JP5541813B2 - Reflective light modulator - Google Patents

Description

  The present invention relates to a reflection type light modulation device.

  As a reflection type light modulation device, a reflection type liquid crystal (LCoS (registered trademark): Liquid crystal on silicon) device is known. The reflective liquid crystal device includes a plurality of pixel electrodes arranged two-dimensionally, a conductive light transmission layer, and a liquid crystal layer (light modulation layer) disposed between the plurality of pixel electrodes and the conductive light transmission layer. In addition, while reflecting light incident through the conductive light transmitting layer, an electric field is formed between any pixel electrode and the conductive light transmitting layer to cause a modulation effect on the liquid crystal layer. Obtain an image. A dielectric multilayer film is provided between the liquid crystal layer and the plurality of pixel electrodes in order to increase the light reflectance and obtain a light image with higher brightness.

For example, Non-Patent Documents 1 and 2 disclose a liquid crystal light valve (LCLV) having a reflective liquid crystal structure. The dielectric multilayer film described in Non-Patent Document 1 is formed by alternately laminating a plurality of Si layers and SiO ₂ layers having an optical film thickness of λ / 4 (λ: wavelength of incident light). The dielectric multilayer film described in Non-Patent Document 2 is formed by alternately laminating a plurality of TiO ₂ layers and SiO ₂ layers having an optical film thickness of λ / 4.

U. Efron et al., “Siliconliquid crystal light valves: status and issues”, Optical Engineering, November, December 1983, Vol. 22, No. 6, pp. 682-686 (1983) A. Jacobson et al., “Areal-time optical data processing device”, Information Display, Vol.12, September 1975, PP.17-22 (1975)

According to the knowledge of the present inventors, a dielectric multilayer film laminated on the surface of a glass substrate or the like is used in a conventional reflective liquid crystal device. And by increasing the number of layers, a high reflectance of over 99% is obtained. For example, in order to obtain 99% or more reflectivity at the dielectric multilayer film on the glass _substrate, 13 layers with TiO 2 / SiO _2, and requires 19 layers with HfO 2 / SiO _2, reflectivity 99.8% or more to obtain _the 17 layers with TiO 2 / SiO _2, it requires a 25-layer with HfO ₂ / SiO 2.

  However, since the dielectric multilayer film is disposed between the liquid crystal layer and the pixel electrode, the electric field formed between the pixel electrode and the conductive light transmission layer is applied not only to the liquid crystal layer but also to the dielectric multilayer film. Is done. If the number of dielectric multilayer films increases, the thickness (physical film thickness) of the dielectric multilayer films increases and the ratio of the electric field applied to the dielectric multilayer films increases, so the electric field applied to the liquid crystal layer Efficiency will decrease.

  The present invention has been made in view of the above-described problems, and provides a reflection type light modulation device including a dielectric multilayer film capable of realizing a high reflectance while suppressing a decrease in electric field application efficiency to the light modulation layer. For the purpose.

  In order to solve the above-described problems, a reflection type light modulation device according to the present invention modulates light for each of a plurality of pixels arranged two-dimensionally and outputs a light image forward while reflecting light incident from the front. A reflective light modulation device comprising: a conductive light transmission layer including a conductive material that transmits light; a plurality of metal pixel electrodes that are two-dimensionally arranged along the conductive light transmission layer; A light modulation layer that is disposed between the pixel electrode and the conductive light transmission layer and modulates light according to an electric field formed by each pixel electrode and the conductive light transmission layer, and is formed on the plurality of pixel electrodes. A dielectric multilayer film, the dielectric multilayer film including a first layer in contact with the pixel electrode, and a second layer having a higher refractive index than the first layer and in contact with the first layer. To do.

  As described above, the conventional general reflection type light modulation device uses a dielectric multilayer film formed on a glass substrate. On the other hand, in the reflection type light modulation device according to the present invention, the dielectric multilayer film is formed on the plurality of metal pixel electrodes. Thereby, the high reflectance of a metal surface can be utilized. In addition, when forming the dielectric multilayer film on the metal surface, the present inventors first formed a low refractive index layer (first layer) on the metal surface, and then formed a high refractive index layer (second layer). It has been found that a sufficient reflectance can be obtained with a significantly smaller number of layers as compared with the case where the layers are laminated thereon, as compared with the case where lamination is started from a high refractive index layer. Therefore, according to the reflection type light modulation device described above, the physical film thickness of the dielectric multilayer film can be made thinner than before, and the reduction in the electric field application efficiency to the light modulation layer can be suppressed, and a sufficiently high reflectance can be obtained. This can be realized to increase the light extraction efficiency.

  The reflective light modulation device may be characterized in that the optical film thickness of the first layer is within a range of (λ / 4) ± 30% where λ is the wavelength of light. Alternatively, the reflective light modulation device may be characterized in that the optical film thickness of the first layer is substantially equal to (λ / 4) × n (n is an odd number) where λ is the wavelength of light. With any of these configurations, a high reflectance can be suitably realized for light of a predetermined wavelength.

  In the reflection type light modulation device, the optical film thickness of the first layer is within the range of (λ / 4 cos θ) ± 30%, where θ is the incident angle of light inside the first layer, and λ is the wavelength of the light. It is good also as a feature. Alternatively, in the reflection type light modulation device, the optical film thickness of the first layer is such that the incident angle of light inside the first layer is θ and the wavelength of light is λ (λ / 4 cos θ) × n (n is an odd number) ) And substantially the same. With any one of these configurations, high reflectance can be suitably realized even for light incident on the dielectric multilayer film from an oblique direction.

  In the reflection type light modulation device, the dielectric multilayer film includes a plurality of low refractive index layers including a first layer, and a plurality of high refractive indexes including a second layer and having a higher refractive index than the plurality of low refractive index layers. The refractive index layers may be alternately stacked, and the sum of the number of the low refractive index layers and the number of the high refractive index layers may be 10 or less. As described above, the number of laminated dielectric multilayer films in a general reflection type light modulation device requires 13 layers or more. On the other hand, according to the above-described reflection type light modulation device, a sufficiently high reflectance can be realized even with a small number of layers, such as 10 layers or less, so that it is possible to effectively suppress a decrease in the efficiency of electric field application to the light modulation layer. it can.

