JP5256843B2 - Optical element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical element utilizing an electrowetting effect (electrocapillary phenomenon) and a manufacturing method thereof.

  In recent years, development of optical elements using the electrowetting effect has been advanced. The electrowetting effect is that when a voltage is applied between a conductive liquid and an electrode via an insulator, the insulator is charged, and the free energy at the interface between the insulator and the liquid is reduced. This is a phenomenon in which the shape (contact angle) changes.

  By utilizing this phenomenon, an optical element capable of changing optical characteristics by voltage has been proposed. For example, Patent Document 1 below describes an optical element that can use this effect and change the focal length by an applied voltage.

  The optical element described in Patent Document 1 includes an electrode layer in which a through hole is formed, a first transparent substrate that is bonded to one surface of the electrode layer and closes one end of the through hole, and the other surface of the electrode layer. A cell for containing a liquid is formed by a second transparent substrate disposed opposite to each other via a sealing layer. Further, the inner wall surface of the through hole and the surface facing the second transparent substrate of the electrode layer are covered with a water-repellent insulating layer. And in this cell, the electroconductive 1st liquid and the insulating 2nd liquid which has a different refractive index and is not mixed with the 1st liquid are 2 in the above-mentioned through-hole. It is filled so that the liquid interface is located.

  According to this configuration, when a voltage is applied between the electrode layer and the first liquid, the electrode layer and the first liquid are opposed to each other via the insulating layer, so that charges are accumulated, that is, a capacitor is configured. . Due to the accumulated electric charge, the first liquid is attracted to the electrode layer and spreads on the insulating layer, and the contact angle of the first liquid with respect to the inner wall surface of the through hole changes (electrowetting effect). As a result, the shape of the interface (that is, the lens) between the first liquid and the second liquid changes, and the focal length of the light transmitted through the cell can be arbitrarily adjusted.

Japanese Patent Laying-Open No. 2007-212943 ([0087], FIG. 9)

  In the optical element described in Patent Document 1, in order to insulate the electrode layer from the first liquid, the insulating layer is also formed on the surface other than the through hole, that is, on the surface of the electrode layer facing the second transparent substrate. Need to be done. As a result, the capacitor is located in a region other than the region (inner wall surface of the through hole) that contributes to the shape change of the original liquid interface, specifically, the region in which the electrode layer faces the first liquid through the insulating layer. Composed. Due to the parasitic capacitance generated by the unintended capacitor, when changing the focal length by applying an AC voltage to the optical element, there arises a problem that power consumption increases and response speed also decreases.

  In view of the circumstances as described above, an object of the present invention is to provide an optical element with low power consumption and high response speed by suppressing parasitic capacitance, and a method for manufacturing the same.

  In order to solve the above-described problems, an optical element according to a main aspect of the present invention has a first surface and a second surface facing the first surface, from the first surface side to the second surface side. An insulating substrate in which a through-hole whose opening size gradually increases is formed, a first transparent substrate bonded to the first surface side of the insulating substrate, and the first substrate of the insulating substrate. A second transparent substrate that is bonded to the second surface side and forms a liquid storage portion together with the first transparent substrate and the through hole, and a conductive material that is stored on the first surface side of the liquid storage portion. A first liquid, an insulating second liquid that is accommodated on the second surface side of the liquid container and has a refractive index different from that of the first liquid and that does not mix, and the penetration A conductive layer continuously formed on a peripheral surface of the hole and the second surface; and an insulating layer covering the conductive layer.

  According to this configuration, the insulating substrate forming the liquid container is insulative, and there is no conductive layer on the first surface side. Therefore, there is no region where the electrode faces the conductive first liquid through the insulating layer on the first surface side of the insulating substrate, that is, a region constituting an unintended capacitor, and no parasitic capacitance is generated. As a result, an optical element with low power consumption and a fast response speed can be obtained.

  In the optical element according to the present invention, the through hole may have an opening shape whose length in one direction is longer than the length in the other direction.

  According to this configuration, incident light can be refracted more largely in the short direction than in the longitudinal direction of the opening of the through hole. In addition, when the opening in the one direction is sufficiently longer than the length in the other direction, an optical element that functions as a cylindrical lens can be obtained.

  In the optical element according to the present invention, a plurality of the through holes may be arranged in one direction within the surface of the insulating substrate.

  The area of the first surface of the insulating substrate that separates the liquid storage portions is a shape in which the size of the opening gradually increases from the first surface side toward the second surface side (hereinafter referred to as the present specification). In the case where a plurality of through-holes that are “reverse tapered shape” are provided, the size is larger than when the through-holes are provided alone, and between the first surface and the first transparent substrate. When parasitic capacitance occurs, the effect is even greater. However, according to this configuration, since no parasitic capacitance is generated on the first surface, an optical element that is not affected by the parasitic capacitance even when a plurality of through holes are formed can be obtained.

  In the optical element according to the present invention, the insulating substrate may have a liquid passage that allows the second liquid to communicate with each other between the plurality of adjacent through holes.

  According to this configuration, the second liquid stored in the liquid storage portion formed by the plurality of arranged through holes can be communicated between the liquid storage portions, and the second liquid stored in each liquid storage portion. The volume ratio between the first liquid and the second liquid can be maintained at a desired value.

  In the optical element according to the present invention, a boundary portion between the peripheral surface of the through hole and the second surface may be a curved surface.

  In the structure of the optical element, the insulating substrate on which the through hole serving as the peripheral surface of the liquid container is formed is formed of an insulator. Therefore, it is necessary to form a conductive layer on the surface of the through hole, and the conductive layer is also formed on the second surface of the insulating substrate in order to obtain conduction with an external voltage applying means. In this case, the conductive layer needs to be continuously formed on the peripheral surface and the second surface of the through hole.

