Patent Publication Number: US-2007116406-A1

Title: Switch

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention generally relates to switches, and more particularly, to a switch that is mechanically driven and electrically coupled.  
      2. Description of the Related Art  
      In recent years, with the advancements of mobile communications systems, portable information terminals or the like are rapidly wide spreading. For instance, the mobile telephone systems utilize high-frequency bandwidths such as 800 MHz to 1 GHz and 1.5 GHz to 2.0 GHz. So, high-frequency switches are for use in the devices of the mobile communications systems. There is a demand for the high frequency switches in which the sizes are reduced and power is saved, and semiconductor switches with gallium arsenide (GaAs) or the like have been conventionally used. The semiconductor switches, however, have a high power loss and a low isolation. For these reasons, developments of high frequency microelectromechanical system (MEMS) switches are in progress by use of MEMS technology, so that miniaturization, low power loss, and high isolation can be achieved.  
      As disclosed in Japanese Patent Application Publication No. 2005-243576 and Japanese Patent Application Publication No. 2003-522377, there have been proposed MEMS switches having a cantilever beam, which is a movable beam with one end thereof secured to the substrate. The MEMS switches use Silicon-On-Insulator (SOI) substrate, and the cantilever beam is formed of the upper silicon layer. A thin film electrode of Au is provided at an end of the cantilever beam, and the upper electrode is fabricated by Au plating at the upper portion of the thin film electrode. A switch contact portion is configured in such a manner that the thin film electrode and the upper electrode are in connection or disconnection. The cantilever beam is driven by an electrostatic actuator or electromagnetic actuator. For example, the electrostatic actuator includes the lower electrode on the cantilever beam and the upper electrode above the cantilever beam. The cantilever beam is driven by supplying a voltage between the upper electrode and the lower electrode.  
      There is a demand for the MEMS switches in which the driving power is reduced, namely, the power consumption is reduced, the stability is enhanced, and the sizes are reduced. Generally, when the drive voltage is decreased, the contact operation of the switch contact portion becomes unstable. For example, even if a small power is generated from the actuator to decrease the drive voltage of the MEMS switch, the switch contact portion needs to be operable. As a method thereof, the spring constant of the movable beam portion is reduced. Such reduced spring constant of the movable beam portion, however, weakens the opening force when the switch contact portion is opened. This may cause the phenomenon of being unopened and lead to unstable contact operation, when the switch contact portion is opened and closed a number of times. As described above, the reduced drive voltage and the stable contact operation at the switch contact portion are in a trade-off relationship.  
      There has been proposed a method of suppressing the power consumption during operation in the switch having an electromagnetic actuator by use of a latch structure with hysteresis characteristics in the electromagnetic actuator. Also, there has been proposed a seesaw structure with a hinge to realize the latch structure. Nevertheless, the magnetic thin film or coil cannot be easily reduced in size, even if the above-described method or structure is employed. It is difficult to reduce the MEMS switches in size.  
      Meanwhile, the electrostatic actuator has a simple structure, the fabrication thereof is easy, and the size thereof can be reduced. There is a method of reducing the gap between the electrodes of the electrostatic actuator to reduce the drive voltage of the electrostatic actuator. However, when the gap between the electrodes is narrowed, there may cause a sticking problem while the electrostatic actuator is being fabricated.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in view of the above circumstances and provides a switch in which the size thereof can be reduced, the drive voltage thereof can be reduced, or the contact operation at the switch contact portion thereof can be stably performed.  
