JP2003311695A - Planar type actuator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar type actuator and its manufacturing method, the actuator having a large deflection angle of a movable plate by increasing the strength of a torsion bar, and having a long service life. <P>SOLUTION: The planar type actuator 1 comprises a movable plate 2, the torsion bar 3 pivotally supporting the movable plate 2 to be rotatable, and a drive means 4 for generating turning force to turn the movable plate 2. A compression residual stress processing layer 6 formed on the side surface 3a of the torsion bar 3. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar actuator in which a movable plate is pivotally supported by a torsion bar, and more particularly, the deflection angle of the movable plate can be increased, and the fatigue life against repeated load acting on the torsion bar is improved. The present invention relates to a planar actuator and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional planar type actuator is disclosed in, for example, Japanese Patent Publication No. 2722314.
In this planar type actuator, a movable plate and a torsion bar are integrally formed by anisotropically etching a silicon substrate, the movable plate is pivotally supported by a torsion bar on a fixed portion of the silicon substrate, and further, the peripheral edge of the movable plate. A drive coil made of a metal thin film having good electrical conductivity is laid along the section, and a static magnetic field is applied to the drive coil on the opposite side of the movable plate parallel to the axial direction of the torsion bar. It is provided and configured.

When an electric current is supplied to the drive coil of the planar type actuator constructed as described above, the static magnetic field generated by the static magnetic field generation means flows through the opposite side of the movable plate parallel to the axial direction of the torsion bar. A Lorentz force is generated in the drive coil by acting on the electric current, and the movable plate is rotated about the torsion bar. At this time, when a current having a frequency substantially equal to the natural frequency of the torsion bar is supplied to the drive coil, the movable plate resonates at this frequency and rotates efficiently.

[0004]

However, in such a conventional planar type actuator, since the base material of the torsion bar that is twisted with the rotation of the movable plate is a brittle material of silicon member, brittle fracture stress is generated. It can be twisted only up to, and is susceptible to fatigue failure under repeated loading.
For this reason, when the deflection angle of the movable plate is increased, the torsion bar is easily damaged, and when the movable plate is swung and used, there is a problem in durability.

In view of the above problems, the present invention provides a planar actuator in which the deflection angle of the movable plate can be increased by increasing the strength of the torsion bar and the fatigue life is improved, and a manufacturing method thereof. The purpose is to do.

[0006]

In order to achieve the above object, a planar actuator according to the present invention comprises a flat movable plate, a torsion bar for rotatably supporting the movable plate, and the movable plate. And a drive means for generating a turning force, wherein a compression residual stress treatment layer is formed on at least a side surface of the torsion bar.

With such a structure, a compressive residual stress treatment layer is formed on the side surface of the torsion bar on which the torsional force acts when the movable plate is rotated by the driving means, and the strength of the torsion bar is improved.

The compression residual stress treatment layer is provided with a member having a coefficient of thermal expansion larger than that of the base material of the torsion bar on the surface of the torsion bar base material, and the surface of the torsion bar base material is based on the difference in thermal expansion coefficient. It was formed in. Specifically, the base material of the torsion bar is a silicon member, and the member having a large coefficient of thermal expansion is any one of silicon dioxide, zirconium oxide, chromium oxide, and silicon nitride. Alternatively, the member having a large coefficient of thermal expansion may be an organic material. As a result, a compressive residual stress is applied to the surface of the torsion bar base material due to the difference in thermal expansion coefficient between the torsion bar base material and the compression residual stress treatment layer.

Further, the compression residual stress treatment layer may be formed by causing plasma ions excited by electric discharge to collide with the surface of the torsion bar base material. As a result, a compressive residual stress is applied by the effect of shot peening by causing plasma ions to collide with the surface of the torsion bar base material.

Further, in the method of manufacturing the planar type actuator according to the present invention, the step of forming the movable plate, the step of forming the torsion bar for axially supporting the movable plate, and the driving means for generating the turning force in the movable plate. And a step of forming a compressive residual stress treatment layer on at least a side surface of the torsion bar.

In the step of forming the compression residual stress treated layer, a member having a coefficient of thermal expansion larger than that of the torsion bar base material is provided on the surface of the torsion bar base material in a heating atmosphere and then cooled to room temperature. Therefore, it is formed on the surface of the torsion bar base material based on the difference in the coefficient of thermal expansion. Specifically, the base material of the torsion bar is a silicon member, and the member having a large coefficient of thermal expansion is any one of silicon dioxide, zirconium oxide, chromium oxide, and silicon nitride. Alternatively, the member having a large coefficient of thermal expansion may be an organic material.