In the reflection type light modulation device, the first layer includes SiO ₂ , and the second layer includes at least one material of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and HfO _2. May be a feature. Thereby, the dielectric multilayer film including the first layer and the second layer having a higher refractive index than the first layer can be suitably configured.

In the reflection type light modulation device, the first layer has a lower layer in contact with the pixel electrode, and an upper layer sandwiched between the lower layer and the second layer, the upper layer includes SiO ₂ , and the lower layer includes SiO _2. And MgF ₂ may include at least one material. An SiO ₂ film or an MgF ₂ film may be formed as a protective film on the surface of the pixel electrode, and this protective film may be used as a part (lower layer) of the first layer. Even with such a configuration, it is possible to suitably obtain the effects of the above-described reflection type light modulation device.

The reflection type light modulation device according to the present invention is a reflection type light modulation device that reflects light incident from the front and modulates light for each of a plurality of two-dimensionally arranged pixels to output an optical image forward. A conductive light-transmitting layer including a conductive material that transmits light, a plurality of metal pixel electrodes that are two-dimensionally arranged along the conductive light-transmitting layer, and the plurality of pixel electrodes and the conductive light transmitting layer. A light modulation layer that is disposed between the pixel electrodes and modulates light according to an electric field formed by each pixel electrode and the conductive light transmission layer, and a dielectric multilayer film formed on the plurality of pixel electrodes. , the dielectric multilayer film, and then contact the pixel electrode, _Si 3 _{N 4 TiO} 2 provided on the protective film and the protective film made _{of, Nb 2 O 5, Ta 2} O 5, HfO 2, and ZrO ₂ a third layer of the fourth layer comprising at least one kind of material of the third A first layer having a refractive index lower than that of the third layer and in contact with the third layer; and a first layer provided on the first layer and having a higher refractive index than that of the first layer. The optical thickness of the third layer is substantially equal to (λ / 2) × n (n is an odd number) where λ is the wavelength of light.

Thus, even when the high refractive index layer (third layer) is formed on the metal surface, the optical film thickness of the third layer is substantially λ / 2 × n (n is an odd number ). By making them equal, the influence on the reflectance can be made extremely small. Therefore, by forming a dielectric multilayer film starting from the low refractive index layer (first layer) on the third layer, it is possible to realize substantially the same reflection characteristics as those of the reflection type light modulation device described above. it can.

  According to the reflection type light modulation device of the present invention, the light extraction efficiency can be increased while suppressing a decrease in the electric field application efficiency to the light modulation layer.

1 is a plan view showing a configuration of a reflective liquid crystal device as an embodiment of a reflective light modulation device according to the present invention. It is side surface sectional drawing along the II-II line | wire of the reflection type liquid crystal device shown in FIG. It is side surface sectional drawing which expands and shows the structure of a dielectric multilayer film. It is side surface sectional drawing which shows the structure of the modification of a dielectric multilayer. (A) a first layer of a low refractive index film which is in contact with the aluminum substrate is a diagram showing a configuration of a (SiO _2). (B) is a diagram showing an embodiment in a first layer in contact with the aluminum substrate and the high refractive index film (TiO _2). It is a graph which shows the spectral reflectance when not providing a dielectric multilayer on the surface of an aluminum substrate. 6 is a graph showing the spectral reflectance in each case where the number of laminated multilayer dielectric films is 2, 4, 6, and 10 in the embodiment shown in FIG. FIG. 6 is a graph showing the spectral reflectance in each case where the number of layers is 4, 6, 10, and 14 in the form shown in FIG. 6 is a graph showing the spectral reflectance in each case where the number of laminated multilayer dielectric films is 3, 5, 7, and 9 in the embodiment shown in FIG. In the form shown in FIG.5 (b), it is a graph which shows the spectral reflectance in each case which made the number of lamination | stacking into 5, 9, 15, and 21 layers. SiO ₂ film on the surface of the aluminum substrate are various optical thickness nd (50 [nm], 150 [nm], and 250 [nm]) is a graph showing the spectral reflectance characteristic in a case provided with. (A) is a diagram showing an embodiment in the layer in contact with the protective film and the low refractive index film (SiO _2). (B) is a diagram showing a configuration of the layer in contact with the protective film and the high refractive index film (TiO _2). It is a graph which shows the spectral reflectance at the time of setting the optical film thickness of a protective film to 150 [nm], and providing the dielectric multilayer film of 6 layers with the form shown to Fig.12 (a). It is a graph which shows the spectral reflectance at the time of setting the optical film thickness of a protective film to 150 [nm], and providing the dielectric multilayer film of 5 layers with the form shown in FIG.12 (b). In the embodiment shown in FIG. 12A, when the optical film thickness of the protective film is 50 [nm] and the optical film thickness of the protective film is 150 [nm] (that is, the low refractive index as the first layer). It is a graph which shows the spectral reflectance of the case where the optical film thickness of a layer is 200 [nm]. In the embodiment shown in FIG. 12B, when the optical film thickness of the protective film is 50 [nm] (that is, the optical film thickness of the low refractive index layer as the first layer is 50 [nm]). ) Is a graph showing the spectral reflectance. In the embodiment shown in FIG. 12A, when the optical film thickness of the protective film is 250 [nm] and the optical film thickness of the protective film is 150 [nm] (that is, the low refractive index as the first layer). It is a graph which shows the spectral reflectance of the case where the optical film thickness of a layer is 400 [nm]. In the embodiment shown in FIG. 12B, when the optical film thickness of the protective film is 250 [nm] (that is, when the optical film thickness of the low refractive index layer as the first layer is 250 [nm]). ) Is a graph showing the spectral reflectance. (A) is a diagram showing an embodiment in the layer in contact with the protective layer (MgF ₂₎ and the low refractive index film (SiO _2). (B) is a diagram showing a configuration of the layer in contact with the protective film and the high refractive index film (TiO _2). It is a figure which shows a mode that the light L injects into a dielectric multilayer film from the diagonal direction. It is a graph showing an example of the reflectance of the dielectric multilayer film for P-polarized light component and the S-polarized component shows a case of arranging the low-refractive index layer (SiO ₂₎ as the first layer on an aluminum substrate. It is a graph showing an example of the reflectance of the dielectric multilayer film for P-polarized light component and the S-polarized component shows a case of disposing the high-refractive index layer as the first layer on an aluminum substrate the (TiO _2). Nb is ₂ O ₅ / SiO ₂ graphs showing spectral reflection characteristics of the dielectric multilayer film, the low refractive index layer as the first layer on an aluminum substrate when placing the (SiO _2, optical film thickness 150 [nm]) Is shown. Is a graph showing a spectral reflection characteristic in Nb ₂ O ₅ / SiO ₂ dielectric multilayer film, placing a high-refractive index layer _(Nb 2 _{O 5,} the optical film thickness 150 [nm]) as the first layer on an aluminum substrate Shows the case. It is a graph which shows the measurement result of the spectral reflectance of an aluminum mirror. The solid line is a graph showing the result of measuring the reflectance of the dielectric multilayer film formed on the aluminum mirror, and shows the case where the low refractive index layer (SiO ₂ ) is arranged as the first layer in contact with the aluminum mirror. Yes. A broken line is a graph which shows the calculation result of the reflectance of this dielectric multilayer film. The solid line is a graph showing the result of measuring the reflectance of the dielectric multilayer film formed on the aluminum mirror, and shows the case where a high refractive index layer (TiO ₂ ) is disposed as the first layer in contact with the aluminum mirror. Yes. A broken line is a graph which shows the calculation result of the reflectance of this dielectric multilayer film.