      According to one aspect of the present invention, there is provided a switch including: multiple torsion springs with each of one ends thereof secured to a substrate; a beam portion, to which each of the other ends of the multiple torsion springs is secured, and which is swung by an electrostatic actuator; and a switch contact portion in which a first contact provided at the beam portion and a second contact secured to the substrate are in connection or disconnection. Downsizing is enabled by employing the electrostatic actuator. Even if the voltage to be applied to the electrostatic actuator is small, the beam portion can be driven with the reduced spring constant because the spring contact becomes smaller. This enables the drive voltage to be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred exemplary embodiments of the present invention will be described in detail with reference to the following drawings, wherein:  
       FIG. 1  is a top view of a switch in accordance with a first exemplary embodiment of the present invention;  
       FIG. 2A  is a cross-sectional view taken along the line A-A shown in  FIG. 1 ;  
       FIG. 2B  is a cross-sectional view taken along the line B-B shown in  FIG. 1 ;  
       FIG. 2C  is a cross-sectional view taken along the line C-C shown in  FIG. 1 ;  
       FIG. 3A  through  FIG. 3E  are cross-sectional views showing a fabrication method of the switch employed in the first exemplary embodiment of the present invention;  
       FIG. 4A  and  FIG. 4B  respectively show a torsion spring structure and a cantilever beam structure used for calculation of spring constant;  
       FIG. 5  shows calculation results of the spring constants of the two structures with respect to the beam length of a beam portion;  
       FIG. 6  schematically shows a circuit diagram when the switch employed in the first exemplary embodiment is operated;  
       FIG. 7A  and  FIG. 7B  respectively show timing charts when the switch employed in the first exemplary embodiment is operated;  
       FIG. 8  is a perspective view of the switch in accordance with a second exemplary embodiment of the present invention;  
       FIG. 9  is a perspective view of the switch in accordance with a third exemplary embodiment of the present invention;  
       FIG. 10  is a perspective view of the switch in accordance with a fourth exemplary embodiment of the present invention;  
       FIG. 11  is a perspective view of the switch in accordance with a fifth exemplary embodiment of the present invention; and  
       FIG. 12  is a perspective view of the switch in accordance with a sixth exemplary embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A description will now be given, with reference to the accompanying drawings, of exemplary embodiments of the present invention.  
     First Exemplary Embodiment  
      A description will be given, with reference to  FIG. 1 ,  FIG. 2A  through  FIG. 2C , of a configuration of a switch in accordance with a first exemplary embodiment of the present invention.  FIG. 1  is a top view of the switch employed in the first exemplary embodiment of the present invention.  FIG. 2A  is a cross-sectional view taken along the line A-A shown in  FIG. 1 .  FIG. 2B  is a cross-sectional view taken along the line B-B shown in  FIG. 1 .  FIG. 2C  is a cross-sectional view taken along the line C-C shown in  FIG. 1 .  
      As shown in  FIG. 2A  through  FIG. 2C , the switch employed in the first exemplary embodiment has a Silicon-On-Insulator (SOI) substrate  60 , in which there are provided: a silicon substrate  50 ; a silicon oxide layer  52 ; and a silicon layer  54 . In addition, the switch employed in the first exemplary embodiment has a stacked structure in which metal layers  56  and  58  are stacked on the SOI substrate  60 . The silicon substrate  50  may have a thickness of, for example, 600 μm, the silicon oxide layer  52  may have a thickness of, for example, 4 μm, the silicon layer  54  may have a thickness of, for example, 15 μm, the metal layer  56  may have a thickness of, for example, 20 μm, and the metal layer  58  may have a thickness of, for example, 20 μm.  
      Referring to  FIG. 1  and  FIG. 2B , two torsion springs  12   a  and  12   b  are formed of the silicon layer  54 , and each of one ends thereof is secured to the SOI substrate  60 . Here, the torsion spring demonstrates spring characteristics by twisting. Each of the other ends of the torsion springs  12   a  and  12   b  is secured to a common portion  11  in a beam portion  10 . The silicon oxide layer  52  arranged below the torsion springs  12   a  and  12   b  and below the beam portion  10  is removed, and a cavity  66  is defined. Referring to  FIG. 1  and  FIG. 2A , the beam portion  10  includes: sub beam portions  13   a  and  13   b ; and the common portion  11  to which each of one ends of the sub beam portions  13   a  and  13   b  is secured, and the beam portion  10  is integrally formed of the silicon layer  54  to be a rigid body. The silicon oxide layer  52  below the torsion springs  12   a  and  12   b  and below the beam portion  10  is removed and the cavity  66  is defined. In the periphery of the beam portion  10 , the silicon oxide layer  52  is removed except the torsion springs  12   a  and  12   b , and slits  62  are formed. The beam portion  10  is surrounded by the slits  62  and the cavity  66 , except the portion held by the torsion springs  12   a  and  12   b . In other words, the beam portion  10  is held by the torsion springs  12   a  and  12   b  only. The sub beam portions  13   a  and  13   b  are provided at both sides of the common portion  11 .  
