Patent Publication Number: US-8115577-B2

Title: Electromechanical switch, filter using the same, and communication apparatus

Description:
BACKGROUND 
     The present invention relates to an electromechanical switch, and more particularly to a switch, a filter, and a communication apparatus used for switching high frequency signals in a high frequency circuit in a mobile communication terminal, and used in digital television broadcasting, mobile phone and wireless LAN. 
     A conventional RF-MEMS switch is a mechanical switch in which a movable element formed into a membrane or rod shape is fixed at both ends or only at one end thereof so as to be brought into contact with or separated from an electrode to thereby switch propagation paths of signals. While in many publications, electrostatic force is used as a source of force actuating the membrane and the movable element, magnetic force is also used in many other publications as the source of such actuating force. 
     As a minute switch of a size in the order of 100 μm, there is conventionally known one described in Non-Patent Document 1. The configuration of the conventional switch described in Non-Patent Document 1 is shown in  FIGS. 22A and 22B .  FIG. 22A  is a sectional view showing the configuration of the conventional switch, and  FIG. 22B  is a plan view showing the configuration of the conventional switch.  FIG. 22A  is the sectional view sectioned along the line A-A′ in  FIG. 22B . In this switch, a signal line  1  along which a high-frequency signal is transmitted is formed on a membrane, and a control electrode  3  is provided directly below the signal line  1 . 
     When a direct current potential is applied to the control electrode  3 , the membrane is pulled towards the control electrode  3  by virtue of electrostatic pulling force and is then deflected to be brought into contact with a ground electrode  4  formed on a substrate  2 . As a result, the signal line  1  formed on the membrane comes into a short-circuited state, and the signal flowing through the signal line  1  is attenuated to be cut off. 
     On the other hand, when the direct current potential is not applied to the control electrode  3 , the membrane is not deflected. The signal flowing through the signal line  1  on the membrane from the ground electrode  4  passes through the switch with no loss. 
     [Non-Patent Document 1] 
     IEEE Microwave and Wireless Components Letters, Vol. 11 No. 8, August 2001 p 334 
     As properties of the electromechanical switch, it is necessary to ensure isolation when the switch is off as well as reduce pull-in voltage necessary for switching operations. 
     In the conventional electromechanical switch, however, when a configuration is adopted in which the gap is increased to ensure the isolation, resulting in a large displacement, there is caused a problem that the pull-in voltage necessary for switching operations has to be increased, Conversely, when a configuration is adopted in which the gap is decreased to reduce the pull-in voltage, there is caused a problem that the isolation is reduced when the switch is off. Thus, the actuation with the low voltage and the isolation characteristic are in an incompatible or trade-off relationship. 
     SUMMARY 
     Then, the invention has been made in view of these situations and an object thereof is to provide an electromechanical switch which can solve the conventional problems and make low voltage actuation compatible with high isolation. 
     In addition, another object of the invention is to realize such characteristics as small size, low loss and high isolation by a filter and communication apparatus with the electromechanical switch provided by the invention. 
     In order to achieve the above object, according to the present invention, there is provided an electromechanical switch, comprising: 
     a first beam, serves as an actuating portion; 
     a second beam arranged in parallel with the first beam, and connected to the first beam through a connecting portion, the second beam serving as a contact portion; 
     a first electrode formed so as to have a first gap with respect to the first beam, the first electrode serving as a actuating electrode; 
     a voltage applying portion which applies a voltage between the first beam and the first electrode; and 
     a second electrode formed so as to have a second gap with respect to the second beam and served as a contact electrode, the second gap being greater than the first gap, 
     wherein the first beam is displaced when the voltage applying portion applies the voltage between the first beam and the first electrode, so that switching between the second beam and the second electrode is performed in a state that the first beam is not electrically connected to the first electrode. 
     By this configuration, the first beam is displaced by a voltage being applied between the first beam and the first electrode and then transmitting the displacement produced in the actuating portion to the contact portion via the connecting portion so as to displace the contact portion, whereby switching Is implemented. As a result of this, the different gaps can be defined for the actuating portion and the contact portion, whereby not only can the electrical isolation be ensured when the switch is off but also the pull-in voltage at the time of actuation can be reduced. 
     In addition, in this configuration, since the actuating portion and the contact portion do not exist on the same plane, isolation can easily be ensured. Additionally, a low voltage actuation is enabled. In the case of actuation being implemented through the electrostatic approach or piezoelectric approach, since the electric field necessary for actuation concentrates on the first beam and the first electrode, even when the switch is used in such communication apparatus as a mobile phone, there is caused no situation where peripheral circuits are badly affected by the electric field. In addition, when the switch is actuated by the electrostatic approach or piezoelectric approach, since only voltage is applied and no current is generated, the actuation of the switch consumes no electric power. 
     Additionally, electrostatically actuated switches can be fabricated only through the standard CMOS process. Furthermore, since the first electrode and the second electrode are made of the same material, not only is the fabrication facilitated but also the electrostatic force is applied to not only the first electrode but also the second electrode, enabling an actuation with lower voltage. 
     Preferably, the first electrode and the second electrode are formed on a substrate. A pulling force is generated between the first beam and the first electrode when the voltage applying portion applies the voltage between the first beam and the first electrode, so that the first beam is displaced. The connecting portion transmits a displacement of the first beam to the second beam so that the second beam is displaced. The second beam contacts with the second electrode to switch on and off an electric signal by a displacement of the second beam. 
     Preferably, the first beam is displaced by electrostatic force. 
     In this configuration, since the electric field necessary for actuation concentrates on the first beam and the first electrode, even when the switch is used in such communication apparatus as a mobile phone, there is caused no situation where peripheral circuits are badly affected by the electric field, In addition, when the switch is actuated by the electrostatic approach or piezoelectric approach, since only voltage is applied and no current is generated, the actuation of the switch consumes no electric power. Additionally, electrostatically actuated switches can be fabricated only through the standard CMOS process. Furthermore, since the first electrode and the second electrode are made of the same material, not only is the fabrication facilitated but also the electrostatic force is applied to not only the first electrode but also the second electrode, enabling an actuation with lower voltage. 
