Polarizing plate, method for manufacturing the same, and optical apparatus

Abstract

A polarizing plate (1) having a wire grid structure, which has a transparent substrate (10) and a lattice-shaped convex portion (11) arranged on the transparent substrate (10) at a pitch shorter than the wavelength of light in a used wavelength band and extending in a predetermined direction, the lattice-shaped convex portion (11) having, in order from the transparent substrate (10) side, a reflection layer (13), a dielectric layer (14), and an absorption layer (15), the width (b) of the reflection layer (13) being smaller than either of the width of the dielectric layer (14) and the width (grid width (a)) of the absorption layer (15). Thus, a polarizing plate in which the wavelength dispersion of the absorption axis reflectance can be more accurately controlled can be provided.

Description

[0001] This invention patent application is a divisional application of the invention patent application with national application number 201980011250.6 (international application number PCT / JP2019 / 005144) entitled "Polarizing plate and manufacturing method thereof, and optical device". Technical Field

[0002] This invention relates to polarizing plates, methods for manufacturing the same, and optical devices. Background Technology

[0003] A polarizing plate is an optical element that absorbs polarized light along the absorption axis and transmits polarized light along the transmission axis, which is orthogonal to the absorption axis. In recent years, inorganic polarizing plates of the wire grid type have begun to replace organic polarizing plates in optical devices such as liquid crystal projectors that require heat resistance.

[0004] The inorganic polarizing plate is composed of a reflective layer, a dielectric layer, and an absorption layer sequentially from the transparent substrate side. In addition, these inorganic layers are formed by physical film deposition methods, and a grid-type polarizer pattern is formed by photogravure etching techniques.

[0005] However, for LCD projectors, depending on the manufacturer, the light source spectrum sometimes differs, and sometimes the wavelengths of the various channels that constitute the visible light range of 3LCD (Liquid Crystal Display) also differ. Therefore, a polarizing plate with optimal optical characteristics that conforms to the channel wavelengths of each manufacturer is required.

[0006] The absorption axis reflectivity characteristic of a polarizer is generally controlled in the visible light range by adjusting the thickness of the dielectric layer and the absorption layer and suppressing wavelength dispersion of the absorption axis reflectivity characteristic. In this case, adjusting the thickness of the dielectric layer and the absorption layer to minimize the absorption axis reflectivity within the desired channel wavelength range is a dedicated optical design.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-80230 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The inorganic layers constituting an inorganic polarizer are generally designed as rectangular cross-sections with uniform width, and are formed using the aforementioned physical etching technique. Furthermore, the absorption layer at the front end of the polarizer is continuously etched through physical etching, and its thickness and volume vary depending on deviations in the vacuum level and gas pressure control of the etching apparatus. As a result, the wavelength range with the lowest absorption axis reflectivity also varies, making it difficult to obtain absorption axis reflectivity characteristics optimal for the channel wavelength range of each manufacturer.

[0012] The present invention was made in view of the above, and its object is to provide a polarizing plate that can more accurately control the wavelength dispersion of the absorption axis reflectivity.

[0013] Solution for solving the problem

[0014] To achieve the above objectives, the present invention provides a polarizing plate (e.g., polarizing plate 1 described later) having a wire grid structure. The polarizing plate comprises: a transparent substrate (e.g., transparent substrate 10 described later); and lattice-shaped protrusions (e.g., lattice-shaped protrusions 11 described later), which are arranged on the transparent substrate at a spacing shorter than the wavelength of the light used in the band of light and extend in a predetermined direction. The lattice-shaped protrusions, from the transparent substrate side, sequentially have a reflective layer (e.g., reflective layer 13 described later), a dielectric layer (e.g., dielectric layer 14 described later), and an absorption layer (e.g., absorption layer 15 described later). The maximum width of the reflective layer (e.g., width b of the reflective layer described later) is smaller than either the maximum width of the dielectric layer (e.g., width b of the reflective layer described later) or the maximum width of the absorption layer (e.g., grid width a described later).

[0015] Alternatively, the maximum width of the dielectric layer and the maximum width of the absorption layer may be approximately the same.

[0016] Alternatively, the thickness of the dielectric layer can be 1~50nm.

[0017] Alternatively, the thickness of the absorption layer can be 10~50nm.

[0018] Alternatively, the aforementioned transparent substrate may be transparent to the wavelength of light in the band of use and may be made of glass, crystal, or sapphire.

[0019] Alternatively, the reflective layer may be made of aluminum or an aluminum alloy.

[0020] Alternatively, the dielectric layer described above may be composed of Si oxide.

[0021] Alternatively, the absorption layer may consist of Fe or Ta and may also include Si.

[0022] Alternatively, the surface of the polarizing plate on which light is incident may be covered by a protective film made of dielectric (e.g., dielectric protective film 20 described later).

[0023] Alternatively, the surface of the polarizing plate onto which the light is incident may be covered with an organic waterproof membrane.

