JPH09283374A - Electret - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electret capable of increasing the expected life even if the dimension is small. SOLUTION: An SiO2 film 101 is stuck on the fixed substrate 100 consisting of a silicon single crystalline wafer by the vapor phase by plasma, and the center of this SiO2 film 101 is charged to make an electret 18. The uncharged peripheral part of the SiO2 film becomes an insulating film 16 which protects the fixed substrate 100 and also insulates a fixed contact 19 and a metallic film layer 26 for junction from the fixed substrate 100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret made of an electrically charged foil or thin layer of SiO ₂ (silicon dioxide).

[0002]

BACKGROUND OF THE INVENTION Electrets, which are dielectrics with permanent electric polarization, are used in many devices such as microphones or electrostatic relays. Electrets made of SiO ₂ have several advantages over those made from polymeric materials, in particular: In other words, it behaves better at high temperatures, and can be made to a thickness of less than 10μ. Furthermore, surface oxidation on a solid substrate such as a Si substrate, or directly in a gas phase generated from plasma containing Si and oxygen By attaching, it can be easily chemically formed directly.

However, in the currently known methods for realizing these SiO ₂ electrets, the life expectancy is shorter than that of polymer electrets, and such life expectancy is generally limited to several months. To increase this expected life, it has been proposed to chemically treat SiO ₂ with hexamethyldisilanezan (HMDS) before electrically charging, but this method is difficult to operate and the results obtained are I'm not satisfied.

When the SiO ₂ layer to be converted into an electret is obtained by direct surface oxidation of a solid substrate made of Si, the expected life of the final electret by heating the SiO ₂ layer before it is electrically charged. Has also been proposed to study the effects on the [Electret International Symposium at the 7th Electret International Symposium held in Berlin, September 1991 (the 7t
h international symposium
on eletrets) “ISE7”, Publication Proceedings, pp. 663 to 668] In these studies, preheating is the life expectancy (life exp).
For some of these electrets, on the contrary, the effect of preheating on electret charging stability does not significantly increase eetancy), indicating that such stability is "significantly reduced".

According to JP-A-6-316766, S
Si in a gas phase generated from a plasma containing i and oxygen
Experiments have shown that the electret obtained from electrical charging after forming SiO ₂ on a solid substrate consisting of and having a heat treatment shows a remarkably long life expectancy,
That is a very surprising result.

[0006]

However, the life of the above electret made of electrically charged SiO ₂ is as follows.
It was found to correlate with its size. For example, one side is 1
As shown in FIG. 10, the 6.9 mm square SiO ₂ electret had a surface potential of +300 V immediately after charging (solid line), whereas it had a surface potential of +295 V after 830 days had passed (dashed line).

However, the rectangular SiO ₂ electret of 2.7775 × 1.55 mm had a surface potential of +310 V immediately after charging (solid line) as shown in FIG. 11, whereas it had a surface potential of +100 V after 28 days. (Dashed line). Further, the surface potential of the central portion of the square SiO ₂ electret having one side of 16.9 mm was hardly deteriorated, whereas it was considerably deteriorated at the end portion.

It is considered that the above-mentioned two phenomena are that the electric potential trapped in the SiO ₂ electret moves from the end having a steep potential difference onto the solid substrate to deteriorate the surface potential. The present invention has been made in view of the above points, and an object of the present invention is to provide an electret capable of increasing the expected life even if the size is small.

[0009]

In order to achieve the above object, according to the invention of claim 1, a SiO ₂ film is formed on a solid substrate, and at least a part of the SiO ₂ film excluding the peripheral portion is charged. Since the charged film and the uncharged film are integrated and continuous, the creepage distance from the end of the charged part to the fixed substrate can be increased. Therefore, it is possible to prevent the trapped charges from moving along the creeping surface onto the solid substrate. As a result, even if the size is small, the deterioration of the surface potential can be suppressed and the expected life can be increased. The non-existing film acts as a protective film that protects the solid substrate.