  According to this configuration, since the boundary portion is a curved surface, the conductive layer continuous between the peripheral surface of the through hole and the second surface is stabilized as compared with the case where the boundary portion is sharp. Can be formed. As a result, it is possible to obtain a stable conductive layer in which the occurrence of breakage, disconnection, or the like of the conductive layer is suppressed.

  In the optical element according to the present invention, the conductive layer may be a transparent conductive film.

  According to this configuration, since the light passing through the optical element is not blocked by the conductive layer, an optical element having a high transmittance of incident light can be obtained.

  In the method of manufacturing an optical element according to the present invention, an opening is formed in an insulating substrate having a first surface and a second surface facing the first surface from the first surface side toward the second surface side. Forming a through-hole having a gradually increasing length, forming a continuous conductive layer on the second surface and the peripheral surface of the through-hole, and attaching a second transparent substrate to the second surface, A recess is formed by a hole and the second transparent substrate, an insulating layer is formed to cover the conductive layer, and the recess has a refractive index different from that of the conductive first liquid, the first liquid, An insulating second liquid that does not mix is accommodated, and the first transparent substrate is liquid-tightly attached to the first surface.

According to this manufacturing method, it is possible not to form a region where the conductor is opposed via the insulator, that is, a region constituting an unintended capacitor, on the first surface side of the insulating substrate. Further, by forming the insulating layer after forming the conductive layer, the conductive layer can be covered and the conductive layer and the first liquid can be insulated.
That is, it is possible to manufacture an optical element that does not generate the parasitic capacitance described above, consumes less power, and has a high response speed.

  In the method of manufacturing an optical element according to the present invention, in the step of forming the conductive layer on the insulating substrate, the conductive layer is opposed to a sputtering target (hereinafter, target) containing a constituent material of the conductive layer. The insulating substrate may be disposed in a vacuum chamber, and the conductive layer may be selectively formed on the second surface and the peripheral surface of the through hole by a sputtering method.

  According to this manufacturing method, since the sputtering method has directivity in the film forming direction, it is possible not to form the conductive layer on the first surface. In other words, since the particles knocked out of the target scatter linearly, the film formation region greatly depends on the geometrical arrangement relationship between the film formation target and the target. Therefore, by forming the second surface of the insulating substrate opposite to the target, film formation on the first surface of the insulating substrate can be avoided.

  Thereby, the above-described parasitic capacitance is not generated, and an optical element having a low drive voltage and a high response speed can be manufactured. In addition, since the same effect is acquired also in other physical vapor deposition methods, such as a vacuum evaporation method and an ion plating method, you may apply these methods instead of a sputtering method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
An optical element according to the first embodiment of the present invention will be described.
FIG. 1 is a sectional view of an optical element according to the first embodiment of the present invention, and FIG. 2 is a plan view of the optical element. 1 is a cross-sectional view in the direction of line [A]-[A] in FIG. As shown in these drawings, the optical element 1 includes an insulating substrate 3 having a through hole 2, a first transparent substrate 4, and a second transparent substrate 5. The insulating substrate 3 is sandwiched between the first transparent substrate 4 and the second transparent substrate 5, and the space formed by the through hole 2, the first transparent substrate 4, and the second transparent substrate 5 is electrically conductive first. The liquid storage unit 6 stores the first liquid 12 and the insulating second liquid 13.

  The insulating substrate 3 has a first surface 7 and a second surface 8, and the first transparent substrate 4 is bonded to the first surface 7 through a sealing member 14, and the second surface 8 is connected to the second surface 8. Two transparent substrates 5 are joined. The material of the insulating substrate 3 can be appropriately selected from insulating synthetic resin materials having high light transmittance (for example, acrylic, PET (Polyethylene Terephthalate), polycarbonate, etc.), but other materials having high light transmittance. By using (for example, glass or the like), the loss of intensity of light passing through the optical element 1 can be reduced.

  The through hole 2 formed in the insulating substrate 3 penetrates the first surface 7 and the second surface 8 of the insulating substrate 3 and has a large opening from the first surface 7 side to the second surface 8 side. It is a reverse taper shape whose length gradually increases. That is, the peripheral surface of the through-hole 2 is inclined with respect to the first surface 7 and the second surface 8, and the inclination angle is not particularly limited, but is, for example, about 1 to 20 degrees ( In FIG. 1, the inclination angle is highlighted. In the illustrated example, the peripheral surface of the through hole is a linear inclined surface, but is not limited thereto, and may be a curved inclined surface. In addition, in the present embodiment, the planar shape of the through hole 2 is an oval shape having an opening width in the Y direction larger than that in the X direction, but is not limited thereto, and is a polygon such as a circle, an ellipse, or a rectangle. It may be.

  Although the details will be described later, the inclination angle formed by the peripheral surface of the through hole 2 with the first surface 7 or the second surface 8 affects the interface shape of the two liquids. Further, when the insulating substrate 3 and the second transparent substrate 5 are bonded with an adhesive due to this inclination, the protruding adhesive is prevented from being applied to the optically effective area determined by the minimum diameter of the through hole 2. It is possible.

  Moreover, you may form so that the opening edge by the side of the 2nd surface 8 of the through-hole 2 may become a curved surface (The peripheral surface of the through-hole 2 and the 2nd surface 8 side continue smoothly). As a result, the conductive layer 9 continuous with the through hole and the second surface 8 can be stably formed as will be described later.

  The sealing member 14 is formed of a material capable of sealing a liquid, such as rubber or elastomer resin, and is provided on the first surface 7 of the insulating substrate 3 so as to go around the opening of the through hole 2. The first surface 7 of the insulating substrate 3 is provided with a sealing member guide portion 15 formed of a convex portion of the insulating substrate 3, and the sealing member 14 is positioned by the sealing member guide portion 15. Yes.

