Patent Publication Number: US-8110761-B2

Title: Switching device and communication apparatus and method related thereto

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-281311, filed on Oct. 31, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments relate to a switching device manufactured using MEMS techniques, an apparatus including the switching device and method related to same. 
     BACKGROUND 
     In the technical field of wireless communication apparatuses, such as cell phones, a demand for downsizing of an RF circuit has been increased, for example, corresponding to an increase in number of parts mounted on each apparatus with the view of realizing a higher level of performance. To meet such a demand, a further miniaturization of various parts of the circuit has been progressed by utilizing the MEMS (micro-electromechanical systems) techniques. 
     An MEMS switch is generally known as one of those parts. The MEMS switch is a switching device in which various components are formed in very small sizes by the MEMS techniques, and it includes at least one pair of contacts which are mechanically opened and closed to perform switching, a driving mechanism for achieving the mechanical opening and closing operations of the contact pair, and so on. When the MEMS switch is applied to the switching of a high-frequency signal on the GHz order, in particular, the MEMS switch tends to exhibit a higher degree of isolation in the open state and a lower insertion loss in the closed state than other switching devices using, e.g., PIN diodes and MESFETs. Such a tendency is attributable to the facts that the open state is established by spacing mechanically formed between the contact pair, and that parasitic capacitance is small because the MEMS switch is a mechanical switch. Known MEMS switches are described in, e.g., Japanese Unexamined Patent Application Publication No. 2004-1186 and No. 2004-311394, and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-528751. 
       FIGS. 51 to 53  represent a switching device Z 1  as one example of the typical switching devices. Specifically,  FIG. 51  is a plan view of the switching device Z 1 .  FIG. 52  is a plan view, partly omitted, of the switching device Z 1 .  FIG. 53  is a sectional view taken along a line LIII-LIII in  FIG. 51 . 
     The switching device Z 1  includes a substrate S 3 , a signal line  91 , a driving line  92 , and a movable line  93  (omitted in  FIG. 52 ). The signal line  91  is formed by patterning on the substrate S 3 . As illustrated in  FIG. 53 , the signal line  91  has a contact portion  91   a  capable of contacting the movable line  93 . The driving line  92  is formed by patterning on the substrate S 3 , and it has a driving electrode portion  92   a . The movable line  93  is formed in a shape protruding upwards from the substrate S 3 , as illustrated in  FIG. 53 , by a plating process, for example. The movable line  93  includes a projected portion or a contact portion  93   a , which is capable of contacting the signal line  91 , and a portion positioned to face the driving electrode portion  92   a  of the driving line  92 . The signal line  91 , the driving line  92 , and the movable line  93  are each made of a predetermined conductive material. 
     In the switching device Z 1  having the above-described structure, when a predetermined driving voltage is applied to the movable line  93  in a state where the driving line  92  is connected to the ground, an electrostatic attraction force is generated between the driving electrode portion  92   a  of the driving line  92  and the movable line  93 , whereby the movable line  93  is partly operated or elastically deformed until the contact portion  93   a  of the movable line  93  comes into contact with the contact portion  91   a  of the signal line  91 . The closed state of the switching device Z 1  is thus established. In the closed state, the signal line  91  and the movable line  93  are connected to each other so that a current is allowed to pass between the signal line  91  and the movable line  93 . With such a switching-on operation, the on-state of a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device Z 1  in the closed state, the application of the voltage to the movable line  93  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portion  92   a  and the movable line  93 , the movable line  93  returns to its natural state and the contact portion  93   a  of the movable line  93  moves away from the contact portion  91   a  of the signal line  91 . The open state of the switching device Z 1  is thus established. In the open state, the signal line  91  and the movable line  93  are electrically separated from each other, whereby a current is prevented from passing between the signal line  91  and the movable line  93 . With such a switching-off operation, the off-state of a high-frequency signal can be achieved. Further, the switching device Z 1  in the open state can be changed again to the closed state, i.e., the on-state, with the switching-on operation described above. 
     In the switching device Z 1 , the movable line  93  serves as, together with the signal line  91 , a passage route for the high-frequency signal, and the driving voltage is applied to the movable line  93  having the portion that is positioned to face the driving electrode portion  92   a  of the driving line  92  (namely, the movable line  93  serves as not only a signal line, but also a driving line). Because the parasitic capacitance between the movable line  93  and the driving electrode portion  92   a  positioned to face the movable line  93  is comparatively large, the high-frequency signal that is to pass through the movable line  93  is apt to leak to the driving line  92  through a region where the driving electrode portion  92   a  and the movable line  93  are positioned to face each other. In other words, an insertion loss is apt to generate in the switching device n. As the frequency of the signal becomes higher, an extent of signal leakage to the driving line  92  increases and the insertion loss also tends to increase. In that type of the switching device Z 1 , a superior high-frequency characteristic is hard to obtain. 
       FIGS. 54 to 56B  illustrate a switching device Z 2  as another example of the known switching devices.  FIG. 54  is a plan view of the switching device Z 2 .  FIG. 55  is a plan view, partly omitted, of the switching device Z 2 .  FIGS. 56A and 56B  are sectional views taken along a line LVIA-LVIA and a line LVIB-LVIB in  FIG. 54 , respectively. 
     The switching device Z 2  includes a substrate S 4 , a stationary portion  94 , a movable portion  95 , a signal line  96 A, a pair of signal lines  96 B (omitted in  FIG. 55 ), a driving line  97 A, and a driving line  97 B (omitted in  FIG. 55 ). As illustrated in  FIGS. 56A and 56B , the stationary portion  94  is joined to the substrate S 4  through a boundary layer  98 . As most clearly illustrated in  FIG. 55 , the movable portion  95  includes a fixed end  95   a  fixed to the stationary portion  94 , and a free end  95   b , and it is surrounded by the stationary portion  94  with a slit  99  interposed there between. The stationary portion  94  and the movable portion  95  are integrally formed on a single silicon substrate. As most clearly illustrated in  FIG. 55 , the signal line  96 A is disposed on the movable portion  95  near the free end  95   b  thereof and has contact portions  96   a  capable of contacting the signal lines  96 B, respectively. The signal lines  96 B are each formed in a shape protruding upwards from the stationary portion  94 , as illustrated in  FIG. 56A , by a plating process, for example. Further, each of the signal lines  96 B has a projected portion or a contact portion  96   b , which is capable of contacting the signal line  96 A. As most clearly illustrated in  FIG. 55 , the driving line  97 A is disposed to extend over the stationary portion  94  and the movable portion  95  and has a driving electrode portion  97   a  on the movable portion  95 . The driving line  97 B is formed in a shape protruding upwards from the stationary portion  94 , as illustrated in  FIG. 56B , by a plating process, for example, and has a portion positioned to face the driving electrode portion  97   a  of the driving line  97 A. The signal lines  96 A and  96 B and the driving lines  97 A and  97 B are each made of a predetermined conductive material. 
     In the switching device Z 2  having the above-described structure, when a predetermined driving voltage is applied to the driving line  97 A in a state where the driving line  97 B is connected to the ground, an electrostatic attraction force is generated between the driving electrode portion  97   a  of the driving line  97 A and the driving line  97 B. When the electrostatic attraction force is sufficiently large, the movable portion  95  is operated or elastically deformed until the contact portions  96   a  of the signal line  96 A come into contact with the contact portions  96   b  of the signal lines  96 B. The closed state of the switching device Z 2  is thus established. In the closed state, the pair of signal lines  96 B are electrically bridged there between through signal line  96 A so that a current is allowed to pass between the pair of signal lines  96 B. With such a switching-on operation, the on-state of a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device Z 2  in the closed state, the application of the voltage to the driving line  97 A is stopped to extinguish the electrostatic attraction force acting between the driving electrode portion  97   a  and the driving line  97 B, the movable portion  95  returns to its natural state and the contact portions  96   a  of the signal line  96 A on the movable portion  95  move away from the contact portions  96   b  of the signal lines  96 B. The open state of the switching device Z 2  is thus established. In the open state, the pair of signal lines  96 B are electrically separated from each other, whereby a current is prevented from passing between the pair of signal line  96 B. With such a switching-off operation, the off-state of a high-frequency signal can be achieved. Further, the switching device Z 2  in the open state can be changed again to the closed state, i.e., the on-state, with the switching-on operation described above. 
     In the switching device Z 2 , two gaps G′ between the two pairs of contact portions  96   a  and  96   b , illustrated in  FIG. 56A , may differ from each other due to variations occurred in manufacturing operations when the switching device Z 2  is not driven (i.e., when the movable portion  95  is in its natural state). In such a case, even when the predetermined voltage is applied to the driving line  97 A, the movable portion  95  is not elastically deformed to such an extent that one pair of contact portions  96   a  and  96   b , which form the larger gap G′, can be brought into the closed state, thus causing a failure that the switching device Z 2  is not turned to the on-state. When the two gaps G′ illustrated in  FIG. 56A  differ from each other in the not-driven state, the movable portion  95  can be elastically deformed, by applying a sufficiently high voltage to the driving line  97 A, such that after one pair of contact portions  96   a  and  96   b  forming the smaller gap G′ have been brought into the closed state, the other pair of contact portions  96   a  and  96   b  forming the larger gap G′ are also brought into the closed state. With such a voltage application, however, because an excessive load is eventually imposed between the contact portions  96   a  and  96   b  which have been brought into the closed state at earlier timing, a sticking failure, i.e., a phenomenon of sticking to the contact state due to application of excessive pressure, tends to occur between the contact portions  96   a  and  96   b  which have been brought into the closed state at the earlier timing. Such a tendency to cause the sticking failure is not preferable including in realizing a long contact opening/closing life. 
     SUMMARY 
     According to an aspect of the embodiment, a switching device includes a stationary portion, a movable portion having a movable land portion, a first beam portion and a second beam portion coupling the movable land portion and the stationary portion with each other, a first signal line disposed to extend over the movable land portion, the first beam portion, and the stationary portion, and having a movable contact portion on the movable land portion, a second signal line having a stationary contact portion positioned to face the movable contact portion and fixed to the stationary portion, a first driving line disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and having a movable driving electrode portion on the movable land portion, and a second driving line having a stationary driving electrode portion positioned to face the movable driving electrode portion and fixed to the stationary portion. 
     The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the embodiment, as claimed. 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 2  is a plan view, partly omitted, of the switching device illustrated in  FIG. 1 ; 
         FIG. 3A  is a sectional view taken along a line IIIA-IIIA in  FIG. 1 ; 
         FIG. 3B  is a sectional view taken along a line IIIB-IIIB in  FIG. 1 ; 
         FIG. 4A  is a sectional view taken along a line IVA-IVA in  FIG. 1 ; 
         FIG. 4B  is a sectional view taken along the line IVB-IVB in  FIG. 1 , the view illustrating a closed state; 
         FIGS. 5A ,  5 B and  5 C illustrate successive operations in part of a method of manufacturing the switching device illustrated in  FIG. 1 ; 
         FIGS. 6A ,  6 B and  6 C illustrate successive operations subsequent to  FIG. 5C ; 
         FIGS. 7A ,  7 B and  7 C illustrate successive operations subsequent to  FIG. 6C ; 
         FIGS. 8A ,  8 B and  8 C illustrate successive operations subsequent to  FIG. 7C ; 
         FIG. 9  is a plan view of a first modification of the switching device according to an embodiment; 
         FIG. 10  is a plan view, partly omitted, of the switching device illustrated in  FIG. 9 ; 
         FIG. 11  is a plan view of a second modification of the switching device according to an embodiment; 
         FIG. 12  is a plan view, partly omitted, of the switching device illustrated in  FIG. 11 ; 
         FIG. 13A  is a sectional view taken along a line XIIIA-XIIIA in  FIG. 11 ; 
         FIG. 13B  is a sectional view taken along a line XIIIB-XIIIB in  FIG. 11 ; 
         FIG. 14  is a plan view of a third modification of the switching device according to an embodiment; 
         FIG. 15  is a plan view, partly omitted, of the switching device illustrated in  FIG. 14 ; 
         FIG. 16  is a plan view of a fourth modification of the switching device according to an embodiment; 
         FIG. 17  is a plan view, partly omitted, of the switching device illustrated in  FIG. 16 ; 
         FIG. 18A  is a sectional view taken along a line XVIIIA-XVIIIA in  FIG. 16 ; 
         FIG. 18B  is a sectional view taken along a line XVIIIB-XVIIIB in  FIG. 16 ; 
         FIG. 19  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 20  is a plan view, partly omitted, of the switching device illustrated in  FIG. 19 ; 
         FIG. 21A  is a sectional view taken along a line XXIA-XXIA in  FIG. 19 ; 
         FIG. 21B  is a sectional view taken along a line XXIB-XXIB in  FIG. 19 ; 
         FIG. 22  is a sectional view taken along a line XXII-XXII in  FIG. 19 ; 
         FIG. 23  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 24  is a plan view, partly omitted, of the switching device illustrated in  FIG. 23 ; 
         FIG. 25A  is a sectional view taken along a line XXVA-XXVA in  FIG. 23 ; 
         FIG. 25B  is a sectional view taken along a line XXVB-XXVB in  FIG. 23 ; 
         FIG. 26  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 27  is a plan view, partly omitted, of the switching device illustrated in  FIG. 26 ; 
         FIG. 28A  is a sectional view taken along a line XXVIIIA-XXVIIIA in  FIG. 26 ; 
         FIG. 28B  is a sectional view taken along a line XXVIIIB-XXVIIIB in  FIG. 26 ; 
         FIG. 29  is a sectional view taken along a line XXIX-XXIX in  FIG. 26 ; 
         FIG. 30  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 31  is a plan view, partly omitted, of the switching device illustrated in  FIG. 30 ; 
         FIG. 32A  is a sectional view taken along a line XXXIIA-XXXIIA in  FIG. 30 ; 
         FIG. 32B  is a sectional view taken along a line XXXIIB-XXXIIB in  FIG. 30 ; 
         FIG. 33A  is a sectional view taken along a line XXXIIIA-XXXIIIA in  FIG. 30 ; 
         FIG. 33B  is a sectional view taken along a line XXXIIIB-XXXIIIB in  FIG. 30 ; 
         FIG. 34  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 35  is a plan view, partly omitted, of the switching device illustrated in  FIG. 34 ; 
         FIG. 36A  is a sectional view taken along a line XXXVIA-XXXVIA in  FIG. 34 ; 
         FIG. 36B  is a sectional view taken along a line XXXVIB-XXXVIB in  FIG. 34 ; 
         FIG. 37A  is a sectional view taken along a line XXXVIIA-XXXVIIA in  FIG. 34 ; 
         FIG. 37B  is a sectional view taken along a line XXXVIIB-XXXVIIB in  FIG. 34 ; 
         FIG. 38  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 39  is a plan view, partly omitted, of the switching device illustrated in  FIG. 38 ; 
         FIG. 40A  is a sectional view taken along a line XLA-XLA in  FIG. 38 ; 
         FIG. 40B  is a sectional view taken along a line XLB-XLB in  FIG. 38 ; 
         FIGS. 41A and 41B  illustrate two different closed states in the switching device of  FIG. 38 ; 
         FIG. 42  is a plan view of a switching device according to an embodiment of the present invention; 
         FIG. 43  is a plan view, partly omitted, of the switching device illustrated in  FIG. 42 ; 
         FIG. 44A  is a sectional view taken along a line XLIVA-XLIVA in  FIG. 42 ; 
         FIG. 44B  is a sectional view taken along a line XLIVB-XLIVB in  FIG. 42 ; 
         FIG. 45A  is a sectional view taken along a line XLVA-XLVA in  FIG. 42 ; 
         FIG. 45B  is a sectional view taken along a line XLVB-XLVB in  FIG. 42 , the view illustrating a closed state; 
         FIGS. 46A ,  46 B and  46 C illustrate successive operations in part of a method of manufacturing the switching device illustrated in  FIG. 42 ; 
         FIGS. 47A ,  47 B and  47 C illustrate successive operations subsequent to  FIG. 46C ; 
         FIGS. 48A ,  48 B and  48 C illustrate successive operations subsequent to  FIG. 47C ; 
         FIGS. 49A to 49C  illustrate successive operations subsequent to  FIG. 48C ; 
         FIG. 50  illustrates a partial configuration of a communication apparatus according to an embodiment of the present invention; 
         FIG. 51  is a plan view illustrating one example of known switching devices; 
         FIG. 52  is a plan view, partly omitted, of the switching device illustrated in  FIG. 51 ; 
         FIG. 53  is a sectional view taken along a line LIII-LIII in  FIG. 51 ; 
         FIG. 54  is a plan view illustrating another example of known switching devices; 
         FIG. 55  is a plan view, partly omitted, of the switching device illustrated in  FIG. 54 ; 
         FIG. 56A  is a sectional view taken along a line LVIA-LVIA in  FIG. 54 ; and 
         FIG. 56B  is a sectional view taken along a line LVIB-LVIB in  FIG. 54 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     The present invention has been conceived in view of the above-described situations in the art, and an object of the present invention is to provide a switching device in which a signal line and a driving line are electrically separated from each other and which is suitable for realizing a long contact opening/closing life, and to provide a communication apparatus including the switching device. 
