Abstract:
A micro-switching device includes a fixing portion, a movable portion, a first electrode with first and second contacts, a second electrode with a third contact contacting the first contact, and a third electrode with a fourth contact opposing the second contact. In manufacturing the micro-switching device., the first electrode is formed on a substrate, and a sacrifice layer is formed on the substrate to cover the first electrode. Then, a first recess and a shallower second recess are formed in the sacrifice layer at a position corresponding to the first electrode. The second electrode is formed to have a portion opposing the first electrode via the sacrifice layer, and to fill the first recess. The third electrode is formed to have a portion opposing the first electrode via the sacrifice layer; and to fill the second recess. Thereafter the sacrifice layer is removed.

Description:
BACKGROUND OF THE INVENTION. 
     1. Field of the Invention 
     The present invention relates to a micro-switching device manufactured by a MEMS technique. 
     2. Description of the Related Art 
     In the technical field of wireless communication equipments such as a mobile phone, the increase components required to be incorporated in the equipment for achieving higher performance has been giving rise to a growing demand for RF circuits of smaller size. In order to meet this demand, a technique called micro-electromechanical systems (hereinafter, MEMS) has been employed for size reduction of various components constituting the circuit. 
     One of such components is a MEMS switch. The MEMS switch is a switching device that includes components fabricated in reduced sizes based on the MEMS technique, such as a pair of contacts that mechanically opens and closes for switching operation, and a driving mechanism that causes the pair of contacts to perform the mechanical switching operation, to name a few. The MEMS switch generally achieves higher isolation in an open state and lower insertion loss in a closed state than a switching device that includes a PIN diode or MESFET, especially when switching a high frequency signal of the order of GHz. This is because the open state is achieved by a mechanical opening motion between the contacts, and also because the mechanical switch incurs smaller parasitic capacitance. The MEMS switch is disclosed, for example, in patent documents such as JP-A-2004-1186, JP-A-2004-311394, JP-A-2005-293918, and JP-A-2005-528751. 
       FIGS. 25 to 29  depict a micro-switching device X 4 , as an example of the conventional micro-switching devices. FIG.  25  is a plan view of the micro-switching device X 4 , and  FIG. 26  is a fragmentary plan view thereof.  FIGS. 27 to 29  are cross-sectional views taken along the line XXVII-XXVII, XXVIII-XXVIII, and XXIX-XXIX in  FIG. 25 , respectively. 
     The micro-switching device X 4  includes a base substrate S 4 , a fixing portion  41 , a movable portion  42 , a contact electrode  43 , a pair of contact electrodes  44 A,  44 B (indicated by dash-dot lines in  FIG. 26 ), a driving electrode  45 , and a driving electrode  46  (indicated by dash-dot lines in  FIG. 26 ). 
     The fixing portion  41  is joined to the base substrate S 4  via a partition layer  47 , as shown in  FIGS. 27 to 29 . The fixing portion  41  and the base substrate S 4  are formed of monocrystalline silicon, and the partition layer  47  is formed of silicon dioxide. 
     The movable portion  42  includes, as shown in  FIGS. 26 and 29 , a stationary end  42   a  fixed to the fixing portion  41  and a free end  42   b , and is disposed to extend along the base substrate S 4  from the stationary end  42   a , and surrounded by a slit  48 . The movable portion  42  is formed of monocrystalline silicon. 
     The contact electrode  43  is located close to the free end  42   b  of the movable portion  42 , as seen from  FIG. 26 . Each of the contact electrodes  44 A,  44 B is formed partially upright on the fixing portion  41  as shown in  FIGS. 27 and 29 , and includes a portion opposing the contact electrode  43 . The contact electrodes  44 A,  44 B are connected to a predetermined circuit to be switched, via an interconnector (not shown). The contact electrodes  43 ,  44 A,  44 B are formed of an appropriate conductive material. 
     The driving electrode  45  is disposed to extend over a part of the movable portion  42  and of the fixing portion  41 , as shown in  FIG. 26 . The driving electrode  46 , as seen from  FIG. 28 , includes two upright posts jointed to the fixing portion  41  and a horizontal portion connected to the respective posts so as to span over the driving electrode  45 . The driving electrode  46  is also grounded by a conductor (not shown). The driving electrodes  45 ,  46  are formed of an appropriate conductive material. 
     In the micro-switching device X 4  thus constructed, when a potential is applied to the driving electrode  45 , static attraction is generated between the driving electrodes  45 ,  46 . When the applied potential is sufficiently high, the movable portion  42  extending along the base substrate S 4  is elastically deformed until the contact electrode  43  makes contact with the contact electrodes  44 A,  44 B. That is how the micro-switching device X 4  enters a closed state. Under the closed state, the contact electrode  43  serves as an electrical bridge between the pair of contact electrodes  44 A,  44 B, thereby allowing a current to run between the contact electrodes  44 A,  44 B. Thus, for example an on state of a high frequency signal can be attained. 
     On the other hand, in the micro-switching device X 4  under the closed state, disconnecting the potential to the driving electrode  45 , thereby canceling the static attraction acting between the driving electrodes  45 ,  46  causes the movable portion  42  to return to its natural state, so that the contact electrode  43  is separated from the contact electrodes  44 A,  44 B. That is how the micro-switching device X 4  enters an open state as shown in  FIGS. 27 and 29 . Under the open state, the pair of contact electrodes  44 A,  44 B is electrically isolated and hence the current is inhibited from running between the contact electrodes  44 A,  44 B. Thus, for example an off state of the high frequency signal can be attained. 
     The micro-switching device X 4  has the drawback that the contact electrode  43  suffers relatively large fluctuation in orientation toward the contact electrodes  44 A,  44 B. 
     In the manufacturing process of the micro-switching device X 4 , the contact electrode  43  is formed by a thin film formation technique on the movable portion  42 , or on a position on the material substrate where the movable portion is to be formed. More specifically, a sputtering or a vapor deposition process is performed to deposit a predetermined conductive material on a predetermined surface, and the deposited layer is patterned so as to form the contact electrode  43 . The contact electrode  43  thus formed via the thin film formation technique is prone to incur some internal stress. The internal stress often provokes deformation of the movable portion  42  at a position where the contact electrode  43  is adhered and the vicinity thereof, along with the contact electrode  43 , as exaggeratedly illustrated in  FIG. 30(   a )-( b ). Such deformation leads to relatively large difference (i.e. fluctuation) in orientation of the contact electrode  43  toward the contact electrodes  44 A,  44 B among each device. 
