Abstract:
A capacitor manufacturing method provides variable capacitors whose capacitances remain stable under the influence of temperature change. Such a variable capacitor includes a fixed electrode, a movable electrode film facing the fixed electrode, and an anchor portion that provides partial connection between the fixed electrode and the movable electrode film. For making this variable capacitor, a first electrode is formed to serve as the fixed electrode. Then, an anchor portion is formed on the fixed electrode, and a sacrifice film is formed to cover the fixed electrode but partially expose the anchor portion. A second electrode is formed on the sacrifice film to serve as the movable electrode film, bonded to the anchor portion. Finally, the sacrifice film is removed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to variable capacitors, and to a method of making them. 
     2. Description of the Related Art 
     There is an increasing requirement in the field of radio communications apparatuses such as mobile telephones, for smaller high-frequency circuits or RF circuits in order to cope with increase in the number of parts necessary to be mounted for advanced functions. In response to the requirement, numerous efforts have been made for miniaturization of parts or devices which constitute the circuits, using MEMS (micro-electromechanical systems) technologies. Variable capacitors are one of such parts. Variable capacitors are essential in variable frequency transmitters, tuning amplifiers, impedance matcher circuits and so on. Variable capacitors manufactured by using the MEMS technology are disclosed in the following Patent Documents 1 and 2 for example.
         Patent Document 1: JP-A-2004-6588   Patent Document 2: JP-A-2004-127973       

       FIG. 86  is a partial sectional view of a conventional variable capacitor Y. The variable capacitor Y includes a substrate  91 , a fixed electrode  92 , a movable electrode  93  and a pair of supporting portions  94 . The movable electrode  93  is formed to bridge the supporting portions  94 , and has a portion which faces the fixed electrode  92 . The substrate  91  is made of a silicon material, while the fixed electrode  92  and the movable electrode  93  are made of a metal material. 
     In the variable capacitor Y, an electrostatic attraction is generated when a voltage is applied between the fixed electrode  92  and the movable electrode  93 . By using the electrostatic attraction, it is possible to draw the movable electrode  93  toward the fixed electrode  92  thereby varying the distance between the fixed electrode  92  and the movable electrode  93 . The electrostatic capacitance of the variable capacitor Y, i.e. the electrostatic capacitance between the fixed electrode  92  and the movable electrode  93 , changes in accordance with the distance. Therefore, according to the variable capacitor Y, it is possible to vary the electrostatic capacitance by varying the voltage which is applied between the fixed electrode  92  and the movable electrode  93 . With such a structure, the variable capacitor Y is driven so that a predetermined voltage is applied between the fixed electrode  92  and the movable electrode  93  for obtaining a predetermined electrostatic capacitance. 
     In the conventional variable capacitor Y, temperature changes (e.g. a temperature increase) can easily cause the movable electrode  93  to curve as shown in  FIG. 87  and  FIG. 88  for example, even when the device is not being driven (when no voltage is applied between the fixed electrode  92  and the movable electrode  93 ). Such a curving of the movable electrode  93  is caused by a greater thermal expansion rate of the movable electrode  93  than that of the substrate  91 . 
     The distance between the movable electrode  93  and the fixed electrode  92  when the movable electrode  93  is already curved in the initial state (the state when the device is not driven) as shown in  FIG. 87  and  FIG. 88  is different from the distance between the movable electrode  93  and the fixed electrode  92  when the movable electrode  93  is not curved in the initial state as shown in  FIG. 86 . Presence or absence and the extent of the curvature of the movable electrode  93  in the non-operating state change the initial electrostatic capacitance of the variable capacitor Y in the non-operating state. Further, the presence or absence and the extent of the curvature of the movable electrode  93  in the non-operating state also change the relationship between the electrostatic capacitance and the driving voltage (the voltage to be applied in order to obtain a predetermined electrostatic capacitance) in the operation of the variable capacitor Y. The degree of change in these factors is relatively large in the conventional variable capacitor Y. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed under the above-described circumstances. It is therefore an object of the present invention to provide a variable capacitor suitable for reducing electrostatic capacitance inconsistency caused by temperature changes. Another object of the present invention is to provide a method of making such a variable capacitor. 
     According to a first aspect of the present invention, there is provided a variable capacitor. The variable capacitor includes a fixed electrode, a movable electrode film facing the fixed electrode, and an anchor portion (made of a dielectric material) which provides a partial connection between the fixed electrode and the movable electrode film. 
     According to the present variable capacitor, it is possible to generate an electrostatic attraction between the fixed electrode and the movable electrode film by applying a voltage between the fixed electrode and the movable electrode film, and by using the electrostatic attraction, it is possible to draw part of the movable electrode film toward the fixed electrode, excluding a region (junction) of the movable electrode film which is bonded to the anchor portion, and thereby varying the volume of a gap between the fixed electrode and the movable electrode film. (The amount or the distance of the drawing movement of the movable electrode film toward the fixed electrode is not uniform over the entire movable electrode film. The junction in the movable electrode film is not moved at all, and regions of the movable electrode film closer to the junction tend to be drawn by a smaller amount). The electrostatic capacitance of the variable capacitor, i.e. the electrostatic capacitance between the fixed electrode and the movable electrode film, varies in accordance with the gap volume. Therefore, according to the present variable capacitor, it is possible to control the electrostatic capacitance by controlling the drive voltage which is applied between the fixed electrode and the movable electrode film. 
     Further, according to the present variable capacitor, the movable electrode film is partially connected with or joined on the fixed electrode by the anchor portion. This reduces shape deformation or curving of the movable electrode film caused by temperature changes both in operation and in non-operation. For example, in a case where the fixed electrode is provided on a predetermined substrate, shape deformation or curving of the movable electrode film caused by temperature changes becomes less even if the thermal expansion rate of the movable electrode film differs from the thermal expansion rate of the substrate, and even if the difference is relatively large. Since curving of the movable electrode film is reduced in its initial shape (the shape in non-operation), inconsistency in initial electrostatic capacitance during non-operation is reduced in the present variable capacitor. Further, because of the reduced shape deformation of the movable electrode film caused by temperature changes both during operation and during non-operation, inconsistency in operational relationship between electrostatic capacitance and drive voltage is reduced also. As described, the present variable capacitor is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. The variable capacitor as described above is able to operate highly accurately. 
     Preferably, the anchor portion penetrates the fixed electrode and/or the movable electrode film. According to such an arrangement, at least one of the fixed electrode and the movable electrode film has a through hole or an opening to be fitted by the anchor portion. The fixed electrode does not have any portion which faces the movable electrode film via the anchor portion, nor does the movable electrode film have any portion which faces the fixed electrode via the anchor portion. In other words, there is no partial capacitor structure which has an invariable electrode-to-electrode distance via the anchor portion (and therefore has a fixed electrostatic capacitance). If a variable capacitor includes a partial capacitor structure which has a fixed electrostatic capacitance, a minimum electrostatic capacitance for the entire variable capacitor cannot be smaller than the fixed electrostatic capacitance. On the contrary, a variable capacitor which does not include any partial capacitor structure that has a fixed electrostatic capacitance does not have such a limitation to the minimum electrostatic capacitance for the entire variable capacitor. A variable capacitor which does not include any partial capacitor structure that has a fixed electrostatic capacitance is preferable when the device has to provide a small minimum electrostatic capacitance, and therefore preferable in achieving a large rate or amount of variation. As described, the arrangement where the anchor portion penetrates the fixed electrode and/or the movable electrode film is suitable for achieving a large rate or amount of variation. 
     Preferably, in the present variable capacitor, the fixed electrode is provided with a dielectric film on a side facing the movable electrode film and/or the movable electrode film is provided with a dielectric film on a side facing the fixed electrode. Such an arrangement as the above appropriately prevents direct contact between the fixed electrode and the movable electrode film. If a dielectric film is provided, then part of the dielectric film may constitute at least part of the anchor portion. 
     Preferably, the movable electrode film has a portion contactable with the fixed electrode via the dielectric film. Alternatively to or in addition to such an arrangement as the above, the movable electrode film may have a portion contacting with the fixed electrode via the dielectric film. These arrangements are suitable in achieving a large rate or amount of variation in the electrostatic capacitance. When embodying these arrangements, it is preferable that the movable electrode film has a portion curved toward the fixed electrode, or a portion curved away from the fixed electrode. 
     A second aspect of the present invention provides a variable capacitor. The variable capacitor includes: a first movable electrode film and a second movable electrode film facing each other; and an anchor portion (made of a dielectric material) which provides a partial connection between the mutually opposed first movable electrode film and second movable electrode film. 
     According to the present variable capacitor, it is possible to generate an electrostatic attraction between the first movable electrode film and the second movable electrode film by applying a voltage between the first movable electrode films and the second movable electrode film, and by using the electrostatic attraction, it is possible to draw the movable electrode films closely to each other, excluding the regions (junctions) of these movable electrode films which are bonded to the anchor portion, and thereby varying the volume of a gap between the movable electrode films. The electrostatic capacitance of the present variable capacitor, i.e. the electrostatic capacitance between the movable electrode films, varies in accordance with the gap volume. Therefore, according to the present variable capacitor, it is possible to control the electrostatic capacitance by controlling the drive voltage which is applied between the first and the second movable electrode films. 
     Further, according to the present variable capacitor, the first and the second movable electrode films are partially connected with or joined on each other by the anchor portion. This reduces shape deformation or curving of the first and the second movable electrode films caused by temperature changes both in operation and in non-operation. Since curving of both movable electrode films is reduced in their initial shapes (the shapes in non-operation), inconsistency in initial electrostatic capacitance during non-operation is reduced in the present variable capacitor. Further, because of the reduced shape deformation of both movable electrode films caused by temperature changes during operation and during non-operation, inconsistency in operational relationship between electrostatic capacitance and drive voltage is reduced also. As described, the present variable capacitor is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. Such a variable capacitor as the above is well suited to operate highly accurately. 
     Preferably, the anchor portion penetrates the first movable electrode film and/or the second movable electrode film. According to such an arrangement, at least one of the first movable electrode film and the second movable electrode film has a through hole or an opening to be fitted by the anchor portion. The first movable electrode film does not have any portion which faces the second movable electrode film via the anchor portion, nor does the second movable electrode film have any portion which faces the first movable electrode film via the anchor portion. In other words, there is no partial capacitor structure which has an invariable electrode-to-electrode distance via the anchor portion (and therefore has a fixed electrostatic capacitance). As described earlier, a variable capacitor which does not include any partial capacitor structure that has a fixed electrostatic capacitance is preferable when the device has to provide a small minimum electrostatic capacitance, and therefore preferable in achieving a large rate or amount of variation. As described, the arrangement where the anchor portion penetrates the first movable electrode film and/or the second movable electrode film is suitable for achieving a large rate or amount of variation. 
     Preferably, according to the present variable capacitor, the first electrode film is provided with a dielectric film on a side facing the second movable electrode film and/or the second movable electrode film is provided with a dielectric film on a side facing the first electrode film. Such an arrangement appropriately prevents the first and the second movable electrode films from directly contacting with each other. If a dielectric film is provided, the dielectric film may have a portion which constitutes at least part of the anchor portion. 
     Preferably, the first and the second movable electrode films are contactable with each other via the dielectric film. Alternatively to or in addition to such an arrangement, the first and the second movable electrode films may contact partially with each other via the dielectric film. These arrangements are suitable in achieving a large rate or amount of variation in the electrostatic capacitance. When embodying these arrangements, it is preferable that the first movable electrode film has a portion curved toward the second movable electrode film, or a portion curved away from the second movable electrode film. Also, it is preferable that the second movable electrode film has a portion curved toward the first movable electrode film, or a portion curved away from the first movable electrode film. 
     A third aspect of the present invention provides a method of making a variable capacitor. The method includes: a step of forming a first electrode on a substrate; a step of forming an anchor portion on the first electrode; a step of forming a sacrifice film which covers the first electrode while partially exposing the anchor portion; a step of forming a second electrode bonded to the anchor portion, on the sacrifice film; and a step of removing the sacrifice film. 
     A fourth aspect of the present invention provides a method of making a variable capacitor. The method includes: a step of forming a first electrode which has an opening, on a substrate; a step of forming an anchor portion which has a part fitting into the opening and a part projecting on the first electrode; a step of forming a sacrifice film which covers the first electrode while partially exposing the anchor portion; a step of forming a second electrode bonded to the anchor portion, on the sacrifice film; and a step of removing the sacrifice film. 
     A fifth aspect of the present invention provides a method of making a variable capacitor. The method includes: a step of forming a first electrode on a substrate; a step of forming a sacrifice film which covers the first electrode but has a first opening for partial exposure of the first electrode; a step of forming a second electrode which has a second opening communicating with the first opening, on the sacrifice film; a step of forming an anchor portion which penetrates the sacrifice film and the second electrode on the first electrode, by filling at least the first opening and the second opening with a material; and a step of removing the sacrifice film. 
     A sixth aspect of the present invention provides a method of making a variable capacitor. The method includes: a step of forming a first electrode which has a first opening, on a substrate; a step of forming a sacrifice film which has a second opening communicating with the first opening and covers the first electrode; a step of forming a second electrode which has a third opening communicating with the second opening, on the sacrifice film; a step of forming an anchor portion which penetrates the first electrode, the sacrifice film and the second electrode, by filling at least the first opening, the second opening and the third opening with a material; and a step of removing the sacrifice film. 
