JPH10209527A - Electrostatic actuator, its manufacturing method and drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a large displacement with a low drive voltage in an electrostatic actuator having cantilevers as moving portions. SOLUTION: In an electrostatic actuator, an insulation layer 12 is formed on a conductive silicon wafer 10 and an upper electrode 14 for supporting one end of a moving portion 16 is formed. The moving portion 16 has a cantilever construction continuously forming a plurality of beams 20, each consisting of a straight portion 22 and a curved portion 24. In this actuator, if a drive voltage is applied which is able to deform a first beam 20 between the silicon wafer 10 and the upper electrode 14, an electrostatic force occurs by this drive voltage, and the first beam 20a is bent to the silicon wafer 10 side by this force, thereafter, second, third, fourth and fifth beams 20b to 20e are sequentially bent to silicon wafer 10 side. Thus, a large displacement can be obtained by a low drive voltage. Also, since the drive voltage can be made low, a drive circuit or the like can be formed on a silicon substrate the same as that of the electrostatic actuator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electrostatic actuator having a movable portion formed of a cantilever, a method of manufacturing the same, and a drive system using the electrostatic actuator.

[0002]

2. Description of the Related Art Hitherto, there has been known an electrostatic actuator which can displace (bend) a movable portion by a desired amount by using an electrostatic force and elastic deformation of a movable portion in the best way. For example, the following (1) to (3) are such.

(1) An S-shaped film having both ends fixed is disposed between a pair of planar electrodes, and a voltage is alternately applied between the film and each electrode to form an S-shaped portion of the film. Is alternately displaced to both fixed ends of the film by an electrostatic force generated by voltage application, and a predetermined gas flow rate is obtained by the displacement of the film (1992, IEEE "Micro Electro Mechanical Mechanical"). Systems Newsletter, 1
See page 5.)

(2) A large number of corrugated electrodes on which an insulator is laminated are arranged, and the vertexes of the respective electrodes are connected to form a honeycomb-shaped movable portion composed of a large number of electrodes. An electrostatic force is generated between the electrodes by applying a voltage between them, and a distributed electrostatic microactuator (IEEE, 1993, IEEE) which obtains a desired amount of displacement by moving the electrodes toward and away from each other by the electrostatic force. Bulletin of "Micro Electro Mechanical Systems", pp. 18-23).

(3) An upper electrode is formed on a planar lower electrode with an insulating layer interposed, and a movable portion having a curved portion made of a thin film of aluminum and chromium is connected to the upper electrode. An electrostatic actuator having a cantilever structure in which a movable portion is displaced toward an insulating layer by an electrostatic force by applying a voltage between the upper electrode and the upper electrode (IEEE, 1994)
"Micro Machine and Human Science" No.5
Bulletin of the 8th International Conference, pp. 8-31, 1995, "Eighth International Conference on Solid-State Sensors and Actuators" and Technical Digest of "Eurosensor 9", pp. 412-415, 1995, IEEE. Bulletin of "Micro Electro Mechanical Systems"
In particular, among these electrostatic actuators (1) to (3), an electrostatic actuator having a movable portion with a cantilever structure is used.
According to (3), a movable part can be easily formed on a silicon wafer by using surface micromachining technology (see Document A), and mass production thereof is easy, so that an electrostatic actuator is practically used. This is a particularly important technology in making

[0006]

However, in the above-mentioned conventional electrostatic actuator, it is necessary to apply a high driving voltage of several tens to hundreds V or more between the electrodes in order to obtain a desired displacement. When the driving voltage is lowered, there is a problem that the displacement amount becomes too small.

For this reason, when the electrostatic actuator of the above (3) is put to practical use, it is necessary to make the drive system so that a high voltage can be applied between the electrodes of the electrostatic actuator. A drive circuit cannot be formed on the same silicon substrate as the electric actuator, and there is a problem in that a drive system using an electrostatic actuator is disadvantageous in terms of control and power supply.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an electrostatic actuator having a cantilever as a movable portion so that a large displacement can be obtained with a low driving voltage.