  Embodiments of a reflective light modulation device according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment)
FIG. 1 is a plan view showing a configuration of a reflective liquid crystal device as an embodiment of a reflective light modulation device according to the present invention. FIG. 2 is a side cross-sectional view taken along the line II-II of the reflective liquid crystal device shown in FIG. In FIGS. 1 and 2, an XYZ orthogonal coordinate system is shown for ease of explanation. The reflective liquid crystal device 1 according to the present embodiment includes a plurality of pixels 4 that are two-dimensionally arranged along two axes (X axis and Y axis) orthogonal to each other as shown in FIG. The reflective liquid crystal device 1 is a device that outputs an arbitrary light image forward by modulating incident light for each pixel 4 while reflecting light incident from the front (Z-axis positive direction).

  Referring to FIG. 2, the reflective liquid crystal device 1 includes a silicon substrate 12, a drive circuit layer 14, a plurality of pixel electrodes 16, a dielectric multilayer film 18, a liquid crystal layer 20, a transparent conductive film 22, and a transparent substrate 24. Yes.

  The transparent substrate 24 has a surface 24 a along the XY plane, and the surface 24 a constitutes the surface 10 a of the reflective liquid crystal device 1. The transparent substrate 24 mainly includes a light transmissive material such as glass, and transmits light L having a predetermined wavelength incident from the surface 10 a of the reflective liquid crystal device 1 into the reflective liquid crystal device 1. The transparent conductive film 22 is a conductive light transmission layer in the present embodiment. The transparent conductive film 22 is formed on the back surface 24b of the transparent substrate 24, and mainly includes a conductive material (for example, ITO) that transmits the light L.

  The plurality of pixel electrodes 16 are two-dimensionally arranged according to the arrangement of the plurality of pixels 4 shown in FIG. 1 and are arranged on the silicon substrate 12 along the transparent conductive film 22. Each pixel electrode 16 is made of a metal material such as aluminum, and the surface 16a thereof is processed flat and smoothly. The plurality of pixel electrodes 16 are driven by an active matrix circuit provided in the drive circuit layer 14. The active matrix circuit is provided between the plurality of pixel electrodes 16 and the silicon substrate 12, and controls the voltage applied to each pixel electrode 16 according to the optical image to be output from the reflective liquid crystal device 1. Such an active matrix circuit includes, for example, a first driver circuit that controls the applied voltage of each pixel column arranged in the X-axis direction and a second driver circuit that controls the applied voltage of each pixel column arranged in the Y-axis direction. The driver circuit is configured such that a predetermined voltage is applied to the pixel electrode 16 of the pixel 4 designated by both driver circuits.

  The liquid crystal layer 20 is a light modulation layer in the present embodiment. The liquid crystal layer 20 is disposed between the plurality of pixel electrodes 16 and the transparent conductive film 22, and modulates the light L according to the electric field formed by each pixel electrode 16 and the transparent conductive film 22. That is, when a voltage is applied to a certain pixel electrode 16 by the active matrix circuit, an electric field is formed between the transparent conductive film 22 and the pixel electrode 16. This electric field is applied to each of the dielectric multilayer film 18 and the liquid crystal layer 20 at a ratio corresponding to the thickness of each. Then, the alignment direction of the liquid crystal molecules 20 a changes according to the magnitude of the electric field applied to the liquid crystal layer 20. When the light L passes through the transparent substrate 24 and the transparent conductive film 22 and enters the liquid crystal layer 20, the light L is modulated by the liquid crystal molecules 20 a while passing through the liquid crystal layer 20 and reflected by the dielectric multilayer film 18. Then, the light is again modulated by the liquid crystal layer 20 and taken out.