      Referring to  FIG. 1 ,  FIG. 2A , and  FIG. 2C , there are respectively provided a lower electrode  22   a  of an electrostatic actuator  20   a , and a lower electrode  22   b  of an electrostatic actuator  20   b  on top surfaces of the sub beam portions  13   a  and  13   b . There are respectively provided upper electrodes  24   a  and  24   b , formed of the metal layer  58 , above the lower electrodes  22   a  and  22   b . The electrostatic actuator  20   a  is formed of the lower electrode  22   a  and the upper electrode  24   a , and the electrostatic actuator  20   b  is formed of the lower electrode  22   b  and the upper electrode  24   b . Referring to  FIG. 2C , the upper electrodes  24   a  and  24   b  are respectively secured through the metal layer  56  provided at both sides of the sub beam portions  13   a  and  13   b  to the SOI substrate  60 , and are electrically coupled to pads  40 . Referring to  FIG. 1  and  FIG. 2B , the lower electrodes  22   a  and  22   b  are electrically coupled to the pads  40  respectively by wiring electrodes  18   a  and  18   b . The wiring electrodes  18   a  and  18   b  are respectively provided on the torsion springs  12   b  and  12   a . Referring back to  FIG. 1  and  FIG. 2A , the electrostatic actuators  20   a  and  20   b  are respectively driven by the voltages supplied to the lower electrodes  22   a  and  22   b  and the upper electrodes  24   a  and  24   b . Then, the electrostatic actuators  20   a  and  20   b  swings up and down the beam portion  10 .  
      Referring to  FIG. 1  and  FIG. 2A , a first contact  32   a  is arranged at an end of the sub beam portion  13   a . A second contact  36   a  is arranged on the first contact  32   a . The second contact  36   a  is provided in an upper layer  34  composed of the metal layers  58  and  56 . The second contact  36   a  is secured through the upper layer  34  to the SOI substrate  60 , and is electrically coupled to the pad  40 . The first contact  32   a  and the second contact  36   a  compose a switch contact portion  30   a . Two second contacts  36   a  are provided to one first contact  32   a . When the sub beam portion  13   a  is driven upward, the first contact  32   a  and the second contacts  36   a  are in connection. Then, one of the upper layers  34 , one of the second contacts  36   a , and one of the first contact  32   a  become conductive, and each of the other second contacts  36   a  and the other upper layer  34  becomes conductive. Then, the switch contact portion  30   a  is in connection. Meanwhile, when the first contact  32   a  and the second contacts  36   a  are in disconnection, the switch contact portion  30   a  is in disconnection. A switch contact portion  30   b  provided to the sub beam portion  13   b  operates in a similar manner.  
      A description will now be given of a fabrication method of the switch employed in the first exemplary embodiment of the present invention.  FIG. 3A  through  FIG. 3E  show the fabrication method of the switch employed in the first exemplary embodiment of the present invention.  FIG. 3A  through  FIG. 3E  are cross-sectional views taken along the line A-A shown in  FIG. 1 . Referring now to  FIG. 3A , a metal thin film of, for example, Mo, Au, or the like is formed on the SOI substrate  60  composed of: the silicon substrate  50 ; the silicon oxide layer  52 ; and the silicon layer  54 . The first contacts  32   a  and  32   b , the lower electrodes  22   a  and  22   b , and the wiring electrodes  18   a  and  18   b  are formed by use of the lithography and etching techniques.  
      Referring now to  FIG. 3B , the slits  62  are formed in the silicon layer  54 , in the periphery of the beam portion  10  and the torsion springs  12   a  and  12   b . The slits  62  are formed by use of the lithography and etching techniques. Referring now to  FIG. 3C , a sacrifice layer  64  formed, for example, of a silicon oxide film and having a thickness of several microns is formed by plasma Chemical Vapor Deposition (CVD). Then, a given region of the sacrifice layer  64  is removed by use of the lithography and etching techniques.  
      Referring now to  FIG. 3D , a photoresist is formed in a given region and Au is formed by plating. By this process, the upper layer  34  and the upper electrodes  24   a  and  24   b  are formed. Referring now to  FIG. 3E , the sacrifice layer  64  and the silicon oxide layer  52  are removed by use of a hydrofluoric acid based etchant. By this process, the silicon oxide layer  52  arranged below the beam portion  10  is removed and the cavity  66  is defined. As described heretofore, the switch employed in the first exemplary embodiment is fabricated.  
