Abstract:
A micro-switching device includes a base substrate and a cantilever fixed to the base substrate via a spacer or anchor portion. The cantilever has an inner surface facing the substrate and an outer surface opposite to the inner surface. A conductive strip is formed on the outer surface of the cantilever. The switching device also includes a pair of stationary electrodes fixed to the base substrate. Each of the electrodes includes a downward contacting part spaced from the conductive strip on the cantilever. As the cantilever bends upward, the conductive strip is brought into contact with the contacting parts of the respective stationary electrodes.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a minute switching device manufactured using MEMS technology, and a method of manufacturing such a switching device. 
   2. Description of the Related Art 
   In the technical field of wireless communication equipment such as mobile phones, as for example the number of components installed in the equipment is increased to realize improved performance, there have been increased demands to miniaturize high-frequency circuitry and RF circuitry. To answer to these demands, there have been advances in miniaturization using MEMS (micro-electromechanical systems) technology for various components constituting the circuitry. 
   A MEMS switch is an example of such components. Specifically, a MEMS switch is a switching device in which each part is formed minutely using MEMS technology. The switch may include a pair of contacts for carrying out switching by mechanically opening/closing, and a driving mechanism for achieving the mechanical opening/closing operation of the contacts. In switching of high-frequency signals of GHz order in particular, a MEMS switch can exhibit higher insulation in the open state and lower insertion loss in the closed state than a switching device incorporating a PIN diode, a MESFET or the like. This is due to the open state being achieved through mechanical opening between a pair of contacts, and the parasitic capacitance being low due to being a mechanical switch. MEMS switches are disclosed in Japanese Patent Application Laid-open No. 9-17300 and Japanese Patent Application Laid-open No. 2001-143595, for example. 
     FIGS. 24 and 25  show a conventional MEMS micro-switching device X 4 . The micro-switching device X 4  includes a substrate  401 , a movable portion  402 , a movable contact part  403 , a pair of stationary contact electrodes  404 , and driving electrodes  405  and  406 . The movable portion  402  has an anchor portion  402   a  that is joined to the substrate  401 , and an arm portion  402   b  extending out from the anchor portion  402   a  along the substrate  401 . The movable contact part  403  is provided on a lower surface of the arm portion  402   b . The driving electrode  405  is provided on an upper surface side of the arm portion  402   b . A wiring part  407 , continuing on from the driving electrode  405 , is provided on the movable portion  402 . The pair of stationary contact electrodes  404  are disposed on the substrate  401  in a manner such that one end of each of the stationary contact electrodes  404  faces the movable contact part  403 . The driving electrode  406  is grounded and provided on the substrate  401  in a position corresponding to the driving electrode  405 . Prescribed wiring patterns (omitted from the drawings) electrically connected to the stationary contact electrodes  404  and the driving electrode  406  are formed on the substrate  401 . 
   With the micro-switching device X 4  having the above arrangement, when a prescribed potential is applied to the driving electrode  405  via the wiring part  407 , an electrostatic attractive force is generated between the driving electrodes  405  and  406 . As a result, the arm part  402   b  elastically deforms to a position in which the movable contact part  403  contacts the stationary contact electrodes  404 . In this way, the closed state of the micro-switching device X 4  is achieved. In the closed state, the stationary contact electrodes  404  are electrically bridged by the movable contact part  403 , and hence a current is allowed to pass between the stationary contact electrodes  404 . 
   When the electrostatic attractive force acting between the driving electrodes  405  and  406  is eliminated, then the arm part  402   b  returns to its natural state, and hence the movable contact part  403  separates away from the stationary contact electrodes  404 . In this way, the open state of the micro-switching device X 4  as shown in  FIG. 25  is achieved. In the open state, the stationary contact electrodes  404  are electrically isolated from one another, and hence a current is prevented from passing between the stationary contact electrodes  404 . 
     FIGS. 26A-26D  and  27 A- 27 D show some of the steps in a method of manufacturing the micro-switching device X 4 . In the manufacture of the micro-switching device X 4 , first, as shown in  FIG. 26A , the stationary contact electrodes  404  and the driving electrode  406  are pattern-formed onto the substrate  401 . Specifically, a film of a prescribed electrically conductive material is formed on the substrate  401 , and then a prescribed resist pattern is formed on the electrically conductive film using a photolithography method, and the electrically conductive film is subjected to etching treatment using the resist pattern as a mask. Next, as shown in  FIG. 26B , a sacrificial layer  410  is formed. Specifically, using for example a sputtering method, a prescribed material is deposited or grown on the substrate  401  so as to cover the stationary contact electrodes  404  and the driving electrode  406 . Next, through etching treatment carried out using a prescribed mask, as shown in  FIG. 26C , a single recess  411  is formed in the sacrificial layer  410  in a place in correspondence with the stationary contact electrodes  404 . Next, as shown in  FIG. 26D , a film of a prescribed material is formed in the recess  411 , thus forming the movable contact part  403 . 
   Next, as shown in  FIG. 27A , a material film  412  is formed using, for example, a sputtering method. Next, as shown in  FIG. 27B , the driving electrode  405  and the wiring part  407  are pattern-formed on the material film  412 . Specifically, a film of a prescribed electrically conductive material is formed on the material film  412 , and then a prescribed resist pattern is formed on the electrically conductive film using a photolithography method, and the electrically conductive film is subjected to etching treatment using the resist pattern as a mask. Next, as shown in  FIG. 27C , the material film  412  is patterned, thus forming a film body  413  constituting the arm part  402   b  and part of the anchor part  402   a . Specifically, a prescribed resist pattern is formed on the material film  412  using a photolithography method, and then the material film  412  is subjected to etching treatment using the resist pattern as a mask. Next, as shown in  FIG. 27D , the other part of the anchor part  402   a  is formed. Specifically, the sacrificial layer  410  is subjected to isotropic etching treatment via the film body  413  which acts as an etching mask, this being such that an undercut is formed below the arm part  402   b  while the abovementioned other part of the anchor part  402   a  is formed by being left behind. 