     The large fluctuation in orientation of the contact electrode  43  toward the-contact electrodes  44 A,  44 B leads to a higher potential to be applied to the driving electrode  45  in order to achieve the closed state of the micro-switching device X 4 . This is because it becomes necessary to set a sufficiently high driving voltage, to ensure that the device normally works irrespective of the extent of the orientation of the contact electrode  43  within an assumed range. Consequently, from the viewpoint of reduction of the driving voltage of the device, it is not desirable that the contact electrode  43  (movable contact electrode) has large fluctuation in orientation toward the contact electrodes  44 A,  44 B (stationary contact electrode). 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed under the foregoing circumstances. It is therefore an object of the present invention to provide a micro-switching device capable of suppressing fluctuation in orientation of a movable contact electrode toward a stationary contact electrode. It is another object of the present invention to provide a method of manufacturing such a micro-switching device. 
     A first aspect of the present invention provides a micro-switching device. The micro-switching device comprises a fixing portion, a movable portion, a movable contact electrode, a first stationary contact electrode, a second stationary contact electrode, and a driving mechanism. The movable portion includes a first surface and a second surface opposite to the first surface, and is disposed to extend horizontally from its stationary end which is fixed to the fixing portion. The movable contact electrode is provided on the first surface of the movable portion, and includes a first contact portion and a second contact portion. The first stationary contact electrode, joined to the fixing portion, includes a third contact portion which can be brought into contact with the first contact portion of the movable contact electrode even while the device is in an open state (off state). The second stationary contact electrode, also jointed to the fixing portion, includes a fourth contact portion disposed to face the second contact portion of the movable contact electrode. The driving mechanism causes the movable portion to move or to be elastically deformed so that the second contact portion and the fourth contact portion come into contact with each other. 
     In the micro-switching device described above, the first contact portion of the movable contact electrode and the third contact portion of the first stationary contact electrode can be brought into contact with each other in the open state (off state). In this open state (i.e., with the first and the third contact portions held in contact with each other), the freedom of deformation of the movable contact electrode (or of the movable portion upon which this contact electrode is formed) for internal stress occurring in the electrode is lessened in comparison with the case where the first contact portion and the third contact portion are spaced apart from each other. With this feature, the micro-switching device of the present invention is suitable for suppressing the fluctuation in orientation of the movable contact electrode with respect to the first and the second stationary contact electrode. The suppressing of the fluctuation in orientation of the movable contact electrode contributes to reducing the driving voltage of the micro-switching device. 
     According to a second aspect of the present invention, the above-mentioned first and third contact portions are permanently connected to each other. With such an arrangement, the fluctuation in orientation of the movable contact electrode with respect to the first and second stationary contact electrodes can be effectively suppressed. 
     Preferably, the movable contact electrode may comprise a first projecting portion which includes the first contact portion. Further the movable contact electrode may comprise a second projecting portion having a shorter projecting length than the first projecting portion, where the second projecting portion includes the second contact portion. Such a structure is advantageous for attaining a temporary or permanent contacting state between the first contact portion of the movable contact electrode and the third contact portion of the stationary contact electrode in the open state of the device. 
     Preferably, the first stationary contact electrode may comprise a third projecting portion which includes the third contact portion, while the second stationary contact electrode may comprise a fourth projecting portion which has a shorter projecting length than the third projecting portion and which includes the fourth contact portion. Such a structure is advantageous for bringing the first contact portion and the third contact portion into mutual contact in the open state of the device. 
     Preferably, the movable contact electrode may be spaced apart from the stationary end in a predetermined offset direction on the first surface of the movable portion, and further the first contact portion and the second contact portion may be spaced apart in a direction intersecting the offset direction. The driving mechanism may include a driving force generation region on the first surface of the movable portion, where the center of gravity of the driving force generation region is closer to the second contact portion than to the first contact portion of the movable contact electrode. Such a structure is advantageous for reducing the driving voltage for the device. 
     Preferably, the distance between the stationary end of the movable portion and the first contact portion of the movable contact electrode may be different from the distance between the stationary end and the second contact portion are different. For example, the distance between the stationary end and the second contact portion may be shorter than the distance between the stationary end and the first contact portion. The movable portion may be of a bent structure. Preferably, the center of gravity of the driving force generation region and the second contact portion may be located on the same side with respect to an imaginary line passing through the midpoint of the length of the stationary end and the midpoint between the first contact portion and the second contact portion. Such a configuration is advantageous for reducing the driving voltage for the device. 
     Preferably, the micro-switching device according to the present invention may include a static driving mechanism for the driving mechanism mentioned above, where the static driving mechanism may consist of a movable driving electrode provided on the first surface of the movable portion and a stationary driving electrode having a portion opposing the movable-driving electrode and joined to the fixing portion. 
     Preferably, the driving mechanism may have a multilayer structure formed of a first electrode layer provided on the first surface of the movable portion, a second electrode layer, and a piezoelectric layer disposed between the first and the second electrode layer. The micro-switching device of the present invention may include such a piezoelectric driving mechanism for the driving mechanism. 
     Preferably, the driving mechanism may have a multilayer structure formed of a plurality of material layers provided on the first surface of the movable portion and each having a different thermal expansion coefficient. The micro-switching device of the present invention may include such a thermal type driving mechanism for the driving mechanism. 
     A third aspect of the present invention provides a method of manufacturing a micro-switching device according to the first aspect of the present invention. The method comprises the steps of: forming the movable contact electrode on a substrate; forming a sacrifice layer on the substrate to cover the movable contact electrode; forming a first recess and a second recess shallower than the first recess in the sacrifice layer at a position corresponding to the movable contact electrode; forming the first stationary contact electrode having a portion opposing the movable contact electrode via the sacrifice layer in a manner such that the first stationary contact electrode fills the first recess; forming the second stationary contact electrode having a portion opposing the movable contact electrode via the sacrifice layer in a manner such that the second stationary contact electrode fills the second recess; and removing the sacrifice layer. 
