JP2012048258A - Polarizing element and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing element capable of obtaining a desired polarization characteristic in used bandwidth, and to provide a liquid crystal projector using the polarizing element.SOLUTION: A polarizing element comprises: a substrate 11 which is transparent to light in used bandwidth; a reflection layer 12 in which belt-like thin films 12a extended in one direction on the substrate 11 are arranged in one-dimensional grid shape with a pitch smaller than wavelength of the light in the used bandwidth; a dielectric layer 13 formed on the reflection layer 12; and an inorganic fine particle layer 14 which is formed by arranging inorganic fine particles 14a in the one-dimensional grid shape on the dielectric layer 13 located corresponding to the belt-like thin films 12a, and has light absorbing action.

Description

  The present invention relates to a polarizing element represented by a polarizing plate, a polarizing filter, and the like. More specifically, the present invention relates to an inorganic polarized light utilizing a difference in light absorptance due to optical interference in the in-plane axial direction and interference of light in a use band. The present invention relates to a liquid crystal projector using the polarizing element.

  In a liquid crystal display device (particularly, a transmissive liquid crystal display device), it is indispensable to dispose a polarizing plate on the surface of the liquid crystal panel from the principle of image formation. The polarizing plate has a function of absorbing one of orthogonal polarization components (so-called P-polarized wave and S-polarized wave) and transmitting the other. Conventionally, as such a polarizing plate, 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 a general method for producing a dichroic polarizing plate, there is used a method in which a dichroic material such as a polyvinyl alcohol film and iodine is dyed, followed by crosslinking using a crosslinking agent and uniaxial stretching. Since it is produced by stretching as described above, this type of polarizing plate generally tends to shrink. Further, since the polyvinyl alcohol film uses a hydrophilic polymer, it is very easily deformed particularly under humidified conditions. And since the film is fundamentally used, the mechanical strength as a device is weak.

  In recent years, the use of liquid crystal display devices has expanded and their functions have been enhanced. Accordingly, high reliability and durability are required for individual devices 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, the heat resistance required for the polarizing plate used for these is required. However, since the film-based polarizing plate as described above is made of an organic material, there is a limit to improving these characteristics.

  On the other hand, there is an inorganic polarizing plate as a polarizing plate having high heat resistance. For example, an inorganic polarizing plate (trade name “Polarcor”) manufactured by Corning, USA has a structure in which silver fine particles are diffused in glass, and organic substances such as films are not used. For the polarization principle of the inorganic polarizing plate, plasma resonance of island-shaped fine particles is used. When the shape of the metal fine particles is an ellipse, the resonance wavelength differs between the major axis direction and the minor axis direction. That is, optical anisotropy occurs. As a result, a predetermined polarization characteristic of absorbing a polarization component parallel to the major axis and transmitting a polarization component parallel to the minor axis is obtained (selective light absorption of a polarized wave by optical anisotropy).

  The absorption wavelength due to resonance of the metal fine particles depends on the characteristics of the metal, the shape anisotropy of the fine particles, the surrounding dielectric constant, and the like. Various researches have been conducted so far. In particular, there are many studies on Au (gold), Ag (silver), Cu (copper), and the like. For example, as for Au fine particles, there is a method of obtaining shape anisotropy by forming gold fine particles on glass and stretching them (see Non-Patent Document 1). For Ag fine particles, a method of precipitating silver fine particles in glass by thermal reduction of silver halide (see Patent Documents 1 and 2), and a minute columnar structure made of a transparent and opaque substance with respect to the wavelength in the use band is obliquely deposited. There is a method (see Patent Document 3) for producing polarization characteristics by the above method. As for Cu fine particles, there is a method using silver halide (see Patent Document 4).

  Patent Document 5 below discloses a wire grid type polarizing plate. A wire grid type polarizing plate is a substrate in which a plurality of fine metal wires are formed in a lattice pattern with a pitch smaller than the wavelength of light in the band used, and reflects the polarization component parallel to the fine metal wires and is orthogonal to the fine metal wires. By transmitting the polarization component to be transmitted, a predetermined polarization characteristic appears.

  Since Au fine particles, Ag fine particles, and Cu fine particles have a resonance wavelength on the long wavelength side, it is difficult to obtain good polarization characteristics in the visible light region. On the other hand, since Al (aluminum) fine particles have a resonance wavelength shorter than that of Ag fine particles by about 200 nm, it is known that good polarization characteristics can be obtained in the visible light region (see Non-Patent Document 2). However, since aluminum is very easily oxidized, a method of depositing Al metal fine particles on glass by a thermal reduction method like other metal fine particles cannot be employed.

  Therefore, Patent Document 6 below discloses several methods for manufacturing a polarizing plate using Al fine particles as metal fine particles. As an example, after depositing an Al film on a glass substrate, pattern etching is performed in an island shape using a photolithographic technique, and the glass substrate is heated to about 750 ° C. and stretched to form Al particles in an elliptical shape. A method is disclosed. As another example, a method is disclosed in which an Al film is formed on one side surface of a resist pattern formed on a glass substrate and then the resist pattern is removed.

  Non-Patent Document 3 below describes that a high extinction ratio can be realized at a wavelength of 1 μm or less by using Ge (germanium) instead of Al.

US Pat. No. 6,772,608 JP 56-169140 A JP 2002-372620 A JP-A-8-50205 Japanese translation of PCT publication No. 2003-508813 JP 2000-147253 A

OpticalReview Vol.4 No.3 1997 411-416 J.OptSoc. Am.A Vol.8 No.4 619-624 J.LightwaveTec. Vol.15 No.6 19971042-1050 J. Microelectromechanical Systems Vol. 10 No. 1 2001 33-40

  The polarizing element using Al particles described in Patent Document 6 described above is used as a substrate in order to prevent the reaction between Al particles and glass during the substrate stretching step under a temperature condition higher than the melting point of Al (660 ° C.). Calcium aminoborate glass that does not react with the glass is used. However, this type of glass has a problem in that the production cost is high because it is expensive and difficult to obtain compared to a general silicate glass.

  In the method for manufacturing a polarizing element using Al particles described in Patent Document 6, island-shaped particles are formed by pattern etching of an Al film using a resist pattern as a mask. On the other hand, a polarizing plate used in a projector usually requires a large area and requires a high extinction ratio. Therefore, when the purpose is a polarizing plate for visible light, the resist pattern size needs to be sufficiently shorter than the visible light wavelength, for example, several tens of nm. Moreover, in order to obtain a high extinction ratio, it is necessary to form a pattern with high density.

  Therefore, in the method of forming a high-density fine pattern using the lithography technique described in Patent Document 6, it is necessary to use a fine pattern forming method such as an electron beam drawing method. Electron beam writing is a method in which individual patterns are drawn by an electron beam, so that productivity is poor and impractical.

  Further, when the Al film is removed by etching with chlorine plasma, chloride adheres to the side wall of the Al pattern, and thus a separate process is required to remove it. Furthermore, although Al chloride can be removed by wet etching, a chemical solution that reacts with Al chloride reacts with Al to some extent, so that it is difficult to realize a desired fine pattern shape.

  Further, the wire grid type polarization element has a drawback that an undesirable polarization component is reflected. This is an obstacle for many purposes, particularly when used for a display, and may cause image quality degradation due to reflected light.

  SUMMARY An advantage of some aspects of the invention is to provide a polarizing element capable of obtaining a desired polarization characteristic in a use band and a liquid crystal projector using the polarizing element.

  In solving the above-described problems, the polarizing element of the present invention includes a substrate transparent to light in a use band, and a strip-shaped thin film extending in one direction on the substrate at a pitch smaller than the wavelength of light in the use band. Reflective layers arranged in an original lattice shape, a dielectric layer formed on the reflective layer, and inorganic fine particles arranged in a primary lattice shape on the dielectric layer at positions corresponding to the strip-like thin film And an inorganic fine particle layer having a light absorbing action. The inorganic fine particles are materials such as metals and semiconductors that have non-zero extinction constants of optical constants, that is, have a light absorption function.