According to the second aspect of the invention, SiO is formed on the solid substrate.
_TwoA film is formed and the SiO _TwoAnchoring groups around the membrane
An insulating film is formed on the plate, and the insulating film and the SiO 2_Twofilm
At the boundary part with_TwoThe peripheral part of the film is on the insulating film
Overlaid, SiO other than this overlaid part_TwoCharge the membrane
It is characterized in that it is formed at the end of the charged portion of the SiO film.
It is possible to increase the creepage distance from the
Even if the charges trapped by the high resistance insulating film are solid
Moving along the surface of a plate or through an insulating film
Can be prevented, resulting in poor surface potential even with small dimensions.
The life expectancy can be increased by suppressing
The film protects the fixed substrate.

According to the third aspect of the present invention, the insulating film is formed on the solid substrate and the SiO ₂ film is formed on the insulating film.
It is characterized in that the SiO ₂ film is charged, and the creepage distance from the end of the charged portion of the SiO film to the solid substrate can be increased, and trapped charges are transferred onto the solid substrate along the creeping surface. The charges trapped by the insulating film having a high resistance that can prevent the transfer of SiO
It is possible to prevent the film from migrating to the solid substrate through the insulating film under the film, so that even if the size is small, the deterioration of the surface potential can be suppressed and the expected life can be increased.
Further, the fixed substrate can be protected by the insulating film.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) This embodiment is used for an electrostatic relay driven by electrostatic force as shown in FIGS.
This electrostatic relay is composed of an upper fixed piece 1, a movable piece 2 and a lower fixed piece 3, and has a structure in which the movable piece 2 is sandwiched between the upper and lower fixed pieces 1 and 3.

The movable piece 2 is based on a silicon single crystal wafer as shown in FIG. 3, and has a movable electrode 4, a fixed contact terminal 5, a movable contact 6, a metal thin film layer 7 for joining fixed pieces, and an electrode terminal 8. Etc. are formed. The movable electrode 4 is processed into a concave portion from the upper and lower sides of the movable piece 2 by anisotropic etching or the like. The outer periphery of the movable electrode 4 is etched in a U shape and separated from the movable piece 2, and one end of the movable electrode 4 is removed. The movable electrode 4 swings around the support end 9 as a center.

Therefore, the movable electrode 4 moves so as to approach or separate from the upper and lower fixed pieces 1 and 3 which will be described later. A notch 13 is also provided at the corner of the movable piece 2 so that an electric signal can be taken out from the fixed contact 19 of the lower fixed piece 3. The movable contact 6 is provided on the insulating film 14 formed on the surface of the base body, and the two fixed pieces 1 and 3 are simply joined to the upper and lower sides of the movable piece 2 by the concave portion of the movable electrode 4, so that the fixed contact 12 and the fixed contact are formed. It is designed so that a gap can be provided between the gap 19 and 19. The metal thin film layer 7 and the fixed contact terminal 5 are also formed on the insulating film 14, and the metal thin film layer 7 is made of a gold or gold alloy layer and is connected to the silicon single crystal wafer which is the base of the movable piece 2. Has been done.

Similar to the movable piece 2, the upper and lower fixed pieces 1 and 3 use a silicon single crystal wafer as a solid substrate. As shown in FIGS. 2 and 3, an insulating film 15 or 1 formed on the surface of the solid substrate.
6 on the electrets 17, 18, fixed contacts 12, 1
9. Metal thin film layers 25, 26, etc. made of gold or gold alloy layers for joining movable pieces are respectively formed. The fixed electrode 10 provided integrally with the electret 17 is connected through the electrode terminal 23 and provided integrally with the electret 18. The fixed electrode 11 is connected to an electrode terminal formed on the back surface of the base of the lower fixed piece 3.

The fixed contact terminals 5 provided on the upper and lower surfaces of the movable piece 2 are fixed contacts 12 and 19 of the upper and lower fixed pieces 1 and 3, respectively.
Is a fixed contact terminal connected to. Thus, the movable piece 2 and the upper and lower fixed pieces 1, 3 are arranged so that the upper and lower joining metal thin film layers 7 of the movable piece 2 and the upper and lower fixed piece 1, 3 of the joining metal thin film layers 25 and 26 are brought together. When they are brought into contact with each other and heated while applying an appropriate pressure, the bonding metal thin film layers 7 and 25, or 7 and 2
2 and 6 are eutecticized together with the base silicon, and FIG.
As shown in, the connection is made both mechanically and electrically.