[0024] In addition, the present invention provides a method for manufacturing a polarizing plate having a wire grid structure. The method for manufacturing the polarizing plate includes: a reflective layer forming step for forming a reflective layer on a transparent substrate; a dielectric layer forming step for forming a dielectric layer on the reflective layer; an absorber layer forming step for forming an absorber layer on the dielectric layer; and an etching step, wherein the etching step selectively etches the formed laminate to form a grid-like protrusion arranged on the transparent substrate at a spacing shorter than the wavelength of the light used in the band of light and extending in a predetermined direction. In the etching step, the maximum width of the reflective layer is made smaller than the maximum width of the dielectric layer and the maximum width of the absorber layer.

[0025] Alternatively, in the above etching process, the maximum width of the reflective layer can be adjusted to minimize the absorption axis reflectivity of the light in the wavelength range of the used band.

[0026] In addition, the present invention provides an optical device having any of the above-mentioned polarizing plates.

[0027] The effects of the invention

[0028] According to the present invention, a polarizing plate is provided that allows for more accurate control of wavelength dispersion of the absorption axis reflectivity. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of a polarizing plate according to one embodiment of the present invention.

[0030] Figure 2 This is a graph showing the optical characteristics of the polarizer of Example 1, where the width of the reflective layer is 88% of the grid width.

[0031] Figure 3 This is a graph showing the optical characteristics of the polarizer in Example 2, where the width of the reflective layer is 56% of the grid width.

[0032] Figure 4 This is a graph showing the optical characteristics of the polarizer in Comparative Example 1, where the width of the reflective layer is the same as the width of the grid. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] [Polarizing plate]

[0035] One embodiment of the polarizing plate of the present invention is an inorganic polarizing plate having a wire grid structure, comprising: a transparent substrate; and lattice-shaped protrusions arranged on the transparent substrate at a spacing (period) shorter than the wavelength of the light in the used band, and extending in a predetermined direction. Furthermore, the lattice-shaped protrusions sequentially comprise a reflective layer, a dielectric layer, and an absorbent layer from the transparent substrate side.

[0036] Figure 1 This is a cross-sectional schematic diagram showing a polarizing plate 1 according to one embodiment of the present invention. Figure 1 As shown, the polarizing plate 1 includes a transparent substrate 10 that is transparent to light of the operating wavelength and a grid-like protrusion 11 arranged on one side of the transparent substrate 10 at a spacing shorter than the wavelength of the light of the operating wavelength. From the transparent substrate 10 side, the grid-like protrusion 11 sequentially includes a platform 12, a reflective layer 13, a dielectric layer 14, an absorption layer 15, and a dielectric layer 16. That is, the polarizing plate 1 has the following wire grid structure: the grid-like protrusion 11 formed by sequentially stacking the platform 12, reflective layer 13, dielectric layer 14, absorption layer 15, and dielectric layer 16 from the transparent substrate 10 side is arranged in a one-dimensional grid pattern on the transparent substrate 10.

[0037] Here, as Figure 1 As shown, the direction in which the lattice-shaped protrusions 11 extend (a predetermined direction) is called the Y-axis direction. Furthermore, the direction in which the lattice-shaped protrusions 11 are arranged orthogonal to the Y-axis direction along the main surface of the transparent substrate 10 is called the X-axis direction. In this case, light incident on the polarizing plate 1 on the side of the transparent substrate 10 where the lattice-shaped protrusions 11 are formed is preferably incident from a direction orthogonal to both the X-axis and Y-axis directions.

[0038] The polarizing plate 1 utilizes four mechanisms—transmission, reflection, interference, and selective light absorption of polarized waves based on optical anisotropy—to attenuate polarized waves with an electric field component parallel to the Y-axis (TE waves (S waves)) and transmit polarized waves with an electric field component parallel to the X-axis (TM waves (P waves)). Therefore, the Y-axis is the absorption axis of the polarizing plate 1, and the X-axis is the transmission axis of the polarizing plate 1.

[0039] Light incident from the side of the polarizer 1 with its grid-like protrusions 11 is partially absorbed and attenuated as it passes through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14. The polarized light waves (TM waves (P waves)) in the light that have passed through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14 are transmitted through the reflective layer 13 with high transmittance. On the other hand, the polarized light waves (TE waves (S waves)) in the light that have passed through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14 are reflected by the reflective layer 13. The TE waves reflected from the reflective layer 13 are partially absorbed and partially reflected back to the reflective layer 13 as they pass through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14. Furthermore, the TE waves reflected from the reflective layer 13 are attenuated by interference as they pass through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14. As described above, by selectively attenuating the TE waves, the polarizer 1 can obtain the desired polarization characteristics.

