Patent Publication Number: US-7903313-B2

Title: Micro movable element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-53054, filed on Mar. 4, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present embodiment relates to a micro movable element produced using the micromachining technology. 
     BACKGROUND 
     In recent years, micro structures produced using the micromachining technology are attracting attention in various technical fields, and the application of elements having micro structures is being promoted. Such a micro structure includes a micro movable element having a minute movable or vibrating portion and is configured as a micromirror element, an acceleration sensor, an angular velocity sensor or the like. The micromirror element is used as an element having an optical reflection function in the fields of optical disc technology and optical communication technology, for example. The acceleration sensor and the angular velocity sensor are used for the attitude control in robots and vehicles and for image stabilization in cameras, for example. JP-A-2003-19700, JP-A-2004-341364 and JP-A-2006-72252 disclose these micromirror elements. 
     SUMMARY 
     A micro movable element according to the present embodiment includes a movable portion; a first driving electrode for driving the movable portion; a second driving electrode for driving the movable portion; a first conductor portion electrically connected to the first driving electrode; a second conductor portion electrically connected to the second driving electrode; an intermediate insulating portion disposed between the first conductor portion and the second conductor portion; and a partly laminated structure portion having the first conductor portion, the intermediate insulating portion and the second conductor portion, wherein the first conductor portion has an opposed face making contact with the intermediate insulating portion, a side face adjacent to the opposed face and an edge portion forming the boundary between the opposed face and the side face, at least part of the edge portion opposed to the second conductor portion is covered with an insulating film, and at least parts of the first and second driving electrodes are not covered with an insulating film. 
     Additional objects and advantages of the embodiment will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a micro movable element according to a first embodiment; 
         FIG. 2  is a partially omitted plan view of the micro movable element illustrated in  FIG. 1 ; 
         FIG. 3  is a sectional view taken on line III-III of  FIG. 1 ; 
         FIG. 4  is a sectional view taken on line IV-IV of  FIG. 1 ; 
         FIG. 5  is a sectional view taken on line V-V of  FIG. 1 ; 
         FIG. 6  is an enlarged sectional view taken on line VI-VI of  FIG. 1 ; 
         FIG. 7  is an enlarged sectional view taken on line VII-VII of  FIG. 1 ; 
         FIGS. 8A to 8D  illustrate some steps in a method for producing the micro movable element according to the first embodiment; 
         FIGS. 9A to 9D  illustrate steps subsequent to those illustrated in  FIGS. 8A to 8D ; 
         FIGS. 10A to 10C  illustrate steps subsequent to those illustrated in  FIGS. 9A to 9D ; 
         FIGS. 11A to 11C  illustrate steps subsequent to those illustrated in  FIG. 10A to 10C ; 
         FIG. 12  is a sectional view taken on line III-III of  FIG. 1  at the time of driving; 
         FIG. 13  is a sectional view of a micro movable element according to a second embodiment; 
         FIG. 14  is another sectional view of the micro movable element according to the second embodiment; 
         FIG. 15  is still another sectional view of the micro movable element according to the second embodiment; 
         FIG. 16  is yet still another sectional view of the micro movable element according to the second embodiment; 
         FIGS. 17A and 17B  illustrate some steps in a method for producing the micro movable element according to the second embodiment; 
         FIG. 18  is a plan view illustrating irradiation regions near comb electrodes at a laser beam irradiation step in the method for producing the micro movable element according to the second embodiment; 
         FIG. 19  is a sectional view of a micro movable element according to a third embodiment; 
         FIG. 20  is another sectional view of the micro movable element according to the third embodiment; 
         FIG. 21  is a plan view illustrating irradiation regions near comb electrodes at a laser beam irradiation step in a method for producing the micro movable element according to the third embodiment; 
         FIG. 22  illustrates the micro movable element illustrated in  FIG. 19  at the time of driving; 
         FIG. 23  is a plan view of a micro movable element according to a fourth embodiment; 
         FIG. 24  is a partially omitted plan view of the micro movable element illustrated in  FIG. 23 ; 
         FIG. 25  is a sectional view taken on line XXV-XXV of  FIG. 23 ; 
         FIG. 26  is a sectional view taken on line XXVI-XXVI of  FIG. 23 ; 
         FIG. 27  is a sectional view taken on line XXVII-XXVII of  FIG. 23 ; 
         FIG. 28  is an enlarged sectional view taken on line XXVIII-XXVIII of  FIG. 23 ; 
         FIG. 29  illustrates a fifth embodiment; 
         FIG. 30  illustrates a sixth embodiment; 
         FIG. 31  is a fragmentary sectional view of a conventional micro movable element; 
         FIGS. 32A to 32D  illustrate some steps in a method for producing the conventional micro movable element illustrated in  FIG. 31 ; 
         FIG. 33  is a fragmentary enlarged view of  FIG. 31 ; 
         FIG. 34  is a scanning electron micrograph illustrating part of the conventional micro movable element; 
         FIGS. 35A and 35B  illustrate problems that may occur owing to discharge in the conventional micro movable element illustrated in  FIG. 31 ; 
         FIG. 36  is an enlarged fragmentary arrow view taken on line XXXVI-XXXVI of  FIG. 31 ; 
         FIG. 37  is a scanning electron micrograph illustrating another part of the conventional micro movable element; 
         FIGS. 38A to 38C  illustrate problems that may occur owing to a silicon fraction in the conventional micro movable element illustrated in  FIG. 31 ; and 
         FIG. 39  illustrates the conventional micro movable element illustrated in  FIG. 31 , conformally coated. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Comparison Example 1 
       FIG. 31  is a fragmentary sectional view of a micro movable element Y. The micro movable element Y is, for example, a micromirror element, an acceleration sensor or an angular velocity sensor, equipped with a movable portion (not illustrated) and driving electrodes  301  and  302  for generating a driving force (electrostatic attractive force) for driving the movable portion. In addition, the micro movable element Y partly includes a partly laminated structure portion  310  having a conductor portion  311 , a conductor portion  312  and an intermediate insulating portion  313 . The conductor portions  311  and  312  constitute part of an electrically-conducting path in the micro movable element Y having functions. The conductor portion  311  is electrically connected to the driving electrode  301 , and the conductor portion  312  is electrically connected to the driving electrode  302 . Different potentials are applied to the respective conductor portions  311  and  312  when the element is driven (when a voltage is applied across the driving electrodes  301  and  302 ). In other words, when the element is driven, a significant potential difference is generated between the conductor portions  311  and  312  of the micro movable element Y. 
       FIGS. 32A to 32D  illustrate some steps in a method for producing the micro movable element Y with changes in the fragmentary cross-sections of the portions corresponding to those illustrated in  FIG. 31 . In the production of the micro movable element Y, such a material substrate  400  as illustrated in  FIG. 32A  is first prepared. The material substrate  400  is an SOI (silicon-on-insulator) wafer having a laminated structure including silicon layers  401  and  402  and an intermediate insulating layer  403  disposed between the silicon layers  401  and  402 . The silicon layers  401  and  402  are made of a silicon material to which electrical conductivity is imparted by impurity doping. The intermediate insulating layer  403  is made of silicon oxide. The thickness of the silicon layer  401  is, for example, 50 to 100 μm, the thickness of the silicon layer  402  is, for example, 100 to 600 μm, and the thickness of the intermediate insulating layer  403  is, for example, 0.3 to 7 μm. 
     Next, as illustrated in  FIG. 32B , the silicon layer  401  is etched, and portions (including the driving electrode  301  and the conductor portion  311 ) to be formed in the silicon layer  401  are formed. More specifically, after a resist pattern (not illustrated) is formed on the silicon layer  401 , the silicon layer  401  is subjected to anisotropic etching according to the DRIE method while the resist pattern is used as a mask. In the DRIE method, highly anisotropic etching may be carried out in the Bosch process in which the etching performed using SF6 gas and the side wall protection performed using C4F8 gas are carried out alternately. 
     Next, as illustrated in  FIG. 32C , the silicon layer  402  is etched, and portions (including the driving electrode  302  and the conductor portion  312 ) to be formed in the silicon layer are formed. More specifically, after a resist pattern (not illustrated) is formed on the silicon layer  402 , the silicon layer  402  is subjected to anisotropic etching according to the DRIE method while the resist pattern is used as a mask. 
     Next, after the resist patterns (not illustrated) on the silicon layers  401  and  402  are removed as necessary, the intermediate insulating layer  403  is subjected to anisotropic etching using the wet etching method as illustrated in  FIG. 32D  to form the intermediate insulating portion  313 . For example, buffered hydrofluoric acid (BHF) containing hydrofluoric acid and ammonium fluoride may be used as an etching solution in this step. The micro movable element Y having the partial structure illustrated in  FIG. 31  is produced using the method including the steps described above. 
       FIG. 33  is an enlarged fragmentary view of  FIG. 31 . FIG.  34  is a local SEM photograph of a micro movable element produced using the method illustrated in  FIG. 32  and illustrates the shape of the side face of the partly laminated structure portion  310  illustrated in  FIG. 31 . As illustrated in  FIG. 33  and also illustrated in  FIG. 34  corresponding to  FIG. 33 , the conductor portion  311  has an edge portion  311   a  that is relatively sharp and exposed. The edge portion  311   a  is exposed since the intermediate insulating layer  403  being exposed is removed by etching and the intermediate insulating layer  403  disposed between the conductor portions  311  and  312  is partially eroded (in other words, a so-called undercut  314  is formed) in the wet etching step described above referring to  FIG. 32D . 