In this embodiment, the surface of the electret 17 of the upper fixed piece 1 facing the movable electrode 4 is minus,
The surface of the electret 18 of the lower fixed piece 3 facing the movable electrode 4 is permanently polarized so as to be positive. When a negative voltage is applied to the movable electrode 4 by using the electrode terminals 8 and 23, a repulsive force is generated between the upper electret 17 and the movable electrode 4, and an absorbing force is generated between the lower electret 18 and the movable electrode 4. A torque that tends to lean toward the lower electret 18 is generated in the movable electrode 4. In this case, both the repulsive force and the absorbing force contribute to the torque in the same direction, so that a very large contact pressure can be obtained. On the contrary, when a positive voltage is applied to the movable electrode 4, the upper electret 17 and the movable electrode 4 have absorption power, and the movable electrode 4
Then, a repulsive force acts on the lower electret 18, and a torque that tends to tilt toward the upper electret 17 side is generated in the movable electrode 4. In this case, since both the repulsive force and the absorbing force contribute to the torque in the same direction, a very large contact pressure can be obtained.

Here, the electret of the present embodiment will be described in more detail by taking the electret 18 formed on the lower fixed piece 3. First, as shown in FIG. 1, a SiO ₂ film 101 is adhered and formed on a solid substrate 100 made of a silicon single crystal wafer constituting the lower fixing piece 3 by a gas phase of plasma, and the central portion of the SiO ₂ film 101 is charged. Configure the electret 18. The peripheral portion of the uncharged SiO ₂ film 101 serves as an insulating film 16, which protects the solid substrate 100 and also insulates the fixed contact 19 and the bonding metal thin film layer 26 from the solid substrate 100. Also, the creepage distance d ₁ from the electret 18 which is the charging portion to the metal thin film layer 26 for bonding which is the conductor, and the electret 1
The creepage distance d ₂ from 8 to the fixed contact 16 which is a conductor is set to a distance sufficient to prevent the movement of charges from the end of the electret 18 to the solid substrate 100 along the creepage.

Although the electret 18 of the lower fixed piece 3 is shown in FIG. 1, the electret 1 of the upper fixed piece 1 is shown.
It goes without saying that 7 is also configured similarly. As described above, the electret 18 (or 17) of the present embodiment is configured by charging the central portion of the SiO ₂ film 101 formed on the solid substrate 100.
8 (or 17) around the uncharged SiO ₂
SiO 101 in which film 101 is present and is not charged
And the SiO ₂ film of the electret 18 (or 17) are formed of the same and continuous SiO ₂ film 100, the creepage distance between the end of the electret 18 (or 17) and the solid substrate 100 is increased. Can be made sufficiently large, so that the charge can be prevented from moving from the end of the electret 18 (or 17) to the solid substrate 100 or another conductor. In addition, S of the uncharged part
Since the iO ₂ film 101 acts as a protective film of the solid substrate 100, the process of forming the protective film can be shared with the electret 18 (or 17), and there is no waste.

(Embodiment 2) The electret of this embodiment is also used for an electrostatic relay as in Embodiment 1, but the electret of this embodiment has the following features. Here, the electret 18 formed on the lower fixing piece 3 of the electrostatic relay will be described in detail.

First, as shown in FIG. 4, an insulating film 16 made of a SiO ₂ film having a high resistivity is formed so as to form a gap in the central portion on a solid substrate 100 made of a silicon single crystal wafer constituting the lower fixing piece 3. . Then, the SiO ₂ film 101 is adhered and formed in the gap in the central portion of the insulating film 16 by a gas phase by plasma, and the electret 18 is charged.
S that composes the electret 18 with
The non-charged peripheral portion of the iO ₂ film 101 overlaps the inner peripheral edge of the insulating film 16.

