JP2005258050A - Reflection mirror and image projection device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image projection device (rear projector) having less unevenness in the brightness of a projected image by providing a reflection mirror uniform in the incidence angle distribution of reflectivity and the wavelength distribution. <P>SOLUTION: The reflection mirror which utilizes only s-polarized light as reflected light is constituted by laminating an alloy film having at least an Ag film or Ag as a main component, a transparent dielectric film having 1.2 to 1.5 refractive index at principal wavelength of 450nm and 0.8 to 1.0 optical film thickness, and a transparent dielectric film having 2.2 to 2.7 refractive index at principal wavelength of 450nm and 0.8 to 1.0 optical film thickness, in order on a base. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reflecting mirror used in an optical apparatus, and more particularly to a reflecting mirror that uses only S-polarized light applied to an image projection apparatus such as a liquid crystal projector as reflected light.

  In recent years, there has been a demand for larger screens for displaying images and videos, and image display devices are becoming larger and thinner. A projection device (projector) that projects an image generated by a display element such as a liquid crystal onto a screen is used as a display device corresponding to a large screen display.

  A rear projector, which is one configuration of this projector, is configured by housing an image projection device 10, a reflecting mirror 20, and a screen 30 in a housing 40 as shown in FIG. As screens become larger and devices become thinner, the incident angle of light to the reflecting mirror increases as α at the upper end of the reflecting mirror increases and β at the lower end decreases as shown in FIG. The difference in increases.

  A metal film is generally used as such a reflecting mirror. In this case, the reflectivity depends on the incident angle of incident light, and as a result, an in-plane distribution occurs in the brightness of the image projected on the screen, and the in-plane distribution is conspicuous if the difference between α and β is large. Become. At the same time, the angle dependency of the reflectivity differs for each wavelength, so that there is a problem that color distribution also occurs simultaneously in the screen.

  In order to solve such a problem, Patent Document 1 discloses a technique in which a reflective film is an inclined film having an in-plane thickness distribution so that the in-plane brightness distribution is eliminated. ing.

  The image projection apparatus includes a light source that emits light having a predetermined spectral distribution and an image generation element that generates and projects image light by irradiating light emitted from the light source. As the image generation element of the rear projector, a transmissive liquid crystal display element, a reflective liquid crystal display element, a movable reflector array using a micro electro mechanical system, or the like is used.

In a rear projector using a transmissive liquid crystal display element and a reflective liquid crystal display element, it is general to design an optical system so as to use S-polarized light having a high reflectance. Here, S-polarized light refers to light polarized in the horizontal direction of the projected image as shown in FIG.
JP 2003-280093 A

  However, in the method disclosed in Patent Document 1, it is necessary to provide an inclined film in a large area, and technical difficulty increases as the size of the reflecting mirror increases. For example, sputter film formation is generally used to form such a reflector, but the film thickness distribution generally changes with time as the erosion of the sputter target progresses. It is extremely difficult to control this to obtain the desired film thickness distribution.

  The present invention has been made to solve such problems, and an object thereof is to provide a reflecting mirror in which the incident angle distribution and the wavelength distribution of the reflectance are made uniform without using an inclined film. Still another object is to provide an image projection apparatus in which the brightness of the projected image is less uneven.

  In the present invention, in an optical system using S-polarized light that is generally used for a projector using a transmissive liquid crystal display element or a reflective liquid crystal display element, the incident angle of the reflectance is even in the case of a uniform film thickness distribution. This is achieved by finding a film configuration that can reduce (homogenize) the distribution and the wavelength distribution of the reflectance.

  The reflecting mirror using only the S-polarized light of the present invention as reflected light includes at least an Ag film or an alloy film containing Ag as a main component on a substrate, an optical film having a refractive index of 1.2 to 1.5 at a main wavelength of 450 nm. A transparent dielectric film having a thickness of 0.8 to 1.0, and a transparent dielectric film having a refractive index of 2.2 to 2.7 at the same dominant wavelength and an optical film thickness of 0.8 to 1.0. Are sequentially stacked.

  By adopting such a film configuration, it is possible to provide a reflecting mirror in which the incident angle distribution and the wavelength distribution of the reflectance with respect to S-polarized light are made uniform in the visible light wavelength region.

Further, it is preferable to provide an adhesive layer between the base and the Ag film or an alloy film containing Ag as a main component. As the adhesive layer, Cr, Pt, Ti, NiCr alloy, stainless alloy, or the like, a composite oxide mainly containing ZnO, or a composite oxide mainly containing In ₂ O ₃ can be used.
By providing the adhesive layer, the adhesion between the substrate and the Ag film or an alloy film containing Ag as a main component can be improved.

