JPH1195212A - Reflection type liquid crystal display element and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to embody a high light utilization efficiency and high contrast ratio by specifying the product of the thickness and refractive index anisotropy of a phase plate nearly to half the central wavelength of incident light. SOLUTION: The refractive index anisotropy of the phase plate 14 is expressed as Dn PH and the layer thickness thereof as dPH. The relation between the sum Ir of the intensity of the boundary reflected light generated between the phase plate 14 and a liquid crystal layer 8, the retardation (dPH×Dn PH) of the phase plate 14 and the light intensity I0 superposed on image light is expressed like the equation; I0 =Ir Tp Sin<2> (2πdPH×Dn PH/λ). In order to minimize I0 , dPH×Dn PH is merely necessitated to be set at λ/2. Then, the value of the retardation of the phase plate 14 is set at the value of nearly half the central wavelength of the incident light which is made incident on the liquid crystal display element. Namely, the phase plate 14 has a function as a half-wave plate. The phase plate 14 is formed by holding a phase film with two sheets of glass substrates to prevent the change in the retardation of the phase film by the strain and stress occurring in heat, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device, and more particularly to a liquid crystal projector which irradiates illumination light from a white light source to the reflection type liquid crystal display device and projects an image of the reflection type liquid crystal display device on a screen. About.

[0002]

2. Description of the Related Art A liquid crystal projector using a reflection type liquid crystal display device is disclosed in JP-A-1-7021, JP-A-3-276.
No. 122 publication.

[0003] In each of the above, the orientation direction of the liquid crystal is a homogeneous orientation in which the major axis of the liquid crystal is oriented substantially parallel to the supporting substrate.

The liquid crystal display mode of the liquid crystal display element described in Japanese Patent Application Laid-Open No. 1-7021 shows a bright display when the applied voltage is near zero volts, and a dark display when a certain voltage is applied. Mari white mode. In order to reduce the driving voltage, a phase compensation layer having a retardation equal to the retardation which is the product of the thickness of the liquid crystal layer and the refractive index anisotropy at a certain applied voltage is provided.

The liquid crystal display element described in Japanese Patent Application Laid-Open No. 1-7021 has a liquid crystal layer having a thickness of 2 μm or less, so that the liquid crystal display is capable of responding quickly to a rapidly changing image display.
It can be realized.

On the other hand, the liquid crystal display device described in Japanese Patent Application Laid-Open No. 3-276122 has a liquid crystal display mode in which dark display is performed when an applied voltage is near zero volts, and bright display is performed when a certain voltage is applied. In order to realize the normally black mode shown, a phase compensation layer having a retardation equal to the retardation of the driving liquid crystal layer is laminated.

[0007]

However, Japanese Patent Laid-Open No. 1-7 / 1990
No. 021 and JP-A-3-276122 all have the following problems.

A problem specific to the reflection type liquid crystal display element is that the contrast ratio is reduced by the interface reflected light. The cause of the interface reflected light is that the refractive indexes of the optical elements adjacent to each other at the interface between the optical elements constituting the element do not match.

More specifically, slight inconsistencies in the refractive index at the interface between the liquid crystal and the alignment film, the interface between the alignment film and the transparent electrode, and the interface between the phase film as the phase compensation layer and the adhesive, etc.
Generates interfacial reflected light. This interface reflected light is superimposed on the projected image, and causes a reduction in the contrast ratio of the projected image.

However, in any of the liquid crystal display devices described in JP-A-1-7021 and JP-A-3-276122, no consideration is given to the point that interface reflected light lowers the contrast ratio. Therefore, it is difficult for these liquid crystal display elements to obtain an image having a high contrast ratio, which is required for an image display device for multimedia use in recent years.

In the projection type liquid crystal display device described in Japanese Patent Application Laid-Open No. 3-276122, a polarizing beam splitter is formed by using two polarizers and a half mirror. Out of the emitted light, the ratio of usable light is at most one-fourth, so that there is a problem that the light use efficiency is poor.