     When the micro movable element Y having functions is driven, a voltage is applied across the driving electrodes  301  and  302 . Hence, a potential difference may be generated between the conductor portion  311  electrically connected to the driving electrode  301  and the conductor portion  312  electrically connected to the driving electrode  302 . If the potential difference is generated between the conductor portions  311  and  312 , unintended discharge may occur occasionally between the conductor portion  312  extending close to the conductor portion  311  and the exposed edge portion  311   a  of the conductor portion  311  as illustrated in  FIG. 35A . This discharge is more likely to occur as the edge portion  311   a  is shaper. If this discharge occurs, the edge portion  311   a  is eluted by the heat generated at the time of the discharge, whereby an electrically-conducting path  311   b  is formed frequently as illustrated in  FIG. 35B . In the state in which the electrically-conducting path  311   b  is formed, the so-called current leakage occurs, that is, current flows through the electrically-conducting path  311   b  in the case that a potential difference is generated between the conductor portions  311  and  312  when the element is driven. If this current leakage occurs, no appropriate potential difference is generated between the driving electrodes  301  and  302 . For this reason, the current leakage hinders the micro movable element Y having the functions from being driven properly. 
       FIG. 36  is an enlarged fragmentary arrow view taken on line XXXVI-XXXVI of  FIG. 31 .  FIG. 37  is a local SEM photograph of a micro movable element produced using the method illustrated in  FIG. 32  and illustrates the shape of the side face corresponding to that illustrated in  FIG. 36 . As illustrated in  FIG. 36  and also illustrated in  FIG. 37  corresponding to  FIG. 36 , a rough region  311   c ′ is formed on the side face  311   c  of the conductor portion  311 . Although etching is performed for the silicon layer  401  according to the DRIE method in the step described above referring to  FIG. 32B , if the etching is performed according to the DRIE method, the rough region  311   c ′ is formed unintentionally and inevitably on the side face  311   c  of the conductor portion  311  to be formed. 
     The etching according to the DRIE method is cycle etching in which the etching performed using SF6 gas and the side wall protection performed using C4F8 gas are repeated alternately many times. For this reason, strictly speaking, the extent to which the etching progresses by virtue of the action of the SF6 gas in the etching process in each cycle and the extent to which the side wall is protected by virtue of the action of the C4F8 gas in the side wall protection process in each cycle are not uniform at sites in which the silicon layer  401  is processed. Furthermore, the shape of the contour of the resist pattern (not illustrated) formed on the silicon layer  401  and used as a mask when the etching according to the DRIE method is performed is accompanied by minute irregularity and roughness from the very beginning. In addition, the resist pattern is degraded as the etching progresses, and the roughness in the shape of the contour of the resist pattern remains unchanged or increases. For these reasons, it is assumed that the unintended rough region  311   c ′ occurs inevitably on the side face  311   c  of the conductor portion  311 . 
     A minute silicon fraction  311   d  being apt to peel off from the main body of the conductor portion  311  may be present occasionally in the rough region  311   c ′ as illustrated in  FIG. 38A . If a potential difference is generated between the conductor portions  311  and  312  when the element is driven, an electrostatic attractive force is exerted to the silicon fraction  311   d , and the silicon fraction  311   d  may be moved as illustrated in  FIG. 38B . Owing to the movement of the silicon fraction, instantaneous current leakage will occur between the conductor portions  311  and  312  when the element is driven. Furthermore, if a potential difference is generated between the conductor portions  311  and  312  when the element is driven, an electrostatic attractive force is exerted to the silicon fraction  311   d , whereby the silicon fraction  311   d  may be displaced occasionally so as to bridge the distance between the conductor portions  311  and  312  as illustrated in  FIG. 38C . In the state in which the distance between the conductor portions  311  and  312  is bridged using the silicon fraction  311   d , current leakage occurs, that is, current flows through the silicon fraction  311   d  in the case that a potential difference is generated between the conductor portions  311  and  312  when the element is driven. This current leakage hinders the micro movable element Y having the functions from being driven properly. 
     Comparison Example 2 
     As a method for suppressing the occurrence of the above-mentioned current leakage, a method is conceivable in which the micro movable element Y is wholly coated with a thin insulating film  315  for preventing current from flowing, as illustrated in  FIG. 39 . However, in the case of this kind of conformal coating, the driving electrodes  301  and  302  of the micro movable element Y are also wholly covered with the insulating film  315 , whereby the control of the driving force to be generated between the driving electrodes  301  and  302  is apt to be hindered. This is because the so-called charging occurs on the insulating film  315  when the element is driven. In other words, if a voltage is applied across the driving electrodes  301  and  302  when the element is driven, charge is accumulated on the insulating film  315 , which serves as a dielectric substance with which the surfaces of the driving electrodes  301  and  302  are coated, by the action of the electric field generated between the driving electrodes  301  and  302 . Moreover, the amount of the charge accumulated on the insulating film  315  may change occasionally depending on the time during which the voltage is applied across the driving electrodes  301  and  302 . If this kind of charging occurs on the insulating film  315  existing on the surfaces of the driving electrodes  301  and  302 , the electrostatic attractive force (driving force) generated between the driving electrodes  301  and  302  becomes unstable, and the control of the driving force is apt to be hindered. If the control of the driving force is hindered, the control for the displacement amount of the movable portion is hindered, and the functions of the micro movable element Y are also hindered eventually. 
     Example 1 
     This example is intended to eliminate the disadvantages encountered in Comparison examples 1 and 2. This example provides a micro movable element suited to suppress the generation of current leakage and also suited to accurately control the driving force generated between the driving electrodes. Furthermore, this example provides an optical switching apparatus equipped with this kind of micro movable element. Moreover, this example provides a method for producing this kind of micro movable element. 
     According to an aspect of the first example, a micro movable element is provided which is equipped with a movable portion and a first driving electrode and a second driving electrode for driving the movable portion (in other words, for generating an electrostatic attractive force serving as a driving force). This micro movable element includes a partly laminated structure portion having a first conductor portion electrically connected to the first driving electrode, the second conductor portion electrically connected to a second driving electrode and an intermediate insulating portion disposed between the first and second conductor portions. The first conductor portion has an opposed face opposed to the second conductor portion, a side face and an edge portion forming the boundary between the opposed face and the side face. The second conductor portion has an extending face extending beyond the edge portion of the first conductor portion. At least part of the edge portion of the first conductor portion is covered with an insulating film. At least parts of the first and second driving electrodes are not covered with an insulating film. The micro movable element is a microstructure, such as a micromirror element, an acceleration sensor or an angular velocity sensor, equipped with a movable portion. The first and second conductor portions electrically connected to the first and second driving electrodes form part of an electrically-conducting path in the micro movable element having functions. Different potentials may be applied to the first and second driving electrodes when the element is driven. In other words, a potential difference may be generated occasionally between the first conductor portion and the second conductor portion of the micro movable element when the element is driven. 
     In the micro movable element according to the first aspect, the insulating film covering at least part of the edge portion of the first conductor portion suppresses discharge from occurring between the edge portion of the first conductor portion and the second conductor portion and its extending face when a potential difference is generated between the first and second conductor portions. The insulating film configured as described above suppresses the edge portion from being eluted by the heat generated at the time of discharge and from forming an electrically-conducting path for bridging the distance between the first and second conductor portions, thereby suppressing current from flowing through such an electrically-conducting path (current leakage) in the case that a potential difference is generated between the first and second conductor portions when the element is driven. 
     In addition, in the case that a potential difference is generated between the first and second conductor portions, the insulating film of the micro movable element suppresses a fraction of the first conductor portion from peeling off from the side face near the edge portion of the first conductor portion. The insulating film configured as described above suppresses current leakage between the first and second conductor portions owing to the movement of the fraction or the bridging of the distance between the first and second conductor portions via the fraction. 
     Furthermore, in the micro movable element, at least parts of the first and second driving electrodes for generating an electrostatic attractive force serving as a driving force are not covered with the insulating film. In other words, the first and second driving electrodes are not conformally coated with the insulating film. For this reason, the charging described above with respect to the micro movable element Y may be suppressed or dissolved from occurring in the micro movable element. In the micro movable element configured as described above, a stable driving force may be generated easily using the first and second driving electrodes. Hence, the micro movable element is suited to accurately control the driving force. 
     As described above, the micro movable element according to the first example is suited to suppress current leakage from occurring and also suited to accurately control the driving force generated between the driving electrodes. 
     In the first embodiment, it is preferable that the first and second driving electrodes are comb electrodes having multiple electrode teeth arranged in parallel. From the view point of accurate control of the driving force, it is preferable to adopt a pair of comb electrodes serving as a pair of drive electrodes. 
     It is preferable that the micro movable element is further equipped with a frame and a connection portion for connecting the frame to the movable portion and for determining the axial center line of the rotation operation of the movable portion, that the movable portion has an arm portion extending in a direction intersecting the axial center line, that the multiple electrode teeth of the first driving electrode extend from the arm portion while being spaced mutually in the extension direction of the arm portion, and that some of the electrode teeth on the side of the axial center line among the multiple electrode teeth are covered with an insulating film. Parts of the driving electrodes, hardly charged even if coated with an insulating film, may also be coated with the insulating film as in the case of this configuration. 
     It is preferable that the first and second driving electrodes are not covered with an insulating film. Furthermore, it is also preferable that the entire surfaces of the first and second driving electrodes are not covered with an insulating film to solve the problem of the charging owing to the existence of the insulating film covering the driving electrodes. 
     It is preferable that the insulating film is a parylene film, a silicon oxide film or a silicon nitride film. These films are insulating films being excellent in conformality performance. In particular, the parylene film is excellent in conformality performance. 
     Example 2 
     A second example provides an optical switching apparatus. This optical switching apparatus is equipped with a micromirror element including a micromirror element according to the first aspect. The optical switching apparatus is, for example, an optical switching apparatus of a space optical coupling type or an optical switching apparatus of a wavelength selection type. 