     According to an embodiment of the present invention, a switching device is provided. The switching device comprises a stationary portion, a movable portion having a movable land portion, a first beam portion, and a second beam portion, the first and second beam portions coupling the movable land portion and the stationary portion with each other, and a first signal line disposed to extend over the movable land portion, the first beam portion, and the stationary portion, and having a movable contact portion on the movable land portion, a second signal line having a stationary contact portion positioned to face the movable contact portion and fixed to the stationary portion. The switching device according to an embodiment includes a first driving line disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and having a movable driving electrode portion on the movable land portion, and a second driving line having a stationary driving electrode portion positioned to face the movable driving electrode portion and fixed to the stationary portion. According to an embodiment the first and second beam portions are extended, for example, in parallel between the movable land portion and the stationary portion. The movable portion may be supported to the stationary portion in such a cantilevered structure. Alternatively, the movable portion may be supported to the stationary portion in a both-end supported structure. 
     In a switching device of an embodiment, the first signal line is disposed to extend over the movable land portion, the first beam portion, and the stationary portion, and it has the movable contact portion on the movable land portion. The second signal line has the stationary contact portion positioned to face the movable contact portion and is fixed to the stationary portion. Passage and non-passage of, e.g., a high-frequency signal between the first and second signal lines are selected respectively by closing and opening between the movable contact portion of the first signal line on the movable land portion and the stationary contact portion of the second signal line. Stated another way, this switching device includes a single opening/closing point (single contact). The switching device thus constructed is less susceptible to the problems existing in current switching devices including the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, this switching device is suitable for realizing a long contact opening/closing life. 
     Also, in a switching device according to an embodiment, the first driving line is disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and it has the movable driving electrode portion on the movable land portion. The second driving line has the stationary driving electrode portion positioned to face the movable driving electrode portion and is fixed to the stationary portion. With a driving voltage applied between the movable driving electrode portion of the first driving line on the movable land portion and the stationary driving electrode portion of the second driving line, an electrostatic attraction force is generated between those driving electrode portions so that the movable land portion to which the movable driving electrode portion is joined is operated or elastically deformed toward the stationary driving electrode portion. The first driving line is disposed separately from the first signal line (namely, the first driving line is routed from the movable land portion to the stationary portion while passing the second beam portion differing from the first beam portion on which the first signal line passes). Also, the second driving line is disposed separately from the second signal line. Stated another way, in this switching device, the signal lines are electrically separated from the driving lines. The switching device thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, this switching device is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     According to an embodiment of the present invention, a switching device is provided. The switching device comprises a stationary portion, a movable portion having a movable land portion, a first beam portion, and a second beam portion, the first and second beam portions coupling the movable land portion and the stationary portion with each other, a first signal line disposed to extend over the first beam portion of the movable portion and the stationary portion, and having a movable contact portion on the first beam portion, a second signal line having a stationary contact portion positioned to face the movable contact portion and fixed to the stationary portion, a first driving line disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and having a movable driving electrode portion on the movable land portion, and a second driving line having a stationary driving electrode portion positioned to face the movable driving electrode portion and fixed to the stationary portion. The first and second beam portions are extended, for example, in parallel between the movable land portion and the stationary portion. The movable portion may be supported to the stationary portion in such a cantilevered structure. Alternatively, the movable portion may be supported to the stationary portion in a both-end supported structure. 
     In this switching device, the first signal line is disposed to extend over the first beam portion and the stationary portion, and it has the movable contact portion on the first beam portion. The second signal line has the stationary contact portion positioned to face the movable contact portion and is fixed to the stationary portion. Passage and non-passage of, e.g., a high-frequency signal between the first and second signal lines are selected respectively by closing and opening between the movable contact portion of the first signal line on the movable land portion and the stationary contact portion of the second signal line. Stated another way, this switching device includes a single opening/closing point (single contact). The switching device thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, this switching device is suitable for realizing a long contact opening/closing life. 
     Also, in this switching device, the first driving line is disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and it has the movable driving electrode portion on the movable land portion. The second driving line has the stationary driving electrode portion positioned to face the movable driving electrode portion and is fixed to the stationary portion. With a driving voltage applied between the movable driving electrode portion of the first driving line on the movable land portion and the stationary driving electrode portion of the second driving line, an electrostatic attraction force is generated between those driving electrode portions so that the movable land portion to which the movable driving electrode portion is joined is operated or elastically deformed toward the stationary driving electrode portion. The first driving line is disposed separately from the first signal line (namely, the first driving line is routed from the movable land portion to the stationary portion while passing the second beam portion differing from the first beam portion on which the first signal line passes). Also, the second driving line is disposed separately from the second signal line. Stated another way, in this switching device, the signal lines are electrically separated from the driving lines. The switching device thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, this switching device is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In preferred embodiments, the movable portion further has a third beam portion coupling the movable land portion and the stationary portion with each other. The switching device further comprises a third driving line disposed to extend over the movable land portion, the third beam portion, and the stationary portion, and having an additional movable driving electrode portion that is spaced from the movable driving electrode portion on the movable land portion, and a fourth driving line having an additional stationary driving electrode portion positioned to face the additional movable driving electrode portion and fixed to the stationary portion. The movable contact portion of the first signal line is positioned between the movable driving electrode portion and the additional movable driving electrode portion in a direction in which the movable driving electrode portion and the additional movable driving electrode portion are spaced from each other. In the above-described arrangement, the first beam portion, the second beam portion, and the third beam portion are extended, for example, in parallel between the movable land portion and the stationary portion, and the first beam portion is positioned between the second beam portion and the third beam portion. The movable portion may be supported to the stationary portion in such a cantilevered structure. As an alternative, the second beam portion and the third beam portion are extended in parallel between the movable land portion and the stationary portion, and the first beam portion couples the movable land portion and the stationary portion with each other on a side opposite to the second beam portion and the third beam portion. The movable portion may be supported to the stationary portion in such a both-end supported structure. 
     In those preferred embodiments, an opening/closing point (i.e., the movable contact portion and the stationary contact portion) is positioned between two locations where the electrostatic attraction forces are generated (the two locations corresponding to a gap between the movable driving electrode portion and the stationary driving electrode portion and a gap between the additional movable driving electrode portion and the additional stationary driving electrode portion) in the direction in which those two electrostatic-attraction-force generated locations are spaced from each other. Therefore, after the movable contact portion and the stationary contact portion have been brought into contact with each other, uniform loads can be more easily applied to that contact point from both sides of that contact point when this switching device is driven. As a result, stable contact can be more easily realized in that contact point. 
     In a preferred embodiment, the first signal line has an additional movable contact portion on the movable land portion. This switching device further comprises a third signal line having an additional stationary contact portion positioned to face the additional movable contact portion and fixed to the stationary portion, a third driving line disposed to extend over the movable land portion, the second beam portion, and the stationary portion, and having an additional movable driving electrode portion that is spaced from the movable driving electrode portion on the movable land portion, and a fourth driving line having an additional stationary driving electrode portion positioned to face the additional movable driving electrode portion and fixed to the stationary portion. The additional movable contact portion is spaced from the movable contact portion in a direction in which the movable driving electrode portion and the additional movable driving electrode portion are spaced from each other. The movable land portion is positioned between the first beam portion and the second beam portion, the first and second beam portions defining an axis for swing motion of the movable land portion. The axis extends between the movable driving electrode portion and the additional movable driving electrode portion and between the movable contact portion and the additional movable contact portion as viewed in the direction in which the movable driving electrode portion and the additional movable driving electrode portion are spaced from each other. This switching device may be constituted as such an SPDT switch (having one input and two outputs). 
     Preferably, the switching device further comprises a first ground line having a shape extending along at least the first signal line and the second signal line, and a second ground line having a shape extending along at least the first signal line and the second signal line on the side opposite to the first ground line. The first ground line and/or the second ground line are extended, for example, along the first signal line and the second signal line. Such coplanar passages may be used in the switching device. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines. 
     Preferably, the first driving line has, in part thereof on the movable portion, a pattern shape that is congruent to a pattern shape of the first signal line on the movable portion. Such a symmetrical arrangement is preferable including in suppressing generation of improper deformation (such as torsional deformation) in the movable portion that is elastically deformed when the switching device is driven. 
     Preferably, the switching device further comprises a stopper portion positioned to face the movable land portion on the side where the movable contact portion is disposed. The provision of the stopper portion is preferable including in preventing the movable driving electrode portion and the stationary driving electrode portion from contacting with each other and from short-circuiting when driven. 
     Preferably, the first signal line has a thicker portion on the first beam portion. Such a construction is preferable including in suppressing a signal loss occurred in the first signal line. In that case, the first driving line has a thicker portion on the second beam portion. Such a symmetrical arrangement is also preferable including in suppressing generation of improper deformation in the movable portion when driven. 
     According to an embodiment of the present invention, a communication apparatus is provided. The communication apparatus includes the switching device according to any of embodiments of the present invention described herein. For example, the communication apparatus according to an embodiment is an RF communication apparatus, which includes the switching device according to any of the embodiments described herein as a transmission/reception selector switch, a band selector switch, or a switch constituting one component of a variable phase shifter. 
       FIGS. 1 ,  2 ,  3 A,  3 B and  4 A illustrate a switching device X 1  according to an embodiment of the present invention.  FIG. 1  is a plan view of the switching device X 1 .  FIG. 2  is a plan view, partly omitted, of the switching device X 1 .  FIGS. 3A ,  3 B and  4 A are sectional views taken along lines IIIA-IIIA, IIIB-IIIB, and IVA-IVA in  FIG. 1 , respectively. 
     The switching device X 1  includes a substrate S 1 , a stationary portion  11 , a movable portion  12 , a signal line  13 , a signal line  14  (omitted in  FIG. 2 ), a driving line  15 , a driving line  16  (omitted in  FIG. 2 ), and a ground line  17 . 
     As illustrated in  FIGS. 3A to 4A , the stationary portion  11  is joined to the substrate S 1  through a boundary layer  18  and is made of a silicon material, e.g., single-crystal silicon. The silicon material constituting the stationary portion  11  preferably has resistivity of 1000 Ω·cm or more. The boundary layer  18  is made of, e.g., silicon oxide. In an embodiment, the stationary portion  11  corresponds, together with the substrate S 1 , to a stationary portion. 
     As illustrated in  FIGS. 1 and 2 , for example, the movable portion  12  has a movable land portion  12   a  and beam portions  12   b  and  12   c , and it is surrounded by the stationary portion  11  with a slit  19  interposed therebetween. Each of the beam portions  12   b  and  12   c  couples the stationary portion  11  and the movable land portion  12   a  with each other. In an embodiment, the beam portions  12   b  and  12   c  extend side by side parallel to each other between the stationary portion  11  and the movable land portion  12   a . In other words, the movable portion  12  is supported in a cantilevered structure by the stationary portion  11 . The movable portion  12  has a thickness T 1 , denoted in  FIGS. 3A to 4A , of 15 μm or less, for example. Also, the movable portion  12  has a length L L , denoted in  FIG. 2 , of 200 to 400 μm, for example, and a length L 2  of 300 to 500 for example. The slit  19  has a width of 1.5 to 2.5 μm, for example. The movable portion  12  is made of, e.g., single-crystal silicon. 
     As most clearly illustrated in  FIG. 2 , the signal line  13  is disposed to extend over the movable land portion  12   a , the beam portion  12   b , and the stationary portion  11 . Also, the signal line  13  has, on the movable land portion  12   a , a contact portion  13   a  capable of contacting the signal line  14 . The signal line  13  has a thickness of 0.5 to 2 μm, for example. Further, the signal line  13  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). The signal line  13  is made of a predetermined conductive material and has a multilayered structure comprising, for example, an undercoat film of Mo and an Au film overlying the undercoat film. The signal line  13  thus formed corresponds to a first signal line according to an embodiment. 
     As illustrated in  FIG. 3A , the signal line  14  is formed in a shape protruding upwards from the stationary portion  11  and has a region positioned to face the signal line  13 . The signal line  14  includes, in its region positioned to face the signal line  13 , a projected portion or a contact portion  14   a  extending toward the signal line  13 . The signal line  14  has a thickness of 10 μm or more, for example. Further, the signal line  14  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). The signal line  14  can be made of Au. The signal line  14  thus formed corresponds to a second signal line according to an embodiment. 
