JP2012014186A - Wavelength variable filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength variable filter having excellent optical characteristics without causing an increase in a drive voltage.SOLUTION: A second substrate 3 includes two surfaces located at different positions in the thickness direction in the side of a movable section 21. One surface out of the two surfaces is provided with a driving electrode 33, and the other surface is provided with a detecting electrode 40. Based on the capacitance between the detecting electrode 40 and the movable section 21, a potential difference is generated between the driving electrode 33 and the movable section 21 to generate an electrostatic attraction therebetween, thereby displacing the movable section 21. Light reflection is repeated between a fixed reflection film 35 and a movable reflection film 25 to cause interference, and light with a wavelength according to the distance between the fixed reflection film 35 and the movable reflection film 25 is emitted to the outside.

Description

  The present invention relates to a wavelength tunable filter.

A wavelength tunable filter (Optical Tunable Filter) is known as one that separates only light having a specific wavelength from light having a plurality of wavelengths (see, for example, Patent Document 1).
For example, in the wavelength tunable filter according to Patent Document 1, the plate-like movable portion is displaceable in the thickness direction and is provided substantially parallel to the support substrate. Reflective films are provided on the surface and on the surface (opposing surface) on the movable part side of the support substrate, respectively.

  In addition, a drive electrode is provided on the support substrate, and by generating a potential difference between the drive electrode and the movable part, an electrostatic attractive force is generated therebetween, and the movable part is displaced. The distance between the two reflecting films is variable due to the displacement of the movable part. When light having a plurality of wavelengths enters the gap, only light having a wavelength corresponding to the distance of the gap is emitted to the outside due to the interference action.

  In order to preferably cause such interference action, it is necessary to accurately set the distance between the movable portion and the support substrate, or to increase the parallelism between the movable portion and the support substrate. . Therefore, a plurality of drive electrodes are provided, and a plurality of detection electrodes are provided on the support substrate so as to correspond to the drive electrodes, and the movable portion and the support substrate are arranged in parallel based on the capacitance between the detection electrodes and the movable portion. It is necessary to detect the degree and the distance between the movable part and the support substrate.

However, in the wavelength tunable filter of Patent Document 1, since the surface of the support substrate on the movable part side is a plane, the detection electrode must be provided on the same plane as the drive electrode, and the drive electrode and the detection When the distance between the electrodes is small, the coupling capacitance generated between them becomes large, and it is difficult to accurately perform the detection.
If the distance between the drive electrode and the detection electrode is increased in order to reduce the coupling capacitance generated between the drive electrode and the detection electrode, the area of the drive electrode must be reduced accordingly. The driving voltage becomes high.

US Pat. No. 6,747,775

  An object of the present invention is to provide a wavelength tunable filter having excellent optical characteristics without causing an increase in driving voltage.

Such an object is achieved by the present invention described below.
The wavelength tunable filter of the present invention includes a substrate,
A plate-shaped, opposed to the substrate with a gap, and a movable part provided to be displaceable in the thickness direction;
A movable reflective film provided on the substrate-side surface of the movable part;
A plurality of drive electrodes provided on a surface of the substrate on the movable part side;
A plurality of detection electrodes provided on the surface of the movable part side of the substrate while being separated from the drive electrode;
A fixed reflection film provided on the surface of the movable part side of the substrate,
The substrate has two installation surfaces at different positions in the thickness direction on the movable part side,
Of the two installation surfaces, the drive electrode is provided on one installation surface, and the detection electrode is provided on the other installation surface,
Based on the electrostatic capacitance between each detection electrode and the movable part, by generating a potential difference between each drive electrode and the movable part, an electrostatic attractive force is generated between them, and the movable part While changing the position and posture of
Light can be repeatedly reflected between the fixed reflective film and the movable reflective film to cause interference, and light having a wavelength corresponding to the distance between the fixed reflective film and the movable reflective film can be emitted to the outside. It is characterized by being comprised.

  As a result, since the drive electrode and the detection electrode are not located on the same plane, the distance between the drive electrode and the detection electrode can be increased even when the drive electrode and the detection electrode are close to each other in plan view. . As a result, the coupling capacitance generated between the drive electrode and the detection electrode is reduced, and the electrostatic capacitance between the movable portion and the detection electrode is detected with high accuracy, and the movable portion is desired based on the detection result. Can be accurately displaced to the position and posture. In particular, in the present invention, since a plurality of drive electrodes and a plurality of detection electrodes are provided, the distance between the movable reflective film and the fixed reflective film and the parallel between the movable reflective film and the fixed reflective film are provided. The optical characteristics of the wavelength tunable filter can be made excellent by controlling the degree of accuracy with high accuracy. At this time, since the drive electrode and the detection electrode can be brought close to each other in plan view, an increase in drive voltage due to a decrease in the area of the drive electrode can be prevented.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that the number of the drive electrodes is the same as the number of the detection electrodes, and that each drive electrode and each detection electrode are paired.
Thereby, the position and posture of the movable part can be accurately changed while suppressing the number of drive electrodes and detection electrodes. Therefore, the cost of the wavelength tunable filter can be reduced, and the manufacturing process of the wavelength tunable filter can be simplified.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that the drive electrode has a shape similar to the shape of the detection electrode.
Thereby, the correspondence between the drive electrode and the detection electrode can be simplified, and the control of the position and orientation of the movable portion can be simplified.
In the wavelength tunable filter according to the aspect of the invention, of the two installation surfaces of the substrate, the drive electrode is provided on an installation surface closer to the movable portion, and the detection is performed on an installation surface farther from the movable portion. It is preferable that an electrode is provided.
Thereby, the electrostatic force produced between a drive electrode and a movable part can be enlarged. Therefore, the drive voltage can be reduced.

In the wavelength tunable filter of the present invention, it is preferable that a concave portion is formed in the substrate, and the detection electrode is provided on a bottom surface of the concave portion.
Thereby, the detection electrode and the drive electrode can be separated in the thickness direction of the substrate with a relatively simple configuration.
In the wavelength tunable filter according to the aspect of the invention, the concave portion includes a first concave portion and a second concave portion formed on a bottom surface of the first concave portion, and the driving electrode is disposed outside the second concave portion. Preferably, the detection electrode is provided on the bottom surface of the second recess, and the detection electrode is provided on the bottom surface of the second recess.
As a result, the detection electrode and the drive electrode can be separated from each other with a relatively simple configuration, and a gap for generating an electrostatic force can be formed between the drive electrode and the movable portion.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that the fixed reflection film is provided on the bottom surface of the second recess in addition to the detection electrode.
Thereby, regardless of the distance between the drive electrode and the movable part, the usable wavelength band according to the depth of the second recess can be obtained. Therefore, the drive voltage can be reduced even if wavelength tunable filters having various usable wavelength bands are manufactured.