     Preferably, a surface of the first electrode is covered with an insulation membrane. 
     By this configuration, the magnitude of the gap can be decreased by the thickness of the insulation membrane without causing any change in height of the surfaces of the first and second electrodes, the formation of the switch using the MEMS process being thereby facilitated. 
     Preferably, the first electrode and the second electrode are formed on the same plane. 
     By this configuration, the number of fabricating manhours in the MEMS process can be reduced, and the fabrication is facilitated. Furthermore, the magnitude of the gap can be decreased by the thickness of the insulation membrane without causing any change in height of the surfaces of the first and third electrodes, the formation of the switch using the MEMS process being thereby facilitated. 
     Preferably, a top face of the second electrode is lower in the height from a common level than that of the first electrode. 
     By this configuration, isolation when the switch is off can be maintained in a more ensured fashion. 
     Preferably, the first beam is configured as a both-end fixed beam. The second beam is configured as a cantilevered beam. The both-end fixed beam is connected to the cantilevered beam through the connecting portion. 
     In this configuration, the both-end fixed beam constitutes the actuating portion which produces a displacement, while the cantilevered beam constitutes the contact portion which switches on and off an electric signal. In this electromechanical switch, since the displacement produced in the actuating portion can be magnified in the contact portion via the connecting portion for operation, switching can be implemented even in the event that there are provided the different gaps for the actuating portion and the contact portion. In addition, actuation can be implemented through smaller distortion by magnifying in the contact portion the small displacement produced in the actuating portion, thereby making it possible to increase the mechanical reliability of the switch. 
     Preferably, the first beam and the second beam are configured as cantilevered beams. The cantilevered beams are connected to each other through the connecting portion. 
     By this configuration, actuation can be implemented through smaller distortion by making the length of the second beam longer than the length of the first beam, thereby making it possible to increase the mechanical reliability of the switch. 
     Preferably, the first beam and the second beam are configured as both-end fixed beams. The both-end fixed beams are connected to each other through the connecting portion. 
     By this configuration, a stable actuation can be realized. 
     Preferably, a plurality of the first beam or a plurality of the second beam are provided. 
     By this configuration, a construction is made up in which a plurality of both-end fixed beams and a plurality of cantilevered beams are connected by a plurality of connecting portions. As this occurs, the plurality of both-end fixed beams make up the actuating portion, while the plurality of cantilevered beams make up the contact portion. In the electromechanical switch configured in this way, since the displacement produced in the actuating portion can be magnified in the contact portion via the connecting portion for operation, switching can be implemented even in the event that there are provided the different gaps for the actuating portion and the contact portion. 
     Preferably, a mechanical resonance frequency of the first beam is different from that of the second beam. 
     By this configuration, since the second beam is made to realize a larger displace with a smaller force, the displacement produced in the actuating portion can be propagated to the contact portion with good efficiency. 
     Preferably, a length of the connecting portion is not more than one half of a structural body of the electromechanical switch. 
     By this configuration, the magnification of displacement can be enabled. 
     Preferably, a length of the connecting portion is set to one fourth of a structural body of the electromechanical switch. 
     By this configuration, the displacement produced in the actuating portion can be propagated to the contact portion with good efficiency, the effect of magnification of the displacement being thereby made maximum. 
     Preferably, the first beam is displaced by piezoelectric effect. 
     In this configuration, since the electric field necessary for actuation concentrates on the first beam and the first electrode, even when the switch is used in such communication apparatus as a mobile phone, there is caused no situation where peripheral circuits are badly affected by the electric field. In addition, the switch can be fabricated only by the standard CMOS process excluding piezoelectric films of AIN and PZT. Furthermore, since the first electrode and the second electrode are made of the same material, the fabrication of the switch is facilitated. In addition, piezoelectric effect acts on not only the first electrode but also the second electrode, this enabling actuation with lower voltage. 
     Preferably, the first beam is displaced by both electrostatic effect and piezoelectric effect. 
     In the electrostatic approach, it is effective to dispose the actuating electrode in a portion where displacement becomes large, while in the piezoelectric approach, it is effective to dispose the actuating electrode in a portion where distortion becomes large. Because of this, in a hybrid actuation, the actuating portion can be made to match the characteristics of the respective approaches. 
     In other electromechanical switches according to the invention, in a structural element, a plurality of cantilevered beams are made up of the plurality of connecting portions. By adopting this configuration, since the contact portion can be actuated from both sides thereof, stable switching can be implemented. 
     A filter of the present invention is provided with the electromechanical switch. 
     By the filter being configured as described above, the device can be made smaller in size and the loss thereof can be reduced, and the advantage of using the electromechanical switch of the invention is large. 
     A duplexer of the present invention is provided with the electromechanical switch. 
     By the filter being configured as described above, the device can be made smaller in size and the loss thereof can be reduced, and the advantage of using the electromechanical switch of the invention is large. 
     A communication apparatus of the present invention is-provided with the duplexer. As a result of this, the loss of the device can be reduced, and the size thereof can also be reduced. 
     In the electromechanical switch according to the invention, by forming the actuating portion and the contact portion into the different beams, the first gap defined between the actuating electrode and the first beam and the second gap defined between the contact electrode and the second beam can be formed in different magnitudes (the first gap&lt;the second gap), whereby high isolation when the switch is off and low voltage actuation by high electrostatic force when the switch is actuated can be realized. In addition, the displacement of the beam produced in the actuating portion is made to be transmitted to the contact portion via the connecting portion, and the connecting portion is made into the cantilevered beam and is made to operate in the cantilevered fashion, whereby even in the configuration in which the first gap&lt;the second gap, the electromechanical switch can be realized which is highly electrically and mechanically reliable. 
     Furthermore, with the filter and communication apparatus which utilize the electromechanical switch of the invention, the reduction in loss and size can be facilitated, and there can be provided an advantage that even a plurality of communication systems can be made up using a small number of switches. 