     As most clearly illustrated in  FIG. 2 , the driving line  15  is disposed to extend over the movable land portion  12   a , the beam portion  12   c , and the stationary portion  11 . Also, the driving line  15  has a driving electrode portion  15   a  on the movable land portion  12   a . The driving electrode portion  15   a  corresponds to a movable driving electrode portion according to an embodiment. The driving line  15  has a thickness of 0.5 to 2 μm, for example. The driving line  15  can be made of the same material as that of the signal line  13 . The driving line  15  thus formed corresponds to a first driving line according to an embodiment. 
     As illustrated in  FIG. 3B , the driving line  16  is formed in a shape protruding upwards from the stationary portion  11  and straddling over the driving electrode portion  15   a  of the driving line  15 . The driving line  16  has a driving electrode portion  16   a  positioned to face the driving electrode portion  15   a . The driving electrode portion  16   a  corresponds to a stationary driving electrode portion according to an embodiment. The driving line  16  has a thickness of 10 μm or more, for example. Further, the driving line  16  is disposed to extend along the signal lines  13  and  14  as illustrated in  FIG. 1 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  16  serves also as a ground line). The driving line  16  can be made of the same material as that of the signal line  14 . The driving line  16  thus formed corresponds to a second driving line according to an embodiment. 
     The ground line  17  is disposed to extend along the signal lines  13  and  14  as illustrated in  FIG. 1 , and is connected to the ground through predetermined wiring (not shown). The ground line  17  can be made of the same material as that of the signal line  14 . 
     In the switching device X 1  having the above-described structure, when a voltage is applied to the driving line  15 , an electrostatic attraction force is generated between the driving electrode portion  15   a  of the driving line  15  and the driving electrode portion  16   a  of the driving line  16  (connected to the ground). When the applied voltage is sufficiently high, the movable portion  12  is operated or elastically deformed until the contact portion  13   a  of the signal line  13  comes into contact with the contact portion  14   a  of the signal line  14 . The closed state (contact state) of the switching device X 1  is thus established as illustrated in  FIG. 4B . In the closed state (contact state), the signal lines  13  and  14  are connected to each other so that a current is allowed to pass between the signal lines  13  and  14 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 1  in the closed state, the application of the voltage to the driving line  15  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  15   a  and  16   a , the movable portion  12  returns to its natural state and the signal line  13 , specifically the contact portion  13   a , moves away from the signal line  14 , specifically from the contact portion  14   a . The open state of the switching device X 1  is thus established as illustrated in  FIGS. 3A and 4A . In the open state, the signal lines  13  and  14  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  13  and  14 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. Further, the switching device X 1  in the open state can be changed again to the closed state, i.e., the on-state, with the switching-on operation described above. 
     In the switching device X 1 , the signal line  13  is disposed to extend over the movable land portion  12   a , the beam portion  12   b , and the stationary portion  11 , and has the contact portion  13   a  on the movable portion  12 , specifically on the movable land portion  12   a . The signal line  14  has the contact portion  14   a  positioned to face the contact portion  13   a  and is fixed to the stationary portion  11 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  13  and  14  are selected respectively by closing and opening between the contact portions  13   a  and  14   a . Stated another way, the switching device X 1  includes a single opening/closing point (single contact). The switching device X 1  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 1  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 1 , the driving line  15  is disposed to extend over the movable land portion  12   a , the beam portion  12   c , and the stationary portion  11 , and has the driving electrode portion  15   a  on the movable land portion  12   a . The driving line  16  has the driving electrode portion  16   a  positioned to face the driving electrode portion  15   a  and is fixed to the stationary portion  11 . With the driving voltage applied between the driving electrode portions  15   a  and  16   a , an electrostatic attraction force is generated between the driving electrode portions  15   a  and  16   a  so that the movable land portion  12   a  to which the driving electrode portion  15   a  is joined is operated or elastically deformed toward the driving electrode portion  16   a . The driving line  15  is disposed separately from the signal line  13  (namely, the driving line  15  is routed from the movable land portion  12   a  to the stationary portion  11  while passing the beam portion  12   c  differing from the beam portion  12   b  on which the signal line  13  passes). Also, the driving line  16  is disposed separately from the signal line  14 . Stated another way, in the switching device X 1 , the signal lines  13  and  14  are electrically separated from the driving lines  15  and  16 . The switching device X 1  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 1  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 1 , as illustrated in the plan view of  FIG. 1 , a signal path constituted by the signal lines  13  and  14  is disposed between the driving line  16  (ground line) and the ground line  17 , and the driving line  16  and the ground line  17  have shapes extending along the signal path (namely, the signal path, the driving line  16 , and the ground line  17  are disposed parallel to one another). In other words, the signal path (i.e., the signal lines  13  and  14 ) and two ground lines (i.e., the driving line  16  and the ground line  17 ) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  13  and  14 . 
       FIGS. 5A to 8C  illustrate a method of manufacturing the switching device X 1  as successive changes in sections corresponding to part of  FIG. 3A , part of  FIG. 3B , and part of  FIG. 4A . 
     In the manufacturing method, a material substrate  100  illustrated in  FIG. 5A  is first prepared. The material substrate  100  is an SOI (silicon on insulator) substrate. The material substrate  100  has a multilayered structure comprising a first layer  101 , a second layer  102 , and an intermediate layer  103  interposed between the first and second layers  101  and  102 . In an embodiment, the first layer  101  has a thickness of, e.g., 15 μm, the second layer  102  has a thickness of, e.g., 525 μm, and the intermediate layer  103  has a thickness of, e.g., 4 μm. The first layer  101  is made of, e.g., single-crystal silicon and is machined so as to provide the stationary portion  11  and the movable portion  12 . The second layer  102  is made of, e.g., single-crystal silicon and is machined so as to provide the substrate S 1 . The intermediate layer  103  is made of, e.g., silicon oxide and is machined so as to provide the boundary layer  18 . 
     Next, as illustrated in  FIG. 5B , a conductor film  104  is formed on the first layer  101 . The conductor film  104  can be formed by sputtering, for example, such that a Mo film is formed on the first layer  101  and an Au film is successively formed on the Mo film. The Mo film has a thickness of, e.g., 50 nm, and the Au film has a thickness of, e.g., 500 nm. 
     Next, as illustrated in  FIG. 5C , resist patterns  105  and  106  are formed on the conductor film  104  by photolithography. The resist pattern  105  has a pattern shape corresponding to the signal line  13 . The resist pattern  106  has a pattern shape corresponding to the signal line  15 . 
     Next, as illustrated in  FIG. 6A , the signal line  13  and the driving line  15  are formed on the first layer  101  by etching the conductor film  104  with the resist patterns  105  and  106  used as masks. Ion milling (e.g., physical etching with, e.g., Ar ions) can be employed as an etching method in this operation. The ion milling can also be employed as an etching method for a metallic material described later. 
     After removing the resist patterns  105  and  106 , as illustrated in  FIG. 6B , a slit  19  is formed by etching the first layer  101 . More specifically, a predetermined resist pattern is formed on the first layer  101  by photolithography, and anisotropic etching is then performed on the first layer  101  with the resist pattern used as a mask. DRIE (deep reactive ion etching) can be employed as the anisotropic etching. With the DRIE, satisfactory anisotropic etching can be performed in the Bosch process where etching using SF 6  gas and sidewall protection using C 4 F 8  gas are alternately repeated. That Bosch process in the DRIE can also be employed in the DRIE described later. With the above-described operation, the stationary portion  11  and the movable portion  12  are formed. 
     Next, as illustrated in  FIG. 6C , a sacrifice layer  107  is formed over the surface of the material substrate  100  on the side including the first layer  101  so as to close the slit  19  while covering the movable portion  12 , the signal line  13 , and the driving line  15 . The sacrifice layer  107  can be made of, e.g., silicon oxide. Plasma CVD or sputtering, for example, can be employed as a method of forming the sacrifice layer  107 . The sacrifice layer  107  formed in this operation has a thickness of, e.g., 5 μm. Polyimide may also be used as the material of the sacrifice layer. 
     Next, as illustrated in  FIG. 7A , recesses  107   a  are formed in the sacrifice layer  107 . More specifically, a predetermined resist pattern is formed on the sacrifice layer  107  by photolithography, and the sacrifice layer  107  is then etched to a predetermined depth with the resist pattern used as a mask. The etching can be performed as wet etching. For example, buffered hydrogen fluoride (BHF) can be employed as an etchant for the wet etching. BHF can also be employed in later-described wet etching for the sacrifice layer  107 . The recesses  107   a  are each used to form a projection serving as the contact portion  14   a  of the signal line  14 . 
     Next, as illustrated in  FIG. 7B , the sacrifice layer  107  is patterned so as to form openings  107   b ,  107   c  and  107   d . More specifically, a predetermined resist pattern is formed on the sacrifice layer  107  by photolithography, and the sacrifice layer  107  is then etched by, e.g., wet etching with the resist pattern used as a mask. The opening  107   b  is employed to expose a region of the stationary portion  11  where the signal line  14  is joined. The opening  107   c  is employed to expose a region of the stationary portion  11  where the driving line  16  is joined. The opening  107   d  is employed to expose a region of the stationary portion  11  where the ground line  17  is disposed. 
     Next, after forming an undercoat film (not shown) for application of power on the surface of the material substrate  100  where the sacrifice layer  107  is disposed, a resist pattern  108  is formed as illustrated in  FIG. 7C . The undercoat film can be formed by sputtering, for example, such that a Mo film is formed in a thickness of 50 nm and an Au film is successively formed in a thickness of 300 nm on the Mo film. The resist pattern  108  has an opening  108   a  corresponding to the signal line  14 , an opening  108   b  corresponding to the driving line  16 , and an opening  108   c  corresponding to the ground line  17 . 
     Next, as illustrated in  FIG. 8A , the signal line  14 , the driving line  16 , and the ground line  17  are formed. More specifically, for example, Au is grown by electroplating on the undercoat film, which is exposed in regions corresponding to the openings  108   a ,  108   b  and  108   c . The plating material is grown to a thickness of, e.g., 20 μm. 
     Next, as illustrated in  FIG. 8B , the resist pattern  108  is etched away. Thereafter, the exposed portions of the undercoat film, which has been used for the electroplating, are removed. Ion milling or reactive ion etching (RIE) can be employed as a method for removing the undercoat film. 
     Next, as illustrated in  FIG. 8C , the sacrifice layer  107  and the intermediate layer  103  are partly removed. More specifically, wet etching is performed on the sacrifice layer  107  and the intermediate layer  103 . In that wet etching, the sacrifice layer  107  is first removed and the intermediate layer  103  is then partly removed from locations exposed to the slit  19 . That wet etching is stopped after a gap has been appropriately formed between the whole of the movable portion  12  and the second layer  102 . In such a way, the boundary layer  18  is formed in a state remaining in the intermediate layer  103 . Further, the second layer  102  constitutes the substrate S 1 . 
     Next, the above-mentioned undercoat film (not shown) adhering to respective surfaces of the signal line  14  and the driving line  16  are removed as required. Wet etching can be employed as a method for removing the undercoat layer. 
     Thereafter, the entire device is dried, as required, by a supercritical drying method. The supercritical drying method can avoid the movable portion  12  from sticking to the substrate S 1  and so on, i.e., a sticking phenomenon. As a result, the switching device X 1  can be appropriately manufactured. 
     With the above-described manufacturing method, the signal line  14  having the region positioned to face the signal line  13  can be formed in a larger thickness by the plating. Therefore, the signal line  14  can be set to a thickness sufficient to realize the desired low resistance. The thick signal line  14  is preferable including in reducing the insertion loss of the switching device X 1 . 
       FIGS. 9 and 10  illustrate a first modification of the switching device X 1 .  FIG. 9  is a plan view of the first modification.  FIG. 10  is a plan view, partly omitted, of the first modification (in  FIG. 10 , the signal line  14  and the driving line  16  are omitted). 
     The switching device X 1  may include the driving line  15  having a pattern shape illustrated in  FIGS. 9 and 10 . The driving line  15 , illustrated in  FIGS. 9 and 10 , has a portion  15   b  on the movable portion  12 . For clearer understanding from the drawing, the portion  15   b  is denoted by thinner hatching than the other portion of the driving line  15 . The pattern shape of the portion  15   b  is congruent to the pattern shape (denoted by similar thinner hatching to that representing the portion  15   b ) of the signal line  13  on the movable portion  12 . Such a symmetrical arrangement is preferable including in suppressing the generation of improper deformation (such as torsional deformation) in the movable portion  12  that is elastically deformed when driven. 
       FIGS. 11 to 13B  illustrate a second modification of the switching device X 1 .  FIG. 11  is a plan view of the second modification.  FIG. 12  is a plan view, partly omitted, of the second modification (in  FIG. 12 , the signal line  14  and the driving line  16  are omitted).  FIGS. 13A and 13B  are sectional views taken along lines XIIIA-XIIIA and XIIIB-XIIIB in  FIG. 11 , respectively. 
     The switching device X 1  may include a stopper portion  20  (omitted in  FIG. 12 ), as illustrated in  FIGS. 11 ,  13 A and  13 B. The stopper portion  20  is formed in a shape protruding upwards from the stationary portion  11  and has a region positioned to face the movable portion  12 . The stopper portion  20  includes, in its region positioned to face the movable portion  12 , a projected portion  20   a  extending toward the movable portion  12 . When the switching device X 1  is not driven (i.e., when the movable portion  12  is in the natural state), as illustrated in  FIG. 13B , a gap G 2  between the movable portion  12  and the projected portion  20   a  is larger than a gap G 1  between the contact portion  13   a  of the signal line  13  on the movable portion  12  and the contact portion  14   a , i.e., the projected portion, of the signal line  14 . When the switching device X 1  is switched on (i.e., when the movable portion  12  is elastically deformed toward the driving electrode portion  16   a  of the driving line  16 ), the stopper portion  20  is capable of contacting the movable portion  12  after the contact portions  13   a  and  14   a  have been brought into the closed state, and hence it can prevent the movable portion  12  from further deforming closer to the driving electrode portion  16   a . Accordingly, the provision of the stopper portion  20  is preferable including in preventing the driving electrode portions  15   a  and  16   a  from contacting with each other and from short-circuiting the switching device is driven. The above-described stopper portion  20  can be formed on the stationary portion  11  in a similar manner to that for forming the signal line  14  on the stationary portion  11 . 
       FIGS. 14 and 15  illustrate a third modification of the switching device X 1 .  FIG. 14  is a plan view of the third modification.  FIG. 15  is a plan view, partly omitted, of the third modification (in  FIG. 15 , the signal line  14  and the driving line  16  are omitted). 
