JP2003344786A - Electrostatic actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic actuator realizing low power consumption and a large displacement. <P>SOLUTION: The electrostatic actuator which is provided with a supporting base board 1 provided with a fixed electrode 11 and a fulcrum part 12 on the surface, a movable electrode 21 arranged so as to be faced to the fixed electrode 11 and have a gap across it, a fixed part 22 formed in one body with the movable electrode 21 and connected to the base board 1, and a movable arm 2 consisting of the movable electrode 21 and a movable piece 23 communicating therewith on the same plane, and which makes the movable arm 2 flexible centering the movable electrode 21 by the electrostatic attractive force between the fixed electrode 11 and the movable electrode 21, and makes the movable piece 23 turn on a fulcrum part 12 with the lever of the movable arm. <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 an electrostatic actuator operatively displaced by electrostatic attraction, and more particularly to an electrostatic actuator suitable as an optical control element such as an optical switch.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional electrostatic actuator disclosed in Japanese Patent Laid-Open No. 2000-258702. In this device, a square movable electrode plate 102 made of polycrystalline silicon is formed on a conductive silicon substrate 101 which serves as a fixed electrode, and supports 103, 103, which will be described later.
, And fixing portions 105, 105, and so on, and are arranged so as to face the silicon substrate 101 at a predetermined space. Further, rectangular cutouts 106, 106, ... Are formed in the center of each side of the movable electrode plate 102, and folded beam-shaped supports 103, 103 ,. And the fixed parts 105, 105, ...
Are formed. Further, the inner ends of the supports 103, 103, ... Are connected to the movable electrode plate 102, and the outer ends thereof are fixed portions 10.
, 105, ... Are connected to the silicon substrate 101. Further, a mirror 104 made of polycrystalline silicon is erected at a substantially central portion of the movable electrode plate 102.

Reference numerals 107, 108 and 109 denote optical fibers or optical waveguides, which are a silicon substrate 101 and a movable electrode plate 10.
When a voltage is not applied between 2 and 2, the light incident from the input side 107 is reflected by the mirror 104 and
The direction is changed by 0 ° and enters the output side 108. Further, when a voltage is applied between the silicon substrate 101 and the movable electrode plate 102, an electrostatic attractive force is generated between the two and the movable electrode plate 102.
Are sucked into the silicon substrate 101, and the supports 103, 10
3, ... Are elastically deformed to move the mirror 104 to the silicon substrate 10.
Move to 1 side. As a result, the light incident from the input side 107 passes above the mirror 104, goes straight, and is incident on another output side 109.

Therefore, this electrostatic actuator is
The mirror 104 is displaced by controlling whether or not a voltage is applied between the silicon substrate 101 and the movable electrode plate 102, and the light incident from the input side 107 is output to either the output side 108 or 109. It can be incident on one side.

Further, another conventional electrostatic actuator disclosed in Japanese Patent Laid-Open No. 7-177763 is shown in FIG.
Shown in. This substrate 201 has a fixed electrode 205 provided on an insulating film 204 and a dielectric thin film 206 provided so as to cover the insulating film 204 and the fixed electrode 205.
And a movable piece 203 having a substantially quadrangular shape supported rotatably about a beam 208 inside a frame-shaped support body 202 provided from the substrate 201 via a spacer 207. . The beam 208 supports the movable piece 203 at a position apart from the center of the movable piece 203. In addition, the movable piece 203 has substantially the same size as the fixed electrode 205 in the short side direction, and is formed larger than the fixed electrode 205 in the long side direction.

The operation is performed by the fixed electrode 205 and the movable piece 20.
When a voltage is applied between 3 and 3, an electrostatic attractive force is generated between them. At this time, since the movable piece 203 is supported with the beam 208 as the axis of rotation, the movable piece 203 rotates about the beam 208, and one short side 203a of the movable piece 203.
Contacts the fixed electrode 205. When the voltage is increased in this state, the movable piece 203 bends to increase the contact area with the fixed electrode 205, and the movable piece 203 further rotates correspondingly, and as a result, the other short piece of the movable piece 203. Edge 203
It is possible to displace b from the support 202 to the upper side of the substrate 201.