     The methods of making a variable capacitor provided by the third through the sixth aspects of the present invention enable one to manufacture the variable capacitors according to the first and the second aspects. 
     Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a variable capacitor according to a first embodiment of the present invention. 
         FIG. 2  is a partially unillustrated plan view of the variable capacitor according to the first embodiment of the present invention. 
         FIG. 3  is a sectional view taken in lines III-III in  FIG. 1 . 
         FIG. 4  is an enlarged partial sectional view taken in lines IV-IV in  FIG. 1 . 
         FIG. 5  shows different states of operation of the variable capacitor in  FIG. 1 . 
         FIG. 6  shows a method of making the variable capacitor in  FIG. 1 . 
         FIG. 7  is a sectional view of a first variation of the variable capacitor in  FIG. 1 . 
         FIG. 8  shows a method of making the variable capacitor in  FIG. 7 . 
         FIG. 9  is a sectional view of a second variation of the variable capacitor in  FIG. 1 . 
         FIG. 10  shows a method of making the variable capacitor in  FIG. 9 . 
         FIG. 11  is a sectional view of a third variation of the variable capacitor in  FIG. 1 . 
         FIG. 12  shows a method of making the variable capacitor in  FIG. 11 . 
         FIG. 13  is a sectional view of a fourth variation of the variable capacitor in  FIG. 1 . 
         FIG. 14  is a sectional view of a fifth variation of the variable capacitor in  FIG. 1 . 
         FIG. 15  is a sectional view of a sixth variation of the variable capacitor in  FIG. 1 . 
         FIG. 16  is a plan view of a variable capacitor according to a second embodiment of the present invention. 
         FIG. 17  is a partially unillustrated plan view of the variable capacitor according to the second embodiment of the present invention. 
         FIG. 18  is a sectional view taken in lines XVIII-XVIII in  FIG. 16 . 
         FIG. 19  is an enlarged partial sectional view taken in lines XIX-XIX in  FIG. 16 . 
         FIG. 20  shows different states of operation of the variable capacitor in  FIG. 16 . 
         FIG. 21  shows part of a method of making the variable capacitor in  FIG. 16 . 
         FIG. 22  shows steps continued from  FIG. 21 . 
         FIG. 23  is a sectional view of a first variation of the variable capacitor in  FIG. 16 . 
         FIG. 24  is a sectional view of a second variation of the variable capacitor in  FIG. 16 . 
         FIG. 25  is a sectional view of a third variation of the variable capacitor in  FIG. 16 . 
         FIG. 26  is a sectional view of a fourth variation of the variable capacitor in  FIG. 16 . 
         FIG. 27  is a sectional view of a fifth variation of the variable capacitor in  FIG. 16 . 
         FIG. 28  is a sectional view of a sixth variation of the variable capacitor in  FIG. 16 . 
         FIG. 29  is a sectional view of a seventh variation of the variable capacitor in  FIG. 16 . 
         FIG. 30  is a sectional view of an eighth variation of the variable capacitor in  FIG. 16 . 
         FIG. 31  is a sectional view of a ninth variation of the variable capacitor in  FIG. 16 . 
         FIG. 32  is a sectional view of a tenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 33  is a sectional view of an eleventh variation of the variable capacitor in  FIG. 16 . 
         FIG. 34  is a sectional view of a twelfth variation of the variable capacitor in  FIG. 16 . 
         FIG. 35  is a sectional view of a thirteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 36  is a sectional view of a fourteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 37  is a sectional view of a fifteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 38  is a sectional view of a sixteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 39  is a sectional view of a seventeenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 40  is a sectional view of an eighteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 41  is a sectional view of a nineteenth variation of the variable capacitor in  FIG. 16 . 
         FIG. 42  is a sectional view of a twentieth variation of the variable capacitor in  FIG. 16 . 
         FIG. 43  is a sectional view of a twenty-first variation of the variable capacitor in  FIG. 16 . 
         FIG. 44  is a sectional view of a twenty-second variation of the variable capacitor in  FIG. 16 . 
         FIG. 45  is a plan view of a variable capacitor according to a third embodiment of the present invention. 
         FIG. 46  is a partially unillustrated plan view of the variable capacitor according to the third embodiment of the present invention. 
         FIG. 47  is a sectional view taken in lines XLVII-XLVII in  FIG. 45 . 
         FIG. 48  is an enlarged partial sectional view taken in lines XLVIII-XLVIII in  FIG. 45 . 
         FIG. 49  shows different states of operation of the variable capacitor in  FIG. 45 . 
         FIG. 50  shows part of a method of making the variable capacitor in  FIG. 45 . 
         FIG. 51  is a sectional view of a first variation of the variable capacitor in  FIG. 45 . 
         FIG. 52  is a sectional view of a second variation of the variable capacitor in  FIG. 45 . 
         FIG. 53  shows sectional views of plugs having a cap. 
         FIG. 54  is a sectional view of a variable capacitor according to a fourth embodiment of the present invention. 
         FIG. 55  is an enlarged partial sectional view of the variable capacitor according to the fourth embodiment of the present invention. 
         FIG. 56  shows part of a method of making the variable capacitor in  FIG. 54 . 
         FIG. 57  is a sectional view of a first variation of the variable capacitor in  FIG. 54 . 
         FIG. 58  is a sectional view of a second variation of the variable capacitor in  FIG. 54 . 
         FIG. 59  is a sectional view of a variable capacitor according to a fifth embodiment of the present invention. 
         FIG. 60  is an enlarged partial sectional view of the variable capacitor according to the fifth embodiment of the present invention. 
         FIG. 61  shows part of a method of making the variable capacitor in  FIG. 59 . 
         FIG. 62  is a sectional view of a variation of the variable capacitor in  FIG. 59 . 
         FIG. 63  shows sectional views of plugs having a cap. 
         FIG. 64  is a plan view of a variable capacitor according to a sixth embodiment of the present invention. 
         FIG. 65  is a partially unillustrated plan view of the variable capacitor according to the sixth embodiment of the present invention. 
         FIG. 66  is a sectional view taken in lines LXVI-LXVI in  FIG. 64 . 
         FIG. 67  is an enlarged partial sectional view taken in lines LXVII-LXVII in  FIG. 64 . 
         FIG. 68  shows different states of operation of the variable capacitor in  FIG. 64 . 
         FIG. 69  shows part of a method of making the variable capacitor in  FIG. 64 . 
         FIG. 70  shows steps continued from  FIG. 69 . 
         FIG. 71  is a sectional view of a first variation of the variable capacitor in  FIG. 64 . 
         FIG. 72  is a sectional view of a second variation of the variable capacitor in  FIG. 64 . 
         FIG. 73  shows sectional views of plugs having a cap. 
         FIG. 74  is a sectional view of a variable capacitor according to a seventh embodiment of the present invention. 
         FIG. 75  is an enlarged partial sectional view of the variable capacitor according to the seventh embodiment of the present invention. 
         FIG. 76  shows part of a method of making the variable capacitor in  FIG. 74 . 
         FIG. 77  shows steps continued from  FIG. 76 . 
         FIG. 78  is a sectional view of a first variation of the variable capacitor in  FIG. 74 . 
         FIG. 79  is a sectional view of a second variation of the variable capacitor in  FIG. 74 . 
         FIG. 80  is a sectional view of a variable capacitor according to an eighth embodiment of the present invention. 
         FIG. 81  is an enlarged partial sectional view of the variable capacitor according to the eighth embodiment of the present invention. 
         FIG. 82  shows part of a method of making the variable capacitor in  FIG. 80 . 
         FIG. 83  shows steps continued from  FIG. 82 . 
         FIG. 84  is a sectional view of a variation of the variable capacitor in  FIG. 80 . 
         FIG. 85  shows sectional views of plugs having a cap. 
         FIG. 86  is a partial sectional view of a conventional variable capacitor. 
         FIG. 87  shows a state of the conventional variable capacitor in  FIG. 86 , where a movable electrode film is thermally expanded. 
         FIG. 88  shows another state of the conventional variable capacitor in  FIG. 86 , where a movable electrode film is thermally expanded. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  through  FIG. 4  show a variable capacitor X 1  according to a first embodiment of the present invention.  FIG. 1  is a plan view of the variable capacitor X 1 .  FIG. 2  is a partially unillustrated plan view of the variable capacitor X 1 .  FIG. 3  is a sectional view taken in lines III-III in  FIG. 1 .  FIG. 4  is an enlarged partial sectional view taken in lines IV-IV in  FIG. 1 . 
     The variable capacitor X 1  includes a substrate  11 , a fixed electrode  12 , a movable electrode  13  (not illustrated in  FIG. 2 ), and a dielectric film  14 . The substrate  11  is made of a silicon material for example. The fixed electrode  12  is formed on the substrate  11 . The movable electrode  13  is built on the substrate  11 . The movable electrode  13  has a thickness T 1  as shown in  FIG. 4 , of 1 through 2 μm for example. As shown clearly in  FIG. 1 , the fixed electrode  12  and the movable electrode  13  cross each other, opposing partially to each other. The opposed region has an area of 10000 through 40000 μm 2  for example. A distance L 1  in  FIG. 4  between the fixed electrode  12  and the movable electrode  13  is 0.5 through 2 μm for example. Preferably, one of the fixed electrode  12  and the movable electrode  13  is grounded. The fixed electrode  12  and the movable electrode  13  as described are formed of electrically conductive materials such as aluminum (Al) and copper (Cu). The dielectric film  14  is formed on the fixed electrode  12 , on a side facing the movable electrode  13 , and includes an anchor portion  14   a  as shown in  FIG. 3  and  FIG. 4 . The dielectric film  14  appropriately prevents the fixed electrode  12  and the movable electrode  13  from contacting directly with each other. The anchor portion  14   a  is sandwiched between the fixed electrode  12  and the movable electrode  13 , providing partial connection between the fixed electrode  12  and the movable electrode  13 . The dielectric film  14  has a thickness of 0.1 through 0.5 μm for example. The dielectric film  14  is formed of a dielectric material such as alumina (Al 2 O 3 ), silicon oxide (SiO 2 ) and silicon nitride (SiN x ). A predetermined wiring pattern (not illustrated) electrically connected with the fixed electrode  12  or the movable electrode  13  is formed on the substrate  11 . 
     According to the variable capacitor X 1  which has the constitution as described above, it is possible to generate an electrostatic attraction between the fixed electrode  12  and the movable electrode  13  by applying a voltage between the fixed electrode  12  and the movable electrode  13 , and by using the electrostatic attraction, it is possible to draw part of the movable electrode  13  faced by the fixed electrode  12  toward the fixed electrode  12 , excluding the region bonded to the anchor portion  14   a  (junction  13 ′), and thereby varying the volume of a gap G 1  between the fixed electrode  12  and the movable electrode  13  as shown in  FIG. 5 . (The amount or the distance of the drawing movement toward the fixed electrode  12  is not uniform over the entire region of the movable electrode  13  which faces the fixed electrode  12 . The junction  13 ′ is not moved at all, and regions of the movable electrode  13  closer to the junction  13 ′ tend to be drawn by a smaller amount). The electrostatic capacitance of the variable capacitor X 1  varies in accordance with the gap volume. Therefore, according to the variable capacitor X 1 , it is possible to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the fixed electrode  12  and the movable electrode  13 . 
     Further, according to the variable capacitor X 1 , the movable electrode  13  is partially connected with or joined on the fixed electrode  12  at the anchor portion  14   a ; this reduces shape deformation or curving of the movable electrode  13  caused by temperature changes both in operation and in non-operation. Specifically, shape deformation or curving of the movable electrode  13  caused by temperature changes becomes less even if the thermal expansion rate of the movable electrode  93  differs from the thermal expansion rate of the substrate  91 , and even if the difference is relatively large. Since curving of the movable electrode  13  is reduced in its initial shape (the shape in non-operation), inconsistency in initial electrostatic capacitance (0.5 through 1 pF for example) during non-operation is reduced in the variable capacitor X 1 . Further, because of the reduced shape deformation of the movable electrode  13  caused by temperature changes both during operation and during non-operation, inconsistency in the relationship between electrostatic capacitance and drive voltage is reduced also. As described, the variable capacitor X 1  is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. The variable capacitor X 1  as described above is able to operate highly accurately. 
     In addition, according to the variable capacitor X 1 , it becomes possible to vary the electrostatic capacitance widely. In the conventional variable capacitor Y, the movable electrode  93  must be moved within a limited range in order to avoid so called pull-in phenomenon. The pull-in phenomenon is a phenomenon that when the variable capacitor Y for example is driven, the entire region of the movable electrode  93  facing the fixed electrode  92  is drawn swiftly onto the fixed electrode  92 . A reason for this to happen is that when the device is driven, the movable electrode  93  is drawn toward the fixed electrode  92  substantially evenly or by substantially the same amount, over the entire opposed region. The pull-in phenomenon is likely to occur when the distance between the paired capacitor electrodes (the fixed electrode  92  and the movable electrode  93 ) in the variable capacitor (variable capacitor Y) becomes smaller than two-thirds of the original distance which is the distance when the capacitor electrodes are at their initial positions. Once a pull-in phenomenon occurs, the variable capacitor becomes virtually incontrollable. In order to avoid the pull-in phenomenon such as the above, the movement range for the movable electrode  93  is limited in the conventional variable capacitor Y, so it is not possible to vary the electrostatic capacitance over a wide range. On the contrary, according to the variable capacitor X 1  provided by the present invention, the amount of movement caused by the pull toward the fixed electrode  12  when the device is driven is not even over the entire opposed region of the movable electrode  13  or the region facing the fixed electrode  12 , and as shown in  FIG. 5(   c ) and  FIG. 5(   d ), it is possible to make the movable electrode  13  partially contact with, or pressed against, the fixed electrode  12  via the dielectric film  14 , and further to control the area of partial contact. Hence, according to the variable capacitor X 1 , it is possible to vary the gap volume between the fixed electrode  12  and the movable electrode  13  widely from the initial state shown in  FIG. 5(   a ) to the state where the area of contact between the fixed electrode  12  and the movable electrode  13  via the dielectric film  14  reaches a maximum value (e.g. the state as shown in  FIG. 5(   d )). Therefore, the variable capacitor X 1  is capable of offering a large amount or rate, of electrostatic capacitance variation. 