In the wavelength tunable filter of the present invention, each detection electrode is preferably provided so as to surround the fixed reflective film.
Thereby, the attitude | position of the movable part with respect to a board | substrate can be detected easily and correctly.
In the wavelength tunable filter of the present invention, it is preferable that each drive electrode is provided so as to surround the second recess.
Thereby, the attitude | position of the movable part with respect to a board | substrate can be stabilized more.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that at least one of the fixed reflection film and the movable reflection film is formed of a dielectric multilayer film.
As a result, it is possible to prevent light loss at the time of light interference between the movable reflective film and the fixed reflective film, and to improve the optical characteristics.
In the wavelength tunable filter according to the aspect of the invention, a support portion fixed to the substrate and a connection portion that connects the support portion to the movable portion so that the movable portion can be displaced in a thickness direction thereof. It is preferable that the movable portion, the support portion, and the connecting portion are integrally formed.
Thereby, the attitude | position of the movable part with respect to a board | substrate can be stabilized more.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that each of the movable portion, the support portion, and the connection portion is made of silicon as a main material.
Thereby, optical characteristics and durability can be further improved.
In the wavelength tunable filter of the present invention, it is preferable that the substrate is made of glass as a main material.
Thereby, light can be incident between the movable reflective film and the fixed reflective film from the substrate side.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that the substrate is composed mainly of glass containing alkali metal ions.
Thereby, when the support part is composed of silicon as a main material, the support part and the substrate can be easily and firmly joined to each other by anodic bonding.
In the wavelength tunable filter according to the aspect of the invention, it is preferable that the movable portion, the support portion, and the connection portion are formed by processing one Si layer of the SOI wafer.
Thereby, a movable part, a support part, and a connection part can be made more highly accurate comparatively easily.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that an insulating film is provided on the surface of the movable portion on the substrate side.
Thereby, the short circuit by the contact of a movable part and a drive electrode can be prevented.
In the wavelength tunable filter according to the aspect of the invention, it is preferable that the movable reflective film has an insulating property and also serves as the insulating film.
Thereby, it is possible to prevent a short circuit due to contact between the movable portion and the drive electrode with a simpler configuration.

In the wavelength tunable filter according to the aspect of the invention, it is preferable that the detection electrode is closer to the fixed reflective film than the drive electrode.
As a result, the amount of change in capacitance generated between the movable part and the drive electrode with respect to the amount of change in the distance between the movable reflective film and the fixed reflective film becomes relatively large, so that the displacement of the movable part can be more accurately performed. Can be controlled. In addition, the drive voltage can be reduced by making the area of the drive electrode larger than the area of the detection electrode relatively easily.
In the wavelength tunable filter according to the aspect of the invention, it is preferable that the distance between the detection electrode and the drive electrode in the thickness direction of the substrate is 5 to 500 μm.
Thereby, it is possible to make the optical characteristics of the wavelength tunable filter desired as relatively easily while preventing the coupling capacitance generated between the detection electrode and the drive electrode more reliably.

It is a disassembled perspective view which shows the wavelength variable filter which is embodiment of the structure of this invention. It is a top view which shows the wavelength variable filter shown in FIG. It is the sectional view on the AA line in FIG. It is a figure for demonstrating the drive electrode and detection electrode of a wavelength variable filter shown in FIG. It is a figure for demonstrating the manufacturing method of the wavelength variable filter shown in FIG. It is a figure for demonstrating the manufacturing method of the wavelength variable filter shown in FIG. It is a figure for demonstrating the manufacturing method of the wavelength variable filter shown in FIG. It is a figure for demonstrating the manufacturing method of the wavelength variable filter shown in FIG.

Hereinafter, the wavelength tunable filter of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
1 is an exploded perspective view showing an embodiment of a wavelength tunable filter according to the present invention, FIG. 2 is a plan view of such a wavelength tunable filter, FIG. 3 is a cross-sectional view taken along the line AA in FIG. FIG. 5 is a diagram for explaining a drive electrode and a detection electrode of such a wavelength tunable filter. In the following description, the upper side in FIG. 1 is referred to as “upper”, the lower side is referred to as “lower”, the front side in FIG. 2 and FIG. 4 is “upper”, the rear side in FIG. The right side is called “right”, the left side is called “left”, the upper side in FIG. 3 is called “upper”, the lower side is called “lower”, the right side is called “right”, and the left side is called “left side”.

  As shown in FIG. 1, the wavelength tunable filter 1 receives, for example, light, and emits only light (interference light) corresponding to a specific wavelength among the wavelengths of the light by interference action. Such a wavelength tunable filter 1 has a first substrate 2 and a second substrate 3 bonded to each other, and a gap for causing light interference is defined between them. When the light L enters the gap, only light having a wavelength corresponding to the size of the gap is emitted due to the interference action. Hereinafter, each component of the wavelength tunable filter 1 will be described in detail sequentially.

  The first substrate 2 has light transparency and conductivity, and is made of, for example, silicon. The first substrate 2 includes a movable portion 21 for changing a gap between the first substrate 2 and the second substrate 3, a support portion 22, and the movable portion 21 with respect to the support portion 22. It has the connection part 23 which connects these so that it can displace up and down. These are integrally formed by forming an opening 24 having a different shape in the first substrate 2.

The movable portion 21 has a plate shape and is located in a substantially central portion of the first substrate 2 in a plan view and has a circular shape. Such a movable part 21 is opposed to the second substrate 3 with a gap, and is provided so as to be displaceable in the thickness direction. Needless to say, the shape, size, and arrangement of the movable portion 21 are not particularly limited to the illustrated shapes.
The thickness (average) of the movable portion 21 is appropriately selected according to the constituent material, application, and the like, and is not particularly limited, but is preferably about 1 to 500 μm, and more preferably about 10 to 100 μm.

The movable portion 21 has a movable reflective film (HR coat) 25 that reflects light with a relatively high reflectance on the surface on the side facing the second substrate 3 (that is, the lower surface of the movable portion 21). A movable antireflection film (AR coating) 26 that suppresses reflection of light is formed on the surface opposite to the side facing the second substrate 3 (that is, the upper surface of the movable portion 21). .
As shown in FIG. 3, the movable reflective film 25 reflects light incident on a second gap G2 (described later) from below the wavelength tunable filter 1 with a fixed reflective film 35 (described later) multiple times. It is. As shown in FIG. 3, the movable antireflection film 26 reflects light incident on the second gap G2 from below the tunable filter 1 downward in the figure at the interface between the upper surface of the first substrate 2 and the outside air. This is intended to prevent this.

  The movable reflective film (dielectric multilayer film) 25 and the movable antireflection film 26 are not particularly limited as long as necessary optical characteristics can be obtained, but those made of a dielectric multilayer film are preferable. That is, the movable reflective film (dielectric multilayer film) 25 and the movable antireflection film 26 are preferably formed by alternately laminating a plurality of high refractive index layers and low refractive index layers. Thereby, loss of light at the time of interference of light between the movable reflective film 25 and the fixed reflective film 35 can be prevented, and optical characteristics can be improved.