  On the peripheral surface of the through hole 2 of the insulating substrate 3, a conductive layer 9 continuous with the second surface 8 side is provided. A portion of the conductive layer 9 formed on the peripheral surface of the through hole 2 and functioning as an electrode is an electrode portion 9a, and is formed on the second surface 8 to connect the electrode portion 9a to an external power source (not shown). A portion that functions as a wiring portion 9b. The conductive layer 9 is made of a conductive thin film, and can be formed by sputtering or the like from the second surface 8 side of the insulating substrate 3. By using a transparent conductive material such as tin oxide or ITO (Indium Tin Oxide) as the conductive material, it is possible to suppress a decrease in light intensity due to the conductive layer 9. As described above, since the through hole 2 has an inversely tapered shape, the second surface 8 and the entire area of the peripheral surface of the through hole 2 have directivity in the film forming direction from the second surface 8 side. The conductive layer 9 can be selectively formed by a sputtering method.

  The electrode portion 9a does not need to be formed in the entire region of the peripheral surface of the through-hole 2, but is formed in a region necessary for generating a shape change of the two-liquid interface using the electrowetting effect, which will be described later. May be. For example, when the optical element 1 is used as a cylindrical lens to be described later, there may be a region on the peripheral surface of the through hole 2 that does not require the electrowetting effect. In this case, in order to obtain continuity, it is necessary to connect to the wiring portion 9b at any location. Also, the wiring portion 9b need not be formed in the entire region of the second surface 8, but may be formed so as to be connectable to an external power source.

  In the optical element 1 of the present embodiment, the conductive layer 9 is not formed on the first surface 7 of the insulating substrate 3, and the conductive layer is formed on the first surface 7 side with the insulating layer interposed therebetween. Since facing one liquid 12 is avoided, there is no portion constituting an unintended capacitor. Here, the unintended capacitor is different from the capacitor formed on the peripheral surface of the through-hole 2 that is necessary for generating the shape change of the two-liquid interface, which will be described later, and is formed in a portion other than the capacitor. A capacitor that generates

  An insulating layer 10 is formed on the peripheral surface of the through hole 2 in which the conductive layer 9 is formed, the first surface 7 of the insulating substrate 3, and the surface of the second transparent substrate 5 on the liquid storage portion side. The insulating layer 10 needs to completely cover the electrode portion 9a so that the electrode portion 9a does not come into contact with the liquid stored in the liquid storage portion 6 described later.

  The insulating layer 10 can have a high dielectric constant. As will be described later, in this embodiment, a voltage is applied between the electrode portion 9a and the first liquid 12 with the insulating layer 10 interposed therebetween. Here, when the electrostatic capacitance between the electrode portion 9a and the first liquid 12 is relatively large, the applied voltage required for driving the optical element 1 may be low, or the thickness of the insulating layer 10 may be reduced. Because you can.

  The insulating layer 10 has water repellency. Due to the water repellency of the insulating layer 10, the first liquid 12, which has a higher surface energy than the second liquid, gathers so as not to contact the surface on which the insulating layer 10 is provided. In addition, the shape of the two-liquid interface, which will be described later, is affected by the water repellency of the insulating layer 10.

  As described above, the insulating layer 10 has two functions of insulation and water repellency. For this reason, the insulating layer 10 needs to satisfy the condition of completely covering the electrode portion 9a, and is formed at least in the vicinity of the two-liquid interface (a region related to the movement of the first liquid 12 due to the electrowetting effect). Need to be done.

  Parylene (paraxylylene resin), PVDF (PolyVinylidine DiFluoride), and the like are listed as materials for the insulating layer 10 having water repellency and insulation. These are formed by a CVD (Chemical Vapor Deposition) method, a coating method, or the like. Alternatively, a laminated structure in which tantalum oxide, titanium oxide, or the like, which is a material having a high dielectric constant, is formed, and PTFE (PolyTetraFlouroEthylene), which is a material having high water repellency, is formed thereon.

The insulating layer 10 formed in a region where the electrode portion 9a such as a portion formed on the first surface 7 of the insulating substrate 3 and the surface of the second transparent substrate 5 on the liquid storage portion side is not formed. Since the electrode portion 9a is not covered (that is, it is not necessary to have a high dielectric constant), it is not necessary to form a material having a high dielectric constant as a lower layer even in the case of the laminated structure. In addition, as long as electrical insulation between the electrode portion 9a and the first liquid 12 is ensured, the insulating layer 10 is formed over the entire surface of the insulating substrate 3 facing the first transparent substrate 4. It does not have to be.
In the present embodiment, as the insulating layer 10, parylene was formed by a CVD method.

  The first transparent substrate 4 and the second transparent substrate 5 are formed of a glass substrate, a nonconductive plastic, or the like. As will be described later, these substrates can be made of a highly transparent material. In this case, since the decrease in light intensity can be suppressed, even if it is present on the path of incident light or transmitted light of the optical element 1, there is little influence.

  A wiring 11 is provided on the surface of the first transparent substrate 4 on the liquid storage unit side. Since the wiring 11 is for the purpose of obtaining electrical continuity with the first liquid 12, the wiring 11 is not limited to the configuration provided in the entire region on the liquid storage portion side of the first transparent substrate 4, but as shown in FIG. It may be patterned into a predetermined shape so that it can be connected. By using a transparent conductive material such as tin oxide or ITO as a raw material, it is possible to suppress a decrease in light intensity as described above.

