JPH0982569A - Capacitor with variable capacitance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise a Q value and improve stability of frequency and lessen carrier noise by varying the electrostatic capacitance between a detection electrode and a second electrode, using the Coulomb force between a drive electrode and a first electrode and the elastic force of a mobile part. SOLUTION: DC outer bias voltage is applied between a first electrode 25A and a drive electrode 19 through extraction electrodes 27 and 29 to generate Coulomb force between the first electrode 25A and the drive electrode 19. And, a mobile part 23 is drawn to the drive electrode 19, with the upper end side of a support 22 as a fulcrum. On the other hand, elastic force seeking to return to the former position is generated in the mobile part 23. As a result, the mobile part 23 is displaced to the position where the Coulomb force and the elastic force are balanced, and the space between the detection electrode 20 and the second electrode 2513 narrows, which varies the electrostatic capacitance between the detection electrode 20 and the second electrode 25B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitor which is a kind of voltage variable capacitor.

[0002]

2. Description of the Related Art Conventionally, as a voltage variable capacitance element, there is known a variable capacitance diode whose electrostatic capacitance changes when an external bias voltage is applied to a space charge region of a semiconductor surface surrounded by an insulating layer.

Further, a variable capacitor disclosed in Japanese Patent Laid-Open No. 5-74655 is known. As shown in FIG. 8, the variable capacitor includes a fixed electrode 1 and a movable electrode 2 both of which are formed as a thin film body, and these are supported opposite to each other via a space portion 4 provided in an insulating support base 3. It has a different structure. The insulating support base 3 is, for example, a silicon substrate, and the fixed electrode 1 formed by vapor deposition of aluminum or the like is provided on the bottom surface of the space portion 4 which is a recess formed by engraving on one surface side thereof. A movable electrode 2 formed in the same manner is provided on the opening edge of the recess in a state of floating via a space 4, and is formed by being drawn from one end of each of the fixed electrode 1 and the movable electrode 2. An external bias voltage is applied between the terminals (not shown). When an external bias voltage is applied between the fixed electrode 1 and the movable electrode 2, the Coulomb force between the fixed electrode 1 and the movable electrode 2 acts to increase or decrease the distance between them and change the electrostatic capacitance.

Further, the variable capacitance diode and variable capacitance capacitor by the voltage control described above are the voltage controlled oscillator V
CO (Voltage Controlled Osc)
ilator). In addition, V
CO is used in the synthesizer local oscillator of a wireless communication device. FIG. 9 shows a well-known collector grounded Colpitts oscillator circuit as a basic example of a VCO. This circuit is configured with an active element 5 such as a transistor and a resonant element 6 as main elements. In FIG. 9, T1 is a control voltage input terminal, T2 is an oscillation output terminal, 7 is an input resistance, 8 is a bias resistance, 9 and 10 are coupling capacitors, 11 and 12 are feedback capacitors, and 13 is a variable capacitor. The resonant element 6, the variable capacitor 13 and the coupling capacitors 9 and 10 form a resonant circuit 14. Power supply (not shown) for driving the resonance circuit 14
Is applied to the base of the transistor 5.

When the VCO is used, a phase comparator (not shown) is connected between the control voltage input terminal T1 and the oscillation output terminal T2. The phase comparator has an oscillation output terminal T
A pulse signal proportional to the phase difference between the feedback signal from the VCO input to the phase comparator from 2 and the comparison reference frequency is output and supplied to the resonance circuit 14 via the control voltage input terminal T1.

[0006]

However, although the variable capacitance diode can change the electrostatic capacitance by a single element, it is necessary to increase the internal resistance in order to improve the electrical withstand voltage. . When the internal resistance is increased, the Q value indicating the performance index of the capacitor expressed by 1 / 2πfcr (where f is the frequency, c is the electrostatic capacity, and r is the internal resistance) becomes small, and the frequency stability becomes poor. Also, there is a drawback that carrier noise becomes large.

In the case of a variable capacitor, the movable electrode 2
Is to be displaced by ⅓ or more of the distance between the fixed electrode 1 and the movable electrode 2 in the state where the external bias voltage is not applied, the thin plate having the movable electrode 2 formed on its surface returns to its original position. There is a drawback in that the elastic force (restoring force) that occurs and the Coulomb force generated between the fixed electrode 1 and the movable electrode 2 are no longer balanced, and the movable electrode 2 is attracted to the fixed electrode 1. Therefore, the variable rate of the electrostatic capacity cannot be increased.