     A third embodiment provides a method for producing a micro movable element. This method is a method for producing the micro movable element according to the first aspect by processing a material substrate having a laminated structure including a first conductor layer, a second conductor layer and an insulating layer disposed between the first and second conductor layers. The method includes an insulating film forming step and a removing step. In the insulating film forming step, an insulating film is formed on the surface of the element equipped with the movable portion and the first and second driving electrodes and including the partly laminated structure portion. In the removing step, the insulating film formed at the insulating film forming step is subjected to removing treatment while at least part of the edge portion of the first conductor portion in the partly laminated structure portion remains unremoved. With the method, the micro movable element according to the first example may be produced properly. 
     Example 3 
     According to a preferred embodiment of a third example, the removing step includes a first etching step for performing anisotropic dry etching for the material substrate on the side of the first conductor layer and a second etching step for performing anisotropic dry etching for the material substrate on the side of the second conductor layer. In this case, it is preferable that the etching conditions at the first etching step are different from the etching conditions at the second etching step. The etching conditions are etching time, gas pressure inside the chamber of an etching apparatus, applied electric power, etc. 
     According to another preferred embodiment of the third example, a laser beam is irradiated to portions from which the insulating film covering the first and second driving electrodes is desired to be removed. In this case, it is preferable that the irradiation direction of the laser beam is inclined with respect to the thickness direction of the material substrate. It is also preferable to use the excimer laser beam as the laser beam. 
     First Embodiment 
       FIGS. 1 to 7  illustrate a micro movable element X 1  according to a first embodiment.  FIG. 1  is a plan view of the micro movable element X 1 ,  FIG. 2  is a partially omitted plan view of the micro movable element X 1 , and  FIGS. 3 ,  4  and  5  are sectional views taken on line III-III, line IV-IV and line V-V of  FIG. 1 , respectively.  FIGS. 6 and 7  are enlarged sectional views taken on line VI-VI and line VII-VII of  FIG. 1 , respectively. 
     The micro movable element X 1  is a micromirror element equipped with a rocking portion  10 , a frame  20 , a torsion connection portion  30 , comb electrodes  41  and  42  and an insulating film  50 . The micro movable element X 1  is produced by processing a material substrate serving as the so-called SOI (silicon-on-insulator) substrate using the bulk micromachining technology, such as the MEMS technology. The material substrate has a laminated structure comprising first and second silicon layers and an intermediate insulating layer disposed between the silicon layers, and electrical conductivity is imparted to the silicon layers by impurity doping. The above-mentioned portions except for the insulating film  50  in the micro movable element X 1  are portions mainly derived from the first silicon layer and/or the second silicon layer. However, in  FIG. 1 , for the sake of clarification of the drawing, the portions derived from the first silicon layer and protruding upright from the intermediate insulating layer toward the front side of the sheet of the drawing are hatched with oblique lines. Furthermore,  FIG. 2  illustrates a structure derived from the second silicon layer of the micro movable element X 1 . 
     The rocking portion  10  has a mirror-supporting portion  11 , an arm portion  12  and comb electrodes  13 A and  13 B. 
     The mirror-supporting portion  11  is a portion derived from the first silicon layer, and its surface is provided with a mirror face  11   a  having a light-reflecting function. The mirror face  11   a  has, for example, a laminated structure having a Cr layer formed on the first silicon layer and an Au layer formed thereon. The length L 1  of the mirror-supporting portion  11  illustrated in  FIG. 1  is, for example, 20 to 300 μm. 
     The arm portion  12  is a portion mainly derived from the first silicon layer and extends from the mirror-supporting portion  11 . The length L 2  of the arm portion  12  illustrated in  FIG. 1  is, for example, 10 to 100 μm. 
     The comb electrode  13 A includes multiple electrode teeth  13   a . The respective multiple electrode teeth  13   a  extend from the arm portion  12  and are arranged in parallel while being spaced mutually in the extension direction of the arm portion  12 . The comb electrode  13 B includes multiple electrode teeth  13   b . The respective multiple electrode teeth  13   b  extend from the arm portion  12  on the opposite side of the electrode teeth  13   a  and are arranged in parallel while being spaced mutually in the extension direction of the arm portion  12 . The electrode teeth  13   a  and  13   b  are portions mainly derived from the first silicon layer. In this embodiment, the extension directions of the electrode teeth  13   a  and  13   b  are orthogonal to the extension direction of the arm portion  12  as illustrated in  FIG. 1 . The comb electrode  13 A including the electrode teeth  13   a  is electrically connected to the comb electrode  13 B including the electrode teeth  13   b  via the arm portion  12 . 
     The frame  20  has a laminated structure including a first layer portion  21 , a second layer portion  22  and an insulating layer  23  disposed therebetween. The first layer portion  21  is a portion derived from the first silicon layer. The second layer portion  22  is a portion derived from the second silicon layer and has a shape enclosing the rocking portion  10 . In addition, the second layer portion  22  includes a main portion  22 A and a land portion  22 B separated from this main portion  22 A by a space as illustrated in  FIG. 2 . An electrode pad  24 A for external connection is provided on the surface of the main portion  22 A as illustrated in  FIG. 3 , and an electrode pad  24 B for external connection is provided on the surface of the land portion  22 B as illustrated in  FIGS. 4 and 6 . The land portion  22 B is electrically connected to the first layer portion  21  via a conductive plug  25  passing through the insulating layer  23 . Furthermore, the length L 3  of the frame  20  illustrated in  FIG. 1  is, for example, 5 to 50 μm. 
     The torsion connection portion  30  includes a pair of torsion bars  31 . Each torsion bar  31  is a portion mainly derived from the first silicon layer and is connected to the arm portion  12  of the rocking portion  10  and the first layer portion  21  of the frame  20  so as to link these portions. The arm portion  12  is electrically connected to the first layer portion  21  via the torsion bars  31 . Furthermore, the thickness of the torsion bar  31  is thinner than that of the arm portion  12  and also thinner than that of the first layer portion  21  of the frame  20  in the thickness direction H of the element as illustrated in  FIGS. 3 and 4 . The torsion connection portion  30  and the pair of torsion bars  31  configured as described above are used to determine the axial center line A 1  of the rotation operation of the rocking portion  10  and the mirror-supporting portion  11 . The axial center line A 1  orthogonally intersects the direction of the arrow D illustrated in  FIG. 1 , that is, the extension direction of the arm portion  12 . Hence, the extension directions of the above-mentioned electrode teeth  13   a  and  13   b  extending from the arm portion  12  in a direction orthogonal to the extension direction of the arm portion  12  are parallel to the axial center line A 1 . It is preferable that the axial center line A 1  passes through the center of gravity of the rocking portion  10  or its proximity. 
     In this embodiment, one set of torsion bars formed on the first silicon layer and arranged in parallel may also be provided instead of the respective torsion bars  31 . In this case, it is preferable that the interval of the one set of torsion bars increases gradually in the direction from the frame  20  to the arm portion  12 . In the micro movable element X 1 , it may be possible that the axial center line A 1  is determined by providing two sets of two torsion bars arranged in parallel as described above instead of the pair of torsion bars  31 . This is similarly applicable to micro movable elements described later. 
     The comb electrode  41  is a portion that cooperates with the comb electrode  13 A to generate an electrostatic attractive force and includes multiple electrode teeth  41   a  derived from the second silicon layer. The respective multiple electrode teeth  41   a  extend from the second layer portion  22  of the frame  20  and are arranged in parallel while being spaced mutually in the extension direction of the arm portion  12 . In this embodiment, the extension direction of the electrode teeth  41   a  is orthogonal to the extension direction of the arm portion and is parallel to the axial center line A 1  as illustrated in  FIG. 1 . 
     The drive mechanism of the element has the comb electrode  41  and the comb electrode  13 A. The comb electrodes  13 A and  41  are positioned at heights different from each other as illustrated in  FIGS. 3 and 5 , for example, when the rocking portion  10  is not operating. In addition, the comb electrodes  13 A and  41  are disposed so that their electrode teeth  13   a  and  41   a  are displaced so as not to make mutual contact when the rocking portion  10  is operating. 
     The comb electrode  42  is a portion that cooperates with the comb electrode  13 B to generate an electrostatic attractive force and includes multiple electrode teeth  42   a  derived from the second silicon layer. The respective multiple electrode teeth  42   a  extend from the second layer portion  22  of the frame  20  and are spaced mutually in the extension direction of the arm portion  12 . The comb electrode  42  including the electrode teeth  42   a  is electrically connected to the comb electrode  41  including the electrode teeth  41   a  via the main portion  22 A of the second layer portion  22  of the frame  20 . In this embodiment, the extension direction of the electrode teeth  42   a  is orthogonal to the extension direction of the arm portion  12  and is parallel to the axial center line A 1  as illustrated in  FIG. 1 . 
     The drive mechanism of the element has the comb electrode  42  and the comb electrode  13 B. The comb electrodes  13 B and  42  are positioned at heights different from each other as illustrated in  FIGS. 4 and 5 , for example, when the rocking portion  10  is not operating. In addition, the comb electrodes  13 B and  42  are disposed so that their electrode teeth  13   b  and  42   a  are displaced so as not to make mutual contact when the rocking portion  10  is operating. 
     The micro movable element X 1  includes a partly laminated structure portion according to this embodiment as illustrated in  FIGS. 6 and 7 . 