     Thus, judging from the viewpoints described above, the construction of the invention can provide a great advantage in utilizing the electromechanical switch thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1A  is a perspective view of an electromechanical switch according to Embodiment 1 of the invention; 
         FIG. 1B  is a sectional view of the switch taken along the line A-A; 
         FIG. 1C  is a sectional view of the switch taken along the line B-B; 
         FIG. 2A  is a sectional view showing a first beam of the electromechanical switch in an off state depicted in  FIGS. 1A ; 
         FIG. 2B  is a sectional view showing a second beam of the electromechanical switch in the off state depicted in Fig. IA; 
         FIG. 2C  is a sectional view showing the first beam of the electromechanical switch in an on state depicted in  FIGS. 1A ; 
         FIG. 2D  is a sectional view showing a second beam of the electromechanical switch in the on state depicted in  FIG. 1A ; 
         FIG. 3A  is a perspective view of an electromechanical switch for explaining the position of a slit in the electromechanical switch according to Embodiment 1 of the invention; 
         FIG. 3B  is a sectional view of the switch taken along the line A-A; 
         FIG. 3C  is a sectional view of the switch taken along the line B-B; 
         FIG. 4A  is a perspective view of an electromechanical switch according to Embodiment 1 of the invention for explaining the position of a slit in the electromechanical switch; 
         FIG. 4B  is a sectional view of the switch taken along the line A-A; 
         FIG. 4C  is a sectional view of the switch taken along the line B-B; 
         FIG. 5A  is a diagram of an electromechanical switch for explaining the length of a structural element in the electromechanical switch according to Embodiment 1 of the invention; 
         FIG. 5B  is a diagram of the switch for explaining the length of a connecting portion and a displacement of a contact portion; 
         FIG. 6A  is a perspective view of another electromechanical switch according to Embodiment 1 of the invention; 
         FIG. 6B  is a sectional view of the another electromechanical switch in an off state taken along the line A-A; 
         FIG. 6C  is a sectional view of the another electromechanical switch in the off state taken along the line B-B; 
         FIG. 7A  is a sectional view of the electromechanical switch shown in  FIG. 6  in an on state taken along the line A-A; 
         FIG. 7B  is a sectional view of the electromechanical switch in an on state taken along the line B-B; 
         FIG. 8A  is a sectional view of further another electromechanical switch in an on state taken along the line A-A; 
         FIG. 8B  is a sectional view of the further another electromechanical switch in an off state taken along the line B-B; 
         FIG. 9A  is a perspective view of an electromechanical switch according to Embodiment 2 of the invention; 
         FIG. 9B  is a sectional view of the electromechanical switch in an off state taken along the line A-A; 
         FIG. 9C  is a sectional view of the electromechanical switch in an off state taken along the line B-B; 
         FIG. 10A  is a sectional view of the electromechanical switch in an on state taken along the line A-A; 
         FIG. 10B  is a sectional view of the electromechanical switch in an on state taken along the line B-B; 
         FIG. 11  is a sectional view of an electromechanical switch according to Embodiment 3 of the invention; 
         FIG. 12  is a sectional view of an electromechanical switch according to Embodiment 4 of the invention; 
         FIG. 13A  is a perspective view of an electromechanical switch according to Embodiment 5 of the invention; 
         FIG. 13B  is a sectional view of the electromechanical switch taken along the line A-A; 
         FIG. 13C  is a sectional view of the electromechanical switch taken along the line B-B; 
         FIG. 14A  is a sectional view showing the electromechanical switch in an off state depicted in  FIGS. 13A to 13C ; 
         FIG. 14B  is a sectional view showing the electromechanical switch in an on state depicted in  FIGS. 13A to 13C ; 
         FIG. 15A  is a perspective view of an electromechanical switch according to Embodiment 6 of the invention for explaining the position of a slit in the electromechanical switch; 
         FIG. 15B  is a sectional view of the switch taken along the line A-A; 
         FIG. 15C  is a sectional view of the switch taken along the line B-B; 
         FIG. 16A  is a perspective view of an electromechanical switch according to Embodiment 7 of the invention for explaining the position of a slit in the electromechanical switch; 
         FIG. 16B  is a sectional view of the switch taken along the line A-A; 
         FIG. 16C  is a sectional view of the switch taken along the line B-B; 
         FIG. 17A  is a perspective view of an electromechanical switch according to Embodiment 8 of the invention; 
         FIG. 17B  is a sectional view of the electromechanical switch in an off state taken along the line A-A of  FIG. 17A ; 
         FIG. 17C  is a sectional view of the electromechanical switch in an off state taken along the line B-B of  FIG. 17A ; 
         FIG. 18A  is a sectional view of the electromechanical switch in an on state taken along the line A-A; 
         FIG. 18B  is a sectional view of the electromechanical switch in an on state taken along the line B-B; 
         FIG. 19  is block diagram of a filter according to Embodiment 9 of the invention; 
         FIG. 20  is a block diagram of a duplexer according to Embodiment 10 of the invention; 
         FIG. 21  is a block diagram of communication apparatus according to Embodiment 11 of the invention; 
         FIG. 22A  is a sectional view showing a configuration of the conventional switch; and 
         FIG. 22B  is a plan view showing the configuration of the conventional switch. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, an electromechanical switch according to the invention will be described in detail by reference to some preferred embodiments shown in the accompanying drawings. 
     (Embodiment 1) 
     Embodiment 1 will be described by reference to  FIGS. 1A to 1C  and  FIGS. 2A to 2D . 
       FIGS. 1A to 1C  show drawings of a micromachine switch as an electromechanical switch according to Embodiment 1 of the invention.  FIG. 1A  is a perspective view of the electromechanical switch,  FIG. 1B  is a sectional view of the electromechanical switch taken along the line A-A in  FIG. 1A , and  FIG. 1C  is a sectional view of the same taken along the line B-B in  FIG. 1A . 