  The polarizing element having the above-described configuration utilizes the four actions of transmission, reflection, interference, and selective light absorption of the polarized wave due to optical anisotropy, so that the polarized wave (TE) parallel to the grating of the reflective layer (TE Wave (S wave)) is attenuated, and a polarized wave (TM wave (P wave)) having an electric field component perpendicular to the grating is transmitted.

That is, the TE wave is attenuated by the selective light absorption action of the polarized wave due to the optical anisotropy of the inorganic fine particle layer made of inorganic fine particles having shape anisotropy. The one-dimensional lattice-like reflective layer functions as a wire grid and reflects TE waves transmitted through the inorganic fine particle layer and the dielectric layer. By appropriately adjusting the thickness and refractive index of the dielectric layer, the TE wave reflected by the reflective layer is partially absorbed when passing through and passing through the inorganic fine particle layer, and partially reflected and returns to the reflective layer. . Further, the light that has passed through the inorganic fine particle layer interferes and is attenuated. A desired polarization characteristic can be obtained by selectively attenuating the TE wave as described above.
If low reflection is required on the emission side, light may be incident on the reflection layer side. Also in this case, the transmission contrast equivalent to the above can be obtained by the selective absorption effect of the inorganic fine particle layer.

  The inorganic fine particle layer is set according to the wavelength range of light to be applied. That is, by using an aluminum-based material (metal fine particles made of aluminum or an alloy thereof) and a semiconductor material (semiconductor fine particles containing silicon, beta iron silicide, germanium, and tellurium) for the inorganic fine particle layer, high extinction with respect to the visible light region is achieved. A polarizing element having a ratio can be obtained. For example, the inorganic fine particles are made of a simple substance of Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn, an alloy containing these, or a silicide-based semiconductor material. There should be.

  If a board | substrate is transparent with respect to the light of a use zone | band, it will not restrict | limit in particular, The glass material currently used widely can be used suitably. It is also possible to configure the substrate with sapphire or quartz. The reflective layer is not particularly limited as long as it is a material having reflectivity with respect to light in the use band, and preferably a metal film such as aluminum is used.

  The inorganic fine particles in the inorganic fine particle layer are preferably formed in an elliptical shape having a major axis in a direction parallel to the lattice direction of the reflective layer and a minor axis in a direction perpendicular to the lattice direction. This is because the optical anisotropy is enhanced with such a shape. For the inorganic fine particle layer having such shape anisotropy, oblique film formation from the direction perpendicular to the lattice direction of the reflective layer, particularly vapor deposition or ion beam sputtering is suitable. In addition, it is desirable that the inorganic fine particles have a size equal to or smaller than the wavelength in the use band, and the individual particles are completely isolated.

  The dielectric layer has a concavo-convex shape that forms a convex portion directly above the strip-shaped thin film and a concave portion between the strip-shaped thin films, and the inorganic fine particle layer is a top portion of the convex portion of the dielectric layer or at least one side surface thereof. It is preferable that it is formed in the part.

  The other surface of the substrate has a one-dimensional lattice-shaped concavo-convex portion formed in parallel with the direction in which the strip-shaped thin film of the reflective layer extends, and inorganic fine particles on the top or at least one side surface of the concavo-convex portion. It is preferable that a light absorption layer comprising a second inorganic fine particle layer arranged in a shape is provided.

Further, an antireflection layer is preferably formed between the reflective layer and the substrate.
Further, the antireflection layer is rubbed so that the surface of the substrate corresponds to the arrangement direction of the inorganic fine particles, and the surface after the rubbing treatment has a shape anisotropy so as to correspond to the arrangement direction of the inorganic fine particles. It is preferable that the inorganic fine particles having s are attached.

  Moreover, it is preferable that one or a plurality of laminated structures of the dielectric layer / the inorganic fine particle layer are stacked on the inorganic fine particle layer.

  In order to solve the above problems, the polarizing element of the present invention is the same as that of the polarizing element according to claim 1 and is inorganic at the top part or at least one side part of the one-dimensional lattice-like uneven part formed on the surface of another substrate. The polarizing element having the second inorganic fine particle layer in which the fine particles are arranged in a one-dimensional lattice shape is arranged so that the direction in which the strip-like thin film of the reflective layer extends and the lattice longitudinal direction of the uneven portion are aligned. It is characterized by being bonded together on the back surfaces.

  Moreover, it is preferable that a protective layer transparent to the light in the use band is formed on the outermost surface of the polarizing element.

  In order to solve the above problems, a liquid crystal projector of the present invention includes a lamp, a liquid crystal panel, and the polarizing element according to any one of claims 1 to 13.

As described above, according to the present invention, it is possible to improve the polarization characteristics. In particular, desired polarization characteristics in the visible light range (contrast obtained from the extinction ratio or transmission axis transmittance / absorption axis transmittance). In addition, an inorganic polarizing element having higher durability than conventional polarizing elements can be provided. Furthermore, by stacking the dielectric layer / inorganic fine particle layer stack structure, it is possible to realize high contrast and low reflection with a thinner film thickness than in the case of a single layer. There are also significant advantages in the production of polarizing elements.
Moreover, according to the liquid crystal projector of the present invention, since the polarizing element having excellent light resistance against strong light is provided, a highly reliable liquid crystal projector can be realized.

It is a figure which shows schematic structure of the polarizing element by the 1st Embodiment of this invention, A is a sectional side view, B is a top view. It is the schematic which shows the structure of oblique sputtering film-forming. The figure explaining the method of forming a germanium particle film by making germanium sputtered particles enter obliquely (10 °) with respect to a stationary substrate, the measurement result of the optical constant of the formed germanium particle film, and the germanium particles It is a figure which shows the surface structure | tissue of a film | membrane. FIG. 6 is a diagram illustrating a method for forming a germanium particle film by allowing germanium sputtered particles to be incident on a rotating substrate from a vertical (90 °) direction, and a diagram illustrating a measurement result of an optical constant of the formed germanium particle film. is there. It is a figure explaining the effect | action of the polarizing element shown in FIG. It is a figure which shows one polarization characteristic of the polarizing element of the structure shown in FIG. It is a figure which shows the one polarization characteristic of a wire grid type polarizing element. It is a schematic sectional side view which shows the modification of a structure of the polarizing element shown in FIG. It is a schematic sectional side view of the polarizing element by the 2nd Embodiment of this invention. It is a schematic sectional side view of the polarizing element by the 3rd Embodiment of this invention. It is a figure which shows schematic structure of the polarizing element by the 4th Embodiment of this invention. It is a figure which shows the polarization characteristic of the polarizing element of the structure shown in FIG. 1, and the polarizing element of the structure shown in FIG. It is a figure which shows the contrast characteristic of the polarizing element of the structure shown in FIG. 1, and the polarizing element of the structure shown in FIG. It is a figure which shows the output surface stray light countermeasure example (1) in the polarizing element of the structure shown in FIG. It is a figure which shows the output surface stray light countermeasure example (2) in the polarizing element of the structure shown in FIG. It is sectional drawing which shows the structure of the optical engine part of the liquid crystal projector which concerns on this invention. It is explanatory drawing which shows the inorganic fine particle adhesion state to each of the board | substrate which has a flat board | substrate, and a one-dimensional lattice-like convex part. It is an external appearance perspective view of the quartz substrate which has a one-dimensional lattice-like convex part. It is a figure which shows the relationship between the major axis and the film thickness of the inorganic fine particle in oblique film-forming. It is a figure which shows the precondition of the polarizing element in an optical characteristic simulation. It is a figure which shows the optical characteristic of a polarizing element in case the constituent material of an inorganic fine particle layer is Ge fine particle and Ge thin film. FIG. 5 is a relationship diagram between the height of aluminum as a reflective layer and contrast in the polarizing element of the present invention. It is a figure which shows the polarization characteristic of the polarizing element sample of Example 2. FIG. It is a figure which shows the uneven | corrugated state of the texture structure formed by the rubbing process. It is a figure which shows the transmittance | permeability characteristic of the board | substrate before and behind a rubbing process. It is a figure which shows the surface structure | tissue of Ge fine particle film (antireflection film) provided on the board | substrate by which the rubbing process was carried out. It is a figure which shows the improvement of the polarization characteristic of the anti-reflective film by a rubbing process.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments, and various modifications can be made based on the technical idea of the present invention.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a polarizing element 10 according to a first embodiment of the present invention, in which A is a side sectional view and B is a plan view.