The material constituting the high refractive index layer is not particularly limited as long as it can obtain the optical characteristics necessary for the movable reflective film 25 and the movable antireflection film 26, but in the visible light region and the infrared light region. When used, Ti ₂ O, Ta ₂ O ₅ , niobium oxide, and the like can be used. When used in the ultraviolet region, Al ₂ O ₃ , HfO ₂ , ZrO ₂ , ThO _{2, and the} like can be given. In the present embodiment, since the first substrate 2 is made of silicon, infrared light is used for the wavelength tunable filter 1. Therefore, Ti ₂ O, Ta ₂ O ₅ , niobium oxide, or the like is preferably used as a material constituting the high refractive index layer.

The material constituting the low refractive index layer is not particularly limited as long as it can obtain the optical characteristics necessary for the movable reflective film 25 and the movable antireflection film 26. For example, MgF ₂ , SiO _{2, and the} like can be used. Can be mentioned. In particular, as a constituent material of the low refractive index layer, a material mainly composed of SiO ₂ is preferably used.
The number and thickness of the high refractive index layer and the low refractive index layer constituting the movable reflective film 25 and the movable antireflection film 26 are set according to the required optical characteristics. In general, when a reflective film is composed of a multilayer film, the number of layers required to obtain its optical characteristics is 12 or more, and when an antireflection film is composed of a multilayer film, the number of layers necessary for the optical characteristics is About 4 layers.

If the movable reflective film 25 has an insulating property, a short circuit due to contact between the movable portion 21 and the drive electrode 33 can be prevented. That is, when an insulating film is provided on the surface of the movable portion 21 on the second substrate 3 side, a short circuit due to contact between the movable portion 21 and the drive electrode 33 can be prevented.
In this case, since the movable reflection film 25 also serves as an insulating film, a short circuit due to contact between the movable portion 21 and the drive electrode 33 can be prevented with a simpler configuration.
A support portion 22 is formed so as to surround such a movable portion 21, and the movable portion 21 is supported by the support portion 22 via a connecting portion 23.

  A plurality (four in the present embodiment) of the connecting portions 23 are provided at equal intervals in the circumferential direction around the movable portion 21 described above. The connecting portion 23 has elasticity (flexibility), so that the movable portion 21 is spaced substantially parallel to the second substrate 3 in the thickness direction (up and down). Can be displaced. The number, position, and shape of the connecting portions 23 are not limited to those described above as long as the movable portion 21 can be displaced with respect to the support portion 22.

The first substrate 2 is provided with openings 27a and 27b for accessing later-described extraction electrodes 38a and 38b from the outside. The openings 27a and 27b can be used as pressure release openings that prevent a pressure difference from the outside from occurring in the space between the first substrate and the second substrate in the manufacturing process of the wavelength tunable filter 1. Function.
In such a first substrate 2, it is preferable that the movable portion 21, the support portion 22, and the connecting portion 23 are integrally formed. Thereby, the attitude | position of the movable part 21 with respect to the 2nd board | substrate 3 can be stabilized more.

In that case, if the movable part 21, the support part 22, and the connecting part 23 are each composed of silicon as a main material, the optical characteristics and the durability can be further improved.
The second substrate 3 is bonded to the first substrate 2 on the lower surface of the support portion 22.
In particular, when the movable portion 21, the support portion 22, and the connecting portion 23 are formed by processing one Si layer of the SOI wafer, the movable portion 21 and the supporting portion 22 are relatively easily connected. The part 23 can be made more accurate.

The second substrate 3 has optical transparency, and the second substrate 3 has a first gap between the first substrate 2 and the second substrate 3 on one surface side thereof. A first recess 31 for forming G1 and a second recess 32 for forming a second gap G2 between the first substrate 2 and the second substrate 3 inside the first recess 31. And are formed.
The constituent material of the second substrate 3 is not particularly limited as long as it has light transmittance with respect to the wavelength of light to be used. For example, soda glass, crystalline glass, quartz glass, lead glass, potassium Examples thereof include various glasses such as glass, borosilicate glass, sodium borosilicate glass, and alkali-free glass, and silicon.

Among these, as a constituent material of the 2nd board | substrate 3, the glass containing alkali metals (mobile ion) like sodium (Na) or potassium (K) is preferable, for example. Thereby, when the 1st board | substrate 2 is comprised, for example with silicon | silicone, the 1st board | substrate 2 and the 2nd board | substrate 3 can be joined simply and firmly by anodic bonding.
In particular, when the first substrate 2 and the second substrate 3 are bonded by anodic bonding, the difference between the thermal expansion coefficient of the first substrate 2 and the thermal expansion coefficient of the second substrate 3 is as small as possible. More specifically, it is preferably 50 × 10 ⁻⁷ ° C. ⁻¹ or less.

Thereby, even if the first substrate 2 and the second substrate 3 are exposed to a high temperature during anodic bonding, the stress generated between the first substrate 2 and the second substrate 3 is reduced, and the first substrate 2 and the second substrate 3 are reduced. Damage to the substrate 2 or the second substrate 3 can be prevented.
Therefore, it is preferable to use soda glass, potassium glass, sodium borosilicate glass, or the like as the constituent material of the second substrate 3. For example, Pyrex (registered trademark) glass manufactured by Corning, Inc. is preferably used.

In addition, the thickness (average) of the second substrate 3 is appropriately selected depending on the constituent material, application, and the like, and is not particularly limited, but is preferably about 10 to 2000 μm, and more preferably about 100 to 1000 μm. .
The first concave portion 31 has a circular outer shape, and is disposed at a position corresponding to the movable portion 21, the connecting portion 23, and the opening portion 24 described above. On the bottom surface of the first recess 31, an annular drive electrode 33 and an insulating film 34 are laminated in this order at a position corresponding to the outer peripheral portion of the movable portion 21. That is, the drive electrode 33 is provided on the installation surface of the second substrate 3 on the movable part 21 side.

  The drive electrode 33 has a substantially annular shape as a whole, and is composed of two drive electrodes 33a and 33b which are divided into two. And each of drive electrode 33a, 33b and the movable part 21 are connected to the electricity supply circuit which is not shown in figure. Thereby, a potential difference can be generated between the drive electrode 33 and the movable portion 21. The energization circuit is connected to a control means (not shown) for controlling driving of the energization circuit based on a detection result of a detection circuit (not shown) described later.

  The energization circuit (not shown) can generate an arbitrary potential difference independently between the drive electrode 33a and the movable part 21 and between the drive electrode 33b and the movable part 21. Yes. As a result, electrostatic attraction is generated independently between the drive electrode 33a and the movable part 21 and between the drive electrode 33b and the movable part 21, and the position of the movable part 21 (position in the vertical direction). ) And posture can be changed.

The drive electrodes 33a and 33b are provided so as to surround the second recess 32. Thereby, the electrostatic attractive force between each drive electrode 33a, 33b and the movable part 21 can be balanced easily. As a result, the posture of the movable portion 21 with respect to the second substrate 3 can be further stabilized.
The constituent material of the drive electrode 33 (each of the drive electrodes 33a and 33b) is not particularly limited as long as it has conductivity. For example, Cr, Al, Al alloy, Ni, Zn, Ti, etc. Examples thereof include: a metal in which carbon or titanium is dispersed, silicon such as polycrystalline silicon (polysilicon) and amorphous silicon, silicon nitride, a transparent conductive material such as ITO, and Au.