   One of the properties required of a switching device is low insertion loss in the closed state. Moreover, given that a reduction in the insertion loss of the switching device is to be aimed for, it is desirable for the electrical resistance of the stationary contact electrodes to be low. 
   However, with the micro-switching device X 4  described above, it is difficult to make the stationary contact electrodes  404  thick, and in actual practice the thickness of the stationary contact electrodes  404  is about 2 μm at most. This is because it is necessary to secure the flatness of the upper surface in the drawing (the growth end face) of the sacrificial layer  410  that is temporarily formed in the process of manufacturing the micro-switching device X 4 . 
   As described above with reference to  FIG. 26B , the sacrificial layer  410  is formed by a prescribed material being deposited or growing on the substrate  401  so as to cover the stationary contact electrodes  404 . The growth end face of the sacrificial layer  410  will thus become stepped due to the thickness of the stationary contact electrodes  404 . The thicker the stationary contact electrodes  404 , the larger the steps, and the larger the steps, the more difficult it tends to become to form the movable contact part  403  in the proper position or form the arm part  402   b  in the proper shape. Moreover, in the case that the thickness of the stationary contact electrodes  404  is greater than a certain value, the sacrificial layer  410  formed on the substrate  401  may break due to the thickness of the stationary contact electrodes  404 . If the sacrificial layer  410  breaks, then it will not be possible to form the movable contact part  403  and the arm part  402   b  on the sacrificial layer  410  properly. With the micro-switching device X 4 , it is thus necessary to make the stationary contact electrodes  404  sufficiently thin that inappropriate steps are not formed on the growth end face of the sacrificial layer  410 . With the micro-switching device X 4 , it may thus be difficult to realize a sufficiently low resistance for the stationary contact electrodes  404 , and as a result it may not be possible to realize a low insertion loss. 
   SUMMARY OF THE INVENTION 
   The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide a micro-switching device suitable for reducing the insertion loss. Another object of the present invention is to provide a method of manufacturing such a micro-switching device. 
   According to a first aspect of the present invention, there is provided a micro-switching device comprising: a base substrate; a movable portion including an anchor part and an extending part, the anchor part being connected to the base substrate, the extending part extending from the anchor part and facing the base substrate; a movable contact part provided on the extending part on a side opposite to the base substrate; a first stationary contact electrode fixed to the base substrate and including a first contacting part facing the movable contact part; and a second stationary contact electrode fixed to the base substrate and including a second contacting part facing the movable contact part. 
   With the above arrangement, the stationary contact electrodes are not disposed between the base substrate and the extending part of the movable portion. Consequently, in manufacturing the device, there is no need to follow a series of conventional processes of forming the stationary contact electrodes on the base substrate, forming a sacrifice layer so as to cover the stationary contact electrodes, and then forming the extending part on the sacrificial layer. 
   The stationary contact electrodes in the device of the present invention may be formed, for example, by depositing or growing a material using a plating method on the side opposite to the base substrate via the extending part. The thickness of the stationary contact electrodes can thus be set sufficiently great to realize the desired low resistance. Such a micro-switching device is suitable for reducing the insertion loss. 
   Preferably, the micro-switching device of the present invention may further comprise a first driving electrode provided on the movable portion on a side opposite to the base substrate, and a second driving electrode fixed to the base substrate and including a section facing the first driving electrode. 
   Preferably, the micro-switching device of the present invention may further comprise a first driving electrode provided on the movable portion on a side opposite to the base substrate, a piezoelectric film disposed on the first driving electrode, and a second driving electrode disposed on the piezoelectric film. 
   Preferably, the extending part may be made of monocrystalline silicon so as to suppress internal stress in the extending part. The internal stress is unfavorable since it can cause deformation of the extending part. Preferably, the extending part may have a thickness of at least 5 μm, i.e. no smaller than 5 μm. This arrangement is suitable for suppressing unwanted deformation of the extending part. 
   Preferably, the first stationary contact electrode or the second stationary contact electrode or both may have a thickness of no smaller than 5 μm. 
   According to a second aspect of the present invention, there is provided a micro-switching device comprising: a base substrate; a movable portion including an anchor part and an extending part, the anchor part being connected to the base substrate, the extending part extending from the anchor part and facing the base substrate; a stationary member connected to the base substrate; a movable contact part provided on the extending part on a side opposite to the base substrate; a first stationary contact electrode connected to the stationary member and including a first contacting part facing the movable contact part; and a second stationary contact electrode connected to the stationary member and including a second contacting part facing the movable contact part. 
   Preferably, the stationary member may be spaced away from the movable portion. 
   Preferably, the stationary member may entirely surround the movable portion. 
   Preferably, the stationary member may include a plurality of stationary islands that are spaced away from one another and are each connected to the base substrate. 
   The micro-switching device according to the second aspect of the present invention may further comprise a first driving electrode provided on the movable portion on a side opposite to the base substrate, and a second driving electrode connected to the stationary member and including a section facing the first driving electrode. 
   Preferably, the extending part may be made of monocrystalline silicon. 
   Preferably, at least one of the first stationary contact electrode and the second stationary contact electrode may have a thickness of no smaller than 5 μm. 
   Preferably, the extending part may have a thickness of no smaller than 5 μm. 