       FIGS. 2A to 2D  show sectional views which illustrate an on state and an off state of the electromechanical switch according to Embodiment 1.  FIGS. 2A and 2B  are sectional views showing the electromechanical switch in the off state and correspond to  FIGS. 1B and 1C .  FIGS. 2C and 2D  are sectional views showing the switch being in the on state and illustrate that first and second beams shown in  FIGS. 2A and 2B  are displaced, 
     This electromechanical switch is formed through the MEMS process using a silicon substrate as a constituent material. The electromechanical switch includes a first beam  106  and a second beam  107 . The first beam  106  is made up of two both-end fixed beams and constitutes an actuating portion. The second beam  107  is made up of a cantilevered beam and constitutes a contact portion  107 . The first and second beams being placed in parallel in such a manner that the second beam is held between the two both-end fixed beams of the first beam  106 . The electromechanical switch also includes a first electrode as an actuating electrode  105  and a second electrode as a wiring electrode (a contact electrode)  103 . The actuating electrode  105  is formed so as to have a first gap between the first beam  106  and the actuating electrode  105 . The wiring electrode  103  is formed so as to have a second gap between the second beam  107  and the wiring electrode  103 . The second gap is greater than the first gap. While hereinafter, reference numeral  103  shown in  FIG. 1  is understood to denote the wiring electrode, the wiring contact should include a contact with which the second beam is brought into abutment, that is, a contact electrode and its peripheral wiring. 
     Referring to  FIG. 1A , reference numeral  101  denotes a substrate into which constituent elements of a micromachine device are incorporated. Silicone, gallium arsenic, SiC and the like can be used as materials for the substrate. Support portions  102  are provided on the substrate  101  as spacers which support a structural element  108  on the substrate  101  with a predetermined gap provided therebetween. A U-shaped slit is provided in the structural element  108  so as to divide the structural element  108  into the first beam  106  which constitutes the actuating portion and the second beam  107  which constitutes the contact portion. The first beam  106  constituting the actuating portion is constructed as the both-end fixed beam, while the second beam  107  constituting the contact portion is constructed as the cantilevered beam. The displacement of the first beam  106  constituting the actuating portion is made to be transmitted to the second beam  107  via a connecting portion  109 , whereby the second beam  107  is displaced so as to be electrically connected to the wiring electrode  103  for implementation of switching. As this occurs, since the gap defined between the first beam  106  constituting the actuating portion and the first electrode is made smaller than the gap defined between the second beam  107  and the second electrode, a displacement amount of the second beam  107  until the electric connection is made becomes larger than the displacement of the first beam  106 . 
     In addition, the actuating electrode  105  is formed on the substrate  101  below the first beam  106 , so that electrostatic force is generated by applying voltage between the first beam  106  and the actuating electrode  105 , whereby the beam is displaced. In addition, since the second beam  107  is displaced in a symmetrical fashion relative to a width direction of the beam, the first beam  106  is configured so as to be arranged on both sides of the second beam  107 . As this occurs, the actuating electrode  105  is covered with an insulation membrane  104  made up of a silicon oxide membrane so as to prevent an electric contact between the first beam  106  and the actuating electrode  105 , and electrostatic force is made to be generated with this insulation membrane  104  acting as a capacitive insulation membrane. Here, the actuating electrode  105  and the wiring electrode  103  constitute the same plane. In addition, the thickness of the insulation membrane  104  is in the order of 200 nm to several tim, and the difference in magnitude between the first and second gaps is made by the thickness of the insulation membrane  104 . 
     The operation of the electromechanical switch described above will be explained as follows. 
     When the contact portion  107  is positioned apart from the wiring electrode  103  as is shown in  FIGS. 2A and 2B , the switch is in an off state. When an electric field is applied between the first beam  106  and the actuating electrode  105 , the first beam  106  is displaced by virtue of electrostatic force. As this occurs, by the first beam  106  being displaced as is shown in  FIG. 2C , the second beam  107  can be displaced downwards. In this way, the second beam  107  is displaced to be connected to the wiring electrode  103 , whereby the switch is put in an on state ( FIG. 2D ). 
     By this configuration, the actuating portion and the contact portion can be constructed to be separated from each other, and the displacement (force) of the actuating portion is transmitted to the contact portion through the connecting portion  109 , whereby the contact portion can be displaced. As this occurs, since the actuating portion is constructed by the both-end fixed beam and the contact portion is constructed by the cantilevered beam, the displacement generated in the actuating portion can be magnified so as to allow the contact portion to be displaced largely. Thus, the advantage provided by the aforesaid configuration is large. 
     In addition, the gap defined between the first beam  106  constituting the actuating portion and the actuating electrode  105  is made smaller than the gap defined between the second beam  107  and the wiring electrode  103 . By this configuration, an actuating voltage necessary for switching can be reduced or the switching speed can be made faster while ensuring a required electric isolation when the switch is on/off. Thus, the advantage provided by the above configuration is large. 
     Additionally, since the electric field necessary for actuation concentrates on the first beam  106  and the first electrode  105 , even when the switch is used in small communication apparatus such as a mobile phone, there is caused no situation where the peripheral circuits are badly affected by the electric field. Furthermore, when the switch is actuated in the above described approach, since only the voltage is applied and no current is generated, no electric power is consumed by the actuation of the switch. 
     In addition, when the switch is configured to be actuated by the approach described above, the switch can be fabricated only through the standard CMOS process. Additionally, since the first electrode  105  and the second electrode  103  are made of the same material, not only can the fabrication of the switch be facilitated but also the actuation with lower voltage can be enabled by electrostatic force being allowed to act on not only the first electrode but also the second electrode. 
     The electromechanical switch of Embodiment 1 will be described further. Here, a relationship between the slit and the lengths of the actuating portion and the contact portion will be observed.  FIGS. 3A to 3C  show drawings which depict the position of a slit provided in an electromechanical switch of Embodiment 1 of the invention.  FIG. 3A  is a perspective view of the electromechanical switch,  FIG. 3B  is a sectional view of the electromechanical switch taken along the line A-A, and  FIG. 3C  is a sectional view of the electromechanical switch taken along the line B-B in  FIG. 3A . 
     Here, a U-shaped slit S is desirably formed in an area which extends along three-fourth of a structural element  118 . This is because in the event that the slit S is formed up to an area in the proximity of a support portion  102 , a displacement (distortion) generated in a first beam  116  constituting the actuating portion cannot be transmitted sufficiently to a second beam  117  constituting the contact portion due to the effect of the support portion  102 , and hence, a large displacement cannot be obtained. Note that in here, like reference numerals are imparted to like constituent portions to those shown in  FIGS. 1 and 2 . 