The insulating film 16 protects the Si substrate 100 and also insulates the fixed contact 19 and the bonding metal thin film layer 26 from the silicon substrate 100. The distance d ₁ from the electret 18 which is the charging portion to the metal thin film layer 26 for bonding which is a conductor and the distance d ₂ from the fixed contact 19 which is a conductor to the conductor are measured from the end of the electret 18 to the solid substrate 100. The distance is sufficient to prevent the movement of charges along the.

The insulating film 16 is a charged SiO ₂ film 1.
Since it has a sufficiently high resistivity as compared with 01, charges are prevented from moving to the solid substrate 100 through the insulating film 16 which is not charged from the end of the electret 18 which is charged. In FIG. 4, the electret 18 of the lower fixed piece 3
However, it goes without saying that the electret 17 of the upper fixed piece 1 is also configured in the same manner.

5 and 6 are a sectional view and an exploded perspective view of an electrostatic relay using the electret 18 (or 17) of the present embodiment. The electrostatic relay structure shown in the drawings is the same as that of the first embodiment. Since they have basically the same structure, the same components and elements as those of the electrostatic relay shown in FIGS. 2 and 3 are designated by the same reference numerals and the description thereof will be omitted. As described above, in this embodiment, the SiO ₂ film 101 formed on the solid substrate 100 is charged to form the electret 18 (or 17), and the periphery of the electret 18 (or 17) is not charged. Since the SiO ₂ film is formed so as to overlap the peripheral insulating film 16, the creepage distance from the end of the electret 18 (or 17) to the solid substrate 100 can be made sufficiently large, and therefore the electret 18 (or It is possible to prevent electric charges from moving from the end of 17) to the solid substrate 100 or another conductor.

(Embodiment 3) The electret of this embodiment is also used for an electrostatic relay as in Embodiments 1 and 2, but the electret of this embodiment has the following features. Here, the electret 18 formed on the lower fixing piece 3 of the electrostatic relay will be described in detail.

First, as shown in FIG. 7, an insulating film 16 made of a Si ₃ N ₄ film is formed on a solid substrate 100 made of a silicon single crystal wafer constituting the lower fixing piece 3, and a central portion of the insulating film 16 is formed. The SiO ₂ film 101 is further formed on the upper surface and the SiO ₂ film 101 is charged to form the electret 18. The insulating film 16 protects the Si substrate 100, and also fixes the fixed contacts 19 and the metal thin film layer 2 for bonding.
6 for insulating the silicon substrate 100 from each other. The distance d ₁ from the electret 18 that is the charging portion to the metal thin film 26 for bonding that is the conductor, and the electret 1
The distance d ₂ from 8 to the fixed contact 16 which is a conductor is set to a distance sufficient to prevent the movement of charges from the end of the electret 18 to the solid substrate 100 along the surface.

A polysilicon film made of the same material as the fixed substrate 100 may be formed on the insulating film 16, and a SiO ₂ film for forming the electret 18 may be formed thereon. Although the electret 18 of the lower fixed piece 3 is shown in FIG. 7, it goes without saying that the electret 17 of the upper fixed piece 1 is also configured in the same manner. 8 and 9 are a sectional view and an exploded perspective view of an electrostatic relay using the electret 18 (or 17) of the present embodiment, and the electrostatic relay structure shown is basically the same as that of the first embodiment. Have the same structure, the same components as those of the electrostatic relay shown in FIG. 2 and FIG.

As described above, in the present embodiment, the solid substrate 10 is
SiO ₂ forming the electret 18 (or 17) on the insulating film 16 made of Si ₃ N ₄ film formed on
By forming the film, even if the size of the electret 18 (or 17) is small, it is possible to prevent charges from moving from the end portion along the creeping surface to the solid substrate 100, and to pass from the electret 18 through the insulating film 16 to the solid substrate. It is possible to prevent the charge from moving to 100. Further, since the insulating film 16 as the SiN film acts as a protection of the solid substrate 100, the electret and the process of forming the protective film can be made common and there is no waste.