The dielectric multilayer film 18 is disposed between the plurality of pixel electrodes 16 and the liquid crystal layer 20. In particular, the dielectric multilayer film 18 of the present embodiment is directly formed on the surfaces 16 a of the plurality of pixel electrodes 16. The dielectric multilayer film 18 reflects the light L with a high reflectance of, for example, more than 99%, in cooperation with the light reflecting action of the surface 16a of the pixel electrode 16. Here, FIG. 3 is an enlarged side sectional view showing the configuration of the dielectric multilayer film 18. As shown in FIG. 3, the dielectric multilayer film 18 has a plurality of low refractive index layers 18a to 18d including a layer 18a (first layer) in contact with the pixel electrode 16, and a refractive index higher than that of the low refractive index layer 18a. And a plurality of high refractive index layers 18e to 18h including a layer 18e (second layer) in contact with the low refractive index layer 18a. The low refractive index layers 18 a to 18 d and the high refractive index layers 18 e to 18 h are alternately stacked on the pixel electrode 16. As the constituent material of the low refractive index layer 18a~18d illustrated example _SiO 2, MgF ₂ are preferably especially SiO ₂ is contained in the main. Also, the Examples of the material of the high refractive index layer 18e~18h example _{TiO 2,} Nb ₂ O _5, etc. _{Ta 2 O 5, HfO 2,} ZrO 2 and the like, include the at least one kind of material Is preferred. In the present embodiment, the number of stacked dielectric multilayer films 18 is eight (low refractive index layers 18a to 18d and high refractive index layers 18e to 18h are each four layers). The number of layers 18 is 2 or more (that is, each of the low refractive index layer and the high refractive index layer is 1 layer or more) and 10 layers or less (that is, the low refractive index layer and the high refractive index layer are each 5 layers or less). preferable. Further, the number of stacked dielectric multilayer films is not limited to an even number, and may be an odd number. In this case, the dielectric film located closest to the liquid crystal layer 20 in the dielectric multilayer film 18 is a low refractive index layer. Also in the following embodiments, the number of stacked dielectric multilayer films 18 may be an even number or an odd number, but the dielectric film located closest to the liquid crystal layer 20 is preferably a high refractive index layer.

  The optical film thickness of the low refractive index layer 18a (= n × d, where n is the refractive index of the low refractive index layer 18a, d is the physical film thickness of the low refractive index layer 18a), and the wavelength of the light L is λ ( It is preferable to set within the range of λ / 4) ± 30%. Alternatively, the optical film thickness of the low refractive index layer 18a may be set to be substantially equal to (λ / 4) × n (n is an odd number). In addition, when the light L is incident on the dielectric multilayer film 18 from an oblique direction, the optical film thickness of the low refractive index layer 18a is the incident angle of the light L inside the low refractive index layer 18a (that is, low The relative angle between the direction in which the light L travels in the refractive index layer 18a and the layer thickness direction) is preferably set within a range of (λ / 4 cos θ) ± 30%, where θ is θ. Alternatively, the optical film thickness of the low refractive index layer 18a may be set to be substantially equal to (λ / 4 cos θ) × n (n is an odd number). In addition, the preferable value of the optical film thickness of the low refractive index layer 18a will be described in detail in Examples described later.

  The reflective liquid crystal device 1 according to the present embodiment described above has the following effects. In the reflective liquid crystal device 1, since the dielectric multilayer film 18 is formed on the plurality of metal pixel electrodes 16, the reflectance with respect to the light L can be increased using the high reflectance of the metal surface. . Further, as shown in the examples described later, when the dielectric multilayer film 18 is formed on the metal surface, the low refractive index layer (first layer) 18a is first formed on the metal surface, and then the high refractive index layer (first layer). By laminating the second layer) 18e thereon, a sufficient reflectivity can be obtained with a significantly smaller number of layers as compared with the case where lamination is started from the high refractive index layer. Therefore, according to the reflective liquid crystal device 1 of the present embodiment, the physical film thickness of the dielectric multilayer film 18 can be made thinner than before, and the reduction in the electric field application efficiency to the liquid crystal layer 20 can be suppressed, and is sufficiently high. Reflectivity can be realized and light extraction efficiency can be increased.

(Modification)
FIG. 4 is a side cross-sectional view showing the configuration of the dielectric multilayer film 28 as a modification of the embodiment. The reflective liquid crystal device 1 according to the above embodiment may include a dielectric multilayer film 28 shown in FIG. 4 instead of the dielectric multilayer film 18 shown in FIG.

  Referring to FIG. 4, the dielectric multilayer film 28 has a plurality of low refractive index layers 28a to 28d including a layer 28a (first layer) in contact with the pixel electrode 16, and a refractive index higher than that of the low refractive index layer 28a. A plurality of high refractive index layers 28e to 28h including a layer 28e (second layer) in contact with the refractive index layer 28a are alternately stacked. The constituent materials of the low refractive index layers 28b to 28d and the high refractive index layers 28e to 28h excluding the low refractive index layer 28a are the low refractive index layers 18a to 18d and the high refractive index layers 18e to 18e shown in FIG. Same as 18h.

The low refractive index layer 28a of the present modification includes a lower layer 281 that is in contact with the pixel electrode 16, and an upper layer 282 that is sandwiched between the lower layer 281 and the high refractive index layer 28e. The lower layer 281 and the upper layer 282 may be made of the same material, or may be made of different materials. The constituent material of the lower layer 281 are illustrated for example _SiO 2, MgF ₂ may include the at least one kind of material. The constituent material of the upper layer 282 is the same as that of the low refractive index layers 18a to 18d shown in FIG. 3, and it is particularly preferable that SiO ₂ is mainly contained.

The configuration of the dielectric multilayer film 28 of the present modification is preferably applied when an insulating protective film is formed on the surface 16a of the pixel electrode 16, for example. That is, a protective film may be provided on the surface of a component made of a metal such as aluminum (pixel electrode 16 in this embodiment). Such a protective film is made of SiO ₂ or MgF ₂ which is a low refractive index material in most cases. Therefore, when the dielectric multilayer film 28 is manufactured, such a protective film is left on the surface 16a of the pixel electrode 16 as the lower layer 281 and a low refractive index material such as SiO _{2 is formed} thereon to form the upper layer 282. By doing so, the low refractive index layer 28a according to the present modification can be suitably obtained. Thus, the protective film formed on the surface 16a of the pixel electrode 16 may be used as a part (the lower layer 281) of the low refractive index layer 28a. Even with such a configuration, an effect equivalent to that of the reflective liquid crystal device 1 of the above embodiment can be suitably obtained.

  Also in this modification, the number of laminated dielectric multilayer films 28 is preferably not less than 2 and not more than 10 when the low refractive index layer 28a is counted as one layer. The optical film thickness of the low refractive index layer 28a (that is, the sum of the optical film thickness of the lower layer 281 and the optical film thickness of the upper layer 282) is within the range of (λ / 4) ± 30%, where λ is the wavelength of the light L. Preferably, it may be set to be substantially equal to (λ / 4) × n (n is an odd number). When the light L is incident on the dielectric multilayer film 28 from an oblique direction, the optical film thickness of the low refractive index layer 28a is (λ / 4 cos θ) ± 30, where θ is the incident angle of the light L in the low refractive index layer 28a. % Is preferably set, and may be set to be substantially equal to (λ / 4 cos θ) × n (n is an odd number).