     In addition,  FIGS. 4A to 4C  show drawings which depict a case where a slit S is formed up to a portion in the proximity of a central portion of a structural element  128  of an electromechanical switch of Embodiment 1 of the invention.  FIG. 4A  is a perspective view of the electromechanical switch,  FIG. 4B  is a sectional view of the same switch taken along the line A-A and  FIG. 4C  is a sectional view of the switch taken along the line B-B in  FIG. 4A . When the slit S is adopted which extends to the portion in the proximity of the central portion of the structural element  128 , displacement is produced mainly in a first beam  126  which is a both-end fixed beam and which constitutes the actuating portion in a direction in which the first beam  126  is deflected, whereas the displacement of a second beam  127  which is a cantilevered beam and which constitutes the contact portion is restricted, and hence, the second beam  127  cannot be displaced largely. Furthermore, it is considered that the fact that the second beam  127  cannot be displaced largely may cause a fear that the second beam  127  is prevented from being electrically connected with a wiring electrode due to a difference in magnitude between a gap defined between the actuating portion and the actuating electrode and a gap defined between the contact portion and the wiring electrode. The first beam  126  and the second beam  127  are formed integrally via a connecting portion  129 . Note that also in here, like reference numerals are imparted to like constituent portions to those shown in  FIGS. 1A to 1C  and  FIGS. 2A to 2D . 
       FIGS. 5A  an  5 B illustrate a relationship between the length of the connecting portion of the structural element of the electromechanical switch of Embodiment 1 of the invention and a maximum displacement amount of the contact portion.  FIG. 5A  is a drawing which depicts a length L of the structural element, and  FIG. 5B  is a graph showing a relationship between a length L of the connecting portion and a maximum displacement of the contact portion. A displacement direction identical to a direction in which the actuating portion is displaced is referred to a positive direction. As shown in the drawings, in the event that the length L of the connecting portion is in the range of one half or less of the length of the structural element, the contact portion can be displaced in the same direction in which the actuating portion is displaced. In addition, in the event that the length L of the connecting portion is one fourth of the length of the structural element, the displacement of the actuating portion can be transmitted to the contact portion with good efficiency so as to be transformed into a displacement of the contact portion, thereby making it possible to obtain a maximum displacement. 
     Note that in this embodiment, while the example is illustrated in which the gap defined between the actuating portion and the actuating electrode is made substantially different in magnitude from the gap defined between the contact portion and the wiring electrode by the insulation layer formed on the actuating electrode. However, the invention is not limited to the illustrated embodiment. A similar advantage can also be obtained by forming a recessed portion using a method of etching the substrate so as to provide a difference in level between the portion where the wiring electrode is formed and the portion where the actuating electrode is formed ( FIGS. 6A to 6C  and  FIGS. 7A and 7B ). 
       FIGS. 6A to 6C  show drawings which illustrate a modified example of an electromechanical switch according to Embodiment 1.  FIG. 6A  is a perspective view of a modified electromechanical switch,  FIG. 6B  is a sectional view of the electromechanical switch taken along the line A-A, and  FIG. 6C  is a sectional view of the electromechanical switch in an off state taken along the line B-B in  FIG. 6A . 
       FIGS. 7A and 7B  show sectional views which illustrate the modified electromechanical switch in an on state according to Embodiment 1.  FIGS. 7A and 7B  are sectional views showing the modified electromechanical switch in the on state and corresponding, respectively, to  FIGS. 2C and 2D  which show the state in which the first and second beams are displaced. 
     As is shown in the drawing, a wiring electrode  133  is formed in a recessed portion  139  which is formed on a surface of a substrate  131 . The wiring electrode  133  includes a contact electrode constituting an abutment portion with which a second beam  137  as a contact portion is brought into abutment. Therefore, a difference in magnitude can be made between a gap defined between an actuating portion and an actuating electrode and a gap defined between the contact portion and the wiring electrode. 
     In addition, while in the embodiment, the example is described in which the one actuating electrode is formed, needless to say, the same advantage can be obtained even in the event that an actuating electrode is divided into a plurality of actuating electrode portions on a substrate  141  as shown in  FIGS. 8A and 8B .  FIGS. 8A and 8B  are sectional views of a first beam  146  constituting the actuating portion and a second beam  147  constituting the contact portion when the switch is in the on state and correspond, respectively, to  FIGS. 2C and 2D  which show the state in which the first and second beams are displaced. Furthermore, electric field can be made to be applied uniformly to a plurality of areas by adopting the configuration in which the actuating electrode  144  is so divided. As a result of this, the actuating portion can be made to be displaced largely, the advantage of which becomes very large ( FIGS. 8A and 8B ). Note that surfaces of the actuating electrodes  144  are covered with insulation membranes  145 . 
     (Embodiment 2) 
     Referring to  FIGS. 9 and 10 , Embodiment 2 will be described. 
       FIGS. 9A to 9C  show drawings which illustrate an electromechanical switch according to Embodiment 2.  FIG. 9A  is a perspective view of the switch,  FIG. 9B  is a sectional view of the switch taken along the line A-A, and  FIG. 9C  is a sectional view of the switch taken along the line B-B in  FIG. 9A . The electromechanical switch shown in  FIGS. 9A to 9C  are in an off state. In addition,  FIGS. 10A ,  10 B show sectional views which illustrate the electromechanical switch in an on state. 
