection  118 . 
     Referring to  FIG.  1 A , the MEMS switch  100  is in the off-state (may also be referred to as a pull-up state) where the moveable beam  116  of the MEMS switch  100  is pulled up toward the pull-up electrode  102 . In the first position, the moveable beam  116  is disposed adjacent to the first electrode  102 , the input terminal electrode  106 , and the output terminal electrode pull-up electrode  102  and spaced from the pull-down electrode  104 , the input terminal electrode  106 , and the output terminal electrode  108 . 
     Referring to  FIG.  1 B , the MEMS switch  100  is in the on-state (may also be referred to as a pull-down state), where a movable beam  116  of the MEMS switch  100  is pulled down towards the pull-down electrode  104 . In the second position, the moveable beam  116  is disposed adjacent to the pull-down electrode  104  and spaced from the pull-up electrode  102 . 
     The MEMS switch  100  further includes an up isolation circuit  120  between the pull-up electrode  102  and the Vup coupling  112  (may also be referred to as Vup connection, Vup source, etc.), a second isolation circuit  122  disposed between the moveable beam  116  and electrical ground potential  118 , and a down isolation circuit  124  between the pull-down electrode  104  and the Vdn coupling  114  (may also be referred to as Vdn connection, Vdn source, etc.). Each of the isolation circuits  120 ,  122 ,  124  (may be referred to as Ziso) includes at least one resistor. The isolation circuits  120 ,  122 ,  124  isolate the MEMS switch  100  to prevent RE leakage (e.g., through the Vup coupling  112 , the Vdn coupling  114 , and/or the ground connection  118 ) by adding electrical impedance at RF leakage points. The source impedance of the MEMS switch  100  is represented by Zsrc  126 , and the load impedance of the MEMS switch  100  is represented by Zload  128 . Additionally, the first and second isolation circuits  120 ,  124  are utilized to isolate the control voltage sources, such as the Vup coupling  112  and Vdn coupling  114 . 
     The isolation circuits  120 ,  122 ,  124  provide several benefits. The isolation circuits  120 ,  122 ,  124  bias the direct current potential to allow for electrostatic actuation and further provide a path for transient currents during switching. The components of each of the isolation circuits  120 ,  122 ,  124  are chosen such that the resistance levels limit RE leakage while enabling the MEMS switch  100  to function as intended (e.g., movement speed of moveable beam  116 , providing bleed current to withstand electrostatic discharge events, maintain electric potential at the pull-up electrode  102  and pull-down electrode  104  during the switching transients), among other advantages (e.g., accurate engineering of actuation waveforms). In particular, the isolation circuits  120 ,  122 ,  124  provide a high degree of reliability for the MEMS switch  100  by neutralizing charge that may accumulate during life cycling while maintaining a zero potential between touching MEMS elements. The isolation circuits  120 ,  122 ,  124  provide for leakage paths for electrostatic discharge events to further increase the reliability of the MEMS relay. The isolation circuits maintain RF performance (voltage handling, insertion loss, isolation linearity, etc.) while providing proper power handling by uniform RF current distribution. 
       FIG.  1 C  is a circuit diagram of the MEMS switch  100  of  FIGS.  1 A- 1 B  illustrating off-state capacitances. In particular, the off-state capacitances include direct coupling  130  between the pull-up electrode  102  and the pull-down electrode  104 , coupling via pull-up electrode  102  (e.g., input up capacitance  132 A and output up capacitance  132 B), coupling via moveable beam  116  (e.g., input beam capacitance  134 A and output beam capacitance  134 B), coupling via pull-down electrode  104  (e.g., input down capacitance  136 A and output down capacitance  136 B), and/or extra coupling  138  between the moveable beam  116  and the pull-down electrode  104 . It is noted that the greatest coupling is via the pull-down electrode  104  as the pull-down electrode  104  is positioned proximate to and directly in between the terminal electrodes  106 ,  108 . In certain embodiments, the capacitive coupling through the pull-down electrode  104  accounts for 60%-70% of electrical loss. Accordingly, reducing coupling via the pull-down electrode  104  would significantly reduce off-state capacitance and associated losses. 
     In certain embodiments, isolation circuit  120  includes resistor  120 ′ disposed between a pull-up electrode  102  and the Vup coupling  112 . In certain embodiments, isolation circuit  124  includes resistor  124 ′ disposed between a pull-down electrode  104  and the Vdn coupling  114  such that the Vdn coupling  114  is isolated to provide proper control of voltage within the MEMS switch  100 . Resistors  120 ′,  124 ′ are utilized to isolate the control voltage sources, such as the Vup coupling  112  and the Vdn coupling  114 . 