The thickness (average) of the drive electrode 33 is appropriately selected depending on the constituent material, application, and the like and is not particularly limited, but is preferably about 0.1 to 5 μm.
The insulating film 34 has the same shape as that of the drive electrode 33 and has a function of preventing a short circuit due to contact between the movable portion 21 and the drive electrode 33.
A first gap G <b> 1 is formed in the space in the first recess 31 as an electrostatic gap (drive gap) for driving the movable portion 21. That is, the first gap G <b> 1 is formed between the movable portion 21 and the drive electrode 33.

The size of the first gap G1 (that is, the distance between the movable portion 21 and the drive electrode 33) is appropriately selected according to the application and the like, and is not particularly limited, but is about 0.5 to 20 μm. preferable.
The second concave portion 32 has a circular outer shape, is substantially concentric with the first concave portion 31 described above, and has an outer diameter smaller than the outer diameters of the first concave portion 31 and the movable portion 21. On the bottom surface of the second recess 32 (the surface of the second substrate 3 on the movable portion 21 side), a fixed reflection film 35 having a substantially circular shape is provided at the center. A substantially annular detection electrode 40 is provided on the bottom surface (installation surface) of the second recess 32 so as to surround the fixed reflective film 35.

  As described above, the fixed reflection film 35 reflects light incident on the second gap G2 from below the wavelength tunable filter 1 with the movable reflection film 25 a plurality of times as shown in FIG. Is. That is, the fixed reflective film 35 corresponds to the size of the second gap G2 (that is, the distance between the fixed reflective film 35 and the movable reflective film 25) in cooperation with the movable reflective film 25 described above. Wavelength light can be made to interfere. The size of the second gap G2 is larger than the size of the first gap G1 described above.

The size of the second gap G2 is appropriately selected according to the application and is not particularly limited, but is preferably about 1 to 100 μm.
The detection electrode 40 is separated from the drive electrode 33 and is provided on the surface of the second substrate 3 on the movable portion 21 side. The detection electrode has a substantially annular shape as a whole, and includes two detection electrodes 40a and 40b that bisect the detection electrode. Each of the detection electrodes 40a and 40b and the movable portion 21 are connected to a detection circuit (not shown) that detects capacitance between them. Based on the detection signal (detection result) of the detection circuit, the above-described control means (not shown) controls driving of the energization circuit (not shown).

  The detection circuit (not shown) can independently detect the electrostatic capacitance between the detection electrode 40a and the movable portion 21 and the electrostatic capacitance between the detection electrode 40b and the movable portion 21. It has become. Thereby, the control means (not shown) allows the voltage applied between the drive electrode 33a and the movable part 21, the drive electrode 33b, and the movable part 21 so that the movable part 21 has a desired position and posture. Can be independently controlled. That is, an electrostatic attractive force is generated independently between the drive electrode 33a and the movable part 21 and between the drive electrode 33b and the movable part 21, and the movable part 21 is moved to a desired position (in the vertical direction). Position) and posture.

  The detection electrode 40a corresponds to the drive electrode 33a, and the detection electrode 40b is provided corresponding to the drive electrode 33b. That is, the number of drive electrodes is the same as the number of detection electrodes, and each drive electrode 33a, 33b and each detection electrode 40a, 40b are paired. Thereby, the position and posture of the movable portion 21 can be accurately changed while suppressing the number of drive electrodes and detection electrodes. Therefore, the cost of the wavelength tunable filter 1 can be reduced, and the manufacturing process of the wavelength tunable filter 1 can be simplified.

  In addition, the number of each of a drive electrode and a detection electrode should just be plural, and may be three or more. Further, the number of drive electrodes and the number of detection electrodes may be different. In general, as the number of drive electrodes and detection electrodes increases, the resolution increases and the detection accuracy improves. However, if the number of drive electrodes and detection electrodes is too large, it becomes difficult to form extraction electrodes and the control sequence is complicated. It becomes.

  The detection electrodes 40a and 40b have a shape similar to that of the drive electrodes 33a and 33b. In other words, the drive electrodes 33a and 33b are similar in shape to the detection electrodes 40a and 40b. Thereby, the correspondence between the drive electrodes 33a and 33b and the detection electrodes 40a and 40b can be simplified, and the control of the position and orientation of the movable portion 21 can be further simplified.

Each of the detection electrodes 40 a and 40 b is provided so as to surround the fixed reflective film 35. Thereby, the attitude | position of the movable part 21 with respect to the 2nd board | substrate 3 is easily and correctly detectable.
As described above, the second substrate 3 has two installation surfaces (the bottom surface of the first recess 31 and the bottom surface of the second recess 32) on the movable unit 21 side, which are different in the thickness direction. ing. The drive electrode 33 is provided on one of the two installation surfaces (the bottom surface of the first recess 31), and the detection electrode 40 is provided on the other installation surface (the bottom surface of the second recess 32). Is provided. Thereby, the drive electrode 33 and the detection electrode 40 are shifted up and down.

  When the drive electrode 33 and the detection electrode 40 are arranged in this manner, the drive electrode 33 and the detection electrode 40 are not close to each other in a plan view because the drive electrode 33 and the detection electrode 40 are not located on the same plane. However, the distance between the drive electrode 33 and the detection electrode 40 can be increased. As a result, the coupling capacitance generated between the drive electrode 33 and the detection electrode 40 can be reduced, and the electrostatic capacitance between the movable portion 21 and the detection electrode 40 can be detected with high accuracy. In addition, since the drive electrode 33 and the detection electrode 40 can be brought close to each other in plan view, an increase in drive voltage due to a decrease in the area of the drive electrode 33 can be prevented.

  In particular, in the present embodiment, the drive electrode 33 is provided on the installation surface (the bottom surface of the first recess 31) on the side close to the movable unit 21 among the two installation surfaces of the second substrate 3. Since the detection electrode 40 is provided on the installation surface far from 21 (the bottom surface of the second recess 32), the electrostatic force generated between the drive electrode 33 and the movable portion 21 can be increased. Therefore, the drive voltage can be reduced.

In addition, since the detection electrode 40 is provided on the bottom surface of the concave portions (the first concave portion 31 and the second concave portion 32) formed in the second substrate 3, the detection electrode 40 can be formed with a relatively simple configuration. The drive electrode 33 can be separated in the thickness direction of the second substrate 3.
Further, since the drive electrode 33 is provided on the bottom surface of the first recess 31 outside the second recess 32 and the detection electrode 40 is provided on the bottom surface of the second recess 32, it is relatively easy. With this configuration, the detection electrode 40 and the drive electrode 33 can be separated from each other, and a gap for generating an electrostatic force can be formed between the drive electrode 33 and the movable portion 21.