       FIG. 6  shows a method of making the variable capacitor X 1 , in a series of sectional views each corresponding to the section shown in  FIG. 3 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 1 . 
     In the manufacture of the variable capacitor X 1 , first as shown in  FIG. 6(   a ), a fixed electrode  12  and a dielectric film  14  are formed in lamination on a substrate  11 . The dielectric film  14  can be formed by patterning on a film of aluminum for example; by first forming a film of aluminum on the substrate  11  by sputtering, then forming a film of Al 2 O 3  on the Al film by sputtering, and finally etching the Al 2 O 3  film via a mask of a predetermined resist pattern. The fixed electrode  12  can also be patterned on the substrate  11  by etching the film of aluminum via a mask of another predetermined resist pattern. 
     Next, as shown in  FIG. 6(   b ), a sacrifice film  15  is formed. The sacrifice film  15  has an opening  15   a  for partially exposing the dielectric film  14 , and openings  15   b  for partially exposing the substrate  11 . The region of the dielectric film  14  exposed by the opening  15   a  will become the anchor portion  14   a  described earlier. The sacrifice film  15  is provided by a photoresist for example. The sacrifice film  15  can be formed by e.g. first forming a film of sacrifice material by sputtering on the substrate to cover the fixed electrode  12  and the dielectric film  14 , and then etching the film via a mask of a predetermined resist pattern. By controlling the thickness of the sacrifice film  15  formed in this step, it is possible to control the initial-state distance L 1  between the fixed electrode  12  and the movable electrode  13  in the variable capacitor X 1  obtained. 
     Next, as shown in  FIG. 6(   c ), a movable electrode  13  is formed. The movable electrode  13  is formed by e.g. first forming a film of aluminum on the sacrifice film  15  and in the openings  15   a ,  15   b  by sputtering, and then etching the Al film via a mask of a predetermined resist pattern. The movable electrode  13  thus formed is bonded to the dielectric film  14  in the opening  15   a  of the sacrifice film  15 , and to the substrate  11  in the openings  15   b . Note that for the sake of simplicity in the drawing, the two ends of movable electrode  13  are shown as formed by filling the openings  15   b  of the sacrifice film  15  with an electrically conductive material. 
     Next, as shown in  FIG. 6(   d ), the sacrifice film  15  is removed. Specifically, the sacrifice film  15  is removed by wet etching method using a predetermined resist remover. By following the above-described steps, the variable capacitor X 1  can be manufactured successfully. 
       FIG. 7  is a sectional view of a first variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , a dielectric film  14  is formed on the fixed electrode  12 , on the side facing the movable electrode  13 ; instead of this arrangement, a dielectric film  14  may be formed on the movable electrode  13 , on the side facing the fixed electrode  12  as shown in  FIG. 7 . 
       FIG. 8  shows a method of making the first variation, in a series of sectional views each corresponding to the section shown in  FIG. 7 . In the present method, first, a fixed electrode  12  is formed on a substrate  11  as shown in  FIG. 8(   a ). Next, as shown in  FIG. 8(   b ), a sacrifice film  15  is formed. The sacrifice film  15  has an opening  15   a  for partially exposing the fixed electrode  12 , and another opening for partially exposing the substrate  11  as described with reference to  FIG. 6(   b ). Next, as shown in  FIG. 8(   c ), a dielectric film  14  is formed on the sacrifice film  15  and in the opening  15   a . Thus, a part of the dielectric film  14  formed in the opening  15   a  will be an anchor portion  14   a  which connects the fixed electrode  12  with the movable electrode  13 . Next, as shown in  FIG. 8(   d ), the movable electrode  13  is formed, and thereafter, the sacrifice film  15  is removed by wet etching. By following the above-described steps, the first variation in  FIG. 7  of the variable capacitor X 1  can be manufactured successfully. 
       FIG. 9  is a sectional view of a second variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , a dielectric film  14  is formed on the fixed electrode  12 , on the side facing the movable electrode  13 ; In addition to this, a dielectric film  14  may also be formed on the movable electrode  13 , on the side facing the fixed electrode  12  as shown in  FIG. 9 . 
       FIG. 10  shows a method of making the second variation, in a series of sectional views each corresponding to the section shown in  FIG. 9 . In the present method, first, a fixed electrode  12  and a dielectric film  14  are formed in lamination on a substrate  11  as shown in  FIG. 10(   a ). Next, as shown in  FIG. 10(   b ), a sacrifice film  15  is formed. The sacrifice film  15  has an opening  15   a  for partially exposing the dielectric film  14 , and another opening for partially exposing the substrate  11  as described with reference to  FIG. 6(   b ). A part of the dielectric film  14  exposed by the opening  15   a  will be part of an anchor portion  14   a  which connects the fixed electrode  12  with the movable electrode  13 . Next, as shown in  FIG. 10(   c ), another dielectric film  14  is formed on the sacrifice film  15  and in the opening  15   a . A part of this dielectric film  14  formed in the opening  15   a  will be part of the anchor portion  14   a  which connects the fixed electrode  12  with the movable electrode  13 . Next, as shown in  FIG. 10(   d ), the movable electrode  13  is formed, and thereafter, the sacrifice film  15  is removed by wet etching. By following the above-described steps, the second variation in  FIG. 9  of the variable capacitor X 1  can be manufactured successfully. 
       FIG. 11  is a sectional view of a third variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , the movable electrode  13  may have a shape as shown in  FIG. 11 . The movable electrode  13  according to the present variation has an initial shape which includes portions curved away from the fixed electrode  12 . When the movable electrode  13  having such a shape is driven, the fixed electrode  12  is first contacted, via the dielectric film  14 , by ends  13   a  indicated in  FIG. 11  within a region of the movable electrode  13  which faces the fixed electrode  12 . The ends  13   a  also are the last to leave the dielectric film  14  i.e. the fixed electrode  12 . The shape of the movable electrode  13  as indicated in  FIG. 11  is preferable in that the shape ensures potential partial contact of the movable electrode  13  with the fixed electrode  12  via the dielectric film  14  during operation. In addition, a smaller distance between the capacitor electrodes enables the capacitor electrodes to be driven with a lower voltage. For this reason, such an arrangement as exemplified by the present variation where the distance between the electrodes is short at some portions is preferable in view of low voltage operation. 
       FIG. 12  shows a method of making the third variation, in a series of sectional views each corresponding to the section shown in  FIG. 11 . In the present method, first, a fixed electrode  12 , a dielectric film  14 , and a sacrifice film  15  are formed in lamination on a substrate  11  as shown in  FIG. 12(   a ). Specifically, the same procedures as described with reference to  FIG. 6(   a ) and  FIG. 6(   b ) will be performed. 
     Next, as shown in  FIG. 12(   b ), a resist pattern  16  is formed on the sacrifice film  15 . The resist pattern  16  can be formed by e.g. first forming a predetermined resist film on the substrate  11 , on the sacrifice film  15  and in the opening  15   a , and then by patterning the resist film using photolithography. By controlling the thickness of the resist pattern  16 , it is possible to control the extent of the above-described curving in the movable electrode  13 . Thereafter, a heating process is employed to deform the resist pattern  16  as shown in  FIG. 12(   c ). 
     Next, as shown in  FIG. 12(   d ), a movable electrode  13  is formed. The movable electrode  13  can be formed by e.g. first forming a film of aluminum using sputtering method on the substrate  11 , on the sacrifice film  15 , on the resist pattern  16  and in the opening  15   a , and then etching the Al film via a mask of a predetermined resist pattern. Thereafter, wet etching for example is performed to remove the sacrifice film  15  and the resist pattern  16  in a single step or individual steps. By following the above-described steps, the third variation in  FIG. 11  of the variable capacitor X 1  can be manufactured successfully. 
     The curved electrode such as the movable electrode  13  in the third variation may be made by laminating a plurality (e.g. two) of films each having a different internal stress (tensile stress, compression stress) from the other. Specifically, the laminated electrode is patterned on a sacrifice film such as the sacrifice film  15  in  FIG. 12 , and then the sacrifice film is removed. This procedure leaves the laminated electrode which is curved in a predetermined direction in accordance with internal stresses differences in each layer of the laminated electrode. A movable electrode which has a curved portion as described later can also be formed by these methods. 
       FIG. 13  is a sectional view of a fourth variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , the movable electrode  13  may have a shape as shown in  FIG. 13 . In the present variation, the movable electrode  13  has an initial shape which includes portions curved away from the fixed electrode  12 , and the movable electrode  13  has ends  13   b  shown in  FIG. 13  which contact with, or which is pressed against, the fixed electrode  12  via the dielectric film  14 , within a region of the movable electrode  13  which faces the fixed electrode  12 . When the movable electrode  13  having such a shape is driven, the area of the movable electrode  13  contacting with the fixed electrode  12  via the dielectric film  14  varies as the device is driven, with the ends  13   b  shown in  FIG. 13  serving as a base point. The electrostatic attraction generated between electrodes under a given voltage tends to be greater as the distance between capacitor electrodes is smaller. For this reason, the arrangement where the movable electrode  13  makes partial contact with the fixed electrode  12  via the dielectric film  14  is preferable in view of low voltage operation of the variable capacitor X 1 . 
       FIG. 14  is a sectional view of a fifth variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , the movable electrode  13  may have a shape as shown in  FIG. 14 . The movable electrode  13  according to the present variation has an initial shape which includes portions curved toward the fixed electrode  12 . When the movable electrode  13  having such a shape is driven, the fixed electrode  12  is first contacted, via the dielectric film  14 , by portions  13   c  indicated in  FIG. 14  within a region of the movable electrode  13  which faces the fixed electrode  12 . The portions  13   c  also are the last to leave the dielectric film  14  i.e. the fixed electrode  12 . The shape of the movable electrode  13  as indicated in  FIG. 14  is preferable in that the shape ensures potential partial contact of the movable electrode  13  with the fixed electrode  12  via the dielectric film  14  during operation. 
       FIG. 15  is a sectional view of a sixth variation of the variable capacitor X 1 . The view corresponds to  FIG. 4  which shows a section of the variable capacitor X 1  in  FIG. 1 . In the variable capacitor X 1 , the movable electrode  13  may have a shape as shown in  FIG. 15 . In the present variation, the movable electrode  13  has an initial shape which includes portions curved toward the fixed electrode  12 , and portions  13   d  shown in  FIG. 15  which contact with the fixed electrode  12  via the dielectric film  14 , within a region of the movable electrode  13  that faces the fixed electrode  12 . When the movable electrode  13  having such a shape is driven, the area of the movable electrode  13  contacting with the fixed electrode  12  via the dielectric film  14  varies as the device is driven, with the portions  13   d  shown in  FIG. 13  serving as base points. The arrangement where the movable electrode  13  has an initial shape which makes partial contact with the fixed electrode  12  via the dielectric film  14  is preferable in view of low voltage operation of the variable capacitor X 1 . 
       FIG. 16  through  FIG. 19  show a variable capacitor X 2  according to a second embodiment of the present invention.  FIG. 16  is a plan view of the variable capacitor X 2 .  FIG. 17  is a partially unillustrated plan view of the variable capacitor X 2 .  FIG. 18  is a sectional view taken in lines XVIII-XVIII in  FIG. 16 .  FIG. 19  is an enlarged partial sectional view taken in lines XIX-XIX in  FIG. 16 . 
     The variable capacitor X 2  includes a substrate  21 , a movable electrode  22 , a movable electrode  23  (not illustrated in  FIG. 17 ), and a dielectric film  24 . The substrate  21  has a recess  21   a , and is made of a silicon material for example. The movable electrode  22  has two ends bonded to the substrate  21 , and extends over the recess  21   a . The movable electrode  23  is built on the substrate  21 . The movable electrode  23  has a thickness T 2  as shown in  FIG. 19 , of 1 through 2 μm for example. As shown clearly in  FIG. 16 , the movable electrodes  22 ,  23  cross each other, opposing partially to each other. The opposed region has an area of 10000 through 40000 μm 2  for example. A distance L 2  shown in  FIG. 19  between the movable electrodes  22  and  23  is 0.5 through 2 μm for example. Preferably, one of the movable electrodes  22 ,  23  is grounded. The movable electrodes  22 ,  23  as described are formed of electrically conductive materials such as Al and Cu. The dielectric film  24  is formed on the movable electrode  22 , on a side facing the movable electrode  23 , and includes an anchor portion  24   a  as shown in  FIG. 18  and  FIG. 19 . The dielectric film  24  appropriately prevents the movable electrodes  22 ,  23  from contacting directly with each other. The anchor portion  24   a  is sandwiched between the movable electrodes  22 ,  23 , providing partial connection between the movable electrodes  22 ,  23 . The dielectric film  24  has a thickness of 0.1 through 0.5 μm for example. The dielectric film  24  as described is formed of a dielectric material such as Al 2 O 3 , SiO 2  and SiN x . A predetermined wiring pattern (not illustrated) electrically connected with the movable electrode  22  or with the movable electrodes  23  is formed on the substrate  21 . 