When the above VCO is used in a high frequency band, as shown in FIG. 10, the pulse signal supplied from the phase comparator (not shown) to the resonance circuit 14 via the control voltage input terminal T1 is integrated. In order to insulate the resonance circuit 14 at high frequency from the low-pass filter composed of the resistor 7 and the capacitor 16, an inductor 15 is provided between the connection point of the resistor 7 and the capacitor 16 and the cathode of the variable capacitor 13. Had to connect. For this reason, the number of VCO components has increased and the circuit configuration has become complicated. Also, especially several hundred M
When using the VCO in the high frequency band above Hz, the power supply V
In order to insulate cc from the resonance circuit 14, the inductor 15
It was necessary to increase the inductance of. Therefore, if the inductor 15 is to be formed by the strip line formed on the circuit board, the area occupied by the inductor 15 becomes large and the VCO cannot be miniaturized. Further, when the Q value of the inductor 15 is low, the resonance circuit 14 is affected by this, and there is a problem that the Q value itself of the resonance circuit 14 is lowered.

Therefore, an object of the present invention is to provide a variable capacitor for solving the above problems.

[0010]

The variable capacitance capacitor of the present invention is configured as follows in order to achieve the above object. That is, first, an insulating support base, a drive electrode formed on the surface of the insulation support base, a detection electrode formed on the surface of the insulation support base with a constant distance from the drive electrode, Between the drive electrode and the first electrode, a movable electrode having a movable portion having a first electrode provided to face the drive electrode and a second electrode provided to face the detection electrode. Means for applying a voltage to the electrostatic capacitance between the detection electrode and the second electrode using the Coulomb force between the drive electrode and the first electrode and the elastic force of the movable part. Is variable.

When an external bias voltage is applied between the drive electrode and the first electrode, a Coulomb force is generated between the drive electrode and the first electrode. The movable part is attracted to the drive electrode while maintaining the balance between its own elasticity and the Coulomb force. As a result, the average distance between the detection electrode and the second electrode is narrowed. The capacitance between the detection electrode and the second electrode is inversely proportional to the average distance between them. Therefore, depending on the external bias voltage applied between the drive electrode and the first electrode,
The capacitance between the detection electrode and the second electrode changes.

Further, since the drive electrode and the first electrode are not directly connected to the detection electrode and the second electrode, the electrical insulation between them is maintained. For this reason,
It is not necessary to connect an inductor for isolating the pass filter and the resonance circuit at high frequencies.

Secondly, in the first invention, the movable electrode is provided so as to stand on a fixed portion formed on a surface near an end edge of the insulating support and an end edge of the fixed portion on a central portion side. And a movable portion provided on the upper end of the supporting portion so as to be parallel to the insulating support base. The movable portion is displaced with the upper end of the supporting portion as a fulcrum.

When an external bias voltage is applied between the drive electrode and the first electrode, the movable portion is attracted to the drive electrode with the upper end of the support portion as a fulcrum. Since only one end of the movable portion is supported, the movable portion can be displaced with a relatively small external bias voltage. Thirdly, in the first invention, the movable electrode is provided so as to stand upright on the pair of fixed portions formed on the surfaces of the insulating support near the opposite end edges of the insulating support and the central portion of the fixed portions. A pair of first supporting portions and a movable portion provided on the upper ends of the pair of supporting portions so as to be parallel to the insulating support base. And the second electrode sandwiched between the pair of first electrodes are formed, and the movable portion is displaced with the upper ends of the pair of supporting portions as fulcrums.

When an external bias voltage is applied between the drive electrode and the first electrode, the movable portion is attracted to the drive electrode with the upper ends of the pair of supporting portions as fulcrums. For this reason, the central part of the movable part bends most. Since the second electrode is formed at the center of the movable part, the second electrode is displaced much more than the pair of first electrodes. The capacitance between the second electrode and the detection electrode is proportional to the reciprocal of the average distance between them. Therefore, the variable rate of the capacitance between the second electrode and the detection electrode becomes large.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of a variable capacitor according to the present invention will be described with reference to FIGS.

The variable capacitor is an insulating support 17
A movable electrode 18, a drive electrode 19, and a detection electrode 20.

The insulating support 17 is a square plate made of an insulating material such as glass or ceramic.

The movable electrode 18 includes a fixed portion 21 and a support portion 2.
2 and the movable portion 23 are integrally formed.

The fixed portion 21 of the rectangular plate is provided on the insulating support base 17
On the surface near the edge of the insulating support 17 and the fixing portion 2.
It is fixedly provided such that the long sides of 1 are parallel to each other.