  The polarizing element 10 of the present embodiment includes a substrate 11, a reflective layer 12 in which a strip-like thin film 12 a extending in one direction parallel to the main surface of the substrate 11 is formed on one surface of the substrate 11 in a one-dimensional lattice shape, A dielectric layer 13 formed on the reflective layer 12 and an inorganic fine particle layer 14 formed on the dielectric layer are provided.

  The substrate 11 is made of a material that is transparent with respect to light in the use band (visible light region in the present embodiment), such as glass, sapphire, and quartz. In this embodiment, glass, particularly quartz (refractive index 1.46) or soda lime glass (refractive index 1.51) is 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.

  By using a quartz or sapphire substrate with high thermal conductivity as the constituent material of the substrate 11, it can be advantageously used as a polarizing element for an optical engine of a projector that generates a large amount of heat.

  As a constituent material of the reflective layer 12, a normal wire grid type polarizer lattice material can be used. In this example, aluminum is used, but in addition to this, silver, gold, copper, molybdenum, chromium is used. A metal or a semiconductor material such as titanium, nickel, tungsten, iron, silicon, germanium, or tellurium 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 strip-shaped thin film 12a in the reflective layer 12 is arranged in a one-dimensional lattice pattern on the surface of the substrate 11 at a pitch smaller than the wavelength in the visible light region, and is formed by patterning the metal film using, for example, a photolithography technique. . The reflective layer 12 has a function as a wire grid polarizer, and of the light incident on the surface of the substrate 11, a polarized wave (TE) having an electric field component in a direction parallel to the grating (grating axis direction, Y axis direction). Wave (S wave)) is attenuated, and a polarized wave (TM wave (P wave)) having an electric field component in a direction perpendicular to the grating (the direction perpendicular to the grating, the X-axis direction) is transmitted.

The pitch, line width / pitch, lattice depth, and lattice length of the metal lattice (one-dimensional lattice pattern of the strip-shaped thin film 12a) constituting the reflective layer 12 are preferably set in the following ranges.
0.05μm <pitch <0.8μm
0.1 <(line width / pitch) <0.9
0.01 μm <lattice depth <1 μm
0.05μm <grid length

  Further, in order to reduce the reflection of the substrate surface in the region where the reflective layer 12 is not formed, a non-reflective coating is applied to the surface of the substrate 11 in advance, and then the reflective film 12, the dielectric layer 13, and the inorganic fine particle layer 14 are formed. You may make it perform. The non-reflective coating can be composed of a general laminated film of a high refractive index film and a low refractive index film. By applying the same non-reflective coating to the back surface of the substrate 11, reflection on the substrate surface can be reduced.

  The dielectric layer 13 is an optical material that is transparent to visible light such as SiO2 formed on the surface of the substrate 11 by sputtering or sol-gel method (for example, a method in which a sol is coated by spin coating and gelled by thermal curing). Made of material. The dielectric layer 13 forms an underlayer for the inorganic fine particle layer 14 and, as will be described later, the polarized light that has been transmitted through the inorganic fine particle layer 14 and reflected by the reflective layer 12 with respect to the polarized light reflected by the inorganic fine particle layer 14. It is formed to increase the interference effect by adjusting the phase of the film, and a film thickness shifted by half a wavelength is desirable. However, since the inorganic fine particle layer has an absorption effect, it can absorb the reflected light and the film thickness is not optimized. However, an improvement in contrast can be realized, and in practice, it may be determined based on a balance between desired polarization characteristics and an actual manufacturing process. The practical film thickness range is 1 to 500 nm, more preferably 300 nm or less.

  As a material constituting the dielectric layer 13, a general material such as SiO2, Al2O3, MgF2 can be used. These can be made into a thin film by general vacuum film formation such as sputtering, vapor phase epitaxy, and vapor deposition, or by coating a substrate with a sol-like substance and thermosetting it. The refractive index of the dielectric layer 13 is preferably greater than 1 and not greater than 2.5. Further, since the optical characteristics of the inorganic fine particle layer 14 are also affected by the refractive index of the surroundings, it is possible to control the polarizing element characteristics by the dielectric layer material.

  As shown in FIG. 1B, the inorganic fine particle layer 14 has a major axis direction parallel to the one-dimensional lattice direction (Y-axis direction) of the reflective layer 12 and a minor axis direction perpendicular to the lattice direction (X-axis direction). The elliptical island-shaped inorganic fine particles 14 a are arranged in a line in one direction (one-dimensional lattice direction) parallel to the main surface of the substrate 11. Further, the inorganic fine particle layer 14 is provided on the dielectric layer 13 above the metal lattice (band-like thin film 12a) constituting the reflective layer 12, respectively. Therefore, the inorganic fine particle layer 14 has a wire grid structure having the same pattern as the one-dimensional lattice of the reflective layer 12 on the substrate 11.

  If the inorganic fine particles 14a constituting the inorganic fine particle layer 14 have a shape anisotropy between the X-axis direction and the Y-axis direction, the optical constants can be made different between the major axis direction and the minor axis direction. . As a result, it is possible to obtain a predetermined polarization characteristic of absorbing a polarization component parallel to the major axis and transmitting a polarization component parallel to the minor axis. In addition, when the inorganic fine particles 14a do not have shape anisotropy (for example, circular shape), TM wave absorption is also generated in the TE wave absorption band, which is not preferable.

  In order to control the shape anisotropy of the inorganic fine particle layer 14, the inorganic fine particles 14 a are deposited only on the top of the dielectric layer 13 by reducing the arrangement pitch of the metal lattice (band-like thin film 12 a) constituting the reflective layer 12. It is effective to do so. As a result, the metal fine particles 14a can be isolated. Further, as the film formation method of the metal fine particles 14a, oblique sputtering film formation, for example, an ion beam sputtering method for forming a film in an oblique direction with respect to the surface of the substrate 11 is effective. The metal fine particles 14a do not have to be formed in a perfect island shape, and it is sufficient that a grain boundary is formed.

  FIG. 2 shows a state of oblique sputtering film formation for forming the inorganic fine particle layer 14 of the present invention. Although an example of ion beam sputtering is shown here, the present invention is not limited to this, and any method may be used as long as it is a sputtering method.

  In FIG. 2, 1 is a stage for supporting the substrate 11, 2 is a target, 3 is a beam source (ion source), and 4 is a control plate. The stage 1 is inclined at a predetermined angle θ with respect to the normal direction of the target 2, and the substrate 11 is oriented so that the longitudinal direction of the convex portion 14 a of the concave and convex portion 14 is orthogonal to the incident direction of the inorganic fine particles from the target 2. Is arranged. The angle θ is, for example, 0 ° to 20 °. Ions extracted from the beam source 3 are irradiated to the target 2. The inorganic fine particles knocked out from the target 2 by the irradiation of the ion beam are incident on and adhered to the surface of the substrate 11 from an oblique direction. At this time, if the flat control plate 4 is arranged on the substrate 11 at a constant interval (for example, 50 mm), the direction of the incident particles on the surface of the substrate 11 is controlled, and the particles are deposited only on the side wall portion of the uneven portion 14. Can do. The film thickness of the inorganic fine particle layer 14 at this time is preferably 200 nm or less.

  The inorganic fine particle layer 14 has optical anisotropy in the arrangement direction of the inorganic fine particles 14a and the direction orthogonal to the arrangement direction of the inorganic fine particles 14a. Note that even if the inorganic fine particle layer 14 is not formed into an elliptical aggregate as described above and is in a uniform film state, when the film is formed by a method such as ion beam sputtering from an oblique direction, Since the optical anisotropy of the layer can be strengthened, it is effective as the inorganic fine particle layer of the present invention.

  FIG. 3 shows the experimental results of the optical anisotropy enhancement effect by such oblique ion beam sputtering. As shown in FIG. 3A, germanium sputtered particles were incident and deposited by ion beam sputtering in the direction of 10 ° with respect to the surface of the glass substrate 41 while the substrate 41 was in a stationary state, thereby producing a germanium particle film 44. FIG. 3B shows the measurement results of the optical constants (refractive index, extinction constant) of the produced germanium particle film 44. The measurement was performed with a spectroscopic ellipsometer. The film thickness at this time is 10 nm. Due to the occurrence of optical anisotropy, there is a difference between the refractive index n and the extinction constant k in the plane. This means that the light absorption characteristics differ in the axial direction depending on the wavelength. By using this film as the inorganic fine particle layer of the polarizing element of the present invention, a high polarization contrast can be obtained.