     According to the variable capacitor X 2  which has the constitution as described above, it is possible to generate an electrostatic attraction between the movable electrodes  22 ,  23  by applying a voltage between the movable electrodes  22 ,  23 , and by using the electrostatic attraction, it is possible to draw the movable electrodes  22 ,  23  closely to each other, excluding the regions bonded to the anchor portion  24   a  (bonded regions  22 ′,  23 ′), and thereby varying the volume of a gap G 2  between the movable electrodes  22 ,  23  as shown in  FIG. 20 . The electrostatic capacitance of the variable capacitor X 2  varies in accordance with the gap volume. Therefore, according to the variable capacitor X 2 , it is possible to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the movable electrodes  22 ,  23 . 
     Further, according to the variable capacitor X 2 , the movable electrodes  22 ,  23  are partially connected with or joined on each other by the anchor portion  24   a ; this reduces shape deformation or curving of the movable electrodes  22 ,  23  caused by temperature changes both in operation and in non-operation. Since curving of both movable electrodes  22 ,  23  is reduced in its initial shape (the shape in non-operation), inconsistency in initial electrostatic capacitance (0.5 through 1 pF for example) during non-operation is reduced in the variable capacitor X 2 . Further, because of the reduced shape deformation of both movable electrodes  22 ,  23  caused by temperature changes during operation and during non-operation, inconsistency in the relationship between electrostatic capacitance and drive voltage is reduced also. As described, the variable capacitor X 2  is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. The variable capacitor X 2  as described above is well suited to operate highly accurately. 
     In addition, according to the variable capacitor X 2 , it is possible to vary the electrostatic capacitance widely. As has been described, in the conventional variable capacitor Y it is not possible to vary the electrostatic capacitance widely because the movable electrode  93  must be moved within a limited range in order to avoid the pull-in phenomenon. On the contrary, when driving the variable capacitor X 2  according to the present invention, it is possible as shown in  FIG. 20(   c ) and  FIG. 20(   d ), to make the movable electrodes  22 ,  23  partially contact with each other via the dielectric film  24  and further, to control the area of partial contact. Hence, according to the variable capacitor X 2 , it is possible to vary the gap volume between the movable electrodes  22 ,  23  widely from the initial state shown in  FIG. 20(   a ) to the state where the area of contact between the movable electrodes  22 ,  23  via the dielectric film  14  reaches a maximum value (e.g. the state as shown in  FIG. 20(   d )). Therefore, the variable capacitor X 2  is capable of offering a large amount or rate of electrostatic capacitance variation. 
       FIG. 21  and  FIG. 22  show a method of making the variable capacitor X 2 , in a series of sectional views each corresponding to the section shown in  FIG. 18 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 2 . 
     In the manufacture of the variable capacitor X 2 , first, a substrate  21  which has a recess  21   a  as shown in  FIG. 21(   a ) is prepared. The substrate  21  which has the recess  21   a  can be formed by e.g. performing anisotropic dry etching to a predetermined silicon substrate via a mask of a predetermined resist pattern. An example of the anisotropoic dry etching usable for this process is reactive ion etching (RIE). 
     Next, as shown in  FIG. 21(   b ), a sacrifice material  25  is filled in the recess  21   a  of the substrate  21 . Specifically, sputtering method for example can be used to fill the sacrifice material in the recess  21   a  as well as to cover the substrate  21  with more than a sufficient amount of the sacrifice material  25 , and then the excess amount of the sacrifice material  25  on the substrate  21  is polished off. The sacrifice material  25  is provided by a photoresist for example. 
     Next, as shown in  FIG. 21(   c ), a fixed electrode  22  and a dielectric film  24  are formed in lamination on the substrate  21 . The movable electrode  22  and the dielectric film  24  can be formed using the same procedures as described with reference to  FIG. 6(   a ) used for forming the fixed electrode  12  and the dielectric film  14 . 
     Next, as shown in  FIG. 22(   a ), a sacrifice film  26  is formed. The sacrifice film  26  has an opening  26   a  for partially exposing the dielectric film  24 , and openings  26   b  for partially exposing the substrate  21 . The region of the dielectric film  24  exposed by the opening  26   a  will become the anchor portion  24   a  described earlier. The sacrifice film  26  can be formed of the same material and by the same procedures as used for formation of the sacrifice film  15  described earlier with reference to  FIG. 6(   b ). By controlling the thickness of the sacrifice film  26  formed in this step, it is possible to control the initial-state distance L 2  between the movable electrodes  22 ,  23  in the variable capacitor X 2  obtained. 
     Next, as shown in  FIG. 22(   b ), a movable electrode  23  is formed. The movable electrode  23  can be formed by the same procedures as used for formation of the movable electrode  13  described earlier with reference to  FIG. 6(   c ). The movable electrode  23  formed in this step is bonded to the dielectric film  24  in the opening  26   a  of the sacrifice film  26 , and to the substrate  21  in the openings  26   b . Note that for the sake of simplicity in the drawing, the two ends of movable electrode  23  are shown as formed by filling the openings  26   b  of the sacrifice film  26  with an electrically conductive material. 
     Next, as shown in  FIG. 22(   c ), the sacrifice film  26  and the sacrifice material  25  are removed. Specifically, the sacrifice film  26  and the sacrifice material  25  are removed by wet etching method using a predetermined resist remover. By following the above-described steps, the variable capacitor X 2  can be manufactured successfully. 
       FIG. 23  is a sectional view of a first variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , a dielectric film  24  is formed on the movable electrode  22 , on the side facing the movable electrode  23 ; instead of this arrangement, a dielectric film  24  may be formed on the movable electrode  23 , on the side facing the movable electrode  22  as shown in  FIG. 23 . 
       FIG. 24  is a sectional view of a second variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , a dielectric film  24  is formed on the movable electrode  22 , on the side facing the movable electrode  23 ; In addition to this arrangement, a dielectric film  24  may also be formed on the movable electrode  23 , on the side facing the movable electrode  22  as shown in  FIG. 23 . 
       FIG. 25  is a sectional view of a third variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  23  may have a shape as shown in  FIG. 25 . The movable electrode  23  according to the present variation has an initial shape which includes portions curved away from the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the movable electrode  22  is first contacted, via the dielectric film  24 , by ends  23   a  indicated in  FIG. 25  within a region of the movable electrode  23  which faces the movable electrode  22 . The ends  23   a  also are the last to leave the dielectric film  24  i.e. the movable electrode  22 . The shape of the movable electrode  23  as shown in  FIG. 25  is preferable in that the shape ensures potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 26  is a sectional view of a fourth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  23  may have a shape as shown in  FIG. 26 . In the present variation, the movable electrode  23  has an initial shape which includes portions curved away from the movable electrode  22 , and the movable electrode  23  has ends  23   b  shown in  FIG. 26  which contact with the movable electrode  12  via the dielectric film  24 , within a region of the movable electrode  23  facing the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of mutual contact between the movable electrodes  22 ,  23  via the dielectric film  24  varies as the device is driven, with the ends  23   b  serving as a base point. The arrangement where the movable electrodes  22 ,  23  make mutual partial contact via the dielectric film  24  is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 27  is a sectional view of a fifth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  23  may have a shape as shown in  FIG. 27 . The movable electrode  23  according to the present variation has an initial shape which includes portions curved toward the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the movable electrode  22  is first contacted, via the dielectric film  24 , by portions  23   c  indicated in  FIG. 27  within a region of the movable electrode  23  which faces the movable electrode  22 . The ends  23   c  also are the last to leave the dielectric film  24  i.e. the movable electrode  22 . The shape of the movable electrode  23  as shown in  FIG. 27  is preferable in that the shape ensures potential partial mutual contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 28  is a sectional view of a sixth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  23  may have a shape as shown in  FIG. 28 . In the present variation, the movable electrode  23  has an initial shape which includes portions curved toward the movable electrode  22 , and portions  23   d  shown in  FIG. 28  which contact with the movable electrode  22  via the dielectric film  24 , within a region of the movable electrode  23  that faces the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of mutual contact between the movable electrodes  22 ,  33  via the dielectric film  24  varies as the device is driven, with the portions  23   d  shown in  FIG. 28  serving as a base point. The arrangement that the movable electrodes  22 ,  23  make mutual partial contact via the dielectric film  24  in their initial states is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 29  is a sectional view of a seventh variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  22  may have a shape as shown in  FIG. 29 . In the present variation, the movable electrode  22  has an initial shape which includes a portion curved toward the movable electrode  23  at a place bonded to the anchor portion  24   a  of the dielectric film  24 . The shape of the movable electrode  22  as shown in  FIG. 29  is preferable in that the shape ensures potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. The curved shape of the movable electrode  22  according to the present variation can be achieved by e.g. using a resist pattern, in the same way as a curvature is made by using a resist pattern in the movable electrode  13  in the third variation of the variable capacitor X 1 . 
       FIG. 30  is a sectional view of an eighth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 30 . In the present variation, the movable electrode  22  has an initial shape which includes a portion curved toward the movable electrode  23  at a place bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which include portions curved away from the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 30  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 31  is a sectional view of a ninth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 31 . In the present variation, the movable electrode  22  has an initial shape which includes a portion curved toward the movable electrode  23  at a place bonded to the anchor portion  24   a  of the dielectric film  24 . The movable electrode  23  according to the present variation has an initial shape which includes portions curved away from the movable electrode  22 , and ends  23   e  shown in  FIG. 31  which contact with the movable electrode  22  via the dielectric film  24 , within a region of the movable electrode  23  which faces the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of the movable electrode  23  contacting the movable electrode  22  via the dielectric film  24  varies as the device is driven, with the ends  23   e  shown in  FIG. 31  serving as a base point. The arrangement where the movable electrodes  22 ,  23  make mutual partial contact via the dielectric film  24  in their initial states is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 32  is a sectional view of a tenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 32 . In the present variation, the movable electrode  22  has an initial shape which includes a portion curved toward the movable electrode  23  at a place bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which includes portions curved toward the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 32  are preferable in that they ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 33  is a sectional view of an eleventh variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 33 . In the present variation, the movable electrode  22  has an initial shape which includes a portion curved toward the movable electrode  23  at a place bonded to the anchor portion  24   a  of the dielectric film  24 . The movable electrode  23  according to the present variation has an initial shape which includes portions curved toward the movable electrode  22 , and portions  23   f  shown in  FIG. 33  which contact with the movable electrode  22  via the dielectric film  24 , within a region of the movable electrode  23  that faces the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of the movable electrode  23  contacting the movable electrode  22  via the dielectric film  24  varies as the device is driven, with the portions  23   f  shown in  FIG. 33  serving as base points. The arrangement where the movable electrodes  22 ,  23  contact with each other via the dielectric film  24  is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 34  is a sectional view of a twelfth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrode  22  may be shaped as shown in  FIG. 34 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24 . The shape of the movable electrode  22  as shown in  FIG. 34  is preferable in that the shape ensures potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. The curved shape of the movable electrode  22  according to the present variation can be achieved by e.g. using a resist pattern, in the same way as a curvature is made by using a resist pattern in the movable electrode  13  in the third variation of the variable capacitor X 1 . 
       FIG. 35  is a sectional view of a thirteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 35 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which makes partial contact with the movable electrode  22 . The arrangement that the movable electrodes  22 ,  23  make partial contact with each other in their initial states is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 36  is a sectional view of a fourteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 36 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which includes portions curved away from the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 36  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  14  during operation. 
       FIG. 37  is a sectional view of a fifteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 37 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24 . The movable electrode  23  according to the present variation has an initial shape which includes portions curved away from the movable electrode  22 , and ends  23   g  shown in  FIG. 37  which contact with the movable electrode  22  via the dielectric film  24 , within a region of the movable electrode  23  which faces the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of the movable electrode  23  contacting the movable electrode  22  via the dielectric film  24  varies as the device is driven, with the ends  23   g  shown in  FIG. 37  serving as base points. The arrangement where the movable electrodes  22 ,  23  make mutual partial contact via the dielectric film  24  is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 38  is a sectional view of a sixteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 38 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which includes portions curved toward the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 38  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 39  is a sectional view of a seventeenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . In the variable capacitor X 2 , the movable electrodes  22 ,  23  may be shaped as shown in  FIG. 39 . In the present variation, the movable electrode  22  has an initial shape which includes portions curved toward the movable electrode  23  at places not bonded to the anchor portion  24   a  of the dielectric film  24 . Further, in the present variation, the movable electrode  23  has an initial shape which includes portions curved toward the movable electrode  22  and further, portions  23   h  shown in  FIG. 39  which contact with the movable electrode  22  via the dielectric film  24 , within the region of the movable electrode  23  facing the movable electrode  22 . When the movable electrode  23  having such a shape is driven, the area of the movable electrode  23  contacting the movable electrode  22  via the dielectric film  24  varies as the device is driven, with the portions  23   h  shown in  FIG. 39  serving as base points. The arrangement where the movable electrodes  22 ,  23  contact with each other via the dielectric film  24  in their initial shapes is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 40  is a sectional view of an eighteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . The movable electrodes  22 ,  23  according to the present variation are connected with each other via the dielectric film  24  at two locations. In other words, the present variation has two anchor portions  24   a.    
