JP2015108845A - Polarizing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing element having excellent optical characteristics and high light resistance to strong light.SOLUTION: A polarizing element comprises: a transparent substrate 11; an absorber layer 12 arranged on the transparent substrate 11 with a pitch smaller than the wavelength of light in a used bandwidth and constituting lattice-like protrusions; a dielectric layer 13 formed on the absorber layer 12; and a reflective layer 14 formed on the dielectric layer 13. The absorber layer 12 is composed of two or more layers, and either one layer of them has a refractive index higher than that of the transparent substrate 11. The absorber layer 12 for interfering with and absorbing light is brought into contact with the transparent substrate 11 and therefore heat dissipation can be improved further, which can enhance the heat resistance of a polarizing plate.

Description

  The present invention relates to a polarizing element that absorbs one of orthogonal polarization components (so-called P-polarized wave and S-polarized wave) and transmits the other.

  In the liquid crystal display device, it is indispensable to dispose a polarizing element on the surface of the liquid crystal panel from the principle of image formation. The function of the polarizing element is to absorb one of orthogonally polarized components (so-called P-polarized wave and S-polarized wave) and transmit the other.

  Conventionally, as such a polarizing element, a dichroic polarizing plate in which an iodine-based or dye-based high molecular organic substance is contained in a film is often used. As these general production methods, a method is used in which a polyvinyl alcohol film and a dichroic material such as iodine are dyed, followed by crosslinking using a crosslinking agent and uniaxial stretching. Thus, since the dichroic polarizing plate is produced by stretching, it generally tends to shrink. In addition, since the polyvinyl alcohol film uses a hydrophilic polymer, it is very easily deformed particularly under humidified conditions. Moreover, since a film is fundamentally used, the mechanical strength as a device is weak, and it may be necessary to adhere a transparent protective film.

  In recent years, the use of liquid crystal display devices has been expanded and their functions have been enhanced. Accordingly, high reliability and durability are required for each device constituting the liquid crystal display device. For example, in the case of a liquid crystal display device that uses a light source with a large amount of light, such as a transmissive liquid crystal projector, the polarizing plate receives strong radiation. Therefore, excellent heat resistance is required for the polarizing plate used in these. However, since the film-based polarizing plate as described above is an organic substance, there are naturally limitations in improving these characteristics.

  In the United States, Corning sells a highly heat-resistant inorganic polarizing plate under the name Polarcor. This polarizing plate has a structure in which silver fine particles are diffused in glass, and does not use organic substances such as a film. The principle uses plasma resonance of island-shaped fine particles. That is, light absorption by surface plasma resonance when light is incident on noble metal or transition metal island-like particles is used, and the absorption wavelength is affected by the particle shape and the surrounding dielectric constant. Here, when the shape of the island-shaped fine particles is elliptical, the resonance wavelengths in the major axis direction and the minor axis direction are different, and thereby deflection characteristics are obtained. Specifically, a polarization component parallel to the major axis on the long wavelength side is obtained. A polarization characteristic of absorbing and transmitting a polarization component parallel to the minor axis is obtained. However, in the case of Polarcor, the wavelength range in which the polarization characteristics can be obtained is a region close to the infrared region, and does not cover the visible light range required for a liquid crystal display device. This is due to the physical properties of silver used in the island-shaped fine particles.

  Patent Document 1 discloses a UV polarizing plate by applying the above principle to deposit fine particles in glass by thermal reduction, and proposes to use silver as metal fine particles. In this case, it is considered that absorption in the minor axis direction is used contrary to the previous Polarcor. As shown in Figure 1, although it functions as a polarizing plate even at around 400 nm, the extinction ratio is small and the band that can be absorbed is very narrow, so even if Polarcor and the technique of Patent Document 1 are combined, the entire visible light range It will not be a polarizing plate that can cover.

  Non-Patent Document 1 describes a theoretical analysis of an inorganic polarizing plate using plasma resonance of metal island-shaped fine particles. According to this document, it is described that aluminum fine particles have a resonance wavelength shorter than that of silver fine particles by about 200 nm, and therefore it is possible to produce a polarizing plate that covers the visible light region by using aluminum fine particles.

  Patent Document 2 discloses several methods for producing a polarizing plate using aluminum fine particles. Among them, it is described that a glass based on silicate is not desirable as a substrate because aluminum and glass react with each other, and calcium aluminoborate glass is suitable (paragraphs 0018 and 0019). However, glass using silicate is widely distributed as optical glass, and it is economically undesirable that a highly reliable product can be obtained at a low cost and this is not suitable. In addition, a method for forming island-shaped particles by etching a resist pattern is described (paragraphs 0037 and 0038). Usually, a polarizing plate used in a projector needs to have a size of several centimeters and a high extinction ratio. Therefore, when the polarizing plate for visible light is aimed, the resist pattern size is sufficiently shorter than the visible light wavelength, that is, a size of several tens of nanometers is necessary, and in order to obtain a high extinction ratio, It is necessary to form a pattern with high density. Moreover, when using it for projectors, a large area is required. However, in the method of applying high-density fine pattern formation by lithography as described, it is necessary to use electron beam drawing or the like to obtain such a pattern. Electron beam drawing is a method of drawing individual patterns from an electron beam, and is not practical because of poor productivity.

  Further, Patent Document 2 describes that aluminum is removed by chlorine plasma. However, when etching is usually performed, chloride adheres to the sidewall of the aluminum pattern. Although it can be removed with a commercially available wet etching solution (for example, SST-A2 from Tokyo Ohka Kogyo Co., Ltd.), such a chemical solution that reacts with aluminum chloride reacts with aluminum even though the etching rate is slow. It is difficult to realize a desired pattern shape by such a method.