   According to a third aspect of the present invention, there is provided a method of manufacturing the above micro-switching device. The method comprises: a step of preparing a material substrate including a first layer, a second layer and an intermediate layer disposed between the first layer and the second layer, the first layer including a first section, a second section and a third section, the first section being processed into the extending part, the second section being continuous with the first section and processed into the anchor part, the third section being processed into the stationary member; a first electrode formation step of forming the movable contact part on the first section of the first layer; a first etching step of performing anisotropic etching on the first layer until the intermediate layer is reached, the anisotropic etching being performed via a mask pattern that masks the first section, the second section and the third section of the first layer; a sacrifice layer formation step of forming a sacrifice layer with a first opening and a second opening, the first opening being provided for exposing a first connecting region in the third section, the second opening being provided for exposing a second connecting region in the third section; a second electrode formation step of forming the first stationary contact electrode and the second stationary contact electrode, the first stationary contact electrode being connected to the first connecting region and having the first contacting part facing the movable contact part via the sacrifice layer, the second stationary contact electrode being connected to the second connecting region and having the second contacting part facing the movable contact part via the sacrifice layer; a sacrifice layer removal step of removing the sacrifice layer; and a second etching step of etching away a portion of the intermediate layer disposed between the second layer and the first section of the first layer. 
   Preferably, in the first electrode formation step, a first driving electrode may also be formed on the first section of the first layer. In the sacrifice layer formation step, a third opening may also be formed in the sacrifice layer for exposing a third connecting region in the third section of the first layer. In the second electrode formation step, a second driving electrode may also be formed, which is connected to the third connecting region and includes a portion facing the first driving electrode via the sacrifice layer. 
   Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a micro-switching device according to a first embodiment of the present invention; 
       FIG. 2  is a plan view of the micro-switching device of  FIG. 1  with some parts omitted; 
       FIG. 3  is a sectional view along line III-III in  FIG. 1 ; 
       FIG. 4  is a sectional view along line IV-IV in  FIG. 1 ; 
       FIG. 5  is a sectional view along line V-V in  FIG. 1 ; 
       FIGS. 6A-6D  show some of the steps in a method of manufacturing the micro-switching device of  FIG. 1 ; 
       FIGS. 7A-7C  show steps following the step of  FIG. 6D ; 
       FIGS. 8A-8C  show steps following the step of  FIG. 7C ; 
       FIG. 9  is a plan view of a modified version of the micro-switching device shown in  FIG. 1  with some parts omitted; 
       FIG. 10  is a plan view of another modified version of the micro-switching device shown in  FIG. 1  with some parts omitted; 
       FIG. 11  is a plan view of another modified version of the micro-switching device shown in  FIG. 1  with some parts omitted; 
       FIG. 12  is a sectional view along line XII-XII in  FIG. 11 ; 
       FIG. 13  is a plan view of a micro-switching device according to a second embodiment of the present invention; 
       FIG. 14  is a plan view of the micro-switching device of  FIG. 13  with some parts omitted; 
       FIG. 15  is a sectional view along line XV-XV in  FIG. 13 ; 
       FIG. 16  is a sectional view along line XVI-XVI in  FIG. 13 ; 
       FIG. 17  is a plan view of a micro-switching device according to a third embodiment of the present invention; 
       FIG. 18  is a plan view of the micro-switching device of  FIG. 17  with some parts omitted; 
       FIG. 19  is a sectional view along line XIX-XIX in  FIG. 18 ; 
       FIGS. 20A-20D  show some of the steps in a method of manufacturing the micro-switching device of  FIG. 17 ; 
       FIGS. 21A-21C  show steps following the step of  FIG. 20D ; 
       FIGS. 22A-22C  show steps following the step of  FIG. 21C ; 
       FIGS. 23A-23C  show steps following the step of  FIG. 22C ; 
       FIG. 24  is a partial plan view of a conventional micro-switching device manufactured using MEMS technology; 
       FIG. 25  is a sectional view along line XXV-XXV in  FIG. 24 ; 
       FIGS. 26A-26D  show some of the steps in a method of manufacturing the micro-switching device of  FIG. 24 ; and 
       FIGS. 27A-27D  show steps following the step of  FIG. 26D . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 
     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 of the micro-switching device X 1 ,  FIG. 2  is a plan view of the micro-switching device X 1  with some parts omitted, and  FIGS. 3 to 5  are respectively sectional views along lines III-III, IV-IV and V-V in  FIG. 1 . 
   The micro-switching device X 1  includes a base substrate S 1 , a movable cantilever portion  110 , a fixing member  120 , a movable contact conductor  131 , a pair of stationary contact electrodes  132  (omitted from  FIG. 2 ), a first driving electrode  133 , and a second driving electrode  134  (omitted from  FIG. 2 ). 
   The movable cantilever portion  110  has an anchor part  111  and an extending part  112 . As shown in  FIG. 5 , the anchor part  111  has a layered structure having a main layer  111   a  and a boundary layer  111   b , and is joined to the base substrate S 1  on the boundary layer  111   b  side. As shown for example in  FIGS. 2 and 5 , the extending part  112  has a body  112   a  and a head  112   b , and extends from the anchor part  111  along the base substrate S 1 , i.e. in a manner facing the base substrate S 1 . For the extending part  112 , the thickness T 1  shown in  FIGS. 3 and 4  may be 5 μm or more, in other words, no smaller than 5 μm. For the body  112   a , the length L 1  shown in  FIG. 2  is, for example, 400 μm, and the length L 2  is, for example, 30 μm. For the head  112   b , the length L 3  shown in  FIG. 2  is, for example, 100 μm, and the length L 4  is, for example, 30 μm. The main layer  111   a  of the anchor part  111  and the extending part  112  are made, for example, of, monocrystalline silicon, and the boundary layer  111   b  of the anchor part  111  is made, for example, of, silicon dioxide. In the case that the extending part  112  is made of monocrystalline silicon, inappropriate internal stress will not arise in the extending part  112 . With a conventional MEMS switch, a thin film formation technique may be used as the method of forming the extending part of the movable cantilever portion, but in this case, internal stress will arise in the extending part formed, and due to this internal stress a problem will arise in that the extending part itself will deform inappropriately. Such inappropriate deformation of the extending part will cause deterioration in various properties of the MEMS switch and is thus undesirable. 