  FIG. 3C shows the result of observation of the surface shape of the particle film with an electron microscope. In order to avoid the influence of the roughness of the glass surface, a single crystal Si substrate was used as the substrate, and oblique sputter deposition was performed under the same conditions as in FIG. 3A. The germanium fine particles have a grain boundary and have a vertically long shape in the y-axis direction, and the size is equal to or less than the measurement wavelength. In principle, such isolation and anisotropy of particles are caused by a steering effect in oblique film formation. As a result, when viewed as a film, optical anisotropy occurs. Thus, the surface of the inorganic fine particle layer in the present invention is different from that of a general thin film.

  For comparison, as shown in FIG. 4A, germanium sputtered particles are formed while rotating the substrate 41 from the vertical direction of the substrate 41, and the measured values of the optical constants of the obtained germanium particle film 44 are shown in FIG. 4B. Show. Optical anisotropy of refractive index n and extinction constant k did not occur, and each optical constant was a value close to the literature value. That is, in this case, it is a normal thin film state. The surface state was measured by the same method as in FIG. 3C, but no grain boundary was seen at the same magnification. This suggests that this film is in a homogeneous thin film state.

  The absorption wavelength due to the optical anisotropy of the inorganic fine particles 14a depends on the characteristics of the material, the shape anisotropy of the fine particles, the surrounding dielectric constant, and the like. In the present embodiment, the inorganic fine particle layer 14 is formed so as to obtain polarization characteristics with respect to the visible light region. Here, as the material constituting the inorganic fine particles 14 a, it is necessary to select an appropriate material for the polarizing element 10 according to the use band. That is, a metal material or a semiconductor material is a material satisfying this, and specifically, as a metal material, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn A simple substance or an alloy containing these may be used. Moreover, Si, Ge, and Te are mentioned as a semiconductor material. Further, silicide-based materials such as FeSi2 (particularly β-FeSi2), MgSi2, NiSi2, BaSi2, CrSi2, CoSi2 are suitable. In particular, as the material of the inorganic fine particles 14a, aluminum-based metal fine particles made of aluminum or an alloy thereof, or semiconductor fine particles containing beta iron silicide, germanium, or tellurium are used, so that high contrast (high extinction ratio) is achieved in the visible light region. Can be obtained.

  In order to provide polarization characteristics in a wavelength band other than visible light, for example, in the infrared region, Ag (silver), Cu (copper), Au (gold) fine particles, etc. are used as the inorganic fine particles constituting the inorganic fine particle layer. Is preferred. This is because the resonance wavelength in the major axis direction of these metals is in the vicinity of the infrared region. In addition, materials such as molybdenum, chromium, titanium, tungsten, nickel, iron, and silicon can be used in accordance with the use band.

  Note that the lattice arrangement of the reflective layer 12 is not limited to the one-dimensional periodic arrangement in the X-axis direction as illustrated, and may be a two-dimensional periodic arrangement in the X- and Y-axis directions. In this case, the shape anisotropy of the inorganic fine particle layer 14 can be expressed by the two-dimensional periodic structure of the reflective layer.

  In the polarizing element 10 of the present embodiment configured as described above, the surface side of the substrate 11, that is, the formation surface side of the lattice-like reflective layer 12, dielectric layer 13 and inorganic fine particle layer 14 is the light incident surface. . Then, the polarizing element 10 utilizes the four actions of light transmission, reflection, interference, and selective light absorption of polarized waves due to optical anisotropy, so that an electric field component (grating axis) parallel to the grating of the reflective layer 12 is obtained. Polarized wave (TM wave (P wave)) having an electric field component (lattice perpendicular direction, X axis direction) perpendicular to the grating while attenuating a polarized wave (TE wave (S wave)) having a direction and a Y-axis direction) Permeate.

  That is, as shown in FIG. 5A, the TE wave is attenuated by the selective light absorption action of the polarized wave due to the optical anisotropy of the inorganic fine particle layer 14 having shape anisotropy. The grid-like reflective layer 12 functions as a wire grid and reflects TE waves that have passed through the inorganic fine particle layer 14 and the dielectric layer 13 as shown in FIG. 5B. At this time, the dielectric layer 13 is configured so that the phase of the TE wave transmitted through the inorganic fine particle layer 14 and reflected by the reflective layer 12 is shifted by a half wavelength, so that the TE wave reflected by the reflective layer 12 is reflected by the inorganic fine particle layer 14. The reflected TE waves cancel each other out due to interference and are attenuated. The TE wave can be selectively attenuated as described above. As described above, a film thickness shifted by half a wavelength is desirable. However, since the inorganic fine particle layer has an absorption effect, an improvement in contrast can be realized even if the film thickness of the dielectric layer is not optimized. It may be determined depending on the balance between the characteristics and the actual manufacturing process.

  On the contrary, when low reflection is required on the emission side, light may be incident on the reflection layer side. Also in this case, the transmission contrast equivalent to the above can be obtained by the selective absorption effect of the inorganic fine particle layer. This is because the size of the transmission contrast depends on the thickness of the reflective layer as will be described later. When this is applied to actual use, for example, in the optical engine part (FIG. 16) of the liquid crystal projector of the present invention described later, the polarizing plate of the present invention is applied to the incident polarizing plate 10A for the purpose of avoiding unwanted reflected light to the liquid crystal panel. When used, the polarizing plate is disposed so that the film surface (the inorganic fine particle layer 14 side in FIG. 5) faces the liquid crystal panel side. By doing so, undesirable reflections will return to the light source side. Similarly, when the polarizing plate of the present invention is used as the output polarizing plate 10B or 10C, the film surface of the polarizing plate (the inorganic fine particle layer 14 side in FIG. 5) is preferably directed to the liquid crystal panel side. Although the incident direction of light to the polarizing plate is reversed when used for the incident polarizing plate and the outgoing polarizing plate, the same transmission contrast can be obtained regardless of which side the light is incident as described above. No problem.

  In FIG. 6, an aluminum lattice having a pitch of about 160 nm (line width of about 55 nm) and a lattice depth of 160 nm is formed as a reflective layer 12 on a substrate 11 made of glass (Corning 1737), and a dielectric layer 13 is formed thereon with SiO 2. The polarization characteristics of a polarizing element formed by laminating a germanium fine particle layer as an inorganic fine particle layer 14 by 10 nm by oblique film formation by ion beam sputtering are shown. The transmittance of the absorption axis is almost zero, and the reflectance is also low. The contrast in this case is about 500 at a wavelength of 550 nm, and the polarizing plate has good characteristics. Contrast can be further improved by optimizing parameters such as pitch and film thickness.

  In addition, if necessary, an antireflection film is coated on the front surface and the back surface of the substrate, thereby preventing reflection from air and the substrate surface and improving the transmission axis transmittance. The antireflection film may be a generally used low refractive index film such as MgF2, or a multilayer film composed of a low refractive index film and a high refractive index film. Furthermore, coating the outermost surface of this polarizing element with a transparent material in a usable band such as SiO2 with a film thickness that does not affect the polarization characteristics as a protective film is effective for improving reliability such as improving moisture resistance. is there. However, since the optical characteristics of the inorganic fine particles are also affected by the refractive index of the surroundings, the polarization characteristics may change due to the formation of the protective film. Moreover, since the reflectance with respect to incident light changes also with the optical thickness (refractive index x protective film thickness) of the protective film, the protective film material and the film thickness should be selected in consideration of these. As a material, a material having a refractive index of 2 or less and an extinction coefficient close to zero is desirable. Such materials include SiO2, Al2O3 and the like. These can be formed by a general vacuum film formation method (vapor phase film formation method, sputtering method, vapor deposition method, etc.) or a sol in which these are dispersed in a liquid by a spin coating method or a dipping method. is there. Furthermore, a self-assembled film as described in Non-Patent Document 4 can also be used. For the purpose of improving moisture resistance, a water-repellent self-assembled film is preferable. Perfluorodecyltrichlorosilane (FDTS), Octadecanetrichlorosilane (OTS), and the like are examples thereof, and are effective in terms of antifouling measures because they have water repellency. In the case of a silane-based self-assembled film, for the purpose of improving adhesion, the self-assembled film may be deposited after coating SiO 2 as an adhesion layer on the polarizing element by the above method.