  Furthermore, Patent Document 2 describes another method of depositing aluminum on a patterned photoresist by oblique film formation and removing the photoresist (paragraphs 0045 and 0047). However, in such a method, it is considered that it is necessary to deposit aluminum on the substrate surface to some extent in order to obtain adhesion between the substrate and aluminum. However, this means that the shape of the deposited aluminum film is different from prolate spheres including prolate ellipsoids, which are suitable shapes described in paragraph 0015. In addition, paragraph 0047 describes that the overprecipitation integral is removed by anisotropic etching perpendicular to the surface. In order to function as a polarizing plate, the shape anisotropy of aluminum is extremely important. Therefore, it is considered necessary to adjust the amount of aluminum deposited on the resist portion and the substrate surface so that a desired shape can be obtained by etching. However, as described in paragraph 0047, the submicron is 0.05 μm or less. It is considered very difficult to control these by size, and it is doubtful whether it is suitable as a production method with high productivity. In addition, a high transmittance is required in the direction of the transmission axis as a characteristic of the polarizing plate. Usually, when glass is used for the substrate, reflection of several percent from the glass interface is inevitable, and it is difficult to obtain a high transmittance. .

  Patent Document 3 describes a polarizing plate by oblique vapor deposition. This method obtains polarization characteristics by manufacturing a micro-columnar structure by oblique deposition of a transparent and opaque material with respect to the wavelength of the used band. Unlike Patent Document 1, a fine pattern is obtained by a simple method. Therefore, it is considered a highly productive method. However, the aspect ratio of the micro-columnar structure of the material that is opaque to the band used, the interval between the individual micro-columnar structures, and the linearity are important factors for obtaining good polarization characteristics. However, this method uses the phenomenon that the columnar structure is obtained by the fact that the next flying vapor particles do not deposit in the shadowed part of the initial deposition layer of vapor deposition particles. Therefore, it is difficult to intentionally control the above items. As a method for improving this, a method of providing a polishing mark on a substrate by rubbing before vapor deposition is described, but in general, the particle diameter of the vapor deposition film is about several tens of nanometers at maximum. In order to control the anisotropy of such particles, it is necessary to intentionally produce a submicron pitch by polishing. However, in a general polishing sheet or the like, the limit is about submicron, and it is not easy to manufacture such a fine polishing mark. In addition, as described above, the resonance wavelength of the Al fine particles greatly depends on the refractive index of the surroundings. In this case, a combination of transparent and opaque substances is important. However, Patent Document 3 discloses a good polarization in the visible light region. There is no description of combinations for obtaining characteristics. Similarly to Patent Document 1, when glass is used as the substrate, reflection of several percent from the glass interface is inevitable.

Non-Patent Document 2 describes a polarizing plate for infrared communication called Lamipol. This has a laminated structure of Al and SiO ₂ and shows a very high extinction ratio according to this document. Further, Non-Patent Document 3 describes that a high extinction ratio can be realized at a wavelength of 1 μm or less by using Ge instead of Al that is responsible for Lamipol's light absorption. In addition, it is expected that a high extinction ratio can be obtained from FIG. 3 to Te (tellurium) in the same document. As described above, Lamipol is an absorptive polarizing plate that provides a high extinction ratio. However, since the thickness of the light-absorbing material and the transparent material is the size of the light-receiving surface, Lamipol is used for projector applications that require a size of several cm square Not suitable for polarizing plates.

  Patent Document 4 describes the structure and characteristics of an inorganic polarizing plate having a structure in which a dielectric layer and an inorganic fine particle layer are deposited on a metal lattice, and shows that this structure provides high contrast. If there is an inorganic polarizing plate that can be manufactured with a simple manufacturing process by developing this structure, increasing the contrast, reducing the reflectance, and the like, it is more useful in the industry.

  However, in the technique of Patent Document 4, since an inorganic fine particle layer that absorbs light is present at the air interface, heat converted by light absorption is hardly dissipated, and the temperature of the polarizing plate is likely to rise due to heat absorption. For this reason, the light resistance with respect to strong light is low. [0083] describes a structure in which an antireflection layer is added directly below the reflection layer, but in this case, the upper inorganic fine particle layer is not necessarily required depending on the method of use.

US Pat. No. 6,772,608 JP 2000-147253 A JP 2002-372620 A JP 2008-216957 A

J. et al. Opt. Soc. Am. A Vol. 8, no. 4 619-624 Applied Optics Vol. 25 No. 2 1986 311-314 J. et al. Lightwave Tec. Vol. 15 No. 6 1997 1042-1050

  The present invention has been proposed in view of such a situation, and an object thereof is to provide a polarizing element having excellent optical characteristics and high light resistance against strong light.

  In order to solve the above-described problems, a polarizing element according to the present invention includes a transparent substrate, and an absorption layer that configures a grid-like convex portion arranged on the transparent substrate at a pitch smaller than the wavelength of light in a use band. A dielectric layer formed on the absorption layer and constituting the lattice-shaped convex portion, and a reflective layer formed on the dielectric layer and constituting the lattice-shaped convex portion, the absorption layer comprising: It consists of two or more layers, and any one of them has a higher refractive index than the transparent substrate.

  In addition, a liquid crystal projector according to the present invention includes the polarizing element described above, a light source, and an image display panel, and the polarizing element allows light in a use band from the light source to be incident from the transparent substrate side and pass therethrough. It is characterized by.

  According to the present invention, since the absorption layer that interferes and absorbs light is in contact with the transparent substrate, the heat dissipation can be further improved, and the heat resistance of the polarizing element can be improved. Further, excellent optical characteristics can be obtained by the selective light absorption action of the polarized wave of the absorption layer.