       FIG. 41  is a sectional view of a nineteenth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . The movable electrodes  22 ,  23  according to the present variation are connected with each other via the dielectric film  24  at two locations. (In other words, the present variation has two anchor portions  24   a .) Further, according to the present variation, the movable electrode  22  has an initial shape curved toward the movable electrode  23  at each place bonded to the anchor portion  24   a  of the dielectric film  24 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 41  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 42  is a sectional view of a twentieth variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . The movable electrodes  22 ,  23  according to the present variation are connected with each other via the dielectric film  24  at two locations. (In other words, the present variation has two anchor portions  24   a .) Further, according to the present variation, the movable electrode  22  has an initial shape curved toward the movable electrode  23  at each place bonded to the anchor portion  24   a  of the dielectric film  24 . Further, the movable electrode  23  has an initial shape which includes a portion curved away from the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 42  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 43  is a sectional view of a twenty-first variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . The movable electrodes  22 ,  23  according to the present variation are connected with each other via the dielectric film  24  at two locations. (In other words, the present variation has two anchor portions  24   a .) Further, according to the present variation, the movable electrode  22  has an initial shape curved toward the movable electrode  23  at each place bonded to the anchor portion  24   a  of the dielectric film  24  whereas the movable electrode  23  has an initial shape which includes a portion curved toward the movable electrode  22 . The shapes of the movable electrodes  22 ,  23  as shown in  FIG. 43  are preferable in that the shapes ensure potential partial contact between the movable electrodes  22 ,  23  via the dielectric film  24  during operation. 
       FIG. 44  is a sectional view of a twenty-second variation of the variable capacitor X 2 . The view corresponds to  FIG. 19  which shows a section of the variable capacitor X 2  in  FIG. 16 . The movable electrodes  22 ,  23  according to the present variation are connected with each other, via the dielectric film  24 , at two locations. (In other words, the present variation has two anchor portions  24   a .) Further, according to the present variation, the movable electrode  22  has an initial shape curved toward the movable electrode  23  at each place bonded to the anchor portion  24   a  of the dielectric film  24 . The movable electrode  23  according to the present variation has an initial shape which includes a portion curved toward the movable electrode  22 , and this portion contacts with the movable electrode  22  via the dielectric film  24 . The arrangement where the movable electrodes  22 ,  23  make mutual partial contact via the dielectric film  24  in their initial shapes is preferable in view of low voltage operation of the variable capacitor X 2 . 
       FIG. 45  through  FIG. 48  show a variable capacitor X 3  according to a third embodiment of the present invention.  FIG. 45  is a plan view of the variable capacitor X 3 .  FIG. 46  is a partially unillustrated plan view of the variable capacitor X 3 .  FIG. 47  is a sectional view taken in lines XLVII-XLVII in  FIG. 45 .  FIG. 48  is an enlarged partial sectional view taken in lines XLVIII-XLVIII in  FIG. 45 . 
     The variable capacitor X 3  includes a substrate  31 , a fixed electrode  32 , a movable electrode  33  (not illustrated in  FIG. 46 ), a dielectric film  34  and a plug  35 . The fixed electrode  32  is formed on the substrate  31 . The movable electrode  33  is built on the substrate  31 . The movable electrode  33  has a thickness T 3  as shown in  FIG. 48 , of 1 through 2 μm for example. As shown clearly in  FIG. 45 , the fixed electrode  32  and the movable electrode  33  cross each other, opposing partially to each other. The opposed region has an area of 10000 through 40000 μm 2  for example. A distance L 3  shown in  FIG. 48  between the fixed electrode  32  and the movable electrode  33  is 0.5 through 2 μm for example. Preferably, one of the fixed electrode  32  and the movable electrode  33  is grounded. The dielectric film  34  is formed on the fixed electrode  32 , on a side facing the movable electrode  33 . The dielectric film  34  has a thickness of 0.1 through 0.5 μm for example. The substrate  31 , the fixed electrode  32 , the movable electrode  33 , and the dielectric film  34  are formed of the same materials as are their respective counterparts in the first embodiment, i.e. the substrate  11 , the fixed electrode  12 , the movable electrode  13 , and the dielectric film  14 . The plug  35  penetrates the movable electrode  33 , is bonded to the movable electrode  33 , and is bonded to the dielectric film  34 . The plug  35  as described above is made of a dielectric material such as alumina (Al 2 O 3 ), silicon oxide (SiO 2 ) and silicon nitride (SiN x ). A predetermined wiring pattern (not illustrated) electrically connected with the fixed electrode  32  or with the movable electrodes  33  is formed on the substrate  31 . 
     In the variable capacitor X 3  shown in  FIG. 45 , an anchor portion  36  according to the present invention is constituted by the plug  35  and, as clearly shown in  FIG. 48 , a portion  34   a  of the dielectric film  34  which the plug is bonded to. The anchor portion  36  provides a partial connection between the mutually opposed fixed electrode  32  and movable electrode  33 . 
     According to the variable capacitor X 3  which has the constitution as described above, it is possible to generate an electrostatic attraction between the fixed electrode  32  and the movable electrode  33  by applying a voltage between the fixed electrode  32  and the movable electrode  33 , and by using the electrostatic attraction, it is possible to draw the movable electrode  33  toward the fixed electrode  32 , excluding the region bonded to the anchor portion  36 , and thereby varying the volume of a gap G 3  between the fixed electrode  32  and the movable electrode  33  as shown in  FIG. 49 . (The amount or the distance of the drawing movement toward the fixed electrode  32  is not uniform over the entire region of the movable electrode  33  which faces the fixed electrode  32 . The region bonded to the anchor portion  36  is not moved at all, and regions of the movable electrode  33  closer to the junction tend to be drawn by a smaller amount). The electrostatic capacitance of the variable capacitor X 3  varies in accordance with the gap volume. Therefore, according to the variable capacitor X 3 , it is possible to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the fixed electrode  32  and the movable electrode  33 . 
     Further, according to the variable capacitor X 3 , the movable electrode  33  is partially connected with or joined on the fixed electrode  32  by the anchor portion  36 ; this reduces shape deformation or curving of the movable electrode  33  caused by temperature changes both in operation and in non-operation. Specifically, shape deformation or curving of the movable electrode  33  caused by temperature changes becomes less even if the thermal expansion rate of the substrate  31  differs from the thermal expansion rate of the movable electrode  33 , and even if the difference is relatively large. Since curving of the movable electrode  33  is reduced in its initial shape (the shape in non-operation), inconsistency in initial electrostatic capacitance (0.5 through 1 pF for example) during non-operation is reduced in the variable capacitor X 3 . Further, because of the reduced shape deformation of the movable electrode  33  caused by temperature changes both during operation and during non-operation, inconsistency in the relationship between electrostatic capacitance and drive voltage is reduced also. As described, the variable capacitor X 3  is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. The variable capacitor X 3  as described above is able to operate highly accurately. 
     In addition, according to the variable capacitor X 3 , it is possible to vary the electrostatic capacitance widely. As has been described earlier, in the conventional variable capacitor Y, the movable electrode  93  must be moved within a limited range in order to avoid so called pull-in phenomenon, so it is not possible to vary the electrostatic capacitance over a wide range. On the contrary, according to the variable capacitor X 3  provided by the present invention, it is possible as shown in  FIG. 49(   c ) and  FIG. 49(   d ), to make the movable electrode  33  partially contact with the fixed electrode  32  via the dielectric film  34  and further, to control the area of partial contact. Hence, according to the variable capacitor X 3 , it is possible to vary the gap volume between the fixed electrode  32  and the movable electrode  33  widely from the initial state shown in  FIG. 49(   a ) to the state where the area of contact between the fixed electrode  32  and the movable electrode  33  via the dielectric film  14  reaches a maximum value (e.g. the state as shown in  FIG. 49(   d )). In addition to this, according to the variable capacitor X 3 , the movable electrode  33  has no region which faces the fixed electrode  32  via the anchor portion  36 . In other words, there is no partial capacitor structure which has an invariable electrode-to-electrode distance via the anchor portion  36  (and therefore has a fixed electrostatic capacitance). If a variable capacitor includes a partial capacitor structure which has a fixed electrostatic capacitance, a minimum electrostatic capacitance for the entire variable capacitor cannot be smaller than the fixed electrostatic capacitance. On the contrary, the variable capacitor X 3  which does not include any partial capacitor structure that has a fixed electrostatic capacitance does not have such a limitation to the minimum electrostatic capacitance for the entire variable capacitor. Hence, it is easy in the variable capacitor X 3 , to offer a small minimum electrostatic capacitance. As described, according to the variable capacitor X 3 , it is possible to vary the gap volume between the fixed electrode  32  and the movable electrode  33  widely, and to make a setting for a small value for the minimum electrostatic capacitance because of the structure where there is no fixed electrode-to-electrode distance via the anchor portion  36 . Therefore, the variable capacitor X 3  is capable of offering a large amount or rate, of electrostatic capacitance variation. 
       FIG. 50  shows a method of making the variable capacitor X 3 , in a series of sectional views each corresponding to the section shown in  FIG. 47 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 3 . 
     In the manufacture of the variable capacitor X 3 , first as shown in  FIG. 50(   a ), a fixed electrode  32  and a dielectric film  34  are formed in lamination on a substrate  31 . The fixed electrode  32  and the dielectric film  34  can be formed by the same procedures as used for formation of the fixed electrode  12  and the dielectric film  14  described with reference to  FIG. 6(   a ). 
     Next, as shown in  FIG. 50(   b ), a sacrifice film  37  is formed. The sacrifice film  37  has an opening  37   a  for partially exposing the dielectric film  34 , and openings  37   b  for partially exposing the substrate  31 . A part  34   a  of the dielectric film  34  which is the part exposed by the opening  37   a  will be part of the anchor portion  36  described earlier. The sacrifice film  37  can be formed of the same material and by the same procedures as used for formation of the sacrifice film  15  described earlier with reference to  FIG. 6(   b ). By controlling the thickness of the sacrifice film  37  formed in this step, it is possible to control the initial-state distance L 3  between the fixed electrode  32  and the movable electrodes  33  in the variable capacitor X 3  obtained. 
     Next, as shown in  FIG. 50(   c ), a movable electrode  33  is formed. The movable electrode  33  has an opening  33   a  which communicates with the opening  37   a  of the sacrifice film  37 . The movable electrode  33  is formed by e.g. first forming a film of aluminum on the sacrifice film  37  and in the openings  37   a ,  37   b  by sputtering method, and then etching the film of aluminum via a mask of a predetermined resist pattern. Note that for the sake of simplicity in the drawing, the two ends of movable electrode  33  are shown as formed by filling the openings  37   b  in the sacrifice film  37  with an electrically conductive material. 
     Next, a plug  35  is formed as shown in  FIG. 50(   d ). The plug  35  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  33   a ,  37   a , with a dielectric material. 
     Thereafter, wet etching is performed with a predetermined resist remover, to remove the sacrifice film  37 . By following the above-described steps, the variable capacitor X 3  can be manufactured successfully. 
       FIG. 51  is a sectional view of a first variation of the variable capacitor X 3 . The view corresponds to  FIG. 48  which shows a section of the variable capacitor X 3  in  FIG. 45 . As shown in  FIG. 51 , in the variable capacitor X 3 , the plug  35  may penetrate the dielectric film  34 , to be bonded to the fixed electrode  32 . In such a variation, the plug  35  constitutes an anchor portion  36  which provides partial connection between the mutually opposed fixed electrode  32  and movable electrode  33 . The present variation can be manufactured by the same method as described above as for the manufacture of the variable capacitor X 3 , with an additional step after the one shown in  FIG. 50(   a ), of making an opening in the dielectric film  34  which is to be fitted by the plug  35  according to the present variation. 
       FIG. 52  is a sectional view of a second variation of the variable capacitor X 3 . The view corresponds to  FIG. 48  which shows a section of the variable capacitor X 3  in  FIG. 45 . In the variable capacitor X 3 , a dielectric film  34  is formed on the fixed electrode  32 , on the side facing the movable electrode  33 ; instead of this arrangement, a dielectric film  34  may be formed on the movable electrode  33 , on the side facing the fixed electrode  32  as shown in  FIG. 52 . In such a variation, the plug  35  constitutes an anchor portion  36  which provides partial connection between the mutually opposed fixed electrode  32  and movable electrode  33 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 3 , with the following changes for example: Specifically, the step of forming the sacrifice film  37  after the formation of the dielectric film  34  is replaced by a step of forming a sacrifice film  37  which has an opening  37   a  and covers the fixed electrode  32 , and a step thereafter of forming a dielectric film  34  which has a predetermined opening that communicates with the opening  37   a  on the dielectric film  37 . 
     As shown in  FIG. 53 , the plug  35  according to the variable capacitor X 3  including the first variation and the second variation may have a cap  35   a . The caps  35   a  as shown help ensure the bonding relationship between the movable electrode  33  and the plug  35 . 