     A fourth aspect of the present invention provides a method of manufacturing a micro-switching device according to the second aspect of the present invention. The method comprises the steps of: forming the movable contact electrode on a substrate; forming a sacrifice layer on the substrate to cover the movable contact electrode; forming a through-hole for partially exposing the movable portion and forming a recess both in the sacrifice layer at a position corresponding to the movable contact electrode; forming the first stationary contact electrode having a portion opposing the movable contact electrode via the sacrifice layer in a manner such that the first stationary contact electrode fills the through-hole; forming the second stationary contact electrode having a portion opposing the movable contact electrode via the sacrifice layer in a manner such that the second stationary contact electrode fills the recess; and removing the sacrifice layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a micro-switching device according to a first embodiment of the present invention; 
         FIG. 2  is a fragmentary plan view of the micro-switching device shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along a line IV-IV in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along a line V-V in  FIG. 1 ; 
         FIG. 6  shows, in section, steps of a manufacturing process of the micro-switching device shown in  FIG. 1 ; 
         FIG. 7  shows, in section, manufacturing steps subsequent to those shown in  FIG. 6 ; 
         FIG. 8  shows, in section, manufacturing steps subsequent to those shown in  FIG. 7 ; 
         FIG. 9  shows, in section, manufacturing steps subsequent to those shown in  FIG. 7 ; 
         FIG. 10  is a plan view showing a variation of the micro-switching device according to the first embodiment of the present invention; 
         FIG. 11  is a cross-sectional view taken along a line XI-XI in  FIG. 10 ; 
         FIG. 12  is a plan view showing another variation of the micro-switching device according to the first embodiment of the present invention; 
         FIG. 13  is a cross-sectional view taken along a line XIII-XIII in  FIG. 12 ; 
         FIG. 14  is a plan view showing a micro-switching device according to a second embodiment of the present invention; 
         FIG. 15  is a cross-sectional view taken along a line XV-XV in  FIG. 14 ; 
         FIG. 16  is a cross-sectional view taken along a line XVI-XVI in  FIG. 14 ; 
         FIG. 17  shows, in section, steps of a manufacturing process of the micro-switching device shown in  FIG. 14 ; 
         FIG. 18  is a plan view showing a micro-switching device according to a third embodiment of the present invention; 
         FIG. 19  is a plan view showing the micro-switching device of  FIG. 18 , with some parts omitted; 
         FIG. 20  is a cross-sectional view taken along a line XX-XX in  FIG. 18 ; 
         FIG. 21  is a cross-sectional view taken along a line XXI-XXI in  FIG. 18 ; 
         FIG. 22  is a cross-sectional view taken along a line XXII-XXII in  FIG. 18 ; 
         FIG. 23  illustrates a variation of the micro-switching device shown in  FIG. 1 ; 
         FIG. 24  illustrates another variation of the micro-switching device shown in  FIG. 1 ; 
         FIG. 25  is a plan view showing a conventional micro-switching device; 
         FIG. 26  is a plan view showing the micro-switching device of  FIG. 25 , with some parts omitted; 
         FIG. 27  is a cross-sectional view taken along a line XXVII-XXVII in  FIG. 25 ; 
         FIG. 28  is a cross-sectional view taken along a line XXVIII-XXVIII in  FIG. 25 ; 
         FIG. 29  is a cross-sectional view taken along a line XXIX-XXIX in  FIG. 25 ; and 
         FIG. 30  illustrates, in section, how the conventional movable portion, with a contact electrode formed thereon, deforms (depicted in an exaggerated manner). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 5  show a micro-switching device X 1  according to a first embodiment of the present invention.  FIG. 1  is a plan view showing the micro-switching device X 1 , and  FIG. 2  is a fragmentary plan view of the micro-switching device X 1 .  FIGS. 3 to 5  are cross-sectional views taken along lines III-III, IV-IV, and V-V in  FIG. 1 , respectively. 
     The micro-switching device X 1  includes a base substrate S 1 , a fixing portion  11 , a movable portion  12 , a contact electrode  13 , a pair of contact electrodes  14 A,  14 B (indicated by dash-dot lines in  FIG. 2 ), a driving electrode  15 , and a driving electrode  16  (indicated by dash-dot lines in  FIG. 2 ). 
     The fixing portion  11  is joined to the base substrate S 1  via a partition layer  17 , as shown in  FIGS. 3 to 5 . The fixing portion  11  is formed of a silicon material such as monocrystalline silicon. It is preferable that the silicon material constituting the fixing portion  11  has resistivity not lower than 1000 Ω·cm. The partition layer  17  is formed of silicon dioxide, for example. 
     The movable portion  12  includes, as shown in  FIGS. 1 ,  2  and  5 , a first surface  12   a  and a second surface  12   b , as well as a stationary end  12   c  fixed to the fixing portion  11  and a free end  12   d , and is disposed to extend along the base substrate S 1  from the stationary end  12   a , and surrounded by the fixing portion  11  via a slit  18 . The thickness T of the movable portion  12  (shown in  FIGS. 3 and 4 ) is, for example, not greater than 15 μm. The length L 1  of the movable portion  12  shown in  FIG. 2  is 650 to 1000 μm for example, and the length L 2  is 200 to 400 μm, for example. The slit  18  has a width of 1.5 to 2.5 μm for example. The movable portion  12  is formed of, for example, monocrystalline silicon. 
     The contact electrode  13  is a movable contact electrode and, as shown in  FIG. 2 , is located on the first surface  12   a  of the movable portion  12 , at a position close to the free end  12   d  (in other words, the contact electrode  13  is spaced from the stationary end  12   c  of the movable portion  12 ). The contact electrode  13  includes contact portions  13   a ′,  13   b ′. For the sake of explicitness of the drawing, the contact portions  13   a ′,  13   b ′ are indicated by solid circles in  FIG. 2 . The contact electrode  13  has a thickness of 0.5 to 2.0 μm, for example. Such thickness range is advantageous for reducing the resistance of the contact electrode  13 . The contact electrode  13  is formed of an appropriate conductive material, and has a multilayer structure including, for example, a Mo underlying layer and an Au layer provided thereon. 
     The contact electrodes  14 A,  14 B are first and second stationary contact electrodes, respectively. Each of the electrodes  14 A,  14 B is formed upright on the fixing portion  11  and includes a downward projecting portion  14   a  or  14   b  as shown in  FIGS. 3 and 5 . The tip (lower end) of the projecting portion  14   a  serves as a contact portion  14   a ′, which is disposed in contact with the contact portion  13   a ′ on the contact electrode  13 . The tip of the projecting portion  14   b  serves as a contact portion  14   b ′, disposed to face the contact portion  13   b ′ on the contact electrode  13 . The projecting portion  14   a  is longer in projecting length than the projecting portion  14   b . For example, the projecting portion  14   a  has a projection length of 1 to 4 μm, while the projecting portion  14   b  may have a projection length of 0.8 to 3.8 μm, but should always be shorter than the projecting portion  14   a . The contact electrodes  14 A,  14 B are connected to a predetermined circuit to be switched, via a certain interconnector (not shown). The contact electrodes  14 A,  14 B may be formed of the same material as that of the contact electrode  13 . 
     The driving electrode  15  is, as shown in  FIG. 2 , disposed to extend over a part of the movable portion  12  and of the fixing portion  11 . The driving electrode  15  has a thickness of, for example, 0.5 to 2 μm. The driving electrode  15  may be formed of Au. 