It is a schematic sectional drawing which shows the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing which shows the structure of the optical engine part of the liquid-crystal projector which concerns on one embodiment of this invention. It is a figure for demonstrating the manufacturing method of a polarizing element. It is a schematic sectional drawing which shows the polarizing element whose absorption layer is Ta. It is a graph which shows the optical characteristic of the polarizing element whose absorption layer is Ta. It is the SEM image (the 1) of the cross section of the polarizing element whose absorption layer is Ta. It is a SEM image (the 2) of the cross section of the polarizing element whose absorption layer is Ta. It is a schematic sectional drawing which shows the polarizing element whose absorption layer is Si. It is a graph which shows the optical characteristic of the polarizing element whose absorption layer is Si. It is a schematic sectional drawing which shows the polarizing element whose absorption layer is Ta / Si. It is a graph which shows the optical characteristic of the polarizing element whose absorption layer is Ta / Si. It is a graph which shows the relationship of the absorption-axis transmittance | permeability with respect to a grid width. It is a schematic sectional drawing which shows the polarizing element which laminated | stacked Ta and Si in this order on the quartz substrate (stacking order A). It is a schematic sectional drawing which shows the polarizing element which laminated | stacked Si and Ta in this order on the quartz substrate (stacking order B). 4 is a SEM image of a cross section of a polarizing element in a stacking order A. 3 is an SEM image of a cross section of a polarizing element in a stacking order B. It is a graph which shows the optical characteristic of the polarizing element of the lamination order A. 5 is a graph showing optical characteristics of polarizing elements in a stacking order B. It is a graph which shows the transmittance | permeability in the transmission axis and absorption axis of a green area. It is a graph which shows the reflectance in the transmission axis and absorption axis of a green area. It is a schematic sectional drawing which shows the polarizing element which made width W of an absorption layer small. It is a graph which shows the simulation result of the transmission-axis transmittance | permeability Tp with respect to the width W of an absorption layer. It is a graph which shows the simulation result of the transmission axis reflectance Rp with respect to the width W of an absorption layer. It is a graph which shows the simulation result of the absorption-axis transmittance | permeability Ts with respect to the width W of an absorption layer. It is a graph which shows the simulation result of the absorption-axis reflectance Rs with respect to the width W of an absorption layer. It is a SEM image of the cross section of the polarizing element which made width W of an absorption layer small. It is a graph which shows the measurement result of the transmission-axis transmittance | permeability Tp of samples A and B from which the width W of an absorption layer differs. It is a graph which shows the measurement result of the transmission axis reflectance Rp of the samples A and B from which the width W of an absorption layer differs. It is a graph which shows the measurement result of absorption-axis transmittance | permeability Ts of the samples A and B from which the width W of an absorption layer differs. It is a graph which shows the measurement result of absorption axis reflectance Rs of samples A and B from which width W of an absorption layer differs. It is a schematic sectional drawing which shows the polarizing element in which the protective film was formed. It is a SEM image of the cross section of the polarizing element in which the protective film was formed. It is a graph which shows the transmittance | permeability of the polarizing element in which the protective film was formed. It is a graph which shows the reflectance of the polarizing element in which the protective film was formed.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings.
1. 1. Configuration of polarizing element 2. Manufacturing method of polarizing element 3. Configuration example of liquid crystal projector Example

<1. Configuration of polarizing element>
FIG. 1 is a schematic sectional view showing a polarizing element according to an embodiment of the present invention. As shown in FIG. 1, the polarizing element 1 includes a transparent substrate 11, an absorption layer 12 that forms lattice-shaped convex portions arranged on the transparent substrate 11 at a pitch smaller than the wavelength of light in the use band, and an absorption layer. 12 includes a dielectric layer 13 formed on the dielectric layer 12 and a reflective layer 14 formed on the dielectric layer 13. That is, the polarizing element 1 has a one-dimensional lattice-like structure in which convex portions in which the absorption layer 12, the dielectric layer 13, and the reflective layer 14 are laminated in this order from the transparent substrate 11 side are arranged on the transparent substrate 11 at regular intervals. It has a wire grid structure.

  The transparent substrate 11 is made of a material having a refractive index of 1.1 to 2.2, such as glass, sapphire, and quartz, which is transparent to light in the use band. In the present embodiment, it is preferable to use a crystal or sapphire substrate with high thermal conductivity as a constituent material of the transparent substrate 11. Thereby, it has high light resistance with respect to intense light, and is useful as a polarizing element for an optical engine of a projector that generates a large amount of heat.

  Further, when the transparent substrate 11 is made of an optically active crystal such as quartz, excellent optical characteristics can be obtained by arranging lattice-like convex portions in a direction parallel or perpendicular to the optical axis of the crystal. . Here, the optical axis is a direction axis that minimizes the difference in refractive index between O (ordinary ray) and E (extraordinary ray) of light traveling in that direction.

  Depending on the application of the polarizing element, glass, particularly quartz (refractive index 1.46) or soda lime glass (refractive index 1.51) may be used. The component composition of the glass material is not particularly limited. For example, an inexpensive glass material such as silicate glass widely distributed as optical glass can be used, and the manufacturing cost can be reduced.

The absorption layer 12 is composed of one or more kinds of substances having a light absorption action, such as metals and semiconductors, whose optical constants are not zero, and the material is selected according to the wavelength range of light to be applied. Examples of the metal material include Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Sn alone, or an alloy containing these. Examples of the semiconductor material include Si, Ge, Te, ZnO, and silicide materials (β-FeSi ₂ , MgSi ₂ , NiSi ₂ , BaSi ₂ , CrSi ₂ , COSi ₂ , TaSi, etc. In addition, when a semiconductor material is used, Since the band gap energy of the semiconductor is involved in the absorption action, it is necessary that the band gap energy is equal to or lower than the band to be used. It is necessary to use a material of less than 1 eV.