A plate-shaped support portion 22 is provided upright on the long side edge of the fixed portion 21 on the central portion side of the insulating support base 17.

One long side edge of the movable portion 23 of the rectangular plate is provided at the upper end of the support portion 22. The length of the long side of the movable portion 23 is the same as the length of the support portion 22, and the length of the short side of the movable portion 23 is the length from the support portion 22 to the free tip. As a result, the movable portion 23 is supported by the support portion 22, and is kept parallel to the insulating support base 17 while floating above the surface.

The movable electrode 18 is made of silicon dioxide (S
iO2) layer 24, a first electrode 25A formed on the back surface of the silicon dioxide layer 24, a second electrode 25B, and a conductor layer 26 formed on the surface of the silicon dioxide layer 24. The first electrode 25A and the second electrode 2
5B is formed symmetrically with respect to the center line L1 of the movable electrode 18 with a predetermined gap W1. Therefore, the insulation between the first electrode 25A and the second electrode 25B is maintained.
Since the silicon dioxide layer 24 is formed in a laminated structure that is substantially symmetrical with respect to the silicon dioxide layer 24, the stresses generated on the front and back surfaces of the silicon dioxide layer 24 cancel each other out, and the warp of the movable electrode 18 is prevented. Since the movable portion 23 is formed to have a thin thickness of about 1 μm, it becomes extremely light. As a result, the tip portion of the movable portion 23 does not hang down, and the dimension H of the gap between the movable portion 23 and the insulating support 17 is kept constant. Further, the mechanical resonance frequency of the movable portion 23 is set high in order to prevent the movable portion 23 from easily vibrating due to vibration or the like applied to the variable capacitor from the outside. Therefore, the first electrode 25A,
For the second electrode 25B and the conductor layer 26, a thin film of aluminum having a low specific gravity is generally used. First electrode 25A
And the second electrode 25B is electrically connected to the rectangular lead electrodes 27 and 28 formed on the surface of the insulating support 17. The shape of the extraction electrode 28 is made as large as possible to reduce the influence of the resistance component.

The drive electrode 19 is a rectangular thin-film electrode made of a material having a low resistivity such as aluminum or gold. The length of the long side of the drive electrode 19 is the same as the short side of the movable portion 23, and the length of the short side is 1 / the length of the long side of the movable portion 23.
It is formed to be slightly shorter than 2. The drive electrode 19 is provided with a constant distance W2 from the support portion 22, and the long side direction of the drive electrode 19 is aligned with the short side direction of the movable portion 23 so that the surface of the insulating support base 17 faces the movable portion 23. Is formed.
The short side of the drive electrode 19 is electrically connected to the extraction electrode 29 formed on the surface of the insulating support base 17.

The detection electrode 20 is a rectangular thin film electrode made of a material having a low resistivity such as aluminum or gold. The length of the long side of the detection electrode 20 is the same as the short side of the movable portion 23, and the length of the short side is 1 / the length of the long side of the movable portion 23.
It is formed to be slightly shorter than 2. The detection electrode 20 is provided with a constant distance W2 from the support portion 22 so that the long side direction of the detection electrode 20 coincides with the short side direction of the movable portion 23 so that the insulating support base 17 facing the movable portion 23 is provided. Formed on the surface. The short side of the detection electrode 20 is electrically connected to the extraction electrode 30 formed on the surface of the insulating support base 17. Make the shape of the extraction electrode 30 as large as possible,
Reduce the effect of the resistance component.

Next, an outline of the method of manufacturing the variable capacitor will be described with reference to FIGS. 3 (a) to 3 (e). Note that FIGS. 3A to 3D show A- in FIG.
It is sectional drawing of A '. Further, FIG. 3 (e) corresponds to FIG. 1 (a).
3 is a cross-sectional view parallel to the central axis L1 in FIG.

The drive electrode 19, the detection electrode 20, and the extraction electrodes 27, 28, 29, 30 are formed on the surface of the insulating support 17 by means of vapor deposition or sputtering using a mask pattern of a predetermined shape. To be done.

Next, a sacrificial layer 31 made of, for example, zinc oxide (ZnO) and having a thickness H of a rectangular plate is formed so as to cover the surfaces of the drive electrodes 19 and the detection electrodes 20. The sacrificial layer 31 is formed by a method such as vapor deposition or sputtering using a mask pattern having a predetermined shape.