[0009]

In the electrostatic actuator according to the present invention, an upper electrode is formed on a side of the insulating layer formed on one side of the lower electrode opposite to the lower electrode, and the upper electrode is formed on the upper electrode. Is a first part composed of a curved part and a straight part.
Of the beam are supported. Further, a curved portion of a second beam having the same shape as the first beam is connected to the straight portion of the first beam. That is, the electrostatic actuator of the present invention has the movable portion in which the plurality of beams are continuously connected to the upper electrode.

[0010] In the electrostatic actuator of the present invention configured as described above, it is possible to generate an electrostatic force between the upper electrode and the lower electrode for bringing the linear portion of the first beam into contact with the insulating layer. When a drive voltage is applied, first, the first beam is brought into contact with the insulating layer by an electrostatic force generated between the first beam and the lower electrode by the drive voltage, and then the second beam is applied by the drive voltage. The second beam comes into contact with the insulating layer due to the electrostatic force generated between the lower beam and the lower electrode. Therefore,
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to make a 1st beam and a 2nd beam contact an insulating layer in order by the drive voltage required to make a 1st beam contact an insulating layer, At the open end of the second beam, a larger displacement can be obtained than at the open end of the first beam.

Further, as described above, according to the present invention, the movable portion supported by the upper electrode is constituted by a plurality of beams including the curved portion and the linear portion, so that the voltage applied between the lower electrode and the upper electrode is increased. Since the amount of displacement with respect to the driving voltage is increased, the same method as the method of connecting the second beam to the first beam is used.
For the first beam, a third beam of the same shape is connected to the second beam, and a fourth beam of the same shape is connected to the third beam. If the second, third, fourth,... Beams are continuously connected, a larger displacement can be obtained on the open end side of the last stage beam.

Therefore, according to the present invention, it is possible to realize an electrostatic actuator capable of obtaining a desired displacement with a small driving voltage. The connecting position of the curved portion of the second beam to the first beam may be any location as long as it is a straight portion of the first beam. The curved portion of the second beam may be connected, or the curved portion of the second beam may be connected near the curved portion of the linear portion of the first beam.

Next, in each of the beams constituting the movable portion of the electrostatic actuator of the present invention, the straight portion is formed of one kind of metal thin film, and the curved portion has different residual stress. If it is constituted by a laminated body of two types of metal thin films, a movable portion composed of a plurality of beams can be easily formed by using a semiconductor process.

Further, regarding the lower electrode and the insulating film,
If the lower electrode is made of a conductive silicon wafer and the insulating film is made of a silicon oxide film, the lower electrode can be easily formed using a semiconductor process. Then, as in the electrostatic actuator according to claim 2 or 3, the linear portion of each beam constituting the movable portion is formed of one type of metal thin film, and the curved portion is formed of two types of metal thin films. In this case, for example, the metal thin film forming the linear portion may be an aluminum thin film, and the two types of metal thin films forming the curved portion may be an aluminum thin film and a chromium thin film.

When the curved portion of each beam is formed of a laminate of an aluminum thin film and a chromium thin film,
The thickness h1 of the aluminum thin film as set forth in claim 5.
The ratio h2 / h1 of the chromium thin film to the thickness h2 of the chromium thin film is 0.06
It is desirable to make the above. This is the film thickness ratio h of each thin film.
If 2 / h1 is 0.06 or more, the thickness ratio h2 of each thin film
This is because even if there is a manufacturing error in / h1, the change in the curvature of the curved portion caused by this error can be kept small and kept substantially constant.

The relationship between the drive voltage and the amount of displacement in the electrostatic actuator of the present invention is determined by the curvature of the curved portion of each beam and the length of each beam (see the embodiments described later).
If the curvature of the curved portion can be kept substantially constant, the driving voltage of the electrostatic actuator can be set according to the length of each beam. It becomes possible to easily design the drive system that was used.