[0007]

However, the above-mentioned 2
Mirror 1 in the former of the two electrostatic actuators
The maximum displacement amount of 04 is determined by the gap between the silicon substrate 101 and the movable electrode plate 102. That is, the luminous flux of the optical signal to be controlled depends on the maximum displacement amount of the mirror 104. Therefore, it is necessary to increase the maximum displacement amount of the mirror 104 with respect to the silicon substrate 101 in order to completely control an optical signal having a large luminous flux. However, if the maximum displacement amount is increased, it is necessary to increase the drive voltage in order to increase the electrostatic attraction, and if the drive voltage is increased, it is necessary to increase the electrical withstand voltage of the electrostatic actuator, which hinders miniaturization. Will end up.

In the latter case, the movable piece 203 is the beam 20.
8 is used as a fulcrum, and the movable piece 203 is further bent to obtain the displacement, so that the fixed electrode 205 and the movable piece 2
It is possible to obtain a displacement equal to or larger than the gap with respect to No. 03, but when the amount of bending of the movable piece 203 increases (the amount of displacement of the movable piece increases), the force acting on the beam 208 in the substrate direction increases, resulting Beam 208 itself flexes toward the substrate, and the movable piece 2
There is a concern that the displacement amount of 03 will be saturated.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electrostatic actuator capable of achieving low power consumption and large displacement. .

[0010]

In order to achieve the above object, an electrostatic actuator of the invention according to claim 1 has a supporting substrate having a fixed electrode and a fulcrum portion on the surface, a fixed electrode and a void. A movable electrode arranged so as to face each other, and a fixed portion integrally formed with the movable electrode and connected to the support substrate,
A movable arm composed of a movable electrode and a movable element continuously arranged in the same plane, and the movable arm is made to flex around the movable electrode by an electrostatic attraction between the fixed electrode and the movable electrode. The movable arm is used as a lever to rotate the movable element around the fulcrum.

According to a second aspect of the invention, in the optical switch according to the first aspect, the movable electrode is wider than the movable element.

According to a third aspect of the present invention, in the electrostatic actuator according to the first or second aspect, the movable electrode has at least one recess on the surface thereof that is orthogonal to the longitudinal direction of the mover. I am going to

According to a fourth aspect of the present invention, in the electrostatic actuator according to the third aspect, the recess is formed on the fulcrum side from the middle of the movable electrode.

According to a fifth aspect of the present invention, in the electrostatic actuator according to the first aspect, the movable electrode has at least one through hole on its surface. There is.

According to a sixth aspect of the present invention, there is provided an electrostatic actuator according to any one of the first to fifth aspects, wherein the support substrate has a sticking prevention means at a position facing the mover. There is.

According to a seventh aspect of the present invention, in the electrostatic actuator according to the sixth aspect, the sticking prevention means is an uneven portion provided on the surface of the support substrate.

According to an eighth aspect of the present invention, in the electrostatic actuator according to any one of the first to seventh aspects, the movable arm is formed of the same member as the supporting substrate.

An electrostatic actuator according to a ninth aspect of the present invention is the electrostatic actuator according to any one of the first to eighth aspects, wherein the movable element has a switch plate at an end facing the movable electrode. There is.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an optical switch using an electrostatic actuator according to the present embodiment. (A) is a plan view thereof, (b) is a cross section taken along line AA. It is a figure.

The optical switch of this embodiment has a supporting substrate 1
And the movable arm 2 are the main constituent elements.

Of these, the supporting substrate 1 is for fixing and supporting the movable arm 2 described later without hindering the rotation of the movable arm 2, and is formed of, for example, a semiconductor substrate made of silicon. In addition, this one has a fixed electrode 11 and a fulcrum portion 1.
2 and an uneven portion 13. Furthermore, the fixed electrode 1
An electrode 16 for applying a potential to 1 is provided at a predetermined position.

The fixed electrode 11 rotates the movable arm 2 by generating an electrostatic attractive force by a voltage applied between the fixed electrode 11 and the movable electrode 21, which will be described later. This is, for example, a flat plate formed of aluminum (Al) and having a substantially quadrangular shape in plan view, and its size is
For example, it is about 400 μm square. The fixed electrode 11 is formed on the bottom surface of the recess 14 formed at a predetermined position on the support substrate 1. Further, a nitride film (Si ₃ N ₄ ) 15 for electrically insulating the movable arm 2 is formed on the support substrate 1 including the fixed electrode 11.