  The liquid container 6 formed as described above contains the first liquid 12 and the second liquid 13. Here, the two liquids need not be mixed with each other and have different absolute refractive indexes. This is because when the two liquids are mixed, if the two-liquid interface does not occur and the refractive index is the same, the optical characteristics due to the interface shape cannot be obtained. Further, by making the specific gravity of the two liquids equal, it is possible to prevent the two liquid interface from changing greatly with respect to physical behavior such as vibration of the optical element 1 and affecting the optical characteristics. Further, since the interface between the two liquids is deformed and used as will be described later, both the first liquid 12 and the second liquid 13 may have a low viscosity. In addition, at least one of the two liquids may be colored.

  The first liquid 12 is a conductive or polar liquid. Those having high light transmittance are preferred. Water, electrolytic solution (sodium chloride aqueous solution, lithium chloride aqueous solution, etc.), alcohols (methanol, ethanol, etc.), room temperature molten salt, etc. can be used. In this embodiment, a lithium chloride aqueous solution (3.36 wt%, absolute refractive index 1.34) is used as the first liquid 12.

  The second liquid 13 is an insulating non-aqueous liquid. Those having high light transmittance can be used, and for example, hydrocarbons (decane, dodecane, hexadecane, undecane, etc.), hydrophobic silicone oil, fluorine-based materials, and the like can be used. In the present embodiment, silicone oil (TSF437 manufactured by Momentive Performance Materials Japan GK, absolute refractive index 1.49) is used as the second liquid 13.

  As shown in FIG. 1, when the first liquid 12 and the second liquid 13 are stored in the liquid storage unit 6, the two liquids are not mixed and are separated into two layers. In this embodiment, the insulating layer 10 having water repellency is formed on the peripheral surface of the through hole 2 of the insulating substrate 3 and the surface (hereinafter referred to as a water repellent region) of the second transparent substrate 5 on the liquid storage portion side. Therefore, the first liquid 12 having a surface energy larger than that of the second liquid is bounced and gathers on the first transparent substrate 4 side, and the second liquid 13 gathers on the second transparent substrate 5 side.

Next, the shape of the interface between the two liquids will be described.
FIG. 3 is a schematic view showing a state of contact between the peripheral surface of the through hole 2 and the interface between the two liquids.
As shown in the figure, the two-liquid interface and the peripheral surface are in contact with each other with a contact angle θ.

Here, the contact angle θ is determined between the first liquid 12 and the second liquid 13 (γ ₁ ), between the second liquid 13 and the peripheral surface (γ ₂ ), and between the peripheral surface and the first liquid 12. It is determined by the interaction of the interfacial tension generated in each of the gaps (γ ₃ ).
The interfacial tensions γ ₂ and γ ₃ are affected by the material of the peripheral surface (that is, the material of the insulating layer 10).

The shape of the interface is affected by the interfacial tension between the first liquid 12 and the second liquid 13 (γ ₁ ) in addition to the influence of the contact angle θ described above. That is, when the interfacial tension γ ₁ is small, the above-described interaction is received in the vicinity of the peripheral surface of the through-hole 2, but a flat two-liquid interface is formed in a region (bulk region) far from the peripheral surface.

The shape of the two-liquid interface is affected by the inclination of the peripheral surface of the through hole 2 and the shape of the opening of the through hole 2.
The description will be made according to the X, Y, and Z directions shown in FIGS.
The shape of the interface on the ZX plane (or YZ plane), that is, the cross-sectional shape, is affected by the inclination of the peripheral surface of the through hole 2.
When the peripheral surface is perpendicular to the XY plane, the two-liquid interface has a certain contact angle θ with respect to the peripheral surface as described above. On the other hand, when the peripheral surface is inclined with respect to the XY plane, the contact angle θ is the same as that when the peripheral surface is vertical, so the curvature of the two-liquid interface is different in both cases. .

  In addition, the shape of the interface on the XY plane is the same as the shape of the opening of the through hole 2. When the opening of the through-hole 2 is circular, the interface shape is also circular, and since it is a curved surface as described above, it has an aspherical shape, a spherical shape, or a shape that approximates a spherical surface. Further, when the shape of the through hole 2 is an oval shape that is sufficiently long in the Y direction with respect to the length in the X direction, the shape of the interface has a curvature in the Y direction of approximately 0, and moves away from the peripheral surface of the through hole 2. It becomes linear and becomes a cylindrical (cylindrical) shape that curves only in the X direction.

As described above, the shape of the two-liquid interface is determined by the contact angle θ, the interface tension (γ ₁ ), and the shape of the through hole 2.
In the configuration of the present embodiment, the two-liquid interface formed by the first liquid 12 and the second liquid 13 is a curved surface in which the first liquid 12 is convex and the second liquid 13 is concave. Since the length in the X direction is sufficiently longer than the length in the Y direction, the through hole 2 has a cylindrical shape that is curved only in the X direction. And since the through-hole 2 is formed in the reverse taper shape (namely, the surrounding surface inclines), a curvature becomes large compared with the case where a surrounding surface is vertical.

  Next, the operation of the optical element 1 configured as described above will be described.

  When no voltage is applied, the two-liquid interface becomes a curved surface defined by the shape of the through-hole 2 and the physical properties of the first liquid 12, the second liquid 13, and the insulating layer 10 as described above. Since the two-liquid interface is a boundary having different refractive indexes, it converges or diverges incident light, that is, functions as a lens surface. The greater the difference in refractive index, the greater the lens power. The lens effect for light incident from the Z direction will be described below.

FIG. 4 is a diagram showing paths of incident light and transmitted light. (A) is when no voltage is applied, and (B) is when voltage is applied.
As shown in FIG. 4A, in the Z direction toward the optical element 1 and the incident light from the first transparent substrate 4, the absolute refractive index of the first liquid 12 is higher than the absolute refractive index of the second liquid 13. Since it is small, it is refracted at the two-liquid interface and diverges at a certain focal length.