     The driving electrode  16  serves to generate static-attraction (driving force) in the space between the driving electrode  16  and the driving electrode  15 , and is formed so as to span over the driving electrode  15  with the respective ends connected to the fixing portion  11 , as shown in  FIG. 4 . The driving electrode  16  has a thickness not less than 15 μm, for example. The driving electrode  16  is grounded by a conductor (not shown). The driving electrode  16  may be formed of the same material as that of the contact electrode  15 . 
       FIGS. 6-9  are cross-sectional views showing the same portion of the micro-switching device X 1  as  FIGS. 3 and 4 , and representing a manufacturing process thereof. In this process, firstly a material substrate S 1 ′ shown in  FIG. 6(   a ) is prepared. The material substrate S 1 ′ is a silicon-on-insulator (SOI) substrate, and has a multilayer structure including a first layer  101 , a second layer  102 , and an intermediate layer  103  interposed therebetween. In this embodiment, for example, the thickness of the first layer  101  is 15 μm, the thickness of the second layer  102  is 5105 μm, and the thickness of the intermediate layer  103  is 4 μm. The first layer  101  is formed of monocrystalline silicon for example, to be processed to turn into the fixing portion  11  and the movable portion  12 . The second layer  102  is formed of monocrystalline silicon for example, to be processed to turn into the base substrate S 1 . The intermediate layer  103  is formed of silicon dioxide for example, to be processed for formation of the partition layer  17 . 
     Then a conductor layer  104  is formed on the first layer  101 , as shown in  FIG. 6(   b ). For example, a sputtering process is performed to deposit Mo on the first layer  101 , and Au is deposited on the Mo layer. The Mo layer has a thickness of 30 nm for example, and the Au layer 500 nm, for example. 
     A photolithography process is then performed so as to form resist patterns  105 ,  106  on the conductor layer  104 , as shown in  FIG. 6(   c ). The resist pattern  105  has a pattern shape corresponding to the contact electrode  13 . The resist pattern  106  has a pattern shape corresponding to the driving electrode  15 . 
     Proceeding to  FIG. 7(   a ), an etching process is performed on the conductor layer  104  utilizing the resist patterns  105 ,  106  as the mask, to thereby form the contact electrode  13  and the driving electrode  15  on the first layer  101 . For example, an ion milling process (physical etching with Ar ion) may be adopted in this process. The ion milling process may also be adopted for the subsequent etching processes for metal materials. 
     After removing the resist pattern  105 ,  106 , an etching process is performed on the first layer  101  to form the slit  18 , as shown in  FIG. 7(   b ). Specifically, a photolithography process is performed to thereby form a predetermined resist pattern on the first layer  101 , after which an anisotropic etching process is performed on the first layer  101  utilizing the resist pattern as the mask. Here, a reactive ion etching process may be adopted. At this stage, the fixing portion  11  and the movable portion  12  are formed in the predetermined pattern. 
     Then as shown in  FIG. 7(   c ), a sacrifice layer  107  is formed over the first layer  101  of the material substrate S 1 , so as to cover the slit  18 . Suitable materials for the sacrifice layer include silicon dioxide. Suitable methods to form the sacrifice layer  107  include a plasma CVD process and a sputtering process. 
     Referring now to  FIG. 8(   a ), recessed portions  107   a ,  107   b  are formed on the sacrifice layer  107  at positions corresponding to the contact electrode  13 . More specifically, a photolithography process is performed to thereby form a predetermined resist pattern on the sacrifice layer  107 , after which an etching process is performed on the sacrifice layer  107  utilizing the resist pattern as the mask. Here, a wet etching process may be adopted. For the wet etching process, buffered hydrofluoric acid (BHF) may be employed as the etching solution. The BHF may also be adopted for the subsequent etching process performed on the sacrifice layer  107 . The recessed portion  107   a  serves for formation of the projecting portion  14   a  of the contact electrode  14 A. The distance between the bottom portion of the recessed portion  107   a  and the contact electrode  13 , i.e. the thickness of the sacrifice layer  107  between the recessed portion  107   a  and the contact electrode  13  is, for example, not thicker than 12 μm. In  FIG. 8(   a ) and the subsequent drawings, the thickness of the sacrifice layer  107  between the recessed portion  107   a  and the contact electrode  13  is exaggerated. The recessed portion  107   b  serves for formation of the projecting portion  14   b  of the contact electrode  14   b , and is shallower than the recessed portion  107   a.    
     Then the sacrifice layer  107  is patterned so as to form openings  107   c ,  107   d ,  107   e , as shown in  FIG. 8(   b ). More specifically, a photolithography process is performed to thereby form a predetermined resist pattern on the sacrifice layer  107 , after which an etching process is performed on the sacrifice layer  107  utilizing the resist pattern as the mask. Here, a wet etching process may be adopted. The openings  107   c ,  107   d  serve to expose the regions of the fixing portion  11  to which the contact electrodes  14 A,  14 B are to be joined, respectively. The opening  107   e  serves to expose the region of the fixing portion  11  to which the driving electrode  16  is to be joined. 
     After forming an underlying layer (not shown) for electrical conduction on the surface of the material substrate S 1 ′ where the sacrifice layer  107  is provided, a resist pattern  108  is then formed as shown in  FIG. 8(   c ). The underlying layer may be formed, for example, by a sputtering process for depositing Mo in a thickness of 50 nm, and depositing Au thereon in a thickness of 500 nm. The resist pattern  108  includes openings  108   a ,  108   b  corresponding to the contact electrodes  14 A,  14 B, and an opening  108   c  corresponding to the driving electrode  16 . 
     Proceeding to  FIG. 9(   a ), the contact electrodes  14 A,  14 B and the driving electrode  16  are formed. More specifically, an electric plating process is performed to grow Au on the underlying layer, in the regions exposed through the openings  107   a  to  107   e , and  108   a  to  108   c.    
     Then the resist pattern  108  is removed by etching, as shown in  FIG. 9(   b ). After that, exposed portions of the underlying layer for electric plating are removed by etching. For these removal steps, a wet etching process may be employed. 
     Referring now to  FIG. 9(   c ), the sacrifice layer  107  and a part of the intermediate layer  103  are removed. Specifically, a wet etching process is performed on the sacrifice layer  107  and the intermediate layer  103 . By this etching process the sacrifice layer  107  is removed first, and then a part of the intermediate layer  103  is removed at and near the position corresponding to the slit  18 . This etching process is stopped after a gap is properly formed between the entirety of the movable portion  12  and the second layer  102 . Thus, the remaining portion of the intermediate layer  103  serves as the partition layer  17 . Also, the second layer  102  constitutes the base substrate S 1 . 