      In  FIG. 3D  and  FIG. 3E , the second contacts  36   a  and  36   b  are provided in the upper layer  34 . The second contacts  36   a  and  36   b  may be included in the upper layer  34  as described. When the second contacts  36   a  and  36   b  are provided at the lower surface of the upper layer  34  as shown in  FIG. 2A , recess portions are provided to form the second contacts  36   a  and  36   b  in the sacrifice layer  64 . Subsequently, the processes shown in  FIG. 3D  and  FIG. 3E  are performed. It is therefore possible to arrange the second contacts  36   a  and  36   b  at the lower surface of the upper layer  34 .  
      Here, the calculation is executed and compared between the spring constant of the torsion structure in which the beam portion is held by the torsion springs  12   a  and  12   b  and that of the cantilever beam structure in which each of one ends of the torsion springs  12   a  and  12   b  is secured.  FIG. 4A  and  FIG. 4B  respectively show the torsion spring structure and the cantilever beam structure used for the calculation. Referring to  FIG. 4A , the beam portion held by the torsion springs is made of silicon with a width of 100 μm and a thickness of 15 μm. Two ends thereof at one side are secured to the two torsion springs, and the other end at the other side is loaded. There are provided two tension springs, each of which has a length of 100 μm, a width of 10 μm, and a thickness of 15 μm. Each one end of the two torsion springs is secured to the beam portion, and each of the other ends thereof is secured to, for example, the substrate. Referring to  FIG. 4B , the cantilever beam is made of silicon with a width of 100 μm and a thickness of 15 μm. One end of the cantilever beam is secured and each of the other end thereof is loaded.  
       FIG. 5  shows calculation results of the spring constants of the above-described two structures with respect to the beam length of the beam portion. In both of the torsion spring structure and the cantilever beam structure, the longer the beam length, the smaller the spring constant. The spring constant of the torsion spring structure can be reduced by one digit or more as compared to that of the cantilever beam structure.  
      A description will now be given, with reference to  FIG. 6 ,  FIG. 7A , and  FIG. 7B , of the operation of the switch employed in the first exemplary embodiment of the present invention.  FIG. 6  schematically shows a circuit diagram when the switch employed in the first exemplary embodiment is operated. Hereinafter, in  FIG. 6 , the same components and configurations as those employed in  FIG. 2A  have the same reference numerals and a detailed explanation will be omitted. As shown in  FIG. 6 , a drive signal Vd 2  is input from a signal generator  80  into the electrostatic actuator  20   b  (hereinafter, referred to as second electrostatic actuator) provided at the sub beam portion  13   b , which is one of the sub beam portions  13   a  and  13   b  opposing each other and interposing the common portion  11  of the switch employed in the first exemplary embodiment. A drive signal Vd 1  is input into the electrostatic actuator  20   a  (hereinafter, referred to as first electrostatic actuator) provided at the other sub beam portion  13   a , whereas the drive signal Vd 1  is an inverted signal of the signal generator  80  and inverted at an inverter  82 . The high level and low level of the drive signal may be configured as, for example, TTL level.  
       FIG. 7A  and  FIG. 7B  respectively show the voltage Vdl applied to the first electrostatic actuator  20   a  and the voltage Vd 2  applied to the second electrostatic actuator  20   b . The voltage Vd 2  is passed through the inverter and turned into the voltage Vd 1 . That is, the Vd 1  and Vd 2  function as inverted signals. When the voltage Vd 1  is a low voltage and the voltage Vd 2  is a high voltage, a repulsive force is applied to the first electrostatic actuator  20   a  and an attractive force is applied to the second electrostatic actuator  20   b . For this reason, the switch contact portion  30   a  (hereinafter, referred to as first switch contact portion) is in disconnection (turned off), whereas the switch contact portion  30   b  (hereinafter, referred to as second switch contact portion) is in connection (turned on). Meanwhile, when the voltage Vd 1  is a high voltage and the voltage Vd 2  is a low voltage, an attractive force is applied to the first electrostatic actuator  20   a  and a repulsive force is applied to the second electrostatic actuator  20   b . For this reason, the switch contact portion  30   a  is in connection (turned on), whereas the switch contact portion  30   b  is in disconnection (turned off).  