  The absorption layer 12 preferably has a higher refractive index than the transparent substrate 11 among the above-described metal materials and semiconductor materials. The absorbing layer 12 is preferably two or more layers of different materials, and any one of them preferably has a higher refractive index than the transparent substrate 11. By combining the metal material and / or the semiconductor material described above, the interference effect is enhanced with respect to the light in the use band, and the contrast in the transmission axis direction at a desired wavelength is increased. The reflection component from the plate can be reduced.

  A specific material combination is selected based on optical constants such as refractive index n and extinction constant k. For example, when Si having a high refractive index (n = 0.48 (550 nm), k = 0.04) is used, Ta (n = 2.48 (550 nm), k = 1.83) having a large refractive index difference and a larger extinction constant k than Si. ) Can be used to enhance the absorption effect and interference effect, thereby increasing the contrast. Further, when quartz (n = 1.54 (550 nm), k = 0.00) is used for the transparent substrate 11, a Ta layer having a small refractive index difference is formed on the substrate, and a Si layer is formed on the Ta layer. Reflection can be suppressed and the transmittance can be improved.

  Further, by making the width of the absorption layer 12 in the transmission axis direction (X-axis direction) smaller than other layers (reflection layer, dielectric layer), the wavelength at which the reflectance is minimized can be shifted to the short wavelength side. it can. Therefore, it is possible to reduce the reflectance in a desired wavelength band by optimally designing the pitch and grid width. Further, the specific width in the transmission axis direction of the absorption layer 12 is preferably 50% or more of the grid (reflection layer, dielectric layer) width, and more preferably 80% or more of the grid width. When the width (X-axis direction) of the absorption layer 12 is less than 50% of the grid width, the thermal conductivity is deteriorated and the physical strength is reduced.

  The absorption layer 12 is preferably formed with a high density film by vapor deposition or sputtering. Since the density of the film is high, thermal conductivity can be improved and heat dissipation can be improved.

  In addition, as a method for obtaining the film of the absorption layer 12, inorganic fine particles may be deposited by using an evaporation method using a shadowing effect or an oblique film formation method by sputtering. In this case, it is desirable that the inorganic fine particles have a size equal to or smaller than the wavelength of the use band, and the individual particles are completely isolated. The inorganic fine particles have an elliptical shape, the major axis direction of the ellipse is arranged in parallel to the Y axis direction that is the absorption axis, and the minor axis direction of the ellipse is arranged in parallel to the X axis direction that is the transmission axis. . The thus formed absorption layer 12 has an optical anisotropy in which the optical constant in the Y-axis direction, which is the absorption axis, is larger than the optical constant in the transmission axis X direction. Specifically, the refractive index in the absorption axis Y direction is larger than the refractive index in the transmission axis X direction, and the extinction coefficient in the absorption axis Y direction is larger than the extinction coefficient in the transmission axis X direction.

  The dielectric layer 13 is formed in such a thickness that the polarized light reflected by the absorbing layer 12 is transmitted through the absorbing layer 12 and reflected by the reflecting layer 14 so that the phase of the polarized light is shifted by a half wavelength. The specific film thickness is appropriately set within a range of 1 to 500 nm that can adjust the phase of polarized light and enhance the interference effect. In this embodiment mode, since the light reflected by the absorption layer 12 is absorbed, an improvement in contrast can be realized even if the film thickness is not optimized. In practice, the desired polarization characteristics are balanced with the actual manufacturing process. You can decide on

A general material such as SiO ₂ , Al ₂ O ₃ , or MgF ₂ can be used as the material constituting the dielectric layer 13. In addition, the refractive index of the dielectric layer 13 is preferably greater than 1.0 and 2.5 or less. In addition, since the optical characteristics of the absorption layer 12 are also affected by the surrounding refractive index, the polarizing element characteristics may be controlled by the material of the dielectric layer 13.

  The reflective layer 14 is formed by arranging a metal thin film extending in a band shape in the Y direction as an absorption axis on the dielectric layer 13. That is, the reflective layer 14 has a function as a wire grid polarizer, and has polarized light having an electric field component in a direction parallel to the longitudinal direction of the wire grid (Y-axis direction) out of light incident from the transparent substrate 11 side. A wave (TE wave (S wave)) is attenuated, and a polarized wave (TM wave (P wave)) having an electric field component in a direction (X-axis direction) orthogonal to the longitudinal direction of the wire grid is transmitted.

  The constituent material of the reflective layer 14 is not particularly limited as long as it is a material having reflectivity with respect to light in the use band. For example, Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, A single metal such as Ge or Te, an alloy containing these, or a semiconductor material can be used. In addition to the metal material, for example, it may be composed of an inorganic film or a resin film other than a metal formed with high surface reflectance by coloring or the like.

The pitch, line width / pitch, thin film height (thickness, lattice depth), and thin film length (lattice length) of the reflective layer 22 are preferably in the following ranges, respectively.
0.05μm <pitch <0.8μm
0.1 <(line width / pitch) <0.9
0.01 μm <thin film height <1 μm
0.05μm <thin film length

Moreover, it is preferable to provide the protective film which coat | covers the surface of the transparent substrate 11 and a grid | lattice-shaped convex part in the range which the change of an optical characteristic does not have practical influence. For example, by depositing SiO ₂ or the like, reliability such as moisture resistance can be improved. As a method for forming the protective film, it is preferable to use plasma CVD (Chemical Vapor Deposition). By using plasma CVD, a protective film can be deposited also in the gaps between the lattice-shaped convex portions.

