Patent Publication Number: US-10770253-B2

Title: Switch arrangements for microelectromechanical systems

Description:
RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser. No. 62/593,549, filed Dec. 1, 2017, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present invention relates to microelectromechanical system (MEMS) switch devices, and in particular to arrangements for MEMS switch devices and related methods. 
     BACKGROUND 
     As electronics evolve, there is an increased need for miniature switches that are provided on semiconductor substrates along with other semiconductor components to form various types of circuits. These miniature switches often act as relays, generally range in size from a micrometer to a millimeter, and are generally referred to as microelectromechanical system (MEMS) switches. 
     In some applications, MEMS switches are configured as switches and replace field effect transistors (FETs). Such MEMS switches reduce insertion losses due to added resistance, and reduce parasitic capacitance and inductance inherent in providing FET switches in a signal path. MEMS switches are currently being deployed in many radio frequency (RF) applications, such as antenna switches, load switches, transmit/receive switches, tuning switches, and the like. For instance, transmit/receive systems requiring complex RF switching capabilities may utilize a MEMS switch. 
     For such applications, MEMS switches are subjected to a large number of open and close contact cycles where switch contacts are actuated between an open position where corresponding contacts are spaced apart and a closed position where corresponding contacts are in contact with each other. As the open and close contact cycles are repeated, maintaining a low overall contact resistance for the MEMS switches can be challenging for a number of reasons. For example, residual manufacturing contaminants may be present on one or both of the corresponding contacts that can contribute to reduced contact area during repeated open and close cycles, thereby increasing contact resistance. In a similar manner, material transfer between the corresponding contacts after repeated open and close cycles can contribute to an increased contact resistance. Additionally, MEMS switches may be subjected to hot switching events that can exacerbate the problems associated with contaminants and/or material transfer. During switching cycles, a difference in potential may be present across corresponding contacts during the periods in which the corresponding contacts approach each other, touch, and separate from one another. When the distance between the corresponding contacts is small, electric fields can enable field emission of electrons and eventually breakdown and arcing between the corresponding contacts. This can lead to significant material transfer between the corresponding contacts, which in turn can reduce contact force and/or contact area, thereby increasing contact resistance. Additionally, this can lead to pyrolysis, or thermal decomposition, at contact surfaces which can create non-conductive and load bearing films. 
     The art continues to seek improved MEMS switches that provide desirable performance characteristics over multiple open and close cycles while being capable of overcoming challenges associated with conventional MEMS switches. 
     SUMMARY 
     The present disclosure relates to microelectromechanical system (MEMS) switches and more particularly to arrangements for MEMS switches that provide a low contact resistance over a large number of open and close contact cycles. In certain embodiments, a MEMS switch device may include a plurality of parallel MEMS switches and at least one of the MEMS switches is configured differently in such a manner to close first and/or open last during open and close cycles. In this regard, the MEMS switch that closes before and/or opens after the other MEMS switches may experience increased contact resistance over a large number of open and close cycles while the other MEMS switches maintain a low contact resistance. In certain embodiments, at least one of the MEMS switches is controlled by a different control signal to open and close differently than other MEMS switches. In certain embodiments, a common control signal controls a plurality of MEMS switches and at least one of the MEMS switches is mechanically different such that it opens and closes differently than other MEMS switches. 
     In one aspect, a MEMS switch device comprises: a first MEMS switch configured to receive a first MEMS switch control signal; a plurality of second MEMs switches configured to receive a second MEMS switch control signal that is different than the first MEMS switch control signal, wherein the first MEMS switch and the plurality of second MEMS switches are arranged in parallel with each other; and control circuitry configured to provide the first MEMS switch control signal and the second MEMS switch control signal. In certain embodiments, the first MEMS switch is configured to close before the plurality of second MEMS switches close during an open and close cycle. In certain embodiments, the first MEMS switch is configured to reopen after the plurality of second MEMS switches reopen during the open and close cycle. In certain embodiments, the first MEMS switch is configured to (i) close before the plurality of second MEMS switches close, (ii) reopen after the plurality of second MEMS switches close, (iii) close again before the plurality of second MEMS switches open, and (iv) reopen again after the plurality of second MEMS switches open during an open and close cycle. 