     The movable electrode  33  according to the variable capacitor X 3  including the first variation and the second variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 11  and  FIG. 14 , i.e. may have an initial shape which includes curved portions. Otherwise, the movable electrode  33  according to the variable capacitor X 3  including the first variation and the second variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 13  and  FIG. 15 , i.e. may have an initial shape which includes curved portions as well as having portions contacting with the fixed electrode via the dielectric film. 
       FIG. 54  and  FIG. 55  show a variable capacitor X 4  according to a fourth embodiment of the present invention.  FIG. 54  is a sectional view of the variable capacitor X 4 , and corresponds to  FIG. 47  which shows a section of the variable capacitor X 3  described above.  FIG. 55  is an enlarged partial sectional view of the variable capacitor X 4 , and corresponds to  FIG. 48  which shows a section of the variable capacitor X 3  described above. 
     The variable capacitor X 4  includes a substrate  41 , a fixed electrode  42 , a movable electrode  43 , a dielectric film  44  and a plug  45 . The fixed electrode  42  is formed on the substrate  41 . The movable electrode  43  is built on the substrate  41 . The fixed electrode  42  and the movable electrode  43  cross each other, opposing partially to each other. A distance L 4  shown in  FIG. 55  between the fixed electrode  42  and the movable electrode  43  is 0.5 through 2 μm for example. Preferably, one of the fixed electrode  42  and the movable electrode  43  is grounded. The dielectric film  44  is formed on the movable electrode  43 , on a side facing the fixed electrode  42 . The plug  45  penetrates the fixed electrode  42 , is bonded to the fixed electrode  42 , and is bonded to the dielectric film  44 . A predetermined wiring pattern (not illustrated) electrically connected with the fixed electrode  42  or with the movable electrodes  43  is formed on the substrate  41 . The substrate  41 , the fixed electrode  42 , the movable electrode  43 , and the dielectric film  44  are formed of the same materials as are their respective counterparts in the first embodiment, i.e. the substrate  11 , the fixed electrode  12 , the movable electrode  13 , and the dielectric film  14 . The plug  45  is formed of the same material as is the plug  35  in the third embodiment. 
     In the variable capacitor X 4  shown in  FIG. 54 , an anchor portion  46  according to the present invention is constituted by the plug  45  and, as clearly shown in  FIG. 55 , a portion  44   a  of the dielectric film  44  which the plug is bonded to. The anchor portion  46  provides a partial connection between the mutually opposed fixed electrode  42  and movable electrode  43 . 
     According to the variable capacitor X 4  which has the constitution as described above, it is possible, as described earlier for the variable capacitor X 3 , to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the fixed electrode  42  and the movable electrode  43 . Further, according to the variable capacitor X 4 , the movable electrode  43  is partially connected with or joined on the fixed electrode  42  by the anchor portion  46 , and therefore shape deformation or curving of the movable electrode  43  caused by temperature changes is reduced both during operation and during non-operation. The variable capacitor X 4  as described is able to operate highly accurately as is the variable capacitor X 3 . In addition, according to the variable capacitor X 4 , it is possible to vary the gap volume between the fixed electrode  42  and the movable electrode  43  widely, and to make a setting for a small value for the minimum electrostatic capacitance because of the structure where there is no fixed electrode-to-electrode distance via the anchor portion  46 . Therefore, the variable capacitor X 4  is capable of offering a large amount or rate, of electrostatic capacitance variation as is the variable capacitor X 3 . 
       FIG. 56  shows a method of making the variable capacitor X 4 , in a series of sectional views each corresponding to the section shown in  FIG. 55 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 4 . 
     In the manufacture of the variable capacitor X 4 , first as shown in  FIG. 56(   a ), a fixed electrode  42  and a sacrifice film  47  are formed in lamination on a substrate  41 . The fixed electrode  42  has an opening  42   a , and the sacrifice film  47  has an opening  47   a  which communicates with the opening  42   a , and an unillustrated opening for partially exposing the substrate  41 . The fixed electrode  42  can be formed by e.g. first forming a film of aluminum on the substrate  41  by sputtering method to cover the fixed electrode  43 , and then etching the film of aluminum via a mask of a predetermined resist pattern. The sacrifice film  47  can be formed by e.g. first forming a film of sacrifice material on the substrate  41  by sputtering method, and then etching the film via a mask of a predetermined resist pattern. By controlling the thickness of the sacrifice film  47 , it is possible to control the initial-state distance L 4  between the fixed electrode  42  and the movable electrodes  43  in the variable capacitor X 4  obtained. 
     Next, a plug  45  is formed as shown in  FIG. 56(   d ). The plug  45  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  42   a ,  47   a , with a dielectric material. 
     Next, a dielectric film  44  is formed as shown in  FIG. 56(   c ). The dielectric film  44  is formed by e.g. forming a film of a predetermined dielectric material at predetermined locations by sputtering method, and then etching the film via a mask of a predetermined resist pattern. The dielectric film  44  obtained in this way bonds to the plug  45 . 
     Next, a movable electrode  43  is formed as shown in  FIG. 56(   d ). The movable electrode  43  is formed by e.g. forming a film of aluminum on the sacrifice film  47  and in the above-mentioned unillustrated opening in the sacrifice film  47  by sputtering, and then etching the film via a mask of a predetermined resist pattern. 
     Thereafter, the sacrifice film  47  is removed by wet etching which is performed with a predetermined resist remover. By following the above-described steps, the variable capacitor X 4  can be manufactured successfully. 
       FIG. 57  is a sectional view of a first variation of the variable capacitor X 4 . The view corresponds to  FIG. 55  which shows a section of the variable capacitor X 4  in  FIG. 54 . In the variable capacitor X 4 , the plug  45  may penetrate the dielectric film  44  to be bonded to the movable electrode  43  as shown in  FIG. 57 . In such a variation, the plug  45  constitutes an anchor portion  46  which provides partial connection between the mutually opposed fixed electrode  42  and movable electrode  43 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 4 , with the following change for example: Specifically, the steps of forming the plug  45  and then the dielectric film  44  are replaced by a step of forming a dielectric film  44  which has a predetermined opening that communicates with the opening  47   a  of the sacrifice film  47  on the sacrifice film  47 , and a step thereafter of forming a plug  45  according to the present variation that penetrates the fixed electrode  42 , the sacrifice film  47 , and the dielectric film  44 . 
       FIG. 58  is a sectional view of a second variation of the variable capacitor X 4 . The view corresponds to  FIG. 55  which shows a section of the variable capacitor X 4  in  FIG. 54 . In the variable capacitor X 4 , a dielectric film  44  is formed on the movable electrode  43 , on the side facing the fixed electrode  42 ; instead of this arrangement, a dielectric film  44  may be formed on the fixed electrode  42 , on the side facing the movable electrode  43  as shown in  FIG. 58 . In such a variation, the plug  45  constitutes an anchor portion  46  which provides partial connection between the mutually opposed fixed electrode  42  and movable electrode  43 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 4 , with the following change for example: Specifically, the steps of forming the plug  45  and then the dielectric film  44  are replaced by a step of forming a fixed electrode  42  which has an opening  42   a , and a step thereafter of forming a dielectric film  44  which has a predetermined opening that communicates with the opening  42   a , on the fixed electrode  42 . 
     The movable electrode  43  according to the variable capacitor X 4  including the first variation and the second variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 11  and  FIG. 14 , i.e. may have an initial shape which includes curved portions. Otherwise, the movable electrode  43  according to the variable capacitor X 4  including the first variation and the second variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 13  and  FIG. 15 , i.e. may have an initial shape which includes curved portions as well as having portions contacting with the fixed electrode via the dielectric film. 
       FIG. 59  and  FIG. 60  show a variable capacitor X 5  according to a fifth embodiment of the present invention.  FIG. 59  is a sectional view of the variable capacitor X 5 , and corresponds to  FIG. 47  which shows a section of the variable capacitor X 3  described above.  FIG. 60  is an enlarged partial sectional view of the variable capacitor X 5 , and corresponds to  FIG. 48  which shows an enlarged partial sectional view of the variable capacitor X 3  described above. 
     The variable capacitor X 5  includes a substrate  51 , a fixed electrode  52 , a movable electrode  53 , a dielectric film  54  and a plug  55 . The fixed electrode  52  is formed on the substrate  51 . The movable electrode  53  is built on the substrate  51 . The fixed electrode  52  and the movable electrode  53  cross each other, opposing partially to each other. A distance L 5  shown in  FIG. 60  between the fixed electrode  52  and the movable electrode  53  is 0.5 through 2 μm for example. Preferably, one of the fixed electrode  52  and the movable electrode  53  is grounded. The dielectric film  54  is formed on the movable electrode  53 , on a side facing the fixed electrode  52 . The plug  55  penetrates the fixed electrode  52  and is bonded to the fixed electrode  52 ; and further, penetrates the dielectric film  54  and the movable electrode  53  and is bonded to the movable electrode  53 . A predetermined wiring pattern (not illustrated) electrically connected with the fixed electrode  52  or with the movable electrode  53  is formed on the substrate  51 . The substrate  51 , the fixed electrode  52 , the movable electrode  53 , and the dielectric film  54  are formed of the same materials as are their respective counterparts in the first embodiment, i.e. the substrate  11 , the fixed electrode  12 , the movable electrode  13 , and the dielectric film  14 . The plug  55  is formed of the same material as is the plug  35  in the third embodiment. 
     In the variable capacitor X 5  shown in  FIG. 59 , an anchor portion  56  according to the present invention is constituted by the plug  55 . The anchor portion  56  provides a partial connection between the mutually opposed fixed electrode  52  and the movable electrode  53 . 
     According to the variable capacitor X 5  which has the constitution as described above, it is possible, as described earlier for the variable capacitor X 3 , to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the fixed electrode  52  and the movable electrode  53 . Further, according to the variable capacitor X 5 , the movable electrode  53  is partially connected with or joined on the fixed electrode  52  by the anchor portion  56 , and therefore shape deformation or curving of the movable electrode  53  caused by temperature changes is reduced both during operation and during non-operation. The variable capacitor X 5  as described is able to operate highly accurately as is the variable capacitor X 3 . In addition, according to the variable capacitor X 5 , it is possible to vary the gap volume between the fixed electrode  52  and the movable electrode  53  widely, and to make a setting for a small value for the minimum electrostatic capacitance because of the structure where there is no fixed electrode-to-electrode distance via the anchor portion  56 . Therefore, the variable capacitor X 5  is capable of offering a large amount or rate, of electrostatic capacitance variation as is the variable capacitor X 3 . 
       FIG. 61  shows a method of making the variable capacitor X 5 , in a series of sectional views each corresponding to the section shown in  FIG. 60 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 5 . 
     In the manufacture of the variable capacitor X 5 , first as shown in  FIG. 61(   a ), a fixed electrode  52  and a sacrifice film  57  are formed in lamination on a substrate  51 . The fixed electrode  52  has an opening  52   a , and the sacrifice film  57  has an opening  57   a  which communicates with the opening  52   a , and an unillustrated opening for partially exposing the substrate  51 . The fixed electrode  52  and the sacrifice film  57  can be formed by the same procedures as used for formation of the fixed electrode  42  and the sacrifice film  47  described earlier with reference to  FIG. 56(   a ). 
     Next, as shown in  FIG. 61(   b ), a dielectric film  54  which has an opening  54   a  that communicates with the opening  57   a  is formed. The dielectric film  54  is formed by e.g. forming a film of a predetermined dielectric material at predetermined locations by sputtering method, and then etching the film via a mask of a predetermined resist pattern. 
     Next, as shown in  FIG. 61(   c ), a movable electrode  53  which has an opening  53   a  that communicates with the opening  54   a  is formed. The movable electrode  53  is formed by e.g. forming a film of aluminum on the dielectric film  54 , the sacrifice film  57 , and in the above-mentioned unillustrated opening in the sacrifice film  57  by sputtering method, and then etching the film of aluminum via a mask of a predetermined resist pattern. 
     Next, a plug  55  is formed as shown in  FIG. 61(   d ). The plug  55  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  52   a ,  53   a ,  54   a  and  57   a  with a dielectric material. 
     Thereafter, the sacrifice film  57  is removed by wet etching which is performed with a predetermined resist remover. By following the above-described steps, the variable capacitor X 5  can be manufactured successfully. 
       FIG. 62  is a sectional view of a variation of the variable capacitor X 5 . The view corresponds to  FIG. 60  which shows a section of the variable capacitor X 5  in  FIG. 59 . In the variable capacitor X 5 , a dielectric film  54  is formed on the movable electrode  53 , on the side facing the fixed electrode  52 ; instead of this arrangement, a dielectric film  54  may be formed on the fixed electrode  52 , on the side facing the movable electrode  53 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 5 , with the following change for example: Specifically, the steps of forming a fixed electrode  52  and then forming a sacrifice film  57  and a dielectric film  54  in this sequence are replaced by a step of forming a fixed electrode  52  and a step thereafter of forming a dielectric film  54  and the sacrifice film  57  in this sequence. 
     According to the variable capacitor X 3  including such a variation as described above, the plug  55  may have a cap  55   a  as shown in  FIG. 63 . The caps  35   a  as shown help ensure the bonding relationship between the movable electrode  53  and the plug  55 . 
     The movable electrode  53  according to the variable capacitor X 5  including the above-described variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 11  and  FIG. 14 , i.e. may have an initial shape which includes curved portions. Otherwise, the movable electrode  53  according to the variable capacitor X 5  including the above-described variation may be like the movable electrode  13  according to one of the variations of the variable capacitor X 1  shown in  FIG. 13  and  FIG. 15 , i.e. may have an initial shape which includes curved portions as well as having portions contacting with the fixed electrode via the dielectric film. 