   As shown in  FIGS. 3 and 4 , the fixing member  120  has a layered structure having a main layer  120   a  and a boundary layer  120   b , and is joined to the base substrate S 1  on the boundary layer  120   b  side. The main layer  120   a  of the fixing member  120  is made, for example, of, monocrystalline silicon, and the boundary layer  120   b  is made, for example, of, silicon dioxide. Moreover, as shown in  FIG. 2 , the fixing member  120  includes two island plinths  121 , and surrounds the movable portion  110  with a slit  141  therebetween. Each of the island plinths  121  is separated from the rest of the fixing member  120  by a slit  142 . The widths of the slits  141  and  142  are, for example, 2 μm. The slits  141  and  142  are helpful in securing an insulated state (a nonconductive state) between the stationary contact electrodes  132 , the first driving electrode  133  and the second driving electrode  134 . 
   As shown in  FIG. 2 , the contact conductor  131  is provided on the head  112   b  of the movable portion  110 . As shown in  FIGS. 3 and 5 , each of the stationary contact electrodes  132  is provided on one of the island plinths  121  of the fixing member  120 , and has a contacting part  132   a  facing the contact conductor  131 . The thickness T 2  of the stationary contact electrodes  132  is, for example, 5 μm or more. Moreover, the stationary contact electrodes  132  are connected via prescribed wiring (omitted from the drawings) to prescribed circuitry to be subjected to switching. The contact conductor  131  and the stationary contact electrodes  132  are each made of an appropriate electroconductive material. 
   As shown in  FIG. 2 , the first driving electrode  133  extends over the body  112   a  of the movable portion  110  and the anchor part  111 . As shown in  FIG. 4 , the second driving electrode  134  is provided in a manner such that the two edges thereof are joined to the fixing member  120 , thereby straddling over the first driving electrode  133 . For the second driving electrode  134 , the length L 5  shown in  FIG. 1  is, for example, 200 μm. Moreover, the second driving electrode  134  is grounded via prescribed wiring (omitted from the drawings). The first driving electrode  133  and the second driving electrode  134  are each made of an appropriate electroconductive material. 
   With the micro-switching device X 1  having the above arrangement, when a prescribed potential is applied to the first driving electrode  133 , an electrostatic attractive force is generated between the first driving electrode  133  and the second driving electrode  134 . As a result, the extending part  112  elastically deforms to a position in which the contact conductor  131  contacts the stationary contact electrodes  132  or the contacting parts  132   a  of the electrodes. In this way, the closed state of the micro-switching device X 1  is achieved. In this closed state, the stationary contact electrodes  132  are electrically bridged by the contact conductor  131 , and hence a current is allowed to pass between the stationary contact electrodes  132 . 
   With the micro-switching device X 1  in the closed state, when the electrostatic attractive force acting between the first driving electrode  133  and the second driving electrode  134  is eliminated by stopping the application of the voltage to the first driving electrode  133 , then the extending part  112  returns to its natural state, and hence the contact conductor  131  separates away from the stationary contact electrodes  132 . In this way, the open state of the micro-switching device X 1  as shown in  FIGS. 3 and 5  is achieved. In the open state, the stationary contact electrodes  132  are electrically isolated from one another, and hence a current is prevented from passing between the stationary contact electrodes  132 . 
     FIGS. 6A-6D ,  7 A- 7 C and  8 A- 8 C illustrate a method of manufacturing the micro-switching device X 1  through successive changes in two cross sections of the material substrate, one cross section (on the left) corresponding to the view shown in  FIG. 3 , the other (on the right) corresponding to the view shown in  FIG. 4 . 
   In the manufacture of the micro-switching device X 1 , first a substrate S′ as shown in  FIG. 6A  is prepared. The substrate S′ is an SOI (silicon on insulator) substrate, and has a layered structure having a first layer  101 , a second layer  102 , and an intermediate layer  103  therebetween. In the present embodiment, for example, the thickness of the first layer  101  is 10 μm, the thickness of the second layer  102  is 400 μm, and the thickness of the intermediate layer  103  is 2 μm. The first layer  101  and the second layer  102  are made, for example, of monocrystalline silicon. The intermediate layer  103  is made, for example, of silicon dioxide. 
   Next, as shown in  FIG. 6B , the contact conductor  131  and the first driving electrode  133  are formed on the first layer  101  of the substrate S′. Specifically, first, using a sputtering method, a film of, for example, Cr is formed on the first layer  101 , and then a film of, for example, Au is formed thereon. The thickness of the Cr film is, for example, 50 nm, and the thickness of the Au film is, for example, 500 nm. Next, a prescribed resist pattern is formed on the resulting multi-layered conductor film using a photolithography method, and then the multi-layered conductor film is subjected to etching treatment using the resist pattern as a mask. In this way, the contact conductor  131  and the first driving electrode  133  can be pattern-formed on the first layer  101 . 
   Next, as shown in  FIG. 6C , the first layer  101  is subjected to etching treatment, thus forming the slits  141  and  142 . Specifically, a prescribed resist pattern is formed on the first layer  101  using a photolithography method, and then the first layer  101  is subjected to etching treatment using the resist pattern as a mask. Ion etching (physical etching using, for example, Ar ions) can be used as the etching method. 
   Next, as shown in  FIG. 6D , a sacrificial layer  104  is formed on the first layer  101  side of the substrate S′ such as to block up the slits  141  and  142 . As the sacrificial layer material, for example silicon dioxide can be used. Moreover, as the method for forming the sacrificial layer  104 , for example plasma CVD or sputtering can be used. The thickness of the sacrificial layer  104  is, for example, 2 μm. In the present step, the sacrificial layer material is also deposited on parts of the sidewalls of the slits  141  and  142 , and hence the slits  141  and  142  are blocked up. 