     The switching device X 1  may include the movable portion  12 , the signal lines  13  and  14 , and the driving line  15 , which are shaped as illustrated in  FIGS. 14 and 15 . The signal line  13 , illustrated in  FIGS. 14 and 15 , is formed in a pattern extending over the beam portion  12   b  of the movable portion  12  and the stationary portion  11 , and it has the contact portion  13   a  on the beam portion  12   b . The signal line  13 , illustrated in  FIGS. 14 and 15 , is shorter than, e.g., the signal line  13  illustrated in  FIGS. 1 and 2 . The signal line  13  having a shorter length has lower resistance. Therefore, the arrangement that the signal line  13  having a fairly smaller thickness than the signal line  14  is relatively short, as illustrated in  FIG. 15 , is preferable including in suppressing the signal loss generated in the signal path (i.e., the signal lines  13  and  14 ). Further, the movable portion  12  in the third modification has a symmetrical shape with a phantom (imaginary) line P being an axis of symmetry, as illustrated in the plan views of  FIGS. 14 and 15 . Such a symmetrical arrangement is preferable in suppressing the generation of improper deformation (such as torsional deformation) in the movable portion  12  that is elastically deformed when driven. 
       FIGS. 16 to 18B  illustrate a fourth modification of the switching device X 1 .  FIG. 16  is a plan view of the fourth modification.  FIG. 17  is a plan view, partly omitted, of the fourth modification (in  FIG. 17 , the signal line  14  and the driving line  16  are omitted).  FIGS. 18A and 18B  are sectional views taken along lines XVIIIA-XVIIIA and in  FIG. 16 , respectively. 
     The switching device X 1  may include the signal line  13  and the driving line  15  each having a partly thicker portion, as illustrated in  FIGS. 18A and 18B . The signal line  13 , illustrated in  FIG. 18A , has a thicker portion  13   b  primarily on the beam portion  12   b  of the movable portion  12 . The provision of the thicker portion  13   b  in the signal line  13  is preferable including in reducing the resistance of the signal line  13  and hence desirable in suppressing the signal loss occurred in the signal path (i.e., the signal lines  13  and  14 ). Further, similarly to the arrangement that the signal line  13  has the thicker portion  13   b  primarily on the beam portion  12   b  of the movable portion  12 , the driving line  15  illustrated in  FIG. 18B  has a thicker portion  15   b  primarily on the beam portion  12   c  of the movable portion  12 . Such a symmetrical arrangement is preferable including in suppressing the generation of improper deformation (such as torsional deformation) in the movable portion  12  that is elastically deformed when driven. 
       FIGS. 19 ,  20 ,  21 A,  21 B and  22  illustrate a switching device X 2  according to an embodiment of the present invention.  FIG. 19  is a plan view of the switching device X 2 .  FIG. 20  is a plan view, partly omitted, of the switching device X 2 .  FIGS. 21A ,  21 B and  22  are sectional views taken along lines XXIA-XXIA, XXIB-XXIB and XXII-XXII in  FIG. 19 , respectively. 
     The switching device X 2  includes a substrate S 1 , a stationary portion  21 , a movable portion  22 , a signal line  23 , a signal line  24  (omitted in  FIG. 20 ), a driving line  25 , a driving line  26  (omitted in  FIG. 20 ), and a ground line  27 . As illustrated in  FIGS. 21A and 21B , the stationary portion  21  is joined to the substrate S 1  through a boundary layer  28 . As illustrated in  FIGS. 19 and 20 , the movable portion  22  has a movable land portion  22   a  and beam portions  22   b  and  22   c , and it is surrounded by the stationary portion  21  with a slit  29  interposed therebetween. In an second embodiment, the beam portions  22   b  and  22   c  couple the stationary portion  21  and the movable land portion  22   a  with each other, and they extend side by side parallel to each other between the stationary portion  21  and the movable land portion  22   a . As most clearly illustrated in  FIG. 20 , the signal line  23  is disposed to extend over the movable land portion  22   a , the beam portion  22   b , and the stationary portion  21 . Also, the signal line  23  has, on the movable land portion  12   a , a contact portion  23   a  capable of contacting the signal line  14 . Further, the signal line  23  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 21A , the signal line  24  is formed in a shape protruding upwards from the stationary portion  21  and has a region positioned to face the signal line  23 . The signal line  24  includes, in its region positioned to face the signal line  13 , a projected portion or a contact portion  24   a  extending toward the signal line  23 . Further, the signal line  24  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). A signal path constituted by the signal lines  23  and  24  is bent on the movable land portion  22   a  of the movable portion  22  as appearing in the plan view of  FIG. 19  (the contact portions  23   a  and  24   a  being positioned on the movable land portion  22   a ). As most clearly illustrated in  FIG. 20 , the driving line  25  is disposed to extend over the movable land portion  22   a , the beam portion  22   c , and the stationary portion  21 . Also, the driving line  25  has a driving electrode portion  25   a  on the movable land portion  22   a . As illustrated in  FIGS. 21B and 22 , the driving line  26  is formed in a shape protruding upwards from the stationary portion  21  and straddling over the driving electrode portion  25   a  of the driving line  25 . The driving line  26  has a driving electrode portion  26   a  positioned to face the driving electrode portion  25   a . Further, the driving line  26  has a shape extending along the signal lines  23  and  24  as illustrated in  FIG. 19 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  26  serves also as a ground line). The ground line  27  has a shape extending along the signal lines  23  and  24  as illustrated in  FIG. 19 , and is connected to the ground through predetermined wiring (not shown). Other constructions of the stationary portion  21 , the movable portion  22 , the signal lines  23  and  24 , the driving lines  25  and  26 , and the ground line  27  are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , the driving lines  15  and  16 , and the ground line  17  in the above-described embodiment. The switching device X 2  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 2  having the above-described structure, when a driving voltage is applied to the driving line  25 , an electrostatic attraction force is generated between the driving electrode portion  25   a  of the driving line  25  and the driving electrode portion  26   a  of the driving line  26  (connected to the ground), and the movable portion  22  is operated or elastically deformed until the contact portion  23   a  of the signal line  23  comes into contact with the contact portion  24   a  of the signal line  24 . The closed state of the switching device X 2  is thus established. In the closed state, the signal lines  23  and  24  are connected to each other so that a current is allowed to pass between the signal lines  23  and  24 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 2  in the closed state, the application of the voltage to the driving line  25  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  25   a  and  26   a , the movable portion  22  returns to its natural state and the signal line  23 , specifically the contact portion  23   a , moves away from the signal line  24 , specifically from the contact portion  24   a . The open state of the switching device X 2  is thus established. In the open state, the signal lines  23  and  24  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  23  and  24 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 2 , the signal line  23  is disposed to extend over the movable land portion  22   a , the beam portion  22   b , and the stationary portion  21 , and has the contact portion  23   a  on the movable portion  22 , specifically on the movable land portion  22   a . The signal line  24  has the contact portion  24   a  positioned to face the contact portion  23   a  and is fixed to the stationary portion  21 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  23  and  24  are selected respectively by closing and opening between the contact portions  23   a  and  24   a . Stated another way, the switching device X 2  includes a single opening/closing point (single contact). The switching device X 2  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 2  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 2 , the driving line  25  is disposed to extend over the movable land portion  22   a , the beam portion  22   c , and the stationary portion  21 , and has the driving electrode portion  25   a  on the movable land portion  22   a . The driving line  26  has the driving electrode portion  26   a  positioned to face the driving electrode portion  25   a  and is fixed to the stationary portion  21 . With the driving voltage applied between the driving electrode portions  25   a  and  26   a , an electrostatic attraction force is generated between the driving electrode portions  25   a  and  26   a  so that the movable land portion  22   a  to which the driving electrode portion  25   a  is joined is operated or elastically deformed toward the driving electrode portion  26   a . The driving line  25  is disposed separately from the signal line  23  (namely, the driving line  25  is routed from the movable land portion  22   a  to the stationary portion  21  while passing the beam portion  22   c  differing from the beam portion  22   b  on which the signal line  23  passes). Also, the driving line  26  is disposed separately from the signal line  24 . Stated another way, in the switching device X 2 , the signal lines  23  and  24  are electrically separated from the driving lines  25  and  26 . The switching device X 2  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 2  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 2 , as illustrated in the plan view of  FIG. 19 , a signal path constituted by the signal lines  23  and  24  is disposed between the driving line  26  (ground line) and the ground line  27 , and the driving line  26  and the ground line  27  have shapes extending along the signal path. In other words, the signal path (i.e., the signal lines  23  and  24 ) and two ground lines (i.e., the driving line  26  and the ground line  27 ) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  23  and  24 . 
     In the switching device X 2 , the signal lines  23  and  24  are disposed such that the signal path (constituted by the signal lines  23  and  24 ) is bent on the movable land portion  22   a  of the movable portion  22 , as appearing in the plan view of  FIG. 19 . Therefore, the switching device X 2  can be more easily designed such that the signal line  23  has a shorter length on the movable land portion than the signal line  13  in the above-described embodiment, and that an area in which the driving electrode portions  25   a  and  26   a  are positioned to face each other is larger than an area in which the driving electrode portions  15   a  and  16   a  in the above-described embodiment are positioned to face each other. The signal line  23  having a smaller thickness is preferably formed to be shorter from the viewpoint of suppressing the signal loss occurred in the signal path (signal lines  23  and  24 ). Also, the area in which the driving electrode portions  25   a  and  26   a  for generating the electrostatic attraction force (driving force) are positioned to face each other is preferably set to be larger from the viewpoint of reducing the driving voltage. Thus, the switching device X 2  has the structure suitable for not only suppressing the signal loss in the signal path, but also reducing the driving voltage. 
     In the switching device X 2 , similarly to the arrangement described above in the first modification of the switching device X 1  regarding the signal line  13  and the driving line  15  on the movable portion  12 , the signal line  23  and the driving line  25  on the movable portion  22  may be arranged in a symmetrical pattern shape. Similarly to the second modification of the switching device X 1 , the switching device X 2  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  25   a  and  26   a  from contacting with each other and short-circuiting when driven. Similarly to the third modification of the switching device X 1  in which the signal lines  13  and  14  have the contact portions  13   a  and  14   a  on the beam portion  12   b , the switching device X 2  may be modified such that the contact portions  23   a  and  24   a  of the signal lines  23  and  24  are positioned on the beam portion  22   b . Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 2  may be modified such that the signal line  23  and the driving line  25  may partly have thicker portions. 
       FIGS. 23 ,  24 ,  25 A and  25 B illustrate a switching device X 3  according to an embodiment of the present invention.  FIG. 23  is a plan view of the switching device X 3 .  FIG. 24  is a plan view, partly omitted, of the switching device X 3 .  FIGS. 25A and 25B  are sectional views taken along lines XXVA-XXVA and XXVB-XXVB in  FIG. 23 , respectively. 
     The switching device X 3  includes a substrate S 1 , a stationary portion  31 , a movable portion  32 , a signal line  33 , a signal line  34  (omitted in  FIG. 24 ), a driving line  35 , a driving line  36  (omitted in  FIG. 24 ), and a ground line  37 . As illustrated in  FIGS. 25A and 25B , the stationary portion  31  is joined to the substrate S 1  through a boundary layer  38 . As illustrated in  FIGS. 23 and 24 , the movable portion  32  has a movable land portion  32   a  and beam portions  32   b  and  32   c , and it is surrounded by the stationary portion  31  with a slit  39  interposed therebetween. The beam portions  32   b  and  32   c  are oppositely extended in one direction and are spaced from each other in the extending direction with the movable land portion  32   a  disposed therebetween. Further, each of the beam portions  32   b  and  32   c  couples the movable land portion  32   a  and the stationary portion  31  with each other. In other words, the movable portion  32  is supported by the stationary portion  31  in a both-end supported structure. As most clearly illustrated in  FIG. 24 , the signal line  33  is disposed to extend over the movable land portion  32   a , the beam portion  32   b , and the stationary portion  31 . Also, the signal line  33  has, on the movable land portion  32   a , a contact portion  33   a  capable of contacting the signal line  34 . Further, the signal line  33  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 25A , the signal line  34  is formed in a shape protruding upwards from the stationary portion  31  and has a region positioned to face the signal line  33 . The signal line  34  includes, in its region positioned to face the signal line  33 , a projected portion or a contact portion  34   a  extending toward the signal line  33 . Further, the signal line  34  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As most clearly illustrated in  FIG. 24 , the driving line  35  is disposed to extend over the movable land portion  32   a , the beam portion  32   c , and the stationary portion  31 . Also, the driving line  35  has a driving electrode portion  35   a  on the movable land portion  32   a . As illustrated in  FIG. 25B , the driving line  36  is formed in a shape protruding upwards from the stationary portion  31  and straddling over the driving electrode portion  35   a  of the driving line  35 . The driving line  36  has a driving electrode portion  36   a  positioned to face the driving electrode portion  35   a . Further, the driving line  36  has a shape extending along the signal lines  33  and  34  as illustrated in  FIG. 23 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  36  serves also as a ground line). The ground line  37  has a shape extending along the signal lines  33  and  34  as illustrated in  FIG. 23 , and is connected to the ground through predetermined wiring (not shown). Other constructions of the stationary portion  31 , the movable portion  32 , the signal lines  33  and  34 , the driving lines  35  and  36 , and the ground line  37  are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , the driving lines  15  and  16 , and the ground line  17  in the above-described embodiment. The switching device X 3  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 3  having the above-described structure, when a driving voltage is applied to the driving line  35 , an electrostatic attraction force is generated between the driving electrode portion  35   a  of the driving line  35  and the driving electrode portion  36   a  of the driving line  36  (connected to the ground), and the movable portion  32  is operated or elastically deformed until the contact portion  33   a  of the signal line  33  comes into contact with the contact portion  34   a  of the signal line  34 . The closed state of the switching device X 3  is thus established. In the closed state, the signal lines  33  and  34  are connected to each other so that a current is allowed to pass between the signal lines  33  and  34 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 3  in the closed state, the application of the voltage to the driving line  35  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  35   a  and  36   a , the movable portion  32  returns to its natural state and the signal line  33 , specifically the contact portion  33   a , moves away from the signal line  34 , specifically from the contact portion  34   a . The open state of the switching device X 3  is thus established. In the open state, the signal lines  33  and  34  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  33  and  34 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 3 , the signal line  33  is disposed to extend over the movable land portion  32   a , the beam portion  32   b , and the stationary portion  31 , and has the contact portion  33   a  on the movable portion  32 , specifically on the movable land portion  32   a . The signal line  34  has the contact portion  34   a  positioned to face the contact portion  33   a  and is fixed to the stationary portion  31 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  33  and  34  are selected respectively by closing and opening between the contact portions  33   a  and  34   a . Stated another way, the switching device X 3  includes a single opening/closing point (single contact). The switching device X 3  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 3  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 3 , the driving line  35  is disposed to extend over the movable land portion  32   a , the beam portion  32   c , and the stationary portion  31 , and has the driving electrode portion  35   a  on the movable land portion  32   a . The driving line  36  has the driving electrode portion  36   a  positioned to face the driving electrode portion  35   a  and is fixed to the stationary portion  31 . With the driving voltage applied between the driving electrode portions  35   a  and  36   a , an electrostatic attraction force is generated between the driving electrode portions  35   a  and  36   a  so that the movable land portion  32   a  to which the driving electrode portion  35   a  is joined is operated or elastically deformed toward the driving electrode portion  36   a . The driving line  35  is disposed separately from the signal line  33  (namely, the driving line  35  is routed from the movable land portion  32   a  to the stationary portion  31  while passing the beam portion  32   c  differing from the beam portion  32   b  on which the signal line  33  passes). Also, the driving line  36  is disposed separately from the signal line  34 . Stated another way, in the switching device X 3 , the signal lines  33  and  34  are electrically separated from the driving lines  35  and  36 . The switching device X 3  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 3  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 3 , as illustrated in the plan view of  FIG. 23 , a signal path constituted by the signal lines  33  and  34  is disposed between the driving line  36  (ground line) and the ground line  37 , and the driving line  36  and the ground line  37  have shapes extending along the signal path. In other words, the signal path (i.e., the signal lines  33  and  34 ) and two ground lines (i.e., the driving line  36  and the ground line  37 ) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  33  and  34 . 