     In certain embodiments, the MEMS switch device may further comprise a resistor configured in series with the first MEMS switch. 
     In certain embodiments, the MEMS switch device may further comprise an additional MEMS switch arranged in parallel with the first MEMS switch and the plurality of second MEMS switches, wherein the additional MEMS switch is configured to receive the first MEMS switch control signal. In further embodiments, a resistor is configured in series with the first MEMS switch and the additional MEMS switch. 
     In certain embodiments, the MEMS switch device may further comprise a plurality of additional switches arranged in parallel with the first MEMS switch and the plurality of second MEMS switches, wherein the plurality of additional MEMS switches are configured to receive the first MEMS switch control signal. In certain embodiments, the MEMS switch device may further comprising a shunt device that is connected to ground. The shunt device may comprise a shunt MEMS switch configured to receive a third MEMS switch control signal. The plurality of second MEMS switches may comprise a range of about two to about one hundred MEMS switches. 
     In one aspect, a method of operating a MEMS switch device comprises: providing a plurality of MEMS switches that are arranged in parallel with each other; closing a first MEMS switch of the plurality of MEMS switches before closing a second MEMS switch of the plurality of MEMS switches; and opening the second MEMS switch of the plurality of MEMS switches before opening the first MEMS switch of the plurality of MEMS switches. Closing the first MEMS switch may comprise sending a first MEMS switch control signal to the first MEMS switch, and closing the second MEMS switch comprises sending a second MEMS switch control signal to the second MEMS switch. In other embodiments, closing the first MEMS switch and closing the second MEMS switch may comprise sending a common MEMS switch control signal to both the first MEMS switch and the second MEMS switch. 
     In another aspect, a MEMS switch device comprises: a plurality of MEMS switches that are arranged in parallel with each other, wherein the plurality of MEMS switches are configured to receive a common MEMS switch control signal; and control circuitry configured to provide the common MEMS switch control signal; wherein a first MEMS switch of the plurality of MEMS switches is configured to close before a second MEMS switch of the plurality of MEMS switches in response to the common MEMS switch control signal. In certain embodiments, the first MEMS switch of the plurality of MEMS switches is configured to open after the second MEMS switch of the plurality of MEMS switches in response to the common MEMS switch control signal. In certain embodiments, the first MEMS switch comprises a first switch contact over a substrate and the second MEMS switch comprises a second switch contact over the substrate, and in an open position, the first switch contact is configured closer to the substrate than the second switch contact. In certain embodiments, the first MEMS switch comprises a first actuator and the second MEMS switch comprises a second actuator, and the second actuator has a higher spring constant than the first actuator. In certain embodiments, the first MEMS switch comprises a lighter mass than the second MEMS switch. The plurality of MEMS switches may comprise a range of about two to about one hundred MEMS switches. 
     In another aspect, any of the foregoing aspects, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein. 
     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. 
         FIGS. 1A and 1B  illustrate a representative microelectromechanical system (MEMS) switch in an open and closed position, respectively. 
         FIG. 2A  illustrates a block diagram of a single MEMS switch arranged between a radio frequency (RF) input and an RF output. 
         FIG. 2B  illustrates a block diagram of a plurality of MEMS switches arranged in parallel between an RF input and an RF output. 
         FIG. 3  illustrates a block diagram of a MEMS switch device according to embodiments disclosed herein. 
         FIG. 4A  illustrates a timing diagram of a first MEMS switch control signal and a second MEMS switch control signal for the MEMS switch device of  FIG. 3  during an open and close cycle. 
         FIG. 4B  illustrates an alternative timing diagram of the first MEMS switch control signal and the second MEMS switch control signal for the MEMS switch device of  FIG. 3  during an open and close cycle. 
         FIGS. 5A and 5B  are block diagrams illustrating a contact resistance of a first MEMS switch in the MEMS switch device of  FIG. 3 . 
         FIG. 6  illustrates a block diagram of a MEMS switch device according to embodiments disclosed herein that includes a resistor in series with a first MEMS switch. 