   Next, as shown in  FIG. 7A , two recesses  104   a  are formed in the sacrificial layer  104  in places in correspondence with the contact conductor  131 . Specifically, a prescribed resist pattern is formed on the sacrificial layer  104  using a photolithography method, and then the sacrificial layer  104  is subjected to etching treatment using the resist pattern as a mask. Wet etching may be used as the etching method. Each of the recesses  104   a  is for forming the contacting part  132   a  of one of the stationary contact electrodes  132 , and has a depth of, for example, 1 μm. 
   Next, as shown in  FIG. 7B , the sacrificial layer  104  is patterned, thus forming openings  104   b  and  104   c . Specifically, a prescribed resist pattern is formed on the sacrificial layer  104  using a photolithography method, and then the sacrificial layer  104  is subjected to etching treatment using the resist pattern as a mask. Wet etching can be used as the etching method. The openings  104   b  are for exposing regions where the stationary contact electrodes  132  will be joined to the island plinths  121  of the fixing member  120 . The openings  104   c  are for exposing regions where the second driving electrode  134  will be joined to the fixing member  120 . 
   Next, a foundation film (omitted from the drawings) for passing electricity is formed on the surface of the substrate S′ on the side on which the sacrificial layer  104  has been provided, and then as shown in  FIG. 7C , a mask  105  is formed. The foundation film can be formed, for example, using a sputtering method by forming a Cr film of thickness 50 nm, and then forming an Au film of thickness 500 nm thereon. The mask  105  has therein openings  105   a  in correspondence with the pair of stationary contact electrodes  132 , and an opening  105   b  in correspondence with the second driving electrode  134 . 
   Next, as shown in  FIG. 8A , the stationary contact electrodes  132  and the second driving electrode  134  are formed. Specifically, for example gold is grown using an electroplating method on the foundation film exposed in the openings  105   a  and  105   b.    
   Next, as shown in  FIG. 8B , the mask  105  is removed by etching. After that, the exposed parts of the foundation film are removed by etching. Wet etching may be used in each of these steps of removal by etching. 
   Next, as shown in  FIG. 8C , the sacrificial layer  104  and parts of the intermediate layer  103  are removed. Specifically, the sacrificial layer  104  and the intermediate layer  103  are subjected to wet etching treatment. Buffered hydrofluoric acid (BHF) can be used as the etchant. In this etching treatment, first the sacrificial layer  104  is removed, and then the intermediate layer  103  starts to be removed from places adjacent to the slits  141  and  142 . The etching treatment is stopped after the whole of the extending part  112  of the movable portion  110  has become suitably separated from the substrate S′ or the first layer  101 . In this way, the boundary layer  111   b  of the anchor part  111  and the boundary layer  120   b  of the fixing member  120  are formed by being left behind. The second layer  102  is to constitute the base substrate S 1 . 
   Next, if necessary, part of the foundation film (e.g. the Cr film) attached to the lower surface of each of the stationary contact electrodes  132  and the second driving electrode  134  is removed by wet etching, and then the whole of the device is dried using a supercritical drying method. Due to the supercritical drying, a sticking phenomenon in which the extending part  112  of the movable portion  110  sticks to the base substrate S 1  can be avoided. 
   Through the above procedure, the micro-switching device X 1  can be manufactured. With the above method, the stationary contact electrodes  132  each having a contacting part  132   a  facing the contact conductor  131  can be formed to a great thickness on the sacrificial layer  104  using plating. The thickness of the pair of stationary contact electrodes  132  can thus be set sufficiently great to realize the desired low resistance. Such a micro-switching device X 1  is suitable for reducing the insertion loss in the closed state. 
   With the micro-switching device X 1 , the lower surface of the contacting part  132   a  of each of the stationary contact electrodes  132  (i.e. the surface that contacts the contact conductor  131 ) has a high degree of flatness, and hence the air gap between the contact conductor  131  and each contacting part  132   a  can be formed with high dimensional precision. This is because the lower surface of each contacting part  132   a  is the starting face of the plating growth for forming the stationary contact electrode  132  in question. Air gaps with high dimensional precision are suitable for reducing the insertion loss of the device in the closed state, and are also suitable for improving the isolation properties of the device in the open state. 
   In general, in the case that the dimensional precision of the air gaps between the contact conductor and the stationary contact electrodes in a micro-switching device is low, variations in the air gaps between devices will arise. The longer the formed air gaps relative to the design dimension, the more difficult it will be for the contact conductor to contact the stationary contact electrodes during the closing operation of the switching device, and hence the larger the insertion loss of the device will tend to become. On the other hand, the shorter the formed air gaps relative to the design dimension, the lower the insulation between the contact conductor and the stationary contact electrodes will become during the open state of the switching device, and hence the isolation properties of the device will tend to deteriorate. Control of the film thickness is more difficult with plating than with sputtering, CVD or the like, and hence the growth end face of a thick plating film has relatively large undulations and thus a low degree of flatness, and moreover the precision of the position of formation of the growth end face is relatively low. Consequently, with a micro-switching device, in the case that the stationary contact electrodes were each constituted from a thick plating film, with the growth end face of the plating film being used as the surface that is to contact the contact conductor, the dimensional precision of the air gaps between the contact conductor and the stationary contact electrodes would be low, and hence variations in the air gaps would arise between devices. In contrast with this, with the micro-switching device X 1 , the lower surface of the contacting part  132   a  of each of the stationary contact electrodes  132  is the plating growth starting face and thus has a high degree of flatness, and hence the air gap between the contact conductor  131  and each contacting part  132   a  can be formed with high dimensional precision. 