     In certain embodiments, isolation circuit  122  includes resistor  122 A′,  122 B′, and/or  122 C′. In particular, resistor  122 C′ is disposed between the movable beam  116  and DC ground connection  118  to provide a direct current bias of the movable beam  116  to DC ground connection  118 . In certain embodiments, resistors  122 A′,  122 B′ are disposed adjacent to anchored ends of the movable beam  116 . The resistor  122 A′ is disposed between the movable beam  116  and input electrode  106 , and resistor  122 B′ is disposed between the movable beam  116  and output electrode  108 . In certain embodiments, resistors  122 A′,  122 B′ are equivalent in value (e.g., about 75 Kohm to about 1.5 Mohm). In certain embodiments, the value of resistors  120 ′,  124 ′ is greater than resistor  122 A′- 122 C′. In certain embodiments, resistors  122 A′- 122 C′ and may have about the same value. 
     In certain embodiments, resistors  122 A′,  122 B′ provide for RF isolation and provide for extra reliability of the MEMS switch  100  by neutralizing electrical change that may accumulate within the MEMS switch  100 . Resistors  122 A′,  122 B′ having the second value also provides a sufficient level of “bleed” current for dissipating externally applied charge due to electrostatic discharge events. Additionally, resistors  122 A′,  122 B′ are utilized to avoid the RF-terminals from floating to an uncontrolled direct current potential when left open. 
       FIGS.  2 A- 2 C  are diagrams of a MEMS switch  200  in an off-state, including a pull-up electrode  102  and a plurality of pull-down electrodes  104 A,  104 B between terminal electrodes  106 ,  108 . The MEMS switch  200  includes similar features as those discussed above with reference to  FIGS.  1 A- 1 C  unless otherwise noted. In particular, the MEMS switch  200  includes an input terminal electrode  106  and an output terminal electrode  108 , a pull-up electrode  102 , a plurality of pull-down electrodes  104 A,  104 B positioned between the input terminal electrode  106  and the output terminal electrode  108 , and a movable beam t  116 . The pull-up electrode  102  is configured to electrically bias the movable beam  116  toward the off-state. In certain embodiments, the input terminal electrode  106  includes an input RF electrode and/or the output terminal electrode  108  includes an output RF electrode. 
     The movable beam  116  is configured to move between an on-state adjacent to the plurality of pull-down electrodes  104 A,  104 B to electrically couple the input terminal electrode  106  and the output terminal electrode  108  to the movable beam  116 , and an off-state away from the plurality of pull-down electrodes  104 A,  104 B to electrically isolate the input terminal electrode  106  and the output terminal electrode  108  from the movable beam  116 . In certain embodiments, the moveable beam  116  is coupled to an RF node. 
     In certain embodiments, each of the plurality of pull-down electrodes  104 A,  104 B are respectively coupled to an isolation circuit  124 A,  124 B to isolate a lower voltage source from the plurality of pull-down electrodes  104 A,  104 B. In certain embodiments, an isolation circuit  122  is positioned between the movable beam  116  and an electrical common ground connection  118 . In certain embodiments, the pull-up electrode  102  is coupled to an up isolation circuit  120  to isolate an upper voltage source from the pull-up electrode  102 . 
     The plurality of pull-down electrodes  104 A,  104 B are offset (and electrically isolated) from each other to limit off-state capacitance between the input terminal electrode  106  and the output terminal electrode  108 . In certain embodiments, the plurality of pull-down electrodes  104 A,  104 B consists of two pull-down electrodes  104 . In certain embodiments, the plurality of pull-down electrodes  104 A,  104 B includes three or more pull-down electrodes  104 . Similarly, in certain embodiments, the MEMS switch  200  includes a plurality of pull-up electrodes  102  configured to electrically bias the movable beam  116  toward the off-state. 