In addition to the detection electrode 40, the fixed reflective film 35 is also provided on the bottom surface of the second recess 32, so that the second electrode 32 regardless of the distance between the drive electrode 33 and the movable portion 21. The usable wavelength band can be set according to the depth of the recess 32. Therefore, even if the wavelength tunable filter 1 having various usable wavelength bands is manufactured, the drive voltage can be reduced.
In addition, since the detection electrode 40 is closer to the fixed reflection film 35 than the drive electrode 33, the static generated between the movable portion 21 and the detection electrode 40 with respect to the amount of change in the distance between the movable reflection film 25 and the fixed reflection film 35. The amount of change in capacitance is relatively large. As a result, the displacement of the movable portion 21 can be controlled more accurately. In addition, the drive voltage can be reduced by making the area of the drive electrode 33 larger than the area of the detection electrode 40 relatively easily.

The distance D between the detection electrode 40 and the drive electrode 33 in the thickness direction of the second substrate 3 is preferably 1 to 1000 μm, and more preferably 5 to 500 μm. As a result, the optical characteristics of the wavelength tunable filter 1 can be made relatively easy while reducing the coupling capacitance generated between the detection electrode 40 and the drive electrode 33 more reliably.
On the other hand, when the distance is less than the lower limit, depending on the constituent material of the second substrate 3 and the like, the reduction of the coupling capacitance generated between the detection electrode 40 and the drive electrode 33 can be sufficiently reduced. There are cases where it is not possible. On the other hand, when the distance exceeds the upper limit value, the capacitance generated between the detection electrode 40 and the movable portion 21 becomes small, so that the detection becomes difficult.

  The constituent material of the detection electrode 40 can be the same as the constituent material of the drive electrode 33 described above, and is not particularly limited as long as it has conductivity. For example, Cr, Al, Examples include Al alloys, metals such as Ni, Zn, and Ti, resins in which carbon and titanium are dispersed, silicon such as polycrystalline silicon (polysilicon) and amorphous silicon, silicon nitride, transparent conductive materials such as ITO, and Au. It is done.

  If the optical characteristics of the wavelength tunable filter 1 are not impaired, the detection electrode can be provided over almost the entire bottom surface of the second recess 32, and the fixed reflective film 35 can be provided thereon. Thereby, the area of a detection electrode can be enlarged and the detection accuracy of the electrostatic capacitance between the movable part 21 and a detection electrode can be improved. Further, by configuring the constituent material of the fixed reflection film with a conductive material, the fixed reflection film can be provided almost over the entire bottom surface of the second recess 32, and the movable reflection film can also serve as the detection electrode. This also increases the area of the detection electrode and improves the detection accuracy of the capacitance between the movable portion 21 and the detection electrode.

Further, the third recesses 37a and 37b, the third recesses 37a and 37b, and the first recess 31 are communicated with the second substrate 3 in order to draw out the drive electrodes 33a and 33b described above. Grooves 36a and 36b are formed.
The depth of the groove 36a and the third recess 37a is substantially the same as the depth of the first recess 31, and an extraction electrode 38a connected to the drive electrode 33a is provided on the bottom surface thereof. Yes. Similarly, the depth of the groove 36b and the third recess 37b is substantially equal to the depth of the first recess 31, and on these bottom surfaces, the extraction electrode connected to the drive electrode 33b is provided. 38b is provided.

  The constituent material of the extraction electrode 38 (extraction electrodes 38a and 38b) can be the same as the constituent material of the drive electrode 33 described above, and is not particularly limited as long as it has conductivity. For example, metal such as Cr, Al, Al alloy, Ni, Zn, Ti, resin dispersed with carbon, titanium, etc., silicon such as polycrystalline silicon (polysilicon), amorphous silicon, silicon nitride, transparent like ITO A conductive material, Au, etc. are mentioned.

Further, the thickness (average) of the extraction electrode 38 is appropriately selected depending on the constituent material, application, etc., and is not particularly limited, but is preferably about 0.1 to 5 μm. The extraction electrode 38a is preferably formed integrally with the drive electrode 33a described above, and the extraction electrode 38b is formed integrally with the drive electrode 33b described above.
A fixed antireflection film 39 is formed on the other surface of the second substrate 3 (that is, the surface opposite to the surface on which the first concave portion 31 and the like described above are formed).
As shown in FIG. 3, the fixed antireflection film 39 reflects light irradiated toward the second gap G <b> 2 from below the wavelength tunable filter 1 downward in the drawing at the interface between the lower surface of the second substrate 3 and the outside air. It is for preventing it from being done. The configuration of the movable reflection film 25 and the movable antireflection film 26 is the same as the configuration of the fixed reflection film 35 and the fixed antireflection film 39 described above.

The operation (action) of the wavelength tunable filter 1 having such a configuration will be described.
When a voltage is applied between the movable portion 21 and the drive electrode 33 by an energization circuit (not shown), the movable portion 21 and the drive electrode 33 are charged with opposite polarities, and a Coulomb force (electrostatic attractive force) is generated between the two. ) Occurs. At this time, a detection circuit (not shown) detects the electrostatic capacitance between the detection electrode 40 and the movable portion 21, and a control means (not shown) controls driving of the energization circuit based on the detection signal (detection result).

Due to this Coulomb force, the movable portion 21 moves (displaces) downward toward the drive electrode 33 and stops at a position where the elastic force of the connecting portion 24 and the Coulomb force balance. Thereby, the magnitude | size of the 1st gap G1 and the 2nd gap G2 changes.
On the other hand, as shown in FIG. 3, when the light L is irradiated from below the wavelength tunable filter 1 toward the second gap G2, the light L is emitted from the fixed antireflection film 39, the second substrate 3, and the fixed reflection film. 35, and enters the second gap G2. At this time, the light L is incident on the second gap G2 by the fixed antireflection film 39 with almost no loss.

The incident light is repeatedly reflected (interfered) between the movable reflective film 25 and the fixed reflective film 35. At this time, the loss of the light L can be suppressed by the movable reflective film 25 and the fixed reflective film 35.
As described above, in the process in which light is repeatedly reflected between the movable reflective film 25 and the fixed reflective film 35, the interference corresponding to the size of the second gap G2 between the movable reflective film 25 and the fixed reflective film 35. Light having a wavelength that does not satisfy the condition is rapidly attenuated, and only light having a wavelength that satisfies the interference condition remains and is finally emitted from the wavelength tunable filter 1. Therefore, if the voltage applied between the movable portion 21 and the drive electrode 33 is changed, and the second gap G2 is changed (that is, the interference condition is changed), the wavelength of light transmitted through the variable wavelength filter 1 Can be changed.

As a result of the interference of the light L, light having a wavelength corresponding to the size of the second gap G1 (interference light) is transmitted through the movable reflective film 25, the movable portion 21, and the movable antireflection film 26, and the wavelength tunable filter 1 Is emitted upward. At this time, since the movable antireflection film 26 is formed on the upper surface of the movable portion 21, the interference light is emitted to the outside of the wavelength tunable filter 1 with almost no loss.
In the present embodiment, the light incident on the second gap G2 is emitted above the wavelength tunable filter 1, but the light incident on the second gap G2 may be emitted below the wavelength tunable filter 1. .