     The partly laminated structure portion illustrated in  FIG. 6  has a conductor portion  21   a , a conductor portion  22   a  and an intermediate insulating portion  23   a . The first layer portion  21  of the frame  20  includes the conductor portion  21   a . The main portion  22 A of the second layer portion  22  includes the conductor portion  22   a . The intermediate insulating layer  23  includes the intermediate insulating portion  23   a . The conductor portion  21   a  (the first layer portion  21 ) is electrically connected to the comb electrodes  13 A and  13 B via the torsion bars  31  and the arm portion  12  of the rocking portion  10 . The torsion connection portion  30  includes the torsion bars  31 . The conductor portion  22   a  (the main portion  22 A of the second layer portion  22 ) is electrically connected to the comb electrodes  41  and  42 . The conductor portion  21   a  is electrically isolated from the conductor portion  22   a . Furthermore, the conductor portion  22   a  has an opposed face S 1  opposed to the conductor portion  21   a , a side face S 2  and an edge portion E 1  forming the boundary therebetween. The conductor portion  21   a  has an extending face S 3  extending beyond the edge portion E 1  of the conductor portion  22   a . The insulating film  50  is provided so as to cover the edge portion E 1  of the conductor portion  22   a.    
     The partly laminated structure portion illustrated in  FIG. 7  has a conductor portion  21   b , a conductor portion  22   b  and an intermediate insulating portion  23   b . The first layer portion  21  of the frame  20  includes the conductor portion  21   b . The main portion  22 A of the second layer portion  22  includes the conductor portion  22   b . The intermediate insulating layer  23  includes the intermediate insulating portion  23   b . The conductor portion  21   b  (the first layer portion  21 ) is electrically connected to the comb electrodes  13 A and  13 B via the torsion bars  31  and the arm portion  12  of the rocking portion  10 . The torsion connection portion  30  includes the torsion bars  31 . The conductor portion  22   b  (the main portion  22 A of the second layer portion  22 ) is electrically connected to the comb electrodes  41  and  42 . The conductor portion  21   b  is electrically isolated from the conductor portion  22   b . Furthermore, the conductor portion  21   b  has an opposed face S 4  opposed to the conductor portion  22   b , a side face S 5  and an edge portion E 2  forming the boundary therebetween. The conductor portion  22   b  has an extending face S 6  extending beyond the edge portion E 2  of the conductor portion  21   b . The insulating film  50  is provided so as to cover the edge portion E 2  of the conductor portion  21   b.    
     The insulating film  50  is provided so as to cover the edge portion (a portion in which a level difference is formed between a portion derived from the first silicon layer and a portion derived from the second silicon layer and in which a potential difference is generated between the portion derived from the first silicon layer and the portion derived from the second silicon layer in this embodiment) of the partly laminated structure portion included in the micro movable element X 1  as illustrated in  FIGS. 6 and 7 . The insulating film  50  is made of, for example, parylene, silicon oxide or silicon nitride. The thickness of the insulating film  50  is, for example, 10 to 500 nm. 
       FIGS. 8A to 8D  to  FIGS. 11A to 11C  illustrate an example of a method for producing the micro movable element X 1 . This method is a method for producing the micro movable element X 1  using the bulk micromachining technology. In  FIGS. 8A to 8D  to  FIGS. 11A to 11C , the process for forming a mirror-supporting portion M, an arm portion AR, frames F 1  and F 2 , torsion bars T 1  and T 2  and a pair of comb electrodes E 1  and E 2  illustrated in  FIG. 11C  is illustrated as changes in one cross-section. The one cross-section is obtained by modeling the multiple cross-sections included in one micro movable element forming compartment in a material substrate (a wafer having a multilayer structure) to be processed and by representing them as a continuous cross-section. The mirror-supporting portion M corresponds to part of the mirror-supporting portion  11 . The arm portion AR corresponds to part of the arm portion  12  and represents the transverse cross-section of the arm portion  12 . The frames F 1  and F 2  respectively correspond to the frame  20  and represent the transverse cross-section of the frame  20 . The torsion bar T 1  corresponds to the torsion bar  31  and represents the cross-section of the torsion bar  31  in the extension direction thereof. The torsion bar T 2  corresponds to the torsion bar  31  and represents the transverse cross-section of the torsion bar  31 . The comb electrode E 1  corresponds to parts of the comb electrodes  13 A and  13 B and represents the transverse cross-sections of the electrode teeth  13   a  and  13   b . The comb electrode E 2  corresponds to parts of the comb electrodes  41  and  42  and represents the transverse cross-sections of the electrode teeth  41   a  and  42   a.    
     In the production of the micro movable element X 1 , first, a material substrate  100  illustrated in  FIG. 8A  is prepared. The material substrate  100  is an SOI substrate having a laminated structure including silicon layers  101  and  102  and an insulating layer  103  disposed between the silicon layers  101  and  102 . The silicon layers  101  and  102  are made of a silicon material to which electrical conductivity is imparted by impurity doping. As impurities, p-type impurities, such as B, and n-type impurities, such as P and Sb, may be adopted. The insulating layer  103  is made of, for example, silicon oxide. The thickness of the silicon layer  101  is, for example, 10 to 100 μm, the thickness of the silicon layer  102  is, for example, 50 to 500 μm, and the thickness of the insulating layer  103  is, for example, 0.3 to 3 μm. Furthermore, the above-mentioned conductive plug  25  is formed so as to be embedded in the material substrate  100 . The conductive plug  25  may be formed, for example, by forming a plug-forming concave portion passing through the silicon layer  101  and the insulating layer  103  and then by filling the concave portion with a conductive material. 
     Next, as illustrated in  FIG. 8B , the mirror face  11   a  is formed on the silicon layer  101 , and the electrode pads  24 A and  24 B are formed on the silicon layer  102 . When the mirror face  11   a  is formed, first, for example, a Cr film (50 nm) is formed on the silicon layer  101  and then an Au film (200 nm) is formed thereon using the sputtering method. Next, the mirror face  11   a  is pattern-formed by sequentially etching these metal films via a mask. As an etching solution for Au, it is possible to use an aqueous potassium iodide-iodine solution, for example. As an etching solution for Cr, it is possible to use the mixture solution of an aqueous ceric ammonium nitrate solution and perchloric acid, for example. The electrode pads  24 A and  24 B are formed by forming a film of a conductive material on the surface of the silicon layer  102  using the sputtering method and then by etching the film of the conductive material via a mask. 
     Next, as illustrated in  FIG. 8C , an oxide film pattern  110  and a resist pattern  111  are formed on the silicon layer  101 , and an oxide film pattern  112  is then formed on the silicon layer  102 . The oxide film pattern  110  has a pattern shape corresponding to the rocking portion  10  (the mirror-supporting portion M, the arm portion AR and the comb electrode E 1 ) and the frame  20  (the frames F 1  and F 2 ). The oxide film pattern  110  configured as described above is formed using the CVD method, for example. The resist pattern  111  has a pattern shape corresponding to both the torsion bars  31  (the torsion bars T 1  and T 2 ). The resist pattern  111  configured as described above may be formed by forming a film of photoresist on the silicon layer  101  using the spin-coating method, by exposing the photoresist to light through a mask and by developing the photoresist using a developing solution. Furthermore, an oxide film pattern  112  has a pattern shape corresponding to the frame  20  (the frames F 1  and F 2 ) and the comb electrodes  41  and  42  (the comb electrode E 2 ). 
     Next, as illustrated in  FIG. 8D , the silicon layer  101  is etched to a given depth according to the DRIE (deep reactive ion etching) method by using the oxide film pattern  110  and the resist pattern  111  as masks. The given depth is a depth corresponding to the thickness of the torsion bars T 1  and T 2 , for example, 5 μm. In the DRIE method, proper anisotropic etching may be carried out in the Bosch process in which the etching performed using SF6 gas and the side wall protection performed using C4F8 gas are repeated alternately. Even in the DRIE method described later, the Bosch process described above may be adopted. Degradation occurring in the oxide film pattern  110  and the resist pattern  111  during the etching treatment is not illustrated for the sake of simplicity of the drawing. 
     Next, as illustrated in  FIG. 9A , the resist pattern  111  is removed by reacting a removing solution therewith. As the removing solution, it is possible to use AZ remover  700  (made by AZ Electronic Materials), for example. 
     Next, as illustrated in  FIG. 9B , the silicon layer  101  is etched until the insulating layer  103  is reached while the torsion bars T 1  and T 2  are formed so as to remain according to the DRIE method by using the oxide film pattern  110  as a mask. By this etching treatment, parts of the rocking portion  10  (the mirror-supporting portion M, the arm portion AR and the comb electrode E 1 ), both the torsion bars  31  (the torsion bars T 1  and T 2 ) and the frame  20  (the frames F 1  and F 2 ) are formed. Degradation occurring in the oxide film pattern  110  during the etching treatment is not illustrated for the sake of simplicity of the drawing. 
     Next, as illustrated in  FIG. 9C , the silicon layer  102  is etched until the insulating layer  103  is reached according to the DRIE method by using the oxide film pattern  112  as a mask. By this etching treatment, part of the frame  20  (the frames F 1  and F 2 ) and the comb electrodes  41  and  42  (the comb electrode E 2 ) are formed. Degradation occurring in the oxide film pattern  112  during the etching treatment is not illustrated for the sake of simplicity of the drawing. 
     Next, as illustrated in  FIG. 9D , the sites and the oxide film patterns  110  and  112  exposed on the insulating layer  103  are removed. As a removing method, it is possible to adopt dry etching or wet etching, for example. In the case that dry etching is adopted, it is possible to adopt, for example, CF4 and CHF3, as etching gases. In the case that wet etching is adopted, it is possible to use, for example, buffered hydrofluoric acid (BHF) containing hydrofluoric acid and ammonium fluoride, as an etching solution. At this step, a so-called undercut is apt to occur between the portions derived from the silicon layers  101  and  102  in the above-mentioned partly laminated structure portion included in the micro movable element X 1 . 