   With the micro-switching device X 1 , as shown in  FIG. 9 , through-holes  110   a  may be formed in the extending part  112  of the movable portion  110 . The through-holes  110   a  pass through the body  112   a  of the extending part  112  at the end of the body  112   a  adjacent to the head  112   b . This arrangement is suitable for improving the electrical insulation between the contact conductor  131  and the first driving electrode  133  on the movable portion  110 . 
   With the micro-switching device X 1 , as shown in  FIG. 10 , the body  112   a  of the extending part  112  may have a relatively narrow end adjacent to the anchor part  111 . This arrangement is suitable for allowing the extending part  112  to undergo elastic deformation, which is advantageous to the reduction of the driving power. 
   As shown in  FIGS. 11 and 12 , the micro-switching device X 1  may have a movable cantilever portion  150  instead of the above-described cantilever portion  110 , and may have a first driving electrode  135  instead of the above-mentioned first driving electrode  133 . The movable portion  150  has an anchor part  151  and an extending part  152 . As shown in  FIG. 12 , the anchor part  151  is joined to the base substrate S 1 . The extending part  152  has a body  152   a , a head  152   b , and connecting parts  152   c , and extends out from the anchor part  151  along the base substrate S 1 . The body  152   a  has a section broader than the body  112   a  described earlier, and has a plurality of through-holes  153  as shown in  FIG. 12 . The first driving electrode  135  is pattern-formed over the anchor part  151 , the connecting parts  152   c  and the body  152   a , and has a main part  136  over the body  152   a . The main part  136  is formed with openings  136   a  that communicate with the through-holes  153  in the body  152   a.    
   The above arrangement, i.e., the first driving electrode  135  having a broad-area main part  136 , is suitable for reducing the driving power. Moreover, because the end part of the extending part  152  on the anchor part  151  side is constituted from the two narrow connecting parts  152   c,  approximately the same degree of elastic deformability can be realized with the extending part  152  as with the extending part  112  described earlier. In addition, in a step of removing the sacrificial layer by etching in the process of manufacturing the present variant (the step corresponding to the step described earlier with reference to  FIG. 8C ), the etchant can pass through the openings  136   a  in the main part  136  and the through-holes  153  in the body  152   a , and hence the intermediate layer  103  present below the broad body  152   a  can be removed well by the etching. 
     FIGS. 13 to 16  show a micro-switching device X 2  according to a second embodiment of the present invention.  FIG. 13  is a plan view of the micro-switching device X 2 ,  FIG. 14  is a plan view of the micro-switching device X 2  with some parts omitted, and  FIGS. 15 and 16  are respectively sectional views along lines XV-XV and XVI-XVI in  FIG. 13 . 
   The micro-switching device X 2  includes a base substrate S 2 , four movable cantilever portions  210 , a fixing member  220 , four movable contact conductors  231 , a common contact electrode  232  (omitted from  FIG. 14 ), four stationary individual contact electrodes  233  (omitted from  FIG. 14 ), four first driving electrodes  234 , and two second driving electrodes  235  (omitted from  FIG. 14 ). The micro-switching device X 2  is provided with four micro-switching devices X 1  of the first embodiment. 
   Each of the movable portions  210  has an anchor part  211  and an extending part  212 . As with the anchor part  111  described earlier, the anchor part  211  has a layered structure having a main layer and a boundary layer, and is joined to the base substrate S 2  on the boundary layer side. As shown for example in  FIG. 14 , the extending part  212  has a body  212   a  and a head  212   b , extending from the anchor part  211  along the base substrate S 2 , i.e. in a manner facing the base substrate S 2 . The main layer of the anchor part  211  and the extending part  212  are made, for example, of monocrystalline silicon. The boundary layer of the anchor part  211  is made, for example, of silicon dioxide. 
   As shown in  FIGS. 15 and 16 , the fixing member  220  has a layered structure having a main layer  220   a  and a boundary layer  220   b , and is joined to the base substrate S 2  on the boundary layer  220   b  side. Moreover, as shown in  FIG. 14 , the fixing member  220  includes a central island plinth  221  and four island plinths  222 , surrounding the movable portions  210  with slits  241  therebetween. The island plinths  221  and  222  are separated from the other sections of the fixing member  220  by slits  242 . The slits  241  and  242  are helpful in securing an insulated state (a nonconductive state) between the stationary contact electrodes  232  and  233 , the first driving electrodes  234  and the second driving electrodes  235 . The main layer  220   a  of the fixing member  220  is made, for example, of monocrystalline silicon, and the boundary layer  220   b  is made, for example, of silicon dioxide. 
   As shown in  FIG. 14 , each of the contact conductors  231  is provided on the head  212   b  of the corresponding movable portion  210 . As shown in  FIG. 15 , the stationary contact electrode  232  stands on the island plinth  221  of the fixing member  220 , and has four contacting parts  232   a . Each of the contacting parts  232   a  faces one of the contact conductors  231 . As shown in  FIG. 15 , each of the stationary contact electrodes  233  stands on one of the island plinths  222  of the fixing member  220 , and has a contacting part  233   a  facing one of the contact conductors  231 . Moreover, the stationary contact electrodes  232  and  233  are connected via prescribed wiring (omitted from the drawings) to prescribed circuitry to be subjected to switching. The contact conductors  231  and the stationary contact electrodes  232  and  233  are each made of an appropriate electroconductive material. 
   Each of the first driving electrodes  234  extends over the body  212   a  of the corresponding movable portion  210  and to the anchor part  211 . As shown in  FIG. 16 , each of the second driving electrodes  235  is provided in standing fashion such as to be joined to the fixing member  220  at three places and so as to straddle over two of the first driving electrodes  234 . Moreover, the second driving electrodes  235  are grounded via prescribed wiring (omitted from the drawings). The first driving electrodes  234  and the second driving electrodes  235  are each made of an appropriate electroconductive material. 