  FIG. 7 shows an example of the polarization characteristic of a polarizing element having a wire grid structure in which only a reflective layer is formed on a substrate. It can be seen that the reflectance of the absorption axis (TE wave, S wave) is as high as about 80%. The contrast in the transmission direction was about 200. Comparing FIG. 6 with FIG. 7, it is clear that according to the present embodiment, the reflectance of the absorption axis can be greatly reduced, and transmission and reflection of the TE wave or S wave are suppressed, and the quenching in the transmission direction is performed. The ratio can be greatly improved.

  The polarizing element 10 can be manufactured as follows, for example. That is, after laminating a metal film and a dielectric film on the substrate 11 and forming a lattice pattern of the metal film and the dielectric film by photolithography or the like, the inorganic fine particle layer 14 is formed by an oblique sputtering film forming method. By adjusting the incident angle during oblique sputtering film formation, fine particles can be concentrated in the vicinity of the apex of the convex portion formed of the strip-shaped thin film 12 a and the dielectric layer 13.

  In addition to the above, it is also possible to apply a method in which a transparent material is formed on a transparent substrate in a one-dimensional lattice shape, and a metal layer, a dielectric layer, and an inorganic fine particle layer are sequentially laminated on the convex portions of the lattice by oblique film formation. is there. Furthermore, a method may be used in which a metal film, a dielectric film, and a fine particle film are sequentially laminated on a substrate, and then these are collectively etched into a one-dimensional lattice shape.

  Further, as shown in FIG. 8, after the reflective layer 12 is formed on the substrate 11 in a one-dimensional lattice shape, the dielectric layer 13 is formed over the entire surface of the substrate 11. As a result, the dielectric layer 13 has a concavo-convex shape that forms a convex portion directly above the strip-shaped thin film 12a of the reflective layer 12 and a concave portion between the strip-shaped thin films 12a. Thereafter, by forming the inorganic fine particle layer 14 on the side surface portion of the top of the convex portion of the dielectric layer 13 by an oblique sputtering film forming method, a polarizing element having the same function and effect as the example of FIG. 1 can be manufactured. it can. The formation region of the inorganic fine particle layer 14 is not limited to one side surface portion of the top portion of the dielectric layer 13 shown in the drawing, and may be both side surface portions.

(Second Embodiment)
FIG. 9 is a side sectional view showing a schematic configuration of the polarizing element 20 according to the second embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the polarizing element 20 of the present embodiment, a one-dimensional lattice-like reflective layer 12 is formed on the surface (one surface) of the substrate 11, and the dielectric layer 13 and the inorganic fine particle layer 14 are formed on the reflective layer 12. Are sequentially formed. And, on the back surface (the other surface) of the substrate 11, the uneven portion 15 made of a dielectric material and the second second fine inorganic particle layer 16 formed on the top portion or at least one side surface portion of the uneven portion 15. A selective light absorption layer 17 for polarized waves by optical anisotropy is provided.

  In the polarizing element 10 of the first embodiment in which the selective light absorption layer 17 for the polarized wave due to the optical anisotropy is not provided, the back surface side of the substrate 11 exhibits a mirror surface by the reflective layer 12, and thus transmits through the polarizing element. The light reflected and returned by another optical element such as a lens arranged at the next stage of the polarizing element is reflected again by the mirror surface. Such stray light causes image quality deterioration such as ghost in the liquid crystal projector.

  In the present embodiment, by providing the selective light absorption layer 17 of the polarized wave due to the optical anisotropy having the above configuration on the back side of the substrate 11, the stray light is absorbed and reflection on the reflection layer 12 is prevented. The concavo-convex portion 15 constituting the selective light absorption layer 17 of the polarized wave due to optical anisotropy is made of the same material as that of the dielectric layer 13 and is formed in parallel with the direction in which the strip-like thin film 12a of the reflective layer 12 extends. It is formed in a one-dimensional lattice shape. The second inorganic fine particle layer 16 is formed by linearly arranging inorganic fine particles on the top or side surface of the convex portion of the concavo-convex portion 15 and is made of the same material as the inorganic fine particle layer 14 on the surface side of the substrate 11. As a result, the optical anisotropy is exhibited and an absorption effect for incident light from the back surface of the substrate 11 appears.

  As a method for forming the concavo-convex portion 15, it is formed by a sputtering method, a sol-gel method, or the like, similarly to the method for forming the dielectric layer 13. For imparting the uneven shape, pattern processing using a photolithography technique or press formation by a nanoimprint method is suitable. As a method for forming the second inorganic fine particle layer 16, an oblique film formation similar to the method for forming the inorganic fine particle layer 14 on the surface side of the substrate 11 is suitable. The second inorganic fine particle layer 16 is formed on the top portion, one side surface portion, or both side surface portions of the uneven portion 15.

  Alternatively, as another manufacturing method of the polarizing element 20, the polarizing element 10 shown in FIG. 1, the uneven portion 15 made of a dielectric material on another substrate, and the top portion or at least one side surface portion of the uneven portion 15 are formed. The back surfaces of the substrates are bonded to each other with a transparent adhesive using a polarizing element provided with a selective light absorption layer 17 of a polarized wave due to optical anisotropy comprising the second second inorganic fine particle layer 16. Thus, the polarizing element 20 may be used. In this case, the arrangement direction of the inorganic fine particles in the inorganic fine particle layers 15 and 25 is preferably aligned.

(Third embodiment)
FIG. 10 is a side sectional view showing a schematic configuration of a polarizing element 30 according to the third embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  The polarizing element 30 of the present embodiment is configured for the same purpose as that of the second embodiment described above. That is, in the polarizing element 30 of this embodiment, the antireflection layer 18 is formed between the substrate 11 and the reflective layer 12. In this way, by providing the antireflection layer 18 directly below the one-dimensional grid-like reflection layer 12, reflection of incident light from the back surface of the substrate 11 is prevented.

  The antireflection layer 18 is preferably a black layer such as a carbon black film. Thereby, incident light from the back surface of the substrate 11 can be efficiently absorbed. In addition to carbon, a silicon oxide layer deficient in oxygen or a low reflection material having a lower reflectance than the reflection layer 12 can be applied. Alternatively, the antireflection layer 18 may be the same as the inorganic fine particle layer 14. In the illustrated example, a dielectric layer 19 is provided for the purpose of reducing the reflectance by obtaining an interference effect between the reflective layer 12 and the antireflection layer 18. The processing of the dielectric layer 19 and the antireflection layer 18 into a lattice shape can be simultaneously performed by pattern processing of the reflective layer 12, for example.

  As a modification of the present embodiment, there is the following method. That is, the surface of the substrate 11 is composed of irregularities in which fine streaks are aligned in one direction so as to correspond to the arrangement direction of the inorganic fine particles 14a of the inorganic fine particle layer 14 to be subsequently formed on the surface by rubbing the surface. A texture structure is formed, and then a thin film (antireflection layer) made of inorganic fine particles having shape anisotropy is formed on the surface after the rubbing treatment by the aforementioned oblique sputtering method so as to correspond to the arrangement direction of the inorganic fine particles 14a. Good. Due to the texture structure, the alignment of the inorganic fine particles is improved so that the long axis direction of the inorganic fine particles becomes the longitudinal direction of the stripes, the polarization characteristics of the thin film are improved, and the ghost countermeasure effect can be enhanced. At the same time, an increase in transmission contrast characteristics as a polarizing element can be expected.