The fulcrum portion 12 is a portion serving as a fulcrum of a lever formed by the movable arm 2, that is, a portion serving as a fulcrum of rotation of a movable element 23 described later. The shape is a trapezoidal rod body narrowing upward from the support substrate 1 (upper side in FIG. 1B) in a cross-sectional view, and bears a part of the side wall of the recess 14 in which the fixed electrode 11 is formed. ing. Further, the upper surface (upper side of FIG. 1B) is formed thin so as to make almost line contact with the mover 23.

In the uneven portion 13, the movable arm 2 has the supporting substrate 1
This is to reduce sticking due to intermolecular force or the like generated between and. Its shape is a wavy body in which substantially triangular shapes are continuous in a cross-sectional view, and its size is at least approximately the same as the size of the mover 23. Further, this is provided at a position facing the mover 23 on the support substrate 1, and is configured by forming a V groove in a direction orthogonal to the longitudinal direction of the mover 23.

Subsequently, the movable arm 2 controls an optical signal by rotating on the support substrate 1, and is composed of a movable electrode 21, a fixed portion 22, and a mover 23. Further, this is formed of, for example, polycrystalline silicon.

The movable electrode 21 generates an electrostatic attractive force by the voltage applied between the movable electrode 21 and the fixed electrode 11 to move the movable arm 2.
To rotate. The shape is a flat plate having a substantially quadrangular shape in plan view, the size thereof is formed to be substantially the same as that of the fixed electrode 11, and the thickness thereof is, for example,
It is about 10 μm. In addition, this is the fixed electrode 11
And have a predetermined gap and are opposed to each other, and the interval is set to, for example, about 10 μm. In addition, the movable electrode 2
A plurality of grooves 24 are formed in a direction orthogonal to the longitudinal direction of the mover 23 in a region extending from the middle of the upper surface (upward in FIG. 1B) toward the direction in which the mover 23 is formed. There is. The groove 24 has a substantially quadrangular shape in a sectional view, and its width is, for example, about 10 μm and its length is
For example, it is substantially the same as the movable electrode 21. The depth is set to about 7 μm, for example, so as not to be damaged when the movable electrode 21 bends. In addition, the movable electrode 21
In the remaining area of the through hole 25 formed in the thickness direction thereof.
Are formed. The opening surface is formed in a substantially circular shape in plan view, and the opening diameter is, for example, 10 μm.
It is a degree. Further, the through hole 25 is, for example, 50 μm.
They are arranged with an interval of about m. Further, impurities are added to the movable electrode 21 to improve conductivity.

The fixed portion 22 fixes a part of the movable arm 2 to the support substrate 1. The shape is a flat plate having a substantially quadrangular shape in a plan view, and is substantially equal to the size of the movable electrode 21 in the direction orthogonal to the mover 23. Also,
This is integrally formed on the side surface of the movable electrode 21 opposite to the side surface on which the mover 23 is provided. Further, the lower surface of the fixing portion 22 (downward in FIG. 1B) is fixed to the support substrate 1. In addition, the fixed portion 22 has a movable electrode 21.
Similarly to the above, impurities are added to improve conductivity, and an electrode 26 for applying a potential to the movable electrode 21 is formed at a predetermined position thereof.

The mover 23 displaces a switch plate 27, which will be described later, up and down (up and down direction in FIG. 1B) about the fulcrum 12 in conjunction with the movable electrode 21 which rotates in response to electrostatic attraction. It is a thing. Its shape is a rectangular body having a substantially quadrangular shape in plan view, and its thickness is substantially the same as that of the movable electrode 21. A switch plate 27 is provided at one end facing the side of the mover 23 connected to the movable electrode 21, and the mover 23 is erected on the upper surface of the mover 23 (upper side in FIG. 1B). Is provided so as to be substantially parallel to the longitudinal direction of.