         FIG. 7  illustrates a block diagram of a MEMS switch device according to embodiments disclosed herein that includes at least one additional MEMS switch configured to receive a first MEMS control switch signal. 
         FIG. 8  illustrates a block diagram of a MEMS switch device according to embodiments disclosed herein that includes a shunt device configured to attenuate power entering the MEMS switch device. 
         FIGS. 9A-9C  illustrates cross-sectional views of a MEMS switch device that includes a plurality of MEMS switches at various steps of an open and close cycle according to embodiments disclosed herein. 
     
    
    
     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 will 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 will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will 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. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. 
     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 a meaning that is consistent with their meaning 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. 
     The present disclosure relates to microelectromechanical system (MEMS) switches and more particularly to arrangements for MEMS switches that provide a low contact resistance over a large number of open and close contact cycles. In certain embodiments, a MEMS switch device may include a plurality of parallel MEMS switches and at least one of the MEMS switches is configured differently in such a manner to close first and/or open last during open and close cycles. In this regard, the MEMS switch that closes before and/or opens after the other MEMS switches may experience an increased contact resistance over a large number of open and close cycles while the other MEMS switches maintain a low contact resistance. In certain embodiments, at least one of the MEMS switches is controlled by a different control signal to open and close differently than other MEMS switches. In certain embodiments, a common control signal controls a plurality of MEMS switches and at least one of the MEMS switches is mechanically different such that it opens and closes differently than other MEMS switches. 
     Before describing particular embodiments of the present disclosure further, a general discussion of MEMS switch devices is provided. Turning to  FIGS. 1A and 1B , a MEMS device  10  having a main MEMS switch  12  is illustrated. The main MEMS switch  12  is formed on an appropriate substrate  14 . In certain embodiments, the substrate  14  may comprise a semiconductor or insulator substrate, examples of which may include silicon, glass, and glass-fiber composite materials. The main MEMS switch  12  includes an actuator  16 , which is formed from a conductive material, such as gold. The actuator  16  has a first end and a second end. The first end is coupled to the substrate  14  by an anchor  18 . The first end of the actuator  16  is also electrically coupled to a first conductive pad  20  at or near the point where the actuator  16  is anchored to the substrate  14 . Notably, the first conductive pad  20  may play a role in anchoring the first end of the actuator  16  to the substrate  14  as depicted. The first conductive pad  20  may form a portion of or be connected to a first terminal (not shown) of the main MEMS switch  12 . 
     The second end of the actuator  16  forms or is provided with a switch contact  22 , which is suspended over a corresponding terminal contact  24  and/or a second conductive pad  26 . The second conductive pad  26  may form a portion of or be connected to a second terminal (not shown) of the main MEMS switch  12 . Thus, when the main MEMS switch  12  is actuated, the actuator  16  moves the switch contact  22  into electrical contact with the terminal contact  24  of the second conductive pad  26  to electrically connect the first conductive pad  20  to the second conductive pad  26 . To actuate the main MEMS switch  12 , and in particular to cause the actuator  16  to move the switch contact  22  into contact with the terminal contact  24  of the second conductive pad  26 , an actuator plate  28  is formed over a portion of the substrate  14 , preferably under the middle portion of the actuator  16 . To actuate the main MEMS switch  12 , an electrostatic voltage is applied to the actuator plate  28 . The presence of the electrostatic voltage creates an electromagnetic field that effectively moves the actuator  16  against a restoring force toward the actuator plate  28  from an “open” position illustrated in  FIG. 1A  to a “closed” position illustrated in  FIG. 1B . Likewise, removing the electrostatic voltage from the actuator plate  28  releases the actuator  16  for return to the open position illustrated in  FIG. 1A . As illustrated, the open position occurs when the switch contact  22  is out of contact with the terminal contact  24 , and the closed position occurs when the switch contact  22  comes into contact with the terminal contact  24 . Other embodiments may differ. The main MEMS switch  12  may be encapsulated by one or more encapsulation layers  30 , which form a substantially hermetically sealed cavity around the actuator  16 . The cavity is generally filled with an inert gas and sealed in a near vacuum state. Once the encapsulation layers  30  are in place, an overmold  32  may be provided over the encapsulation layers  30 . In  FIGS. 1A and 1B , the actuator  16  is illustrated as a cantilever actuator where the first end is anchored and the second end is suspended. According to embodiments disclosed herein, the actuator  16  may comprise other configurations as well, including a membrane actuator where both ends are anchored and the membrane actuator flexes between the two ends. 