On the other hand, the invention according to claim 6 is based on claim 4
Or the method of manufacturing an electrostatic actuator according to claim 5, wherein a silicon dioxide film, a polysilicon film, an aluminum film, and a chromium film are sequentially deposited on a conductive silicon wafer by sputtering, and The upper chromium film is etched according to the shape of the curved portion of each beam, then the aluminum film is etched according to the shape of the upper electrode and each beam extending continuously from the upper electrode, and finally, the aluminum film is used. It is characterized in that the polysilicon film under each beam to be formed is plasma-etched.

According to the method of the present invention, the electrostatic actuator of the present invention can be realized using a semiconductor process.
Moreover, since the cantilever structure of the movable portion can be achieved by plasma etching, unlike the case where the cantilever is formed by wet etching, the phenomenon of adhesion between the beam and the silicon wafer does not occur, and the static electricity of the present invention can be obtained. An electric actuator can be easily realized without lowering the yield.

Next, a drive system according to any one of claims 7 to 9 is a drive system for driving and displacing an object using the electrostatic actuator according to any one of claims 1 to 5. The drive system according to claim 7,
The driving system according to claim 8, wherein the electrostatic actuator and the driving circuit are formed on a silicon substrate, and the driving circuit drives the electrostatic actuator. Are formed on a silicon substrate, and are configured to drive an electrostatic actuator using a solar cell as a power supply. The driving system according to claim 9, wherein the electrostatic actuator, the solar cell, the driving circuit, Is formed on a silicon substrate, and the electrostatic actuator is driven by a drive circuit using a solar cell as a power supply.

That is, according to the electrostatic actuator of the present invention (claims 1 to 5), a desired displacement can be obtained with a low drive voltage. The various gate circuits of the CMOS structure formed in the above can be used directly, and a low power supply such as a solar cell can be used as the power supply. Further, as described above, the electrostatic actuator of the present invention can be easily formed on a silicon substrate by utilizing a semiconductor process. Therefore, in the drive system according to claims 7 to 9, the electrostatic actuator, the drive circuit and / or the solar cell are formed on the same silicon substrate, so that the drive system can be reduced in size and weight. In addition, the entire drive system can be easily realized by a semiconductor process.

When actually constructing the drive system,
Since the force obtained by the displacement of one electrostatic actuator is very small, many electrostatic actuators are formed on the same substrate, and the desired object is driven and displaced by the cooperative operation of these many electrostatic actuators. What should be done is.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. [Structure] FIGS. 1A and 1B show the structure of an electrostatic actuator according to an embodiment. FIG. 1A is a perspective view and FIG. 1B is a plan view.
However, FIG. 1B shows a state in which the movable portion of the cantilever structure is in contact with the substrate.

As shown in FIG. 1A, an electrostatic actuator 1 of this embodiment has a conductive silicon wafer 10 formed in a planar shape and an insulating layer 12 laminated on the entire upper surface thereof.
And an upper electrode 14 laminated on the upper surface thereof, and a movable portion 16 having a cantilever structure having one end supported by the upper electrode 14.

The movable portion 16 is composed of a plurality of beams (nine in this embodiment) of the same shape. Each beam 20
A linear portion 22 made of an aluminum film (Al thin film) having a thickness of 0.8 to 1.5 μm;
Curved portion 24 in which a chromium film (Cr thin film) having a thickness of 0.1 to 0.3 μm is laminated on an Al thin film having the same thickness as
The curved portion 24 is warped upward with respect to the surface direction of the silicon wafer 10 due to a difference in residual stress between the Al thin film and the Cr thin film.

Further, as shown in FIG. 1B, two of the nine beams 20 (first beams 20a) have the curved portion 24 side end connected to the end surface of the upper electrode 14 respectively. Has been
It protrudes from the upper electrode 14 in the same direction (parallel).
In the straight portions 22 of the pair of first beams 20a, positions facing each other near the curved portion 24 are respectively:
A connecting portion 26a is provided to protrude. And the connecting portion 26a
Is connected to the end of the second beam 20b on the curved portion 24 side, and each of the second beams 20b projects from each of the connecting portions 26a in the same direction as the first beam 20a. Similarly, the second
The third beam 20c is connected to the beam 20b via the connecting portion 26b.
Are connected, and the fourth beam 20d is connected to the third beam 20c via the connecting portion 26c. The straight portion 22 of the fourth beam 20d is connected to each other via a connecting portion 26d at a position near the curved portion 24.
The end of the fifth beam 20e on the curved portion 24 side is connected to d, and the fifth beam 20e projects in the same direction as the other beams.