Furthermore, it is desirable to provide an additional layer at the interface between the Ag film or an alloy film containing Ag as a main component and the transparent dielectric film having a refractive index of 1.2 to 1.5. As this additional layer, Ti, Cr, Si, NiCr, Zn, stainless alloy, Ta, W, Al, Au, Pd, Pt or a layer of an oxide of these metals, or Al-added ZnO, Ga-added ZnO, Sn It is preferable to use an oxide layer such as added In ₂ O ₃ , Nb-added TiO ₂ , NbOx (0 <x <2.5), TiOx (0 <x <2).

  By providing an additional layer made of these materials, the adhesion between the Ag film or an alloy film containing Ag as a main component and the transparent dielectric film can be improved. Further, these metal films function as a protective film against corrosion of an Ag film or an alloy film containing Ag as a main component.

  It is preferable that at least one of Au, Pd, Pt, Zn, Sn, and Al is contained as a component added to the alloy containing Ag as a main component. Note that the content of these additive components is approximately 5% or less, and the main component is Ag.

  Since the above-described component has an effect of suppressing corrosion of the Ag film in the environment, it is preferable that the amount of the additive is large in terms of corrosion resistance. However, when the amount of these additives increases, the inherent high reflectance of the Ag layer is impaired. For this reason, the addition amount is preferably 5% or less.

An image projection apparatus according to the present invention includes a light source that emits light having a predetermined spectral distribution, an image generation element that generates and projects image light by irradiating light emitted from the light source, and the image generation element. The above-described reflecting mirror that reflects the image light that is generated and projected, and a screen that projects the image light reflected by the reflecting mirror. The image generating element includes a liquid crystal display element.
By adopting such a configuration, it is possible to provide an image projection apparatus with high uniformity of brightness of the projected image.

  ADVANTAGE OF THE INVENTION According to this invention, the reflection mirror which made uniform the incident angle distribution and wavelength distribution of the reflectance with respect to S polarization | polarized-light in a visible light wavelength range can be provided. Further, by using this reflecting mirror, it is possible to provide an image projection apparatus with high uniformity of the projected image.

  Hereinafter, the present invention will be described in detail with reference to the drawings. However, the present invention is not limited by this embodiment.

  In the present invention, it is considered to provide a reflecting mirror having a small incidence angle distribution and wavelength distribution of reflectance by a combination of a film having a uniform material and thickness. For this reason, based on the metal / low-refractive index dielectric layer / high-refractive index dielectric layer structure, which is a so-called increased reflection film structure, search for a film structure in which the reflectance with respect to S-polarized light varies little with the incident angle and wavelength did.

  As a result, it has been found that the real part of the refractive index of the metal layer is preferably smaller in order to reduce the dependency of the reflectance on the incident angle. From this viewpoint, it was found that an Ag layer or an alloy containing Ag as a main component is most preferable when a metal is selected.

  However, if the main wavelength when the low refractive index dielectric layer / high refractive index dielectric layer is generated on the Ag layer or the layer containing Ag as a main component is set to the center wavelength (550 nm) in the visible light region, blue It turned out that the reflection of becomes low. Thus, by setting the center wavelength to the short wavelength side (450 nm), the inventors succeeded in producing a unique mirror with extremely small both S-polarized reflectance wavelength dispersion and incident angle dispersion.

  Further, as a result of specific examination, Ag or an alloy containing Ag as a main component is adopted as a metal, and a refractive index is 1.2 to 1.5 and an optical film thickness is 0.8 to 1. It has been found that a structure in which a transparent dielectric film of 0 and a transparent dielectric film having a refractive index of 2.2 to 2.7 at the same wavelength and an optical film thickness of 0.8 to 1.0 are laminated is most excellent. It was.

  Examples of the reflecting mirror having the film structure in the above preferable range will be described below along the manufacturing method thereof.

[Example 1]
Three types of targets of Ag, Si, and Ti were attached to an in-line type sputtering apparatus, and soda lime glass having a transparent and smooth surface was inserted into the sputtering apparatus as a reflector substrate, and the apparatus was evacuated to a vacuum. Thereafter, Ar gas was introduced into the sputtering apparatus, and the gas flow rate and the exhaust speed were adjusted so that the pressure in the apparatus was 0.3 Pa.

  DC power was supplied to the Ag target to start discharging, and the power was adjusted to 0.4 kW. Thereafter, the substrate (soda lime glass) was transported and passed through the front surface of the target to form an Ag film having a thickness of 200 nm.