Further, a strip-shaped first electrode 25A is formed from the surface portion of the sacrificial layer 31 facing the drive electrode 19 to the lead electrode 27. The first electrode 25A is electrically connected to the extraction electrode 27. Further, a band-shaped second electrode 25B is formed from the surface portion of the sacrificial layer 31 facing the drive electrode 20 to the lead electrode 28. The second electrode 25B is electrically connected to the extraction electrode 28. The first electrode 25A and the second electrode 25B are aluminum thin films formed by means such as vapor deposition or sputtering using a mask pattern of a predetermined shape.

Further, the silicon dioxide layer 24 is formed so as to cover the first electrode 25A, the second electrode 25B, and the gap between the first electrode 25A and the second electrode 25B. The silicon dioxide layer 24 is formed by using a mask pattern of a predetermined shape.
It is formed by means such as spattering or plasma CVD. The silicon dioxide layer 24 formed on the sacrificial layer 31, that is, the portion corresponding to the movable portion 23 is thinner than the portions corresponding to the fixed portion 21 and the support portion 22, and has a thickness of about 1 μm.

Further, on the surface of the silicon dioxide layer 24,
Using a mask pattern having a predetermined shape, the aluminum conductor layer 26 is formed by means such as vapor deposition or sputtering. After that, the sacrificial layer 31 is removed by a means such as chemical etching to form a variable capacitance capacitor.

Next, the outline of the operation of the variable capacitor will be described.

When a direct current external bias voltage is applied between the first electrode 25A and the driving electrode 19 via the extraction electrodes 27 and 29, a black voltage is applied between the first electrode 25A and the driving electrode 19. Power is generated. Therefore, the movable part 23
Are attracted to the drive electrode 19 with the upper end side of the support portion 22 as a fulcrum. On the other hand, in the movable portion 23, an elastic force to return to the original position is generated. As a result, the movable portion 23 displaces to a position where the Coulomb force and the elastic force are balanced and stands still.
Along with this, the distance between the detection electrode 20 and the second electrode 25B is narrowed, and the electrostatic capacitance between the detection electrode 20 and the second electrode 25B is changed. The detection electrode 20 and the second electrode 25
The electrostatic capacitance between B is extracted via the extraction electrode 27 and the extraction electrode 30.

Further, in the variable capacitor of the present invention, since the drive electrode 19 and the first electrode 25A and the detection electrode 20 and the second electrode 25B are not directly connected to each other, the electrical capacitance therebetween is not provided. Insulation is maintained. Therefore, as shown in FIG. 4, a low-pass filter including a resistor 7 and a capacitance between the drive electrode 19 and the first electrode 25A.
Since the resonance circuit 14 and the resonance circuit 14 are insulated from each other at high frequencies, the inductor 15 connected in the conventional VCO becomes unnecessary.

(Embodiment 2) An embodiment of another variable capacitor according to the present invention will be described with reference to FIGS. The same numbers are used for the components corresponding to those in the first embodiment. Further, a schematic description of the method of manufacturing the variable capacitor is omitted because it is similar to that of the first embodiment.

The variable capacitor is an insulating support 17
A movable electrode 18, drive electrodes 19A and 19B, and a detection electrode 20.

The insulating support 17 is a square plate made of an insulating material such as glass or ceramic.

The movable electrode 18 includes fixed portions 21A and 21B.
And the support portions 22A and 22B and the movable portion 23 are integrally formed.

The fixed portion 21A is provided on the surface near one end edge of the insulating support base 17 and the end portion of the insulating support base 17 and the fixed portion 21.
It is fixed so that the long sides of A are parallel. The fixed portion 21B is provided on the surface near the other end edge of the insulating support 17 at a predetermined distance from the fixed portion 21A.
The fixed edge is fixed so that the long edge of the fixed edge and the long side of the fixed portion 21B are parallel.

A plate-shaped support portion 22A is provided upright on the long side edge of the fixed portion 21A on the center side of the insulating support base 17. Similarly, a plate-shaped support portion 22B is provided upright on the long side edge of the fixed portion 21B on the central portion side of the insulating support base 17.

The long side edges of the movable portion 23 of the rectangular plate are provided at the upper ends of the support portions 22A and 22B. As a result, the movable portion 23 is supported by the support portions 22A and 22B, and is kept parallel to the insulating support base 17 while floating above the surface.