(Fourth embodiment)
FIG. 11 is a side sectional view showing a schematic configuration of a polarizing element 40 according to the fourth embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  The polarizing element 40 of the present embodiment is characterized in that one or a plurality of laminated structures of the dielectric layer 13 / inorganic fine particle layer 14 are stacked on the inorganic fine particle layer 14 of the polarizing element 10 of the first embodiment. Yes. That is, in FIG. 11, the polarizing element 40 has a strip-like thin film 12 a constituting the reflective layer 12, a dielectric layer 13, and an inorganic fine particle layer 14 laminated on the substrate 11 in this order. It has a wire grid structure in which the laminated structure 1a of the dielectric layer 13 / inorganic fine particle layer 14 is further stacked. Further, the laminated structure 1a may be further stacked on the laminated structure 1a. As a result, the interference effect between the respective layers can be enhanced to increase the transmission axis direction contrast at a desired wavelength, and at the same time, the reflection component from the polarizing element which is not preferable in the transmissive liquid crystal display device can be reduced over a wide range.

  In order to confirm the effect of stacking the laminated structure 1a in the present embodiment, the polarizing element 10 without the laminated structure 1a shown in FIG. 1 and the polarizing element 40 having the single laminated structure 1a shown in FIG. Simulation calculation of polarization optical characteristics with respect to wavelength was performed by wavelength rigorous coupled wave analysis (RCWA). Here, the reflective layer 12 is a layer made of Al (notation Al), the dielectric layer 13 is a layer made of SiO 2 (notation SiO 2), and the inorganic fine particle layer 14 is a layer made of Ge (notation Ge). And the contrast required as the ratio of the transmittance in the transmission axis X direction and the absorption axis Y direction in the green light region (near wavelength 550 nm), which is practically important for liquid crystal display devices, is about 4000 to 5000, and the reflectance is the lowest. Thus, optimization calculation was performed using the thickness of the reflective layer 12, the thickness of the dielectric layer 13, and the thickness of the inorganic fine particle layer 14 as parameters. The one-dimensional lattice pitch of the reflective layer 12 was 150 nm, and the lattice width (width of the strip-shaped thin film 12a): space (interval of the strip-shaped thin film 12a) = 0.275: 0.725. Further, in order to suppress the influence of stray light due to re-reflection of the return light to the polarizing element exit surface, a 15 nm-thick Ge layer is added to the polarizing element exit surface (between the reflective layer 12 and the substrate 11). .

As a result of the above condition setting, the layer structure optimized with a contrast of 4000 to 5000 was as follows. The parentheses are the film thicknesses of the respective layers, and the polarizing element 40 is thinner than the polarizing element 10 as the total film thickness. This contributes to a reduction in thin film deposition time and etching time, which is advantageous in manufacturing.
Polarizing element 10: Ge (15 nm) / Al (240 nm) / SiO2 (205 nm) / Ge (90 nm) from the surface of the substrate 11
Polarizing element 40: Ge (15 nm) / Al (220 nm) / SiO 2 (90 nm) / Ge (45 nm) / SiO 2 (90 nm) / Ge (45 nm) from the surface of the substrate 11

As a result, FIG. 12 shows the obtained polarization optical characteristics. FIG. 13 shows the contrast result in that case.
In FIG. 12, the absorption axis reflectance near a wavelength of 550 nm is smaller in the polarizing element 40 (solid line data described as two layers) than in the polarizing element 10 (dotted data described as a single layer). Correspondingly, in FIG. 13, the contrast in the vicinity of the wavelength of 550 nm is larger in the polarizing element 40 (two layers) than in the polarizing element 10 (single layer).

  Here, the calculation is performed on the assumption that the structure is for the green light region (wavelength 550 nm) and one stacked structure 1a is stacked (two layers), but the film thickness of each layer is optimized also in other wavelength regions. The same effect can be obtained. Moreover, the same effect can be acquired also in the structure (two or more layers) which laminated | stacked multiple laminated structure 1a.

  For example, there are the following three methods for manufacturing the polarizing element 40 of the present invention. That is, as a first method, a reflective layer material (metal lattice material) and a dielectric film are laminated on the substrate 11, a one-dimensional lattice pattern is formed or etched by a technique such as nanoimprint or photolithography, and then oblique sputtering is performed. Fine particles are formed by a film method. According to this, by adjusting the incident angle at the time of oblique sputtering film formation, it is possible to deposit inorganic fine particles intensively in the vicinity of the apex of the dielectric layer 13 that has become a convex portion. As a second method, a transparent material is used to form a one-dimensional lattice-shaped concavo-convex portion on a transparent substrate, and a reflective layer material, a dielectric film, and an inorganic fine particle material are sequentially stacked by the number of layers. Is. As a third method, a stacked structure of (dielectric film / inorganic fine particle thin film) is sequentially stacked on the thin film (metal lattice film) of the reflective layer by the number of stacked layers and then etched. In addition, the inorganic fine particle material does not need to be a complete island shape, and it is sufficient that a grain boundary is formed. The dielectric layer 13 and the inorganic fine particle layer 14 may be manufactured by combining a formation method by sputtering film formation and etching and a formation method by oblique sputtering film formation. In executing the above manufacturing process, the type of substrate material is not limited, but a quartz or sapphire substrate with high thermal conductivity is suitable for application to a projector with a large amount of heat generation.

  Similarly to the first embodiment, a protective film made of SiO2 or the like is deposited on the uppermost portion of the polarizing element 40 for the purpose of improving reliability such as moisture resistance, as long as the change in optical characteristics does not affect the application. May be. Further, for the purpose of reducing the reflection of the substrate 11, a non-reflective coating (a general laminated film of a high refractive film and a low refractive film) is performed in advance, and then the polarizing element 40 is manufactured by the manufacturing process. Can be improved.

By the way, if the polarizing element 40 having the structure described so far is used, the light exit surface (reflective layer 12) is made of metal, and therefore the reflectance increases when there is return light. Therefore, in this embodiment as well, it is preferable to take measures against stray light on the exit surface as shown in the second embodiment or the second embodiment.
FIG. 14 and FIG. 15 show examples of the exit surface stray light countermeasure in this embodiment.

FIG. 14 shows an example in which the configuration of FIG. 9 is applied to this embodiment.
The polarizing element 40A is formed in the polarizing element 40 on the surface (back surface) opposite to the surface on which the reflective layer 12 is formed of the substrate 11 and the uneven portion 15 made of a dielectric material, and on the top portion or at least one side surface portion of the uneven portion 15. A selective light absorption layer 17 for polarized waves due to optical anisotropy composed of the second second inorganic fine particle layer 16 is provided.

FIG. 15 shows an example in which the configuration of FIG. 10 is applied to this embodiment.
The polarizing element 40B is provided with an antireflection layer 18 immediately below the one-dimensional lattice-like reflecting layer 12 in the polarizing element 40, and for the purpose of obtaining an interference effect between the reflecting layer 12 and the antireflection layer 18. A layer 19 is provided. In FIG. 15, the dielectric layer 19 under the reflective layer 12 may be omitted, and the antireflection layer 18 may be simply formed under the reflective layer 12. Further, when the antireflection layer 18 is the same as the inorganic fine particle layer 14, it contributes to the improvement of contrast. However, for the purpose of simply preventing the reflection of the return light, the antireflection layer 18 is provided under the reflection layer 12. As the layer 18, a layer having a lower reflectance than the reflective layer 12 (low reflective layer) may be provided. The low reflection material is effective when the reflectance is lower than that of the reflection layer 12, and an oxide film such as carbon or oxygen deficient SiOx, or metal or semiconductor fine particles can be used.

  When the antireflection layer 18 and the dielectric layer 19 are added under the reflection layer 12, or when the antireflection layer 18 is formed directly under the reflection layer 12, these films are formed before forming the film for the reflection layer. When the film is formed and etched simultaneously to form the reflective layer 12, these layers can be formed only directly below the strip-like thin film 12a of the reflective layer 12, so that it is possible to prevent the transmission characteristics from being affected.

Next, a liquid crystal projector according to the present invention will be described.
The liquid crystal projector of the present invention includes a lamp serving as a light source, a liquid crystal panel, and the polarizing elements 10, 20, 30, and 40 of the present invention described above.

FIG. 16 shows a configuration example of the optical engine portion of the liquid crystal projector according to the present invention. Here, description will be made on the assumption that the polarizing element 10 is used.
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 elements 10, 20, and 30 of the present invention are applied to the incident side polarizing element 10A, the outgoing pre-polarizing element 10B, and the outgoing main polarizing element 10C, respectively.