That is, the movable portion 16 is provided with the first to fourth beams 2.
Nos. 0a to 20d are continuously connected to form a two-system cantilever.
Are connected by connecting the beams 20e. still,
This is to increase the strength of the movable portion 16 with respect to the force (lateral force) along the surface direction of the silicon wafer 10. [Operation] In the thus configured electrostatic actuator 1 of the present embodiment, as shown in FIG. 2A, a voltage is applied between the silicon wafer 10 serving as the lower electrode and the upper electrode 14. Then, a large electrostatic force is generated between the first beam 20a having a small gap and the silicon wafer 10 along the longitudinal direction of the first beam 20a. As a result, first, the first beam 20 a is bent toward the silicon wafer 10 and comes into contact with the insulating layer 12.

Then, as shown in FIG. 2B, the second beam 20b is disposed at the same position with respect to the silicon wafer 10 as the first beam 20a in FIG. 2A. Therefore, the second beam 20b and the silicon wafer 1
The second beam 20b is bent toward the silicon wafer 10 due to the electrostatic force generated between zero and zero, and comes into contact with the insulating layer 12. Similarly, the third, fourth, and fifth beams 20c,
20d and 20e also bend toward the silicon wafer 10 due to the electrostatic force generated between each beam and the silicon wafer 10,
Finally, all the beams 20a to 20e come into contact with the insulating layer 12 (FIG. 2D).

Therefore, the electrostatic actuator 1 of the present embodiment
According to the above, all the beams 20a to 20e are driven by the driving voltage required to bend the first beam 20a toward the silicon wafer 10 side.
Can be bent toward the silicon wafer 10 side, and the tip of the fifth beam 20e can obtain a displacement that is many times the displacement of the tip of the first beam 20a. As a result, according to the present embodiment, it is possible to realize an electrostatic actuator capable of obtaining a large displacement with a low driving voltage. [Manufacturing Procedure] Next, the manufacturing procedure (method) of the electrostatic actuator of this embodiment will be described with reference to FIG. In addition, each figure shown in FIG. 3 is a view showing the A-beam along the first beam 20a shown in FIG.
FIG. 3 is a sectional view taken along line A.

First, 1 μm thick silicon dioxide (SiO ₂ ) to be an insulating layer 12 is formed on a silicon wafer 10.
Film 30, 1 μm thick polysilicon film 32, upper electrode 14
And an aluminum film 34 constituting the movable portion 16, and
A chromium film 36 constituting the curved portion 24 of each beam 20 is sequentially deposited by sputtering (FIG. 3A).

Next, a pattern of the curved portion 24 of each beam 20 is formed on the uppermost chromium film 36 by photolithography, and the chromium is formed with an aqueous solution of Ce (NH ₄ ) ₂ (NO ₃ ) ₆ and HClO _4. The film 36 is etched. As a result, each beam 2
The Cr thin film forming the curved portion 24 of FIG.
(B)).

Thus, the Cr thin film of the curved portion 24 is formed.
Then, the aluminum exposed by the etching
The upper electrode 14 and the movable part 16 are
Turns are formed with another photomask, and aluminum film 3 is formed.
4 is etched. The etching of the aluminum film 34
To "H_ThreePO_Four: HNO_Three: CH_ThreeCOOH: H _Two
An etchant of “O = 10: 1: 1: 2” is used.
As a result, the aluminum film 34 is
Dissolves into a shape corresponding to the upper electrode 14 and the movable portion 16
(FIG. 3C).