In FIG. 4B showing the optical element 1 when a voltage is applied, which will be described later, since the curvature of the two-liquid interface is smaller than when no voltage is applied, the focal length becomes longer.
In the present embodiment, since the absolute refractive index of the first liquid 12 is smaller than the absolute refractive index of the second liquid 13, the light intensity due to reflection at the interface between the two liquids is larger than when the magnitude of the refractive index is reversed. There is little loss.

  As described above, the shape of the through hole 2 on the XY plane defines the shape of the two-liquid interface on the XY plane. When the shape of the two-liquid interface is a spherical shape (or a shape approximating a spherical surface), incident light from the Z direction diverges with a single focal point on the light incident side in both the X direction and the Y direction. When the shape of the two-liquid interface is a cylindrical shape that is curved only in the X direction, incident light from the Z direction has a focal line (a set of focal points) extending in the Y direction and diverges only in the X direction. Go straight ahead.

  As described above, the optical element 1 according to the present embodiment has a large curvature at the two-liquid interface when no voltage is applied as shown in FIG. This means that the ability to refract incident light, that is, the lens power is larger.

  Unlike this embodiment, when the absolute refractive index of the first liquid 12 is larger than the absolute refractive index of the second liquid 13, the incident light converges by passing through the two-liquid interface.

The shape change of the two-liquid interface due to voltage application will be described below.
Note that the contact angle of the first liquid 12 when no voltage is applied is θ ₀ , and the contact angle when a voltage is applied is θ _V.
Here, the electrode part 9a is demonstrated as what is formed in the whole area | region of the surrounding surface of the through-hole 2. FIG.
As described above, in the optical element 1 according to this embodiment, a two-liquid interface is formed in which the first liquid 12 is convex and the second liquid 13 is concave. When a voltage is applied between the first liquid 12 and the electrode portion 9a of the optical element 1 by an external power source, the two-liquid interface is deformed due to the electrowetting effect. The external power source may be a DC power source or an AC power source.

When the voltage V is applied between the first liquid 12 and the electrode part 9a, an electrostatic potential is generated, and the charges in the first liquid 12 and the electrode part 9a move. As a result, different charges are accumulated on the surface of the first liquid 12 and the electrode portion 9a via the insulating layer 10 and the second liquid 13 to form a capacitor. As the charges are attracted, pressure (Π) is generated due to charges opposite to the interfacial tension (γ ₃ ) between the first liquid 12 and the peripheral surface of the through-hole 2, and the interfacial tension (γ ₃ ) is canceled out. is therefore, the contact angle of the first liquid 12 increases to the contact angle theta _V from the contact angle theta _0. Since the first liquid 12 volume of the second liquid 13 is constant, in order to meet the contact angle theta _V, the first liquid 12 along the circumferential surface of the through hole 2, a second transparent substrate 5 Moving to the side (wetting and spreading), the second liquid 13 moves to the bulk region. This reduces the curvature of the two-liquid interface.

When the application of the voltage is stopped, the charges accumulated in the first liquid 12 and the electrode portion 9a are eliminated, and the shape of the two-liquid interface at the time of no voltage application is restored.
Depending on the magnitude of the applied voltage, the pressure (Π) due to the charge increases or decreases, so that the curvature of the two-liquid interface can be changed linearly.

  The above will be described using equations.

γ ₃ = γ ₂ + γ ₁ cos θ _V + Π (1)
cos θ ₀ = (γ ₃ −γ ₂ ) / γ ₁ (2)
Π = ε ₀ · ε · V ² / 2e (3)
cos θ _V = cos θ ₀ −ε ₀ · ε · V ² / (2e · γ ₃ ) (4)

In FIG. 3, the balance of forces acting on the point where the two-liquid interface and the peripheral surface come into contact is expressed by Equation (1). Here, the contact angle θ ₀ when no voltage is applied is expressed by equation (2), and the pressure drop due to electric charge is expressed by equation (3). Therefore, equation (2) and equation (3) are expressed by equation (1). By substituting, Equation (4) in which the contact angle θ _V is expressed as a function of the voltage V is obtained. Here, ε ₀ is the dielectric constant of vacuum, ε is the relative dielectric constant of the insulating layer, and e is the film thickness of the insulating layer.

  As described above, the charges in the conductor (first liquid 12, electrode part 9a) are opposed to each other through the insulator (insulating layer 10, second liquid 13), and when a voltage is applied. Functions as a capacitor. It is better that the region functioning as the capacitor, that is, the region where the two conductors to which the voltage is applied is opposed to each other through the insulator is the minimum necessary. Since there is a region constituting a capacitor that does not contribute (unintentionally) to the shape change of the two-liquid interface, it is necessary to accumulate electric charge in the region, so that the amount of charge necessary for the shape change of the two-liquid interface, that is, This is because power consumption increases and response speed also decreases.

  In the optical element 1, the substrate provided with the through hole 2 is made of an insulator, and only the region where the electrode portion 9 a is provided serves as a capacitor. Therefore, there is no unintended capacitor (parasitic capacitance). Therefore, an optical element with low power consumption and high response speed can be obtained.

  Capacitors (limited to the part that contributes to the shape change of the two-liquid interface) can accumulate more charges (change the shape of the two-liquid interface) at a lower voltage when the capacitance is larger. Is preferred. As described above, this large capacitance can be obtained by forming the insulating layer 10 from a material having a high dielectric constant.

An operation when the optical element 1 is actually used will be described here. Take as an example the case of adjusting the light distribution angle of a strobe flash of a camera. Here, an example will be described in which the first transparent substrate 4 is mounted on the front surface of the strobe flash light source and reflector, but the second transparent substrate 5 side may be mounted on the light source side. Good.
When no voltage is applied, the light emitted from the strobe flash and reflected by the reflector enters the optical element 1 from the first transparent substrate 4 side. This incident light is refracted and diffused at the two-liquid interface as described above.