     In the switching device X 3 , the distance of spacing between the contact portions  33   a  and  34   a  and the distance of spacing between the driving electrode portions  35   a  and  36   a  in the not-driven state are easier to accurately control. The reason is that, in the not-driven state, the movable portion  32  supported to the stationary portion  31  in the both-end supported structure is less apt to improperly displace in a direction H of thickness, denoted in  FIGS. 25A and 25B . The signal line  33  in the switching device X 3  can be formed in a similar manner to that for forming the signal line  13  in the above-described embodiment. In the signal line  33  thus formed, there may occur internal stress acting in the direction of contraction. The driving line  35  can be formed in a similar manner to that for forming the driving line  15  in the above-described embodiment. In the driving line  35  thus formed, there may occur internal stress acting in the direction of contraction. The internal stresses occurred in the signal line  33  and the driving line  35  act on the movable portion  32  as forces causing the movable portion  32  to deform such that the movable land portion  32   a  comes closer toward the signal line  34  and the driving line  36 . However, the movable portion  32  supported to the stationary portion  31  in the both-end supported structure is more resistant against those deformation forces. As a result, in the not-driven state, the movable portion  32  is less apt to improperly displace in the direction H of thickness, denoted in  FIGS. 25A and 25B . 
     Similarly to the second modification of the switching device X 1 , the switching device X 3  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  35   a  and  36   a  from contacting with each other and short-circuiting when driven. Similarly to the third modification of the switching device X 1  in which the signal lines  13  and  14  have the contact portions  13   a  and  14   a  on the beam portion  12   b , the switching device X 3  may be modified such that the contact portions  33   a  and  34   a  of the signal lines  33  and  34  are positioned on the beam portion  32   b . Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 3  may be modified such that the signal line  33  and the driving line  35  may partly have thicker portions. 
       FIGS. 26 ,  27 ,  28 A,  28 B and  29  illustrate a switching device X 4  according to an embodiment of the present invention.  FIG. 26  is a plan view of the switching device X 4 .  FIG. 27  is a plan view, partly omitted, of the switching device X 4 .  FIGS. 28A ,  28 B and  29  are sectional views taken along lines XXVIIIA-XXVIIIA, XXVIIIB-XXVIIIB and XXIX-XXIX in  FIG. 26 , respectively. 
     The switching device X 4  includes a substrate S 1 , a stationary portion  41 , a movable portion  42 , a signal line  43 , a signal line  44  (omitted in  FIG. 27 ), a driving line  45 , a driving line  46  (omitted in  FIG. 27 ), and a ground line  47 . As illustrated in  FIGS. 28A and 28B , the stationary portion  41  is joined to the substrate S 1  through a boundary layer  48 . As illustrated in  FIGS. 26 and 27 , the movable portion  42  has a movable land portion  42   a  and beam portions  42   b  and  42   c , and it is surrounded by the stationary portion  41  with a slit  49  interposed therebetween. The beam portions  42   b  and  42   c  are oppositely extended in one direction and are spaced from each other in the extending direction with the movable land portion  42   a  disposed therebetween. Further, each of the beam portions  42   b  and  42   c  couples the movable land portion  42   a  and the stationary portion  41  with each other. In other words, the movable portion  42  is supported by the stationary portion  41  in a both-end supported structure. As most clearly illustrated in  FIG. 27 , the signal line  43  is disposed to extend over the beam portion  42   b  of the movable portion  42  and the stationary portion  41 . Also, the signal line  43  has, on the beam portion  42   b , a contact portion  43   a  capable of contacting the signal line  44 . Further, the signal line  43  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 28A , the signal line  44  is formed in a shape protruding upwards from the stationary portion  41  and has a region positioned to face the signal line  43 . The signal line  44  includes, in its region positioned to face the signal line  43 , a projected portion or a contact portion  44   a  extending toward the signal line  43 . Further, the signal line  44  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As most clearly illustrated in  FIG. 27 , the driving line  45  is disposed to extend over the movable land portion  42   a , the beam portion  42   c , and the stationary portion  41 . Also, the driving line  45  has a driving electrode portion  45   a  on the movable land portion  42   a . As illustrated in  FIG. 28B , the driving line  46  is formed in a shape protruding upwards from the stationary portion  41  and straddling over the driving electrode portion  45   a  of the driving line  45 . The driving line  46  has a driving electrode portion  46   a  positioned to face the driving electrode portion  45   a . Further, the driving line  46  has a shape extending along the signal lines  43  and  44  as illustrated in  FIG. 26 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  46  serves also as a ground line). The ground line  47  has a shape having sides adjacent to and extending along the signal lines  43  and  44  as illustrated in  FIG. 26 , and is connected to the ground through predetermined wiring (not shown). Other constructions of the stationary portion  41 , the movable portion  42 , the signal lines  43  and  44 , the driving lines  45  and  46 , and the ground line  47  are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , the driving lines  15  and  16 , and the ground line  17  in the above-described embodiment. The switching device X 4  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 4  having the above-described structure, when a driving voltage is applied to the driving line  45 , an electrostatic attraction force is generated between the driving electrode portion  45   a  of the driving line  45  and the driving electrode portion  46   a  of the driving line  46  (connected to the ground), and the movable portion  42  is operated or elastically deformed until the contact portion  43   a  of the signal line  43  comes into contact with the contact portion  44   a  of the signal line  44 . The closed state of the switching device X 4  is thus established. In the closed state, the signal lines  43  and  44  are connected to each other so that a current is allowed to pass between the signal lines  43  and  44 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 4  in the closed state, the application of the voltage to the driving line  45  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  45   a  and  46   a , the movable portion  42  returns to its natural state and the signal line  43 , specifically the contact portion  43   a , moves away from the signal line  44 , specifically from the contact portion  44   a . The open state of the switching device X 4  is thus established. In the open state, the signal lines  43  and  44  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  43  and  44 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 4 , the signal line  43  is disposed to extend over the beam portion  42   b  and the stationary portion  41 , and has the contact portion  43   a  on the beam portion  42   b . The signal line  44  has the contact portion  44   a  positioned to face the contact portion  43   a  and is fixed to the stationary portion  41 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  43  and  44  are selected respectively by closing and opening between the contact portions  43   a  and  44   a . Stated another way, the switching device X 4  includes a single opening/closing point (single contact). The switching device X 4  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 4  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 4 , the driving line  45  is disposed to extend over the movable land portion  42   a , the beam portion  42   c , and the stationary portion  41 , and has the driving electrode portion  45   a  on the movable land portion  42   a . The driving line  46  has the driving electrode portion  46   a  positioned to face the driving electrode portion  45   a  and is fixed to the stationary portion  41 . With the driving voltage applied between the driving electrode portions  45   a  and  46   a , an electrostatic attraction force is generated between the driving electrode portions  45   a  and  46   a  so that the movable land portion  42   a  to which the driving electrode portion  45   a  is joined is operated or elastically deformed toward the driving electrode portion  46   a . The driving line  45  is disposed separately from the signal line  43  (namely, the driving line  45  is routed from the movable land portion  42   a  to the stationary portion  41  while passing the beam portion  42   c  differing from the beam portion  42   b  on which the signal line  43  is disposed). Also, the driving line  46  is disposed separately from the signal line  44 . Stated another way, in the switching device X 4 , the signal lines  43  and  44  are electrically separated from the driving lines  45  and  46 . The switching device X 4  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 4  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 4 , as illustrated in the plan view of  FIG. 26 , a signal path constituted by the signal lines  43  and  44  is disposed between the driving line  46  (ground line) and the ground line  47 , and the driving line  46  and the ground line  47  have shapes extending along the signal path. In other words, the signal path (i.e., the signal lines  43  and  44 ) and two ground lines (i.e., the driving line  46  and the ground line  47 ) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  43  and  44 . 
     In the switching device X 4 , the distance of spacing between the contact portions  43   a  and  44   a  and the distance of spacing between the driving electrode portions  45   a  and  46   a  in the not-driven state are easier to accurately control. The reason is that, in the not-driven state, the movable portion  42  supported to the stationary portion  41  in the both-end supported structure is less apt to improperly displace in a direction H of thickness, denoted in  FIG. 29 . The signal line  43  in the switching device X 4  can be formed in a similar manner to that for forming the signal line  13  in the above-described embodiment. In the signal line  43  thus formed, there may occur internal stress acting in the direction of contraction. The driving line  45  can be formed in a similar manner to that for forming the driving line  15  in the above-described embodiment. In the driving line  45  thus formed, there may occur internal stress acting in the direction of contraction. The internal stresses occurred in the signal line  43  and the driving line  45  act on the movable portion  42  as forces causing the movable portion  42  to deform such that the movable land portion  42   a  comes closer toward the signal line  44  and the driving line  46 . However, the movable portion  42  supported to the stationary portion  41  in the both-end supported structure is more resistant against those deformation forces. As a result, in the not-driven state, the movable portion  42  is less apt to improperly displace in the direction H of thickness, denoted in  FIG. 29 . 
     In the switching device X 4 , the signal lines  43  and  44  are disposed such that the signal path (i.e., the signal lines  43  and  44 ) is bent on the movable land portion  42  and the beam portion  42   b , as appearing in the plan view of  FIG. 26 . Therefore, the switching device X 4  can be more easily designed such that the signal line  43  has a shorter length on the movable land portion than the signal line  13  in the above-described embodiment, and that an area in which the driving electrode portions  45   a  and  46   a  are positioned to face each other is larger than an area in which the driving electrode portions  15   a  and  16   a  in the above-described embodiment are positioned to face each other. The signal line  43  having a smaller thickness is preferably formed to be shorter from the viewpoint of suppressing the signal loss occurred in the signal path (signal lines  43  and  44 ). Also, the area in which the driving electrode portions  45   a  and  46   a  for generating the electrostatic attraction force (driving force) are positioned to face each other is preferably set to be larger from the viewpoint of reducing the driving voltage. Thus, the switching device X 4  has the structure suitable for not only suppressing the signal loss in the signal path, but also reducing the driving voltage. 
     Similarly to the second modification of the switching device X 1 , the switching device X 4  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  45   a  and  46   a  from contacting with each other and short-circuiting when driven. Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 4  may be modified such that the signal line  43  and the driving line  45  may partly have thicker portions. 
       FIGS. 30 ,  31 ,  32 A,  32 B,  33 A and  33 B illustrate a switching device X 5  according to an embodiment of the present invention.  FIG. 30  is a plan view of the switching device X 5 .  FIG. 31  is a plan view, partly omitted, of the switching device X 5 .  FIGS. 32A ,  32 B,  33 A and  33 B are sectional views taken along lines) XXXIIA-XXXIIA, XXXIIB-XXXIIB, XXXIIIA-XXXIIIA and XXXIIIB-XXXIIIB in  FIG. 30 , respectively. 