      In the switch employed in the first exemplary embodiment, the beam portion  10  is driven by the electrostatic actuators  20   a  and  20   b , and each of one ends of the torsion springs  12   a  and  12   b  is secured to the SOI substrate  60  and the other ends thereof are secured to the beam portion  10 . As shown in  FIG. 5 , by employing the torsion spring structure, the spring constant is made smaller. Even if a small voltage is applied to the electrostatic actuators  20   a  and  20   b , it is possible to activate the beam portion. This enables the drive voltage to be reduced. Here, in the first exemplary embodiment, a description has been given of a case where there are provided two sub beam portions  13   a  and  13   b , two electrostatic actuators  20   a  and  20   b , and two switch contact portions  30   a  and  30   b . However, there may be provided at least one sub beam portion, at least one electrostatic actuator, and at least one switch contact portion. If there are provided at least one electrostatic actuator, and at least one switch contact portion and the torsion spring structure is employed, the spring constant is made smaller and the drive voltage can be reduced.  
      The switch employed in the first exemplary embodiment has the beam portion  10  provided with: two sub beam portions  13   a  and  13   b ; and the common portion  11  to which each of one ends of the sub beam portions  13   a  and  13   b  is secured. The common portion  11  is connected and held by the two torsion springs  12   a  and  12   b . The two sub beam portions  13   a  and  13   b  respectively include: the electrostatic actuators  20   a  and  20   b ; and the first contacts  32   a  and  32   b . In addition, the switch contact portions  30   a  and  30   b  are respectively provided to correspond to the first contacts  32   a  and  32   b  respectively arranged at the sub beam portions  13   a  and  13   b . With such configuration, when the first switch contact portion  30   a  is in connection, the second switch contact portion  30   b  is in disconnection. When the second switch contact portion  30   b  is in connection, the first switch contact portion  30   a  is in disconnection. In this manner, the switch employed in the first exemplary embodiment functions as a Single-Pole Double-Throw (SPDT) switch.  
      Furthermore, as shown in  FIG. 7A  and  FIG. 7B , when a high voltage (first voltage) is applied to the first electrostatic actuator  20   a , a low voltage (second voltage) is applied to the second electrostatic actuator  20   b . When a low voltage (third voltage) is applied to the first electrostatic actuator  20   a , a high voltage (fourth voltage) is applied to the second electrostatic actuator  20   b . Accordingly, when a high voltage is applied to the first electrostatic actuator  20   a  and a low voltage is applied to the second electrostatic actuator  20   b , the first switch contact portion  30   a  is in disconnection (off state) and the second switch contact portion  30   b  is in connection (on state). Meanwhile, when a high voltage is applied to the first electrostatic actuator  20   a  and a low voltage is applied to the second electrostatic actuator  20   b , the first switch contact portion  30   a  is in connection (on state) and the second switch contact portion  30   b  is in disconnection (off state).  
      The first voltage and the fourth voltage may be different, and the second voltage and the third voltage may be different. However, preferably, the first voltage and the fourth voltage are same, and the second voltage and the third voltage are same in accordance with the first exemplary embodiment. This is because the first switch contact portion  30   a  and the second switch contact portion  30   b  can be in connection by means of the same force.  
      As shown in  FIG. 7A  and  FIG. 7B , preferably, the voltage Vd 1  applied to the first electrostatic actuator  20   a  is changed from a high voltage (first voltage) to a low voltage (third voltage) and the voltage Vd 2  applied to the second electrostatic actuator  20   b  is changed from a low voltage (second voltage) to a high voltage (fourth voltage) at the same time. Also, preferably, the voltage Vd 1  applied to the first electrostatic actuator  20   a  is changed from a low voltage (third voltage) to a high voltage (first voltage) and the voltage Vd 2  applied to the second electrostatic actuator  20   b  is changed from a high voltage (fourth voltage) to a low voltage (second voltage) at the same time. At the moment when the voltage Vd 2  becomes a high voltage and an attractive force is exerted onto the first electrostatic actuator  20   a , the voltage Vd 1  becomes a low voltage and a repulsive force is exerted onto the second electrostatic actuator  20   b . This allows the two electrostatic actuators  20   a  and  20   b  to exert the forces to open the switch contact portions  30   a  and  30   b . Accordingly, even in a switch of the torsion spring structure with a small spring constant, it is possible to suppress the phenomenon of being unopened when the switch contact portion is opened and closed a number of times.  