     As is shown in  FIG. 9A , this embodiment is characterized in that both a first beam  206  constituting an actuating portion and a second beam  207  constituting a contact portion are made up of cantilevered beams. Reference numeral  201  denotes a substrate in which constituent elements of the electromechanical switch of the embodiment are incorporated. Also, in this embodiment, silicon, gallium arsenic, SiC and the like can be used as materials for the substrate. A support portion  202  is provided on the substrate  201  for supporting a structural element  208 . The structural element  208  is constructed to be made up of three beams which are connected together in such a manner that two short beams  206  are formed on both sides of a longest beam  207 . The two short beams make up the first beam  206 , and the long beam makes up the second beam  207 , the first beam  206  and the second beam  207  being then connected together by a connecting portion  209 . The second beam  207  is electrically connected with a wiring electrode  203  formed on the substrate  201 , whereby switching is implemented. In addition, an actuating electrode  205  is formed on the substrate  201  below the first beam  206  which make up the actuating portion, and electrostatic force is produced by applying voltage between the first beam  206  and the actuating electrode  205 , whereby the beam is displaced. By the first beam  206  formed on both the sides of the second beam  207 , a displacement (distortion) in the first beam  206  is transmitted therefrom in a symmetrical fashion to the second beam  207 . The actuating electrode  205  is covered with an insulation membrane  204  so as to prevent the first beam  206  from being electrically connected to the actuating electrode  205  as the displacement is so transmitted, and electrostatic force is made to be generated using the insulation membrane  204  as a capacitive insulation membrane. 
     The Embodiment 2 differs from Embodiment 1 in that the first beam  206  is formed as not a beam which is fixed at both ends thereof but a beam which is fixed at only one end thereof or a cantilevered beam. 
     The operation of the electromechanical switch according to Embodiment 2 will be described. 
     Firstly, as shown in  FIGS. 9B and 9C , when the second beam  207  is positioned apart from the wiring electrode  203 , the electromechanical switch is in an off state. When an electric field is applied between the first beam  206  and the actuating electrode  205 , the first beam  206  is displaced by virtue of electrostatic force produced as a result of the application of the electric field. As this occurs, by the displacement of the first beam  206  as shown in  FIG. 10A , the second beam  207  constituting the contact portion can be displaced downwards. Since the second beam  207  is displaced so as to contact with the wiring electrode  203 , the electromechanical switch is turned in an on state ( FIG. 10B ). 
     By adopting the configuration described above, the construction can be realized in which the actuating portion and the contact portion are separated from each other, whereby a displacement (distortion) in the actuating portion can be transmitted to the contact portion through the connecting portion so as to displace the contact portion. As this occurs, since the length of the actuating portion differs from the length of the contact portion, a small displacement produced in the actuating portion can be magnified so that a large displacement is produced in the contact portion. Namely, in the event that a gap  1  defined between the actuating portion and the actuating electrode is made to differ in magnitude from a gap  2  defined between the contact portion and the wiring electrode, even when the gap  1 &lt;the gap  2 , the displacement produced in the actuating portion can be magnified to produce a large displacement in the contact portion, the advantage of which is large. 
     (Embodiment 3) 
     Referring to  FIG. 11 , Embodiment 3 will be described. 
       FIG. 11  is a perspective view showing an electromechanical switch according to Embodiment 3.  FIG. 11  shows a construction that a plurality of electromechanical switches described in Embodiment 1 can be switched therebetween. 
     The Embodiment 3 differs from Embodiment 1 and Embodiment 2 in that actuating portions  306  are formed at three locations and contact portions  307  are formed at two locations, and the other features and the operation principle of the embodiment remain the same as those of Embodiments 1 and 2. 
     By forming the electromechanical switch in described above, two signals can be used while being switched. In addition, when attempting to implement switching between a plurality of signals, this can be attained by forming as many contact portions as the number of switches (with a plurality of actuating portions required to be formed in accordance with the formation of contact portions). 
     (Embodiment 4) 
     Referring to  FIG. 12 , Embodiment 4 will be described. 
       FIG. 12  is a perspective view showing an electromechanical switch according to Embodiment 4.  FIG. 12  shows a construction in which the electromechanical switches according to Embodiment 2 can be switched. 
     This embodiment also differs from Embodiment 2 in that actuating portions  316  are formed at three locations and contact portions  317  are formed at two locations, and the other features and the operation principle of the embodiment remain the same as those of Embodiment 2. 
     By forming the electromechanical switch in the manner described above, two signals can be used while being switched. In addition, when attempting to implement switching between a plurality of signals, this can be attained by forming as many contact portions as the number of switches (with a plurality of actuating portions required to be formed in accordance with the formation of contact portions). 
     (Embodiment 5) 
     Referring to  FIGS. 13A to 13C , Embodiment 5 will be described. 
       FIGS. 13A to 13C  show drawings which depict an electromechanical switch according to Embodiment 5.  FIG. 13A  is a perspective view of the switch,  FIG. 13B  is a sectional view of the switch taken along the line A-A, and  FIG. 13C  is a sectional view of the switch taken along the line B-B in  FIG. 13A . In the drawings, the switch is in an off state. In addition,  FIGS. 14A and 14B  show sectional views of the electromagnetic switch in an on state. 
     This embodiment differs from Embodiment 1 in that a second beam  157  constituting a contact portion is made up of a beam which is fixed at both ends thereof while in Embodiment 1, the second beam constituting the contact portion was made up of the cantilevered beam. In addition, in this embodiment, a second electrode which faces to the second beam  157  is formed in a recessed portion  159  which is formed on a surface of a substrate, and a second gap defined between the second beam and the second electrode is made larger than a first gap defined by a first electrode and an actuating portion. 
     Namely, as with those described in Embodiments 1 to 4, the electromechanical switch of this embodiment is fabricated through the MEMS process using a silicon substrate  1  as a constituent material. The electromechanical switch includes a first beam  156  which is made up of two both-end fixed beams and which constitute the actuating portion and the second beam  157  which is made up of the both-end fixed beam and which constitutes the contact portion. The first beam  156  and the second beam  157  are placed in parallel in such a way that the second beam  157  is held between the two beams of the first beam  156 . In addition, the electromechanical switch further includes the first electrode  155  which is formed as an actuating electrode for the first beam  156  via the first gap and the second electrode  153  which is formed as a wiring electrode for the second beam  157  via the second gap, and the second gap is made larger than the first gap. 
     The operation of the above electromechanical switch will be described. 