     In light of the electromechanical structure of the main MEMS switch  12 , the main MEMS switch  12  cannot provide switching action as fast as typical solid state switches, such as n-type metal-oxide-semiconductor field effect transistor (NMOSFET) switches. A switching time of the main MEMS switch  12  typically depends upon the electromagnetic field applied to the actuator  16 , a mass of the actuator  16 , and a restoring force or spring constant of the actuator  16 . However, an FET switch may generate higher insertion loss than is generated by the main MEMS switch  12 . Moreover, at high power levels in a radio frequency (RF) circuit (not shown), parasitic capacitance at semiconductor junctions of the FET switch may alter RF signals. 
     During switching events, such as a hot switching event, a difference in potential between the switch contact  22  and the terminal contact  24  may cause an electrical arc resulting from an electrical current flowing through normally non-conductive media, such as air. Undesired or unintended electrical arcing may have detrimental effects on the switch contact  22  and the terminal contact  24  of the main MEMS switch  12 . For instance, as the main MEMS switch  12  is being either actuated to the closed position of  FIG. 1B  or released to the open position of  FIG. 1A , arcing from a difference in potential between the switch contact  22  and the terminal contact  24  may cause significant aging, unintended wear and tear, degradation, sticking, destruction, significant material transfer, and/or reduced contact area of one or both of the switch contact  22  and the terminal contact  24 . Unintended power dissipation through arcing should be limited for optimum contact lifetime with a low contact resistance of the switch contact  22  and the terminal contact  24 . 
     In various RF applications, MEMS switch devices may include a single switch or a plurality of parallel switches. For instance,  FIG. 2A  illustrates a block diagram of a single MEMS switch M arranged between an RF input (RF in ) terminal and an RF output (RF out ) terminal. Control circuitry  34  provides a MEMS switch control signal MS to control actuation of the single MEMS switch M. In operation, an increased contact resistance may be realized with any degradation of the single MEMS switch M.  FIG. 2B  illustrates a block diagram of a plurality of MEMS switches M 1  to M 5  arranged in parallel between the RF input (RF in ) and the RF output (RF out ). In this arrangement, the MEMS switch control signal MS from the control circuitry  34  controls actuation of the plurality of MEMS switches M 1  to M 5 . While five MEMS switches are illustrated in in  FIG. 2B , there may be any number of parallel (N-parallel) MEMS switches as indicated by the vertical dashed line between M 3  and M 4 . In certain embodiments, the N-parallel MEMS switches may comprise a number in a range of about two to about one hundred MEMS switches or more. In certain embodiments, the plurality of MEMS switches M 1  to M 5  may comprise a smaller size than the single MEMS switch M of  FIG. 2A . In operation, each of the plurality of MEMS switches M 1  to M 5  contribute to an overall contact resistance and as individual ones of the MEMS switches M 1  to M 5  experience degradation, the overall contact resistance is increased. 
     In certain embodiments disclosed herein, a MEMS switch device includes at least a first MEMS switch and a second MEMS switch that are arranged in parallel with each other. Control circuitry is configured to provide a separate MEMS switch control signal to each of the first MEMS switch and the second MEMS switch. This configuration allows the first MEMS switch to be separately controlled to close before the second MEMS switch closes and/or open after the second MEMS switch is opened in an open and close cycle. In this manner, a common potential is established by the first MEMS switch while the second MEMS switch opens and closes. Accordingly, the first MEMS switch may experience arcing and degradation over a number of open and close cycles while arcing in the second MEMS switch is reduced. In certain embodiments, a first MEMS switch may operate in such a manner to reduce arcing in a plurality of second MEMS switches. 