  For example, when imaging is desired with a longer focal length, a voltage is applied to the optical element 1. As a result, the shape of the two-liquid interface changes as described above, and the curvature decreases. In this case, the light incident on the optical element 1 from the first transparent substrate 4 side is refracted at the two-liquid interface, but the degree of curvature is small because the curvature of the two-liquid interface is reduced. That is, the light distribution angle is reduced compared to when no voltage is applied, and the light is irradiated further away.

  Since the optical element 1 according to the present embodiment does not have a mechanical configuration, it can be reduced in size and weight as compared with the conventional light distribution angle adjustment mechanism, and the response speed is also high. In addition, since almost no current flows when a voltage is applied, the power consumption is extremely small.

  In addition, the case where the electrode part 9a is formed only in a part of peripheral surface of the through-hole 2 is demonstrated. For example, this is a case where the two-liquid interface has the above-described cylindrical shape and the interface need not be curved in the Y direction. In this case, it is not necessary to form the electrode portion 9a in a region (a region parallel to the XY plane) that contributes only to the curvature in the Y direction on the peripheral surface of the through hole 2. Thus, since the electrowetting effect is generated only in the region where the electrode portion 9a is formed, the two-liquid interface can be curved only in a desired direction. As a comparative example, when a component corresponding to the insulating substrate 3 of this embodiment is formed of a conductive material, an optical element that generates an electrowetting effect only in an arbitrary region as in this embodiment is used. It is impossible to get.

Next, a method for manufacturing the optical element 1 will be described.
5, 6 and 7 show the manufacturing process of the optical element 1 according to this embodiment.
In these drawings, the XZ plane shown in FIGS. 1 and 2 is shown, and the inclination angle of the through hole 2 is emphasized.

FIG. 5 is a diagram showing a substrate process in the manufacturing process of the optical element 1.
An insulating substrate 3 having a through-hole 2, a first surface 7, and a second surface 8, as shown in FIG. Form.

  The through-hole 2 is formed so that the size of the opening gradually increases (reverse taper) from the first surface 7 side toward the second surface 8 side. This reverse taper shape can be a draft when the insulating substrate 3 is removed from the mold. This is, for example, a mold (mold a) for forming the second surface 8 and the through-hole 2 and a mold (mold b) for forming the first surface 7 and the sealing member guide portion 15. When the insulating substrate 3 is formed using two molds, the sliding resistance received from the peripheral surface of the through hole 2 when the mold a is removed is reduced. Since the peripheral surface of the through-hole 2 in the present embodiment extends toward the second surface 8, the inclination of the peripheral surface can be used as a draft from the mold (mold a). .

Next, as shown in FIG. 5B, a conductive layer 9 is formed on the peripheral surface of the through hole 2 and the second surface 8.
FIG. 8 is a diagram showing a state of film formation of the conductive layer 9 by the sputtering method. In the vacuum chamber 16, a sputtering target (hereinafter referred to as a target) 17 made of the raw material of the conductive layer 9, and the insulating substrate 3 at a position facing the target 17, so that the second surface 8 faces the target 17. Has been placed. Sputtered particles generated from the target surface by sputtering are scattered linearly from the target 17 toward the insulating substrate 3 as indicated by arrows in the figure. In general, sputtered particles having high directivity reach only the region facing the target. However, as described above, the peripheral surface of the through hole 2 of the present embodiment has an inversely tapered shape, and therefore, the entire region of the peripheral surface. To form a film. That is, the conductive layer 9 can be formed on the second surface 8 and the peripheral surface of the through hole 2.

Here, by previously masking the peripheral surface of the through-hole 2 or the second surface 8, the conductive layer 9 (electrode portion 9a and wiring portion 9b) is formed only in an arbitrary region as described above. Is possible.
Although the method for forming the conductive layer 9 by the sputtering method has been described above, it is also possible to use a method such as plating. For example, a method of forming a film by the above-described sputtering method and performing electrolytic plating using the film as an electrode is also effective because the film formation rate is relatively low in the sputtering method.

Next, as shown in FIG. 5C, the second transparent substrate 5 is attached to the second surface 8 of the insulating substrate 3. Thereby, a recess having the through hole 2 as a side surface and the second transparent substrate 5 as a bottom surface is formed.
Also, a method of applying an adhesive to the second surface 8 and bonding the second transparent substrate 5, a method of providing a seal ring on the second surface 8, and fastening the second transparent substrate 5 with screws or the like, etc. Therefore, it is necessary to attach so that the liquid in the liquid storage part 6 does not leak. Here, in the case of bonding using an adhesive, at the location where the boundary between the through hole 2 and the second surface 8 and the second transparent substrate 5 are in contact (location indicated by 501 in the same figure) May stick out. In the optical element 1 according to the present embodiment, since the through hole 2 has a reverse taper shape, the protruding adhesive is optically effective determined by the minimum diameter of the through hole 2 (except when the amount is large). It does not relate to the area. Examples of the adhesive include UV (UltraViolet) curable resin, thermosetting resin, and thermoplastic resin.

Next, as shown in FIG. 5D, the insulating layer 10 is formed on the first surface 7 of the insulating substrate 3, the peripheral surface of the through hole 2, and the surface of the second transparent substrate 5 on the liquid container 6 side. Form.
This can be formed by, for example, a CVD method. Since the insulating layer 10 is formed on the entire area of the outer surface of the insulating substrate 3 and the second transparent substrate 5 at the present stage, the film forming method is not limited to having directivity. As described above, the first surface 7 of the insulating substrate 3, the peripheral surface of the through hole 2, the surface of the second transparent substrate 5 on the liquid storage unit 6 side, that is, the inner surface of the liquid storage unit 6, The insulating layer 10 needs to be provided, but it may or may not be provided on other surfaces. Further, as described above, a layer made of a highly dielectric material may be formed in advance on the surface of the electrode portion 9a, and a layer made of a highly water-repellent material may be formed thereon. The method for forming the insulating layer 10 is not limited to the CVD method shown here, and a coating method or other film forming methods can be used.