Next, the Ti target was discharged in an Ar gas atmosphere, the substrate was transported, passed through the front surface of the Ti target, and a Ti film having a thickness of 2 nm was formed. This film is oxidized by a SiO ₂ film forming process to be formed later, and changes to TiO _x (0 <x <2). This TiOx film is an additional layer no optical function, it is desirable to insert in order to increase the adhesion of the Ag film and the SiO ₂ film.

  In addition, when oxygen-containing plasma is used to form a transparent dielectric film on an Ag film or an alloy film containing Ag as a main component, the Ag film or a film containing Ag as a main component is easily corroded by oxygen plasma. These metal films function as a protective film against this corrosion phenomenon.

Thereafter, the sputtering gas was changed from Ar to O ₂ mixed with 30% Ar, and the gas pressure was adjusted to 0.3 Pa. Next, DC pulse power was supplied to the Si target, discharge was started, and the discharge power was adjusted to 2 kW. The substrate was transported and passed through the front surface of the Si target to form a transparent SiO ₂ film having a thickness of 76.5 nm. This SiO ₂ film has a refractive index of 1.47 at a main wavelength of 450 nm and an optical film thickness of 1.00.

Furthermore, DC pulse power was supplied to the Ti target in an O ₂ gas atmosphere in which 30% of Ar was mixed, and discharge was started. Thereafter, the discharge power was adjusted to 2 kW. The substrate was transported and passed through the front surface of the Ti target to form a transparent TiO ₂ film having a thickness of 42.8 nm. This TiO ₂ film has a refractive index of 2.63 at a main wavelength of 450 nm and an optical film thickness of 1.00. The film configuration (material and stacking order of each layer, and film thickness of each layer) is shown in Table 1 (the same applies to the following examples and comparative examples).

  Regarding the film surface side reflection characteristics of the obtained sample, the incident angle dependence of the reflectance was measured using a spectrophotometer at three wavelengths of 450 nm, 550 nm, and 650 nm.

  The S-polarized light reflectance at a wavelength of 450 nm and an incident angle of 0 ° (perpendicular incidence) was 95.7%, and the S-polarized light reflectance at the same wavelength at an incident angle = 75 ° was 99.5%. The S-polarized reflectance at the incident angle during the period was 95.7% or more and 99.5% or less, and the dependency of the reflectance on the incident angle was very small.

  The S-polarized light reflectance at a wavelength of 550 nm and an incident angle = 0 ° (perpendicular incidence) was 97.7%, and the S-polarized light reflectance at the same wavelength at an incident angle = 75 ° was 99.4%. . The S-polarized reflectance at the incident angle during the period was 97.7% or more and 99.4% or less, and the dependency of the reflectance on the incident angle was very small.

  The S-polarized light reflectance at a wavelength of 650 nm and an incident angle = 0 ° (perpendicular incidence) was 97.5%, and the S-polarized light reflectance at the same wavelength at an incident angle = 75 ° was 99.1%. . The S-polarized reflectance at the incident angle during the period was 97.5% or more and 99.1% or less, and the dependency of the reflectance on the incident angle was very small.

As an index indicating the uniformity of the incident angle dispersion of the S-polarized reflectance at each wavelength, the reflectance ratio is expressed by the following equation:
Reflectance ratio = (maximum reflectance / minimum reflectance)
Defined by
At 450 nm, the reflectance ratio = 1.04
At 550 nm, the reflectance ratio = 1.02
At 650 nm, the reflectance ratio = 1.02
In the entire wavelength range of 450 nm to 650 nm, as shown in Table 2, the reflectance ratio is 1.04.

  From this, it can be seen that the reflection mirror has extremely high uniformity of reflectance when the wavelength is in the range of 450 to 650 nm and the incident angle is in the range of 0 to 75 °.

[Example 2]
In this embodiment, a Cr film having a film thickness of 5 nm is formed on the surface of a soda-lime glass substrate by vacuum deposition, and thereafter, a reflector having the same film thickness as that of the first embodiment is composed of Ag / TiOx / SiO ₂ / TiO _2. Produced. The inserted Cr film functions as an adhesive layer that improves the adhesion between the soda-lime glass and the Ag film. Since the presence of the adhesive layer does not affect the optical characteristics, the reflectance measured in the same manner as in Example 1 was the same as that in Example 1, as shown in Table 2.

[Example 3]
The film configuration of this example is Ag / TiOx / SiO ₂ / TiO ₂ similar to that of Example 1, but the film thickness of SiO ₂ is 61.2 nm (equivalent to optical film thickness: 0.80), and TiO ₂ The film thickness was 34.2 nm (optical film thickness: equivalent to 0.80).
As shown in Table 2, a highly reflective mirror having a reflectance ratio of 1.04 was obtained within a wavelength range of 450 to 650 nm and an incident angle of 0 to 75 °.