       FIG. 64  and  FIG. 67  show a variable capacitor X 6  according to a sixth embodiment of the present invention.  FIG. 64  is a plan view of the variable capacitor X 6 .  FIG. 65  is a partially unillustrated plan view of the capacitor X 6 .  FIG. 66  is a sectional view taken in lines LXVI-LXVI in  FIG. 64 .  FIG. 67  is an enlarged partial sectional view taken in lines LXVII-LXVII in  FIG. 64 . 
     The variable capacitor X 6  includes a substrate  61 , a movable electrode  62 , a movable electrode  63  (not illustrated in  FIG. 65 ), a dielectric film  64  and a plug  65 . The substrate  61  has a recess  61   a . The movable electrode  62  has two ends bonded to the substrate  61 , and extends over the recess  61   a . The movable electrode  63  is built on the substrate  61 . The movable electrode  63  has a thickness T 6  as shown in  FIG. 67 , of 1 through 2 μm for example. As shown clearly in  FIG. 64 , the movable electrodes  62 ,  63  cross each other, opposing partially to each other. The opposed region has an area of 10000 through 40000 μm 2  for example. A distance L 6  shown in  FIG. 67  between the movable electrodes  62 ,  63  is 0.5 through 2 μm for example. Preferably, one of the movable electrodes  62 ,  63  is grounded. The dielectric film  64  is formed on the movable electrode  62 , on a side facing the movable electrode  63 . The dielectric film  64  has a thickness of 0.1 through 0.5 μm for example. The substrate  61 , the movable electrodes  62 ,  63 , and the dielectric film  64  are formed of the same materials as are their respective counterparts in the second embodiment, i.e. the substrate  21 , the movable electrodes  22 ,  23 , and the dielectric film  24 . The plug  65  penetrates the movable electrode  63 , is bonded to the movable electrode  63 , and is bonded to the dielectric film  64 . The plug  65  as described is formed of a dielectric material such as alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), and silicon nitride (SiN x ). A predetermined wiring pattern (not illustrated) electrically connected with the movable electrode  62  or with the movable electrodes  63  is formed on the substrate  61 . 
     In the variable capacitor X 6  shown in  FIG. 64 , an anchor portion  65  according to the present invention is constituted by the plug  65  and, as clearly shown in  FIG. 67 , a portion  64   a  of the dielectric film  64  which the plug is bonded to. The anchor portion  66  provides a partial connection between the mutually opposed movable electrodes  62 ,  63 . 
     According to the variable capacitor X 6  which has the constitution as described above, it is possible to generate an electrostatic attraction between the movable electrodes  62 ,  63  by applying a voltage between the movable electrodes  62 ,  63 , and by using the electrostatic attraction, it is possible to draw the movable electrodes  62 ,  63  each other, excluding the regions of the movable electrodes  62 ,  63  bonded to the anchor portion  66 , and thereby varying the volume of a gap G 6  between the movable electrodes  62 ,  63  as shown in  FIG. 68 . The electrostatic capacitance of the variable capacitor X 6  varies in accordance with the gap volume. Therefore, according to the variable capacitor X 6 , it is possible to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the movable electrodes  62 ,  63 . 
     Further, according to the variable capacitor X 6 , the movable electrodes  62 ,  63  are partially connected with or joined on each other by the anchor portion  66 ; this reduces shape deformation or curving of the movable electrodes  62 ,  63  caused by temperature changes both in operation and in non-operation. Since curving of both movable electrodes  62 ,  63  is reduced in its initial shape (the shape in non-operation), inconsistency in initial electrostatic capacitance (0.5 through 1 pF for example) during non-operation is reduced in the variable capacitor X 6 . Further, because of the reduced shape deformation caused by temperature changes in both of the movable electrodes  62 ,  63  during operation as well as during non-operation, inconsistency in the relationship between electrostatic capacitance and drive voltage is reduced also. As described, the variable capacitor X 6  is well suited to reduce electrostatic capacitance inconsistency caused by temperature changes. The variable capacitor X 6  as described above is able to operate highly accurately. 
     In addition, according to the variable capacitor X 6 , it is possible to vary the electrostatic capacitance widely. As has been described earlier, in the conventional variable capacitor Y, the movable electrode  93  must be moved within a limited range in order to avoid so called pull-in phenomenon, so it is not possible to vary the electrostatic capacitance over a wide range. On the contrary, according to the variable capacitor X 6  provided by the present invention, it is possible as shown in  FIG. 68(   c ) and  FIG. 68(   d ), to make the movable electrodes  62 ,  63  partially contact with each other via the dielectric film  64  and further, to control the area of partial contact. Hence, according to the variable capacitor X 6 , it is possible to vary the gap volume between the movable electrodes  62 ,  63  widely from the initial state shown in  FIG. 68(   a ) to the state where the area of contact between the movable electrodes  62 ,  63  via the dielectric film  64  reaches a maximum value (e.g. the state as shown in  FIG. 68(   d )). In addition to this, according to the variable capacitor X 6 , the movable electrodes  62 ,  63  have no region which faces to each other via the anchor portion  66 . In other words, there is no partial capacitor structure which has an invariable electrode-to-electrode distance via the anchor portion  36  (and therefore has a fixed electrostatic capacitance). If a variable capacitor includes a partial capacitor structure which has a fixed electrostatic capacitance, a minimum electrostatic capacitance for the entire variable capacitor cannot be smaller than the fixed electrostatic capacitance. On the contrary, the variable capacitor X 6  which does not include any partial capacitor structure that has a fixed electrostatic capacitance does not have such a limitation to the minimum electrostatic capacitance for the entire variable capacitor. Hence, it is easy in the variable capacitor X 6 , to make a setting for a small minimum electrostatic capacitance. As described, according to the variable capacitor X 6 , it is possible to vary the gap volume between the movable electrodes  62 ,  63  widely, and to make a setting for a small value for the minimum electrostatic capacitance because of the structure where there is no fixed electrode-to-electrode distance via the anchor portion  66 . Therefore, the variable capacitor X 6  is capable of offering a large amount or rate, of electrostatic capacitance variation. 
       FIG. 69  and  FIG. 70  show a method of making the variable capacitor X 6 , in a series of sectional views each corresponding to the section shown in  FIG. 66 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 6 . 
     In the manufacture of the variable capacitor X 6 , first, a substrate  61  which has a recess  61   a  as shown in  FIG. 69(   a ) is prepared. Specifically, the same step is performed as for the substrate  21  described with reference to  FIG. 21(   a ). 
     Next, as shown in  FIG. 69(   b ), the recess  61   a  in the substrate  61  is filled with a sacrifice material  67 . Specifically, the same step is performed as described with reference to  FIG. 21(   b ) for filling with the sacrifice material  25 . 
     Next, as shown in  FIG. 69(   c ), a movable electrode  62  and a dielectric film  64  are formed in lamination on the substrate  61 . The movable electrode  62  and the dielectric film  64  can be formed by the same procedures as used for formation of the fixed electrode  12  and the dielectric film  14  described with reference to  FIG. 6(   a ). 
     Next, as shown in  FIG. 70(   a ), a sacrifice film  68  is formed. The sacrifice film  68  has an opening  68   a  for partially exposing the dielectric film  64 , and openings  68   b  for partially exposing the substrate  61 . The region  64   a  of the dielectric film  64  exposed by the opening  68   a  will become part of the anchor portion  66   a  described earlier. The sacrifice film  68  can be formed of the same material and by the same procedures as used for formation of the sacrifice film  15  described earlier with reference to  FIG. 6(   b ). By controlling the thickness of the sacrifice film  68  formed in this step, it is possible to control the initial-state distance L 6  between the movable electrodes  62 ,  63  in the variable capacitor X 6  obtained. 
     Next, as shown in  FIG. 70(   b ), a movable electrode  63  is formed. The movable electrode  63  has an opening  63   a  which communicates with the opening  68   a  of the sacrifice film  68 . The movable electrode  63  can be formed by the same procedures as used for formation of the movable electrode  33  described earlier with reference to  FIG. 50(   c ). Note that for the sake of simplicity in the drawing, the two ends of movable electrode  63  are shown as formed by filling the openings  68   b  in the sacrifice film  68  with an electrically conductive material. 
     Next, a plug  65  is formed as shown in  FIG. 70(   c ). The plug  65  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  63   a ,  68   a , with a dielectric material. 
     Thereafter, wet etching is performed with a predetermined resist remover, to remove the sacrifice film  68  and the sacrifice material  67 . By following the above-described steps, the variable capacitor X 6  can be manufactured successfully. 
       FIG. 71  is a sectional view of a first variation of the variable capacitor X 6 . The view corresponds to  FIG. 67  which shows a section of the variable capacitor X 6  in  FIG. 64 . As shown in  FIG. 71 , in the variable capacitor X 6 , the plug  65  may penetrate the dielectric film  64 , to be bonded to the movable electrode  62 . In such a variation, the plug  65  constitutes an anchor portion  66  which provides partial connection between the mutually opposed movable electrodes  62 ,  63 . The present variation can be manufactured by the method as described above for the manufacture of the variable capacitor X 6 , with an additional step after the one shown in  FIG. 69(   c ), of making an opening in the dielectric film  64  which is to be fitted by the plug  65  according to the present variation. 
       FIG. 72  is a sectional view of a second variation of the variable capacitor X 6 . The view corresponds to  FIG. 67  which shows a section of the variable capacitor X 6  in  FIG. 64 . In the variable capacitor X 6 , a dielectric film  64  is formed on the movable electrode  62 , on the side facing the movable electrode  63 ; instead of this arrangement, a dielectric film  64  may be formed on the movable electrode  63 , on the side facing the movable electrode  62  as shown in  FIG. 52 . In such a variation, the plug  65  constitutes an anchor portion  66  which provides partial connection between the mutually opposed movable electrodes  62 ,  63 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 6 , with the following change for example: Specifically, the step of forming the sacrifice film  68  after the formation of the dielectric film  64  is replaced by a step of forming a sacrifice film  68  which has an opening  68   a  and covers the movable electrode  62 , and a step thereafter of forming a dielectric film  64  which has a predetermined opening that communicates with the opening  68   a  on the sacrifice film  68 . 
     As shown in  FIG. 73 , the plug  65  according to the variable capacitor X 6  including the first variation and the second variation may have a cap  65   a . The caps  65   a  as shown help ensure the bonding relationship between the movable electrode  63  and the plug  65 . 
     The movable electrodes  62 ,  63  according to the variable capacitor X 6  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 25 ,  FIG. 27 ,  FIG. 29 ,  FIG. 30 ,  FIG. 32 ,  FIG. 34 ,  FIG. 36 , and  FIG. 38 , i.e. may have initial shapes which include curved portions. Otherwise, the movable electrodes  62 ,  63  according to the variable capacitor X 6  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 26 ,  FIG. 28 ,  FIG. 31 ,  FIG. 33 ,  FIG. 35 ,  FIG. 37 , and  FIG. 39 , i.e. may have initial shapes which include curved portions as well as having portions contacting with the fixed electrode via the dielectric film. Still further, the movable electrodes  62 ,  63  according to the variable capacitor X 6  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 40  through  FIG. 44 , i.e. may be connected with each other at two locations each by an anchor portion  66 , and having initial shapes like those of the movable electrodes  22 ,  23  in the variations shown in  FIG. 40  through  FIG. 44 . 
       FIG. 74  and  FIG. 75  show a variable capacitor X 7  according to a seventh embodiment of the present invention.  FIG. 74  is a sectional view of the variable capacitor X 7 , and corresponds to  FIG. 66  which shows a section of the variable capacitor X 6  described earlier.  FIG. 75  is an enlarged partial sectional view of the variable capacitor X 7 , and corresponds to  FIG. 67  which shows an enlarged partial sectional view of the variable capacitor X 6 . 
     The variable capacitor X 7  includes a substrate  71 , a movable electrodes  72 ,  73 , a dielectric film  74  and a plug  75 . The substrate  71  has a recess  71   a . The movable electrode  72  has two ends bonded to the substrate  71 , and extends over the recess  71   a . The movable electrode  73  is built on the substrate  71 . The movable electrodes  72 ,  73  cross each other, opposing partially to each other. A distance L 7  shown in  FIG. 75  between the movable electrodes  72 ,  73  is 0.5 through 2 μm for example. Preferably, one of the movable electrodes  72 ,  73  is grounded. The dielectric film  74  is formed on the movable electrode  73 , on a side facing the movable electrode  72 . The plug  75  penetrates the movable electrode  72 , is bonded to the movable electrode  72 , and is bonded to the dielectric film  74 . A predetermined wiring pattern (not illustrated) electrically connected with the movable electrode  72  or with the movable electrodes  73  is formed on the substrate  71 . The substrate  71 , the fixed electrode  72 , the movable electrode  73 , and the dielectric film  74  are formed of the same materials as are their respective counterparts in the second embodiment, i.e. the substrate  21 , the movable electrodes  22 ,  23 , and the dielectric film  24 . The plug  75  is formed of the same material as is the plug  65  in the sixth embodiment. 
     In the variable capacitor X 7  shown in  FIG. 74 , an anchor portion  76  according to the present invention is constituted by the plug  75  and, as clearly shown in  FIG. 75 , a portion  74   a  of the dielectric film  74  which the plug is bonded to. The anchor portion  76  provides a partial connection between the mutually opposed movable electrodes  72 ,  73 . 