  According to the polarizing element 1 having such a configuration, a polarized wave (TE) having an electric field component parallel to the grating of the reflective layer is obtained by utilizing four actions of transmission, reflection, interference, and selective light absorption of the polarized wave. Wave (S wave)) can be attenuated, and a polarized wave (TM wave (P wave)) having an electric field component perpendicular to the grating can be transmitted. That is, the TE wave is attenuated by the selective light absorption action of the polarized wave of the absorption layer 12, and the TE wave transmitted through the absorption layer 12 and the dielectric layer 13 is reflected by the grid-like reflection layer 14 functioning as a wire grid. Is done. Here, by appropriately adjusting the thickness and refractive index of the dielectric layer 13, the TE wave reflected by the reflective layer 14 is partially reflected when passing through the absorbing layer 12 and returned to the reflective layer 14. In addition, the light that has passed through the absorption layer 12 can be attenuated by interference. A desired polarization characteristic can be obtained by selectively attenuating the TE wave as described above.

  Further, in the polarizing element 1 according to the present embodiment, since the absorption layer 12 that interferes and absorbs light is in contact with the transparent substrate 11, heat dissipation can be further improved, and heat resistance of the polarizing plate can be improved. it can. In addition, since the polarizing element 1 in the present embodiment is made of an inorganic material that is more durable than an organic material, the polarizing element 1 exhibits high light resistance against strong light used in a liquid crystal projector and obtains high reliability. be able to.

  As a specific configuration of the polarizing element 1 for obtaining high light resistance, quartz (about 10 W / (m · K) at 300 K) or sapphire (about 40 W / (m · K) having high thermal conductivity is used as the transparent substrate 11. ) at 300 K). Moreover, since the absorption layer 12 is in contact with the transparent substrate 11, it is preferable that the thermal conductivity of the material constituting the absorption layer 12 is higher than the thermal conductivity of the material constituting the transparent substrate 11. More specifically, Ta (about 60 W / (m · K) at 300 K), Al (about 235 W / (m · K) at 300 K) having a thermal conductivity of 50 W / (m · K) at 300 K or more. K), Ag (about 430 W / (m · K) at 300 K), Cu (about 400 W / (m · K) at 300 K), Au (about 315 W / (m · K) at 300 K), Mo ( 140W / (m · K) at 300K), Cr (about 95W / (m · K) at 300K), W (about 175W / (m · K) at 300K), Ni (about 90W / (m・ K) at 300 K), Fe (about 80 W / (m · K) at 300 K), Sn (about 65 W / (m · K) at 300 K), or Si materials (about 150 W / (m It is preferable to use a semiconductor material such as K) at 300 K), Ge (about 60 W / (m · K) at 300 K), ZnO (about 55 W / (m · K) at 300 K). For example, when the absorption layer 12 is composed of two layers of Ta and Si, it is preferable that Si having a higher thermal conductivity than Ta be on the transparent substrate 11 side. According to the polarizing element having such a configuration, the contact thermal resistance can be reduced at the interface between the transparent substrate 11 and the absorption layer 12, and excellent heat resistance can be obtained.

<2. Manufacturing method of polarizing element>
Next, the manufacturing method of the polarizing element in this Embodiment is demonstrated. First, the absorption layer 12, the dielectric layer 13, and the reflective layer 14 are formed in this order on the transparent substrate 11.

  The absorption layer 12 is formed by vapor deposition or sputtering. Specifically, the transparent substrate 11 is arranged to face the target during film formation, the argon gas particles are collided with the target, the target component blown off by the impact is attached on the substrate, and the absorption layer 12 is formed. obtain. Further, the absorption layer 12 may be formed by depositing inorganic fine particles by using an oblique film formation method by vapor deposition or sputtering utilizing the shadowing effect.

  The dielectric layer 13 and the reflective layer 14 are formed by a general vacuum film forming method such as a sputtering method, a vapor phase growth method, or a vapor deposition method, or a sol-gel method (for example, a method in which a sol is coated by spin coating and gelled by thermal curing. ).

On the reflective layer 14 thus formed, a lattice-like mask pattern is formed by nanoimprinting, photolithography, or the like, and then a lattice-like convex portion is formed by dry etching. Examples of the dry etching gas include Ar / O ₂ for the antireflection film (BARC), Cl ₂ / BCl _{3 for} AlSi, SiO ₂ , Si, and Ta for CF ₄ / Ar. Further, by optimizing the etching conditions (gas flow rate, gas pressure, power, substrate cooling temperature), a highly perpendicular lattice shape is realized. Further, the width (X-axis direction) of the absorption layer 12 can be adjusted depending on the etching conditions.

  When Al or AlSi is used for the reflective layer 14, it is desirable to select materials that can be etched with fluorine for the absorbing layer 12 and the dielectric layer 13. By doing so, a high etching selection ratio can be obtained, the width of the designed film thickness of the absorption layer 12 and the dielectric layer 13 can be widened, which is advantageous in process construction.

In addition, a protective film such as SiO ₂ can be deposited on the uppermost portion for the purpose of improving reliability such as moisture resistance, as long as the change in optical characteristics does not affect the application.

<3. Example of LCD projector configuration>
Next, a liquid crystal projector according to an embodiment of the present invention will be described. The liquid crystal projector 100 includes a lamp serving as a light source, a liquid crystal panel, and the polarizing element 1 described above.

  FIG. 2 shows a configuration example of the optical engine portion of the liquid crystal projector according to the present invention. The optical engine portion of the liquid crystal projector 100 includes an incident side polarizing element 10A for the red light LR, a liquid crystal panel 50, an outgoing pre-polarizing element 10B, an outgoing main polarizing element 10C, and an incident side polarizing element 10A for the green light LG, the liquid crystal panel 50, Outgoing pre-polarizing element 10B, outgoing main polarizing element 10C, incident side polarizing element 10A for blue light LB, liquid crystal panel 50, outgoing pre-polarizing element 10B, outgoing main polarizing element 10C, and outgoing main polarizing element 10C And a cross dichroic prism 60 for synthesizing the incoming light and emitting it to the projection lens. Here, the polarizing element 1 described above is applied to each of the incident side polarizing element 10A, the outgoing pre-polarizing element 10B, and the outgoing main polarizing element 10C, and the light in the use band from the light source is incident from the transparent substrate 11 side and allowed to pass therethrough. .