[Example 4]
The film structure of this example is a structure of Ag / MgF ₂ / NbTiO x in which MgF ₂ is used for the low refractive index layer and NbTiO x is used for the high refractive index layer. The film thickness of MgF ₂ is 73.0 nm (optical The film thickness of NbTiOx was 38.5 nm (corresponding to an optical film thickness: 0.90). The MgF ₂ film has a refractive index of 1.39 at a main wavelength of 450 nm and an optical film thickness of 0.90. The NbTiOx film has a refractive index of 2.63 at a main wavelength of 450 nm and an optical film thickness of 0.90. This film sample was prepared by sputtering using MgF ₂ , NbTi alloy, and Ag as targets.

  As shown in Table 2, a reflection mirror having a very high uniformity with a reflectance ratio of 1.02 to 1.03 is obtained within a wavelength range of 450 to 650 nm and an incident angle of 0 to 75 °. It was.

[Example 5]
In the film configuration of this example, an AgPd alloy containing 3% Pd was used as a metal film. MgF ₂ was used for the low refractive index layer, and TiO ₂ was used for the high refractive index layer. The film configuration is AgPd / TiOx / MgF ₂ / TiO ₂ . The film thickness of MgF ₂ was 73.0 nm (optical film thickness: corresponding to 0.90), and the film thickness of TiO ₂ was 38.5 nm (optical film thickness: corresponding to 0.90).

  As shown in Table 2, a reflector having a very high uniformity with a reflectance ratio of 1.03 to 1.04 is obtained within a wavelength range of 450 to 650 nm and an incident angle of 0 to 75 °. It was.

[Comparative Example 1]
In contrast to the film configuration of Example 1, only the metal film was replaced with Al. As shown in Table 1, the reflectance ratio in the entire wavelength range was 1.07, and the result that the dispersion of the reflectance was large was obtained.

[Comparative Example 2]
With respect to the film configuration of Example 1, the film thickness of SiO ₂ was 57.4 nm (corresponding to optical film thickness: 0.75). The film thickness of TiO ₂ was 32.1 nm (equivalent to optical film thickness: 0.75). As shown in Table 2, the reflectance ratio in the entire wavelength region was 1.05, and the result that the dispersion of the reflectance was large was obtained.

[Comparative Example 3]
With respect to the film configuration of Example 1, the film thickness of SiO ₂ is 95.6 nm (equivalent to optical film thickness: 1.25), and the film thickness of TiO ₂ is 53.5 nm (optical film thickness: 1.25). Equivalent). As shown in Table 2, the reflectance ratio at a short wavelength of 450 nm was 1.17, and the total wavelength range was 1.18. Thus, a large dispersion of reflectance was obtained.

[Comparative Example 4]
For the film configuration of Example 1, Al ₂ O ₃ was used instead of SiO ₂ of the low refractive index layer. The refractive index of the Al ₂ O ₃ film at a main wavelength of 450 nm was 1.65, and the film thickness was 68.3 nm corresponding to an optical film thickness of 1.00. As shown in Table 2, the reflectance ratio in the entire wavelength range was 1.05, and the result that the dispersion of the reflectance was large was obtained.

[Comparative Example 5]
For the film configuration of Example 1, SnO ₂ was used instead of TiO ₂ of the high refractive index layer. The refractive index of the SnO ₂ film at a main wavelength of 450 nm was 2.03, and the film thickness was 55.3 nm corresponding to an optical film thickness of 1.00. As shown in Table 2, the reflectance ratio in the entire wavelength range was 1.07, and the result that the dispersion of the reflectance was large was obtained.

  In the various film configurations of Comparative Examples 1 to 5, the reflectance ratio in the wavelength range of 450 to 650 nm and the incident angle in the range of 0 to 75 ° is 1.05 to 1.18, and S It was found that the reflecting mirror has a high wavelength dependency or incident angle dependency of the polarization reflectance.

  When these reflecting mirrors were used as reflecting mirrors for rear projectors using transmissive liquid crystal display elements, a clear brightness distribution was observed in the plane of the screen.

  In summary of the above results, a reflecting mirror that uses only S-polarized light as reflected light has an Ag film or an alloy film containing Ag as a main component on the substrate, and a refractive index at a main wavelength of 450 nm of 1.2 to 1. 5. Transparent dielectric film having an optical film thickness of 0.8 to 1.0 and transparent dielectric film having a refractive index of 2.2 to 2.7 at the same main wavelength and an optical film thickness of 0.8 to 1.0 It turns out that it is preferable to laminate | stack a body film in order.