     Next, as illustrated in  FIG. 10A , the insulating film  50  is formed. More specifically, the insulating film  50  may be formed by forming a film of an insulating material using the thin-film forming technology. For example, in the case that parylene is used as the material of the insulating film  50 , the insulating film  50  may be formed properly using the CVD method. More specifically, the insulating film  50  may be formed from polymeric para-xylylene resin by polymerizing para-xylylene monomer on the surface of an element using the CVD method. Since the insulating film  50  formed of this kind of a parylene film is generated by polymerizing a gas of a low-molecular-weight monomer on the surface of a substance, the insulating film  50  becomes a uniform coating film (conformal coating film) being thin and having a shape following the minute uneven shape of the surface of the substance. For example, in the case that silicon oxide is adopted as the material of the insulating film  50 , the insulating film  50  may be formed properly by performing the oxygen plasma treatment. 
     Next, as illustrated in  FIG. 10B , a resist mask  113  is formed by spraying a photoresist in one direction. At this step, the resist mask  113  is apt to be formed thick at the level difference portion of the partly laminated structure portion. As a photoresist that may form a resist mask using the spraying method, it is possible to use AZ6112 (made by AZ Electronic Materials), for example. 
     Next, as illustrated in  FIG. 10C , a resist mask  114  is formed by spraying a photoresist in another direction. At this step, the resist mask  114  is apt to be formed thick at the level difference portion of the partly laminated structure portion. 
     Next, as illustrated in  FIG. 11A , part of the resist mask is removed by etching and part of the insulating film  50  is also removed by etching by carrying out the RIE (reactive ion etching) method using oxygen plasma or the like in one direction. At this step, the etching treatment is carried out so that part of the resist mask  113  formed sufficiently thickly at the level difference portion of the partly laminated structure portion at the step described above referring to  FIG. 10B  remains. 
     Next, as illustrated in  FIG. 11B , part of the resist mask is removed by etching and part of the insulating film  50  is also removed by etching by carrying out the RIE method in another direction. At this step, the etching treatment is carried out so that part of the resist mask  114  formed sufficiently thickly at the level difference portion of the partly laminated structure portion at the step described above referring to  FIG. 10C  remains. Furthermore, the etching conditions at this step are made different from the etching conditions at the previous step as necessary. For example, at this step, the etching conditions, such as etching time, gas pressure inside the chamber of an etching apparatus and applied electric power, different from those at the previous step are adopted, and the etching rate and anisotropy are adjusted, whereby it is possible to carry out a desired etching treatment suited for this step. 
     Next, as illustrated in  FIG. 11C , the remaining resist masks  113  and  114  are removed. As a result, the insulating film  50  is formed so as to remain in the partly laminated structure portion included in the micro movable element X 1 . 
     The mirror-supporting portion M, the arm portion AR, the frames F 1  and F 2 , the torsion bars T 1  and T 2  and one set of the comb electrodes E 1  and E 2  are formed and the insulating film  50  is also formed by carrying out the sequence of the above-mentioned steps, whereby the micro movable element X 1  is produced. 
     In the micro movable element X 1 , the rocking portion  10  including the mirror-supporting portion  11  is rotationally displaced around the axial center line A 1  by applying potentials to the comb electrodes  13 A,  13 B,  41  and  42  as necessary. The potentials to be applied to the comb electrodes  13 A and  13 B are applied via the electrode pad  24 B, the land portion  22 B of the second layer portion  22  of the frame  20 , the conductive plug  25 , the first layer portion  21  of the frame  20 , the torsion connection portion  30  including both the torsion bars  31 , and the arm portion  12 . The comb electrodes  13 A and  13 B are connected to the ground, for example. On the other hand, the potentials to be applied to the comb electrodes  41  and  42  are applied via the electrode pad  24 A and the main portion  22 A of the second layer portion  22  of the frame  20 . 
     When a desired electrostatic attractive force is generated between the comb electrodes  13 A and  41  and between the comb electrodes  13 B and  42  by applying potentials to the comb electrodes  13 A,  13 B,  41  and  42 , the comb electrode  13 A is pulled into the comb electrode  41 , and the comb electrode  13 B is pulled into the comb electrode  42 . Hence, the rocking portion  10  including the mirror-supporting portion  11  is rocked around the axial center line A 1  and rotationally displaced to an angle at which the electrostatic attractive force is balanced with the total of the torsion-resisting forces of the torsion bars  31 . In this balanced state, the comb electrodes  13 A and  41  are oriented as illustrated in  FIG. 12  and the comb electrodes  13 B and  42  are also oriented similarly, for example. The rotational displacement amount of the rocking operation is controlled by adjusting the potentials applied to the comb electrodes  13 A,  13 B,  41  and  42 . Furthermore, when the electrostatic attractive force between the comb electrodes  13 A and  41  and the electrostatic attractive force between the comb electrodes  13 B and  42  are eliminated, the respective torsion bars  31  return to their original states, and the rocking portion  10  including the mirror-supporting portion  11  is oriented as illustrated in  FIGS. 3 and 4 . The reflection direction of the light reflected using the mirror face  11   a  provided on the mirror-supporting portion  11  is changed as necessary by the above-mentioned rocking operation of the rocking portion  10  including the mirror-supporting portion  11 . 
     In the micro movable element X 1 , in the case that a potential difference is generated between the first conductor portion (the conductor portion  22   a  in the partly laminated structure portion illustrated in  FIG. 6  or the conductor portion  21   b  in the partly laminated structure portion illustrated in  FIG. 7 ) and the second conductor portion (the conductor portion  21   a  in the partly laminated structure portion illustrated in  FIG. 6  or the conductor portion  22   b  in the partly laminated structure portion illustrated in  FIG. 7 ), the insulating film  50  provided for the partly laminated structure portion suppresses discharge from occurring between the edge portion (the edge portion E 1  in the partly laminated structure portion illustrated in  FIG. 6  or the edge portion E 2  in the partly laminated structure portion illustrated in  FIG. 7 ) of the first conductor portion and the second conductor portion including its extending face (the extending face S 3  in the partly laminated structure portion illustrated in  FIG. 6  or the extending face S 6  in the partly laminated structure portion illustrated in  FIG. 7 ). The insulating film  50  configured as described above suppresses the edge portion from being eluted by the heat generated at the time of discharge and from forming an electrically-conducting path for bridging the distance between the first and second conductor portions, thereby suppressing current from flowing through such an electrically-conducting path (current leakage) in the case that a potential difference is generated between the first and second conductor portions when the element is driven. 
     In addition, in the case that a potential difference is generated between the first and second conductor portions, the insulating film  50  of the micro movable element X 1  suppresses a fraction of the first conductor portion from peeling off from the side face near the edge portion of the first conductor portion. The insulating film  50  configured as described above suppresses current leakage between the first and second conductor portions owing to the movement of the fraction or the bridging of the distance between the first and second conductor portions via the fraction. 
     Furthermore, in the micro movable element X 1 , the comb electrodes  13 A,  13 B,  41  and  42  for generating an electrostatic attractive force serving as a driving force is not covered with the insulating film. For this reason, the charging described above with respect to the micro movable element Y does not occur in the micro movable element X 1 . In the micro movable element X 1  configured as described above, a stable driving force may be generated easily using the comb electrodes  13 A,  13 B,  41  and  42  serving as driving electrodes. Hence, the micro movable element X 1  is suited to accurately control the driving force. 
     As described above, the micro movable element X 1  is suited to suppress current leakage from occurring and also suited to accurately control the driving force generated between the driving electrodes. 
     Second Embodiment 
       FIGS. 13 to 16  illustrate a micro movable element X 2  according to a second embodiment.  FIG. 13  is a sectional view of the micro movable element X 2 , corresponding to  FIG. 3  illustrating the above-mentioned micro movable element X 1 .  FIG. 14  is another sectional view of the micro movable element X 2 , corresponding to  FIG. 4  illustrating the above-mentioned micro movable element X 1 .  FIG. 15  is still another sectional view of the micro movable element X 2 , corresponding to FIG.  6  illustrating the above-mentioned micro movable element X 1 .  FIG. 16  is yet still another sectional view of the micro movable element X 2 , corresponding to  FIG. 7  illustrating the above-mentioned micro movable element X 1 . 
     The micro movable element X 2  is a micro movable element equipped with the rocking portion  10 , the frame  20 , the torsion connection portion  30  and the comb electrodes  41  and  42  as in the case of the micro movable element X 1 . However, the regions on which the insulating film  50  is formed are different from those in the micro movable element X 1 . In the micro movable element X 2 , the insulating film  50  does not cover the face of the mirror-supporting portion  11  on which the mirror face  11   a  is formed, the comb electrodes  13 A,  13 B,  41  and  42  and the electrode pads  24 A and  24 B on the surface of the second layer portion  22  of the frame  20 . 
     In the production of the micro movable element X 2  configured as described above, the sequence of the steps described above referring to  FIGS. 8A to 10A  for the production of the micro movable element X 1  is carried out first. 
     Next, as illustrated in  FIG. 17A , the insulating film  50  is partially removed by irradiating a laser beam to the silicon layer  101  of the material substrate  100 . More specifically, a laser beam is irradiated to regions, from which the insulating film  50  is desired to be removed, via a mask (not illustrated) having openings, thereby removing the insulating film  50  from the irradiated sites.  FIG. 18  is a plan view of the element, in which the laser beam irradiated regions at this step are indicated so as to be enclosed by broken lines. The laser beam irradiation in a micro movable element forming compartment may be carried out once or in multiple times. It is preferable to use the excimer laser beam as the laser beam. It is also preferable that the laser beam irradiation to at least the comb electrodes E 1  and E 2  (the comb electrodes  13 A,  13 B,  41  and  42 ) is inclined with respect to the thickness direction of the material substrate  100  as indicated by inclined arrows in  FIG. 17A . The irradiation direction is inclined to properly remove the insulating film  50  covering the side faces of the comb electrodes E 1  and E 2 . 