In the present embodiment, light is incident on the wavelength tunable filter 1 from below, but light may be incident from above.
In the wavelength tunable filter 1 as described above, the second substrate 3 has two installation surfaces whose positions in the thickness direction are different on the movable portion 21 side, and among the two installation surfaces, The drive electrode 33 is provided on one installation surface, and the detection electrode 40 is provided on the other installation surface. In other words, the drive electrode 33 and the detection electrode 40 are arranged so as to be shifted vertically.

  Thereby, since the drive electrode 33 and the detection electrode 40 are not located on the same plane, even if the drive electrode 33 and the detection electrode 40 are close to each other in plan view, the distance between the drive electrode 33 and the detection electrode 40 Can be increased. As a result, the coupling capacitance generated between the drive electrode 33 and the detection electrode 40 is reduced, and the electrostatic capacitance between the movable portion 21 and the detection electrode 40 is detected with high accuracy. Based on the detection result, The movable part 21 can be accurately displaced to a desired position and posture. In particular, since the plurality of drive electrodes 33a and 33b and the plurality of detection electrodes 40a and 40b are provided, the distance between the movable reflective film 25 and the fixed reflective film 35, and the movable reflective film 25 are provided. Therefore, the optical characteristics of the wavelength tunable filter 1 can be improved by controlling the parallelism between the tunable filter 1 and the fixed reflective film 35 with high accuracy. At this time, since the drive electrode 33 and the detection electrode 40 can be brought close to each other in plan view, an increase in drive voltage due to a decrease in the area of the drive electrode 33 can be prevented.

<Method for manufacturing wavelength tunable filter>
Next, an example of a method for manufacturing the wavelength tunable filter 1 will be described with reference to FIGS.
5-8 is a figure for demonstrating the manufacturing process of the wavelength tunable filter 1. FIG. 5-8 has shown the cross section corresponding to the AA line cross section of FIG.
The method of manufacturing the wavelength tunable filter 1 according to the present embodiment includes: [A] a step of manufacturing the second substrate 3, [B] a step of bonding the SOI substrate to the second substrate 3, and [C] an SOI substrate. And processing to manufacture the first substrate 2. Hereinafter, each process will be described sequentially.

[A] Production of second substrate 3 -A1-
First, as a substrate for forming the second substrate 3, as shown in FIG. 5A, a substrate 4 having optical transparency is prepared.
As the substrate 4, a substrate having a uniform thickness and having no deflection or scratch is preferably used. As the constituent material of the substrate 4, those described in the description of the second substrate 3 can be used. As described above, the constituent material of the substrate 4 is preferably glass containing an alkali metal (mobile ion) such as sodium (Na) or potassium (K). Therefore, in the following description, the case where glass containing an alkali metal is used as the constituent material of the substrate 4 will be described.

-A2-
Next, as shown in FIG. 5B, a mask layer 5 is formed (masked) on one surface of the substrate 4.
Examples of the material constituting the mask layer 5 include metals such as Au / Cr, Au / Ti, Pt / Cr, and Pt / Ti, silicon such as polycrystalline silicon (polysilicon) and amorphous silicon, and silicon nitride. It is done. When silicon is used as the constituent material of the mask layer 5, the adhesion between the mask layer 5 and the substrate 4 is improved. When a metal is used for the constituent material of the mask layer 5, the visibility of the mask layer 5 to be formed is improved.

The thickness of the mask layer 5 is not particularly limited, but is preferably about 0.01 to 1 μm, and more preferably about 0.09 to 0.11 μm. If the mask layer 5 is too thin, the substrate 4 may not be sufficiently protected. If the mask layer 5 is too thick, the mask layer 5 may be easily peeled off due to internal stress of the mask layer 5.
The mask layer 5 can be formed by, for example, a chemical vapor deposition method (CVD method), a vapor deposition method such as a sputtering method or an evaporation method, a plating method, or the like.

-A3-
Next, as shown in FIG. 5C, an opening 51 having a planar view shape corresponding to the planar view shapes of the first concave portion 31, the groove portion 36, and the third concave portion 37 is formed in the mask layer 5. .
More specifically, first, for example, using a photolithography method, a photoresist is applied on the mask layer 5, and exposure and development are performed to form a resist mask having an opening corresponding to the opening 51. Next, the mask layer 5 is etched through the resist mask to remove a part of the mask layer 5, and then the resist mask is removed. In this way, an opening 51 is formed in the mask layer 5. As this etching, for example, dry etching with CF gas, chlorine-based gas, etc., wet etching with hydrofluoric acid + nitric acid aqueous solution, alkaline aqueous solution or the like can be used.

-A4-
Next, one surface of the substrate 4 is etched through the mask layer 5 to form a first recess 31, a groove 36, and a third recess 37, as shown in FIG.
As this etching, a dry etching method or a wet etching method can be used, but a wet etching method is preferably used. Thereby, the 1st recessed part 31 formed can be made into a more ideal column shape. In this case, for example, a hydrofluoric acid-based etchant is preferably used as the etchant for wet etching. Moreover, when alcohol (especially polyhydric alcohol), such as glycerol, is added to etching liquid, the bottom face of the 1st recessed part 31 formed can be made very smooth.

-A5-
Next, after removing the mask layer 5, the plan view shape corresponding to the plan view shape of the second concave portion 32 is used as shown in FIG. The mask layer 6 having the openings is formed.
The method for removing the mask layer 5 is not particularly limited. For example, wet etching using an alkaline aqueous solution (for example, tetramethylammonium hydroxide aqueous solution), hydrochloric acid + nitric acid aqueous solution, hydrofluoric acid + nitric acid aqueous solution, CF gas, or chlorine-based gas. For example, dry etching or the like can be used.
In particular, when wet etching is used as a method for removing the mask layer 5, the mask layer 5 can be efficiently removed by a simple operation.

-A6-
Next, the substrate 4 is etched through the mask layer 6 using the same method as in the step A4 described above to form the second recess 32 as shown in FIG. A mask layer 6A having an opening in a plan view shape corresponding to the plan view shape of the film 35 is formed. The formation of the mask layer 6A may be performed after removing the mask layer 6 or may be performed without removing the mask layer 6.

-A7-
Next, as shown in FIG. 6A, the fixed reflective film 35 is formed on the bottom surface of the second recess 32 using the mask layer 6 </ b> A.
More specifically, the fixed reflective film 35 is formed on the bottom surface of the second recess 32 by alternately laminating the high refractive index layer and the low refractive layer as described above.
As a method for forming the high refractive index layer and the low refractive index layer, for example, chemical vapor deposition (CVD) or physical chemical vapor deposition (PVD) is preferably used.

-A8-
Next, the mask layer 6A is removed as shown in FIG. 6B by using the same method as in the step-A5- described above.
-A9-
Next, as shown in FIG. 6C, in order to uniformly form the drive electrodes 33a and 33b and the extraction electrodes 38a and 38b on the surface of the substrate 4 on the side where the first recesses 31 and the like are formed. The conductive layer 7 is formed.
As a method for forming the conductive layer 7, for example, chemical vapor deposition (CVD) or physical chemical vapor deposition (PVD) is preferably used.
Further, as the constituent material of the conductive layer 7, the constituent material of the drive electrode 33 described above can be used.