The movable electrode 18 is formed by the silicon dioxide layer 24. On the back surface of the movable portion 23, a pair of rectangular first electrodes 25A is formed. A pair of first electrodes 25A
Is such that the long side direction of the first electrode 25A is parallel to the central axis L2 of the movable portion 23 in the short side direction, and the central axis L2
They are arranged symmetrically with respect to. A space W3 is provided between the pair of first electrodes 25A.

The short side ends on the same side of the pair of first electrodes 25A are electrically connected to each other by a lead wire 32 formed on the back surface of the movable electrode 18. Furthermore, the lead wire 32
Are electrically connected to the rectangular lead electrode 28 formed on the surface of the insulating support 17.

A rectangular second electrode 25 is provided in the gap W3 between the pair of first electrodes 25A provided on the back surface of the movable portion 23.
B is formed. The second electrode 25B is the second electrode 25
The long side direction of B is arranged parallel to the central axis L2 and symmetrical with respect to the central axis L2. Second electrode 25
The short side edge of B is a lead formed on the back surface of the movable electrode 18.
It is electrically connected to the rectangular lead electrode 27 via the lead wire 33. The shapes of the lead wire 33 and the lead electrode 27 are made as large as possible to reduce the influence of the resistance component.

A conductor layer 26 is formed on the surface of the movable electrode 18.

A conductor layer 26 is formed on the surface of the silicon dioxide layer 24.
And a pair of first electrodes 25A, second electrodes 25B, and lead wires 32 and 33 are formed on the back surface of the silicon dioxide layer 24. The generated stresses cancel each other out, and the warp of the movable electrode 18 is prevented.

Since the movable portion 23 is formed as thin as about 1 μm, it becomes extremely light. As a result, the movable part 23
Without hanging down, the gap H between the movable portion 23 and the insulating support 17 is kept constant. Further, the mechanical resonance frequency of the movable portion 23 is set high in order to prevent the movable portion 23 from easily vibrating due to vibration or the like applied to the variable capacitor from the outside. Therefore, the first electrode 25A, the second electrode 25B, the conductor layer 26, and the lead wires 32 and 33 are generally thin aluminum films having a low specific gravity.

Driving electrodes 19A and 19B are respectively formed on the surface of the insulating support 17 which faces the pair of first electrodes 25A. The drive electrodes 19A and 19B are rectangular thin-film electrodes formed of a material having a low resistivity such as aluminum and gold. The long side ends of the drive electrodes 19A and 19B are electrically connected to each other by a lead wire 34 formed on the surface of the insulating support 17. The short side of the drive electrode 19A is electrically connected to the rectangular lead electrode 29 formed on the surface of the insulating support 17.

Insulating support base 1 facing the second electrode 25B
A rectangular detection electrode 20 made of a material having a low resistivity such as aluminum or gold is formed on the surface of 7. One short side of the detection electrode 20 is electrically connected to the rectangular lead electrode 30 formed on the surface of the insulating support 17. Make the shape of the extraction electrode 30 as large as possible,
Reduce the effect of the resistance component.

Next, the outline of the operation of the variable capacitor will be described.

The extraction electrode 28 and the lead wire 32,
When a DC external bias voltage is applied between the pair of first electrodes 25A and the drive electrodes 19A and 19B via the extraction electrodes 29, the first electrodes 25A and the drive electrodes 19A
A Coulomb force is generated between B and 19B. Therefore, the movable portion 23 is attracted to the drive electrodes 19A and 19B with the upper ends of the support portions 22A and 22B as fulcrums. On the other hand, in the movable portion 23, an elastic force to return to the original position is generated. As a result, the movable portion 23 displaces to a position where the Coulomb force and the elastic force are balanced and stands still. Along with this, the average distance between the detection electrode 20 and the second electrode 25B narrows. In this case, since the second electrode 25B is located at the center of the movable portion 23, the second electrode 25B is displaced more than the first electrode 25A as shown in FIG. Therefore, the capacitance between the detection electrode 20 and the second electrode 25B is proportional to the reciprocal of the average distance between the two, so that the variable rate of the capacitance can be increased. The capacitance between the detection electrode 20 and the second electrode 25B is extracted via the extraction electrode 27 and the extraction electrode 30.

Further, the variable capacitor of the present invention includes the drive electrodes 19A and 19B and the pair of first electrodes 25A.
Since the detection electrode 20 and the second electrode 25B are not directly connected to each other, the electrical insulation between them is maintained. Therefore, the resistor 7, the low-pass filter formed of the electrostatic capacitance between the drive electrodes 19A and 19B and the pair of first electrodes 25A, and the resonance circuit 14 are insulated from each other at a high frequency, and thus the conventional VCO is used. The inductor 15 connected at is no longer necessary.