  In the liquid crystal projector 100, light emitted from a light source lamp (not shown) is separated into red light LR, green light LG, and blue light LB by a dichroic mirror (not shown), and incident side polarization elements corresponding to the respective lights. The light LR, LG, and LB incident on 10A and then polarized by the respective incident-side polarizing elements 10A are spatially modulated by the liquid crystal panel 50 and emitted, and pass through the outgoing pre-polarizing element 10B and the outgoing main polarizing element 10C. Thereafter, the image is synthesized by the cross dichroic prism 60 and projected from a projection lens (not shown). Even if the light source lamp has a high output, since the polarizing element 1 having excellent light resistance against strong light is used, a highly reliable liquid crystal projector can be realized.

  The polarizing element of the present invention is not limited to application to the liquid crystal projector, but is suitable as a polarizing element that receives heat as a use environment. For example, the present invention can be applied as a polarizing element for a car navigation system of an automobile or a liquid crystal display of an instrument panel.

<4. Example>
Examples of the present invention will be described below. Here, samples of a single layer structure (Ta, Si) and a two layer structure (Ta / Si) were prepared for the absorption layer 12 and evaluated for optical characteristics. The present invention is not limited to these examples.

[Example 1: Absorbing layer Ta]
As shown in FIG. 3A, first, Ta was formed as an absorption layer, SiO ₂ as a dielectric layer, and AlSi as a reflection layer on a quartz substrate. Further, an antireflection film (BARC) was formed on the reflective layer, and a lattice-like mask pattern was formed with a resist. In addition, an absorption layer, a dielectric layer, and a reflection layer were laminated in a direction parallel to the optical axis of the quartz crystal.

Next, as shown in FIG. 3B, the antireflection film was removed by scum treatment with Ar / O ₂ gas, and AlSi was etched with Cl ₂ / BCl ₃ . Thereafter, as shown in FIG. 3C, the corrosive layer (chlorinated compound) was removed by H ₂ O plasma, and the resist and the reflective protective film were removed by O ₂ ashing. Then, as shown in FIG. 3D, SiO ₂ , Ta, and quartz were etched with CF ₄ / Ar gas to form lattice-shaped convex portions, and the polarizing element of Example 1 was manufactured.

FIG. 4 is a schematic cross-sectional view showing the polarizing element of Example 1. This polarizing element has a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and a minimum reflectance in a green region (near 550 nm) that is practically important for liquid crystal display devices. The pitch is 150 nm, the grid width is 45 nm, the thickness of Ta is 20 nm, the thickness of SiO ₂ is 50 nm, and the thickness of AlSi is 45 nm.

  In FIG. 5, the optical characteristic of the polarizing element of Example 1 is shown. From the results shown in FIG. 5, it was found that the polarizing element using Ta as the absorption layer has a good contrast on the long wavelength side.

FIG. 6 shows an SEM (Scanning Electron Microscope) image of the cross section of the polarizing element of Example 1. From this cross-sectional photograph, it can be seen that the width of the absorption layer in the transmission axis direction is smaller than other layers (reflection layer, dielectric layer). This is due to the etching with CF ₄ / Ar gas, but the wavelength at which the absorption axis reflectivity Rs is minimum is set to the short wavelength side as will be described later because the width of the absorption layer is smaller than the other layers. Can be shifted.

  In the polarizing element of Example 1, the quartz substrate is dug by over-etching in order to expose the quartz substrate. However, the etching conditions may be changed so that the quartz substrate is not dug. In FIG. 7, the SEM image of the cross section of the polarizing element in which the quartz substrate is not dug is shown. There was no significant change in the optical characteristics of the polarizing element depending on whether or not the quartz substrate was dug by overetching.

[Example 2: Absorbing layer Si]
FIG. 8 is a schematic cross-sectional view showing the polarizing element of Example 2. This polarizing element has a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and a minimum reflectance in a green region (near 550 nm) that is practically important for liquid crystal display devices. The pitch was 150 nm, the grid width was 45 nm, the thickness of Si was 20 nm, the thickness of SiO ₂ was 30 nm, and the thickness of AlSi was 45 nm. In addition, the polarizing element of Example 2 was produced like Example 1 except having made the absorption layer into Si.

  In FIG. 9, the optical characteristic of the polarizing element of Example 2 is shown. From the results shown in FIG. 9, it was found that the polarizing element using Si as the absorption layer has a good contrast on the short wavelength side.

[Example 3: Absorbing layer Ta / Si]
FIG. 10 is a schematic cross-sectional view showing the polarizing element of Example 3. This polarizing element has a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and a minimum reflectance in a green region (near 550 nm) that is practically important for liquid crystal display devices. The pitch is 150 nm, the grid width is 45 nm, the thickness of Ta is 10 nm, the thickness of Si is 10 nm, the thickness of SiO ₂ is 30 nm, and the thickness of AlSi is 45 nm. In addition, the polarizing element of Example 3 was produced like Example 1 except having made the absorption layer into 2 layer structure of Ta and Si.

  In FIG. 11, the optical characteristic of the polarizing element of Example 3 is shown. From the results shown in FIG. 11, it was found that the polarizing element in which Ta and Si were laminated as the absorption layer had both the good contrast on the long wavelength side of Example 1 and the good contrast on the short wavelength side of Example 2. .

[Characteristics of Green Area of Polarizing Elements of Examples 1 to 3]
Table 1 shows the average values of the transmittance and the reflectance when the measurement wavelength is 520 to 590 nm in the green region for the polarizing elements of Examples 1 to 3.