-A10-
Next, as shown in FIG. 6D, unnecessary portions of the conductive layer 7 are removed to form the drive electrode 33 and the detection electrode 40, and the insulating film 34 is formed on the drive electrode 33. Further, a fixed antireflection film 39 is formed on the surface of the substrate 4 opposite to the side on which the first concave portion 31 and the like are formed.

As a method for removing unnecessary portions of the conductive layer 7, a method similar to the above-described step A3 can be used.
In addition, as a method for forming the drive electrode 33, the same method as the method for forming the mask layer 5 described above can be used.
As a method of forming the fixed antireflection film 39, the same method as the method of forming the fixed reflection film 35 described above can be used.
As described above, the second substrate 3 can be manufactured.

[B] Joining of SOI substrate and second substrate 3 -B1-
First, as shown in FIG. 7A, an SOI (Silicon on Insulator) substrate 8 is prepared.
This SOI substrate 8 is formed by laminating these three layers in the order of a base layer 81 made of Si, an insulating layer 82 made of SiO ₂ , and an active layer 83 made of Si. Instead of the SOI substrate 8, an SOS (Silicon on Sapphire) substrate, a silicon substrate, or the like can be used.
The thickness of the SOI substrate 8 is not particularly limited, but the thickness of the active layer 83 is particularly preferably about 10 to 100 μm.

-B2-
Next, prior to the bonding of the SOI substrate 8 and the second substrate 3, as shown in FIG. 7B, the movable reflective film 25 is formed on the surface of the SOI substrate 8 on the active layer 83 side.
As a method of forming the movable reflective film 25, the same method as the method of forming the fixed reflective film 35 described above can be used.

-B3-
Next, as shown in FIG. 7C, the SOI substrate 8 and the second substrate 3 are bonded.
As a bonding method between the SOI substrate 8 and the second substrate 3, for example, anodic bonding, bonding with an adhesive, surface activation bonding, bonding using low melting point glass, or the like can be used, and anodic bonding is used. Is preferred.

  When anodic bonding is used as a bonding method between the SOI substrate 8 and the second substrate 3, for example, first, a negative terminal of a DC power supply (not shown) is used as the second substrate 3, and a positive terminal is used as an active layer of the SOI substrate 8. 83. Then, a voltage is applied between the second substrate 3 and the active layer 83 of the SOI substrate 8 while heating the second substrate 3. This heating facilitates the movement of alkali metal positive ions of the second substrate 3, such as sodium ions (Na +). As a result, of the bonding surfaces between the second substrate 3 and the active layer 83, the bonding surface on the second substrate 3 side is negatively charged, and the bonding surface on the active layer 83 side is relatively charged positively. As a result, the second substrate 3 and the active layer 83 are firmly bonded by a covalent bond in which silicon (Si) and oxygen (O) share an electron pair.

[C] Production of first substrate 2 -C1-
Next, as shown in FIG. 8A, the base layer 81 is removed by etching or polishing.
As this etching method, for example, wet etching or dry etching can be used, but dry etching is preferably used. In any case, when the base layer 81 is removed, the insulating layer 82 serves as a stopper, but since dry etching does not use an etching solution, damage to the active layer 83 facing the drive electrode 33 is suitably prevented. be able to. Thereby, the yield at the time of manufacturing the wavelength tunable filter 1 can be improved.

-C2-
Next, as shown in FIG. 8B, the insulating layer 82 is removed by etching.
As this etching method, for example, wet etching or dry etching can be used, but wet etching with an etchant containing hydrofluoric acid is preferably used. Thereby, the insulating layer 82 can be easily removed, and the surface of the active layer 83 exposed by the removal of the insulating layer 82 can be made extremely smooth.
In the above-described step B1, when a silicon substrate having an optimum thickness for performing the subsequent steps is used instead of the SOI substrate 8, the steps C1 and C1 are not performed. Also good. Thereby, the manufacturing process of the wavelength tunable filter 1 can be simplified.

-C3-
Next, as shown in FIG. 8C, the movable antireflection film 26 is formed on the upper surface of the active layer 83.
As a method of forming the movable antireflection film 26, the same method as the method of forming the fixed reflection film 35 described above can be used.

-C4-
Next, as shown in FIG. 8D, a resist layer 9 having openings corresponding to the openings 24 and 27 is formed.
As a method for forming the resist layer 9, the same method as in the steps A2 and A3 described above can be used.

-C5-
Next, the active layer 83 is etched through the resist layer 9 by dry etching, particularly ICP etching to form the opening 27 as shown in FIG. As shown, the opening 24 is formed. Thereby, the movable part 21, the support part 22, and the connection part 23 are formed.

  More specifically, when the active layer 83 is dry-etched via the resist layer 9, the etching rate in each opening region of the opening 24 is slower than the etching rate in the opening 27 due to the microloading effect. As shown in FIG. 8E, the formation of the opening 27 is completed before the opening 24 is formed. At this time, since the opening 27 is formed above the third recess 37 communicating with the first recess 31 via the groove 36, the space between the active layer 83 and the second substrate 3 is exposed to the outside. The pressure difference between the space and the outside is released.

  Here, the microloading effect is a phenomenon in which the etching rate decreases as the opening size decreases. Therefore, the opening 27 has a dimension that allows the etching rate to be higher than the etching rate in each opening region of the opening 24. In the present embodiment, as shown in FIG. 1, the shape of the opening 27 is a square shape having a width that is wider than the opening width in the short direction of each opening region of the opening 24. The size and shape of the opening 27 are not limited to those described above as long as the etching rate at the opening 27 is higher than the etching rate at each opening region of the opening 24. A configuration can be employed.

When the microloading effect is used in this way, the opening 24 and the opening 27 can be formed while the opening 24 and the opening 27 are formed by the same etching process without separately providing an etching process for forming the opening 27. These can be formed in the order of 24, and the manufacturing process can be simplified.
When the dry etching is continued after the opening 27 is formed, the opening 24 is formed through as shown in FIG. 8F, and the formation of the movable portion 21, the support portion 22, and the connecting portion 23 is completed. To do.

At this time, as described above, before forming the movable portion 21 in the active layer 83 (that is, before forming the opening 24), the space between the active layer 83 and the second substrate 3 and the external Therefore, it is possible to prevent the connecting portion 23 from being damaged along with the formation of the opening 24.
In particular, in this step, ICP etching is performed. That is, the movable portion 21 is formed by alternately and repeatedly performing etching with an etching gas and formation of a protective film with a deposition gas.

Examples of the etching gas include SF ₆ , and examples of the deposition gas include C ₄ F ₈ .
In this step, the anisotropic etching is performed using the dry etching technique for the following reason.
When the wet etching technique is used, an etching solution enters between the active layer 83 and the second substrate 3 from the hole formed in the active layer 83 as the etching progresses, and the drive electrode 33 and the insulating film 34 are removed. There is a risk of it. On the other hand, when dry etching technology is used, there is no such danger.