       FIG.  2 C  is a circuit diagram of the MEMS switch  200  of  FIGS.  2 A- 2 B  illustrating off-state capacitances, including a capacitance between the terminal electrodes  106 ,  108  through the plurality of pull-down electrodes  104 A,  104 B. The off-state capacitances include direct coupling  130 , coupling via pull-up electrode  102 , coupling via moveable beam  116 . The off-state capacitances further include coupling  136 A,  136 B,  202  via the pull-down electrodes  104 A,  104 B, and/or extra coupling  138 A,  138 B between the moveable beam  116  and each of the pull-down electrodes  104 A,  104 B. Coupling via the pull-down electrodes  104 A,  104 B includes input down capacitance  136 A, output down capacitance  136 B, and intermediate down capacitance  202 . Intermediate down capacitance  202  is between the first pull-down electrode  104 A and the second pull-down electrode  104 B. Separating the single pull-down electrode  104  of the MEMS switch  100  of  FIG.  1    into multiple pull-down electrodes  104 A,  104 B further insulates the input terminal electrode  106  and the output terminal electrode  108  from each other and weakens the coupling therebetween. Reducing coupling via the pull-down electrodes  104 A,  104 B significantly reduces off-state capacitance and associated losses. Further, such a configuration may enable more advanced applications of relays as tuning elements, such as in high-end, front-ends (e.g., mobile handset). 
     In certain embodiments, isolation circuit  124  includes resistors  124 A′,  124 B′ disposed between a pull-down electrodes  104 A,  104 B, and the Vdn coupling  114  such that the Vdn coupling  114  is isolated to provide proper control of voltage within the MEMS switch  100 . 
     Although described above as a single switch, other arrangements may be utilized. Multiple relays may be included together into one arrangement. In some non-limiting embodiments, four relays may be provided. 
       FIGS.  3 A- 3 B  are views of one embodiment of the MEMS switch  200  of  FIGS.  2 A- 2 C . The MEMS ohmic switch  300  includes an input terminal electrode  106 , an output terminal electrode  108 , a pull-up electrode  102 , a plurality of pull-down electrodes  104 A,  104 B positioned between the input terminal electrode  106  and the output terminal electrode  108 , a movable beam  116 , and anchor electrodes  302 A,  302 B. The MEMS switch  300  further includes a substrate  304  with the input terminal electrode  106 , output terminal electrode  108 , plurality of pull-down electrodes  104 A,  104 B, and anchor electrodes  302 A,  302 B mounted on the substrate  304 . 
     The pull-down electrodes  104 A,  104 B are covered with a dielectric layer  306  to avoid a short-circuit between the movable beam  116  and the pull-down electrodes  104 A,  104 B in the on-state. Suitable materials for the dielectric layer  306  include silicon-based materials including silicon-oxide, silicon-dioxide, silicon-nitride, and silicon-oxynitride. The thickness of the dielectric layer  306  is typically in the range of 50 nm to 150 nm to limit the electric field in the dielectric layer  306 . 
     On top of the input terminal electrode  106  is the input terminal contact  308  (may also be referred to as an input RF contact), and on top of the output terminal electrode  108  is the output terminal contact  310  (may also be referred to as an output RF contact). The movable beam  116  forms an ohmic contact with the input terminal electrode  106  and the output terminal electrode  108  in the pulled-down state. On top of the anchor electrodes  302 A,  302 B are anchor contacts  312 A,  312 B to which the movable beam  116  is anchored. Suitable materials used for the contacts  308 ,  310 ,  312 A,  312 B include Ti, TiN, TiAl, TiAlN, AlN, Al, W, Pt, Ir, Rh, Ru, RuO 2 , ITO, and Mo and combinations thereof. 
     In certain embodiments, the MEMS switch  300  includes a center stopper  314  positioned on the dielectric layer  306 . The center stopper  314  extends above the substrate  304  by a greater distance than the terminal contacts  308 ,  310 , so that upon actuation, the moveable beam  116  comes into contact with center stopper  314  first. In one embodiment, the center stopper  314  extends above the substrate  304  by a distance that is equal to the terminal contacts  308 ,  310 . Suitable materials that may be used for the stopper  314  include Ti, TiN, TiAl, TiAlN, AlN, Al, W, Pt, Ir, Rh, Ru, RuO 2 , ITO, Mo, and silicon-based materials such as silicon-oxide, silicon-dioxide, silicon-nitride, and silicon-oxynitride and combinations thereof. 