<Reflectance of dielectric multilayer on aluminum>
The spectral reflectance when a dielectric multilayer film was formed on an aluminum substrate was examined. Constituent materials for the dielectric multilayer film were SiO ₂ for the low refractive index layer and TiO ₂ for the high refractive index layer. The wavelength of incident light was assumed to be λ = 600 [nm], and the optical film thickness of each layer was set to 150 [nm] (that is, λ / 4). As the laminated form of the dielectric multilayer film, as shown in FIG. 5A, the form A in which the first layer 32 in contact with the aluminum substrate 30 is a low refractive index film (SiO ₂ ) and FIG. As shown, there is a form B in which the first layer 42 in contact with the aluminum substrate 30 is a high refractive index film (TiO ₂ ).

  FIG. 6 is a graph showing the spectral reflectance when the dielectric multilayer film is not provided on the surface of the aluminum substrate. FIG. 7 is a graph showing the spectral reflectance in each case where the number of laminated multilayer dielectric films is 2, 4, 6, and 10 in the form A shown in FIG. FIG. 8 is a graph showing the spectral reflectance in each case where the number of stacks is 4, 6, 10, and 14 in the form A. FIG. 9 is a graph showing the spectral reflectance in each case where the number of laminated multilayer dielectric films is 3, 5, 7, and 9 in the form B shown in FIG. 5B. FIG. 10 is a graph showing the spectral reflectance in each case where the number of layers is 5, 9, 15, and 21 layers in Form B.

In the form A shown in FIG. 5A, as shown in FIG. 7, the number of stacked layers is two (that is, one SiO ₂ low refractive index layer and one TiO ₂ high refractive index layer). It can be seen that the reflectance at a wavelength of 600 [nm] exceeds 95% and is larger than the reflectance of the aluminum substrate (see FIG. 6). As shown in FIGS. 7 and 8, reflection at a wavelength of 600 [nm] when the number of stacked layers is six (three each of a SiO ₂ low refractive index layer and a TiO ₂ high refractive index layer). The ratio exceeded 99%, and when the number of layers was 10 (5 layers each of a low refractive index layer of SiO _{2 and a} high refractive index layer of TiO ₂ ), it was 99.8%.

  On the other hand, in the form B shown in FIG. 5B, as shown in FIGS. 9 and 10, a phenomenon in which the reflectance decreases at a wavelength near the wavelength 600 [nm] of the incident light appears. This degree of decrease in reflectance is reduced when the number of laminated layers is 21 or more, but when the number of laminated layers is less than 10 layers, the reflectance at a desired wavelength cannot be sufficiently obtained. Become.

Table 1 below is a table summarizing the number of laminated dielectric multilayer films, the reflectance, and the thickness (physical film thickness) in each of modes A and B. It should be noted that bold characters in Table 1 indicate preferable numerical values in the reflective liquid crystal device. As shown in Table 1, in Form B, if the number of stacked layers is 11 or more, the reflectivity is 99% or more, and if it is 15 or more, the reflectivity is 99.8% or more. Thus, it can be seen that even in the form B, if the number of stacked layers is increased, a sufficient reflectance can be obtained in the reflective liquid crystal device. However, if the number of layers is 11 or more, the thickness exceeds 0.9 [μm], and if the number is 15 or more, the thickness exceeds 1.2 [μm]. When the dielectric multilayer film becomes thick as described above, the electric field application efficiency to the liquid crystal layer (light modulation layer) decreases as described above, which is not preferable. On the other hand, in the form A, the reflectance is 99% or more even when the number of laminated layers is only 6 layers, and the reflectance becomes 99.8% or more when 10 layers are formed. In these cases, the thickness is about 0.5 [μm] when the number of stacked layers is 6, and the thickness is about 0.8 [μm] when the number of layers is 10, and the dielectric multilayer film can be configured to be extremely thin as compared with Form B. I understand.

  From the above, it has been shown that if a dielectric multilayer film is formed on an aluminum substrate, a high reflectance can be realized with a small number of layers, such as 10 layers or less. However, in order to increase the reflectance with respect to light of a predetermined wavelength by preferable reflection characteristics, a low refractive index layer is first formed on the surface of the aluminum substrate 30 as the first layer 32 as in the form A, and then the second layer. A high refractive index layer 34 may be laminated thereon. Thereby, compared with the case where lamination is started from the high refractive index layer as in the form B, a sufficient reflectance can be obtained with a significantly smaller number of laminations, so that the electric field application efficiency to the light modulation layer is effectively reduced. Can be suppressed.

<When a protective film is applied to the surface of aluminum>
A case where a protective film is applied to the aluminum surface will be described. Most of the constituent materials of the protective film are SiO ₂ and MgF ₂ which are low refractive index substances. FIG. 11 is a graph showing spectral reflectance characteristics when a SiO ₂ film is provided on the surface of an aluminum substrate with various optical film thicknesses nd (50 [nm], 150 [nm], and 250 [nm]). is there. Referring to FIG. 11, at a wavelength that is four times the optical film thickness nd, the reflectance when the SiO ₂ film is provided on the aluminum substrate is compared with the reflectance of the aluminum surface due to the reflection reducing effect of the SiO ₂ film. It is decreasing. On the other hand, at a wavelength that is twice the optical film thickness nd, the SiO ₂ film has little influence on the reflectance, and the reflectance when the SiO ₂ film is provided on the aluminum substrate is equal to the reflectance of the aluminum surface. Become. For example, in FIG. 11, the reflectance at a wavelength of 500 [nm] when the optical film thickness nd is 250 [nm] is equal to the reflectance of the aluminum surface. Therefore, the optical film thickness of the protective film is generally set to ½ of the wavelength used in order to prevent the reflectance from decreasing.