Finally, in CF ₄ / O ₂ plasma,
The polysilicon film 32 under the movable portion 16 is over-etched by plasma etching the polysilicon film 32, and the movable portion 16 is separated from the silicon wafer 10.
Then, the laminated portion of the aluminum film 34 and the chromium film 36 (that is, the curved portion 24 of each beam 20) is
Each beam 20 is curved upward in accordance with the difference between the tensile stress 4 and the residual tensile stress in the chromium film 36 and forms the movable portion 16 (FIG. 3D).

The plasma etching is an isotropic etching, and the isotropic changes depending on a gas flow ratio, a gas pressure, a high-frequency power and the like during the etching. The highest condition of the flow rate is CF ₄ : 5
0 ml / min and O ₂ : 10 ml / min, and it was found that the gas pressure and the high frequency power should be 0.4 torr and 50 W, respectively.

As described above, in this embodiment, the electrostatic actuator 1 is manufactured by utilizing the surface micromachining technology at the time of manufacturing a semiconductor, and when the movable portion 16 is released from the silicon wafer 10 side. Since the plasma etching is used, the movable portion 16 can be formed more favorably than when wet etching is used. In other words, release by wet etching often causes a problem that the surfaces of the micro mechanisms are attached to each other due to the adhesive force of the etchant, but according to the manufacturing method of this embodiment, such a problem does not occur. . [Design] The configuration of the electrostatic actuator 1 of the present embodiment
Although the operation and the manufacturing procedure have been described, the operating characteristic of the electrostatic actuator 1 having the movable portion 16 in which a number of beams are connected as in the present embodiment is such that one beam 20 constituting the movable portion 16
(The length Ls of the straight portion 22 and the length Lc of the curved portion 24 shown in FIG. 3C) and the radius of curvature of the curved portion 24 of the beam 20 (ρ shown in FIG. 3D). .

Next, a description will be given of a method of designing the beam 20 when manufacturing an electrostatic actuator having the movable portion 16 in which a number of beams are connected as in this embodiment and obtaining good operation characteristics. First, the radius of curvature ρ of the curved portion 24 of the beam 20 can be calculated using the following relational expression.

Ρ = (x ² + z ² ) / 2z where x is the horizontal length of the curved portion 24 in the curved state, and z is the vertical height (including the thickness of the curved portion 24). (Not shown) (see FIG. 3D). And a radius of curvature ρ obtained by measuring the values x and z under a microscope;
The relationship between the ratio n (n = h2 / h1) of the thickness h1 of the Al thin film and the thickness h2 of the Cr thin film constituting the curved portion 24 was determined by experiment, and the measurement results indicated by black circles in FIG. 5 were obtained. Was done. In this measurement, the thickness h1 of the Al thin film was set to 0.8 μm
, And changing the thickness h2 of the Cr thin film.

On the other hand, the radius of curvature ρ is determined by the thickness (h) of each film,
An equation relating to the Young's modulus (E) and the residual stress (σ) of each film can be expressed as the following equation (1991,
IEEE Bulletin of Micro Electro Mechanical Systems, pp. 51-56).

[0038]

(Equation 1)

However, in the above equation, the subscript “1”
Represents the value for the Al thin film, and the suffix “2” represents the value for the Cr thin film (see FIG. 4). In the above equation, the Young's modulus E1 of the Al thin film and the Young's modulus E
The values of 2 are 70.3 GPa and 25 GPa, respectively. Assuming that the unknown value (mσ1−σ2) is 0.3 GPa, the relational expression between the radius of curvature ρ and the film thickness ratio n is as shown in FIG. It becomes as shown by the solid line, and substantially matches the measured value indicated by the black circle in FIG.

Therefore, from the above relational expression (the solid line shown in FIG. 5), the amount of change in the radius of curvature ρ is
When the film thickness ratio n between the thin film and the Cr thin film increases, the film thickness ratio (n) decreases when the film thickness ratio (n) is 0.06 or more. It can also be seen that the radius of curvature can be made substantially constant.