       FIG. 3  illustrates a block diagram of a MEMS switch device  36  according to embodiments disclosed herein. In  FIG. 3 , the plurality of MEMS switches M 1  to M 5  are arranged in parallel between the RF input (RF in ) and the RF output (RF out ) as previously described. While five MEMS switches are illustrated, there may be any number of parallel (N-parallel) MEMS switches as indicated by the vertical dashed line between the MEMS switches M 3  and M 4 . In certain embodiments, the N-parallel MEMS switches may comprise a number in a range of about two to about one hundred MEMS switches or more. The control circuitry  34  in  FIG. 3  is configured to provide a first MEMS switch control signal MS 1  and a second MEMS switch control signal MS 2  that may be different than the first MEMS switch control signal MS 1 . A first MEMS switch M 1  is configured to receive the first MEMS switch control signal MS 1  and a plurality of second MEMS switches M 2  to M 5  are configured to receive the second MEMS switch control signal MS 2 . During repeated open and close cycles, the first MEMS switch M 1  is configured to close in response to the first MEMS switch control signal MS 1  before the plurality of second MEMS switches M 2  to M 5  close in response to the second MEMS switch control signal MS 2 . Additionally, the first MEMS switch M 1  may be configured to reopen after the plurality of second MEMS switches M 2  to M 5  reopen during the open and close cycle. In this manner, the first MEMS switch M 1  establishes a common potential between the RF in  and the RF out  while the plurality of second MEMS switches M 2  to M 5  actuate between open and closed positions. While the first MEMS switch M 1  may experience arcing, degradation, and an increased contact resistance over a number of open/close cycles, arcing and degradation is reduced in the plurality of second MEMS switches M 2  to M 5 , thereby increasing the lifetime of the MEMS switch device  36  while maintaining a low overall or average contact resistance. Accordingly, the first MEMS switch M 1  serves as a degradation protection switch for the plurality of second MEMS switches M 2  to M 5 . In this regard, a method of operating the MEMS switch device  36  may include providing a plurality of MEMS switches M 1  to M 5  that are arranged in parallel with each other, closing a first MEMS switch M 1  of the plurality of MEMS switches before closing a second MEMS switch M 2  to M 5  of the plurality of MEMS switches, and opening the second MEMS switch M 2  to M 5  of the plurality of MEMS switches before opening the first MEMS switch M 1  of the plurality of MEMS switches. In certain embodiments, closing the first MEMS switch M 1  comprises sending the first MEMS switch control signal MS 1  to the first MEMS switch M 1 , and closing the second MEMS switch M 2  to M 5  comprises sending a second MEMS switch control signal MS 2  to the second MEMS switch M 2  to M 5 . 
       FIG. 4A  illustrates a timing diagram  38  of the first MEMS switch control signal MS 1  and the second MEMS switch control signal MS 2  for the MEMS switch device  36  of  FIG. 3  during an open and close cycle. At a first time  39 - 1 , the first MEMS switch control signal MS 1  signals the first MEMS switch (M 1  of  FIG. 3 ) to actuate to a closed position, thereby establishing a common potential as previously described. At a second time  39 - 2  that comes after the first time  39 - 1 , the second MEMS switch control signal MS 2  signals the second MEMS switches (M 2  to M 5  of  FIG. 3 ) to also actuate to a closed position. Since the common potential has already been established, about the same voltage is provided across the RF in  and the RF out  at the second time  39 - 2 , thereby reducing arcing effects for the second MEMS switches (M 2  to M 5  of  FIG. 3 ). At a later third time  39 - 3 , the second MEMS switch control signal MS 2  signals the second MEMS switches (M 2  to M 5  of  FIG. 3 ) to also actuate to an open position, followed by the first MEMS switch control signal MS 1  signaling the first MEMS switch (M 1  of  FIG. 3 ) to subsequently actuate to an open position at a later fourth time  39 - 4 . 