[0040] like Figure 1 As shown, when viewed from the direction in which each one-dimensional lattice extends (hereinafter, the predetermined direction), that is, in a cross-section orthogonal to the predetermined direction, the lattice-shaped protrusion 11 has a rectangular pedestal 12, a rectangular lattice foot 17, and a rectangular lattice front end 18. However, the shapes of these pedestals 12, lattice foot 17, and lattice front end 18 are not limited to rectangular shapes and can be arbitrary shapes. For example, the corners of the lattice front end 18 of the lattice-shaped protrusion 11 can be rounded or conical by etching.

[0041] The grid foot 17 extends vertically from the base 12. The grid foot 17 is formed by a reflective layer 13. That is, the boundary between the grid foot 17 and the front end 18 of the grid is located at the boundary between the reflective layer 13 and the dielectric layer 14.

[0042] like Figure 1 As shown, the front end portion 18 of the grid in this embodiment has a rectangular shape when viewed from a predetermined direction. The front end portion 18 of the grid is composed of a dielectric layer 14, an absorption layer 15, and a dielectric layer 16.

[0043] However, dielectric layer 16 is not necessary, and the front end of the grid 18 can also be composed of dielectric layer 14 and absorption layer 15.

[0044] In the following description, the height direction refers to the direction perpendicular to the main surface of the transparent substrate 10, and the width refers to the dimension in the X-axis direction orthogonal to the height direction when viewed from the Y-axis direction along the direction extending along the lattice protrusions 11. Furthermore, when viewing the polarizing plate 1 from the Y-axis direction along the direction extending along the lattice protrusions 11, the repeating interval of the lattice protrusions 11 in the X-axis direction is referred to as the spacing P.

[0045] The spacing P of the lattice-shaped protrusions 11 is not particularly limited as long as it is shorter than the wavelength of the light used in the band. From the viewpoint of ease of manufacture and stability, the spacing P of the lattice-shaped protrusions 11 is preferably, for example, 100 nm to 200 nm. This spacing P of the lattice-shaped protrusions 11 can be measured by observation using a scanning electron microscope or a transmission electron microscope. For example, the spacing P can be measured at any four locations using a scanning electron microscope or a transmission electron microscope, and the arithmetic mean of these measurements can be taken as the spacing P of the lattice-shaped protrusions 11. Hereinafter, this measurement method will be referred to as the electron microscopy method.

[0046] In addition, such as Figure 1 As shown, the width of the grid front end portion 18 of the lattice-shaped protrusion 11 in the X-axis direction is called the grid width a. The grid width a is the same as the width of the dielectric layer 14, the absorber layer 15, and the dielectric layer 16 in the X-axis direction. Specifically, the grid width a is preferably 35~45 nm. Furthermore, the grid width a can be measured, for example, by the electron microscopy method described above.

[0047] In this invention, when the shape of the reflective layer 13 constituting the grid foot 17, the shapes of the dielectric layer 14, the absorber layer 15, and the dielectric layer 16 constituting the grid front end 18, and the shape of the pedestal 12 (described later) are not rectangular and their width varies in the height direction, the width of each layer in the X-axis direction refers to the maximum width of each layer in the X-axis direction. In this case, the aforementioned grid width 'a' refers to the maximum width of the grid front end 18 in the X-axis direction.

[0048] Furthermore, especially regarding the shape of the dielectric layer 14 and the absorption layer 15, compared to a rectangular shape that satisfies the desired optical characteristics, any shape that can satisfy the aforementioned optical characteristics with a smaller volume is acceptable.

[0049] As for the transparent substrate 10, there are no particular limitations as long as it is a substrate that indicates light transmittance in the wavelength range in which it is used, and it can be appropriately selected according to the purpose. "Indicating light transmittance in the wavelength range in which it is used" does not mean that the transmittance of the light in the wavelength range in which it is used is 100%, as long as it exhibits light transmittance that can maintain its function as a polarizing plate. For example, visible light with wavelengths of around 380nm to 810nm can be listed as the wavelength range in the wavelength range of used light.

[0050] The shape of the main surface of the transparent substrate 10 is not particularly limited, and the shape can be appropriately selected according to the purpose (e.g., rectangular). The average thickness of the transparent substrate 10 is preferably, for example, 0.3 mm to 1 mm.

[0051] As the constituent material of the transparent substrate 10, a material with a refractive index of 1.1 to 2.2 is preferred, such as glass, crystal, and sapphire. From the viewpoint of cost and light transmittance, glass, especially quartz glass (refractive index 1.46) and sodium silicate glass (refractive index 1.51), is preferred. The composition of the glass material is not particularly limited; for example, low-cost glass materials such as silicate glass, which are widely used as optical glass, can be used.

[0052] Furthermore, from the viewpoint of thermal conductivity, crystal and sapphire, which have high thermal conductivity, are preferred. This results in high light resistance under strong light, making them ideal for use as polarizing plates in the optical engines of projectors that generate a lot of heat.