     By the foregoing process, the movable portion  12  incurs warp and displaced toward the contact electrodes  14 A,  14 B, as exaggeratedly shown in  FIG. 9(   c ). In the driving electrode  15  formed as above bears internal stress that has emerged by the formation process, and such internal stress causes the driving electrode  15 , as well as the movable portion  12  joined thereto, to warp. More specifically, the movable portion  12  incurs deformation or warp that biases the free end  12   d  of the movable portion  12  comes closer to the contact electrode  14 . Consequently, the movable portion  12  is deformed until the contact portion  13   a ′ of the contact electrode  13  and the contact portion  14   a ′ on the projecting portion  14   a  of the contact electrode  14 A come into mutual contact. The projecting portion  14   a  is preferably formed with a sufficient length, so that a pressing force acts between the contact portions  13   a ′,  14   a ′ in mutual contact. 
     Then a wet etching- is performed, if necessary, to remove residue of the underlying layer (for example, Mo layer) stuck to the lower surface of the contact electrodes  14 A,  14 B and the driving electrode  16 , after which a supercritical drying process is performed to dry the entire device. Employing the supercritical drying process enables effectively avoiding a sticking phenomenon that the movable portion  12  sticks to the base substrate S 1 . 
     The micro-switching device X 1  can be obtained by the foregoing process. This method allows forming the contact electrodes  14 A,  14 B including the portions opposing the contact electrode  13  in a sufficient thickness on the sacrifice layer  107  by plating. Such method allows, therefore, forming the pair of contact electrodes  14 A,  14 B in a sufficient thickness for achieving the desired low resistance. The contact electrodes  14 A,  14 B formed in the sufficient thickness are advantageous for reducing insertion loss of the micro-switching device X 1 . 
     In the micro-switching device X 1  thus manufactured, when a potential is applied to the driving electrode  15 , static attraction is generated between the driving electrodes  15 ,  16 . When the applied potential is sufficiently high, the movable portion  12  moves, or is elastically deformed, until the contact portion  13   b ′ of the contact electrode  13  and the contact portion  14   b ′ on the projecting portion  14   b  of the contact electrode  14 B come into mutual contact. That is how the micro-switching device X 1  enters a closed state. Under the closed state, the contact electrodes  13  serves as an electrical bridge between the pair of contact electrodes  14 A,  14 B, thereby allowing a current to run between the contact electrodes  14 A,  14 B. Such closing action of the switch can realize, for example, an on-state of a high frequency signal. 
     On the other hand, in the micro-switching device X 1  under the closed state, disconnecting the potential to the driving electrode  15 , thereby canceling the static attraction acting between the driving electrodes  15 ,  16  causes the movable portion  12  to return to its natural state, so that the contact portion  13   b ′ of the contact electrode  13  is separated from the contact portion  14   b ′ on the projecting portion  14   b  of the contact electrode  14 B. That is how the micro-switching device X 1  enters an open state as shown in  FIGS. 3 and 5 . Under the open state, the pair of contact electrodes  14 A,  14 B is electrically isolated and hence the current is inhibited from running between the contact electrodes  14 A,  14 B. Such opening action of the switch can realize, for example, an off state of the high frequency signal. The micro-switching device X 1  in such open state can be again switched to the closed state or the on state, by the above closing action. 
     In the micro-switching device X 1 , the contact portion  13   b ′ of the contact electrode  13  and the contact portion  14   a ′ on the projecting portion  14   a  of the contact electrode  14 A are in mutual contact in the open state (off state). In the contact electrode  13  of the micro-switching device X 1 , configured to form such open state, and the movable portion  12  to which the contact electrode  13  is joined, the freedom of deformation due to the internal stress in the contact electrode  13  is depressed, compared with the case where the contact portions  13   a ′ and  14   a ′ are not in contact but spaced from each other. Accordingly, the micro-switching device X 1  is capable of suppressing the fluctuation in orientation of the contact electrode  13  (movable contact electrode) toward the contact electrodes  14 A,  14 B (stationary contact electrode). Suppressing the fluctuation in orientation of the contact electrode  13  toward the contact electrodes  14 A,  14 B contributes to reducing the driving voltage of the. micro-switching device X 1 . 
     In the micro-switching device X 1 , the contact electrode  13  may include a first projecting portion that projects toward the contact electrode  14 A so as to be in contact with the contact electrode  14 A even in the open state of the device, and a second projecting portion that projects toward the contact electrode  14 B to such an extent that the second projecting portion does not reach the contact electrode  14 B in the open state of the device, instead of the projecting portions  14   a ,  14   b  of the contact electrodes  14 A,  14 B. To manufacture the micro-switching device X 1  having such structure, the first and the second projecting portion may be formed on the contact electrode  13 , for example after the process described referring to  FIG. 7(   b ), after which the sacrifice layer  107  may be formed so as to cover the first and the second projecting portion, by the process described referring to  FIG. 7(   c ). In this case, the recessed portions  107   a ,  107   b  described referring to  FIG. 8(   a ) are not formed. 
       FIGS. 10 and 11  depict a micro-switching device X 1 ′ which is a variation of the micro-switching device X 1 .  FIG. 10  is a plan view showing the micro-switching device X 1 ′, and  FIG. 11  is a cross-sectional view taken along a line XI-XI in  FIG. 10 . 
     The micro-switching device X 1 ′ includes the base substrate S 1 , the fixing portion  11 , the movable portion  12 , the contact electrode  13 , the pair of contact electrodes  14 A,  14 B, and a piezoelectric driving unit  21 . The micro-switching device X 1 ′ is different from the micro-switching device X 1  in including the piezoelectric driving unit  21  as the driving mechanism, in place of the driving electrodes  15 ,  16 . 
     The piezoelectric driving unit  21  includes driving electrodes  21   a ,  21   b , and a piezoelectric layer  21   c  interposed therebetween. The driving electrodes  21   a ,  21   b  each have a multilayer structure including, for example, a Ti underlying layer and an Au main layer. The driving. electrode  21   b  is grounded by a conductor (not shown). The piezoelectric layer  21   c  is formed of a piezoelectric material bearing a nature of being distorted when an electric field is applied (converse piezoelectric effect). Such piezoelectric materials include PZT (solid solution of PbZrO 3  and PbTiO 3 ), ZnO doped with Mn, ZnO, and AlN. The driving electrodes  21   a ,  21   b  have a thickness of 0.55 μm, and the piezoelectric layer  21   c  has a thickness of 1.5 μm, for example. Through the operation of the piezoelectric driving unit  21  thus configured, the closing action of the micro-switching device X 1 ′ can be achieved. 
     The piezoelectric driving unit  21  may be employed as the driving mechanism of the micro-switching device according to the present invention. In the micro-switching devices according to the subsequent embodiments also, the piezoelectric driving unit  21  may be employed as the driving mechanism. 