With respect to a polarizing element capable of obtaining an equivalent contrast, ideal characteristics are high transmission axis transmittance and low reflectance, but when looking at the characteristics of Examples 1 and 2, Example 1 is advantageous. As a disadvantage, the transmittance was low. On the other hand, Example 2 had high transmittance as an advantage but high reflectance as a disadvantage. On the other hand, in Example 3, an ideal characteristic that the transmission axis transmittance is high and the reflectance is low was obtained. In Example 3, the wavelength selectivity of the absorption axis reflectivity is strong, but it is possible to control the wavelength band of low reflection by adjusting the Si film thickness or the SiO ₂ film thickness.

[Example 4: Absorption axis transmittance with respect to grid width]
Next, the grid width in the polarizing element was changed, and the absorption axis transmittance was measured. FIG. 12 shows the relationship of the absorption axis transmittance with respect to the grid width. In addition, absorptivity transmittance | permeability is an average value when the green wavelength of 520-590 nm is made into a measurement wavelength. The pitch of the convex portions of the polarizing element was 150 nm, the thickness of the absorption layer (Ta, Si, Ta / Si) was 20 nm, the thickness of SiO ₂ was 30 nm, and the thickness of AlSi was 45 nm.

  From the results shown in FIG. 12, it was found that the polarizing element in which Ta and Si are stacked as the absorbing layer can reduce the absorption axis transmittance to the same level as the polarizing element having a single Si layer. It was also found that the absorption axis transmittance can be controlled by the grid width.

[Example 5: Optical characteristics with respect to stacking order of absorbing layers]
As shown in FIG. 13, a polarizing element in which Ta and Si are laminated in this order (lamination order A) on a quartz substrate, and Si and Ta are laminated in this order on a quartz substrate (lamination order B) as shown in FIG. ) Was produced. 15 and 16 show SEM images of cross sections of polarizing elements in the stacking order A and the stacking order B, respectively.

These polarizing elements have a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and the lowest reflectance in the green region (near 550 nm) that is practically important for liquid crystal display devices. The pitch is 150 nm, the grid width is 45 nm, the thickness of Ta is 5 nm, the thickness of Si is 20 nm, the thickness of SiO ₂ is 30 nm, and the thickness of AlSi is 35 nm. A polarizing element having a stacking order of A and B was produced in the same manner as in Example 1 except that the absorption layer had a two-layer structure of Ta and Si.

  17 and 18 show optical characteristics of polarizing elements in the stacking order A and the stacking order B, respectively. Table 2 shows the transmittance and reflection of polarizing elements of stacking order A and stacking order B when the measurement wavelength is 430 to 510 nm in the blue region, 520 to 590 nm in the green region, and 600 to 680 nm in the red region. The average value of the rate is shown.

  From the results shown in Table 2, it was found that the polarizing element in which Ta and Si were stacked as the absorption layer had a low reflectance in the green range (520 to 590 nm) in both the stacking orders A and B, and good contrast was obtained.

  FIGS. 19 and 20 are graphs plotting the transmittance and the reflectance on the transmission axis and the absorption axis when the measurement wavelength is 520 to 590 nm in the green region. In these results, although there was no difference in reflectance in both the stacking order A and the stacking order B, it was found that the stacking order B was better than the stacking order A in terms of transmittance.

[Example 6: Optical characteristics with respect to width of absorbing layer]
Next, as shown in FIG. 21, the width W of the absorption layer was changed, and the influence on the optical characteristics was evaluated. First, the optical characteristics of a polarizing element having a width W of 40.0 nm, 37.5 nm, 30.0 nm, and 22.5 nm were calculated using simulation software (manufactured by GSD, Gsolver). The model of the polarizing element is that the pitch is 150 nm, the grid width is 45 nm, the thickness of Ta is 5 nm, the thickness of Si is 20 nm, the thickness of SiO ₂ is 30 nm, and the thickness of AlSi is 35 nm. The thing of the lamination order B which laminated | stacked was used.

  22 to 25 show simulation results of the transmission axis transmittance Tp, the transmission axis reflectance Rp, the absorption axis transmittance Ts, and the absorption axis reflectance Rs. In the transmission axis shown in FIG. 22 and FIG. 23, a large difference due to the difference in the width W of the absorption layer was not observed. On the other hand, in the absorption axis shown in FIGS. 24 and 25, it was found that the transmittance Ts increases as the width W decreases, and the wavelength at which the reflectance Rs is minimum shifts to the short wavelength side.

In addition, polarizing elements having different absorption layer widths W were produced, and the above-described simulation results were verified. The width W (side etching amount) of the absorption layer was adjusted by the etching time in etching with CF ₄ / Ar gas. The polarizing element (width W = 46.6 nm) in the stacking order B shown in FIG.

FIG. 26 shows an SEM image of a cross section of the polarizing element in which the width W of the absorption layer is smaller than the grid width. In this polarizing element, the width W of the absorption layer was 41.0 nm. This was designated as Sample B. In addition, this polarizing element has a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and a minimum reflectance in a green region (near 550 nm) which is practically important for liquid crystal display devices. The pitch is 150 nm, the grid width is 45 nm, the thickness of Ta is 5 nm, the thickness of Si is 20 nm, the thickness of SiO ₂ is 30 nm, and the thickness of AlSi is 35 nm. A polarizing element having a stacking order B was produced in the same manner as in Example 1 except that the absorption layer had a two-layer structure of Ta and Si.