  In the liquid crystal projector 100 of the present invention, 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 sides corresponding to the respective lights. Lights LR, LG, and LB that are incident on the polarizing element 10A and then polarized by the respective incident-side polarizing elements 10A are spatially modulated by the liquid crystal panel 50 and emitted, and the outgoing pre-polarizing element 10B and the outgoing main polarizing element 10C are output. After passing, it is composed 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 10 (20, 30, 40) of the present invention having excellent light resistance against strong light is used, a highly reliable liquid crystal projector is realized. can do.

  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.

Below, the result of having verified the polarization characteristic in the polarizing element which concerns on this invention is shown.
Example 1
In the polarizing element 10 of FIG. 1, the method of forming the inorganic fine particle layer 14 by the oblique sputtering film forming method is advantageous from the viewpoint of improving the polarization characteristics. The reason for this will be described with reference to FIG. That is, as shown in FIG. 3C, the inorganic fine particles have a vertically long shape in the direction orthogonal to the particle incidence direction of oblique film formation within the substrate surface. However, when the film is formed on a flat surface such as Si or glass (FIG. 17A), the isolation and shape of the particles depend on the distribution in the direction of the incident particles and the self-organization effect due to the steering effect. The major axis direction of each particle cannot be completely matched with the y-axis direction of FIG. 3A. As a result, the polarization axis is disturbed. On the other hand, when the reflective layer (metal lattice) and dielectric layer are formed, the convexity on the surface of the substrate becomes a one-dimensional lattice, and if the film is formed obliquely from the direction perpendicular to the longitudinal direction of the one-dimensional lattice (Fig. 17 (b)), the fine particles inevitably follow the lattice direction, and the disturbance of the polarization axis of the fine particle layer is greatly eliminated. Therefore, it is considered that the inorganic fine particles formed on the lattice have a larger optical anisotropy than when formed on a flat substrate. In the case where an inorganic fine particle layer made of Ge is formed on a substrate on which a reflective layer made of Al is provided in a one-dimensional lattice shape, it is difficult to measure the optical constant of Ge fine particles alone, but it is more than FIG. 3A. It is considered to have large optical properties.

  Therefore, as a lattice substrate imitating a substrate provided with a reflective layer made of Al in a one-dimensional lattice shape, a quartz substrate having a lattice pitch of 150 nm as shown in FIG. Characteristics were evaluated. Moreover, what used Corning 1737 glass as a flat substrate for a comparison was also evaluated. Here, when the oblique sputtering film forming method shown in FIG. 3A is used to obliquely form Ge with an ion beam sputtering of about 30 nm, the transmission axis contrast at a wavelength of 550 nm is 1.3 (flat substrate). ), 2.7 (lattice substrate), and the contrast was about twice as high when the film was formed on the lattice shape. This confirms the above effect.

  In the oblique film formation, as shown in FIG. 19, the shape of the film formation particle changes with the film thickness (thickness in the growth direction of the inorganic fine particles), which affects the optical anisotropy. That is, when the film thickness b of the inorganic fine particles is smaller than the major axis a of the particles (FIG. 19A), it has optical anisotropy in two directions (X and Y directions) on the substrate surface, and the direction of the major axis a is the absorption axis. It becomes. On the other hand, when the film thickness b of the inorganic fine particles is larger than the major axis a of the particles (FIG. 19B), it has optical anisotropy in the thickness direction of the inorganic fine particles and the in-plane axial direction. 19a and 19B, the direction of optical anisotropy is substantially reversed. In the present invention, since the grating direction is used as the absorption axis, a thick film means that the polarization characteristics deteriorate. Therefore, as shown in FIG. 19A, it is desirable to use in a region where the relationship of (particle major axis a)> (particle thickness b).

  By the way, even if a thin film having no optical anisotropy (for example, a germanium thin film) is formed on the dielectric layer 13 instead of the inorganic fine particle layer 14, the reflectance is improved in the absorption axis direction by optimizing the film thickness. Suppression is possible. However, in this case, since the interference effect is dominant in the suppression, there is a problem that the transmission band transmittance decreases because the wavelength band is narrow and there is absorption in the transmission axis direction. Furthermore, since the interference effect is sensitive to the film thickness, in order to obtain desired characteristics, it is necessary to strictly control the film thickness of the dielectric layer 13 and the film thickness of the germanium thin film. On the other hand, in the present invention, germanium fine particles having optical anisotropy are used, so that the design range is wide and the manufacture is easy.

Therefore, a difference in optical characteristics between the case where the inorganic fine particle layer 14 in the polarizing element 10 is a thin film and the case where it is a fine particle was simulated by a wavelength rigorous coupled wave analysis (RCWA) method. Here, film thickness (aluminum thickness): 200 nm, lattice pitch: 150 nm, aluminum width: 45 nm for the reflective layer 12, and film thickness (SiO2): 30 nm for the dielectric layer 13, with respect to the film thickness of the Ge thin film and Ge fine particles. The dependence of absorption axis reflectance, transmission axis transmittance, and transmission contrast at a wavelength of 450 nm was calculated. In addition, the optical constant of the Ge thin film uses the value shown in FIG. 4B, and the optical constant of the Ge fine particle takes into account the increase in anisotropy when deposited on the lattice. The calculation was performed on the assumption that fine particles sufficiently smaller than the wavelength were distributed in the dielectric layer with the axial direction aligned. Further, the volume ratio of Ge in the dielectric layer 13 was calculated as 0.4 and the aspect ratio was 20.
The result is shown in FIG. FIG. 21A shows the absorption axis reflectance, FIG. 21B shows the transmission axis transmittance, and FIG. 21C shows the transmission contrast. It can be seen that the Ge fine particles have the same contrast, higher transmittance, and wider film thickness range in which the reflectance can be reduced than the Ge thin film.

(Example 2)
In the polarizing element 10 having the configuration shown in FIG. 1, the transmission contrast can be easily controlled by changing the height (film thickness) of the reflective layer 12. As an example, FIG. 22 shows a wavelength-strictly coupled wave of a reflective layer thickness (aluminum height) and a transmission contrast at a wavelength of 550 nm when the pitch is 150 nm and the aluminum width is 37.5 nm as the primary lattice-like reflective layer 12 made of Al. The calculation result by analysis (RCWA) is shown.

  In the polarizing element 10 having the configuration shown in FIG. 1, the optical characteristics can be easily controlled by changing the height (film thickness) of the dielectric layer 13. Here, on the substrate 11 made of glass (Corning 1737), the primary lattice-like reflective layer 12 made of Al has a thickness (aluminum height) of 200 nm, a pitch of 150 nm, a lattice width of 50 nm, and RF sputtering. The thickness of the dielectric layer 13 made of SiO2 by deposition is changed to 0, 19, 37, 56, and 74 nm, and the thickness of the inorganic fine particle layer 14 made of Ge fine particles is 30 nm. The sample was prepared, and the relationship between the thickness of the dielectric layer at the wavelengths of 450, 550, and 650 nm, the transmission axis transmittance, the contrast, and the absorption axis reflectance of the obtained sample was determined. The results are shown in Table 1.

From the obtained results, for example, when it is desired to reduce the absorption axis reflectivity, the film thickness of the dielectric layer 13 may be in the range of 19 to 37 nm. In addition, when used in applications where the influence of reflection is small, the film thickness of the dielectric layer 13 can be set to zero. This means a reduction in the production process and leads to an improvement in productivity. In addition, it achieves high contrast at a wavelength of 450 to 650 nm, and is suitable for projector applications with a wide operating wavelength range.
On the other hand, the transmittance is as high as 70% or higher at a wavelength of 450 nm and 80% or higher at wavelengths of 550 and 650 nm. The transmittance can be further improved by narrowing the pitch of the grating.
The contrast can be adjusted by the height of the metal grid. If higher contrast is required, the aluminum grid should be raised, and lower if desired.