     The switching device X 5  includes a substrate S 1 , a stationary portion  51 , a movable portion  52 , a signal line  53 , a signal line  54  (omitted in  FIG. 31 ), driving lines  55 A and  55 B, and driving lines  56 A and  56 B (omitted in  FIG. 31 ). As illustrated in  FIGS. 32A to 33B , the stationary portion  51  is joined to the substrate S 1  through a boundary layer  58 . As illustrated in  FIGS. 30 and 31 , the movable portion  52  has a movable land portion  52   a  and beam portions  52   b ,  52   c  and  52   d , and it is surrounded by the stationary portion  51  with a slit  59  interposed therebetween. In an embodiment, three beam portions  52   b  to  52   d  each couple the stationary portion  51  and the movable land portion  52   a  with each other, and they are arranged side by side to extend parallel to each other between the stationary portion  51  and the movable land portion  52   a . In other words, the movable portion  52  is supported by the stationary portion  51  in a cantilevered structure. As most clearly illustrated in  FIG. 31 , the signal line  53  is disposed to extend over the movable land portion  52   a , the beam portion  52   b , and the stationary portion  51 . Also, the signal line  53  has, on the movable land portion  52   a , a contact portion  53   a  capable of contacting the signal line  54 . Further, the signal line  53  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 32A , the signal line  54  is formed in a shape protruding upwards from the stationary portion  51  and has a region positioned to face the signal line  53 . The signal line  54  includes, in its region positioned to face the signal line  53 , a projected portion or a contact portion  54   a  extending toward the signal line  53 . Further, the signal line  54  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As most clearly illustrated in  FIG. 31 , the driving line  55 A is disposed to extend over the movable land portion  52   a , the beam portion  52   c , and the stationary portion  51 . Also, the driving line  55 A has a driving electrode portion  55   a  on the movable land portion  52   a . The driving line  55 B is disposed to extend over the movable land portion  52   a , the beam portion  52   d , and the stationary portion  51 . Also, the driving line  55 B has a driving electrode portion  55   b  on the movable land portion  52   a . As illustrated in  FIG. 32B , the driving line  56 A is formed in a shape protruding upwards from the stationary portion  51  and straddling over the driving electrode portion  55   a  of the driving line  55 A. The driving line  56 A has a driving electrode portion  56   a  positioned to face the driving electrode portion  55   a . Further, the driving line  56 A has a shape extending along the signal lines  53  and  54  as illustrated in  FIG. 30 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  56 A serves also as a ground line). As illustrated in  FIG. 33A , the driving line  56 B is formed in a shape protruding upwards from the stationary portion  51  and straddling over the driving electrode portion  55   b  of the driving line  55 B. The driving line  56 B has a driving electrode portion  56   b  positioned to face the driving electrode portion  55   b . Further, the driving line  56 B has a shape extending along the signal lines  53  and  54  as illustrated in  FIG. 30 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  56 B serves also as a ground line). Other constructions of the stationary portion  51 , the movable portion  52 , the signal lines  53  and  54 , and the driving lines  55 A,  55 B,  56 A and  56 B are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , and the driving lines  15  and  16  in the above-described embodiment. The switching device X 5  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 5  having the above-described structure, when a driving voltage is applied to the driving lines  55 A and  55 B, electrostatic attraction forces are generated between the driving electrode portion  55   a  of the driving line  55 A and the driving electrode portion  56   a  of the driving line  56 A (connected to the ground) and between the driving electrode portion  55   b  of the driving line  55 B and the driving electrode portion  56   b  of the driving line  56 B (connected to the ground), whereby the movable portion  52  is operated or elastically deformed until the contact portion  53   a  of the signal line  53  comes into contact with the contact portion  54   a  of the signal line  54 . The closed state of the switching device X 5  is thus established. In the closed state, the signal lines  53  and  54  are connected to each other so that a current is allowed to pass between the signal lines  53  and  54 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 5  in the closed state, the application of the voltage to the driving lines  55 A and  55 B is stopped to extinguish the electrostatic attraction forces acting between the driving electrode portions  55   a  and  56   a  and between the driving electrode portions  55   b  and  56   b , the movable portion  52  returns to its natural state and the signal line  53 , specifically the contact portion  53   a , moves away from the signal line  54 , specifically from the contact portion  54   a . The open state of the switching device X 5  is thus established. In the open state, the signal lines  53  and  54  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  53  and  54 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 5 , the signal line  53  is disposed to extend over the movable land portion  52   a , the beam portion  52   b , and the stationary portion  51 , and has the contact portion  53   a  on the movable portion  52 , specifically on the movable land portion  52   a . The signal line  54  has the contact portion  54   a  positioned to face the contact portion  53   a  and is fixed to the stationary portion  51 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  53  and  54  are selected respectively by closing and opening between the contact portions  53   a  and  54   a . Stated another way, the switching device X 5  includes a single opening/closing point (single contact). The switching device X 5  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 5  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 5 , the driving line  55 A is disposed to extend over the movable land portion  52   a , the beam portion  52   c , and the stationary portion  51 , and has the driving electrode portion  55   a  on the movable land portion  52   a . The driving line  55 B is disposed to extend over the movable land portion  52   a , the beam portion  52   d , and the stationary portion  51 , and has the driving electrode portion  55   b  on the movable land portion  52   a . The driving line  56 A has the driving electrode portion  56   a  positioned to face the driving electrode portion  55   a , and the driving line  56 B has the driving electrode portion  56   b  positioned to face the driving electrode portion  55   b . With the driving voltage applied between the driving electrode portions  55   a  and  56   a  and between the driving electrode portions  55   b  and  56   b , electrostatic attraction forces are generated between the driving electrode portions  55   a  and  56   a  and between the driving electrode portions  55   b  and  56   b  so that the movable land portion  52   a  to which the driving electrode portions  55   a  and  55   b  are joined is operated or elastically deformed toward the driving electrode portions  56   a  and  56   b . The driving lines  55 A and  55 B are disposed separately from the signal line  53  (namely, the driving lines  55 A and  55 B are routed from the movable land portion  52   a  to the stationary portion  51  while passing respectively the beam portions  52   c  and  52   d  differing from the beam portion  52   b  over which the signal line  53  passes). Also, the driving lines  56 A and  56 B are disposed separately from the signal line  54 . Stated another way, in the switching device X 5 , the signal lines  53  and  54  are electrically separated from the driving lines  55 A,  55 B,  56 A and  56 B. The switching device X 5  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 5  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 5 , the electrostatic attraction force (driving force) can be generated between the driving electrode portions  55   a  and  56   a , and the electrostatic attraction force (driving force) can be generated between the driving electrode portions  55   b  and  56   b  as well. Locations where those driving forces are generated are spaced from each other in a direction denoted by an arrow D 1  in  FIGS. 30 and 33B . Further, in the switching device X 5 , the contact portions  53   a  and  54   a  (opening/closing point) are positioned, as illustrated in  FIG. 33B , between the two locations where the driving forces are generated, in a direction in which those two driving-force generated locations are spaced from each (i.e., in the direction denoted by the arrow D 1 ). In the driven state of the switching device X 5 , therefore, after the contact portions  53   a  and  54   a  have been brought into contact with each other, uniform loads can be more easily applied to the contact point formed by the contact portions  53   a  and  54   a  from both sides of the contact point. As a result, stable contact can be more easily realized at the contact point. 
     In the switching device X 5 , as illustrated in the plan view of  FIG. 30 , a signal path constituted by the signal lines  53  and  54  is disposed between the driving lines  56 A and  56 B (both being ground lines), and the driving lines  56 A and  56 B have shapes extending along the signal path. In other words, the signal path (i.e., the signal lines  53  and  54 ) and two ground lines (i.e., the driving line  56 A and  56 B) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  53  and  54 . 
     In the switching device X 5 , similarly to the arrangement described above in the first modification of the switching device X 1  regarding the signal line  13  and the driving lines  15  on the movable portion  12 , the driving lines  55 A and  55 B on the movable portion  52  are preferably arranged in a symmetrical pattern shape. Similarly to the second modification of the switching device X 1 , the switching device X 5  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  55   a  and  56   a  and the driving electrode portions  55   b  and  56   b  from contacting with each other and short-circuiting when driven. Similarly to the third modification of the switching device X 1  in which the signal lines  13  and  14  have the contact portions  13   a  and  14   a  on the beam portion  12   b , the switching device X 5  may be modified such that the contact portions  53   a  and  54   a  of the signal lines  53  and  54  are positioned on the beam portion  52   b . Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 5  may be modified such that the signal line  53  and the driving lines  55 A and  55 B may partly have thicker portions. 
       FIGS. 34 ,  35 ,  36 A,  36 B,  37 A and  37 B illustrate a switching device X 6  according to an embodiment of the present invention.  FIG. 34  is a plan view of the switching device X 6 .  FIG. 35  is a plan view, partly omitted, of the switching device X 6 .  FIGS. 36A ,  36 B,  37 A and  37 B are sectional views taken along lines) XXXVIA-XXXVIA, XXXVIB-XXXVIB, XXXVIIA-XXXVIIA and XXXVIIB-XXXVIIB in  FIG. 34 , respectively. 
     The switching device X 6  includes a substrate S 1 , a stationary portion  61 , a movable portion  62 , a signal line  63 , a signal line  64  (omitted in  FIG. 35 ), driving lines  65 A and  65 B, and driving lines  66 A and  66 B (omitted in  FIG. 35 ). As illustrated in  FIGS. 36A to 37B , the stationary portion  61  is joined to the substrate S 1  through a boundary layer  68 . As illustrated in  FIGS. 34 and 35 , the movable portion  62  has a movable land portion  62   a  and beam portions  62   b ,  62   c  and  62   d , and it is surrounded by the stationary portion  61  with a slit  69  interposed therebetween. In an embodiment, the beam portions  62   c  and  62   d  each couple the stationary portion  61  and the movable land portion  62   a  with each other, and they are arranged side by side to extend parallel to each other between the stationary portion  61  and the movable land portion  62   a . Further, the beam portion  62   b  couples the stationary portion  61  and the movable land portion  62   a  with each other on the side opposite to the beam portions  62   c  and  62   d . In other words, the movable portion  62  is supported by the stationary portion  61  in a both-end supported structure. 
     As most clearly illustrated in  FIG. 35 , the signal line  63  is disposed to extend over the movable land portion  62   a , the beam portion  62   b , and the stationary portion  61 . Also, the signal line  63  has, on the movable land portion  62   a , a contact portion  63   a  capable of contacting the signal line  64 . Further, the signal line  63  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 36A , the signal line  64  is formed in a shape protruding upwards from the stationary portion  61  and has a region positioned to face the signal line  63 . The signal line  64  includes, in its region positioned to face the signal line  63 , a projected portion or a contact portion  64   a  extending toward the signal line  63 . Further, the signal line  64  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As most clearly illustrated in  FIG. 35 , the driving line  65 A is disposed to extend over the movable land portion  62   a , the beam portion  62   c , and the stationary portion  61 . Also, the driving line  65 A has a driving electrode portion  65   a  on the movable land portion  62   a . The driving line  65 B is disposed to extend over the movable land portion  62   a , the beam portion  62   d , and the stationary portion  61 . Also, the driving line  65 B has a driving electrode portion  65   b  on the movable land portion  62   a.    
     As illustrated in  FIG. 36B , the driving line  66 A is formed in a shape protruding upwards from the stationary portion  61  and straddling over the driving electrode portion  65   a  of the driving line  65 A. The driving line  66 A has a driving electrode portion  66   a  positioned to face the driving electrode portion  65   a . Further, the driving line  66 A has a shape extending along the signal lines  63  and  64  as illustrated in  FIG. 34 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  66 A serves also as a ground line). As illustrated in  FIG. 37A , the driving line  66 B is formed in a shape protruding upwards from the stationary portion  61  and straddling over the driving electrode portion  65   b  of the driving line  65 B. The driving line  56 B has a driving electrode portion  56   a  positioned to face the driving electrode portion  55   b . Further, the driving line  66 B has a shape extending along the signal lines  63  and  64  as illustrated in  FIG. 34 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  66 B serves also as a ground line). Other constructions of the stationary portion  61 , the movable portion  62 , the signal lines  63  and  64 , and the driving lines  65 A,  65 B,  66 A and  66 B are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , and the driving lines  15  and  16  in the above-described embodiment. The switching device X 6  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 6  having the above-described structure, when a driving voltage is applied to the driving lines  65 A and  65 B, electrostatic attraction forces are generated between the driving electrode portion  65   a  of the driving line  65 A and the driving electrode portion  66   a  of the driving line  66 A (connected to the ground) and between the driving electrode portion  65   b  of the driving line  65 B and the driving electrode portion  66   b  of the driving line  66 B (connected to the ground), whereby the movable portion  62  is operated or elastically deformed until the contact portion  63   a  of the signal line  63  comes into contact with the contact portion  64   a  of the signal line  64 . The closed state of the switching device X 6  is thus established. In the closed state, the signal lines  63  and  64  are connected to each other so that a current is allowed to pass between the signal lines  63  and  64 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 6  in the closed state, the application of the voltage to the driving lines  65 A and  65 B is stopped to extinguish the electrostatic attraction forces acting between the driving electrode portions  65   a  and  66   a  and between the driving electrode portions  65   b  and  66   b , the movable portion  62  returns to its natural state and the signal line  63 , specifically the contact portion  63   a , moves away from the signal line  64 , specifically from the contact portion  64   a . The open state of the switching device X 6  is thus established. In the open state, the signal lines  63  and  64  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  63  and  64 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 6 , the signal line  63  is disposed to extend over the movable land portion  62   a , the beam portion  62   b , and the stationary portion  61 , and has the contact portion  63   a  on the movable portion  62 , specifically on the movable land portion  62   a . The signal line  64  has the contact portion  64   a  positioned to face the contact portion  63   a  and is fixed to the stationary portion  61 . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  63  and  64  are selected respectively by closing and opening between the contact portions  63   a  and  64   a . Stated another way, the switching device X 6  includes a single opening/closing point (single contact). The switching device X 6  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 6  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 6 , the driving line  65 A is disposed to extend over the movable land portion  62   a , the beam portion  62   c , and the stationary portion  61 , and has the driving electrode portion  65   a  on the movable land portion  62   a . The driving line  65 B is disposed to extend over the movable land portion  62   a , the beam portion  62   d , and the stationary portion  61 , and has the driving electrode portion  65   b  on the movable land portion  62   a . The driving line  66 A has the driving electrode portion  66   a  positioned to face the driving electrode portion  65   a , and the driving line  66 B has the driving electrode portion  66   b  positioned to face the driving electrode portion  65   b . With the driving voltage applied between the driving electrode portions  65   a  and  66   a  and between the driving electrode portions  65   b  and  66   b , electrostatic attraction forces are generated between the driving electrode portions  65   a  and  66   a  and between the driving electrode portions  65   b  and  66   b  so that the movable land portion  62   a  to which the driving electrode portions  65   a  and  65   b  are joined is operated or elastically deformed toward the driving electrode portions  66   a  and  66   b.    
     The driving lines  65 A and  65 B are disposed separately from the signal line  63  (namely, the driving lines  65 A and  65 B are routed from the movable land portion  62   a  to the stationary portion  61  while passing respectively the beam portions  62   c  and  62   d  differing from the beam portion  62   b  on which the signal line  63  passes). Also, the driving lines  66 A and  66 B are disposed separately from the signal line  64 . Stated another way, in the switching device X 6 , the signal lines  63  and  64  are electrically separated from the driving lines  65 A,  65 B,  66 A and  66 B. The switching device X 6  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 6  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 6 , the electrostatic attraction force (driving force) can be generated between the driving electrode portions  65   a  and  66   a , and the electrostatic attraction force (driving force) can be generated between the driving electrode portions  65   b  and  66   b  as well. Locations where those driving forces are generated are spaced from each other in a direction denoted by an arrow D 2  in  FIGS. 34 and 37B . Further, in the switching device X 6 , the contact portions  63   a  and  64   a  (opening/closing point) are positioned, as illustrated in  FIG. 37B , between the two locations where the driving forces are generated, in a direction in which those two driving-force generated locations are spaced from each (i.e., in the direction denoted by the arrow D 2 ). In the driven state of the switching device X 6 , therefore, after the contact portions  63   a  and  64   a  have been brought into contact with each other, uniform loads can be more easily applied to the contact point formed by the contact portions  63   a  and  64   a  from both sides of the contact point. As a result, stable contact can be more easily realized at the contact point. 
     In the switching device X 6 , as illustrated in the plan view of  FIG. 34 , a signal path constituted by the signal lines  63  and  64  is disposed between the driving lines  66 A and  66 B (both being ground lines), and the driving lines  66 A and  66 B have shapes extending along the signal path. In other words, the signal path (i.e., the signal lines  63  and  64 ) and two ground lines (i.e., the driving line  66 A and  66 B) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  63  and  64 . 
     In the switching device X 6 , similarly to the arrangement described above in the first modification of the switching device X 1  regarding the signal line  13  and the driving lines  15  on the movable portion  12 , the driving lines  65 A and  65 B on the movable portion  62  are preferably arranged in a symmetrical pattern shape. Similarly to the second modification of the switching device X 1 , the switching device X 6  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  65   a  and  66   a  and the driving electrode portions  65   b  and  66   b  from contacting with each other and short-circuiting when driven. Similarly to the third modification of the switching device X 1  in which the signal lines  13  and  14  have the contact portions  13   a  and  14   a  on the beam portion  12   b , the switching device X 6  may be modified such that the contact portions  63   a  and  64   a  of the signal lines  63  and  64  are positioned on the beam portion  62   b . Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 6  may be modified such that the signal line  63  and the driving lines  65 A and  65 B may partly have thicker portions. 