[0053] Furthermore, when using a transparent substrate made of optically active crystals such as crystal, it is preferable to arrange the lattice-shaped protrusions 11 in a direction parallel or perpendicular to the optical axis of the crystal. This results in excellent optical properties. Here, the optical axis refers to the axis along which the difference in refractive index between the O (normal ray) and E (abnormal ray) of light traveling in its direction is minimized.

[0054] The shape of the transparent substrate 10 is not particularly limited; for example, it can be a wafer shape of φ6 inches or φ8 inches. When the transparent substrate 10 is set to a wafer shape, a polarizing plate 1 of a rectangular shape can be obtained by cutting out arbitrary sizes using a scribing device or the like after forming the grid-like protrusions 11.

[0055] like Figure 1 As shown, the pedestal 12 of this embodiment is rectangular when viewed from the direction extending from each one-dimensional lattice (a predetermined direction), that is, in a cross-sectional view orthogonal to the predetermined direction.

[0056] The width of the pedestal 12 in the X-axis direction is preferably greater than or equal to the width of the reflective layer 13. Furthermore, these widths can be measured, for example, by the electron microscopy method described above.

[0057] The film thickness of the stage 12 is not particularly limited, but is preferably 10 nm to 100 nm. Furthermore, the film thickness of the stage 12 can be measured, for example, by the electron microscopy method described above.

[0058] The pedestal 12 is formed by arranging a dielectric film, which extends in a strip shape along the Y-axis direction, which serves as the absorption axis, on the transparent substrate 10. The constituent material of the pedestal 12 is limited to a material that is transparent to light with respect to the wavelength used and has a smaller refractive index than the transparent substrate 10, wherein Si oxide such as SiO2 is preferred.

[0059] The pedestal 12 can be formed, for example, by varying the balance between isotropic and anisotropic etching based on dry etching in stages over the base layer 19, which is composed of the dielectric material formed on the transparent substrate 10. In this case, such as Figure 1 As shown, the pedestal 12 is disposed on the base layer 19 formed on the transparent substrate 10.

[0060] The reflective layer 13 is formed on the pedestal 12 and is arranged by means of strip-shaped metal films extending along the Y-axis, which is the absorption axis. More specifically, as... Figure 1 As shown, the reflective layer 13 of this embodiment extends vertically from the pedestal 12 and is rectangular when viewed from the predetermined direction, that is, in a cross-sectional view orthogonal to the predetermined direction. The reflective layer 13 functions as a wire grid polarizer, attenuating polarized light waves (TE waves (S waves)) with an electric field component in a direction parallel to the long side direction of the reflective layer 13, and transmitting polarized light waves (TM waves (P waves)) with an electric field component in a direction orthogonal to the long side direction of the reflective layer 13.

[0061] The material constituting the reflective layer 13 is not particularly limited as long as it is reflective of light in the band of use. Examples include individual elements such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, and Te, or alloys containing one or more of these elements. Preferably, the reflective layer 13 is made of aluminum or an aluminum alloy. Furthermore, in addition to these metallic materials, the reflective layer 13 can also be made of inorganic films or resin films other than metals, which have high surface reflectivity achieved through coloring or other methods.

[0062] The thickness of the reflective layer 13 is not particularly limited, but is preferably 100 nm to 300 nm. Furthermore, the thickness of the reflective layer 13 can be measured, for example, by the electron microscopy method described above.

[0063] The width b of the reflective layer 13 in the X-axis direction is preferably less than or equal to the width of the pedestal 12. Furthermore, the width b of the reflective layer 13 is designed to be smaller than the grid width a (the width of the dielectric layer 14 and the width of the absorption layer 15). Additionally, the width b of the reflective layer 13 can be measured, for example, by the electron microscopy method described above.

[0064] As a method to make the width b of the reflective layer 13 smaller than the width of the pedestal 12 and the grid width a, as described in detail later, examples include isotropic etching based on wet etching or additional processing of wet etching. As mentioned above, the reflective layer 13 reflects light, but by controlling the width b of the reflective layer 13, the area of ​​the reflective layer 13 as observed from the incident direction of light can be changed, thus changing the amount of light reflected by the reflective layer 13. Therefore, by controlling the ratio of the width b of the reflective layer 13 to the grid width a, the light transmission characteristics of the polarizing plate 1 can be controlled.

[0065] In addition, by making the width b of the reflective layer 13 smaller than the grid width a (the width of the dielectric layer 14 and the width of the absorption layer 15), the wavelength of the absorption axis reflectivity Rs can be dispersed to the longer wavelength side.

[0066] Here, the absorption axis reflectivity Rs is the reflectivity of polarized light incident on the polarizer 1 along the absorption axis (Y-axis direction). This absorption axis reflectivity Rs has the characteristic of being the lowest in the wavelength range within the visible light range. That is, the curve obtained by plotting the absorption axis reflectivity Rs relative to wavelength has a very small downward convex peak (see below). Figures 2-4 ).