Here, a case where a dielectric multilayer film is formed on the protective film of the aluminum substrate is considered. In this case, the protective film may be considered as part of the configuration of the dielectric multilayer film. In this case, as a laminated form of the dielectric multilayer film, as shown in FIG. 12A, a form C in which the layer 38 in contact with the protective film 36 is a low refractive index film (SiO ₂ ), and FIG. As shown, there is a form D in which the layer 44 in contact with the protective film 36 is a high refractive index film (TiO ₂ ). In the form C, the protective film 36 and the layer 38 constitute a low refractive index layer (first layer) in contact with the aluminum substrate. In the form D, the protective film 36 alone forms the low refractive index layer (first layer) in contact with the aluminum substrate. Layer).

  FIG. 13 is a graph showing the spectral reflectance when the protective film 36 has an optical film thickness of 150 [nm] and a six-layer dielectric multilayer film is provided in Form C. FIG. 14 is a graph showing the spectral reflectance when the protective film 36 has an optical film thickness of 150 [nm] and a five-layer dielectric multilayer film is provided in Form D. 13 and 14, the wavelength of incident light is assumed to be 600 [nm], and the optical film thickness of each layer constituting the dielectric multilayer film is set to 150 [nm].

When the protective film 36 with the optical film thickness λ / 4 is provided on the aluminum substrate 30 as in the present embodiment, as shown in FIGS. 13 and 14, the lamination starts from the high refractive index film (TiO ₂ ). Form D (see FIG. 12 (b)) has better spectral reflection characteristics than Form C (see FIG. 12 (a)), which has started to be laminated from a low refractive index film (SiO ₂ ), and the wavelength of incident light. The reflectance at λ = 600 [nm] increased.

  In the case of Form C, the protective film 36 and the layer 38 constitute a low refractive index layer (first layer). However, since the optical film thicknesses of the protective film 36 and the layer 38 are λ / 4, respectively. The optical film thickness of this layer becomes λ / 2 (300 [nm]), and the protective film 36 and the layer 38 hardly affect the reflectance. Accordingly, the spectral reflection characteristics of Form C are substantially the same as those of Form B (see FIG. 5B) in which the first layer in contact with the aluminum substrate is a high refractive index film, and the characteristics are as shown in FIG. It is thought that.

  FIG. 15 shows the case where the optical film thickness of the protective film 36 is set to 50 [nm] and the optical film thickness of the layer 38 is set to 150 [nm] in the embodiment C of the present embodiment (that is, the low thickness of the first layer). It is a graph which shows the spectral reflectance of the case where the optical film thickness of a refractive index layer is 200 [nm]. FIG. 16 shows the case where the optical film thickness of the protective film 36 is 50 [nm] in Embodiment D of the present embodiment (that is, the optical film thickness of the low refractive index layer as the first layer is 50 [nm]. ] Is a graph showing the spectral reflectance. FIG. 17 shows a case where the optical film thickness of the protective film 36 is 250 [nm] and the optical film thickness of the layer 38 is 150 [nm] in the form C (that is, the low refractive index which is the first layer). It is a graph which shows the spectral reflectance of the case where the optical film thickness of a layer is 400 [nm]. FIG. 18 shows a case where the optical film thickness of the protective film 36 is 250 [nm] in the form D (that is, the optical film thickness of the low refractive index layer which is the first layer is 250 [nm]). ) Is a graph showing the spectral reflectance.

Table 2 below shows the optical film thickness of the low refractive index layer as the first layer, the deviation of the optical film thickness with respect to λ / 4 or 3λ / 4 (λ = 600 [nm]), and the reflection at the wavelength λ. It is a table | surface which shows the suitability of the reflectance at the time of employ | adopting as a reflectance and a reflection type light modulation apparatus. In Table 2, a reflectance of 99% or more was determined to be suitable (◯).

  As shown in FIGS. 13 to 18 and Table 2, when the optical film thickness of the low refractive index layer, which is the first layer, is λ / 4 (150 [nm] in this embodiment), or 3λ / 4 From time to time (450 nm in this example), it can be seen that the highest reflectance is obtained. It can also be seen that even if the optical film thickness of the low refractive index layer is slightly deviated from λ / 4, a sufficient reflectivity can be obtained in the reflective light modulator.

Here, Tables 3 to 5 show that the incident light wavelength λ is 1550 [nm], 1200 [nm], 1000 [nm], 800 [nm], 600 [nm], and 400 [nm], respectively. It is a table | surface which shows the optical film thickness of the low refractive index layer which is a 1st layer, the shift | offset | difference of the optical film thickness with respect to (lambda) / 4, and the reflectance in wavelength (lambda). In addition, the bold letters in Tables 3 to 5 indicate preferable numerical values in the reflective liquid crystal device.

  Since wavelength dispersion exists in the refractive index of the low refractive index layer and the aluminum substrate surface, as shown in Tables 3 to 5, the reflectance value shows a different value for each wavelength. However, at any wavelength, if the optical film thickness of the low refractive index layer (first layer) is within a range of ± 30% with respect to λ / 4, sufficient reflectance can be obtained in the reflective liquid crystal device. I understand that

Next, the result of examining the case where the protective film is made of MgF ₂ is shown. In this case, as shown in FIG. 19A, a form E in which the layer 48 in contact with the protective film 46 (MgF ₂ ) is a low refractive index film (SiO ₂ ), and as shown in FIG. 19B, the protective film 46 is formed. There is a form F in which the layer 50 in contact with the film is a high refractive index film (TiO ₂ ). In form E, the protective film 46 and the layer 48 constitute a low refractive index layer (first layer) in contact with the aluminum substrate, and in form F, only the protective film 46 is in contact with the aluminum substrate (low refractive index layer (first layer)). Layer). Table 6 shows the optical film thickness of the low refractive index layer, which is the first layer, λ / 4 or 3λ / 4 (λ = 600 [nm] when the optical film thicknesses of the protective film 46 and the layer 48 are variously set. ]), The reflectivity at the wavelength λ, and the suitability of the reflectivity when employed in a reflective light modulator. In Table 6, a reflectance of 99% or more was determined to be suitable (◯).