FIG. 6 is a diagram showing a liquid adding step in the manufacturing process of the optical element 1.
As shown in FIG. 6A, a predetermined amount of the first liquid 12 is filled into the substrate manufactured in the substrate process. Since the shape of the interface between the two liquids is also affected by the volume of the first liquid 12, it is necessary to reliably fill a predetermined amount.
Next, as shown in FIG. 6B, the sealing member 14 is attached. This is attached by fitting or the like to the sealing member guide portion 15.
Next, as shown in FIG. 6C, a predetermined amount of the second liquid 13 is filled. This is injected into the liquid container 6 by, for example, a dispenser.

  The order of filling the two liquids in the above liquid filling process is not particularly limited. However, as will be described later, in the case where an optical element in which a plurality of liquid storage portions 6 are formed and the first liquid can pass between the liquid storage portions 6 is shown in the present embodiment. By setting the order, the volume ratio of the two liquids in each liquid storage unit 6 can be easily set to a desired ratio. As shown in this embodiment, by filling the first liquid 12 first, the second liquid 13 to be injected later is covered with the first liquid 12 repelled by water repellency. A predetermined amount is accommodated. Since the first liquid 12 can pass through the other liquid storage unit 6, the first liquid 12 is naturally stored in a predetermined amount if the predetermined amount of the second liquid 13 is stored. When the second liquid 13 is filled before the first liquid 12, the second liquid 13 can pass through the other liquid storage units 6, and therefore, in each liquid storage unit 6, the volume ratio of the two liquids is There is a possibility of deviating from the desired ratio.

FIG. 7 is a diagram showing a sealing step in the manufacturing process of the optical element 1.
As shown in FIG. 7A, the first transparent substrate 4 is attached to the one filled with the two liquids described above. Here, the first transparent substrate 4 is provided with wirings 11 in advance. The wiring 11 is formed by depositing a metal or the like by a sputtering method or the like and then performing an etching process to form a circuit pattern, or by forming a resist pattern in the film formation region in advance and removing the resist pattern after the film formation. (Lift-off method) can be used.

  After the first transparent substrate 4 is disposed, pressure is applied to the first transparent substrate 4 and the second transparent substrate 5 by the pressurizing device 23 as shown in FIG. As a result, the sealing member 14 is deformed, and the liquid in the liquid container 6 is sealed by its elasticity. Next, a clamp 18 capable of holding the state where the pressure is applied is disposed.

Next, as shown in FIG. 7 (B), the clamp 18 is deformed by applying pressure to the clamp 18 using a crimping device 19. The clamp 18 is not particularly limited to a certain shape, but it is necessary that the wiring portion 9b and the wiring 11 of the conductive layer 9 be electrically connected to an external power source.
By the above manufacturing method, the optical element 1 is manufactured as shown in FIG. Note that the clamp 18 is used to fix the first transparent substrate 4 to the insulating substrate 3, but it is also possible to adopt a structure in which the clamp is fixed by other means such as bonding using an adhesive.

(Second Embodiment)
An optical element according to the second embodiment of the present invention will be described. In the following description, the description of the same configuration and function of the optical element according to the first embodiment will be simplified or omitted, and different points will be mainly described.

FIG. 9 is a cross-sectional view of the optical element 20 according to the second embodiment of the present invention, and FIG. 10 is a plan view of the optical element 20. 9 is a cross-sectional view in the direction of line [B]-[B] in FIG.
As shown in these drawings, the optical element 20 includes an insulating substrate 3 in which three oval through holes 2a, 2b and 2c having an inversely tapered shape are arranged in the X direction, and a first transparent substrate. 4 and a second transparent substrate 5. The through holes 2a, 2b and 2c, the first transparent substrate 4 and the second transparent substrate 5 form liquid storage portions 6a, 6b and 6c, and the first liquid 12 and the second liquid 13 are stored. Yes.

  As shown in FIG. 9, the liquid storage portions 6 a, 6 b and 6 c are separated from each other by the partition walls of the insulating substrate 3, but there is a gap between these partition walls and the first transparent substrate 4. The first liquid 12 passes through the gap and can communicate between the liquid storage portions 6a, 6b, and 6c. Similarly to the optical element 1 according to the first embodiment, the conductive layer 9 is formed on the peripheral surfaces of the through holes 2a, 2b, and 2c and the second surface 8, and the insulating layer 10 is formed thereon. Has been. Here, the number of through holes is not limited to three, and the arrangement can be changed as appropriate.

  A liquid passage 22 for communicating the second liquid 13 may be provided between the liquid storage portions 6a, 6b, and 6c. By providing this liquid passage 22, even if the volume ratio of the two liquids in each of the liquid storage portions 6a, 6b, 6c varies from a predetermined value due to the physical behavior of the optical element 21, the first liquid 12 In order to balance the water repellent effect received by the first liquid 12, the first liquid 12 moves through the gap and the second liquid 13 moves through the liquid passage 22 (so as to satisfy the conventional volume ratio). That is, it is possible to obtain the optical element 21 that naturally returns to a predetermined volume ratio. Also in the above-described liquid filling step, if the first liquid 12 and the second liquid 13 are filled (regardless of the filling order), a predetermined volume ratio is obtained in each of the liquid storage portions 6a, 6b, 6c. be able to.