[0067] That is, in this embodiment, by making the width b of the reflective layer 13 smaller than the grid width a (the width of the dielectric layer 14 and the width of the absorption layer 15), the wavelength range with the lowest absorption axis reflectivity Rs can be shifted to the longer wavelength side, and the absorption axis reflectivity Rs of the polarizing plate 1 can be accurately controlled.

[0068] A dielectric layer 14 is formed on the reflective layer 13 and is arranged by means of dielectric films extending in a strip shape along the Y-axis direction, which is the absorption axis. The dielectric layer 14 is formed with a film thickness that is half a wavelength off-phase with respect to the polarized light reflected from the absorption layer 15 and transmitted through the absorption layer 15 and reflected from the reflective layer 13. Specifically, the film thickness of the dielectric layer 14 is appropriately set within a range of 1 to 500 nm, which allows for adjustment of the phase of the polarized light and improvement of the interference effect. A more preferred film thickness range is 1 to 50 nm. The film thickness of the dielectric layer 14 can be measured, for example, by the electron microscopy method described above.

[0069] Materials constituting the dielectric layer 14 may include Si oxides such as SiO2, metal oxides such as Al2O3, beryllium oxide, bismuth oxide, MgF2, cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, carbon, or combinations thereof. The dielectric layer 14 is preferably composed of Si oxides.

[0070] The refractive index of the dielectric layer 14 is preferably greater than 1.0 and less than 2.5. Since the optical properties of the reflective layer 13 are also affected by the surrounding refractive index, the polarizer characteristics can be controlled by selecting the material of the dielectric layer 14.

[0071] Furthermore, by appropriately adjusting the thickness and refractive index of the dielectric layer 14, a portion of the TE wave reflected from the reflective layer 13 can be reflected back to the reflective layer 13 when it passes through the absorption layer 15, and the light passing through the absorption layer 15 will be attenuated due to interference. In this way, by selectively attenuating the TE wave, the desired polarization characteristics can be obtained.

[0072] An absorption layer 15 is formed on the dielectric layer 14 and is arranged in a strip-like configuration extending along the Y-axis, which serves as the absorption axis. As a constituent material of the absorption layer 15, one or more substances with non-zero extinction constants and light absorption properties, such as metallic materials and semiconductor materials, can be included, and the material is appropriately selected according to the wavelength range of the light being applied. As metallic materials, single elements such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, and Sn, or alloys containing one or more of these elements, can be included. Furthermore, as semiconductor materials, Si, Ge, Te, ZnO, and silicide materials (β-FeSi2, MgSi2, NiSi2, BaSi2, CrSi2, CoSi2, TaSi, etc.) can be included. By using these materials, the polarizer 1 can achieve a high extinction ratio relative to the applied visible light range. Preferably, the absorption layer 15 contains Fe or Ta and is composed of Si.

[0073] When a semiconductor material is used as the absorption layer 15, the band gap energy of the semiconductor is related to the absorption effect, so a band gap energy below the operating wavelength is required. For example, when used in visible light, a material with a band gap of 3.1 eV or less is required as the absorption wavelength above 400 nm.

[0074] The thickness of the absorber layer 15 is not particularly limited; for example, it is preferably 10 nm to 100 nm. A more preferred thickness range is 10 to 50 nm. The thickness of the absorber layer 15 can be measured, for example, by the electron microscopy method described above.

[0075] Furthermore, the absorber layer 15 can be formed into a high-density film by vapor deposition or sputtering. Alternatively, the absorber layer 15 can also be composed of two or more layers made of different materials.

[0076] The dielectric layer 16 is composed of a dielectric film. The dielectric layer 16 can be formed into a high-density film by vapor deposition or sputtering, similar to the absorber layer 15.

[0077] The polarizing plate 1 of this embodiment, which has the above structure, may also have a diffusion barrier layer between the dielectric layer 14 and the absorption layer 15. That is, in this case, the lattice-shaped protrusions 11 sequentially include a platform 12, a reflective layer 13, a dielectric layer 14, a diffusion barrier layer, an absorption layer 15, and a dielectric layer 16 from the transparent substrate 10 side. By having a diffusion barrier layer, the diffusion of light from the absorption layer 15 can be prevented. This diffusion barrier layer is composed of a metal film such as Ta, W, Nb, or Ti.

[0078] In addition, such as Figure 1As shown, in this embodiment, the polarizing plate 1 may also have its light incident side surface covered by a dielectric protective film 20. The dielectric protective film 20 may be formed, for example, on the surface of the polarizing plate 1 (the surface where the wire grid is formed) by using CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition). This can suppress excessive oxidation of the metal film.

[0079] Furthermore, in this embodiment, the polarizing plate 1 may also have its light incident side surface covered by an organic waterproof membrane (not shown). The organic waterproof membrane can be formed, for example, using the aforementioned CVD or ALD methods. This improves the reliability of the polarizing plate 1, such as its moisture resistance.