The switch plate 27 passes or reflects an optical signal by interposing it on the optical path of the optical signal input to the optical switch. This is made of, for example, a photosensitive organic material, and its shape is
It is a flat plate having a substantially rectangular shape in a plan view. Further, the surface thereof is plated with gold (Au), for example. The size thereof is at least approximately equal to or larger than the luminous flux of the optical signal to be controlled, and the size in the horizontal direction is, for example, approximately 1.4 times the size in the vertical direction.

Next, the manufacturing method thereof will be described.

First, a nitride film (Si ₃ N ₄ ) serving as a mask is formed on one surface of the supporting substrate 1, and then a photosensitive organic material is applied to the surface, followed by photolithography technology and etching technology. After removing the photosensitive organic material and the nitride film of the concave portion 14 and the concave-convex portion 13 for forming the fixed electrode 11, the entire photosensitive organic material is removed.
The exposed portion of the supporting substrate 1 is anisotropically etched using a KOH aqueous solution to form the depression 14 and the uneven portion 13 (FIG. 2).
(A)).

Next, after removing the nitride film from one end, aluminum is vapor-deposited on the upper surface of the nitride film, and then a photosensitive organic material is applied to form a region where electrodes (not shown) are formed and a region other than the bottom surface of the recess 14 is exposed. Organic materials are removed. Then, unnecessary aluminum is removed by an etching technique, and a nitride film 15 as an insulating film is formed again on the upper surface of the support substrate 1 excluding the electrodes. Then, except for a region fixed to the fixing portion 22 of the support substrate 1, for example, boron-phosphorus glass (BPS).
G) 16 is deposited, and further an oxide film 17 is formed on the upper surface thereof. (Fig. 2 (b))

Next, polycrystalline silicon is deposited on the upper surface of the oxide film 17, a photosensitive organic material is applied thereto, and then the movable arm 2 is formed by using a photolithography technique and an etching technique.
To form. Subsequently, after removing the photosensitive organic material, the photosensitive organic material is applied again, and the photosensitive organic material at the positions of the fixed portion 22 and the movable electrode 21 is removed to form impurities (conductivity type opposite to that of the semiconductor substrate). Element) to give conductivity to the fixed portion 22 and the movable electrode 21. Subsequently, after removing the photosensitive organic material, the photosensitive organic material is applied again, and the groove 24 and the through hole 25 are formed in the movable electrode 21 by using the photolithography technique and the etching technique (FIG. 2C).

Then, a photosensitive organic material is deposited, and the photosensitive organic material other than the region to be the switch plate 27 is removed by using the photolithography technique and the etching technique. For example, gold is sputtered to form the electrode 26 and the switch plate. 27 is formed (FIG. 2D).

Finally, the photosensitive organic material, the oxide film 17 and the boron-phosphorus glass 16 are removed by etching technique, and the movable arm 2 is rotatably separated to complete the optical switch (FIG. 2 (e)). )).

The optical switch thus formed is
First, when the voltage is not applied between the fixed electrode 11 and the movable electrode 21, the movable arm 2 is substantially parallel to the support substrate 1, and the mover 23 is in contact with the uneven portion 13. Next, when a voltage is applied to both electrodes 11 and 21 via an electrode (not shown) connected to the fixed electrode 11 and an electrode 26 formed on the fixed portion 22, an electrostatic attractive force is generated between the electrodes 11 and 21. Occurs, the movable electrode 21 is attracted to the fixed electrode 11. At that time, the movable electrode 21 includes the fixed portion 22 and the fulcrum portion 1.
Since the movable electrode 21 is supported by the movable electrode 21, the movable electrode 21 bends around the center in a direction orthogonal to the longitudinal direction of the movable element 23. Then, when the voltage applied to both electrodes 11 and 21 is increased, the movable electrode 21 further bends. At this time, the movable arm 2 is a kind of lever having the fulcrum portion 12 as a fulcrum, As the deflection of the movable electrode 21 increases, the mover 23 rotates upward about the fulcrum 12. Then, the electrostatic attraction and the movable electrode 2
When the restoring force of 1 is balanced, the maximum displacement of the mover 23 is reached. In this state, the optical switch is installed so as to intervene on the optical path of the optical signal controlled by the switch plate 27, thereby reflecting the optical signal. That optical path can be blocked. On the contrary, the fixed electrode 11 and the movable electrode 21
If the voltage application between and is stopped, the movable arm 2 becomes substantially parallel to the support substrate 1 due to the restoring force of the movable electrode 21, and an optical signal can pass therethrough.