     As is shown in  FIGS. 13B and 13C , when the second beam  157  is positioned apart from the wiring electrode  153 , the electromechanical switch is in the off state. When an electric field is applied between the first beam  156  and the actuating electrode  155 , the first beam  156  is displaced by virtue of electrostatic force as is shown in  FIG. 14A . The second beam  157  can be displaced downwards by the first beam  156 . As a result, the second beam  157  is connected to the wiring electrode  153 , and the electromechanical switch is turned to the on state ( FIG. 14B ). 
     The actuating portion and the contact portion can be constructed to be separated from each other by adopting the configuration described above, and a displacement (distortion) of the actuating portion is transmitted to the contact portion via a connecting portion  109 . Thereby, the contact portion can be displaced. As this occurs, since the actuating portion and the contact portion are constructed to be fixed at both the ends thereof, a stable operation is ensured, In addition, a small displacement produced in the actuating portion which is made up of the two beams lying on both sides of the contact portion is transmitted to the contact portion in a magnified fashion, whereby a large displacement can be produced in the contact portion. 
     In addition, the gap defined between the first beam  156  and the actuating electrode  155  is made smaller than the gap defined between the contact portion  157  and the wiring electrode  163 . By adopting this configuration, an actuating voltage necessary for switching can be reduced or the switching speed can be made faster while ensuring a required isolation when the switch is on/off, thus a large advantage being provided in utilizing the switch. 
     (Embodiment 6) 
     Referring to  FIGS. 15A to 15C , Embodiment 6 will be described. 
       FIGS. 15A to 15C  show drawings which depict an electromechanical switch according to Embodiment 6.  FIG. 15A  is a perspective view of the switch,  FIG. 15B  is a sectional view of the switch taken along the line A-A, and  FIG. 15C  is a sectional view of the switch taken along the line B-B in  FIG. 15A . In the drawings,  FIGS. 15B and 15C  show sectional views of the electromechanical switch in an on state. 
     Here, a power feeding method to an electrode will be described, and in this embodiment, after a structural element has been fabricated, a wiring electrode  113  is finally formed on a top layer lying on a first beam  106  constituting an actuating portion and a contact portion  107  with an aluminum wiring pattern. 
     Energization can be facilitated by this configuration. 
     (Embodiment 7) 
     Referring to  FIGS. 16A to 16C , Embodiment 7 will be described. 
       FIGS. 16A to 16C  show drawings which depict an electromechanical switch according to Embodiment 7.  FIG. 16A  is a perspective view of the switch,  FIG. 16B  is a sectional view of the switch taken along the line A-A, and  FIG. 16C  is a sectional view of the switch taken along the line B-B in  FIG. 16A . In the drawings,  FIGS. 16B and 16C  show sectional views of the electromagnetic switch in an on state. 
     Here, a power feeding method to an electrode will be described, and in this embodiment, a feeding portion is formed at the same time as a wiring electrode  103  is formed, and support elements  102 S are made of a conductive material such as doped polysilicone. 
     According to this configuration, a step of forming an energization portion and a step of forming a wiring electrode are made to occur at the same time, thereby making it possible to reduce the number of fabrication man-hours for simplified fabrication. 
     (Embodiment 8) 
     Next, Embodiment 8 of the invention will be described by reference to  FIGS. 17A to 17C  and  FIGS. 18A and 18B . 
       FIGS. 17A to 17C  show drawings of a electromechanical switch according to Embodiment 8.  FIG. 17A  is a perspective view of the electromechanical switch,  FIG. 17B  is a sectional view of the electromechanical switch in an off state taken along the line A-A, and  FIG. 17C  is a sectional view of the electromechanical switch in the off sate taken along the line B-B in  FIG. 17A . In addition,  FIG. 18A  is a sectional view of the electromechanical switch in an on state taken along the line A-A and  FIG. 18B  is a sectional view of the electromechanical switch in the on state taken along the line B-B in  FIG. 17A . 
     The electromechanical switch of this embodiment differs from that in Embodiment 1 in that the first and second beams  106 ,  107  are actuated not only by electrostatic force but also by making use of piezoelectric effect since piezo electric thin films  106 P,  107 P are held by electrodes  106   e ,  107   e , respectively. 
     Referring to  FIG. 17A , reference numeral  101  denotes a substrate into which constituent elements of a micromachine device are incorporated. Silicone, gallium arsenic, SiC and the like can be used as materials for the substrate. Support portions  102  are provided on the substrate  101  as spacers which support a structural element  108  on the substrate  101  with a predetermined gap provided therebetween. The structural element  108  is configured by disposing metallic thin films which make up electrodes on upper and lower sides of piezoelectric thin films. A U-shaped slit is provided in the structural element  108  so as to divide the structural element  108  into a first beam  106  which makes up an actuating portion and a second beam  107  which makes up a contact portion, and the first beam  106  is constructed as the both-end fixed beam, while the second beam  107  is constructed as the cantilevered beam, The displacement of the first beam  106  is made to be transmitted to the second beam  107  via a connecting portion  109 , whereby the second beam  107  is displaced so as to be electrically connected to a wiring electrode  103  for implementation of switching. As this occurs, since a gap defined between the first beam  106  which makes up the actuating portion and a first electrode is made smaller than a gap defined between the second beam  107  which makes up the contact portion and a second electrode, a displacement amount of the second beam  107  until the electric connection is made becomes larger than the displacement of the first beam  106 . 
     In addition, an actuating electrode  105  is formed on the substrate  101  below the first beam  106 , so that electrostatic force is generated by applying voltage between the first beam  106  and the actuating electrode  105 . Furthermore, in this embodiment, distortion due to piezoelectric effect is generated by applying voltage between the electrodes disposed on the upper and lower sides of the piezoelectric thin film. The beams are displaced by virtue of the electrostatic force and the distortion based on the piezoelectric effect. 
     On and off operations of the electromechanical switch are similar to those of Embodiment 1. 
     Thus, by the electromechanical switch, in addition to the advantage described in Embodiment 1, an advantage can also be provided that the electromechanical switch of the embodiment can be actuated with a lower voltage and at higher speeds compared with the case where the same switch would be actuated only by electrostatic force. 
     (Embodiment 9) 
       FIG. 19  is a drawing showing the configuration of a filter according to Embodiment 9. In  FIG. 19 , an example of a frequency switching filter including an electromechanical switch and a piezoelectric thin film resonator filter will be shown. 