       FIGS. 38-39 ,  40 A and to  40 B illustrate a switching device X 7  according to an embodiment of the present invention.  FIG. 38  is a plan view of the switching device X 7 .  FIG. 39  is a plan view, partly omitted, of the switching device X 7 .  FIGS. 40A and 40B  are sectional views taken along lines XLA-XLA and XLB-XLB in  FIG. 38 , respectively. 
     The switching device X 7  includes a substrate S 1 , a stationary portion  71 , a movable portion  72 , a signal line  73 , signal lines  74 A and  74 B (omitted in  FIG. 39 ), driving lines  75 A and  75 B, driving lines  76 A and  76 B (omitted in  FIG. 35 ), and ground lines  77 A and  77 B. The switching device X 7  is constituted as an SPDT switch (having one input and two outputs). As illustrated in  FIGS. 40A and 40B , the stationary portion  71  is joined to the substrate S 1  through a boundary layer  78 . As illustrated in  FIGS. 38 and 39 , the movable portion  72  has a movable land portion  72   a  and beam portions  72   b  and  72   c , and it is surrounded by the stationary portion  71  with a slit  79  interposed therebetween. The beam portions  72   b  and  72   c  are oppositely extended in one direction and are spaced from each other in the extending direction with the movable land portion  72   a  disposed therebetween. Further, each of the beam portions  72   b  and  72   c  couples the movable land portion  72   a  and the stationary portion  71  with each other. In other words, the movable portion  72  is supported by the stationary portion  71  in a both-end supported structure. Further, the beam portions  72   b  and  72   c  define an axis Ax about which the movable land portion  72   a  is rotationally displaced with respect to the stationary portion  71 . As most clearly illustrated in  FIG. 39 , the signal line  73  is disposed to extend over the movable land portion  72   a , the beam portion  72   b , and the stationary portion  71 . Also, the signal line  73  has, on the movable land portion  72   a , a contact portion  73   a  capable of contacting the signal line  74 A and a contact portion  73   b  capable of contacting the signal line  74 B. As illustrated in the plan view of  FIG. 39 , for example, the contact portions  73   a  and  73   b  are spaced from each other on the movable land portion  72   a  with the axis Ax disposed therebetween. Further, the signal line  73  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). As illustrated in  FIG. 40A , the signal line  74 A is formed in a shape protruding upwards from the stationary portion  71  and has a region positioned to face the signal line  73 . The signal line  74 A includes, in its region positioned to face the signal line  73 , a projected portion or a contact portion  74   a  extending toward the signal line  73 . Further, the signal line  74 A is connected to a predetermined first circuit, which is a switching target, through predetermined wiring (not shown). The signal line  74 B is also formed in a shape protruding upwards from the stationary portion  71  and has a region positioned to face the signal line  73 . The signal line  74 B includes, in its region positioned to face the signal line  73 , a projected portion or a contact portion  74   b  extending toward the signal line  73 . Further, the signal line  74 B is connected to a predetermined second circuit, which is a switching target, through predetermined wiring (not shown). As most clearly illustrated in  FIG. 39 , the driving line  75 A is disposed to extend over the movable land portion  72   a , the beam portion  72   c , and the stationary portion  71 . Also, the driving line  75 A has a driving electrode portion  75   a  on the movable land portion  72   a . The driving line  75 B is disposed to extend over the movable land portion  72   a , the beam portion  72   c , and the stationary portion  71 . Also, the driving line  75 B has a driving electrode portion  75   b  on the movable land portion  72   a . As illustrated in the plan view of  FIG. 39 , for example, the driving electrode portions  75   a  and  75   b  are spaced from each other on the movable land portion  72   a  with the axis Ax disposed therebetween. As illustrated in  FIG. 40B , the driving line  76 A is formed in a shape protruding upwards from the stationary portion  71  and has a driving electrode portion  76   a  positioned to face the driving electrode portion  75   a . Further, the driving line  76 A has a shape extending along the signal lines  73  and  74 A as illustrated in  FIG. 38 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  76 A serves also as a ground line). As illustrated in  FIG. 40B , the driving line  76 A is formed in a shape protruding upwards from the stationary portion  71  and has a driving electrode portion  76   a  positioned to face the driving electrode portion  75   a . Further, the driving line  76 A has a shape extending along the signal lines  73  and  74 A as illustrated in  FIG. 38 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  76 A serves also as a ground line). Also, as illustrated in  FIG. 40B , the driving line  76 B is formed in a shape protruding upwards from the stationary portion  71  and has a driving electrode portion  76   b  positioned to face the driving electrode portion  75   b . Further, the driving line  76 B has a shape extending along the signal lines  73  and  74 B as illustrated in  FIG. 38 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  76 B serves also as a ground line). The ground line  77 A has a shape having sides adjacent to and extending along the signal lines  73  and  74 A as illustrated in  FIG. 38 , and is connected to the ground through predetermined wiring (not shown). The ground line  77 B has a shape having sides adjacent to and extending along the signal lines  73  and  74 B, and is connected to the ground through predetermined wiring (not shown). Other constructions of the stationary portion  71 , the movable portion  72 , the signal lines  73 ,  74 A and  74 B, the driving lines  75 A,  75 B,  76 A and  76 B, and the ground line  77 A and  77 B are similar to those described above regarding the stationary portion  11 , the movable portion  12 , the signal lines  13  and  14 , the driving lines  15  and  16 , and the ground line  17  in the above-described embodiment. The switching device X 7  thus constructed can be manufactured by a method similar to that for manufacturing the switching device X 1  according to the above-described embodiment. 
     In the switching device X 7  having the above-described structure, when a driving voltage is applied to the driving line  75 A, an electrostatic attraction force is generated between the driving electrode portion  75   a  of the driving line  75 A and the driving electrode portion  76   a  of the driving line  76 A (connected to the ground), and the movable portion  72  is operated or elastically deformed, as illustrated in  FIG. 41A , until the contact portion  73   a  of the signal line  73  comes into contact with the contact portion  74   a  of the signal line  74 A (while the beam portions  72   b  and  72   c  are twisted). A first closed state of the switching device X 7  is thus established. In the first closed state, the signal lines  73  and  74 A are connected to each other so that a current is allowed to pass between the signal lines  73  and  74 A. With such a switching-on operation, a first on-state of, e.g., a high-frequency signal can be achieved. 
     When, in the switching device X 7  in the first closed state, the application of the voltage to the driving line  75 A is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  75   a  and  76   a , the movable portion  72  and the beam portions  72   b  and  72   c  return to their natural states and the contact portion  73   a  of the signal line  73  moves away from the contact portion  74   a  of the signal line  74 A. The open state of the switching device X 7  is thus established. 
     Further, in the switching device X 7 , when a driving voltage is applied to the driving line  75 B, an electrostatic attraction force is generated between the driving electrode portion  75   b  of the driving line  75 B and the driving electrode portion  76   b  of the driving line  76 B (connected to the ground), and the movable portion  72  is operated or elastically deformed, as illustrated in  FIG. 41B , until the contact portion  73   b  of the signal line  73  comes into contact with the contact portion  74   b  of the signal line  74 B (while the beam portions  72   b  and  72   c  are twisted). A second closed state of the switching device X 7  is thus established. In the second closed state, the signal lines  73  and  74 B are connected to each other so that a current is allowed to pass between the signal lines  73  and  74 B. With such a switching-on operation, a second on-state of, e.g., a high-frequency signal can be achieved. 
     When, in the switching device X 7  in the second closed state, the application of the voltage to the driving line  75 B is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  75   b  and  76   b , the movable portion  72  and the beam portions  72   b  and  72   c  return to their natural states and the contact portion  73   b  of the signal line  73  moves away from the contact portion  74   b  of the signal line  74 B. The open state of the switching device X 7  is thus established. 
     As described above, the switching device X 7  is able to function as an SPDT switch. 
     More specifically, the switching device X 7  is constituted as a pair of SPST switches (each having one input and one output), which partly share the structure. One SPST switch (first switch) includes the contact portion  73   a , the signal line  74 A, i.e., the contact portion  74   a , and the driving lines  75 A and  76 A. The other SPST switch (second switch) includes the contact portion  73   b , the signal line  74 B, i.e., the contact portion  74   b , and the driving lines  75 B and  76 B. 
     In the first switch of the switching device X 7 , passage and non-passage of, e.g., a high-frequency signal between the signal lines  73  and  74 A are selected respectively by closing and opening between the contact portions  73   a  and  74   a . Stated another way, the first switch includes a single opening/closing point (single contact). The first switch thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Similarly, in the second switch, passage and non-passage of, e.g., a high-frequency signal between the signal lines  73  and  74 B are selected respectively by closing and opening between the contact portions  73   b  and  74   b . Stated another way, the second switch includes a single opening/closing point (single contact). The second switch thus constructed is also less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 7 , i.e., the SPDT switch including the first and second switches, is suitable for realizing a long contact opening/closing life of the SPDT switch. 
     In the switching device X 7 , the driving lines  75 A and  75 B extending over the movable land portion  72   a , the beam portion  72   c , and the stationary portion  71 , as well as the driving lines  76 A and  76 B arranged on the stationary portion  71  are all disposed separately from the signal lines  73 ,  74 A and  74 B. Stated another way, in the switching device X 7 , the signal lines  73 ,  74 A and  74 B are electrically separated from the driving lines  75 A,  75 B,  76 A and  76 B. The switching device X 7  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 7  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 7 , as illustrated in the plan view of  FIG. 38 , a first signal path constituted by the signal lines  73  and  74 A is disposed between the driving line  76 A (ground line) and the ground line  77 A and between the ground line  77 A and  77 B, and the driving line  76 A and the ground lines  77 A and  77 B have shapes extending along the first signal path. In other words, the first signal path (i.e., the signal lines  73  and  74 A) and the ground lines (i.e., the driving line  76 A and the ground lines  77 A and  77 B) constitute coplanar passages. Also, as illustrated in the plan view of  FIG. 38 , a second signal path constituted by the signal lines  73  and  74 B is disposed between the driving line  76 B (ground line) and the ground line  77 B and between the ground line  77 A and  77 B, and the driving line  76 B and the ground lines  77 A and  77 B have shapes extending along the second signal path. In other words, the second signal path (i.e., the signal lines  73  and  74 B) and the ground lines (i.e., the driving line  76 B and the ground lines  77 A and  77 B) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  73 ,  74 A and  74 B. 
     Similarly to the second modification of the switching device X 1 , the switching device X 7  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  75   a  and  76   a  and the driving electrode portions  75   b  and  76   b  from contacting with each other and short-circuiting when driven. Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 7  may be modified such that the signal line  73  and the driving lines  75 A and  75 B may partly have thicker portions. 
       FIGS. 42 ,  43 ,  44 A,  44 B and  45 A  45 B illustrate a switching device X 8  according to an embodiment of the present invention.  FIG. 42  is a plan view of the switching device X 8 .  FIG. 43  is a plan view, partly omitted, of the switching device X 8 .  FIGS. 44A ,  44 B and  45 A ( 45 B) are sectional views taken along lines XLIVA-XLIVA, XLIVB-XLIVB and XLVA-XLVA (XLVB-XLVB) in  FIG. 42 , respectively. 
     The switching device X 8  includes a substrate S 2 , a stationary portion  81  (omitted in  FIG. 43 ), a movable portion  82  (omitted in  FIG. 43 ), signal lines  83  and  84 , driving lines  85  and  86 , and a ground line  87 . 
     The substrate S 2  is made of, e.g., glass or GaAs and has a surface on which the signal line  84 , the driving line  86 , and the ground line  87  are formed by patterning. 
     As illustrated in  FIG. 44A , the stationary portion  81  is joined to the substrate S 2  and is made of, e.g., silicon oxide or polysilicon. In an embodiment, the stationary portion  81  corresponds, together with substrate S 2 , to the stationary portion according to an embodiment. 
     The movable portion  82  has a movable land portion  82   a  and beam portions  82   b  and  82   c , as most clearly illustrated in  FIG. 42 , and it is spaced from the substrate S 2  as illustrated in  FIGS. 44A to 45A . In an embodiment, the beam portions  82   b  and  82   c  each couple the stationary portion  81  and the movable portion  82  with each other, and they are arranged side by side to extend parallel to each other between the stationary portion  81  and the movable portion  82 . In other words, the movable portion  82  is supported by the movable portion  81  in a cantilevered structure. A thickness T 2  of the movable portion  82 , denoted in  FIG. 44A to 45A , is 15 μm or less, for example. Further, a length L 3  of the movable portion  82 , denoted in  FIG. 42 , is 200 to 400 μm, for example, and a length L 4  thereof is 300 to 500 μm, for example. The movable portion  82  thus formed is made of, e.g., silicon oxide or polysilicon. 
     As most clearly illustrated in  FIG. 42 , the signal line  83  is disposed to extend over the movable land portion  82   a , the beam portion  82   b , and the stationary portion  81 . Also, as illustrated in  FIGS. 44A and 45A , the signal line  83  has a projected portion or a contact portion  83   a  which penetrates through the movable land portion  82   a  toward the signal line  84  to be capable of contacting the signal line  84 . A thickness of the signal line  83  is, e.g., 0.5 to 5 μm. Further, the signal line  83  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). The signal line  83  is made of a predetermined conductive material and has a multilayered structure comprising, for example, an undercoat film of Mo and an Au film overlying the undercoat film. The signal line  83  thus formed corresponds to a first signal line according to an embodiment. 
     As illustrated in  FIG. 44A , for example, the signal line  84  is disposed on the substrate S 2  and has a region positioned to face the signal line  83 . The signal line  84  includes, in its region positioned to face the signal line  83 , a contact portion  84   a  capable of contacting the signal line  83 . A thickness of the signal line  84  is, e.g., 0.5 to 5 μm. Further, the signal line  84  is connected to a predetermined circuit, which is a switching target, through predetermined wiring (not shown). The signal line  84  is made of a predetermined conductive material and has a multilayered structure comprising, for example, an undercoat film of Mo and an Au film overlying the undercoat film. The signal line  84  thus formed corresponds to a second signal line according to an embodiment. 
     As most clearly illustrated in  FIG. 42 , the driving line  85  is disposed to extend over the movable land portion  82   a , the beam portion  82   c , and the stationary portion  81 . Also, the driving line  85  has a driving electrode portion  85   a  on the movable land portion  82   a . The driving electrode portion  85   a  corresponds to a movable driving electrode portion according to an embodiment. A thickness of the driving line  85  is, e.g., 0.5 to 5 μm. The driving line  85  can be made of the same material as that of the signal line  83 . The driving line  85  thus formed corresponds to a first driving line according to an embodiment. 