     The movable beam  116  (may also be referred to as a switching element, MEMS bridge, etc.) includes lower conductive layer  316  and upper conductive layer  318 , which are joined together using an array of vias  320 . Opposing ends of the upper layer  318  are anchored to opposing ends of the lower layer  316  by vias  322 A,  322 B. Opposing ends of the lower conductive layer  316  of the moveable beam  116  are anchored to the anchor contacts  312 A,  312 B by vias  324 A,  324 B, which provides low compliance to permit operating voltages (e.g., 25 V to 40 V) to pull the moveable beam  116  in contact with the terminal contacts  308 ,  310  and center stopper  314 . This allows for a cheap integration of the CMOS (complementary metal-oxide-semiconductor) controller with a charge-pump to generate the voltages to drive the MEMS switch  300 . In other words, ends of the movable beam  116  are mounted to the substrate  304  such that the movable beam  116  is suspended above the input terminal electrode  106 , output terminal electrode  108 , and plurality of pull-down electrodes  104 A,  104 B in the off state. 
       FIG.  3 A  illustrates the MEMS switch  300  in an off-state with the pull-up electrode  102  drawing the moveable beam  116  upward toward the pull-up electrode  102  and away from the pull-down electrodes  104 A,  104 B, input electrode  106 , and output electrode  108 .  FIG.  3 B  illustrates the MEMS switch  300  in an on-state with the pull-down electrodes  104 A,  104 B drawing the moveable beam  116  downward toward the pull-down electrodes  104 A,  104 B and away from the pull-up electrode  102 . Current injected from the input terminal contact  308  into the moveable beam  116  when the MEMS switch  300  is actuated downflows out through the moveable beam  116  and output terminal contact  310 . The thicknesses of terminal contacts  308 ,  310  and center stopper  314  is set such that the center stopper  314  is engaged first upon pull-down actuation. 
     In certain embodiments, the MEMS switch  300  includes a cover  326  mounted to the substrate  304  and defines a cavity  328  between the cover  326  and the substrate  304 . The movable beam  116  is positioned within the cavity  328 . 
       FIG.  4    is a graph illustrating a ratio of off-state capacitance relative to the amount of coupling to pull-down electrodes  104 A,  104 B. In particular, the graph illustrates increasing the number of pull-down electrodes  104 A,  104 B decreases the off-state capacitance and accordingly decreases electrical losses. 
       FIGS.  5 A- 5 B  illustrate a MEMS switch  500  including a plurality of the pull-down electrodes  104 A,  104 B between the terminal electrodes  106 ,  108  and is devoid of a pull-up electrode  102 . MEMS switch  500  is similar to the MEMS switch  200  of  FIGS.  2 A- 2 C  except where otherwise noted. Instead, the moveable beam  116  includes a stiffness (e.g., mechanical spring constant) to bias the moveable beam  116  to the off state away from the input electrode  106 , output electrode  108 , and pull-down electrodes  104 A,  104 B. Accordingly, in the on-state, the moveable beam  116  bends toward the pull-down electrodes  104 A,  104 B, and when voltage from Vdn coupling  114  is cut off, the moveable beam  116  mechanically returns to the off state. In other words, the moveable beam  116  is mechanically biased toward the off state. 
       FIGS.  6 A- 6 B  are cross-sectional side views of one embodiment of the MEMS switch  500  of  FIGS.  5 A- 5 B  in an off state. The MEMS switch  600  is similar to the MEMS switch  300  of  FIGS.  3 A- 3 B  except where otherwise noted. As similarly noted in  FIGS.  5 A- 5 B , the MEMS switch  600  is devoid of a pull-up electrode  102 . Instead, the moveable beam  116  includes a stiffness to bias the moveable beam  116  to the off state away from the input electrode  106 , output electrode  108 , and pull-down electrodes  104 A,  104 B. 
       FIGS.  7 A- 7 B  illustrate a MEMS switch  700  including a plurality of proximal pull-down electrodes  104 A( 1 ),  104 B( 1 ) between the terminal electrodes  106 ,  108 , distal pull-down electrodes  104 A( 2 ),  104 B( 2 ), and a pull-up electrode  102 . MEMS switch  700  is similar to the MEMS switch  200  of  FIGS.  2 A- 2 C  except where otherwise noted. The MEMS switch  700  includes two sets of pull-down electrodes. The first set includes a proximal pull-down electrode  104 A( 1 ) (may also be referred to as a center pull-down electrode, interior pull-down electrode, etc.) and a distal pull-down electrode  104 A( 2 ) (may also be referred to as an edge pull-down electrode, exterior pull-down electrode, etc.) positioned on opposite sides of input electrode  106 . The second set includes a proximal pull-down electrode  104 B( 1 ) and a distal pull-down electrode  104 B( 2 ) positioned on opposite sides of the output electrode  108 . In particular, proximal electrodes  104 A( 1 ),  104 B( 1 ) are positioned between the input electrode  106  and the output electrode  108 . 