[0080] Furthermore, the thickness of the dielectric protective film 20 and the organic waterproof film is very small compared to the thickness of the reflective layer 13, the dielectric layer 14, the absorbing layer 15, etc. Therefore, when the dielectric protective film 20 and the organic waterproof film are provided, the grid width a mentioned above does not include the thickness of these dielectric protective films 20 and the thickness of the organic waterproof film.

[0081] [Manufacturing method of polarizing plate]

[0082] The manufacturing method of the polarizing plate 1 in this embodiment includes a base layer forming process, a reflective layer forming process, a dielectric layer forming process, an absorber layer forming process, and an etching process.

[0083] In the substrate formation process, a substrate is formed on the transparent substrate 10. In the reflective layer formation process, a reflective layer is formed on the substrate formed in the substrate formation process. In the dielectric layer formation process, a dielectric layer is formed on the reflective layer formed in the reflective layer formation process. In the absorber layer formation process, an absorber layer is formed on the dielectric layer formed in the dielectric layer formation process. Each of these layer formation processes can be formed by, for example, sputtering or vapor deposition.

[0084] In the dielectric layer formation process, the thickness of the dielectric layer 14 is set such that the position of the minimum peak of the absorption axis reflectivity Rs is closer to the shorter wavelength side than the desired visible light range (hereinafter referred to as the channel).

[0085] Similarly, in the absorption layer formation process, the thickness of the absorption layer 15 is set such that the position of the minimum peak of the absorption axis reflectivity Rs is shorter than the wavelength side of the desired visible light range (hereinafter referred to as the channel).

[0086] This is because, through the etching process described later, the width b of the reflective layer 13 is selectively etched to be smaller than the grid width a, thereby enabling the wavelength dispersion of the absorption axis reflectivity Rs to shift towards the longer wavelength side.

[0087] In the etching process, the laminate formed through the aforementioned layer-forming processes is selectively etched, thereby forming a lattice-shaped protrusion 11 arranged on the transparent substrate 10 at a spacing shorter than the wavelength of the light used. Specifically, a one-dimensional lattice-shaped mask pattern is formed by, for example, photolithography or nanoimprint lithography.

[0088] Then, by selectively etching the aforementioned laminate, lattice-shaped protrusions 11 are formed on the transparent substrate 10 at a spacing shorter than the wavelength of the light used. As an etching method, for example, a dry etching method using an etching gas corresponding to the object being etched can be cited.

[0089] In particular, in this embodiment, by optimizing the etching conditions (gas flow rate, gas pressure, output, and cooling temperature of the transparent substrate), the width b of the reflective layer 13 can be made smaller than the grid width a (the width of the dielectric layer 14 and the width of the absorber layer 15). Specifically, the width b of the reflective layer 13 can be controlled, for example, by reactive etching (isotropic etching) that increases the etching gas ratio corresponding to the dry etching of the reflective layer 13. Alternatively, it can be achieved by adding a wet etching method suitable for the reflective layer 13.

[0090] Specifically, for example, in the case of a reflective layer 13 with Al as the main material, by immersing it in an etching solution with hydrofluoric acid as the main component, the reflective layer 13 can be selectively etched to make it fine due to the difference in etching rate with other inorganic layers.

[0091] In addition, the base layer 19 is etched by using a dry etching method with an etching gas corresponding to the etched object, and when viewed from the extending direction of the lattice-shaped protrusion 11, it forms, for example, a rectangular pedestal 12.

[0092] Furthermore, the method for manufacturing the polarizing plate 1 in this embodiment may also include a step of coating the surface on the light incident side with a dielectric protective film 20. Further, the method for manufacturing the polarizing plate 1 in this embodiment may also include a step of coating the dielectric protective film 20 with an organic waterproof film. These dielectric protective films 20 and organic waterproof films are formed using the aforementioned CVD, ALD, etc.

[0093] Through the above, the polarizing plate 1 of this embodiment is manufactured.

[0094] [Optical Equipment]

[0095] The optical device of this embodiment includes the polarizing plate 1 described above. Examples of optical devices include liquid crystal projectors, head-up displays, and digital cameras. The polarizing plate 1 of this embodiment is an inorganic polarizing plate with superior heat resistance compared to organic polarizing plates, and is therefore suitable for applications requiring heat resistance, such as liquid crystal projectors and head-up displays.

[0096] In the case where the optical device of this embodiment has multiple polarizing plates, it is sufficient that at least one of the multiple polarizing plates is polarizing plate 1 of this embodiment. For example, in the case where the optical device of this embodiment is a liquid crystal projector, it is sufficient that at least one of the polarizing plates disposed on the incident side and the emission side of the liquid crystal panel is polarizing plate 1 of this embodiment.