      In accordance with the first exemplary embodiment of the present invention, the first drive signal Vdl that drives the first electrostatic actuator  20   a  is applied to the first electrostatic actuator  20   a , and the second drive signal Vd 2  that drives the second electrostatic actuator  20   b  is applied to the second electrostatic actuator  20   b . There is provided the inverter  82  that inverts the first drive signal Vd 1  and outputs the second drive signal Vd 2 . The first drive signal Vd 1  is inverted to generate the second drive signal Vd 2  by use of the inverter  82 , thereby making it possible to change the second drive signal Vd 2  to a low voltage at a moment when the first voltage Vd 1  becomes a high voltage and to change the second drive signal Vd 2  to a high voltage at a moment when the first voltage Vd 1  becomes a low voltage, with the above-described simple configuration.  
     Second Exemplary Embodiment  
      There are provided four sub beam portions in accordance with a second exemplary embodiment of the present invention.  FIG. 8  is a perspective view of the switch in accordance with the second exemplary embodiment of the present invention. The beam portion  10  includes: four sub beam portions  13 ; and the common portion  11  to which each of one ends of the four sub beam portions  13  is secured. Four torsion springs  12  are secured to the common portion  11 . Each one end of the four torsion springs  12  is secured to the common portion  11 , and each of the other ends is secured through a fixed portion  42  to the SOI substrate  60 . The fixed portion  42  is composed of: the silicon layer  54 ; and the silicon oxide layer  52 , and is secured to the silicon substrate  50 . The beam portion  10  and the torsion springs  12  are formed of the silicon layer  54 , and the silicon oxide layer  52  arranged below the beam portion  10  and below the torsion spring  12  is removed and a cavity is defined. For this reason, the beam portion  10  is held only by the torsion springs  12  secured through the fixed portion  42  to the SOI substrate  60 . The electrostatic actuators  20  and the switch contact portions  30  have the same configurations as those employed in the first exemplary embodiment, and a detailed explanation will be omitted.  
      In the switch employed in the second exemplary embodiment, two electrostatic actuators  20  provided at the two sub beam portions opposing each other and interposing the common portion  11  are operated as described with reference to  FIG. 6 ,  FIG. 7A  and  FIG. 7B  in the first exemplary embodiment. At this time, it is preferable that no drive signal be input into any electrostatic actuator, except the two opposing electrostatic actuators being operated. In this manner, the switch employed in the second exemplary embodiment functions as a Single-Pole Four-Throw (SP4T) switch. The number of the sub beam portions  13  and that of the switch contact portions  30  are not limited to four. For instance, when the switch includes N (two or more) sub beam portions  13  and N (two or more) switch contact portions  30 , the switch functions as a Single-Pole N-Throw (SPNT) switch. As described heretofore; the SPNT switch can be integrated and fabricated onto a single substrate.  
      In accordance with the first and second exemplary embodiments, it may be configured that the sub beam portion and the torsion spring be alternately secured to the common portion  11 . By this configuration, the beam portion  10  is held by the torsion springs  12  in a well-balanced manner.  
     Third Exemplary Embodiment  
      There are arranged two torsion springs in a V-shaped manner in accordance with a third exemplary embodiment of the present invention.  FIG. 9  is a perspective view of the switch in accordance with a third exemplary embodiment of the present invention. There are two torsion springs  12   c  respectively provided at both sides of the common portion  11  of the beam portion  10  with each of one ends thereof secured to the common portion  11  in close proximity to each other. The other ends of the torsion springs  12   c  are secured to the SOI substrate  60  apart from each other. In this manner, two torsion springs  12   c  are arranged in a V-shaped manner. In the third exemplary embodiment, the same components and configurations as those employed in the first exemplary embodiment have the same reference numerals and a detailed explanation will be omitted.  
     Fourth Exemplary Embodiment  
      There are arranged two torsion springs in a V-shaped manner in accordance with a third exemplary embodiment of the present invention.  FIG. 10  is a perspective view of the switch in accordance with a third exemplary embodiment of the present invention. There are two torsion springs  12   c  respectively provided at both sides of the common portion  11  of the beam portion  10  with each of one ends thereof secured to the common portion  11  apart from each other. The other ends of the torsion springs  12   c  are secured to the SOI substrate  60  in close proximity to each other. In this manner, two torsion springs  12   c  are arranged in a V-shaped manner. In the fourth exemplary embodiment, the same components and configurations as those employed in the first exemplary embodiment have the same reference numerals and a detailed explanation will be omitted.  