An object of the present invention is to provide a reflective liquid crystal display device having a high light utilization efficiency and a high contrast ratio, and a liquid crystal projector using the same.

[0013]

The gist of the present invention to achieve the above object is as follows.

[1] An active matrix in which a plurality of pixels each having a reflection mirror and a pixel electrode (or a pixel electrode serving also as a reflection mirror) and a switching element are arranged in rows and columns, and an alignment film is provided on the reflection mirror. A substrate (a first support substrate), a transparent substrate (a second support substrate) including an opposing transparent electrode provided with an alignment film and facing the first support substrate at a predetermined gap; A liquid crystal layer filled between the second support substrates, a phase plate, a polarizer, and an analyzer, wherein an alignment axis of the liquid crystal layer is substantially parallel to the substrate;
In a reflection type liquid crystal display element in which a twist angle is oriented to substantially 0 degrees and a slow axis of the phase plate is arranged to be substantially orthogonal to an orientation axis of the liquid crystal layer, and a thickness of the (d _PH) and approximately one half of the refractive index anisotropy (delta _nph) and the product _{(d PH} · Δ nPH) the center wavelength of the incident light _{(λ 0) (λ 0/} 2) A reflective liquid crystal display device is characterized in that:

[2] A white light source, a color separation element for separating light from the white light source into three primary colors of red, green and blue, and a plurality of liquid crystal display elements for modulating each of the separated three primary colors based on image information And a liquid crystal projector having a projection lens system for projecting the modulated light, wherein the liquid crystal display element uses the reflective liquid crystal display element according to [1] as the liquid crystal display element.

[3] A white light source, a color separation element for separating light from the white light source into three primary colors of red, green, and blue, and a plurality of liquid crystal display elements for modulating each of the separated three primary colors based on image information. And a liquid crystal projector having a projection lens system for projecting the modulated light, wherein a thickness (d _PH ) and a refractive index anisotropy (Δ _PH ) of each phase plate used for each of the plurality of reflective liquid crystal display elements are provided. _nPH ) (d _PH
ΔnPH ) is set to approximately one half of the center wavelength of the light incident on each liquid crystal display element. The liquid crystal projector using the reflection type liquid crystal display element in the above [1].

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The reflection type liquid crystal display device of the present invention comprises:
An electric field birefringence control method was used in which the molecular arrangement of the liquid crystal layer was deformed by an electric field, and the birefringence change of the liquid crystal layer generated at that time was used for image display.

An advantage of using the electric field birefringence control method is that a large change in birefringence is caused by a small change in voltage, so that the liquid crystal driving voltage can be reduced. Further, by using the reflective element, the required thickness can be reduced to half that of the transmissive element.

Generally, it is known that the liquid crystal response time is inversely proportional to the square of the layer thickness. Therefore, it is possible to improve the liquid crystal response time to approximately one-fourth as compared with a transmissive element having the same optical path length.

In order to realize a good contrast ratio, it is necessary to realize a good black display over a wide wavelength range. By setting the polarizer and the analyzer in a crossed Nicols arrangement and making the retardation therebetween substantially zero at all wavelengths of the incident light, a good black display can be obtained.

When the liquid crystal layer has a homogeneous alignment, a very high voltage is required to make the retardation almost zero. Therefore, some kind of phase compensation layer is required to compensate for the retardation of the liquid crystal layer.

Generally, the refractive index anisotropy of a phase plate formed by stretching a polymer film such as polycarbonate has wavelength dependence of inverse dispersion, and the relative magnitude of the wavelength dispersion is substantially equal to that of a liquid crystal material. It is. Therefore, by arranging the slow axis of the phase plate orthogonally to the alignment direction of the liquid crystal layer,
The retardation of the phase plate and the retardation of the phase plate can be canceled each other, and at a liquid crystal driving voltage at which the retardation of the liquid crystal layer and the retardation of the phase plate match, the sum of the retardations of the phase plate and the liquid crystal layer is almost zero at all wavelengths of incident light. It can be.