[0097] The polarizing plate 1, its manufacturing method, and optical equipment described above achieve the following effects.

[0098] In this embodiment, in the polarizing plate 1 having a grid structure with a grid-shaped protrusion 11 having a reflective layer 13, a dielectric layer 14, and an absorption layer 15 sequentially from the transparent substrate 10 side, the width b of the reflective layer 13 is made smaller than the grid width a (the width of the dielectric layer 14 and the width of the absorption layer 15).

[0099] This allows for more precise control of the wavelength dispersion of the absorption axis reflectivity Rs. More specifically, it allows for shifting the wavelength dispersion of the absorption axis reflectivity Rs towards longer wavelengths, and shifting the wavelength range with the lowest absorption axis reflectivity Rs towards longer wavelengths. As a result, a polarizing plate 1 can be obtained more reliably in a manner that minimizes the absorption axis reflectivity Rs.

[0100] Furthermore, by etching the reflective layer 13 to make its width b smaller than the grid width a, the wavelength dispersion of the absorption axis reflectivity Rs can be accurately controlled. Therefore, as long as it is located on the shorter wavelength side than the channel wavelength range of each LCD projector manufacturer, the thicknesses of the dielectric layer 14 and the absorption layer 15 can be set with a certain degree of freedom. Thus, according to this embodiment, it is not limited by the proprietary designs of each LCD projector manufacturer, and optimal reflective characteristics can be obtained regardless of deviations in the thickness, shape, etc. of the dielectric layer 14 and the absorption layer 15 during the manufacturing process. Furthermore, a polarizing plate with optimal optical characteristics can be provided for the different light source spectra of each LCD projector manufacturer. In addition, a polarizing plate that improves the transmission axis transmittance Tp and increases the projection brightness of the LCD projector can be provided for a basic design structure in which the width of the reflective layer is the same as the grid width.

[0101] Furthermore, the present invention is not limited to the above-described embodiments, and variations and improvements within the scope of achieving the objectives of the present invention are also included in the present invention.

[0102] For example, the polarizing plate of this embodiment is not limited to liquid crystal projectors and can be used for various purposes.

[0103] Example

[0104] The embodiments of the present invention will be described next, but the present invention is not limited to these embodiments.

[0105] <Examples 1 and 2, Comparative Example 1>

[0106] As an example 1, Figure 1 An inorganic polarizing plate with a reflective layer width that is 88% of the grid width (width of the dielectric layer and the absorber layer) in the inorganic polarizing plate of this embodiment is used for simulation. Additionally, as Example 2, an inorganic polarizing plate with a reflective layer width that is 88% of the grid width (width of the dielectric layer and the absorber layer) is used for simulation. Figure 1 The inorganic polarizer of this embodiment, in which the width of the reflective layer is 56% of the grid width (width of the dielectric layer and the absorption layer), was used for simulation. Further, as Comparative Example 1, an inorganic polarizer with the same structure as Examples 1 and 2 was used for simulation, except that the width of the reflective layer is the same as the grid width (width of the dielectric layer and the absorption layer).

[0107] More specifically, the optical properties of these inorganic polarizers were verified through electromagnetic field simulations based on the RCWA (Rigorous Coupled Wave Analysis) method. The simulations used the Gsolver grating simulator from Grating Solver Development.

[0108] Figure 2 This is a graph showing the optical characteristics of the inorganic polarizer of Example 1, where the width of the reflective layer is 88% of the grating width (the width of the dielectric layer and the absorber layer). Figure 3 This is a graph showing the optical characteristics of the inorganic polarizer of Example 2, where the width of the reflective layer is 56% of the grating width (the width of the dielectric layer and the absorption layer). Figure 4 This is a graph showing the optical characteristics of an inorganic polarizing plate of Comparative Example 1, where the width of the reflective layer is the same as the width of the grid (the width of the dielectric layer and the absorption layer).

[0109] Figures 2-4 In the diagram, the horizontal axis represents wavelength λ (nm), the left vertical axis represents transmission axis transmittance Tp or absorption axis transmittance Ts, and the right vertical axis represents transmission axis reflectance Rp or absorption axis reflectance Rs. Here, transmission axis transmittance Tp is the transmittance of polarized light incident on the polarizer along the transmission axis (X-axis), and absorption axis transmittance Ts is the transmittance of polarized light incident on the polarizer along the absorption axis (Y-axis). Similarly, transmission axis reflectance Rp is the reflectance of polarized light incident on the polarizer along the transmission axis (X-axis), and absorption axis reflectance Rs is the reflectance of polarized light incident on the polarizer along the absorption axis (Y-axis), as described above.

[0110] Comparing the absorption axis reflectivity Rs of Examples 1, 2, and Comparative Example 1, the minimum peak position of the absorption axis reflectivity Rs in Comparative Example 1 is around 540 nm, while the minimum peak position of the absorption axis reflectivity Rs in Example 1 is around 560 nm, indicating a shift towards longer wavelengths. Furthermore, the minimum peak position of the absorption axis reflectivity Rs in Example 2 is around 580 nm, indicating a further shift towards longer wavelengths.