     As illustrated in  FIG. 44B , the driving line  86  is disposed on the substrate S 2  and has a driving electrode portion  86   a  positioned to face the driving electrode portion  85   a  of the driving line  85 . The driving electrode portion  86   a  corresponds to a stationary driving electrode portion according to an embodiment. A thickness of the driving line  86  is, e.g., 0.5 to 5 μm. Further, the driving line  86  is extended along the signal lines  83  and  84  as illustrated in  FIG. 42 , and is connected to the ground through predetermined wiring (not shown) (hence the driving line  86  serves also as a ground line). The driving line  86  can be made of the same material as that of the signal line  84 . The driving line  86  thus formed corresponds to a second driving line according to an embodiment. 
     The ground line  87  is extended along the signal lines  83  and  84  as illustrated in  FIG. 42 , and is connected to the ground through predetermined wiring (not shown). The ground line  87  can be made of the same material as that of the signal line  84 . 
     In the switching device X 8  having the above-described structure, when a driving voltage is applied to the driving line  85 , an electrostatic attraction force is generated between the driving electrode portion  85   a  of the driving line  85  and the driving electrode portion  86   a  of the driving line  86  (connected to the ground), and the movable portion  82  is operated or elastically deformed until the contact portion  83   a  of the signal line  83  comes into contact with the contact portion  84   a  of the signal line  84 . The closed state of the switching device X 8  is thus established as illustrated in  FIG. 45B . In the closed state, the signal lines  83  and  84  are connected to each other so that a current is allowed to pass between the signal lines  83  and  84 . With such a switching-on operation, the on-state of, e.g., a high-frequency signal can be achieved. 
     On the other hand, when, in the switching device X 8  in the closed state, the application of the voltage to the driving line  85  is stopped to extinguish the electrostatic attraction force acting between the driving electrode portions  85   a  and  86   a , the movable portion  82  returns to its natural state and the signal line  83 , specifically the contact portion  83   a , moves away from the signal line  84 , specifically from the contact portion  84   a . The open state of the switching device X 8  is thus established as illustrated in  FIGS. 44A and 45A . In the open state, the signal lines  83  and  84  are electrically separated from each other, whereby a current is prevented from passing between the signal lines  83  and  84 . With such a switching-off operation, the off-state of, e.g., a high-frequency signal can be achieved. 
     In the switching device X 8 , the signal line  83  is disposed to extend over the movable land portion  82   a , the beam portion  82   b , and the stationary portion  81 , and has the contact portion  83   a  on the movable portion  82 , specifically on the movable land portion  82   a . The signal line  84  has the contact portion  84   a  positioned to face the contact portion  83   a . Passage and non-passage of, e.g., a high-frequency signal between the signal lines  83  and  84  are selected respectively by closing and opening between the contact portions  83   a  and  84   a . Stated another way, the switching device X 8  includes a single opening/closing point (single contact). The switching device X 8  thus constructed is less susceptible to the sticking failure that has been described above in connection with the known switching device Z 2 . Accordingly, the switching device X 8  is suitable for realizing a long contact opening/closing life. 
     In the switching device X 8 , the driving line  85  is disposed to extend over the movable land portion  82   a , the beam portion  82   c , and the stationary portion  81 , and has the driving electrode portion  85   a  on the movable land portion  82   a . The driving line  86  has the driving electrode portion  86   a  positioned to face the driving electrode portion  85   a . With the driving voltage applied between the driving electrode portions  85   a  and  86   a , an electrostatic attraction force is generated between the driving electrode portions  85   a  and  86   a  so that the movable land portion  82   a  to which the driving electrode portion  85   a  is joined is operated or elastically deformed toward the driving electrode portion  86   a . The driving line  85  is disposed separately from the signal line  83  (namely, the driving line  85  is routed from the movable land portion  82   a  to the stationary portion  81  while passing the beam portion  82   c  differing from the beam portion  82   b  on which the signal line  83  passes). Also, the driving line  86  is disposed separately from the signal line  84 . Stated another way, in the switching device X 8 , the signal lines  83  and  84  are electrically separated from the driving lines  85  and  86 . The switching device X 8  thus constructed is less susceptible to the signal leakage from the signal line to the driving line, which has been described above in connection with the known switching device Z 1 . Accordingly, the switching device X 8  is suitable for not only reducing an insertion loss, but also obtaining a superior high-frequency characteristic. 
     In the switching device X 8 , as illustrated in the plan view of  FIG. 42 , a signal path constituted by the signal lines  83  and  84  is disposed between the driving line  86  (ground line) and the ground line  87 , and the driving line  86  and the ground line  87  have shapes extending along the signal path (the signal path, the driving line  86 , and the ground line  87  are arranged parallel to one another). In other words, the signal path (i.e., the signal lines  83  and  84 ) and two ground lines (i.e., the driving line  86  and the ground line  87 ) constitute coplanar passages. Using the coplanar passages is preferable including in suppressing the signal leakage from the signal lines  83  and  84 . 
     In the switching device X 8 , similarly to the arrangement described above in the first modification of the switching device X 1  regarding the signal line  13  and the driving lines  15  on the movable portion  12 , the signal line  83  and the driving line  85  on the movable portion  82  may be arranged in a symmetrical pattern shape. Similarly to the second modification of the switching device X 1 , the switching device X 8  may include the stopper portion  20  (including the projected portion  20   a ) to prevent the driving electrode portions  85   a  and  86   a  and the driving electrode portions  85   b  and  86   b  from contacting with each other and short-circuiting when driven. Similarly to the third modification of the switching device X 1  in which the signal lines  13  and  14  have the contact portions  13   a  and  14   a  on the beam portion  12   b , the switching device X 8  may be modified such that the contact portions  83   a  and  84   a  of the signal lines  83  and  84  are positioned on the beam portion  82   b . Further, similarly to the fourth modification of the switching device X 1  in which the signal line  13  and the driving line  15  partly have the thicker portions  13   a  and  15   a , respectively, the switching device X 8  may be modified such that the signal line  83  and the driving line  85  may partly have thicker portions. 
       FIGS. 46A to 49C  illustrate a method of manufacturing the switching device X 8  as successive changes in sections corresponding to part of  FIG. 44A  and part of  FIG. 45A . 
     In the manufacturing method, as illustrated in  FIG. 46A , a conductor film  201  is first formed on the substrate S 2 . The conductor film  201  can be formed by sputtering, for example, such that a Mo film is formed on the substrate S 2  and an Au film is successively formed on the Mo film. The Mo film has a thickness of, e.g., 50 nm, and the Au film has a thickness of, e.g., 500 nm. 
     Next, as illustrated in  FIG. 46B , resist patterns  202 ,  203  and  204  are formed on the conductor film  201  by photolithography. The resist pattern  202  has a pattern shape corresponding to the signal line  84 . The resist pattern  203  has a pattern shape corresponding to the driving line  86 . The resist pattern  204  has a pattern shape corresponding to the ground line  87 . 
     Next, as illustrated in  FIG. 46C , the signal line  84 , the driving line  86 , and the ground line  87  are formed on the substrate S 2  by etching the conductor film  201  with the resist patterns  202  to  204  used as masks. 
     After removing the resist patterns  202  to  204  as illustrated in  FIG. 47A , a sacrifice layer  205  is formed on the substrate S 2  so as to cover the signal line  84 , the driving line  86 , and the ground line  87  as illustrated in  FIG. 47B . The sacrifice layer  205  can be made of, e.g., polyimide. Spin coating, for example, can be employed as a method of forming the sacrifice layer  205 . The sacrifice layer  205  formed in this operation has a thickness of, e.g., 5 μm. Silicon oxide may also be used as the material of the sacrifice layer. 
     Next, as illustrated in  FIG. 47C , the sacrifice layer  205  is patterned. More specifically, a predetermined resist pattern is formed on the sacrifice layer  205  by photolithography, and the sacrifice layer  205  is then etched with the resist pattern used as a mask. 
     Next, as illustrated in  FIG. 48A , a material film  206  for constituting the stationary portion  81  and the movable portion  82  is formed so as to cover the sacrifice layer  205  and the substrate S 2 . The material film  206  can be formed, for example, by coating a film of silicon oxide or polysilicon in a thickness of 5 μm over the sacrifice layer  205  and the substrate S 2  by CVD. 
     Next, as illustrated in  FIG. 48B , the material film  206  is patterned. More specifically, a predetermined resist pattern is formed on the material film  206  by photolithography, and the material film  206  is then etched with the resist pattern used as a mask. The stationary portion  81  and the movable portion  82  are formed in this operation. 
     Next, as illustrated in  FIG. 48C , recesses  205   a  are formed in the sacrifice layer  205 . More specifically, a predetermined resist pattern is formed on the sacrifice layer  205  and the material film  206  by photolithography, and the sacrifice layer  205  is then etched to a predetermined depth with the resist pattern used as a mask. The etching can be performed as ion etching (RIE), for example. The recesses  205   a  are each used to form a projection serving as the contact portion  83   a  of the signal line  83 . 
     Next, a conductor film  207  is formed as illustrated in  FIG. 49A . The conductor film  207  can be formed by sputtering, for example, such that a Mo film is formed in a thickness of 200 nm and an Au film is successively formed in a thickness of 500 nm on the Mo film. 
     Next, the conductor film  207  is patterned as illustrated in  FIG. 49B . More specifically, a predetermined resist pattern is formed on the conductor film  207  by photolithography, and the conductor film  207  is then etched with the resist pattern used as a mask. The signal line  83  and the driving line  85  are formed in this operation. 
     Next, the sacrifice layer  205  is removed as illustrated in  FIG. 49C . For example, oxygen plasma ashing can be employed as a method for removing the sacrifice layer  205 . In this operation, the movable portion  82  can be released from the substrate S 2 . As a result, the switching device X 8  can be appropriately manufactured. 
     The above-described switching devices X 1  to X 8  according to the embodiments of the present invention can be each used as a switch constituting part of a variable phase shifter. Alternatively, the switching devices X 1  to X 8  can be each used an RF circuit selector switch which is included in a semiconductor tester for electrically inspecting an LSI. 
       FIG. 50  illustrates a partial configuration of a communication apparatus  300  according to an embodiment of the present invention. The communication apparatus  300  includes an antenna  310 , a transmission/reception selector switch  320 , a reception circuit unit  330 , a transmission circuit unit  340 , and a base band unit  350 . The communication apparatus  300  is constituted as a wireless communication apparatus, e.g., a cell phone, which employs a time-division communication system and can perform transmission and reception in multiple frequency bands. 
     The transmission/reception selector switch  320  serves, in a communicating mode of the communication apparatus  300 , to selectively change over at a high speed a state where the antenna  310  is connected to the reception circuit unit  330  and a state where the antenna  310  is connected to the transmission circuit unit  340 . The switching speed is, e.g., 0.1 to 10 μsec. The time-division communication system can be realized with such high-speed changing-over. The transmission/reception selector switch  320  is constituted by the above-described switching device X 7 , which is the SPDT switch (having one input and two outputs). For example, the signal line  73  in the switching device X 7 , illustrated in  FIG. 49 , is electrically connected to the antenna  310 , the signal line  74 A is electrically connected to the reception circuit unit  330 , and the signal line  74 B is electrically connected to the transmission circuit unit  340 . 
     The reception circuit unit  330  has a circuit configuration for processing (such as amplifying, frequency-converting, and demodulating) a signal of a predetermined frequency, which is taken from the antenna  310 . The reception circuit unit  330  includes, as part thereof, a plurality of band pass filters (BPFs)  331 , a plurality of band selector switches  332  and  333 , and a wide-band low noise amplifier (LNA)  334 , and it is connected to the base band unit  350 . The plurality of band pass filters  331  are each constituted so as to allow passage of a signal in a predetermined frequency band. The frequency bands allowing the signal passage differ among the plurality of band pass filters  331 . The plurality of band pass filters  331  serve to select one desired frequency band in the system. The band selector switches  332  are disposed on respective input terminal sides of the band pass filters  331  (i.e., on the side closer to the antenna  310 ). The band selector switches  333  are disposed on respective output terminal sides of the band pass filters  331  (i.e., on the side closer to the wide-band low noise amplifier  334 ). When a set of band selector switches  332  and  333  with one predetermined band pass filter  331  interposed between them are both turned to a closed state, that one band pass filter  331  is selected in the reception circuit unit  330 . Those band selector switches  332  and  333  are each constituted by any one of the above-described switching devices X 1  to X 6  and X 8 . The wide-band low noise amplifier  334  amplifies the intensity of a signal having passed through the one band pass filter  331 . 
     The transmission circuit unit  340  has a circuit configuration for generating a signal to be transmitted from the antenna  310 . The transmission circuit unit  340  includes, as part thereof, an oscillation circuit (not shown), a plurality of power amplifiers  341 , a plurality of band pass filters (BPFs)  342 , and a plurality of band selector switches  343 , and it is connected to the base band unit  350 . Each power amplifier  341  serves to amplify the transmitted signal to a required level of output. Each band pass filter  342  serves to select the desired frequency band in the system. The band selector switches  343  are disposed on respective output terminal sides of the power amplifiers  341  (i.e., on the side closer to the antenna  310 ) and serve to selectively change over the communication apparatus  300  to be adapted for the desired frequency band in the system. When one predetermined band selector switch  343  is turned to a closed state, one predetermined set of power amplifier  341  and band pass filter  342  is selected in the transmission circuit unit  340 . Those band selector switches  343  are each constituted by any one of the above-described switching devices X 1  to X 6  and X 8 . 
     By including the above-described antenna  310 , transmission/reception selector switch  320 , reception circuit unit  330 , and transmission circuit unit  340 , the communication apparatus  300  is able to operate as a multiband communication apparatus adaptable for a communication system that utilizes a plurality of different frequency bands in the time-division communication system. 
     Further, while modification(s) and component(s) are described herein with relation to one another, no limitation is intended thereby. All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. 
     The embodiments can be implemented in computing hardware (computing apparatus) and/or software, such as (in a non-limiting example) any computer that can store, retrieve, process and/or output data and/or communicate with other computers. The results produced can be displayed on a display of the computing hardware. A program/software implementing the embodiments may be recorded on computer-readable media comprising computer-readable recording media. The program/software implementing the embodiments may also be transmitted over transmission communication media. Examples of the computer-readable recording media include a magnetic recording apparatus, an optical disk, a magneto-optical disk, and/or a semiconductor memory (for example, RAM, ROM, etc.). Examples of the magnetic recording apparatus include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape (MT). Examples of the optical disk include a DVD (Digital Versatile Disc), a DVD-RAM, a CD-ROM (Compact Disc-Read Only Memory), and a CD-R (Recordable)/RW. An example of communication media includes a carrier-wave signal. 
     Further, according to an aspect of the embodiments, any combinations of the described features, functions and/or operations can be provided. 
     Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention, the scope of which is defined in the claims and their equivalents.