       FIG. 4B  illustrates an alternative timing diagram  40  of the first MEMS switch control signal MS 1  and the second MEMS switch control signal MS 2  for the MEMS switch device  36  of  FIG. 3  during an open and close cycle. In  FIG. 4B , the first MEMS switch control signal MS 1  and the second MEMS switch control signal MS 2  respectively signal the first MEMS switch (M 1  of  FIG. 3 ) and the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) at various sequential times  42 - 1  to  42 - 6 . As illustrated in the timing diagram  40 , the first MEMS switch (M 1  of  FIG. 3 ) is configured to (i) close at a first time  42 - 1  before the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) close at a second time  42 - 2 , (ii) reopen at a third time  42 - 3  after the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) close at the second time  42 - 2 , (iii) close again at a fourth time  42 - 4  before the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) open at a fifth time  42 - 5 , and (iv) reopen again at a sixth time  42 - 6  after the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) open at the fifth time  42 - 5  during an open and close cycle. As previously described, the first MEMS switch (M 1  of  FIG. 3 ) may degrade and have an increased contact resistance over a number of open/close cycles. In the timing diagram  40  of  FIG. 4B , the first MEMS switch (M 1  of  FIG. 3 ) reopens for a portion of time while the plurality of second MEMS switches (M 2  to M 5  of  FIG. 3 ) are closed so as to reduce any negative impact of the first MEMS switch (M 1  of  FIG. 3 ) on the overall contact resistance of the MEMS switch device  36 . 
       FIGS. 5A and 5B  are block diagrams illustrating the contact resistance of the first MEMS switch (M 1  of  FIG. 3 ) in the MEMS switch device  36  of  FIG. 3 . In  FIG. 5A , the first MEMS switch (M 1  of  FIG. 3 ) is represented as having a first resistance R 1  in parallel with the plurality of second MEMS switches M 2  to M 5 . In  FIG. 5B , the plurality of second MEMS switches (M 2  to M 5  of  FIG. 5A ) are represented as having the same second resistance R. Before the first MEMS switch (M 1  of  FIG. 3 ) experiences degradation, the first resistance R 1  may be equal to the second resistance R. In the parallel arrangement where R 1 =R, a total resistance R tot  may be represented as R tot =R/N, where N is the total number of resistors (M 1  to M 5  in this case). After degradation of the first MEMS switch (M 1  of  FIG. 3 ), the first resistance R 1  may have a higher resistance value as represented by R 1 =R/α where 0&lt;α≤1. Accordingly, the total resistance R tot  may be represented as R tot =R/(N−1+α) where 0&lt;α≤1 and N−1 represents the total number of second MEMS switches M 2  to M 5  that have not degraded. In this manner, the total resistance R tot  will be bounded by R/N (no degradation in M 1 ) and R/(N−1+α) (degradation in M 1 ). Notably, no matter how high a resistance value the first resistance R 1  degrades to, the total resistance R tot  will remain less than R/(N−1). By way of a non-limiting example, if a MEMS switch device includes 5 switches that all have a resistance value of 1 ohms (Ω), then the total resistance R tot =0.2Ω. If a first MEMS switch of the same MEMS switch device degrades to a resistance value of 10Ω, the total resistance R tot =0.24Ω. Accordingly, for a MEMS switch device with a large number of switches, limiting the degradation to a single switch or a few switches only has a minimal impact on the total resistance of the MEMS device. 
       FIG. 6  illustrates a block diagram of a MEMS switch device  44  according to embodiments disclosed herein that includes a resistor  45  in series with the first MEMS switch M 1 . The block diagram additionally illustrates the control circuitry  34  configured to provide the first MEMS switch control signal MS 1  to the first MEMS switch M 1  and the second MEMS switch control signal MS 2  to the plurality of second MEMS switches M 2  to M 5  as previously described. While five MEMS switches are illustrated, there may be any number of parallel (N-parallel) MEMS switches as indicated by the vertical dashed line between the second MEMS switches M 3  and M 4 . In certain embodiments, the N-parallel MEMS switches may comprise a number in a range of about two to about one hundred MEMS switches or more. In operation, high current pulses may be present when the first MEMS switch M 1  opens or closes that further contribute to degradation of the first MEMS switch M 1 . In  FIG. 6 , the resistor  45  is added in series with the first MEMS switch M 1  to limit current flow and reduce the impact of such high current pulses. In this regard, the first MEMS switch M 1  may be protected from high current pulses while continuing to provide degradation protection to the plurality of second MEMS switches M 2  to M 5 . In certain embodiments, the resistor  45  may be sized to have a resistance value in a range of about 5Ω to about 100Ω to limit current flow. In other embodiments, the resistor  45  may comprise a larger resistance value, such as 10 kiloohms (kΩ) or more, to provide RF isolation which may reduce or diminish any undesirable impact to isolation provided by the protection network including the first MEMS switch M 1 . 