[0111] Based on these results, it was confirmed that the polarizing plate of this embodiment, which designs the width of the reflective layer to be smaller than the grid width, can more accurately control the wavelength dispersion of the absorption axis reflectivity Rs. More specifically, the result that the wavelength range with the lowest absorption axis reflectivity Rs can be shifted towards the longer wavelength side confirms that a polarizing plate that can control the absorption axis reflectivity Rs in a way that minimizes it can be obtained more reliably. Thus, according to the present invention, an inorganic polarizing plate with optimal optical properties can be provided to meet the different requirements of various liquid crystal projector manufacturers.

[0112] Furthermore, comparing the transmission axis transmittance Tp of Examples 1 and 2 with that of Comparative Example 1, it can be seen that Examples 1 and 2 improved the value of transmission axis transmittance Tp compared with Comparative Example 1.

[0113] The results confirm that, compared to the existing basic design where the width of the reflective layer is the same as the width of the grid, the polarizer of this embodiment, where the width of the reflective layer is smaller than the width of the grid, can improve the transmittance Tp of the transmission axis.

[0114] Symbol Explanation

[0115] 1—Polarizing plate, 10—Transparent substrate, 11—Grid-shaped protrusions, 12—Base, 13—Reflective layer, 14—Dielectric layer, 15—Absorbing layer, 16—Dielectric layer, 17—Grid feet, 18—Grid front end, 19—Base layer, 20—Dielectric protective film, P—Spacing of grid-shaped protrusions, a—Grid width (width of dielectric layer, width of absorbing layer), b—Width of reflective layer.

Claims

1. A polarizing plate having a wire grid structure, characterized in that it comprises: Transparent substrate; and The lattice-shaped protrusions are arranged on the transparent substrate at a spacing shorter than the wavelength of the light used, and extend along a predetermined direction. The aforementioned lattice-shaped protrusions, starting from the transparent substrate side, sequentially include a reflective layer, a first dielectric layer, an absorbent layer, and a second dielectric layer. The maximum width of the aforementioned reflective layer is smaller than the maximum width of the aforementioned first dielectric layer, the maximum width of the aforementioned absorbent layer, and the maximum width of the aforementioned second dielectric layer. The maximum width of the first dielectric layer, the maximum width of the absorption layer, and the width of the second dielectric layer are approximately the same. The aforementioned lattice-shaped protrusions have a rectangular shape at the front end of the grid when viewed from a predetermined direction. The front end of the grid is composed of the aforementioned first dielectric layer, the aforementioned absorption layer, and the aforementioned second dielectric layer. By using etching to make the width of the reflective layer smaller than the grid width including the width of the first dielectric layer, the width of the second dielectric layer, and the width of the absorption layer, and the ratio of the width of the reflective layer to the grid width is 56% to 88%, the wavelength range with the lowest absorption axis reflectivity is shifted to the longer wavelength side. Thus, the polarizing plate is controlled in such a way that the wavelength range with the lowest absorption axis reflectivity is obtained, and the absorption axis reflectivity characteristics for each channel wavelength range are optimal.

2. The polarizing plate according to claim 1, characterized in that, The thickness of the first dielectric layer is 1~50nm.

3. The polarizing plate according to claim 1, characterized in that, The thickness of the absorption layer is 10~50nm.

4. The polarizing plate according to claim 2, characterized in that, The thickness of the absorption layer is 10~50nm.

5. The polarizing plate according to any one of claims 1 to 4, characterized in that, The aforementioned transparent substrate is transparent to the wavelength of light in the band of use and is made of glass, crystal, or sapphire.

6. The polarizing plate according to any one of claims 1 to 4, characterized in that, The aforementioned reflective layer is made of aluminum or an aluminum alloy.

7. The polarizing plate according to any one of claims 1 to 4, characterized in that, The first dielectric layer mentioned above is composed of Si oxide.

8. The polarizing plate according to any one of claims 1 to 4, characterized in that, The aforementioned absorbent layer comprises Fe or Ta and is composed of Si.

9. The polarizing plate according to any one of claims 1 to 4, characterized in that, The surface of the polarizing plate into which light is incident is covered by a protective film made of dielectric material.

10. The polarizing plate according to any one of claims 1 to 4, characterized in that, The surface of the polarizing plate into which light is incident is covered with an organic waterproof membrane.

11. The polarizing plate according to any one of claims 1 to 4, characterized in that, The second dielectric layer is composed of a dielectric film, and the second dielectric layer, like the absorption layer, is formed into a high-density film by vapor deposition or sputtering.

12. An optical device, characterized in that, A polarizing plate comprising any one of claims 1 to 11.

Images