As shown in Table 6, when the protective film 46 (MgF ₂ ) and the layer 48 (SiO ₂ ) are evaluated as one low refractive index layer (first layer), the same results as in Table 2 described above are obtained. It was. Even when the wavelength other than 600 [nm] is designed as λ, the sum of the optical film thicknesses of the protective film 46 (MgF ₂ ) and the layer 48 (SiO ₂ ) is within ± 30% with respect to λ / 4. Then, sufficient reflectivity was obtained for the reflective liquid crystal device.

  That is, according to the result of this example, a protective film is included in the low refractive index layer (first layer) in contact with the aluminum substrate, and the optical film thickness of the first layer is λ / 4 × n (n is an odd number). It is shown that sufficient reflectivity can be obtained for the reflection type light modulation device. Further, it was shown that sufficient reflectance for the reflection type light modulation device can be obtained even when the optical film thickness of the first layer is within a range of ± 30% with respect to λ / 4.

Si ₃ N ₄ can also be considered as a constituent material of the protective film. Si ₃ N ₄ has a refractive index of 2.0 to 2.1, and is classified as a high refractive index material in the dielectric multilayer film. As described above, it is preferable to arrange a low refractive index layer directly on the aluminum substrate. However, when a high refractive index protective film such as Si ₃ N ₄ is already provided, the protective film First, a high refractive index layer is formed thereon, and the optical film thickness of the high refractive index layer and the layer made of the protective film (third layer) is made substantially equal to λ / 2 × n (n is an odd number ). Thus, the influence on the reflectance can be extremely reduced. Therefore, by forming a dielectric multilayer film starting from the low refractive index layer (first layer) on the third layer having a high refractive index, substantially the same as in the form A (see FIG. 5A). The reflection characteristics can be realized.

<When light is incident on the dielectric multilayer film from an oblique direction>
Next, the influence of the incident angle of light on the dielectric multilayer film on the reflectance will be described. The optical distance by which light incident on a certain layer at an incident angle θ travels through the layer can be obtained by dividing the optical film thickness in the thickness direction of the layer by cos θ. Further, between the refractive indexes n ₁ and n ₂ of each medium and the incident angle θ ₁ and the refractive angle θ ₂ of the light at the interface between the media having different refractive indexes, the following formula (1) (Snell's law) Is established.

と表すことができる。従って、式（２）により、誘電体多層膜５２内の各層内における光の進行方向の傾きを求めることができる。 As shown in FIG. 20, the refractive index of the medium in contact with the surface of the dielectric multilayer film 52 is n ₀ , the incident angle of the light L to the surface 52a of the dielectric multilayer film 52 is θ ₀ , and the refractive index of the substrate is n _sub. When the incident angle of the light L to the substrate and theta _sub, relationship from the surface of the dielectric multilayer film 52 and the refractive index n _i of the i-th layer and the incident angle (refraction angle) theta _i is described above Applying Snell's law, the following formula (2)

It can be expressed as. Therefore, the inclination of the traveling direction of light in each layer in the dielectric multilayer film 52 can be obtained from the equation (2).

From the above, when designing a dielectric multilayer film for oblique incidence, a value obtained by dividing the optical film thickness when the incident angle is zero by cos θ _i may be newly set as the optical film thickness. Therefore, when applied to the results of Example 2 described above, the optical film thickness of the low refractive index layer (first layer) in contact with the aluminum substrate is substantially (λ / 4 cos θ _i ) × n (n is an odd number). It is preferable that they are equal or within the range of (λ / 4 cos θ _i ) ± 30%. And this (theta) _i is calculated _| required by following Numerical formula (3).

Specific numerical examples are shown. For example, when light is incident on a dielectric multilayer film in which TiO ₂ high refractive index layers and SiO ₂ low refractive index layers are alternately stacked at an incident angle of 45 °, the incident angle (refractive angle in the TiO ₂ high refractive index layer). ) Θ _TiO2 has the value shown in the following mathematical formula (4). In Equation (4), the refractive index n _TiO2 of TiO ₂ is 2.27. The medium in contact with the surface of the dielectric multilayer film is the atmosphere (n ₀ = 1).

Similarly, the incident angle (refractive angle) θ _SiO2 in the SiO ₂ low refractive index layer has a value represented by the following mathematical formula (5). In the formula (5), the refractive index n _SiO2 of SiO ₂ is 1.46.

ＳｉＯ_２低屈折率層の光学膜厚ｎｄを、

とするとよい。このように、斜め方向からの入射に対応させる場合についても、光学膜厚ｎｄ＝λ／４を基準として、入射角に応じて各層の光学膜厚を補正すれば、斜入射用の誘電体多層膜を好適に実現できる。 Therefore, the result obtained by multiplying each optical film thickness of the TiO ₂ high refractive index layer and the SiO ₂ low refractive index layer by cos (18.1 °) and cos (29.0 °) is 150 [nm]. Then, a dielectric multilayer film for 45 ° incidence at a wavelength λ = 600 [nm] can be suitably realized. That is, the optical film thickness nd of the TiO ₂ high refractive index layer is

The optical film thickness nd of the SiO ₂ low refractive index layer is

It is good to do. As described above, even in the case of corresponding to the incidence from the oblique direction, if the optical film thickness of each layer is corrected according to the incident angle with the optical film thickness nd = λ / 4 as a reference, the dielectric multilayer for oblique incidence is used. A film | membrane can be implement | achieved suitably.

となる。このように、各偏光成分によって層内における屈折率が異なるので、誘電体多層膜による反射率も異なる。図２１及び２２は、Ｐ偏光成分およびＳ偏光成分に対する誘電体多層膜の反射率の例を示すグラフである。なお、図２１はアルミニウム基板上に第１の層として低屈折率層（ＳｉＯ_２）を配置した場合（図５（ａ）参照）を示しており、図２２はアルミニウム基板上に第１の層として高屈折率層（ＴｉＯ_２）を配置した場合（図５（ｂ）参照）を示している。 In the case of oblique incidence, the refractive indexes n _S and n _P for the S-polarized component and the P-polarized component of light are expressed as follows: n is the refractive index in the layer, and θ is the incident angle (refractive angle) in the layer.