     Next, as illustrated in  FIG. 17B , the insulating film  50  is partially removed by irradiating a laser beam to the silicon layer  102  of the material substrate  100 . More specifically, a laser beam is irradiated to regions, from which the insulating film  50  is desired to be removed, via a mask (not illustrated) having openings, thereby removing the insulating film  50  from the irradiated sites. It is preferable that the laser beam irradiation to at least the comb electrodes E 1  and E 2  (the comb electrodes  13 A,  13 B,  41  and  42 ) is inclined with respect to the thickness direction of the material substrate  100  as indicated by inclined arrows in  FIG. 17B . The irradiation direction is inclined to properly remove the insulating film  50  covering the side faces of the comb electrodes E 1  and E 2 . 
     The mirror-supporting portion M, the arm portion AR, the frames F 1  and F 2 , the torsion bars T 1  and T 2  and one set of the comb electrodes E 1  and E 2  are formed and the insulating film  50  is also formed so as to remain by carrying out the sequence of the above-mentioned steps, whereby the micro movable element X 2  may be produced. 
     The micro movable element X 2  configured as described above may perform rocking operation in a way similar to that for the micro movable element X 1 . 
     Furthermore, in the micro movable element X 2 , the edge portions of the partly laminated structure portion are covered with the insulating film  50 , but the comb electrodes  13 A,  13 B,  41  and  42  are not covered with the insulating film  50 . Hence, because of reasons similar to those described above with respect to the micro movable element X 1 , the micro movable element X 2  is suited to suppress current leakage from occurring and also suited to accurately control the driving force generated between the driving electrodes when the element is driven. 
     Third Embodiment 
       FIGS. 19 to 20  illustrate a micro movable element X 3  according to a third embodiment.  FIG. 19  is a sectional view of the micro movable element X 3 , corresponding to  FIG. 3  illustrating the above-mentioned micro movable element X 1  and also corresponding to  FIG. 13  illustrating the above-mentioned micro movable element X 2 .  FIG. 20  is another sectional view of the micro movable element X 3 , corresponding to  FIG. 4  illustrating the above-mentioned micro movable element X 1  and also corresponding to  FIG. 14  illustrating the above-mentioned micro movable element X 2 . 
     The micro movable element X 3  is a micro movable element equipped with the rocking portion  10 , the frame  20 , the torsion connection portion  30  and the comb electrodes  41  and  42  as in the case of the micro movable elements X 1  and X 2 . However, the regions on which the insulating film  50  is formed are different from those in the micro movable elements X 1  and X 2 . In the micro movable element X 3 , the insulating film  50  does not cover the face of the mirror-supporting portion  11  on which the mirror face  11   a  is formed, parts of the comb electrodes  13 A,  13 B,  41  and  42  and the electrode pads  24 A and  24 B on the surface of the second layer portion  22  of the frame  20 . Furthermore, in the micro movable element X 3 , some of the electrode teeth  13   a  on the side of the axial center line A 1  among the multiple electrode teeth  13   a  of the comb electrode  13 A are covered with the insulating film  50 , some of the electrode teeth  13   b  on the side of the axial center line A 1  among the multiple electrode teeth  13   b  of the comb electrode  13 B are covered with the insulating film  50 , some of the electrode teeth  41   a  on the side of the axial center line A 1  among the multiple electrode teeth  41   a  of the comb electrode  41  are covered with the insulating film  50 , and some of the electrode teeth  42   a  on the side of the axial center line A 1  among the multiple electrode teeth  42   a  of the comb electrode  42  are covered with the insulating film  50 . 
     The micro movable element X 3  configured as described above may be produced in a way similar to that for the micro movable element X 2  except that the regions illustrated in  FIG. 18  and irradiated at the laser beam irradiation step described above referring to  FIGS. 17A and 17B  are changed to the regions illustrated in  FIG. 21  (the regions enclosed by broken lines). 
     The micro movable element X 3  produced as described above may be driven, for example, as illustrated in  FIG. 22  in a way similar to that for the micro movable element X 1 . 
     Furthermore, in the micro movable element X 3 , the edge portions of the partly laminated structure portion are covered with the insulating film  50 , but parts of the comb electrodes  13 A,  13 B,  41  and  42  are not covered with the insulating film  50 . Hence, because of reasons similar to those described above with respect to the micro movable element X 1 , the micro movable element X 3  is suited to suppress current leakage from occurring and also suited to accurately control the driving force generated between the driving electrodes when the element is driven. As the electrode teeth  13   a ,  14   a ,  41   a  and  42   a  of the comb electrodes  13 A,  13 B,  41  and  42  are disposed closer to the axial center line A 1 , the extent to which the electrode teeth substantially overlap with those opposed thereto at the time of driving is smaller. Even if the electrode teeth configured as described above are coated with the insulating film  50 , the extent of the charging generated on the insulating film  50  is considerably small in many cases. In such a case, it may be possible that some of the electrode teeth inside a single comb electrode are covered with an insulating film as in the case of the micro movable element X 3 . 
     Fourth Embodiment 
       FIGS. 23 to 28  illustrate a micro movable element X 4  according to a fourth embodiment.  FIG. 23  is a plan view of the micro movable element X 4 .  FIG. 24  is a partially omitted plan view of the micro movable element X 4 .  FIGS. 25 and 26  are sectional views taken on line XXV-XXV and line XXVI-XXVI of  FIG. 23 , respectively.  FIGS. 27 and 28  are enlarged sectional views taken on line XXVII-XXVII and line XXVIII-XXVIII of  FIG. 23 , respectively. 
     The micro movable element X 4  is a micromirror element equipped with a movable function portion  60 , an inner frame  70 , an outer frame  74 , a pair of torsion bars  81 , a pair of torsion bars  82 , comb electrodes  91 ,  92 ,  93 ,  94 ,  95 ,  96 ,  97  and  98  and an insulating film  50 . The micro movable element X 4  is produced by processing a material substrate serving as an SOI substrate using the bulk micromachining technology, such as the MEMS technology. The material substrate has a laminated structure comprising first and second silicon layers and an intermediate insulating layer disposed between the silicon layers, and electrical conductivity is imparted to the silicon layers by impurity doping. The above-mentioned portions except for the insulating film  50  in the micro movable element X 4  are portions mainly derived from the first silicon layer and/or the second silicon layer. However, in  FIG. 23 , for the sake of clarification of the drawing, the portions derived from the first silicon layer and protruding upright from the intermediate insulating layer toward the front side of the sheet of the drawing are hatched with oblique lines. Furthermore,  FIG. 24  illustrates a structure derived from the second silicon layer of the micro movable element X 4 . 
     The movable function portion  60  is a portion derived from the first silicon layer, and its surface is provided with a mirror face  61  having a light-reflecting function. The mirror face  61  has, for example, a laminated structure having a Cr layer formed on the first silicon layer and an Au layer formed thereon. 
     The inner frame  70  has a laminated structure including a first layer portion  71 , a second layer portion  72  and an insulating layer  73  disposed therebetween as illustrated in  FIG. 25 . The first layer portion  71  is a portion derived from the first silicon layer and has a shape enclosing the movable function portion  60  as illustrated in  FIG. 23 . The second layer portion  72  is a portion derived from the second silicon layer. 
     The outer frame  74  has a shape enclosing the inner frame  70  as illustrated in  FIG. 23 , and has a laminated structure including a first layer portion  75 , a second layer portion  76  and an insulating layer  77  disposed therebetween as illustrated in  FIGS. 25 and 26 . The first layer portion  75  is a portion derived from the first silicon layer. The second layer portion  76  is a portion derived from the second silicon layer. The second layer portion  76  includes land portions  76 A,  76 B,  76 C,  76 D and  76 E that are separated mutually by a space as illustrated in  FIG. 24 . Electrode pads  78 A,  78 B,  78 C,  78 D and  78 E for external connection are provided on the surfaces of the land portions  76 A,  76 B,  76 C,  76 D and  76 E, respectively. The land portion  76 A is electrically connected to the first layer portion  75  via a conductive plug  79  passing through the insulating layer  77 . 
     Each of the pair of torsion bars  81  is thinner than that of the movable function portion  60  as well illustrated in  FIG. 26  and is connected to the movable function portion  60  and the first layer portion  71  of the inner frame  70 . The pair of torsion bars  81  determines the axial center line A 2  of the rotation operation of the movable function portion  60 . 
     Each of the pair of torsion bars  82  has a laminated structure including a first layer portion  82   a  derived from the first silicon layer, a second layer portion  82   b  derived from the second silicon layer and an insulating layer  82   c  disposed therebetween as illustrated in  FIG. 25 . The first layer portion  82   a  is electrically isolated from the second layer portion  82   b  using the insulating layer  82   c . The first layer portion  82   a  of each of the pair of torsion bars  82  is connected to the first layer portion  71  of the inner frame  70  and the first layer portion  75  of the outer frame  74 . The second layer portion  82   b  of one of the torsion bars  82  is connected to one of the second layer portions  72  of the inner frame  70  and to the land portion  76 B of the second layer portion  76  of the outer frame  74 . The second layer portion  82   b  of the other torsion bar  82  is connected to the other second layer portions  72  of the inner frame  70  and the land portion  76 C of the second layer portion  76  of the outer frame  74 . The pair of torsion bars  82  configured as described above determines the axial center line A 3  of the rotation operation of the inner frame  70  and the rotation operation of the movable function portion  60  associated therewith. 