That is, when the film thickness ratio n is smaller than 0.06, the rate of decrease in the radius of curvature ρ is large, and
And the amount of displacement of the beam 20 determined by the curvature (d shown in FIG. 3D) is set by the film thickness ratio n of the Al thin film and the Cr thin film constituting the curved portion 24. Is difficult.

Next, FIG. 6 shows a measurement result obtained by measuring the relationship (static characteristic) between the displacement d of the actually manufactured beam 20 and the drive voltage using a laser displacement meter. As shown in FIG. 6, the beam 20 gradually displaces as the drive voltage increases, and when the drive voltage reaches the critical voltage Vc, the displacement suddenly increases and reaches the maximum displacement amount. Further, even if the drive voltage is reduced while the beam 20 is displaced by the maximum displacement amount, the beam 20 hardly displaces until the drive voltage decreases to the return voltage Vr, and the drive voltage is reduced to the return voltage Vr. When it drops to, it suddenly returns to a place close to the initial position. That is, each beam 20 constituting the movable portion 16 of the electrostatic actuator 1 has a large hysteresis with respect to the drive voltage, and in order to drive this with the maximum displacement, the drive voltage is set to a value larger than the critical voltage Vc. Must be set to

On the other hand, the critical voltage Vc is
Even if the radius of curvature ρ of the fourth is constant, it changes depending on the length of the beam 20 (the length Ls of the straight portion 22 and the length Lc of the curved portion 24). That is, FIG. 7 shows that the entire length of the beam 20 is 400
μm, a number of experimental beams were manufactured in which the relationship between the length Ls of the straight portion 22 and the length Lc of the curved portion 24 was changed, and the measurement results of measuring the critical voltage Vc for each beam were obtained. Represent.
Further, FIG. 8 shows that a number of experimental beams in which the length Lc of the curved portion 24 was fixed at 40 μm and the length Ls of the straight portion 22 was changed were manufactured, and the critical voltage Vc was measured for each beam. Shows the measurement results.

From the measurement results shown in FIG. 7, it is understood that the critical voltage Vc increases as the bending portion 24 becomes longer. Therefore, in order to lower the critical voltage Vc (and, consequently, the drive voltage), the bending portion 2 of the beam 20 constituting the electrostatic actuator is required.
It is understood that it is better to shorten 4. However, when the critical voltage Vc is reduced, the displacement amount of the entire beam 20 is reduced. Therefore, in order to increase the displacement amount of the entire electrostatic actuator 1, the beam 20 continuously coupled in the movable portion 16 is required.
Needs to be increased.

On the other hand, from the measurement results of FIG. 8, when the length Lc of the curved portion 24 is fixed, the critical voltage Vc is
It can be seen that the value decreases as the length increases. This is probably because the straight portion 22 increases the area of the capacitor formed between the beam 20 and the silicon wafer 10. Therefore, in order to lower the critical voltage Vc (and, consequently, the driving voltage), each beam 2 constituting the electrostatic actuator is required.
The zero straight section 22 should be sufficiently long.

In view of the above, in the electrostatic actuator 1 of the present embodiment having the movable portion 16 in which a number of beams 20 are connected, in order to obtain a desired displacement with a low driving voltage, the bending portion 24 must be formed. The thickness ratio n between the Al thin film and the Cr thin film is set to 0.06 or more so that the curvature of the bending portion 24 does not change due to a manufacturing error, and the length of each beam 20 is adjusted according to the driving voltage and the displacement amount. It can be seen that the length and the number of connection stages may be determined.

Based on the above points, the dimensions of each part of the electrostatic actuator 1 of the present embodiment shown in FIG. 1 were determined, and the static characteristics were measured. The measurement results shown in FIG. 9 were obtained. . That is, nine beams 20 constituting the movable portion 16
The length of the straight portion 22 and the length of the curved portion 24 are each 400 μm.
m, 40 μm, the thickness of the Al thin film constituting the straight portion 22 and the curved portion 24 is 1.5 μm, and the thickness of the Cr thin film laminated on the Al thin film in the curved portion 24 is 0.1 μm.
m. The width of each beam 20 was 10 μm.