According to the optical switch using the electrostatic actuator of the above-described embodiment, the movable arm 2 is flexed around the center of the movable electrode 21 by the electrostatic attraction between the fixed electrode 11 and the movable electrode 21. The mover 23 to the fulcrum 1
Since the movable arm 2 is rotated about 2, the movable arm 21 is a kind of lever having the movable electrode 21 as a force point, the fulcrum portion 12 as a fulcrum, and the switch plate 27 as an action point. Even if the gap between the movable electrode 21 and the movable electrode 21 is relatively small, about 10 μm, the switch plate 2
It is possible to obtain a large displacement of 7 in the order of several hundreds of μm. Moreover, since the distance between the electrodes 11 and 21 is small, power consumption can be reduced. In addition, the movable element 23 of the movable electrode 21
Since the size in the direction orthogonal to is wider than that of the movable element 23, it is possible to relatively easily bend the movable element 23 at the fulcrum portion 12. Further, since at least one groove 24 orthogonal to the longitudinal direction of the mover 23 is formed on the fulcrum portion 12 side from the middle of the surface of the movable electrode 21, the flexural rigidity of the movable electrode 21 can be reduced. The movable arm 2 can be flexed even with a small electrostatic attraction. Also,
At least one through hole 25 is formed on the surface of the movable electrode 21.
Since it is formed, it is possible to reduce air resistance when the movable electrode 21 is driven up and down, and it is possible to suppress vibration. Further, since the support substrate 1 has the uneven portion 13 at a position facing the mover 23, the contact area between the support substrate 1 and the mover 23 is small, and sticking can be suppressed. Further, since the movable arm 2 is formed of the same silicon as the supporting substrate 1, all the optical switches can be formed by using the semiconductor manufacturing process, and the manufacturing accuracy thereof can be improved.

The concave-convex portion 13 is not limited to a wavy body having a substantially triangular continuous shape in cross section, and may be, for example, a wavy body having a substantially rectangular continuous shape in cross section. In short, the more the contact portion between the mover 23 and the support substrate 1 contacts in a small area, the higher the effect of reducing the sticking.

Further, the sizes and thicknesses of the fixed electrode 11 and the movable electrode are not limited to the above-mentioned numerical values, and the design can be appropriately changed within a range satisfying this function.

Further, the groove 24 is not limited to a substantially quadrangular shape in cross section, and for example, the same effect can be obtained if the groove 24 is V-shaped narrowing in the thickness direction of the movable electrode 21 in cross section. Further, the formation position thereof may be the lower surface of the movable electrode 21 (downward in FIG. 1B). further,
The depth is not limited to about 7 μm, and the design can be appropriately changed in consideration of the relationship with the electrostatic attractive force and the displacement amount of the mover 23.

The shape of the opening surface of the through hole 25 is not limited to a substantially circular shape in plan view.
It may be a substantially rectangular shape. Further, the aperture diameter and the arrangement interval are not limited to the above-mentioned numerical values, and the design can be appropriately changed within the range that satisfies this function.

[0043]

According to the electrostatic actuator of the first aspect of the present invention, the movable arm is flexed around the movable electrode by the electrostatic attraction between the fixed electrode and the movable electrode, and the movable element is moved about the fulcrum. Since it is rotated, even if the gap between the fixed electrode and the movable electrode is relatively small, the displacement of the tip of the mover can be as large as several hundred μm. Also,
Since the gap between the electrodes is small, power consumption can be reduced.

In the electrostatic actuator of the invention according to claim 2, in addition to the effect of claim 1, since the movable electrode is wider than the movable element, it is relatively easy to bend the movable element at the fulcrum portion. Can be

In the electrostatic actuator of the invention according to claim 3, in addition to the effect of claim 1 or 2, the movable electrode is
Since at least one concave portion orthogonal to the longitudinal direction of the mover is provided on the surface, the flexural rigidity of the movable electrode can be reduced, and the movable arm can be flexed even with a small electrostatic attraction.