  Similarly to the first embodiment, the lens effect is obtained by the respective interfaces of the first liquid 12 and the second liquid 13 accommodated in the liquid accommodating portions 6a, 6b, 6c, and the electrode portion 9a of the conductive layer 9 is obtained. The voltage applied to the first liquid 12 causes a change in the shape of each two-liquid interface due to the electrowetting effect, that is, a change in optical characteristics.

With this configuration, similarly to the optical element 1 according to the first embodiment, incident light from the Z direction can be converged or diverged. Here, since the liquid storage portions 6a, 6b, and 6c are arranged in the X direction, the XY plane of the through holes 2a, 2b, and 2c necessary for obtaining the effect of divergence in the X direction with respect to the incident light. The area of the opening may be smaller than in the case of the first embodiment in which the liquid container 6 is provided alone. If the area of the aperture is small, the depth of the aperture (in the Z direction) required to generate the same curvature at the two-liquid interface (both when voltage is applied and when no voltage is applied) may be shallow. The length (thickness) can be reduced.

  Further, by connecting the wiring portion 9b of the conductive layer 9 to an external power source so as to form a circuit for each liquid storage portion by patterning as described above, the electrowetting effect can be independently achieved in each liquid storage portion. It is also possible to generate

  In the optical element 21 according to this embodiment, the area of the first surface 7 of the insulating substrate 3 is larger than when the through hole 2 is formed alone (in the case of the first embodiment). This is because there is a region (region indicated by 901 in the figure) on the partition wall that separates the liquid storage portions 6a, 6b, and 6c. However, in the configuration according to the present embodiment, as described above, since the parasitic capacitance is not generated on the first surface 7, it is not a problem that the area of the first surface 7 is large.

  Embodiments according to the present invention are not limited to the embodiments described above, and other various embodiments are conceivable.

In the above-described embodiment, the sealing member guide portion 15 is provided on the insulating substrate 3, but it is also possible not to provide this. FIG. 11 shows an optical element 24 that does not have a sealing member guide portion.
Even in the optical element 24, there is no unintended capacitor on the first surface 7 of the insulating substrate 3.

It is sectional drawing of the optical element which concerns on 1st Embodiment. It is a top view of the optical element concerning a 1st embodiment. It is a schematic diagram which shows the mode of contact of the surrounding surface of a through-hole, and the interface of 2 liquids. It is a figure which shows the path | route of incident light and transmitted light. It is a figure which shows the manufacturing method (board | substrate process) of the optical element which concerns on this invention. It is a figure which shows the manufacturing method (liquid filling process) of the optical element which concerns on this invention. It is a figure which shows the manufacturing method (sealing process) of the optical element which concerns on this invention. It is a figure which shows the mode of preparation of the conductive layer by sputtering method. It is sectional drawing of the optical element which concerns on 2nd Embodiment. It is a top view of the optical element which concerns on 2nd Embodiment. It is sectional drawing of the modification of the optical element which concerns on 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2 Through-hole 3 Insulating substrate 4 1st transparent substrate 5 2nd transparent substrate 6 Liquid accommodating part 7 1st surface 8 2nd surface 9 Conductive layer 10 Insulating layer 12 1st liquid 13 2nd Liquid 16 Vacuum chamber 17 Sputtering target

Claims (8)

An insulating substrate having a first surface and a second surface opposite to the first surface, and having a through-hole in which the size of the opening gradually increases from the first surface side toward the second surface side When,
A first transparent substrate bonded to the first surface side of the insulating substrate;
A second transparent substrate that is bonded to the second surface side of the insulating substrate and forms a liquid storage portion together with the first transparent substrate and the through hole;
A conductive first liquid stored on the first surface side of the liquid storage unit , which is an aqueous liquid and has a first surface energy;
An insulating second liquid that is accommodated on the second surface side of the liquid container and has a refractive index different from that of the first liquid and does not mix, and is a non-aqueous liquid, A second liquid having a second surface energy less than the first surface energy;
A conductive layer continuously formed on the peripheral surface of the through hole and the second surface;
An optical element comprising: an insulating layer that covers the conductive layer and has water repellency . The optical element according to claim 1,
The through-hole has an opening shape in which a length in one direction is longer than a length in another direction. The optical element according to claim 1 or 2,
A plurality of the through holes are arranged in one direction within the plane of the insulating substrate. The optical element according to claim 3,
The insulating substrate includes a liquid passage that allows the second liquid to communicate with each other between the plurality of adjacent through holes. The optical element according to claim 1,
The boundary between the peripheral surface of the through hole and the second surface is a curved surface. The optical element according to claim 1, wherein the conductive layer is a transparent conductive film. Forming a through-hole in which the size of the opening gradually increases from the first surface side toward the second surface side in the insulating substrate having the first surface and the second surface opposite to the first surface,
Forming a continuous conductive layer on the peripheral surface of the second surface and the through hole;
A second transparent substrate is attached to the second surface, and a recess is formed by the through hole and the second transparent substrate,
Forming an insulating layer having water repellency covering the conductive layer;
The recessed portion has a conductive first liquid that is a water-based liquid and has a first surface energy, and a second surface energy that is a non-aqueous liquid and is smaller than the first surface energy. Containing an insulating second liquid that has a refractive index different from that of the liquid and does not mix;
A method for manufacturing an optical element, wherein the first transparent substrate is liquid-tightly attached to the first surface. It is a manufacturing method of the optical element according to claim 7,
The step of forming the conductive layer on the insulating substrate includes:
The insulating substrate is disposed in a vacuum chamber so that the second surface faces a sputtering target containing the constituent material of the conductive layer,
The method of manufacturing an optical element, wherein the conductive layer is selectively formed on the second surface and the peripheral surface of the through hole by a sputtering method.

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