In addition, when isotropic etching is used, the active layer 83 is isotropically etched and side etching occurs. In particular, when side etching occurs with respect to the connecting portion 23, the strength of the connecting portion 23 becomes weak, and the durability deteriorates. On the other hand, when anisotropic etching is used, side etching does not occur. Therefore, the etching dimension is excellent, and the side surface of the connecting portion 23 is also formed perpendicular to the plate surface of the active layer 83. The strength of the connecting portion 23 can be improved.
In the present invention, in this step, the movable portion 21, the support portion 22, and the connecting portion 23 may be formed using a dry etching method different from the above, and the movable portion 21 may be moved using a method other than the dry etching method. You may form the part 21, the support part 22, and the connection part 23. FIG.

-C6-
Thereafter, the resist layer 9 is removed, and the wavelength tunable filter 1 is obtained as shown in FIG.
The wavelength tunable filter of the present invention has been described based on the illustrated embodiment. However, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. can do. In addition, any other component may be added to the present invention.

For example, in the above-described embodiment, the drive electrode 33 is closer to the movable part 21 than the detection electrode 40. However, the detection electrode may be configured to be closer to the movable part 21 than the drive electrode. .
In the above-described embodiment, the bottom surface of the recess formed in the substrate (second substrate 3) is the installation surface of the detection electrode and the drive electrode. However, the installation surface of the detection electrode and / or the drive electrode is As long as the position in the thickness direction is different, it is not limited to this, and may be the upper surface of a convex portion formed on the substrate.
In the above-described embodiment, the first gap G <b> 1 is formed by the first recess 31, but the first recess 31 is not formed and a spacer is provided between the second substrate 3 and the first substrate 2. By providing the first gap G1 may be formed.

  DESCRIPTION OF SYMBOLS 1 ... Wavelength variable filter 2 ... 1st board | substrate 21 ... Movable part 22 ... Supporting part 23 ... Connection part 24 ... Opening part 25 ... Movable reflective film 26 ... Movable antireflection film 27, 27a, 27b ....... Opening 3 ... 2nd substrate 31 ... 1st recessed part 32 ... 2nd recessed part 33, 33a, 33b ... Drive electrode 34 ... Insulating film 35 ... Fixed reflection film 36, 36a, 36b …… Groove portion 37, 37a, 37b …… Third recess 38, 38a, 38b …… Extraction electrode 39 …… Fixed antireflection film 40, 40a, 40b …… Detection electrode 4 …… Substrate (second substrate) 5, 6, 6A ... Mask layer 51 ... Opening 7 ... Conductive layer 8 ... SOI substrate 81 ... Base layer 82 ... Insulating layer 83 ... Active layer (first substrate) 9 ... Resist layer G1 …… First gap G2 …… Second Gap L ...... light.

If the optical characteristics of the wavelength tunable filter 1 are not impaired, the detection electrode can be provided over almost the entire bottom surface of the second recess 32, and the fixed reflective film 35 can be provided thereon. Thereby, the area of a detection electrode can be enlarged and the detection accuracy of the electrostatic capacitance between the movable part 21 and a detection electrode can be improved. In addition, by configuring the constituent material of the fixed reflection film with a conductive material, the fixed reflection film can be provided over almost the entire bottom surface of the second recess 32, and the fixed reflection film can also serve as the detection electrode. This also increases the area of the detection electrode and improves the detection accuracy of the capacitance between the movable portion 21 and the detection electrode.

Claims (19)

A substrate,
A plate-shaped, opposed to the substrate with a gap, and a movable part provided to be displaceable in the thickness direction;
A movable reflective film provided on the substrate-side surface of the movable part;
A plurality of drive electrodes provided on a surface of the substrate on the movable part side;
A plurality of detection electrodes provided on the surface of the movable part side of the substrate while being separated from the drive electrode;
A fixed reflection film provided on the surface of the movable part side of the substrate,
The substrate has two installation surfaces at different positions in the thickness direction on the movable part side,
Of the two installation surfaces, the drive electrode is provided on one installation surface, and the detection electrode is provided on the other installation surface,
Based on the electrostatic capacitance between each detection electrode and the movable part, by generating a potential difference between each drive electrode and the movable part, an electrostatic attractive force is generated between them, and the movable part While changing the position and posture of
Light can be repeatedly reflected between the fixed reflective film and the movable reflective film to cause interference, and light having a wavelength corresponding to the distance between the fixed reflective film and the movable reflective film can be emitted to the outside. A wavelength tunable filter configured as described above.   The wavelength tunable filter according to claim 1, wherein the number of drive electrodes is the same as the number of detection electrodes, and each drive electrode and each detection electrode are paired.   The wavelength tunable filter according to claim 2, wherein the drive electrode has a shape similar to the shape of the detection electrode.   The drive electrode is provided on an installation surface on the side closer to the movable part of the two installation surfaces of the substrate, and the detection electrode is provided on an installation surface on the side far from the movable part. The wavelength tunable filter according to any one of 1 to 3.   The wavelength tunable filter according to claim 4, wherein the substrate has a recess, and the detection electrode is provided on a bottom surface of the recess.   The concave portion includes a first concave portion and a second concave portion formed on a bottom surface of the first concave portion, and the driving electrode is provided on a bottom surface of the first concave portion outside the second concave portion. The wavelength tunable filter according to claim 4, wherein the tunable filter is provided on the bottom surface of the second recess.   The wavelength tunable filter according to claim 6, wherein in addition to the detection electrode, the fixed reflective film is also provided on the bottom surface of the second recess.   The wavelength tunable filter according to claim 7, wherein each detection electrode is provided so as to surround the fixed reflective film.   The wavelength tunable filter according to claim 6, wherein each drive electrode is provided so as to surround the second recess.   The wavelength tunable filter according to claim 1, wherein at least one of the fixed reflection film and the movable reflection film is formed of a dielectric multilayer film.   A support portion fixed to the substrate; and a connecting portion that connects the movable portion to the support portion so that the movable portion can be displaced in a thickness direction thereof. The wavelength tunable filter according to claim 1, wherein the support portion and the connecting portion are integrally formed.   The wavelength tunable filter according to claim 11, wherein each of the movable portion, the support portion, and the connecting portion is made of silicon as a main material.   The wavelength tunable filter according to claim 12, wherein the substrate is made of glass as a main material.   The wavelength tunable filter according to claim 13, wherein the substrate is composed mainly of glass containing alkali metal ions.   15. The wavelength tunable filter according to claim 12, wherein the movable part, the support part, and the connection part are formed by processing one Si layer of an SOI wafer.   The wavelength tunable filter according to claim 1, wherein an insulating film is provided on a surface of the movable portion on the substrate side.   The wavelength tunable filter according to claim 16, wherein the movable reflective film has an insulating property and also serves as the insulating film.   The tunable filter according to claim 1, wherein the detection electrode is closer to the fixed reflective film than the drive electrode.   19. The wavelength tunable filter according to claim 1, wherein a distance between the detection electrode and the drive electrode in the thickness direction of the substrate is 5 to 500 μm.

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