Then, the displacement of the electrostatic actuator 1 thus configured (the displacement of the tip of the fifth beam 22e).
d is measured range using laser displacement meter (several tens of μm)
, The relationship between the drive voltage and the displacement d was measured. As a result, the displacement amount of the electrostatic actuator 1 in which the dimensions of the movable section 16 are set as described above is 245 μm at the maximum, and the critical voltage Vc for realizing the maximum displacement amount is 11.8 V; Release voltage is 3.6V
It turned out to be.

Therefore, the electrostatic actuator 1 of the present embodiment
Sets the driving voltage to 11.8 V or higher, and switches between applying the driving voltage between the silicon wafer 10 and the upper electrode 14 or short-circuiting between the two using a predetermined driving circuit. Then, it can be driven well.

Since this drive voltage is a voltage value which can be sufficiently generated in a drive circuit using a CMOS device, a dedicated high voltage circuit (power for current amplification) is used as a drive circuit as in the prior art. It is not necessary to use an IC or the like. [Driving System] As described above, according to the electrostatic actuator 1 of the present embodiment, the driving circuit can be configured using CMOS elements.

Therefore, when a drive system using the electrostatic actuator 1 is actually constructed, for example, as shown in FIG.
An AND gate composed of a MOS element is used, the upper electrode 14 of the electrostatic actuator 1 is connected to the output of the AND gate, the silicon wafer 10 as the lower electrode is grounded to the ground line GND, and the AND gate is connected via an external switch. DC voltage (12V) is applied to each input of
By switching whether each input of the gate is grounded to the ground GND, the electrostatic actuator 1 can be easily driven.

Since a CMOS circuit such as an AND gate can be formed on a silicon substrate by a well-known semiconductor process, it can be formed together with the electrostatic actuator 1 on the same silicon substrate. Therefore, according to the electrostatic actuator 1 of the present embodiment, a one-chip drive system including a drive circuit can be configured, and the drive system can be reduced in size and weight.

Further, according to the electrostatic actuator 1 of this embodiment, since the driving voltage is low, the driving power can be supplied even from the solar cell. Then, when the electrostatic actuator 1 of the present example manufactured as described above was directly connected to several amorphous solar cells, it could be driven by every five solar cells. In addition, the solar cell is an open circuit.
A voltage of 4 V is generated, and a current of 3.4 μA flows through a short circuit.

Since the solar cell can be formed on the silicon substrate as in the case of the electrostatic actuator 1, if the solar cell and the electrostatic actuator 1 are formed on the same silicon substrate, the power The built-in electrostatic actuator 1 can be configured, and the drive system can be reduced in size and weight.

Similarly, the electrostatic actuator 1 and a driving circuit including a solar cell and a CMOS element can be formed on the same silicon substrate. In this case, a driving system using the electrostatic actuator 1 is used. Can be realized more easily. The manufacturing procedure and the like when forming a drive circuit composed of a solar cell or a CMOS element together with the electrostatic actuator 1 on the same silicon substrate are described with respect to a semiconductor that has been conventionally used for forming a CMOS integrated circuit. Since the process may be used, the description is omitted.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an electrostatic actuator according to an embodiment.

FIG. 2 is an explanatory diagram illustrating an operation of the electrostatic actuator according to the embodiment.

FIG. 3 is an explanatory diagram illustrating a manufacturing procedure of the electrostatic actuator according to the embodiment.

FIG. 4 is an explanatory diagram showing the thickness and residual stress of an Al thin film and a Cr thin film forming a curved portion.

FIG. 5 is a graph showing a relationship between a film thickness ratio of a curved portion and a radius of curvature.

FIG. 6 is a graph showing a relationship between a displacement d of each beam constituting the movable portion and a drive voltage.

FIG. 7 is a graph showing the relationship between the length of a curved portion and the critical voltage when the length of the entire beam is constant.

FIG. 8 is a graph showing the relationship between the length of a straight portion and the critical voltage when the length of a curved portion is constant.

FIG. 9 is a graph illustrating a relationship between a driving voltage and a displacement amount of the electrostatic actuator according to the example.