FIGS. 2 and 3 show the relative relationship between the optical axes of the respective optical elements constituting the reflection type liquid crystal display element of the present invention. 2, the driving voltages V ₁ for displaying a black image shows the case of applying the liquid crystal layer, Fig. 3 shows the case of applying a driving voltage V ₂ for a white image is displayed on the liquid crystal layer ing.

The reflection type liquid crystal display device of the present invention comprises a reflection type active matrix substrate 12 having a polarizing beam splitter 15, a phase plate 14, and a reflection mirror, which also functions as a polarizer and an analyzer; And a liquid crystal layer 8 sandwiched between a glass substrate having FIG. 2,
In FIG. 3, the illustration of a glass substrate having a transparent electrode is omitted.

The polarizing beam splitter 15, which also functions as a polarizer and an analyzer, has a rectangular parallelepiped shape in which two 45-degree prisms are bonded. A dielectric multilayer film that separates polarized light having a vibration direction parallel to the interface (hereinafter referred to as s-polarized light) and polarized light having a vibration direction perpendicular thereto (hereinafter referred to as p-polarized light) by reflection and transmission is formed. An optical element having a function.

The advantage of using the polarizing beam splitter as a polarizer and analyzer is that the optical axes of incident light and outgoing light can be made the same. When the polarizing beam splitter is used as both a polarizer and an analyzer, the relationship between the polarizer and the analyzer is orthogonal Nicols in which transmission axes are orthogonal to each other.

As described above, in order to obtain a good contrast ratio, a good result can be obtained by setting the relationship between the polarizer and the analyzer to be orthogonal Nicols.

The unpolarized incident light 17 is separated into an s-polarized light 18 and a p-polarized light 19 at an interface 16 of the polarizing beam splitter 15, the s-polarized light 18 is reflected and removed at the interface 16, and the p-polarized light 19 passes through the interface. The light passes through to the liquid crystal display element. The phase plate 14 is arranged between the polarization beam splitter 15 and the liquid crystal layer 8 at a right angle to the optical axis, and the slow axis 24 is inclined at 45 degrees to the vibration direction of the p-polarized light 19.

On the other hand, the liquid crystal layer 8 is disposed such that its liquid crystal alignment axis (rubbing direction of the substrate) 23 is orthogonal to the slow axis 24 of the phase plate 14.

P emitted from the polarizing beam splitter 15
The polarized light 19 has a phase difference between two eigencomponents of the phase plate 14 with the slow axis 24 and the orthogonal fast axis. Generally, the light emitted from the phase plate is elliptically polarized in accordance with the retardation of the phase plate. Becomes However, in the present invention, the phase plate 14
For litter is set to approximately one half of the center wavelength of the retardation incident light _{(λ 0) (λ 0/} 2), the phase difference is approximately π next between two specific components, light emitted from the phase plate 14 is The s-polarized light (linearly polarized light) 25 is substantially orthogonal to the p-polarized light 19.

The s-polarized light 25 enters the liquid crystal layer 8 and causes a phase difference between two specific components of the liquid crystal layer 8 in the direction perpendicular to the liquid crystal alignment axis 23 and a direction perpendicular to the liquid crystal alignment axis 23. The light is reflected by the active matrix substrate 12, again generates a phase difference by the liquid crystal layer 8, and is emitted from the liquid crystal layer 8. The emitted light 26 from the liquid crystal layer 8 passes through the phase plate 14 again and travels to the polarization beam splitter 15.

The outgoing light 26 is generally elliptically polarized light, of which the s-polarized component is reflected at the interface 16 of the polarizing beam splitter and directed toward the screen, while the p-polarized component is transmitted through the interface 16 of the polarizing beam splitter. And head toward the light source. Therefore, the light intensity projected on the screen is determined according to the degree of polarization of the emitted light.