     Piezoelectric thin film resonators  402   a ,  402   b ,  402   c  are connected in series between a terminal  407   a  and a terminal  401   a . Piezoelectric thin film resonators  403   a  and  403   b  are connected, respectively, between a connection point between the piezoelectric thin film resonators  402   a  and  402   b  and a ground potential and between a connection point between the piezoelectric thin film resonators  402   b  and  402   c  and a ground potential. Similarly, Piezoelectric thin film resonators  405   a ,  405   b ,  405   c  are connected in series between a terminal  407   b  and a terminal  401   b . Piezoelectric thin film resonators  406   a  and  406   b  are connected, respectively, between a connection point between the piezoelectric thin film resonators  405   a  and  405   b  and a ground potential and between a connection point between the piezoelectric thin film resonators  405   b  and  405   c  and a ground potential. 
     The terminals  407   a  and  407   b  are connected, respectively, to different terminals of an electromechanical switch  404 . In addition, the other terminal of the electromechanical switch is connected to a terminal  408 . 
     Next, the operation of the above described frequency switching filter will be described. 
     The electromechanical switch  404  performs the same operation of the electromechanical switch shown in Embodiment 3 and includes two wiring electrodes. The terminal  407   a  or  407   b  is connected with the terminal  408  by switching. When the terminal  408  is connected with the terminal  407   a , a signal is allowed to pass through the terminal  408  and the terminal  401   a . Conversely, when the terminal  408  is connected with the terminal  407   b , the signal is allowed to pass through the terminal  408  and the terminal  401   b.    
     As this occurs, for example, by differentiating the frequency characteristic of the filter which is made up of the piezoelectric thin film resonators  402   a ,  402   b ,  402   c ,  403   a ,  403   b  from the frequency characteristic of the filter made up of the piezoelectric thin film resonators  405   a ,  405   b ,  405   c ,  406   a ,  406   b , a frequency variable filter can be realized which can cope with a plurality of frequency bands. 
     In addition, while in the embodiment, as the example, the filter is described as being made up of the piezoelectric thin film resonators, even in the event that  402   a ,  402   b ,  402   c ,  403   a ,  403   b  are made up of elastic surface wave filters, a similar advantage can, needless to say, be obtained. 
     (Embodiment 10) 
       FIG. 20  is a drawing showing the configuration of a duplexer according to Embodiment 10. A frequency variable duplexer can be realized by using the duplexer of a plurality of filters (two sets of sending filters  501   a ,  501   b  and receiving filters  502   a ,  502   b ) and phase-shifting circuits  505 ,  506 . The references  503   a ,,  503   b ,  504   a ,  504   b ,  508   a ,  508   b ,  509   a ,  509   b  denote nodes, respectively. 
     By this configuration, since it is not necessary to arrange a plurality of switches, not only the duplexer can be made smaller in size but also the duplexer can be realized whose loss is reduced compared with a case where switches are individually packaged. The following is the reason for this. 
     Signals whose frequencies ranging from hundreds MHz to several GHz are handled in radio or wireless communication apparatus. Because of this, the floating capacity and loss caused by a laid out wiring are increased. However, as is described in this embodiment, by the switching configuration in which the actuating portion and the contact portion are separated from each other, isolation can be ensured when the switch is off, and the loss can be reduced. Furthermore, by narrowing the gap of the actuating portion, the voltage necessary for actuation can be reduced, and the response can also be made faster. 
     Note that while in this embodiment, the duplexer includes the electromechanical switch, the sending filters and the receiving filters. However, the same advantage can be obtained even in the event that the duplexer includes the electromechanical switch and a plurality of sending filters or the electromechanical switch and a plurality of receiving filters. 
     In addition, while in this embodiment, the frequency variable duplexer is described as being realized through the combination of the filters whose frequency bands are different, an impedance variable duplexer can, needless to say, be realized by combining filters whose impedances are different. 
     (Embodiment 11) 
       FIG. 21  is a drawing showing the configuration of communication apparatus according to Embodiment 11. 
     Referring to  FIG. 21 , reference numeral  604  denotes the duplexer described in Embodiment 10. This device includes antennas  605   a ,  605   b , an electromechanical switch for switching between two frequency signals, the duplexer  604  which has the piezoelectric thin film resonator filters and other circuit components. By this configuration, the communication apparatus which is small in size and whose loss is small can be realized. 
     Note that while in the embodiment, no electrode is provided for the first and second beams, resistance loss can be reduced further by forming metallic electrodes of aluminum or the like for those first and second beams. In addition, the difference in magnitude between the first and second gaps may be formed by the thickness of electrodes formed on the beams or by existence and non-existence of electrodes. 
     It should be understood that all the embodiments that have been described heretofore are illustrative in all respects and are not such as to limit the scope of the invention. It should be construed that the scope of the invention is determined not by the description of the embodiments that have been made heretofore but by the claims thereof and that all changes and modifications are included in the invention which fall within the spirit and scope of the invention which are determined by the claims. 
     In the electromechanical switch according to the invention, the actuating portion and the contact portion are placed in parallel while being made to be separated from each other, and the displacement generated in the actuating portion is transmitted to the contact portion via the connecting portion for switching. Furthermore, the gap at the actuating portion can be made to differ in magnitude from the gap at the contact portion, whereby the high-speed actuation is enabled while ensuring the required isolation. Because of this, the electromechanical switch of the invention is effective as a switch for a high-frequency circuit or the like which requires good transmission efficiency when transmitting a signal, good insulation when the switch is off or a high-speed operation when a signal is connected or cut off. 
     In addition, with the filter and the communication apparatus which utilize the electromechanical switch according to the invention, high-speed response and low-loss characteristics can be obtained, and the electromechanical switch is also useful as a switch for switching a plurality of filters and communication systems. 
     Thus, as has been described heretofore, the electromechanical switch of the invention and the filter and communication apparatus which utilize the same switch are very useful for high-frequency circuits in mobile communication terminals for digital television broadcasting, mobile phones and wireless LAN.