The step of forming the compressive residual stress treatment layer is to form plasma ions excited by discharge on the surface of the torsion bar base material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing an embodiment of a planar actuator according to the present invention. The planar actuator 1 has a flat plate-shaped movable plate 2, torsion bars 3 and 3 for rotatably supporting the movable plate 2, and a drive means 4 for generating a turning force on the movable plate 2. It has been configured.

The movable plate 2 rotates about the torsion bars 3 and 3 and is provided on the lower surface of the movable plate 2, which will be described later.
The light beam is deflected by (see FIG. 3 (g)). The torsion bars 3 and 3 have one end connected to the side surface of the movable plate 2 and the other end connected to the fixed portion 5 to pivotally support the movable plate 2 on the fixed portion 5 and to rotate the movable plate 2. A spring reaction force is generated, which is formed integrally with the movable plate 2 on the fixed portion 5 by anisotropically etching the silicon substrate. A compressive residual stress treatment layer 6 is formed on at least the side surfaces 3a, 3a of the torsion bars 3, 3.

The compressive residual stress treatment layer 6 is formed by providing a member having a coefficient of thermal expansion larger than that of the base material of the torsion bars 3 and 3 on the surface of the torsion bar base material in a heating atmosphere, and then cooling to room temperature. It is formed on the surface of the torsion bar base material based on the difference in expansion coefficient. For example, if the base material of the torsion bar is a silicon member, any one of silicon dioxide, zirconium oxide, chromium oxide and silicon nitride can be applied to the member having a large thermal expansion coefficient. Alternatively, an organic substance such as polyimide can be applied.
In this case, a member having a coefficient of thermal expansion larger than that of the torsion bar base material formed in the heating atmosphere tries to shrink more than the torsion bar base material during the cooling stage. A compressive residual stress, which is a stress, is generated, and the compressive residual stress processing layer 6 is formed.

Further, the compressive residual stress treatment layer 6 allows the plasma ions excited by the discharge to generate the above-mentioned torsion bar 3,
By colliding with the surface of the base material of No. 3 with energy such that the base materials of the torsion bars 3 and 3 are not etched,
It can also be formed by the effect of shot peening.

The drive means 4 faces the drive coil 7 provided on the upper surface of the movable plate 2 along the peripheral edge thereof, and the opposite sides of the torsion bars 3 supporting the movable plate 2 parallel to the axial direction. The static magnetic field generating means 8 and 8 are thin film or thin piece permanent magnets. The drive coil 7 is electrically connected to the pair of electrode terminal portions 9, 9 via the torsion bars 3, 3.

Therefore, according to the planar type actuator 1 of this embodiment, the compression residual stress treatment layer 6 is provided on the torsion bars 3 and 3 which pivotally support the movable plate 2, and the surface of the base material of the torsion bars 3 and 3 is provided. Since the compressive residual stress is applied, the brittle fracture stress of the torsion bars 3 is increased, and the deflection angle of the movable plate 2 can be increased. Further, since the fatigue life of the torsion bars 3 and 3 against repeated load is also improved, the durability of the planar actuator 1 is also improved.

Next, a method of manufacturing the planar type actuator according to the present invention will be described with reference to FIGS. Note that FIG. 2 shows up to the step of forming the drive coil in the series of manufacturing steps, and FIG. 3 shows from the etching of the silicon substrate to the step of forming the reflection mirror. Further, all of the drawings are shown in the sectional view taken along the line XY in FIG.

First, as shown in FIG. 2, in step (a), a silicon substrate 10 of an SOI (Silicon On Insulator) wafer is prepared. For example, the silicon substrate 10 is 1
Silicon active layer 10a having a thickness of 00 μm and 1 μm
a SiO ₂ intermediate layer 10b having a thickness of m
The silicon support substrate 10c having a thickness of m is laminated.

Next, in step (b), the upper and lower surfaces of the silicon substrate 10 are thermally oxidized to form SiO ₂ insulating layers 10d and 10e of about 1 μm. Then, the drive coil 7 is formed on the insulating layer 10d on the silicon active layer 10a side.
As the method of forming the drive coil 7, first, a thin film of aluminum, for example, as a metal having good conductivity is formed with a thickness of about 1 μm on almost the entire surface of the silicon substrate 10 by a vacuum film forming technique such as sputtering. Next, a resist is applied on the coil, leaving the resist in the portion corresponding to the first contact portion 7b for electrical connection with the first-layer drive coil 7a and the second-layer drive coil, and leaving the coil. A resist pattern having a shape is formed. Then, the aluminum thin film is etched using this as a mask to form the first layer drive coil 7a and the first contact portion 7b. Etching includes wet etching performed using an etching solution or dry etching performed using a reactive gas.