     In a MEMS switch device that includes a first MEMS switch that serves as a degradation protection switch as previously described, degradation of the first MEMS switch may reach a level that prevents it from be able to establish a common potential between an RF in  and an RF out . In certain embodiments as disclosed herein, additional MEMS switches may be configured in a similar manner to the first MEMS switch such that the MEMS switch device comprises two or more protection switches that collectively serve to protect other MEMS switches in the MEMS switch device from degradation. 
       FIG. 7  illustrates a block diagram of a MEMS switch device  46  according to embodiments disclosed herein that includes at least one additional MEMS switch M 6 , M 7  configured to receive the first MEMS control switch signal MS 1 . The at least one additional MEMS switch M 6 , M 7  is arranged in parallel with the first MEMS switch M 1  and the plurality of second MEMS switches M 2  to M 5 . As shown, the control circuitry  34  is configured to provide the first MEMS switch control signal MS 1  to the first MEMS switch M 1  and the at least one additional MEMS switch M 6 , M 7 . The control circuitry  34  additionally is configured to provide the second MEMS switch control signal MS 2  to the plurality of second MEMS switches M 2  to M 5  as previously described. In this manner, the first MEMS control switch M 1  and the at least one additional MEMS switch M 6 , M 7  may all be configured as protection switches that are in a closed position while the plurality of second MEMS switches M 2  to M 5  open and close. Additionally, the resistor  45  may be configured in series with the group of protection switches (M 1 , M 6 , M 7 ) to provide RF isolation as previously described. While the plurality of second MEMS switches M 2  to M 5  are illustrated as five MEMS switches, there may be any number of parallel (N-parallel) MEMS switches as indicated by the vertical dashed line between the second MEMS switches M 3  and M 4 . In a similar manner, as indicated by the dotted vertical line between the at least one additional MEMS switch M 6  and M 7 , the MEMS switch device  46  may include a plurality of additional switches arranged in parallel with the first MEMS switch M 1  and the plurality of second MEMS switches M 2  to M 5 , and the plurality of additional MEMS switches are also configured to receive the first MEMS switch control signal MS 1 . 
     In various RF applications, a MEMS switch device may be linked to an antenna, cable input, or other type of input that provides a hot switching power source. In certain embodiments as disclosed herein, the MEMS switch device may include a shunt device connected between the hot switching power source and ground that is configured to attenuate power entering the MEMS switch device. 
       FIG. 8  illustrates a block diagram of a MEMS switch device  48  according to embodiments disclosed herein that includes a shunt device  49  configured to attenuate power entering the MEMS switch device  48 . The block diagram illustrates the control circuitry  34  configured to provide the first MEMS switch control signal MS 1  to the first MEMS switch M 1  and the second MEMS switch control signal MS 2  to the plurality of second MEMS switches M 2  to M 5  as previously described. The block diagram also illustrates the resistor  45  in series with the first MEMS switch M 1  as previously described. In  FIG. 8 , the shunt device  49  is connected to ground on the RF out  side of the MEMS switch device  48 , which may be linked or otherwise connected to an antenna or other hot switching power sources in certain RF applications. In other embodiments, the order may be reversed and the shunt device  49  may be connected to ground on the RF in  side. In certain embodiments, the shunt device  49  comprises a shunt MEMS switch that is configured to receive a third MEMS switch control signal MS 3  from the control circuitry  34 . The third MEMS switch control signal MS 3  may be configured to close the shunt device  49  just before the first MEMS switch M 1  closes, thereby attenuating power received by the first MEMS switch M 1 . Accordingly, the first MEMS switch M 1  may have a longer lifetime in reducing degradation in the plurality of second MEMS switches M 2  to M 5  over repeated open and close cycles. 