In the electrostatic actuator of the invention according to claim 4, in addition to the effect of claim 3, since the recess is formed on the fulcrum side from the middle of the movable electrode, the deflection of the movable electrode is further increased. The rigidity can be reduced, and the movable arm can be flexed even with a small electrostatic attraction.

In the electrostatic actuator of the invention according to claim 5, in addition to the effect according to any one of claims 1 to 4, the movable electrode has at least one or more through holes on its surface. The air resistance when the movable electrode is driven up and down can be reduced, and vibration can be suppressed.

In the electrostatic actuator according to the sixth aspect of the present invention, in addition to the effect according to any one of the first to fifth aspects, the support substrate has the sticking prevention means at a position facing the mover. , it can.

In the electrostatic actuator of the invention according to claim 7, in addition to the effect of claim 6, since the sticking prevention means is an uneven portion provided on the surface of the support substrate, the support substrate and the mover are The contact area is reduced, and sticking can be suppressed.

In the electrostatic actuator of the invention according to claim 8, in addition to the effect according to any one of claims 1 to 7, since the movable arm is formed of the same member as the support substrate, the electrostatic actuator Can be formed by using the semiconductor manufacturing process, and the manufacturing accuracy can be improved.

In the electrostatic actuator of the invention according to claim 9, in addition to the effect according to any one of claims 1 to 8, the mover has a switch plate at the end facing the movable electrode. By installing an electrostatic actuator so as to intervene on the optical path of the optical signal controlled by the switch plate in a certain state, the optical signal can be reflected and the optical path can be blocked, and an optical switch can be realized. it can.

[Brief description of drawings]

1A and 1B show an optical switch using an electrostatic actuator according to an embodiment of the present invention, FIG. 1A is a plan view thereof, and FIG. 1B is a sectional view taken along the line AA. Is.

FIG. 2 is a cross-sectional view showing the same manufacturing process as above.

3A and 3B show a conventional electrostatic actuator, in which FIG. 3A is a plan view thereof, and FIG. 3B is a sectional view taken along line AA.

4A and 4B show another conventional electrostatic actuator, in which FIG. 4A is a plan view thereof, FIG. 4B is a sectional view taken along the line AA, and FIG. It is sectional drawing which showed the drive state when a voltage is applied to a movable piece.

[Explanation of symbols]

1 Support substrate 11 fixed electrode 12 fulcrums 13 uneven part 14 Dimples 2 movable arm 21 movable electrode 22 Fixed part 23 mover 24 grooves 25 through holes 27 Switch plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Kawada             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company F term (reference) 2H041 AA13 AB13 AC06 AZ03 AZ05                       AZ08

Claims (9)

[Claims] 1. A support substrate provided with a fixed electrode and a fulcrum portion on its surface, a movable electrode disposed so as to face the fixed electrode with a gap, and a movable electrode integrally formed with the movable electrode and connected to the support substrate. A fixed arm and a movable arm composed of a mover continuously arranged in the same plane as the movable electrode. The movable arm is movable around the movable electrode by electrostatic attraction between the fixed electrode and the movable electrode. An electrostatic actuator characterized in that an arm is flexed, and a movable arm is used as a lever to rotate the movable element around a fulcrum. 2. The electrostatic actuator according to claim 1, wherein the movable electrode is wider than the mover. 3. The electrostatic actuator according to claim 1, wherein the movable electrode has at least one recess on the surface thereof that is orthogonal to the longitudinal direction of the mover. 4. The electrostatic actuator according to claim 3, wherein the concave portion is formed on the fulcrum side from the middle of the movable electrode. 5. The electrostatic actuator according to claim 1, wherein the movable electrode has at least one or more through holes on a surface thereof. 6. The electrostatic actuator according to claim 1, wherein the support substrate has a sticking prevention unit at a position facing the mover. 7. The electrostatic actuator according to claim 6, wherein the sticking prevention means is an uneven portion provided on the surface of the support substrate. 8. The electrostatic actuator according to claim 1, wherein the movable arm is formed of the same member as the support substrate. 9. The electrostatic actuator according to claim 1, wherein the mover has a switch plate at an end facing the movable electrode.