     The comb electrode  91  is a portion derived from the first silicon layer and includes multiple electrode teeth  91   a  extending from the movable function portion  60 . The electrode teeth  91   a  are arranged in parallel while being spaced mutually in the direction of the axial center line A 2 . The comb electrode  92  is a portion derived from the first silicon layer and includes multiple electrode teeth  92   a  extending from the movable function portion  60  on the opposite side of the electrode teeth  91   a  of the comb electrode  91 . The electrode teeth  92   a  are arranged in parallel while being spaced mutually in the direction of the axial center line A 2 . 
     The comb electrode  93  is a portion that cooperates with the comb electrode  91  to generate an electrostatic attractive force and includes multiple electrode teeth  93   a  derived from the second silicon layer. The respective multiple electrode teeth  93   a  extend from one of the second layer portions  72  of the inner frame  70  toward the inside of the element and are arranged in parallel while being spaced mutually in the direction of the axial center line A 2 . The drive mechanism of the element has the comb electrode  93  and the comb electrode  91 . The comb electrodes  91  and  93  are positioned at heights different from each other as illustrated in  FIG. 25 , for example, when the movable function portion  60  is not operating. In addition, the comb electrodes  91  and  93  are disposed so that their electrode teeth  91   a  and  93   a  are displaced so as not to make mutual contact when the movable function portion  60  is operating. 
     The comb electrode  94  is a portion that cooperates with the comb electrode  92  to generate an electrostatic attractive force and includes multiple electrode teeth  94   a  derived from the second silicon layer. The respective multiple electrode teeth  94   a  extend from the other second layer portion  72  of the inner frame  70  toward the inside of the element and are arranged in parallel while being spaced mutually in the direction of the axial center line A 2 . The drive mechanism of the element has the comb electrode  94  and the comb electrode  92 . The comb electrodes  92  and  94  are positioned at heights different from each other as illustrated in  FIG. 25 , for example, when the movable function portion  60  is not operating. In addition, the comb electrodes  92  and  94  are disposed so that their electrode teeth  92   a  and  94   a  are displaced so as not to make mutual contact when the movable function portion  60  is operating. 
     The comb electrode  95  is a portion derived from the first silicon layer and includes multiple electrode teeth  95   a  extending from the first layer portion  71  of the inner frame  70  to the outside of the element. The electrode teeth  95   a  are arranged in parallel while being spaced mutually in the direction of the axial center line A 3 . The comb electrode  96  is a portion derived from the first silicon layer and includes multiple electrode teeth  96   a  extending from the first layer portion  71  of the inner frame  70  on the opposite side of the electrode teeth  95   a  of the comb electrode  95 . The electrode teeth  96   a  are arranged in parallel while being spaced mutually in the direction of the axial center line A 3 . 
     The comb electrode  97  is a portion that cooperates with the comb electrode  95  to generate an electrostatic attractive force and includes multiple electrode teeth  97   a  derived from the second silicon layer. The respective multiple electrode teeth  97   a  extend from the land portion  76 D of the second layer portion  76  of the outer frame  74  toward the inside of the element and are arranged in parallel while being spaced mutually in the direction of the axial center line A 3 . The drive mechanism of the element has the comb electrode  97  and the comb electrode  95 . The comb electrodes  95  and  97  are positioned at heights different from each other as illustrated in  FIG. 26 , for example, when the inner frame  70  is not operating. In addition, the comb electrodes  95  and  97  are disposed so that their electrode teeth  95   a  and  97   a  are displaced so as not to make mutual contact when the element is operating. 
     The comb electrode  98  is a portion that cooperates with the comb electrode  96  to generate an electrostatic attractive force and includes multiple electrode teeth  98   a  derived from the second silicon layer. The respective multiple electrode teeth  98   a  extend from the land portion  76 E of the second layer portion  76  of the outer frame  74  toward the inside of the element and are arranged in parallel while being spaced mutually in the direction of the axial center line A 3 . The drive mechanism of the element has the comb electrode  98  and the comb electrode  96 . The comb electrodes  96  and  98  are positioned at heights different from each other as illustrated in  FIG. 26 , for example, when the inner frame  70  is not operating. In addition, the comb electrodes  96  and  98  are disposed so that their electrode teeth  96   a  and  98   a  are displaced so as not to make mutual contact when the element is operating. 
     In the micro movable element X 4 , the insulating film  50  does not cover the face of the movable function portion  60  on which the mirror face  61  is formed, the comb electrodes  91 ,  92 ,  93 ,  94 ,  95 ,  96 ,  97  and  98  and the electrode pads  78 A to  78 E on the surface of the second layer portion  76  of the outer frame  74 . The insulating film  50  is not illustrated in figures other than  FIGS. 27 and 28  for the sake of simplicity of the drawings. 
     The micro movable element X 4  includes a partly laminated structure portion according to this embodiment as illustrated in  FIGS. 27 and 28 , for example. 
     The partly laminated structure portion illustrated in  FIG. 27  has a conductor portion  75   a , a conductor portion  76   a  and an intermediate insulating portion  77   a . The first layer portion  75  of the outer frame  74  includes the conductor portion  75   a . The land portion  76 B of the second layer portion  76  includes the conductor portion  76   a . The intermediate insulating layer  77  includes the intermediate insulating portion  77   a . The conductor portion  75   a  (the first layer portion  75 ) is electrically connected to the comb electrode  91  via the first layer portion  82   a  of the torsion bar  82 , the first layer portion  71  of the inner frame  70 , the torsion bar  81  and the movable function portion  60 . The conductor portion  76   a  (the land portion  76 B of the second layer portion  76 ) is electrically connected to the comb electrode  93  via the second layer portion  82   b  of the torsion bar  82  and the second layer portion  72  of the inner frame  70 . The conductor portion  75   a  is electrically isolated from the conductor portion  76   a . Furthermore, the conductor portion  76   a  has an opposed face S 7  opposed to the conductor portion  75   a , a side face S 8  and an edge portion E 3  forming the boundary therebetween. The conductor portion  75   a  has an extending face S 9  extending beyond the edge portion E 3  of the conductor portion  76   a . The insulating film  50  is provided so as to cover the edge portion E 3  of the conductor portion  76   a.    
     The partly laminated structure portion illustrated in  FIG. 28  has a conductor portion  75   b , a conductor portion  76   b  and an intermediate insulating portion  77   b . The first layer portion  75  of the outer frame  74  includes the conductor portion  75   b . The land portion  76 D of the second layer portion  76  includes the conductor portion  76   b . The intermediate insulating layer  77  includes the intermediate insulating portion  77   b . The conductor portion  75   b  (the first layer portion  75 ) is electrically connected to the comb electrode  95  via the first layer portion  82   a  of the torsion bar  82  and the first layer portion  71  of the inner frame  70 . The conductor portion  76   b  (the land portion  76 D of the second layer portion  76 ) is electrically connected to the comb electrode  97 . The conductor portion  75   b  is electrically isolated from the conductor portion  76   b . Furthermore, the conductor portion  76   b  has an opposed face S 10  opposed to the conductor portion  75   b , a side face S 11  and an edge portion E 4  forming the boundary therebetween. The conductor portion  75   b  has an extending face S 12  extending beyond the edge portion E 4  of the conductor portion  76   b . The insulating film  50  is provided so as to cover the edge portion E 4  of the conductor portion  76   b.    
     The insulating film  50  is provided so as to cover the edge portion (a portion in which a level difference is formed between a portion derived from the first silicon layer and a portion derived from the second silicon layer and in which a potential difference is generated between the portion derived from the first silicon layer and the portion derived from the second silicon layer in this embodiment) of the partly laminated structure portion included in the micro movable element X 4  as illustrated in  FIGS. 27 and 28 . The insulating film  50  is made of, for example, parylene, silicon oxide or silicon nitride. The thickness of the insulating film  50  is, for example, 10 to 500 nm. 
     In the micro movable element X 4 , the movable function portion  60  may be rotationally displaced around the axial center line A 2  by applying potentials to the comb electrodes  91 ,  92 ,  93  and  94  as necessary. The potentials to be applied to the comb electrodes  91  and  92  may be applied via the electrode pad  78 A, the land portion  76 A of the second layer portion  76  of the outer frame  74 , the conductive plug  79 , the first layer portion  75  of the outer frame  74 , the first layer portions  82   a  of both the torsion bars  82 , the first layer portion  71  of the inner frame  70 , both the torsion bars  81  and the movable function portion  60 . The comb electrodes  91  and  92  are connected to the ground, for example. The potential to be applied to the comb electrode  93  may be applied via the electrode pad  78 B, the land portion  76 B of the second layer portion  76  of the outer frame  75 , the second layer portion  82   b  of one of the torsion bars  82  and one of the second layer portions  72  of the inner frame  70 . The potential to be applied to the comb electrode  94  may be applied via the electrode pad  78 C, the land portion  76 C of the second layer portion  76  of the outer frame  75 , the second layer portion  82   b  of the other torsion bar  82  and the other second layer portion  72  of the inner frame  70 . 
     In the micro movable element X 4 , the inner frame  70  may be rotationally displaced and the movable function portion  60  may also be rotationally displaced while being associated with the displacement of the inner frame  70  around the axial center line A 3  by applying potentials to the comb electrodes  95 ,  96 , and  98  as necessary. The potentials to be applied to the comb electrodes  95  and  96  may be applied via the electrode pad  78 A, the land portion  76 A of the second layer portion  76  of the outer frame  74 , the conductive plug  79 , the first layer portion  75  of the outer frame  74 , the first layer portions  82   a  of both the torsion bars  82  and the first layer portion  71  of the inner frame  70 . The comb electrodes  95  and  96  are connected to the ground, for example. The potential to be applied to the comb electrode  97  may be applied via the electrode pad  78 D and the land portion  76 D of the second layer portion  76  of the outer frame  75 . The potential to be applied to the comb electrode  98  may be applied via the electrode pad  78 E and the land portion  76 E of the second layer portion  76  of the outer frame  75 . 