       FIGS. 12 and 13  depict a micro-switching device X 1 ′ which is another variation of the micro-switching device X 1 .  FIG. 12  is a plan view showing the micro-switching device X 1 ′, and  FIG. 13  is a cross-sectional view taken along a line XIII-XIII in  FIG. 12 . 
     The micro-switching device X 1 ′ includes the base substrate S 1 , the fixing portion  11 , the movable portion  12 , the contact electrode  13 , the pair of contact electrodes  14 A,  14 B, and a thermal driving unit  22 . The micro-switching device X 1 ″ is different from the micro-switching device X 1  in including the thermal driving unit  22  as the driving mechanism, in place of the driving electrodes  15 ,  16 . 
     The thermal driving unit  22  is a thermal type driving mechanism, and includes thermal electrodes  22   a ,  22   b  of different thermal expansion coefficients. The thermal electrode  22   a  disposed in direct contact with the movable portion  12  has a greater thermal expansion coefficient than the thermal electrode  22   b . The thermal driving unit  22  is provided so that the thermal electrodes  22   a ,  22   b  generate heat to thereby thermally expand, when power is supplied. The thermal electrode  22   a  is formed of Au, an Fe alloy or a Cu alloy, for example. The thermal electrode  22   b  is formed of, for example, an Al alloy. 
     The thermal driving unit  22  may be employed as the driving mechanism of the micro-switching device according to the present invention. In the micro-switching devices according to the subsequent embodiments also, the thermal driving unit  22  may be employed as the driving mechanism. 
       FIGS. 14 to 16  depict a micro-switching device X 2  according to a second embodiment of the present invention.  FIG. 14  is a plan view showing the micro-switching device X 2 .  FIGS. 15 and 16  are cross-sectional views taken along lines XV-XV and XVI-XVI in  FIG. 14 , respectively. 
     The micro-switching device X 2  includes the base substrate S 1 , the fixing portion  11 , the movable portion  12 , the contact electrode  13 , a pair of contact electrodes  14 B,  14 C, and the driving electrodes  15 ,  16 . The micro-switching device X 2  is different from the micro-switching device X 1  in including the contact electrode  14 C instead of the contact electrode  14 A. 
     The contact electrode  14 C is a first stationary contact electrode, formed upright on the fixing portion  11  and including a projecting portion  14   c  as shown in  FIG. 15 . The tip portion of the projecting portion  14   c  serves as a contact portion  14   c ′, which is joined to the contact portion  13   a ′ on the contact electrode  13 . The contact electrode  14 C is connected to a predetermined circuit to be switched, via an interconnector (not shown). The contact electrode  14 C may be formed of the same material as that of the contact electrode  13 . The remaining portion of the micro-switching device X 2  has a similar structure to that of the micro-switching device X 1 . 
     To manufacture the micro-switching device X 2  thus configured, a recessed portion or through-hole  107   a  is formed in the sacrifice layer  107  as shown in  FIG. 17(   a ), by using the same manufacturing process as that employed for the micro-switching device X 1  described referring to  FIG. 8(   a ). Then by the process described referring to  FIG. 9(   a ), the projecting portion  14   c  is formed in the through-hole  107   a , and at the same time the contact electrode  14 C is also formed as shown in  FIG. 17(   b ). The remaining steps may be performed similarly to those described on the manufacturing process of the micro-switching device X 1 . 
     In the micro-switching device X 2 , when a potential is applied to the driving electrode  15 , static attraction is generated between the driving electrodes  15 ,  16 . When the applied potential is sufficiently high, the movable portion  12  moves, or is elastically deformed, until the contact portion  13   b ′ of the contact electrode  13  and the contact portion  14   b ′ on the projecting portion  14   b , of the contact electrode  14 B come into mutual contact. That is how the micro-switching device X 2  enters the closed state. Under the closed state, the contact electrodes  13  serves as an electrical bridge between the pair of contact electrodes  14 B,  14 C, thereby allowing a current to run between the contact electrodes  14 B,  14 C. Such closing action of the switch can realize, for example, an on state of a high frequency signal. 
     On the other hand, in the micro-switching device X 2  under the closed state, disconnecting the potential to the driving electrode  15 , thereby canceling the static attraction acting between the driving electrodes  15 ,  16  causes the movable portion  12  to return to its natural state, so that the contact portion  13   b ′ of the contact electrode  13  is separated from the contact portion  14   b ′ on the projecting portion  14   b  of the contact electrode  14 B. That is how the micro-switching device X 2  enters the open state as shown in  FIG. 15 . Under the -open state, the pair of contact electrodes  14 B,  14 C is electrically isolated and hence the current is inhibited from running between the contact electrodes  14 B,  14 C. Such opening action of the switch can realize, for example, an off state of the high frequency signal. The micro-switching device X 2  in such open state can be again switched to the closed state or the on state, by the above closing action. 
     In the micro-switching device X 2 , the contact portion  13   b ′ of the contact electrode  13  and the contact portion  14   c ′ on the projecting portion  14   c  of the contact electrode  14 C are in mutual contact in the open state (off state). In the contact electrode  13  of the micro-switching device X 2 , configured to form such open state, and the movable portion  12  to which the contact electrode  13  is joined, the freedom of deformation due to the internal stress in the contact electrode  13  is depressed, compared with the case where the contact portions  13   a ′ and  14   c ′ are not in contact but spaced from each other. Accordingly, the micro-switching device X 2  is capable of suppressing the fluctuation in orientation of the contact electrode  13  (movable contact electrode) toward the contact electrodes  14 B,  14 C (stationary contact electrode). Suppressing the fluctuation in orientation of the contact electrode  13  toward the contact electrodes  14 B,  14 C contributes to reducing the driving voltage of the micro-switching device X 2 . 
       FIGS. 18 to 22  depict a micro-switching device X 3  according to a third embodiment of the present invention.  FIG. 18  is a plan view showing the micro-switching device X 3 , and  FIG. 19  is a fragmentary plan view thereof.  FIGS. 20 to 22  are cross-sectional views taken along lines XX-XX, XXI-XXI, and XXII-XXII in  FIG. 18 , respectively. 
     The micro-switching device X 3  includes a base substrate S 3 , a fixing portion  31 , a movable portion  32 , a contact electrode  33 , a pair of contact electrodes  34 A,  34 B (not shown in  FIG. 19 ), a driving electrodes  35 , and a driving electrodes  36  (not shown in  FIG. 19 ). 
     The fixing portion  31  is joined to the base substrate S 3  via a partition layer  37 , as shown in  FIGS. 20 to 22 . The fixing portion  31  is formed of a silicon material such as monocrystalline silicon. It is preferable that the silicon material constituting the fixing portion  31  has resistivity not lower than 1000 Ω·cm. The partition layer  37  is formed of silicon dioxide, for example. 