     In certain embodiments as disclosed herein, one or more MEMS switches may serve as degradation protection switches for other MEMS switches without the need for separate MEMS switch control signals. In this regard, a MEMS switch device may include a plurality of MEMS switches that are arranged in parallel with each other and the plurality of MEMS switches are configured to receive a common MEMS switch control signal. In certain embodiments, one or more of the MEMS switches may be configured to close before the other MEMS switches in response to the common control signal. This may be accomplished by configuring the one or more MEMS switches with one or more positional and/or structural differences that enable faster closing and slower opening than the other MEMS switches. 
       FIG. 9A  illustrates a cross-sectional view of a MEMS switch device  50  that includes a plurality of MEMS switches M 1  to M 7  over a substrate  51 . The plurality of MEMS switches M 1  to M 7  may be configured in parallel with one another as previously described. Each of the MEMS switches M 1  to M 7  includes a corresponding actuator  52 - 1  to  52 - 7  and a corresponding switch contact  54 - 1  to  54 - 7 . Each of the switch contacts  54 - 1  to  54 - 7  is arranged over a corresponding terminal contact  56 - 1  to  56 - 7  that is positioned on the substrate  51 . As illustrated in  FIG. 9A , all of the MEMS switches M 1  to M 7  are configured in an open position. Notably, a first MEMS switch M 1  and/or M 7  is configured or positioned closer to the substrate  51  than a second MEMS switch M 2  to M 6 . A common MEMS switch control signal may be applied to the plurality of MEMS switches M 1  to M 7  to repeatedly open and close the plurality of MEMS switches M 1  to M 7 .  FIG. 9B  illustrates a cross-sectional view of the MEMS switch device  50  just after the common MEMS switch control signal directs the plurality of MEMS switches M 1  to M 7  to close. As illustrated, the first MEMS switch M 1 , M 7  closes and makes contact between the switch contact  54 - 1 ,  54 - 7  and the corresponding terminal contact  56 - 1 ,  56 - 7  before the second MEMS switches M 2  to M 6  are able to close. Accordingly, the first MEMS switch M 1 , M 7  may establish a common potential before the second MEMS switches M 2  to M 6  close, thereby reducing degradation in the second MEMS switches M 2  to M 6 .  FIG. 9C  illustrates a cross-sectional view of the MEMS switch device  50  after all of the plurality of MEMS switches M 1  to M 7  have had time to close in response to the common MEMS switch control signal. When the common MEMS switch control signal directs the plurality of MEMS switches M 1  to M 7  to reopen, the order of the figures may be reversed such that the second MEMS switches M 2  to M 6  open first as illustrated in  FIG. 9B  before all of the MEMS switches M 1  to M 7  are opened as illustrated in  FIG. 9A . In certain embodiments, in order to open and close in such a manner, the second MEMS switches M 2  to M 6  may comprise the actuators  52 - 2  to  52 - 6  with a higher spring constant than the actuators  52 - 1 ,  52 - 7  of the first MEMS switches M 1 , M 7 . Accordingly, the first MEMS switches M 1 , M 7  comprise weaker springs that close more easily and open slower than the second MEMS switches M 2  to M 6  with stronger springs. In certain embodiments, the first MEMS switches M 1 , M 7  may comprise a lighter mass than the second MEMS switches M 2  to M 6  in order to achieve different open and close timings. Accordingly, in certain embodiments, a method of operating the MEMS switch device  50  includes closing the first MEMS switch M 1 , M 7  before closing the second MEMS switch M 2  to M 6  by sending the common MEMS switch control signal to both the first MEMS switch M 1 , M 7  and the second MEMS switch M 2  to M 6 . As with previous embodiments, while only seven MEMS switches are illustrated, a MEMS switch device as described herein may include any number of MEMS switches. For example, the MEMS switch device may include a number in a range of about two to about one hundred MEMS switches or more. 
     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.