      In accordance with the third and fourth exemplary embodiments, preferably, two torsion springs arranged in a V-shaped manner are secured in the beam portion  10 . This makes it possible to prevent the beam portion  10  from being displaced in a horizontal direction. The torsion springs  12   c  arranged in a V-shaped manner may be employed for the switch having three or more sub beam portions  13 , for example, employed in the second exemplary embodiment.  
     Fifth Exemplary Embodiment  
      There is provided another torsion spring  12   d  between the two torsion springs  12   c  arranged in a V-shaped manner in accordance with a fifth exemplary embodiment of the present invention.  FIG. 11  is a perspective view of the switch in accordance with the fifth exemplary embodiment of the present invention. There are two torsion springs  12   c  respectively provided at both sides of the common portion  11  of the beam portion  10  with each of one ends thereof secured to the common portion  11  in close proximity to each other. There is also provided the torsion spring  12   d  between the two torsion springs  12   c  arranged in a V-shaped manner, with one end thereof secured to the common portion  11 . The other ends of the torsion springs  12   c  and  12   d  are secured to the SOI substrate  60  apart from each other. In the fifth exemplary embodiment, the same components and configurations as those employed in the third exemplary embodiment have the same reference numerals and a detailed explanation will be omitted.  
      In accordance with the fifth exemplary embodiment, it is further possible to prevent the beam portion  10  from being displaced in a horizontal direction, by providing the torsion spring  12   d  between the two torsion springs  12   c  arranged in a V-shaped manner. The two torsion springs  12   c  arranged in a V-shaped manner may be provided with each of one ends thereof secured to the beam portion  10  apart from each other and the other ends thereof secured to the SOI substrate  60  in close proximity to each other, as described in the fourth exemplary embodiment. Two or more torsion springs  12   d  may be provided between the two torsion springs  12   c  arranged in a V-shaped manner. As the number of the torsion springs  12   d  is increased, the displacement toward a horizontal direction can be further prevented. The spring constant, however, is increased. The number of the torsion springs  12   d  may be determined in consideration of the displacement toward a horizontal direction and the spring constant. In addition, the above-described one or more torsion springs  12   d  provided between the two torsion springs  12   c  arranged in a V-shaped manner may be employed for the switch having three or more sub beam portions  13 , for example, as employed in the second exemplary embodiment.  
     Sixth Exemplary Embodiment  
      The sub beam portion includes multiple switch contact portions, which are electrically isolated from each other, in accordance with a sixth exemplary embodiment of the present invention.  FIG. 12  is a perspective view of the switch in accordance with the sixth exemplary embodiment of the present invention. The sub beam portions  13   a  and  13   b  respectively have a substantially T-shape. Two switch contact portions  30   a  are respectively provided at two ends of one side of the substantially T-shaped sub beam portion  13   a . The two switch contact portions  30   a  are electrically isolated from each other, and are simultaneously in connection or disconnection. Two switch contact portions  30   b  provided at the sub beam portion  13   b  are configured in a similar manner. In the sixth exemplary embodiment, the same components and configurations as those employed in the first exemplary embodiment have the same reference numerals and a detailed explanation will be omitted.  
      The switch employed in the sixth exemplary embodiment serves as a double switch in which electrically isolated two switch contact portions  30   a  or  30   b  are in connection or disconnection. Three or more (namely, N) switch contact portions  30  electrically isolated may be provided at one sub beam portion  13 . In this case, the switch serves as an N-series switch. In addition, the switch contact portions employed in the present exemplary embodiment may be applicable to the SPNT switch having three or more sub beam portions  13 , as described in the second exemplary embodiment. Furthermore, it is only necessary that there be provided electrically isolated two switch contact portions  30  in at least one sub beam portion  13 .  
      In accordance with the first through sixth exemplary embodiments, a wiring electrode  18  may be arranged on the torsion spring  12 , the wiring electrode  18  being electrically coupled to a lower electrode  22  of the electrostatic actuator  20  provided in the beam portion  10 . This makes it possible to provide the wiring electrode  18  on the SOI substrate  60 , whereas the wiring electrode  18  is electrically coupled to the lower electrode  22 . The shape of the torsion spring is not limited to a square pole used in the first through sixth exemplary embodiments. The torsion spring may be a spring that demonstrates spring characteristics by twisting.  
      Finally, various aspects of the present invention are summarized in the following.  