     The movable portion  32  includes, as shown in  FIGS. 18 ,  19  and  22 , a first surface  32   a  and a second surface  32   b , as well as a stationary end  32   c  fixed to the fixing portion  31  and a free end  32   d , and is disposed to extend along the base substrate S 3  from the stationary end  32   a , and surrounded by the fixing portion  31  via a slit  38 . The movable portion  32  is formed of, for example, monocrystalline silicon. 
     The contact electrode  33  is a movable contact electrode and, as shown in  FIG. 19 , is located on the first surface  32   a  of the movable portion  32 , at a position close to the free end  32   d  (in other words, the contact electrode  33  is spaced from the stationary end  32   c  of the movable portion  32 ). The contact electrode  33  includes contact portions  33   a ′  33   b ′. For the sake of explicitness of the drawing, the contact portions  33   a ′,  33   b ′ are indicated by solid circles in  FIG. 19 . The contact electrode  33  is formed of an appropriate conductive material, and has a multilayer structure including, for example, a Mo underlying layer and an Au layer provided thereon. 
     The contact electrodes  34 A,  34 B are first and second stationary contact electrodes respectively, each being formed on the fixing portion  31  and including a downward projecting portion  34   a ,  34   b  as shown in  FIGS. 20 and 22 . The tip portion of the projecting portion  34   a  serves as a contact portion  34   a ′, which is either disposed in contact with the contact portion  33   a ′ on the contact electrode  33  as the contact portion  14   a ′ is in contact with the contact portion  13   a ′ in the micro-switching device X 1  according to the first embodiment, or joined to the contact portion  33   a ′ on the contact electrode  33  as the contact portion  14   c ′ is joined to the contact portion  13   c ′ in the micro-switching device X 2  according to the second embodiment. The tip portion of the projecting portion  34   b  serves as a contact portion  34   b ′, disposed to face the contact portion  33   b ′ on the contact electrode  33 . The projecting portion  34   a  is longer in projecting length than the projecting portion  34   b . The contact electrodes  34 A,  34 B are connected to a predetermined circuit to be switched, via an interconnector (not shown). The contact electrodes  34 A,  34 B may be formed of the same material as that of the contact electrode  33 . 
     The driving electrode  35  is, as shown in  FIG. 19 , disposed to extend over a part of the movable portion  32  and of the fixing portion  31 . The driving electrode  35  may be formed of Au. 
     The driving electrode  36  serves to generate static attraction (driving force) in the space between the driving electrode  36  and the driving electrode  35 , and is formed so as to span over the driving electrode  35  with the respective ends connected to the fixing portion  31 , as shown in  FIG. 21 . The driving electrode  36  is grounded by a conductor (not shown). The driving electrode  36  may be formed of the same material as that of the contact electrode  35 . 
     The driving electrodes  35 ,  36  constitute an electrostatic driving mechanism in the micro-switching device X 3 , and include a driving force generation region R on the first surface  32   a  of the movable portion  32 , as shown in  FIG. 19 . The driving force generation region R is, as shown in  FIG. 21 , a region of the driving electrode  35  opposing the driving electrode  36 . 
     In the micro-switching device X 3 , as seen from  FIG. 19 , the movable portion  32  has an asymmetrical shape. For example, the movable portion  32  is asymmetric such that the center of gravity thereof is located on the same side as the contact portion  33   b ′ of the contact electrode  33 , with respect to an imaginary line F 1  passing through the stationary end  32   c  of the movable portion  32  and the contact portion  33   a ′ of the contact electrode  33 . Further, in the micro-switching device X 3 , the location of the contact portions  33   a ′,  33   b ′ of the contact electrode  33  (i.e. location of the contact portions  34   a ′,  34   b ′ of the contact electrodes  34 A,  34 B), as well as-the location of the driving force generation region R in the driving mechanism constituted of the driving electrodes  35 ,  36  are also asymmetric. For example, the center of gravity C of the driving force generation region R is closer to the contact portion  33   b ′ than to the contact portion  33   a ′ of the contact electrode  33 . The distance between the stationary end  32   c  of the movable portion  32  and the contact portion  33   b ′ of the contact electrode  33  is longer than the distance between the stationary end  32   c  and the contact portion  33   a ′ of the contact electrode  33 . The center of gravity C of the driving force generation region R is located on the same side as the contact portion  33   b ′, with respect to an imaginary line F 2  passing through the midpoint P 1  of the length of the stationary end  32   c  of the movable portion  32  and the midpoint P 2  between the contact portions  33   a ′,  33   b ′ of the contact electrode  33 . 
     In the micro-switching device X 3  thus configured, when a potential is applied to the driving electrode  35 , static attraction is generated between the driving electrodes  35 ,  36 . When the applied potential is sufficiently high, the movable portion  32  moves, or is elastically deformed, until the contact portion  33   b ′ of the contact electrode  33  and the contact portion  34   b ′ on the projecting portion  34   b  of the contact electrode  34 B come into mutual contact. That is how the micro-switching device X 3  enters the closed state. Under the closed state, the contact electrodes  33  serves as an electrical bridge between the pair of contact electrodes  34 A,  34 B, thereby allowing a current to run between the contact electrodes  34 A,  34 B. Such closing action of the switch can realize, for example, an on state of a high frequency signal. 
     On the other hand, in the micro-switching device X 3  under the closed state, disconnecting the potential to the driving electrode  35 , thereby canceling the static attraction acting between the driving electrodes  35 ,  36  causes the movable portion  32  to return to its natural state, so that the-contact portion  33   b ′ of the contact electrode  33  is separated from the contact portion  34   b ′ on the projecting portion  34   b  of the contact electrode  34 B. That is how the micro-switching device X 3  enters the open state as shown in  FIGS. 20 and 22 . Under the open state, the pair of contact electrodes  34 A,  34 B is electrically isolated and hence the current is inhibited from running between the contact electrodes  34 A,  34 B. Such opening action of the switch can realize, for example, an off state of the high frequency signal. The micro-switching device X 3  in such open state can be again switched to the closed state or the on state, by the above closing action. 
     In the micro-switching device X 3 , the contact portion  33   b ′ of the contact electrode  33  and the contact portion  34   a ′ on the projecting portion  34   a  of the contact electrode  34 A are in mutual contact, or joined to each other, in the open state (off state). In the contact electrode  33  of the micro-switching device X 3 , configured to form such open state, and the movable portion  32  to which the contact electrode  33  is joined, the freedom of deformation due to the internal stress in the contact electrode  33  is depressed, compared with the case where the contact portions  33   a ′ and  34   a ′ are not in contact or joined, but spaced from each other. Accordingly, the micro-switching device X 3  is. capable of suppressing the fluctuation in orientation of the contact electrode  33  (movable contact electrode) toward the contact electrodes  34 A,  34 B (stationary contact electrode). Suppressing the fluctuation in orientation of the contact electrode  33  toward the contact electrodes  34 A,  34 B contributes to reducing the driving voltage of the micro-switching device X 3 . 