     The first set of pull-down electrodes  104 A( 1 ),  104 A( 2 ) are in electrical communication with isolation circuit  124 A, and the second set of pull-down electrodes  104 B( 1 ),  104 B( 2 ) are in electrical communication with isolation circuit  124 B. In other words, each of the first set of pull-down electrodes  104 A( 1 ),  104 A( 2 ) is coupled to a first down isolation circuit  124 A and each of the second set of pull-down electrodes  104 B( 1 ),  104 B( 2 ) is coupled to a second down isolation circuit  124 B to isolate a Vdn coupling  114  from the plurality of pull-down electrodes  104 A( 1 )- 104 B( 2 ). 
       FIGS.  8 A- 8 B  are cross-sectional side views of one embodiment of the MEMS switch  700  of  FIGS.  7 A- 7 B  in an off-state. The MEMS switch  800  is similar to the MEMS switch  300  of  FIGS.  3 A- 3 B  except where otherwise noted. The MEMS switch  800  includes distal pull-down electrodes  104 A( 2 ),  104 B( 2 ), each with a dielectric layer  802 A,  802 B. Further, the MEMS switch  800  includes edge stoppers  804 A,  804 B positioned on the dielectric layers  802 A,  802 B, respectively. In particular, edge stoppers  804 A,  804 B are disposed between the terminal contacts  308 ,  310  and the anchor contacts  312 A,  312 B. Specifically, edge stopper  804 A is disposed between anchor contact  312 A and terminal contact  308 . Edge stopper  804 B is disposed between anchor contact  312 B and terminal contact  310 . The edge stoppers  804 A,  804 B extend above the substrate  304  by a greater distance than the terminal contacts  308 ,  310  so that upon actuation, the moveable beam  116  comes into contact with the edge stoppers  804 A,  804 B before coming into contact with terminal contacts  308 ,  310 . The edge stoppers  804 A,  804 B also extend above the substrate  304  by a distance greater than the center stopper  314  due to the bending of the moveable beam  116  as the moveable beam  116  is actuated downwards. Suitable materials that may be used for the stoppers  804 A,  804 B,  314  include silicon-based materials including silicon-oxide, silicon-dioxide, silicon-nitride, and silicon-oxynitride and combinations thereof. 
       FIGS.  9 A- 9 B  illustrates a MEMS switch  900 , including a plurality of proximal pull-down electrodes  104 A( 2 ),  104 B( 2 ) between the terminal electrodes  106 ,  108 , distal pull-down electrodes  104 A( 1 ),  104 B( 1 ), and devoid of a pull-up electrode  102 . As similarly noted in  FIGS.  5 A- 5 B , the moveable beam  116  includes a stiffness to bias the moveable beam  116  to the off state away from the input electrode  106 , output electrode  108 , and pull-down electrodes  104 A( 1 ),  104 B( 1 ),  104 A( 2 ),  104 B( 2 ). Accordingly, in the on-state, the moveable beam  116  bends toward the pull-down electrodes  104 A,  104 B, and when voltage from Vdn coupling  114  is cut off, the moveable beam  116  mechanically returns to the off state. In other words, the moveable beam  116  is mechanically biased toward the off state. 
       FIGS.  10 A- 10 B  are cross-sectional side views of one embodiment of the MEMS switch  900  of  FIGS.  9 A- 9 B  in an off state. The MEMS switch  1000  is similar to the MEMS switch  300  of  FIGS.  3 A- 3 B  and MEMS switch  800  of  FIGS.  8 A- 8 B  except where otherwise noted. As similarly noted in  FIGS.  5 A- 5 B , the MEMS switch  1000  is devoid of a pull-up electrode  102 . Instead, the moveable beam  116  includes a stiffness to bias the moveable beam  116  to the off state away from the input electrode  106 , output electrode  108 , and pull-down electrodes  104 A( 1 )- 104 B( 2 ). 
       FIG.  11    is a schematic top view of a switch cell  1100  containing a number of MEMS switches  300 . All MEMS switches  300  in the cell  1100  are turned on simultaneously by applying a sufficiently high voltage to the pull-down electrodes  104 A,  104 B. Although MEMS switch  300  is illustrated, a similar configuration could be used for any of the MEMS switches disclosed herein. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.