      According to an aspect of the present invention, there is provided a switch including: multiple torsion springs with each of one ends thereof secured to a substrate; a beam portion, to which each of the other ends of the multiple torsion springs is secured, and which is swung by an electrostatic actuator; and a switch contact portion in which a first contact provided at the beam portion and a second contact secured to the substrate are in connection or disconnection.  
      In the above-described switch, the beam portion may include multiple sub beam portions and a common portion to which each of the one ends of the multiple sub beam portions is secured; the multiple torsion springs are secured to the common portion; the multiple sub beam portions respectively include the electrostatic actuator and the first contact; and multiple switch contact portions are provided to the first contact respectively provided at the multiple sub beam portions. When N sub beam portions are provided, a SPNT switch can be fabricated and integrated on a single substrate.  
      In the above-described switch, the multiple sub beam portions may be two beam portions. The SPNT switch can be fabricated and integrated on a single substrate.  
      In the above-described switch, a first electrostatic actuator may be provided at one of two sub beam portions opposing each other and interposing the common portion and a second electrostatic actuator is provided at the other of the two sub beam portions; when a first voltage is applied to the first electrostatic actuator, a second voltage is applied to the second electrostatic actuator; when a third voltage is applied to the first electrostatic actuator, a fourth voltage is applied to the second electrostatic actuator; and the first voltage is greater than the second voltage and the third voltage is greater than the fourth voltage. When a low voltage is applied to the first electrostatic actuator and a high voltage is applied to the second electrostatic actuator, the switch contact portion corresponding to the first electrostatic actuator is in disconnection and the switch contact portion corresponding to the second electrostatic actuator is in connection. Meanwhile, when a high voltage is applied to the first electrostatic actuator and a low voltage is applied to the second electrostatic actuator, the switch contact portion corresponding to the first electrostatic actuator is in connection and the switch contact portion corresponding to the second electrostatic actuator is in disconnection.  
      In the above-described switch, the first voltage may be equal to the fourth voltage and the second voltage may be equal to the third voltage. The switch contact portion corresponding to the first electrostatic actuator and the switch contact portion corresponding to the second electrostatic actuator can be operated by the same force. This enables a stable operation.  
      In the above-described switch, a voltage applied to the first electrostatic actuator may be changed from the first voltage to the third voltage and the voltage applied to the second electrostatic actuator is changed from the second voltage to the fourth voltage at the same time; and the voltage applied to the first electrostatic actuator may be changed from the third voltage to the first voltage and the voltage applied to the second electrostatic actuator is changed from the fourth voltage to the second voltage at the same time. An attractive force is applied onto one electrostatic actuator and a repulsive force is applied to the other electrostatic actuator at the same time. It is possible to prevent the phenomenon of being unopened in the switch having a torsion spring structure of a small spring constant, when the switch contact portion is opened and closed a number of times.  
      The above-described switch may further include an inverter that inverts a first drive signal that drives the first electrostatic actuator to output a second drive signal that drives the second electrostatic actuator, and the first drive signal may be applied to the first electrostatic actuator and the second drive signal is applied to the second electrostatic actuator. The first drive signal is inverted at the inverter to generate the second drive signal. With such a simple configuration, the voltage applied to one of the electrostatic actuators and the voltage applied to the other electrostatic actuator can be changed at the same time.  
      In the above-described switch, two torsion springs formed in a V-shaped manner may be secured to the beam portion. It is possible to suppress the displacement of the beam portion to the horizontal.  
      In the above-described switch, another torsion spring may be provided between the two torsion springs formed in the V-shaped manner. It is further possible to suppress the displacement of the beam portion to the horizontal.  
      In the above-described switch, the multiple sub beam portions and the multiple torsion springs may be alternately secured to the common portion. The beam portion can be held by the torsion springs in a well-balanced manner.  
      In the above-described switch, at least one of the multiple sub beam portions may include multiple switch contact portions electrically isolated from each other. The switch may be configured such that multiple switch contact portions electrically isolated from each other are simultaneously in connection or disconnection.  
      In the above-described switch, wiring electrodes may be respectively provided on the multiple torsion springs electrically coupled to a lower electrode of the electrostatic actuator. This configuration eliminates the necessity of providing the wiring coupled to the electrode of the electrostatic actuator, thereby reducing the size of the switch.  
      Although a few specific exemplary embodiments employed in the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.  
      The present invention is based on Japanese Patent Application No. 2005-338532 filed on Nov. 24, 2005, the entire disclosure of which is hereby incorporated by reference.