FIG. 10 is an explanatory diagram illustrating an example of a circuit configuration of a drive system using the electrostatic actuator according to the embodiment.

[Description of Signs] 1 ... Electrostatic actuator 10 ... Silicon wafer
12 insulating layer 14 upper electrode 16 movable part 20, 20a-2
0e Beam 22 Linear part 24 Curved part 26a-26d Connecting part

 ──────────────────────────────────────────────────続 き Continuing from the front page (71) Applicant 591263488 Hirofumi Miura 7-23-2 Tamagawa Gakuen, Machida-shi, Tokyo (72) Inventor Sakai Kanayama 1-1-1 Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO CORPORATION (72) ) Inventor Nao Tsuruzawa 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation (72) Inventor Koji Iwaki 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation (72) Inventor Takashi Yasuda 5-24-10 Taishido, Setagaya-ku, Tokyo Star Heights 103 (72) Inventor Isao 3-9-2-908, Hikarigaoka, Nerima-ku, Tokyo (72) Inventor Hirofumi Miura 7-23-2 Tamagawa Gakuen, Machida-shi, Tokyo

Claims (9)

[Claims] A lower electrode formed in a planar shape; an insulating layer formed on one side of the lower electrode; an upper electrode formed on a side of the insulating layer opposite to the lower electrode; One end is supported by the electrode, and the other end is open. The upper electrode side is formed as a curved portion that is curved so that the distance from the upper electrode becomes longer as the distance from the upper electrode increases. And a first beam having an open end side formed as a linear portion extending straight from the curved portion, wherein the first beam is applied when a predetermined voltage is applied between the lower electrode and the upper electrode. In the electrostatic actuator configured to be displaced toward the insulating layer side by an electrostatic force, a curved portion of a second beam having the same shape as the first beam is connected to a linear portion of the first beam. Thereby, a plurality of beams are continuously coupled to the upper electrode. An electrostatic actuator according to claim Rukoto. 2. The linear part of each beam continuously coupled to the upper electrode is made of one kind of metal thin film, and the curved part is made of a laminate of two kinds of metal thin films having different residual stresses. The electrostatic actuator according to claim 1, wherein: 3. The electrostatic actuator according to claim 2, wherein the lower electrode is a conductive silicon wafer, and the insulating film is a silicon oxide film. 4. The thin metal film forming a straight portion of each beam is an aluminum thin film, and the two types of metal thin films forming a curved portion are an aluminum thin film and a chromium thin film. Item 4. The electrostatic actuator according to item 3. 5. A ratio h2 // of the thickness h1 of the aluminum thin film and the thickness h2 of the chromium thin film constituting the curved portion of each beam.
5. The method according to claim 4, wherein h1 is 0.06 or more.
3. The electrostatic actuator according to claim 1. 6. The method of manufacturing an electrostatic actuator according to claim 4, wherein a silicon dioxide film is formed on the conductive silicon wafer.
A polysilicon film, an aluminum film, and a chromium film are sequentially deposited by sputtering. Next, the chromium film is etched according to the shape of the curved portion of each of the beams. And etching according to the shape of each beam continuously extending from the upper electrode, and finally, plasma etching a polysilicon film below each beam formed by the aluminum film. Actuator manufacturing method. 7. A drive system for driving and displacing an object using the electrostatic actuator according to claim 1, wherein the electrostatic actuator and a drive circuit are formed on a silicon substrate. And a drive system configured to drive the electrostatic actuator by the drive circuit. 8. A drive system for driving and displacing an object using the electrostatic actuator according to claim 1, wherein the electrostatic actuator and a solar cell are formed on a silicon substrate. And a driving system configured to drive the electrostatic actuator using the solar cell as a power supply. 9. A drive system for driving and displacing an object using the electrostatic actuator according to claim 1, wherein the electrostatic actuator, a solar cell, and a drive circuit are mounted on a silicon substrate. A drive system formed above and configured to drive the electrostatic actuator by the drive circuit using the solar cell as a power supply.