In the step (c), the first insulating layer 11a of photosensitive polyimide is formed on the first layer drive coil 7a. In this case, the lead wire portion 7e for electrically connecting to the first contact portion 7b and an external electric circuit, and the electrode terminal portions 9 and 9 not shown.
The first insulating layer 11a is formed except for the corresponding portion (see FIG. 1). Specifically, the photosensitive polyimide is formed on the entire upper surface of the silicon substrate 10 by coating. As a coating method, known techniques such as a spin coating method, a slit die coating method, a spraying method, a roll coating method and a dipping method can be used. Here, for example, when a positive photosensitive polyimide is used, the required portions except the corresponding portions of the contact portion 7b, the lead wire portion 7e and the electrode terminal portions 9 and 9 (not shown) (see FIG. 1) are provided. Mask and expose to UV light.
In the case of a positive type photosensitive polyimide, the exposed portion is dissolved in a developing solution, and therefore, when the corresponding portion of the lead wire portion 7e and the electrode terminal portions 9 and 9 is exposed to ultraviolet rays, the corresponding portion of the contact portion 7b is developed by the development. The photosensitive polyimide is removed.

Next, in the same manner as in step (b), a thin film of aluminum having a thickness of about 1 μm is formed on the entire surface of the silicon substrate 10, and the thin film is etched to form a second layer drive coil 7c, a second contact portion 7d, The lead wire portion 7e and the electrode terminal portions 9, 9 (not shown) are formed (see FIG. 1).

Further, in step (d), step (c)
In the same manner as above, a second insulating layer 11b of photosensitive polyimide is formed so as to cover the second layer drive coil 7c, the second contact portion 7d and the upper portion of the lead wire portion 7e. This serves as a protective film for the purpose of preventing corrosion of the drive coil 7c and the lead wire portion 7e.

Next, as shown in FIG. 3, the silicon substrate 1
0 is etched. First, in step (e), portions of the silicon substrate 10 corresponding to the movable plate 2, the torsion bars 3 and 3 and the fixed portion 5 are covered with a resist mask, and the SiO ₂ insulating layer 10d of the silicon substrate 10 is etched and removed. To do. Further, the exposed silicon active layer 10a by removing the SiO ₂ insulating layer 10d is anisotropically etched. In this case, the etching is performed on the intermediate layer 10b of SiO _2.
Then, the concave portions 12, 12 are formed as shown in FIG. 4, and the movable portion 2 and the torsion bars 3, 3 whose lower surface is connected by the silicon supporting substrate 10c are formed.

Further, in the step (e), the movable plate 2 and the fixed portion 5 are masked to subject at least the side surface 3a of the torsion bars 3 to a compressive residual stress treatment. Specifically, at least the side surfaces of the torsion bars 3 are formed by plasma CVD using an inorganic substance having a thermal expansion coefficient larger than that of the silicon substrate 10, such as silicon dioxide, zirconium oxide, chromium oxide, or silicon nitride, at a temperature of 300 to 400 ° C. 3a and then cooled to room temperature to form the compressive residual stress treatment layer 6 based on the difference in thermal expansion coefficient from the torsion bar base material. Since the inorganic material has a larger coefficient of thermal expansion than the silicon substrate 10 as described above, the silicon substrate 1 is not cooled during cooling.
The compression residual stress treatment layer 6 is formed by attempting to shrink more than 0 to generate a compressive residual stress on the surface of the base material of the torsion bars 3, 3 covered with the inorganic substance.

Further, a photosensitive polyimide organic material may be applied as a member having a coefficient of thermal expansion larger than that of the silicon substrate 10. Since the photosensitive polyimide has a coefficient of thermal expansion larger than that of the above inorganic substances such as silicon dioxide,
Even when dried at a temperature of ℃ or more and returned to room temperature, compressive residual stress is generated on the surface of the base material of the torsion bars 3, 3 coated with polyimide to form the compressive residual stress treatment layer 6 as described above. it can.

Further, the plasma ions excited by the discharge are made to collide with the side surfaces 3a of the torsion bars 3 and 3 with energy such that the silicon substrate 10, which is the base material of the torsion bars 3 and 3, is not etched, The compressive residual stress treatment layer 6 can be formed by giving a compressive residual stress to the side surfaces 3a of the torsion bars 3 and 3 by the effect of so-called shot peening. In this case,
As shown in FIG. 3, a sputtering device, an ion etching device, or the like is applied to generate plasma ions of a rare gas such as Ar, and the plasma ions are caused to collide with energy such that the silicon substrate 10 is not etched. To generate compressive residual stress.
The condition for applying the compressive residual stress at this time is determined by adjusting the flow rate of the rare gas introduced into the apparatus and the electric power of the RF power source for plasma generation.