     According to the variable capacitor X 7  which has the constitution as described above, it is possible, as in the variable capacitor X 6  described earlier, to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the movable electrodes  72 ,  73 . Further, according to the variable capacitor X 7 , the two movable electrodes  72 ,  73  are partially connected with or joined on each other by the anchor portion  76 , and therefore shape deformation or curving of the movable electrodes  72 ,  73  caused by temperature changes is reduced both during operation and during non-operation. The variable capacitor X 7  as described is able to operate highly accurately as is the variable capacitor X 6 . In addition, according to the variable capacitor X 7 , it is possible to vary the gap volume between the fixed electrodes  72 ,  73  widely, and it is easy to make a setting for a small value for the minimum electrostatic capacitance since the capacitor does not include a structure where there is a fixed electrode-to-electrode distance via the anchor portion  76 . Therefore, the variable capacitor X 7  is capable of offering a large amount or rate, of electrostatic capacitance variation as is the variable capacitor X 6 . 
       FIG. 76  and  FIG. 77  show a method of making the variable capacitor X 7 , in a series of sectional views each corresponding to the section shown in  FIG. 75 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 7 . 
     In the manufacture of the variable capacitor X 7 , first as shown in  FIG. 76(   a ), the recess  71   a  in the substrate  71  is filled with a sacrifice material  77 . Specifically, the same step is performed as described with reference to  FIG. 21(   b ) for filling with the sacrifice material  25 . 
     Next, as shown in  FIG. 76(   b ), a movable electrode  72  is formed on the substrate  71 , i.e. on the sacrifice material  77 . The movable electrode  72  has an opening  72   a . The movable electrode  72  can be formed by the same procedures as used for formation of the fixed electrode  42   a  described with reference to  FIG. 56(   a ). 
     Next, as shown in  FIG. 76(   c ), a sacrifice film is formed. The sacrifice film  78  has an opening  78   a  which communicates with the opening  72   a . The sacrifice film  78  can be formed by the same procedures as used for formation of the sacrifice film  47  described with reference to  FIG. 56(   a ). By controlling the thickness of the sacrifice film  78  formed in this step, it is possible to control the initial-state distance L 7  between the movable electrodes  72 ,  73  in the variable capacitor X 7  obtained. 
     Next, as shown in  FIG. 77(   a ), a plug  75  is formed. The plug  75  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  72   a ,  78   a , with a dielectric material. 
     Next, as shown in  FIG. 77(   b ), a dielectric film  74  is formed. The dielectric film  74  can be formed by the same procedures as used for formation of the dielectric film  44  described with reference to  FIG. 56(   c ). The dielectric film  74  obtained in this way bonds to the plug  75 . 
     Next, as shown in  FIG. 77(   c ), a movable electrode  73  is formed. The movable electrode  73  can be formed by the same procedures as used for formation of the movable electrode  43  described with reference to  FIG. 56(   d ). 
     Thereafter, the sacrifice film  78  and the sacrifice material  77  are removed by wet etching which is performed with a predetermined resist remover. By following the above-described steps, the variable capacitor X 7  can be manufactured successfully. 
       FIG. 78  is a sectional view of a first variation of the variable capacitor X 7 . The view corresponds to  FIG. 75  which shows a section of the variable capacitor X 7  in  FIG. 74 . As shown in  FIG. 71 , in the variable capacitor X 7 , the plug  75  may penetrate the dielectric film  74 , to be bonded to the movable electrode  73 . In such a variation, the plug  75  constitutes an anchor portion  76  which provides partial connection between the mutually opposed movable electrodes  72 ,  73 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 7 , with the following change for example: Specifically, the step of forming the dielectric film  74  after the formation of the plug  75  is replaced by a step of forming a dielectric film  74  which has a predetermined opening that communicates with the opening  78   a  of the sacrifice film  78 , on the sacrifice film  78 , and a step thereafter of forming a plug  75  according to the present variation which penetrates the movable electrode  72 , the sacrifice film  78 , and the dielectric film  74 . 
       FIG. 79  is a sectional view of a second variation of the variable capacitor X 7 . The view corresponds to  FIG. 75  which shows a section of the variable capacitor X 7  in  FIG. 74 . In the variable capacitor X 7 , a dielectric film  74  is formed on the movable electrode  73 , on the side facing the movable electrode  72 ; instead of this arrangement, a dielectric film  74  may be formed on the movable electrode  72 , on the side facing the movable electrode  73  as shown in  FIG. 79 . In such a variation, the plug  75  constitutes an anchor portion  76  which provides partial connection between the mutually opposed movable electrodes  72 ,  73 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 7 , with the following change for example: Specifically, the step of forming the plug  75  and the step thereafter of forming the dielectric film  74  are replaced by a step of forming a movable electrode  72  which has an opening  72   a , and a step thereafter of forming a dielectric film  74  which has a predetermined opening that communicates with the opening  72   a.    
     The movable electrodes  72 ,  73  according to the variable capacitor X 7  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 25 ,  FIG. 27 ,  FIG. 29 ,  FIG. 30 ,  FIG. 32 ,  FIG. 34 ,  FIG. 36 , and  FIG. 38 , i.e. may have initial shapes which include curved portions. Otherwise, the movable electrodes  72 ,  73  according to the variable capacitor X 7  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 26 ,  FIG. 28 ,  FIG. 31 ,  FIG. 33 ,  FIG. 35 ,  FIG. 37 , and  FIG. 39 , i.e. may have initial shapes which include curved portions as well as having portions contacting with each other via the dielectric film. Still further, the movable electrodes  72 ,  73  according to the variable capacitor X 7  including the first variation and the second variation may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 40  through  FIG. 44 , i.e. may be connected with each other at two locations each by an anchor portion  76 , and having initial shapes like those of the movable electrodes  22 ,  23  in the variations shown in  FIG. 40  through  FIG. 44 . 
       FIG. 80  and  FIG. 81  show a variable capacitor X 8  according to an eighth embodiment of the present invention.  FIG. 80  is a sectional view of the variable capacitor X 8 , and corresponds to  FIG. 66  which shows a section of the variable capacitor X 6  described earlier.  FIG. 81  is an enlarged partial sectional view of the variable capacitor X 8 , and corresponds to  FIG. 67  which shows an enlarged partial sectional view of the variable capacitor X 6 . 
     The variable capacitor X 8  includes a substrate  81 , movable electrodes  82 ,  83 , a dielectric film  84  and a plug  85 . The substrate  81  has a recess  81   a . The movable electrode  82  has two ends bonded to the substrate  81 , and extends over the recess  81   a . The movable electrode  83  is built on the substrate  81 . The movable electrodes  82 ,  83  cross each other, opposing partially to each other. A distance L 8  shown in  FIG. 81  between the movable electrodes  82 ,  83  is 0.5 through 2 μm for example. Preferably, one of the movable electrodes  82 ,  83  is grounded. The plug  85  penetrates the movable electrode  82  and is bonded to the movable electrode  83 ; and further, penetrates the dielectric film  84  and the movable electrode  83  and is bonded to the movable electrode  83 . A predetermined wiring pattern (not illustrated) electrically connected with the movable electrode  82  or with the movable electrodes  83  is formed on the substrate  81 . The substrate  81 , the movable electrodes  82 ,  83 , and the dielectric film  84  are formed of the same materials as are their respective counterparts in the second embodiment, i.e. the substrate  21 , the movable electrodes  22 ,  23 , and the dielectric film  24 . The plug  85  is formed of the same material as is the plug  65  in the sixth embodiment. 
     In the variable capacitor X 8  shown in  FIG. 80 , an anchor portion  86  according to the present invention is constituted by the plug  85 . The anchor portion  86  provides a partial connection between the mutually opposed movable electrodes  82 ,  83 . 
     According to the variable capacitor X 8  which has the constitution as described above, it is possible, as in the variable capacitor X 6  described earlier, to control the electrostatic capacitance by controlling the drive voltage (0 through 20 V for example) which is applied between the movable electrodes  82 ,  83 . Further, according to the variable capacitor X 8 , the movable electrodes  82 ,  83  are partially connected with or joined on each other by the anchor portion  86 , and therefore shape deformation or curving of the movable electrodes  82 ,  83  caused by temperature changes is reduced both during operation and during non-operation. The variable capacitor X 8  as described is able to operate highly accurately as is the variable capacitor X 6 . In addition, according to the variable capacitor X 8 , it is possible to vary the gap volume between the movable electrodes  82 ,  83  widely, and it is easy to make a setting for a small value for the minimum electrostatic capacitance since the capacitor does not include a structure where there is a fixed electrode-to-electrode distance via the anchor portion  86 . Therefore, the variable capacitor X 8  is capable of offering a large amount or rate, of electrostatic capacitance variation as is the variable capacitor X 6 . 
       FIG. 82  and  FIG. 83  show a method of making the variable capacitor X 8 , in a series of sectional views each corresponding to the section shown in  FIG. 81 . The present method uses so called MEMS technology for the manufacture of the variable capacitor X 8 . 
     In the manufacture of the variable capacitor X 8 , first as shown in  FIG. 82(   a ), a recess  81   a  in a substrate  81  is filled with a sacrifice material  87 . Specifically, the same step is performed as described with reference to  FIG. 21(   b ) for filling with the sacrifice material  25 . 
     Next, as shown in  FIG. 82(   b ), a movable electrode  82  is formed on the substrate  81 , i.e. on the sacrifice material  87 . The movable electrode  82  has an opening  82   a . The movable electrode  82  can be formed by the same procedures as used for formation of the fixed electrode  42  described with reference to  FIG. 56(   a ). 
     Next, as shown in  FIG. 82(   c ), a sacrifice film  88  is formed. The sacrifice film  88  has an opening  88   a  which communicates with the opening  82   a . The sacrifice film  88  can be formed by the same procedures as used for formation of the sacrifice film  47  described with reference to  FIG. 56(   a ). By controlling the thickness of the sacrifice film  88  formed in this step, it is possible to control the initial-state distance L 8  between the movable electrodes  82 ,  83  in the variable capacitor X 8  obtained. 
     Next, as shown in  FIG. 83(   b ), a dielectric film  84  which has an opening  84   a  that communicates with the opening  88   a  is formed. The dielectric film  84  can be formed by e.g. first forming a film of a predetermined dielectric material on predetermined locations by sputtering method, and then etching the film via a mask of a predetermined resist pattern. 
     Next, as shown in  FIG. 83(   b ), a movable electrode  83  which has an opening  83   a  that communicates with the opening  84   a  is formed. The movable electrode  83  can be formed by e.g. first forming a film of aluminum on the dielectric film  84 , the sacrifice film  88 , etc. by sputtering, and then etching the Al film via a mask of a predetermined resist pattern. 
     Next, as shown in  FIG. 83(   c ), a plug  85  is formed. The plug  85  can be formed by e.g. sputtering method thereby filling the through hole provided by the openings  82   a ,  83   a ,  84   a  and  88   a , with a dielectric material. 
     Thereafter, the sacrifice film  88  and the sacrifice material  87  are removed by wet etching performed with a predetermined resist remover. By following the above-described steps, the variable capacitor X 8  can be manufactured successfully. 
       FIG. 84  is a sectional view of a variation of the variable capacitor X 8 . The view corresponds to  FIG. 81  which shows a section of the variable capacitor X 9  in  FIG. 80 . In the variable capacitor X 8 , a dielectric film  84  is formed on the movable electrode  83 , on the side facing the movable electrode  82 ; instead of this arrangement, a dielectric film  84  may be formed on the movable electrode  82 , on the side facing the movable electrode  83  as shown in  FIG. 84 . The present variation can be manufactured by the same method as described above for the manufacture of the variable capacitor X 8 , with the following change for example: Specifically, the step of forming the movable electrode  82  and the step thereafter of forming the sacrifice film  88  and the dielectric film  84  in this sequence are replaced by a step of forming a movable electrode  82 , and a step thereafter of forming a dielectric film  84  and a sacrifice film  88  in this sequence. 
     As shown in  FIG. 85 , the plug  85  according to the variable capacitor X 8  including such a variation as the above may have a cap  65   a . The caps  85   a  as shown help ensure the bonding relationship between the movable electrode  83  and the plug  85 . 
     The movable electrodes  82 ,  83  according to the variable capacitor X 8  including the variation described above may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 25 ,  FIG. 27 ,  FIG. 29 ,  FIG. 30 ,  FIG. 32 ,  FIG. 34 ,  FIG. 36 , and  FIG. 38 , i.e. may have initial shapes which include curved portions. Otherwise, the movable electrodes  82 ,  83  according to the variable capacitor X 8  including the variation described above may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 26 ,  FIG. 28 ,  FIG. 31 ,  FIG. 33 ,  FIG. 35 ,  FIG. 37 , and  FIG. 39 , i.e. may have initial shapes which include curved portions as well as having portions contacting with the fixed electrode via the dielectric film. Still further, the movable electrodes  82 ,  83  according to the variable capacitor X 8  including the variation described above may be like the movable electrodes  22 ,  23  according to one of the variations of the variable capacitor X 2  shown in  FIG. 40  through  FIG. 44 , i.e. may be connected with each other at two locations each by an anchor portion  86 , and having initial shapes like those of the movable electrodes  22 ,  23  in the variations shown in  FIG. 40  through  FIG. 44 .