[0053]

The present invention having the above-mentioned structure has the following effects. That is, the movable part is displaced while maintaining the balance between the Coulomb force generated between the drive electrode and the movable electrode and its own elasticity. The capacitance between the detection electrode and the movable part is proportional to the reciprocal of this average distance. As a result, the capacitance between the detection electrode and the movable portion can be changed. Further, the series resistance becomes extremely small as compared with the varactor diode. Therefore, 1 / 2πfcr
(However, f is the frequency, c is the electrostatic capacitance, and r is the internal resistance.) A very high Q value is obtained, and the frequency stability is improved. Furthermore, since the movable portion and the detection electrode are insulated from each other by air, the withstand voltage of the variable capacitor increases.

Furthermore, since the drive electrode and the first electrode are not electrically connected to the detection electrode and the second electrode, electrical insulation is maintained. For this reason, when a VCO is manufactured using the variable capacitor of the present invention, it is necessary to provide an inductor for high-frequency insulation between the low-pass filter and the resonance circuit as in the conventional VCO. Lost. As a result, the circuit configuration of the VCO can be simplified and the VCO can be manufactured at low cost. Also,
Since the inductor is unnecessary, the VCO can be downsized. Furthermore, the Q value of the resonance circuit does not decrease.

[Brief description of drawings]

1 is a variable capacitance capacitor according to the present invention, FIG.
1A is a perspective view, and FIG. 1B is a cross section taken along the line AA ′ in FIG.

FIG. 2 is an exploded view of a variable capacitor according to the present invention.

FIG. 3 is a schematic diagram showing a method for manufacturing a variable capacitor according to the present invention.

FIG. 4 is a circuit diagram of a VCO configured using a variable capacitor according to the present invention.

FIG. 5 is another variable capacitance capacitor according to the present invention,
5A is a perspective view, and FIG. 5B is a cross section taken along line AA ′ in FIG. 5A.

FIG. 6 is an exploded view of another variable capacitor according to the present invention.

FIG. 7 is a schematic diagram of another variable capacitor according to the present invention when an external bias voltage is applied between a drive electrode and a first electrode.

FIG. 8 is a sectional view of a conventional variable capacitor.

FIG. 9 is a circuit diagram of a collector-grounded Colpitts oscillator circuit, which is a basic example of a VCO using a variable capacitor.

FIG. 10 is a circuit diagram in which an inductor is connected between a low pass filter and a resonance circuit for high frequency insulation in order to use the collector-grounded Colpitts oscillation circuit shown in FIG. 9 in a high frequency band.

[Explanation of symbols]

 17 Insulating Support Base 18 Movable Electrode 19 Driving Electrode 20 Detection Electrode 21 Fixed Part 22 Supporting Part 23 Movable Part 24 Silicon Dioxide Layer 25A First Electrode 25B Second Electrode 26 Conductor Layer

Claims (3)

[Claims] 1. An insulating support base, drive electrodes formed on the surface of the insulation support base, detection electrodes formed on the surface of the insulation support base with a certain distance from the drive electrode, and the drive. Between the drive electrode and the first electrode, a movable electrode having a movable portion provided with a first electrode provided to face the electrode and a second electrode provided to face the detection electrode. A means for applying a voltage is provided, and a Coulomb force between the drive electrode and the first electrode and an elastic force of the movable portion are used to adjust the electrostatic capacitance between the detection electrode and the second electrode. Variable capacitor characterized by being variable. 2. The movable electrode comprises a fixed portion formed on a surface near an end edge of the insulating support, a support portion provided upright on an end edge of the fixed portion on a central portion side, and the support. 2. The variable capacitor according to claim 1, further comprising a movable portion provided on an upper end of the portion so as to be parallel to the insulating support, and the movable portion is displaced with the upper end of the supporting portion as a fulcrum. 3. The movable electrode comprises a pair of fixed portions formed on the surfaces of the insulating support base near opposite edges thereof, and a pair of supporting members provided upright at the central edge of the fixed portions. And a movable part provided on the upper ends of the pair of supporting parts so as to be parallel to the insulating support base. The movable part is provided with a pair of first electrodes adjacent to the supporting part and the pair of first electrodes. 2. The variable capacitor according to claim 1, further comprising a second electrode sandwiched between the first electrode and the movable part, wherein the movable part is displaced with the upper ends of the pair of supporting parts as a fulcrum.