     When the micro-switching device X 3  is in transit from the open state to the closed state, mainly the region of the movable portion  32  that extends from the driving force generation region R to the stationary end  32   c  will undergo torsional deformation. This deformation can be said to be caused by a force exerted on the center of gravity C of the driving force generation region R so as to rotate the movable portion  32  around a fixed axis or rotational axis represented by the imaginary line F 1  passing through the stationary end  32   c  of the movable portion  32  and the contact point between the contact electrodes  33 ,  34 A, as shown in  FIG. 19 . It is advantageous to have the center of gravity C of the driving force generation region R at a position closer to the contact portion  33   b ′ than to the contact portion  33   a ′ of the contact electrode  33 , since this configuration ensures that a long distance is provided between the center of gravity C of the driving force generation region R (point of effort) and the foregoing axis (imaginary line F 1 ). The longer the distance between the center of gravity C of the driving force generation region R (point of effort) and the foregoing axis is, the greater momentum can be generated at the center of gravity C of the driving force generation region R while the movable portion  32  is deformed until the contact electrode  33  and the contact electrode  34 B (more precisely, the projecting portion  34   b  and the contact portion  34   b ′) come into mutual contact, which permits reducing the minimal driving force (minimal static attraction) that has to be generated by the driving mechanism (driving electrodes  35 ,  36 ) in order to achieve the closed state. The smaller the minimal driving force is, the lower minimal voltage is required to be applied to the driving mechanism in order to achieve the closed state. The micro-switching device X 3  is, therefore, appropriate for reducing the driving voltage to be applied to the driving mechanism in order to achieve the closed state. 
     The micro-switching device X 3  includes, as -described above, asymmetrical configuration in the shape of the movable portion  32 , the location of the contact portions  33   a ′,  33   b ′ of the contact electrode  33  (i.e. location of the contact portions  34   a ′,  34   b ′ of the contact electrodes  34 A,  34 B), and the location of the driving force generation region R in the driving mechanism constituted of the driving electrodes  35 ,  36 . For example, the movable portion  32  is asymmetric such that the center of gravity thereof is located on the same side as the contact portion  33   b ′ of the contact electrode  33 , with respect to an imaginary line F 1  passing through the stationary end  32   c  of the movable portion  32  and the contact portion  33   a ′ of the contact electrode  33 . The center of gravity C of the driving force generation region R is closer to the contact portion  33   b ′ than to the contact portion  33   a ′ of the contact electrode  33 . The distance between the stationary end  32   c  of the movable portion  32  and the contact portion  33   b ′ of the contact electrode  33  is longer than the distance between the stationary end  32   c  and the contact portion  33   a ′ of the contact electrode  33 . The center of gravity C of the driving force generation region R is located on the same side as the contact portion  33   b ′, with respect to an imaginary line F 2  passing through the midpoint P 1  of the length of the stationary end  32   c  of the movable portion  32  and the midpoint P 2  between the contact portions  33   a ′,  33   b ′ of the contact electrode  33 . Such asymmetrical configuration is advantageous for ensuring a sufficiently long distance between the center of gravity C of the driving force generation region R (point of effort) on the movable portion  32  and the foregoing fixed axis (imaginary line F 1 ). 
     The movable portion  32  may be bent as shown in  FIG. 23(   a ). The movable portion  32  shown in  FIG. 23(   a ) includes a region  32 A directly fixed to the fixing portion  31  at the stationary end  32   c , and extending in a direction perpendicular to the major extension direction M of the movable portion  32 . 
     In an instance where the movable portion  32  has a bent structure as described above, the region  32 A (see the arrow A 1  in  FIG. 23(   b )), which is connected to the fixing portion  31  via the stationary end  32   c , mainly undergoes bending deformation during the ON transition of the micro-switching device X 3  to change from the open state to the closed state. For this closing action, it can be assumed that a force acts on the center of gravity C of the driving force generation region R, thereby rotating the movable portion  32  around a fixed axis or rotational axis represented by the imaginary line passing through the stationary end  32   c  of the movable portion  32  and the contact point between the contact electrodes  33 ,  34 A. 
     Advantageously the closing action by the bending of the portion  32 A requires for a smaller driving force to be generated by the driving mechanism (driving electrode  35 ,  36 ) than the closing action taken by the movable portion  32  shown in  FIG. 19 , in which case the movable portion  32  undergoes torsional deformation at the region from the driving force generation region R to the stationary end  32   c . In light of this, the bent structure of the movable portion  32  according to this variation contributes to reducing the driving voltage applied to the driving mechanism for achieving the closed state of the micro-switching device X 3 . 
     The movable portion  32  may have another bending configuration as shown in  FIG. 24(   a ). The movable portion  32  shown in  FIG. 24(   a ) includes a portion  32 B directly fixed to the fixing portion  31  at the stationary end  32   c , and extending in a direction intersecting the major extension direction M of the movable portion  32 . 
     In the case where the movable portion  32  is thus bent, during the transition of the micro-switching device X 3  from the open state to the closed state, mainly the region  32 B of the movable portion  32  fixed to the fixing portion  31  at the stationary end  32   c  undergoes bending deformation, as indicated by an arrow A 2  in  FIG. 24(   b ). For this closing action, it can be assumed again that a force is exerted on the center of gravity C of the driving force generation region R, thereby rotating the movable portion  32  around a fixed axis or rotational axis represented by the imaginary line passing through the stationary end  32   c  of the movable portion  32  and the contact point between the contact electrodes  33 ,  34 A. 
     The closing action of bending the portion  32 B according to the above variation is also advantageous for reducing the driving force to be generated by the driving mechanism (driving electrode  35 ,  36 ). Further, this variation facilitates ensuring that a longer distance can be provided between the center of gravity C of the driving force generation region R (point of effort) and the fixed axis or rotational axis for the closing action, than the variation shown in  FIG. 23 . Accordingly, a greater momentum can be generated upon application of force at the center of gravity C of the driving force generation region R, which is advantageous to bringing the contact electrode  33  and the contact electrode  34 B (the projecting portion  34   b  and the contact portion  34   b ′) into contact with each other by a smaller driving force (electrostatic attraction) generated by the driving mechanism (driving electrodes  35 ,  36 ). In summary, the bent structure of the movable portion  32  according to this variation contributes to reducing the driving voltage to be applied to the driving mechanism in order to achieve the closed state in the micro-switching device X 3 .