Next, in step (f), a portion of the lower surface of the silicon substrate 10 corresponding to the fixed portion 5 is masked with a resist and the insulating layer 10e of SiO ₂ is etched and removed. Further exposed support substrate 10c of silicon substrate 10
Is anisotropically etched up to the intermediate layer 10b of SiO ₂ . Then, the SiO ₂ exposed by this etching
If the intermediate layer 10b is removed by etching, the recess 12 of FIG. 4 penetrates from the lower part to the upper part of the silicon substrate 10.

Further, in step (g), after removing the SiO ₂ insulating film 10e on the lower surface of the fixed portion 5 by etching, a reflective film such as aluminum is vacuum-deposited on the lower surface of the movable plate 2 to form the reflective mirror 13. Form. Then, by disposing the static magnetic field generating means 8 on the upper surface of the fixed portion 5 facing the opposite side parallel to the rotation axis of the movable plate 2, the planar type actuator 1 shown in FIG. 1 is completed.

The compressive residual stress treatment may be carried out not only in the step (e) but also after the step (f) before the formation of the reflective film. In this case, compressive residual stress treatment can be applied to the entire circumference of the torsion bars 3 and 3. Further, since the reflection film is not yet formed, the reflectance of the reflection film is not adversely affected.

In the present embodiment, the electromagnetic actuator has been described, but the present invention is not limited to this, and it can be applied to an electrostatic actuator using an electrostatic attraction force, for example. There is no end.

[0033]

According to the planar actuator of the present invention, a compressive residual stress treatment layer is formed on the side surface of the torsion bar that is twisted as the movable plate rotates, thereby improving the strength of the torsion bar. Therefore, even if a large deflection angle is given to the movable plate, the torsion bar is less likely to be broken, the fatigue life of the torsion bar against repeated load can be improved, and the durability of the planar actuator can also be improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of a planar actuator according to the present invention.

FIG. 2 is an explanatory diagram showing a drive coil forming step in the method of manufacturing the planar actuator.

FIG. 3 is an explanatory diagram showing a silicon substrate etching step in the method of manufacturing the planar actuator.

FIG. 4 is a schematic perspective view for explaining a process of forming a movable portion and a torsion bar.

FIG. 5 is an explanatory diagram showing a shot peening method using plasma ions.

[Explanation of symbols]

1 ... Planar actuator 2 ... Movable plate 3 ... torsion bar 3a ... side surface 6 ... Compressive residual stress treatment layer

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Claims (10)

[Claims] 1. A planar actuator having a flat plate-shaped movable plate, a torsion bar rotatably supporting the movable plate, and a drive means for generating a turning force on the movable plate, wherein the torsion is provided. A planar type actuator characterized in that a compressive residual stress treatment layer is formed on at least a side surface of a bar. 2. The compression residual stress treatment layer is provided with a member having a coefficient of thermal expansion larger than that of the base material of the torsion bar on the surface of the torsion bar base material, and the surface of the torsion bar base material is based on the difference in thermal expansion coefficient. The planar type actuator according to claim 1, wherein the planar type actuator is formed in the following manner. 3. The base material of the torsion bar is a silicon member, and the member having a large coefficient of thermal expansion is silicon dioxide,
The planar actuator according to claim 2, which is one of zirconium oxide, chromium oxide, and silicon nitride. 4. The planar actuator according to claim 2, wherein the member having a large coefficient of thermal expansion is an organic material. 5. The planar actuator according to claim 1, wherein the compressive residual stress treatment layer is formed by causing plasma ions excited by discharge to collide with the surface of the torsion bar base material. 6. A step of forming a movable plate, a step of forming a torsion bar that pivotally supports the movable plate, a step of forming a driving means for generating a turning force on the movable plate, and at least the torsion bar. And a step of forming a compressive residual stress treatment layer on a side surface of the planar actuator. 7. In the step of forming the compressive residual stress treatment layer, a member having a coefficient of thermal expansion larger than that of the torsion bar base material is provided on the surface of the torsion bar base material in a heating atmosphere, and then cooled to room temperature. The method of manufacturing a planar actuator according to claim 6, wherein the surface of the torsion bar base material is formed on the basis of the difference in thermal expansion coefficient. 8. A base material of the torsion bar is a silicon member, and the member having a large thermal expansion coefficient is silicon dioxide.
8. The method for manufacturing a planar actuator according to claim 7, wherein the method is one of zirconium oxide, chromium oxide, and silicon nitride. 9. The method of manufacturing a planar actuator according to claim 7, wherein the member having a large coefficient of thermal expansion is an organic material. 10. The planar type according to claim 6, wherein the step of forming the compressive residual stress treatment layer is performed by causing plasma ions excited by electric discharge to collide with the surface of the torsion bar base material. Actuator manufacturing method.