   With the micro-switching device X 2  having the above arrangement, when a prescribed potential is applied to one of the first driving electrodes  234 , an electrostatic attractive force is generated between this first driving electrode  234  and the second driving electrode  235  facing the same. As a result, the corresponding extending part  212  elastically deforms to a position in which the contact conductor  231  contacts the contacting parts  232   a  and  233   a  of the stationary contact electrodes  232  and  233 . In this way, the closed state for one channel of the micro-switching device X 2  is achieved. 
   If the electrostatic attractive force acting between the first driving electrode  234  for the channel in the closed state and the corresponding second driving electrode  235  is eliminated by stopping the application of the voltage to this first driving electrode  234 , then the corresponding extending part  212  returns to its natural state, and hence the contact conductor  231  separates away from the stationary contact electrodes  232  and  233 . In this way, the open state for that channel of the micro-switching device X 2  is achieved. 
   With the micro-switching device X 2 , as noted above, the opening and closing of the four channels can be controlled by selectively controlling the potentials applied to the four first driving electrodes  234 . That is, the micro-switching device X 2  can be used as a 1×4 channel switch. 
   The micro-switching device X 2  can be manufactured through a similar process to that described earlier for the micro-switching device X 1 . Consequently, with the micro-switching device X 2 , the stationary contact electrode  232  having the contacting parts  232   a  facing the contact conductors  231 , and the stationary contact electrodes  233  each having a contacting part  233   a  facing one of the contact conductors  231  can be formed to a great thickness using plating. The stationary contact electrodes  232  and  233  can thus be made sufficiently thick. Such a micro-switching device X 2  is suitable for reducing the insertion loss in the closed state. 
   With the micro-switching device X 2 , the lower surface of each of the contacting parts  232   a  and  233   a  of the stationary contact electrodes  232  and  233  (i.e. the surface that contacts the contact conductor  231 ) has a high degree of flatness, and hence the air gaps between the contact conductors  231  and the contacting parts  232   a  and  233   a  can be formed with high dimensional precision. Air gaps with high dimensional precision are suitable for reducing the insertion loss for each channel in the closed state, and are also suitable for improving the isolation properties for each channel in the open state. 
     FIGS. 17 to 19  show a micro-switching device X 3  according to a third embodiment of the present invention.  FIG. 17  is a plan view of the micro-switching device X 3 .  FIG. 18  is a plan view of the micro-switching device X 3  with some parts omitted, and  FIG. 19  is a sectional view along line XIX-XIX in  FIG. 18 . 
   The micro-switching device X 3  includes a base substrate S 3 , a movable cantilever portion  110 , a fixing member  120 , a movable contact conductor  131 , a pair of stationary contact electrodes  132  (omitted from  FIG. 18 ), and a piezoelectric driving segment  340 . The micro-switching device X 3  differs from the micro-switching device X 1  in that the piezoelectric driving segment  340  is provided in place of the first driving electrode  133  and the second driving electrode  134 . 
   The piezoelectric driving segment  340  includes a first driving electrode  341 , a second driving electrode  342 , and a piezoelectric film  343  provided between the two electrodes. The first driving electrode  341  and the second driving electrode  342  each has, for example, a layered structure including a Ti foundation layer and an Au main layer. The second driving electrode  342  is grounded via prescribed wiring (omitted from the drawings). The piezoelectric film  343  is made of a piezoelectric material, which exhibits strain occurring upon application of an electric field (the reverse piezoelectric effect). As this piezoelectric material, for example PZT (a solid solution of PbZrO3 and PbTiO3), Mn-doped ZnO, ZnO, or AIN can be used. The thicknesses of the first driving electrode  341  and the second driving electrode  342  are, for example, 0.55 μm, and the thickness of the piezoelectric film  343  is, for example, 1.5 μm. 
   The base substrate S 3 , the movable portion  110 , the fixing member  120 , the contact conductor  131 , and the pair of stationary contact electrodes  132  are constituted as described earlier for the micro-switching device X 1 . 
   With the micro-switching device X 3  having the above arrangement, when a prescribed potential is applied to the first driving electrode  341 , an electric field is generated between the first driving electrode  341  and the second driving electrode  342 , and hence a contractive force in the in-plane (or longitudinal) direction arises within the piezoelectric film  343 . The further from the first driving electrode  341 , which is supported directly by the extending part  112 , i.e. the closer to the second driving electrode  342 , the more easily the piezoelectric material in the piezoelectric film  343  contracts in the in-plane direction. The amount of contraction in the in-plane direction caused by the contractive force thus becomes progressively greater from the first driving electrode  341  side toward the second driving electrode  342  side within the piezoelectric film  343 , and hence the extending part  112  elastically deforms to a position in which the contact conductor  131  contacts the pair of stationary contact electrodes  132 . In this way, the closed state of the micro-switching device X 3  is achieved. In this closed state, the stationary contact electrodes  132  are electrically bridged by the contact conductor  131 , and hence a current is allowed to pass between the stationary contact electrodes  132 . 
   With the micro-switching device X 3  in the closed state, if the electric field between the first driving electrode  341  and the second driving electrode  342  is eliminated by stopping the application of the voltage to the first driving electrode  341 , then the piezoelectric film  343  and the extending part  112  return to their natural states, and hence the contact conductor  131  separates away from the stationary contact electrodes  132 . In this way, the open state of the micro-switching device X 3  is achieved. In the open state, the stationary contact electrodes  132  are electrically isolated from one another, and hence a current is prevented from passing between the stationary contact electrodes  132 . 
     FIGS. 20A-20D ,  21 A- 21 C,  22 A- 22 C and  23 A- 23 C illustrate a method of manufacturing the micro-switching device X 3  through successive changes in two cross sections of the material substrate, one cross section (on the left) taken along line XX-XX in  FIG. 17 , the other (on the right) taken along line XXI-XXI in  FIG. 17 . 