The electret 1 according to each of the above-mentioned embodiments.
Reference numerals 7 and 18 are formed by charging a SiO ₂ film, but a silicon-based inorganic insulating film such as Si ₃ N
_The same effect can be expected when the electret is formed by using _four films or a film of a composite of SiO ₂ and Si ₃ N ₄ (SiON).

[0030]

According to the invention of claim 1, SiO is formed on a solid substrate.
_{Since two} films are formed and a part of this SiO ₂ film excluding at least the peripheral part is charged, it is possible to increase the creepage distance from the end of the charged part to the fixed substrate. It is possible to prevent trapped charges from moving along a creeping surface onto a solid substrate, suppress deterioration of the surface potential and increase the expected life even if the dimensions are small, and yet an uncharged film. Has an effect of acting as a protective film for protecting the solid substrate, and further, there is an effect that the process of forming the electret portion can be shared with the protective film, and there is no waste in manufacturing.

According to a second aspect of the invention, SiO ₂ is formed on the solid substrate.
To form a film, the SiO ₂ film near the insulating film is formed on a fixed substrate, and the boundary portion between the insulating film and the SiO ₂ film overlapping peripheral portion of the SiO ₂ film on the insulating film Since the SiO ₂ film other than the overlapped portion is charged, the creepage distance from the end of the charged portion of the SiO film to the solid substrate can be increased, and the high resistance insulating film traps it. It is possible to prevent charges from moving along the surface of the solid substrate or through the insulating film, and even if the dimensions are small, it is possible to suppress the deterioration of the surface potential and increase the expected life. There is an effect that the substrate can be protected.

According to the third aspect of the present invention, the insulating film is formed on the solid substrate, the SiO ₂ film is formed on the insulating film, and the SiO ₂ film is charged. The creepage distance from the edge to the solid substrate can be increased, the trapped charges can be prevented from moving along the creepage on the solid substrate, and the charges trapped by the high resistance insulating film are It is possible to prevent migration from the film to the solid substrate through the insulating film below, so that even if the dimensions are small, the deterioration of the surface potential can be suppressed and the expected life can be extended, and the insulating film protects the fixed substrate. There is an effect that can be achieved.

[Brief description of drawings]

FIG. 1A is a top view of a first embodiment of the present invention. (B) is an AA 'sectional view of Embodiment 1 of the present invention.

FIG. 2 is a side sectional view of an electrostatic relay using the same as above.

FIG. 3 is an exploded perspective view of an electrostatic relay using the same as above.

FIG. 4A is a top view of the second embodiment of the present invention. (B) is an AA 'sectional view of Embodiment 2 of the present invention.

FIG. 5 is a side sectional view of an electrostatic relay using the same as above.

FIG. 6 is an exploded perspective view of an electrostatic relay using the same as above.

FIG. 7A is a top view of the third embodiment of the present invention. FIG. 6B is a sectional view taken along the line AA ′ of the third exemplary embodiment of the present invention.

FIG. 8 is a side sectional view of an electrostatic relay using the same as above.

FIG. 9 is an exploded perspective view of an electrostatic relay using the same as above.

FIG. 10 is a life explanatory diagram of a conventional example.

FIG. 11 is a life explanatory diagram of another conventional example.

[Explanation of symbols]

3 Fixed Piece 11 Fixed Electrode 18 Electret 100 Solid Substrate 101 SiO ₂ Film 16 Insulating Film 19 Fixed Contact 26 Metal Thin Film Layer for Bonding

Claims (3)

[Claims] 1. A SiO ₂ film is formed on a solid substrate, and the S
An electret, characterized in that at least a part of the iO ₂ film excluding the peripheral portion is charged. 2. SiO on a solid substrate_TwoWhen forming a film
And the SiO_TwoForm an insulating film on the fixed substrate around the film
And the insulating film and the above-mentioned SiO_TwoAbove at the boundary with the membrane
Notation SiO_TwoThe peripheral part of the film is overlaid on the insulating film, and this overlapped part
Other than SiO _TwoThe feature is that the film is charged
Electret to do. 3. An electret, characterized in that an insulating film is formed on a solid substrate, a SiO ₂ film is formed on the insulating film, and the SiO ₂ film is charged.