  27 to 30 show the measurement results of the transmission axis transmittance Tp, the transmission axis reflectance Rp, the absorption axis transmittance Ts, and the absorption axis reflectance Rs. In the transmission axis shown in FIGS. 27 and 28, as in the simulation, a large difference due to the difference in the width W of the absorption layer was not observed. On the other hand, in the absorption axis shown in FIG. 29 and FIG. 30, as in the simulation, the transmittance Ts increases as the width W decreases, and the wavelength at which the reflectance Rs is minimized shifts to the short wavelength side. Compared to that, it turned out to be a big shift. Therefore, it was found that a polarizing element having a low reflectance in the blue region (430 to 510 nm) can be obtained by reducing the width W of the absorption layer.

  Table 3 shows the transmittance and reflectance of the polarizing elements of Sample A and Sample B when the measurement wavelengths are 430 to 510 nm in the blue region, 520 to 590 nm in the green region, and 600 to 680 nm in the red region. Average values are shown.

  From the results shown in Table 3, it was found that Sample B having a small width of the absorption layer had high transmittance. Moreover, it turned out that the sample B shows the favorable absorption-axis reflectance Rs in the short wavelength blue region (430-510 nm).

[Example 7: Formation of protective film]
As shown in FIG. 31, for the purpose of improving reliability such as moisture resistance, a protective film made of SiO ₂ was formed so as to cover the lattice shape. The thickness of the protective film was 7.5 nm, and it was confirmed that the protective film was also formed in the gaps between the lattice-shaped convex portions. This polarizing element has a contrast (extinction ratio: transmission axis transmittance / absorption axis transmittance) of about 2 to 10 and a minimum reflectance in a green region (near 550 nm) that is practically important for liquid crystal display devices. The pitch is 150 nm, the grid width including the protective film is 65 nm, the thickness of Ta is 5 nm, the thickness of Si is 20 nm, the thickness of SiO ₂ is 30 nm, and the thickness of AlSi is 35 nm. Further, as for the shape of the convex portion, the width of the Ta / Si layer was narrowed by etching with CF ₄ / Ar gas as compared with other layers, and the quartz substrate was also dug by 5 nm. That is, this polarizing element is manufactured in the same manner as the polarizing element in the stacking order A shown in FIG. 13, and a protective film is further formed. As a method for forming the protective film, plasma CVD (Chemical Vapor Deposition) was used in order to improve the coverage, and TEOS (Tetra Ethyl Ortho Silicate) and O ₂ were used as the source gas.

FIG. 32 is an SEM image of a cross section of the polarizing element on which the protective film is formed. From this cross-sectional photograph, it was confirmed that the width of the absorption layer in the transmission axis direction was smaller than the other layers (reflection layer, dielectric layer). In this cross-sectional photograph, the boundary between the laminated convex part and the protective film is not clear, but the length from the AlSi / SiO ₂ interface to the convex vertex (the thickness obtained by adding AlSi and the protective film) was measured. It was 42 nm. From this, it can be estimated that 7 nm obtained by subtracting 35 nm of the AlSi film thickness design value is the protective film thickness.

FIG. 33 and FIG. 34 are graphs showing the transmittance and the reflectance of the polarizing element on which the protective film is formed, respectively. For the polarizing element after etching with CF ₄ / Ar gas and the polarizing element after forming the protective film by plasma CVD, the transmission axis transmittance, the absorption axis transmittance, the transmission axis reflectance, and the absorption axis reflectance are respectively set. Measured (n = 36).

The average value (n = 36) of the change amount between the polarizing element after etching with CF ₄ / Ar gas and the polarizing element after forming the protective film by plasma CVD has a transmission axis transmittance of −0.1%. The absorption axis transmittance was + 3.4%, the transmission axis reflectance was ± 0.0%, and the absorption axis reflectance was + 0.5%. In the polarizing element according to the present embodiment, since light is incident from the quartz substrate side, there is almost no change in reflectance and the change in transmittance is small. The same result was obtained when a protective film was formed on the polarizing element in the stacking order B shown in FIG.

  DESCRIPTION OF SYMBOLS 1 Polarizing element, 11 Transparent substrate, 12 Absorbing layer, 13 Dielectric layer, 14 Reflecting layer, 50 Liquid crystal panel, 60 Cross dichroic prism, 100 Liquid crystal projector

Claims (11)

A transparent substrate;
An absorption layer comprising lattice-shaped convex portions arranged on the transparent substrate at a pitch smaller than the wavelength of light in the use band; and
A dielectric layer formed on the absorption layer and constituting the lattice-shaped convex portions;
A reflective layer formed on the dielectric layer and constituting the lattice-shaped convex portion, and
The absorbing layer is composed of two or more layers, and any one of them has a higher refractive index than the transparent substrate.   The polarizing element of Claim 1 provided with the protective film which coat | covers the surface of the said transparent substrate and the said grid | lattice-like convex part.   The polarizing element according to claim 2, wherein the protective film is formed by plasma CVD (Chemical Vapor Deposition).   The polarizing element according to claim 1, wherein the absorption layer is made of at least one of a metal and a semiconductor material.   5. The polarizing element according to claim 1, wherein a thermal conductivity of a material constituting the absorption layer is higher than a thermal conductivity of a material constituting the transparent substrate.   The polarizing element according to claim 1, wherein the absorption layer includes two layers of Ta and Si.   The polarizing element according to claim 6, wherein Si is formed on the transparent substrate.   The polarizing element according to claim 1, wherein a width of the absorption layer in a transmission axis direction is 50% or more of a width of the dielectric layer.   The polarizing element according to claim 1, wherein the transparent substrate is made of quartz or sapphire.   The polarizing element according to any one of claims 1 to 9, wherein the transparent substrate is made of quartz, and lattice-like convex portions are arranged in a direction parallel or perpendicular to the optical axis of the quartz. A polarizing element according to any one of claims 1 to 10, a light source, and an image display panel,
The polarizing element is a liquid crystal projector that allows light in a use band from the light source to enter from a transparent substrate side and pass through.