  Further, when the reflectors of Examples 1 to 5 were mounted on the rear projector having the configuration shown in FIG. 1, the brightness in the screen surface was eliminated, and a uniform image quality could be obtained. Therefore, if a reflecting mirror that falls within the above condition range is used, it is possible to provide a rear projector that is an image projection device with high uniformity of brightness within the screen.

As the low refractive index transparent dielectric layer having a refractive index of 1.2 to 1.5, SiO ₂ , MgF ₂ or the like can be used as described above, but is not particularly limited thereto. Moreover, as a high refractive index transparent dielectric layer having a refractive index of 2.2 to 2.5, in addition to the above TiO ₂ , Nb ₂ O ₅ , Ta ₂ O _5, etc., or TiO ₂ as a main component is used. A composite oxide such as NbTiOx can be used, but is not particularly limited thereto.

  As an additional layer, in addition to the above Ti, any layer of Cr, Si, Zn, Ta, W, Al, Au, Pd, Pt, NiCr alloy, or stainless alloy, or a layer of oxide of these metals. There may be. A metal film is preferable because it does not easily cause film defects, but it must be controlled so that a film thickness of about 2 nm or less is obtained in order to oxidize and use the film in the film forming process as in the above embodiment.

The additional layer may be an oxide sintered body target and an oxide film may be formed in a low oxygen concentration atmosphere. In this case, Al-added ZnO, Ga-added ZnO, Sn-added In ₂ O ₃ , Nb-added TiO ₂ , NbOx (0 <x <2.5), TiOx (0 <x <2) and the like are preferable materials. The film thickness may be about 5 to 10 nm.

The same effect can be obtained by using Pt, Ti, NiCr alloy, stainless alloy or the like in addition to the above Cr as the adhesive layer inserted between the metal layer mainly composed of Ag and the glass substrate. Alternatively, a composite oxide mainly containing ZnO or a composite oxide mainly containing In ₂ O ₃ can be used.

  When an Ag alloy is used as the metal layer, the component to be added may be one or more of Au, Pd, Pt, Zn, Sn, and Al in addition to the above Pd.

It is a figure which shows the basic composition of an image projector (rear projector).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image projector 20 Reflector 30 Screen 40 Case

Claims (10)

In a reflecting mirror using only S-polarized light as reflected light, at least an Ag film or an alloy film containing Ag as a main component, a refractive index at a main wavelength of 450 nm of 1.2 to 1.5, and an optical film thickness on a substrate. A transparent dielectric film of 0.8 to 1.0 and a transparent dielectric film having a refractive index of 2.2 to 2.7 and an optical film thickness of 0.8 to 1.0 at the same main wavelength are sequentially laminated. Reflector that is characterized by that. The reflecting mirror according to claim 1, wherein an adhesive layer is provided between the base and the Ag film or an alloy film containing Ag as a main component. 3. The reflecting mirror according to claim 2, wherein the adhesive layer is a layer of any one of Cr, Pt, Ti, NiCr alloy, and stainless alloy. _3. The reflecting mirror according to claim 2, wherein the adhesive layer is a composite oxide layer containing ZnO as a main component or a composite oxide containing In ₂ O ₃ as a main component. The reflecting mirror according to claim 1, wherein an additional layer is provided at an interface between the Ag film or an alloy film containing Ag as a main component and the transparent dielectric film. The additional layer is any one of Ti, Cr, Si, Zn, Ta, W, Al, Au, Pd, Pt, NiCr alloy, or a stainless alloy, or a layer of an oxide of these metals. The reflecting mirror according to claim 5. The additional layer is any one of Al-doped ZnO, Ga-doped ZnO, Sn-doped In ₂ O ₃ , Nb-doped TiO ₂ , NbOx (0 <x <2.5), and TiOx (0 <x <2). The reflecting mirror according to claim 5, wherein The component added to the alloy film containing Ag as a main component in addition to Ag is at least one selected from Au, Pd, Pt, Zn, Sn, and Al. The reflecting mirror as described in any one of -7. A light source that emits light having a predetermined spectral distribution, an image generation element that generates and projects image light by irradiating the light emitted from the light source, and image light that is generated and projected by the image generation element An image projection apparatus comprising: the reflecting mirror according to any one of claims 1 to 8; and a screen that projects image light reflected by the reflecting mirror. The image projection apparatus according to claim 9, wherein the image generation element includes a liquid crystal display element.

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