It becomes. As described above, since the refractive index in the layer is different depending on each polarization component, the reflectance by the dielectric multilayer film is also different. 21 and 22 are graphs showing examples of the reflectance of the dielectric multilayer film with respect to the P-polarized component and the S-polarized component. FIG. 21 shows a case where a low refractive index layer (SiO ₂ ) is disposed as a first layer on an aluminum substrate (see FIG. 5A), and FIG. 22 shows the first layer on the aluminum substrate. As shown in FIG. 5B, a high refractive index layer (TiO ₂ ) is disposed (see FIG. 5B).

<When various materials are used for the high refractive index layer>
Suitable constituent materials for the high refractive index layer include Nb ₂ O ₅ , Ta ₂ O ₅ , HfO ₂ , and ZrO ₂ in addition to TiO ₂ . Since the refractive index values are different from each other, the reflectance values of the dielectric multilayer film are also different. However, any of the materials has the same tendency as in the case of using TiO ₂ . 23 and 24 are graphs showing the spectral reflection characteristics in the Nb ₂ O ₅ / SiO ₂ dielectric multilayer film. FIG. 23 shows a case where a low refractive index layer (SiO ₂ , optical film thickness 150 [nm]) is arranged as a first layer on an aluminum substrate, and FIG. 24 shows a high layer as the first layer on the aluminum substrate. refractive index layer shows the case of arranging the _(Nb 2 _{O 5,} the optical film thickness 150 [nm]). As shown in these figures, even when the constituent material of the high refractive index layer is Nb ₂ O ₅ , the low refractive index layer (first layer) is first formed on the metal surface, and then the high refractive index layer (first layer). It can be seen that a sufficient reflectivity can be obtained with a significantly smaller number of layers compared to the case where the second layer is laminated on the high refractive index layer.

<Experiment by experiment>
A TiO ₂ / SiO ₂ alternating multilayer film was formed on a commercially available metal aluminum mirror by a vacuum deposition method. In a commercially available aluminum mirror, an MgF ₂ film having an optical film thickness of 280 [nm] is formed as a protective film. FIG. 25 is a graph showing the measurement results of the spectral reflectance of this aluminum mirror. In FIG. 25, the calculated value of the reflectance of the aluminum surface without the protective film is also shown by a broken line for comparison.

A dielectric multilayer film was formed on the surface of the aluminum mirror. As a laminated form, a low refractive index layer (SiO ₂ , optical film thickness 150 [nm]) is formed as a first layer in contact with the aluminum mirror, and a high refractive index layer (TiO ₂ , optical film thickness 150) is formed thereon. [Nm]) and low refractive index layers (SiO ₂ , optical film thickness 150 [nm]) were alternately stacked, and the number of stacked layers was four. The solid line shown in FIG. 26 is a graph showing the results of measuring the reflectance of this dielectric multilayer film. Moreover, the broken line shown in FIG. 26 is a graph which shows the calculation result of the reflectance of this dielectric multilayer film. As shown in FIG. 26, the measured values of the reflectivity and the calculated values almost coincided.

As a comparative example, a high refractive index layer (TiO ₂ , optical film thickness 150 [nm]) is formed as a first layer in contact with the aluminum mirror, and a low refractive index layer (SiO ₂ , optical film thickness 150 is formed thereon. [Nm]) and high refractive index layers (TiO ₂ , optical film thickness 150 [nm]) were alternately stacked, and the number of stacked layers was five. The solid line shown in FIG. 27 is a graph showing the result of measuring the reflectance of the dielectric multilayer film. Moreover, the broken line shown in FIG. 27 is a graph which shows the calculation result of the reflectance of this dielectric multilayer film. As shown in FIG. 27, even in this embodiment, the actually measured value and the calculated value of the reflectance almost coincided.

The reflective light modulation device according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, in the above embodiment, SiO ₂ and MgF ₂ are exemplified as the constituent material of the low refractive index layer of the dielectric multilayer film, but the constituent material of the low refractive index layer has a refractive index of 1.35 to 1.75. Other materials may be used as long as they are preferably dielectric materials of 1.35 to 1.50. In the above embodiment, TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and HfO ₂ are exemplified as the constituent material of the high refractive index layer of the dielectric multilayer film, but the constituent material of the high refractive index layer is refracted. Other materials may be used as long as the dielectric has a rate of 1.75 to 2.50, more preferably 1.90 to 2.50.

  DESCRIPTION OF SYMBOLS 1 ... Reflective type liquid crystal device, 4 ... Pixel, 12 ... Silicon substrate, 14 ... Drive circuit layer, 16 ... Pixel electrode, 18, 28, 52 ... Dielectric multilayer film, 18a-18d, 28a-28d ... Low refractive index layer 18e-18h, 28e-28h ... high refractive index layer, 20 ... liquid crystal layer, 22 ... transparent conductive film, 24 ... transparent substrate, 30 ... aluminum substrate, 36,46 ... protective film, 281 ... lower layer, 282 ... upper layer.

Claims (1)

A reflection-type light modulator that modulates the light for each of a plurality of pixels arranged two-dimensionally and outputs an optical image forward while reflecting light incident from the front,
A conductive light-transmitting layer containing a conductive material that transmits the light;
A plurality of metal pixel electrodes arranged two-dimensionally along the conductive light transmission layer;
A light modulation layer that is disposed between the plurality of pixel electrodes and the conductive light transmission layer and modulates the light according to an electric field formed by each pixel electrode and the conductive light transmission layer;
A dielectric multilayer film formed on the plurality of pixel electrodes,
The dielectric multilayer film is:
Has contact to the pixel electrode, _Si 3 _N of ₄ protective film and _TiO 2 provided on the protective _{film, Nb 2 O 5, Ta 2} O 5, HfO 2, and at least one of ZrO ₂ A third layer comprising a fourth layer comprising the material of :
A first layer provided on the third layer and having a refractive index lower than that of the third layer and in contact with the third layer;
A second layer provided on the first layer and having a higher refractive index than the first layer and in contact with the first layer;
A reflective light modulation device, wherein the optical thickness of the third layer is substantially equal to (λ / 2) × n (n is an odd number) where λ is the wavelength of the light.

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