   In the manufacture of the micro-switching device X 3 , first a substrate S′ as shown in  FIG. 20A  is prepared. The substrate S′ is an SOI substrate, and has a layered structure comprising a first layer  101 , a second layer  102 , and an intermediate layer  103  therebetween. In the present embodiment, for example, the thickness of the first layer  101  is 10 μm, the thickness of the second layer  102  is 400 μm, and the thickness of the intermediate layer  103  is 2 μm. The first layer  101  and the second layer  102  are made, for example, of monocrystalline silicon. In the present embodiment, the intermediate layer  103  is made of an insulating material. As this insulating material, use may be made of silicon dioxide, silicon nitride or the like. 
   Next, as shown in  FIG. 20B , the piezoelectric driving segment  340  is formed on the first layer  101  of the substrate S′. In the formation of the piezoelectric driving segment  340 , a first electroconductive film is formed on the first layer  101 . Next, a piezoelectric material film is formed on the first electroconductive film. Then, a second electroconductive film is formed on the piezoelectric material film. After that, the films are patterned using photolithography and then etching. The first and second electroconductive films can be formed, for example, using a sputtering method by forming a film of, for example, Ti, and then forming a film of, for example, Au thereon. The thickness of the Ti film is, for example, 50 nm, and the thickness of the Au film is, for example, 500 nm. The piezoelectric material film can be formed, for example, using a sputtering method by forming a film of an appropriate piezoelectric material. 
   Next, as shown in  FIG. 20C , the contact conductor  131  is formed on the first layer  101  in the same manner as described earlier with reference to  FIG. 6B  for the formation of the contact conductor  131  of the micro-switching device X 1 . 
   Next, as shown in  FIG. 20D , a protective film  106  for covering the piezoelectric driving segment  340  is formed. For example, the protective film  106  can be formed by forming a film of Si using a sputtering method via a prescribed mask. The thickness of the protective film  106  is, for example, 300 nm. 
   In the manufacture of the micro-switching device X 3 , as shown in  FIG. 21A , the first layer  101  is subjected to etching treatment for forming the slits  141  and  142 . This process is performed in the same manner as described earlier with reference to  FIG. 6C  for manufacturing the micro-switching device X 1 . 
   Next, as shown in  FIG. 21B , a sacrificial layer  107  is formed on the first layer  101  side of the substrate S′ such as to block up the slits  141  and  142 . This process is performed in the same manner as described earlier with reference to  FIG. 6D  for the formation of the sacrificial layer  104 . 
   Next, as shown in  FIG. 21C , two recesses  107   a  are formed in the sacrificial layer  107  in places in correspondence with the contact conductor  131 . The process is performed in the same manner as described earlier with reference to  FIG. 7A  for the formation of the recesses  104   a . Each of the recesses  107   a  is for forming the contacting part  132   a  of one of the stationary contact electrodes  132 , and has a depth of, for example, 1 μm. 
   Next, as shown in  FIG. 22A , the sacrificial layer  107  is patterned, thus forming openings  107   b . Specifically, a prescribed resist pattern is formed on the sacrificial layer  107  using a photolithography method, and then the sacrificial layer  107  is subjected to etching treatment using the resist pattern as a mask. Wet etching can be used as the etching method. The openings  107   b  are for exposing regions where the stationary contact electrodes  132  will be joined to the island plinths  121  of the fixing member  120 . 
   Next, a foundation film (omitted from the drawings) for passing electricity is formed on the surface of the substrate S′ on the side on which the sacrificial layer  107  has been provided, and then as shown in  FIG. 22B , a mask  108  is formed. The foundation film can be formed, for example, using a sputtering method by forming a Cr film of thickness 50 nm, and then forming an Au film of thickness 500 nm thereon. The mask  108  has openings  108   a  in correspondence with the pair of stationary contact electrodes  132 . 
   Next, as shown in  FIG. 22C , the stationary contact electrodes  132  are formed. Specifically, for example gold is grown using an electroplating method on the foundation film exposed in the openings  108   a.    
   Next, as shown in  FIG. 23A , the mask  108  is removed by etching. After that, the exposed parts of the foundation film are removed by etching. Wet etching can be used in each of these steps of removal. 
   Next, as shown in  FIG. 23B , the sacrificial layer  107  and parts of the intermediate layer  103  are removed. This process is performed in the same manner as described earlier with reference to  FIG. 8C  for the removal of the sacrificial layer  104  and parts of the intermediate layer  103 . In the present step, the boundary layer  111   b  of the anchor part  111  and the boundary layer  120   b  of the fixing member  120  are formed by being left behind. Moreover, the second layer  102  comes to constitute the base substrate S 3 . 
   Next, if necessary, the part of the foundation film (e.g. the Cr film) attached to the lower surface of each of the stationary contact electrodes  132  is removed by wet etching, and then the whole of the device is dried using a supercritical drying method. After that, as shown in  FIG. 23C , the protective film  106  is removed. As the removal method, for example RIE carried out using SF 6  gas as an etching gas can be used. 
   Through the above, the micro-switching device X 3  can be manufactured. With the above method, the stationary contact electrodes  132  each having a contacting part  132   a  facing the contact conductor  131  can be formed to a high thickness on the sacrificial layer  107  using plating. The thickness of the pair of stationary contact electrodes  132  can thus be set sufficiently high. Such a micro-switching device X 3  is suitable for reducing the insertion loss in the closed state. 
   With the micro-switching device X 3 , the lower surface of the contacting part  132   a  of each of the stationary contact electrodes  132  (i.e. the surface that contacts the contact conductor  131 ) has a high degree of flatness, and hence the air gap between the contact conductor  131  and each contacting part  132   a  can be formed with high dimensional precision. Air gaps with high dimensional precision are suitable for reducing the insertion loss in the closed state, and are also suitable for improving the isolation properties in the open state. 
   The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.