Next, a sample of the polarizing element having the configuration shown in FIG. 1 was produced. Here, on the substrate 11 made of glass (Corning 1737), an aluminum lattice having a pitch of 150 nm and a lattice depth of 30 nm is prepared as the reflective layer 12, and 30 nm of SiO2 is formed thereon as the dielectric layer 13, The ion beam sputtering apparatus of FIG. 2 is used to perform oblique sputtering film formation on a substrate 11 at room temperature with a substrate tilt angle θ = 5 °, and a Ge fine particle layer is deposited as a inorganic fine particle layer 14 to a thickness of 30 nm. A polarizing element sample shown in FIG. 1 was prepared by forming 30 nm of SiO2.
FIG. 23 shows the polarization characteristics of the polarizing element sample. In this case, since the thickness of the reflective layer is thin (the aluminum height is low), the contrast is about 3 in the blue region, but the reflectance is suppressed to 2% or less due to the effect of Ge fine particles. In the case of a polarizing element having such performance, Ge fine particles are deposited on the side wall of the convex portion made of a reflective layer / dielectric layer, and have a good shape as an anisotropic optical absorption element.

  In the polarizing element 10 of the present invention, the lattice shape (the shape and height of the reflective layer 12 / dielectric layer 13 in FIG. 1, the pitch of the primary lattice, etc.) and the steering effect (size, aspect ratio, arrangement, etc. of the inorganic fine particles 14a) ) Can be combined to realize a fine particle shape suitable as an absorption polarizing element.

(Example 3)
In the polarizing element 10 shown in FIG. 1, as a countermeasure against stray light on the exit surface (ghost countermeasure), the surface of the substrate 11 is in a state where fine stripes are aligned in one direction so as to correspond to the arrangement direction of the inorganic fine particles 14a to be formed later. A rubbing treatment is performed so as to have a certain texture structure, and a thin film made of inorganic fine particles having shape anisotropy so as to correspond to the arrangement direction of the inorganic fine particles 14a on the surface after the rubbing treatment (thin film (hereinafter referred to as antireflection layer 18) An antireflection film)) may be formed. Specifically, a texture structure is mechanically formed on the surface of the substrate 11 using an abrasive such as an abrasive tape, and then an antireflection film made of inorganic fine particles is formed on the lattice by an oblique sputtering film formation method. Since the inorganic fine particles having shape anisotropy due to the steering effect can be formed in the same manner as the inorganic fine particle layer 14 to be formed, the polarization effect of the inorganic fine particles is enhanced, and as a result, the ghost suppressing effect can be enhanced. Hereinafter, a specific example will be described.

  Here, the effect was verified using Nippon Micro Coating D20000 as an abrasive. Corning 1737 glass was used as the substrate, and the texture was formed by rubbing the surface in one direction with D20000. FIG. 24 shows the result of measuring the substrate surface after texture formation by AFM (Atomic Force Microscope). The horizontal axis is the position on the substrate, and the vertical axis is the height of the surface irregularities. The average pitch of the irregularities on the substrate surface was 160 nm. Further, when the transmittance of the substrate before and after the texture formation was examined, it was found that the transmittance did not change before and after the texture formation (before and after polishing) as shown in FIG. That is, according to this method, it is possible to easily perform nano-level precision processing without deteriorating the transmission characteristics of the substrate.

  Next, a 10 nm thick antireflection film made of Ge fine particles was formed on the textured substrate by oblique sputtering film formation with a substrate tilt angle θ = 5 ° by the ion beam sputtering apparatus of FIG. At this time, as for the relationship between the Ge incident direction and the substrate, the substrate was disposed so that the y direction in FIG. When the shape of the Ge fine particles in the antireflection film was observed with the AFM (atomic force microscope) for the obtained sample, as shown in FIG. 26, the state where the Ge fine particles were aligned along the texture was observed. It was.

FIG. 27 shows the transmission characteristics of this sample. For comparison, the transmission characteristics were also examined for a sample in which an antireflection layer was formed under the same conditions except that the substrate was a 1737 glass substrate that was not rubbed. In FIG. 27, the sample of this example is expressed as “texture substrate”, and the comparative sample is expressed as “as is”. As a result, both showed polarization characteristics due to the steering effect. However, the texture formation had higher transmittance in the x direction and a larger difference from the transmittance in the y direction, indicating good polarization characteristics. .
In the present invention, the layer structure of the polarizing element 10 in FIG. 1 is formed thereon using the sample of the present example (an antireflection film formed on a substrate having a texture structure). At the same time that the body layer 13 is patterned, the antireflection film is also processed into a lattice shape to form an antireflection layer 18. Thereby, the ghost countermeasure effect can be enhanced, and at the same time, an increase in transmission contrast characteristics as a polarizing element can be expected.

DESCRIPTION OF SYMBOLS 1 ... Stage, 2 ... Target, 3 ... Beam source, 4 ... Control board 10, 10A, 10B, 10C, 20, 30, 40, 40A, 40B ... Polarizing element, 11 ... Substrate 12 ... Reflective layer, 12a ... Band-shaped thin film, 13, 19 ... Dielectric layer, 14 ... Inorganic fine particle layer, 14a ... Inorganic fine particle, l5 ... Uneven portion (polarized wave selective light absorption layer due to optical anisotropy), 16 ... Inorganic fine particle layer (selective light absorbing layer of polarized wave due to optical anisotropy), 17 ... Selective light absorbing layer of polarized wave due to optical anisotropy, 18 ... Antireflection layer, 1a ... Laminated structure, 50 ... Liquid crystal panel, 60 ... Cross dichroic prism, 100 ... Liquid crystal projector

Claims (14)

A substrate transparent to the light in the use band,
A reflective layer in which strip-shaped thin films extending in one direction on the substrate are arranged in a one-dimensional lattice pattern at a pitch smaller than the wavelength of light in the use band;
A dielectric layer formed on the reflective layer;
A polarizing element comprising: an inorganic fine particle layer which has a light absorption function in which inorganic fine particles are arranged in a primary lattice pattern on the dielectric layer at a position corresponding to the belt-like thin film.   2. The polarizing element according to claim 1, wherein the inorganic fine particle layer has optical anisotropy in an arrangement direction of the inorganic fine particles and a direction orthogonal to the arrangement direction of the inorganic fine particles.   The polarizing element according to claim 1, wherein the inorganic fine particles have shape anisotropy.   The polarizing element according to claim 1, wherein the substrate is made of a glass material.   The polarizing element according to claim 1, wherein the reflective layer is a metal layer.   The inorganic fine particles are made of Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, Sn, or an alloy containing these, or a silicide-based semiconductor material. The polarizing element according to claim 1. The dielectric layer has a concavo-convex shape that forms a convex portion immediately above the strip-shaped thin film and a concave portion between the strip-shaped thin films
The polarizing element according to claim 1, wherein the inorganic fine particle layer is formed on a top portion of the convex portion of the dielectric layer or at least one side surface portion thereof.   On the other surface of the substrate, a one-dimensional lattice-shaped concavo-convex portion formed in parallel with the direction in which the strip-shaped thin film of the reflective layer extends, and inorganic fine particles on the top or at least one side surface of the concavo-convex portion are in a primary lattice shape 2. The polarizing element according to claim 1, further comprising a light absorption layer comprising a second inorganic fine particle layer arranged in an array.   The polarizing element according to claim 1, wherein an antireflection layer is formed between the reflection layer and the substrate.   The antireflection layer is rubbed so that the surface of the substrate corresponds to the arrangement direction of the inorganic fine particles, and the surface after the rubbing treatment has shape anisotropy so as to correspond to the arrangement direction of the inorganic fine particles. The polarizing element according to claim 9, wherein inorganic fine particles are attached.   2. The polarizing element according to claim 1, wherein one or more laminated structures of the dielectric layer / the inorganic fine particle layer are stacked on the inorganic fine particle layer.   The polarizing element according to claim 1 and second inorganic fine particles in which inorganic fine particles are arranged in a one-dimensional lattice form on the top or at least one side surface of a one-dimensional lattice-like uneven portion formed on another substrate surface. A polarizing element having a layer is bonded to the back surface of each substrate so that the direction in which the strip-like thin film of the reflective layer extends and the lattice longitudinal direction of the concavo-convex part are aligned.   The polarizing element according to any one of claims 1 to 12, wherein a protective layer transparent to light in a use band is formed on the outermost surface of the polarizing element. A liquid crystal projector comprising: a lamp; a liquid crystal panel; and the polarizing element according to claim 1.

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