     In the micro movable element X 4 , the reflection direction of the light reflected using the mirror face  61  provided on the movable function portion  60  may be changed as necessary by the rocking operations of the movable function portion  60  and the inner frame  70  owing to the rotational displacements thereof around the axial center lines A 2  and A 3 . 
     The micro movable element X 4  is configured as a sensing device, such as an acceleration sensor or an angular velocity sensor. In the case that the micro movable element X 4  is a sensing device, it is not necessary to provide the mirror face on the movable function portion  60 . 
     When the micro movable element X 4  configured as a sensing device is driven, for example, the movable portions (the movable function portion  60 , the inner frame  70  and the comb electrodes  91  to  96 ) are rocked around the axial center line A 3  at a certain frequency or cycle. This rocking operation may be attained by alternately repeating the voltage application across the comb electrodes  95  and  97  and the voltage application across the comb electrodes  96  and  98 . In this embodiment, for example, the comb electrodes  95  and  96  are connected to the ground, and the potential application to the comb electrode  97  and the potential application to the comb electrode  98  are repeated alternately, thereby rocking the movable portions. 
     For example, in a state in which the movable portions are rocked or vibrated as described above, if an angular velocity or acceleration is exerted to the micro movable element X 4  including the movable function portion  60 , the movable function portion  60  is rotationally displaced around the axial center line A 2  together with the comb electrodes  91  and  92 . As a result, the relative positions of the comb electrodes  91  and  93  are changed, and the electrostatic capacitance between the comb electrodes  91  and  93  is changed. In addition, the relative positions of the comb electrodes  92  and  94  are changed, and the electrostatic capacitance between the comb electrodes  92  and  94  is changed. The rotational displacement amount of the movable function portion  60  is detected on the basis of the change in electrostatic capacitance (for example, on the basis of the difference between the two electrostatic capacitances). On the basis of the result of the detection, it is possible to calculate the angular velocity or acceleration exerted to the micro movable element X 4  including the movable function portion  60 . 
     In the micro movable element X 4 , in the case that a potential difference is generated between the first conductor portion (the conductor portion  76   a  in the partly laminated structure portion illustrated in  FIG. 27  or the conductor portion  76   b  in the partly laminated structure portion illustrated in  FIG. 28 ) and the second conductor portion (the conductor portion  75   a  in the partly laminated structure portion illustrated in  FIG. 27  or the conductor portion  75   b  in the partly laminated structure portion illustrated in  FIG. 28 ), the insulating film  50  provided for the partly laminated structure portion contributes to suppress discharge between the edge portion of the first conductor portion (the edge portion E 3  in the partly laminated structure portion illustrated in  FIG. 27  or the edge portion E 4  in the partly laminated structure portion illustrated in  FIG. 28 ) and the second conductor portion and its extending face (the extending face S 9  in the partly laminated structure portion illustrated in  FIG. 27  or the extending face S 12  in the partly laminated structure portion illustrated in  FIG. 28 ). The insulating film  50  configured as described above suppresses the edge portion from being eluted by the heat generated at the time of discharge and from forming an electrically-conducting path for bridging the distance between the first and second conductor portions, thereby suppressing current from flowing through such an electrically-conducting path (current leakage) in the case that a potential difference is generated between the first and second conductor portions when the element is driven. 
     In addition, in the case that a potential difference is generated between the first and second conductor portions, the insulating film  50  of the micro movable element X 4  suppresses a fraction of the first conductor portion from peeling off from the side face near the edge portion of the first conductor portion. The insulating film  50  configured as described above suppresses current leakage between the first and second conductor portions owing to the movement of the fraction or the bridging of the distance between the first and second conductor portions via the fraction. 
     Furthermore, in the micro movable element X 4 , the comb electrodes  91  to  98  for generating an electrostatic attractive force serving as a driving force are not covered with the insulating film. For this reason, the charging described with respect to the micro movable element Y does not occur in the micro movable element X 4 . In the micro movable element X 4  configured as described above, a stable driving force may be easily generated using the comb electrodes  91  to  98  serving as driving electrodes. Hence, the micro movable element X 4  is suited to accurately control the driving force. 
     As described above, the micro movable element X 4  is suited to suppress current leakage from occurring and also suited to accurately control the driving force generated between the driving electrodes. 
     The micro movable elements X 1  to X 4  configured as described above may be adopted as micromirror elements for use in optical switching apparatuses. 
     Fifth Embodiment 
       FIG. 29  illustrates the schematic configuration of an optical switching apparatus  500  of a space optical coupling type according to a fifth embodiment. The optical switching apparatus  500  is equipped with a pair of micromirror array units  501  and  502 , an input fiber array  503 , an output fiber array  504  and multiple micro lenses  505  and  506 . The input fiber array  503  is formed of a given number of input fibers  503   a , and the micromirror array unit  501  is provided with multiple micromirror elements  501   a  respectively corresponding to the input fibers  503   a . The output fiber array  504  is formed of a given number of output fibers  504   a , and the micromirror array unit  502  is provided with multiple micromirror elements  502   a  respectively corresponding to the output fibers  504   a . Each of the micromirror elements  501   a  and  502   a  has a mirror face for reflecting light, and the direction of the mirror face may be controlled. Each of micromirror elements  501   a  and  502   a  has the structure of either one of the above-mentioned micro movable elements X 1  to X 4 . Each of the multiple micro lenses  505  is disposed so as to be opposed to the end portion of each of the input fibers  503   a . Furthermore, each of the multiple micro lenses  506  is disposed so as to be opposed to the end portion of each of the output fibers  504   a.    
     In the optical switching apparatus  500 , the light beams L 1  emitted from the input fibers  503   a  pass through the corresponding micro lenses  505 , become mutually parallel and are directed to the micromirror array unit  501 . The light beams L 1  are reflected by the corresponding micromirror elements  501   a  and deflected toward the micromirror array unit  502 . At this time, the mirror face of the micromirror element  501   a  is oriented in the direction in which the light beam L 1  enters a desired micromirror element  502   a . Next, the light beam L 1  is reflected by the micromirror element  502   a  and deflected toward the output fiber array  504 . At this time, the mirror face of the micromirror element  502   a  is oriented in the direction in which the light beam L 1  enters a desired output fiber  504   a.    
     In the optical switching apparatus  500 , the light beam L 1  emitted from each input fiber  503   a  is deflected by the micromirror array units  501  and  502  and reaches the desired output fiber  504   a  as described above. In other words, the input fibers  503   a  and the output fibers  504   a  are connected in a one-to-one relationship. The output fiber  504   a  to which the light beam L 1  is transmitted is switched by changing the deflection angles of the micromirror elements  501   a  and  502   a  as necessary. 
     Large capacity, high speed, high reliability, etc. for switching operations are regarded as the characteristics required for an optical switching apparatus that is used to switch the transmission path of an optical signal transmitted via an optical fiber serving as a transmission medium from a fiber to another fiber. From these viewpoints, it is preferable to use a micromirror element produced using the micromachining technology as a switching element incorporated in the optical switching apparatus. The reason for this preference is that the micromirror element may perform switching so that an optical signal may be directly switched between the optical transmission path on the input side and the optical transmission path on the output side of an optical switching apparatus without converting the optical signal into an electrical signal, thereby being ideally suited to obtain the above-mentioned characteristics. 
     Sixth Embodiment 
       FIG. 30  illustrates the schematic configuration of an optical switching apparatus  600  of a wavelength selection type according to a sixth embodiment. The optical switching apparatus  600  is equipped with a micromirror array unit  601 , one input fiber  602 , three output fibers  603 , multiple micro lenses  604   a  and  604   b , a spectrometer  605  and a condenser lens  606 . The micromirror array unit  601  has multiple micromirror elements  601   a , and the multiple micromirror elements  601   a  are disposed in a row on the micromirror array unit  601 , for example. Each micromirror element  601   a  has a mirror face for light reflection, and the direction of the mirror face may be controlled. The micromirror element  601   a  has the structure of either one of the above-mentioned micro movable elements X 1  to X 4 . The micro lens  604   a  is disposed so as to be opposed to the end portion of the input fiber  602 . The micro lens  604   b  is disposed so as to be opposed to the end portion of the output fiber  603 . The spectrometer  605  is a reflection diffraction grating in which the intensity of diffraction of the reflected light is different depending on the wavelength. 
     In the optical switching apparatus  600 , the light beam L 2  (having mixed multiple wavelengths) emitted from the input fiber  602  passes through the micro lens  604   a  and becomes parallel. The light beam L 2  is reflected by the spectrometer  605  (at this time, reflected at different angles for respective wavelengths). The reflected light beam passes through the condenser lens  606 . At that time, in the micromirror array unit  601 , the light beam is condensed to the micromirror elements  601   a  corresponding to the wavelengths. The light beam having each wavelength is reflected by the corresponding micromirror element  601   a . At this time, the mirror face of the micromirror element  601   a  is oriented in the direction in which the light beam having the corresponding wavelength is transmitted to a desired output fiber  603 . The light beam reflected by the micromirror element  601   a  then enters the selected output fiber  603  via the condenser lens  606 , the spectrometer  605  and the micro lens  604   b . As a result, the light beam having the desired wavelength may be selected from the light beam L 2  using the optical switching apparatus  600 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to an illustration of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.