However, in FIG. 2, a voltage V ₁ for performing black display is applied to the liquid crystal layer, and in FIG. 3, a voltage V ₂ for performing white display is applied to the liquid crystal layer. The outgoing light 26 and the outgoing light 27 from the phase plate have polarization directions that differ from each other by approximately 90 degrees.

In the above-mentioned reflection mode, since the light passes through the liquid crystal layer 8 and the phase plate 14 twice, the total amount of retardation contributing to display is represented by R _d, and the refractive index anisotropy of the liquid crystal layer is represented by _ΔnLC , Layer thickness d _LC , phase plate refractive index anisotropy Δ
_nph, represented by the following equation (1) is expressed as d _PH layer thickness.

[0035]

R _d = 2 (d _LC × _ΔnLC− d _PH × _{Δn PH} ) (1) In equation (1), the difference between the retardation of the liquid crystal layer and the retardation of the phase plate is _calculated . This is because the orientation axis of the liquid crystal layer is orthogonal to the slow axis of the phase plate as described above.

Using this R _d , the relationship between the polarizer and the analyzer is crossed Nicols, and the reflectance when the orientation axis of the liquid crystal layer is oriented at 45 degrees to the incident polarized light is represented by R. And expressed by the following equation [2]. Here, the parallel transmittance of the polarizer and the analyzer is represented by T _p , and the wavelength is represented by λ.

[0037]

R = T _p sin ² (πR _d / λ) [2] The display at this time is R = 0 when R _d = 0, and the reflectance R is minimized. _{When d} = λ / 2, R =
At T _p , the reflectance R becomes the maximum, and white display is performed.

In an actual liquid crystal projector, slight interface reflected light generated at the interface between the optical elements constituting the reflective liquid crystal display element is superimposed on the image light. In particular, the interface reflection light superimposed on the image light at the time of black display causes a problem because the contrast ratio of the image is reduced. However, the problematic interface reflected light is the interface reflected light generated between the phase plate and the liquid crystal layer.

The interface reflected light generated between the phase plate and the polarizing beam splitter does not change its polarization direction, so it passes through the interface 16 of the polarizing beam splitter 15 again, returns to the light source direction, and is not superimposed on the image light. .

On the other hand, the interface reflection light generated between the phase plate 14 and the liquid crystal layer 8 is superimposed on the image light in accordance with the retardation of the phase plate 14, and in particular, becomes an offset of the image light during black display. This causes a decrease in the contrast ratio.

[0041] represents a sum of I _r of the interfacial reflected light intensity, the retardation of the phase plate represented as _{d PH} × Δ nPH, the light intensity I _0, which is superimposed on the image light, as in equation [3] expressed.

[0042]

The Equation 3] _{I 0 = I r T p sin} 2 (2πd PH × Δ nPH / λ) ... [3] I ₀ in order to minimize, to the _{d PH} × Δ nPH may be set to lambda / 2 I understand. Therefore, the value of retardation of the phase plate was set to a value of approximately half 1 (≒ λ _0/2) of the center wavelength of the incident light incident on the liquid crystal display device (lambda _0).
That is, the phase plate has a function as a half-wave plate.

[Embodiment 1] An embodiment of the reflection type liquid crystal display device of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a liquid crystal display element for a liquid crystal projector according to the present embodiment. FIG. 1 corresponds to a part of a liquid crystal projector including a white light source, an illumination lens system, a color separation element, a color synthesis element, and a projection lens, which are not shown.

The reflection type liquid crystal display device of this embodiment has MOS transistors, each of which is independently arranged on a single crystal silicon substrate 1.
(Metal Oxide Semiconductor) Transistor 2,
A wiring layer 3 including a reflection pixel electrode 4 also serving as a reflection plate, a signal wiring for driving the MOS transistor 2, a wiring for electrically connecting the reflection pixel electrode and the MOS transistor, and a protective film. Reflective active matrix substrate 12 composed of dielectric film 5 and alignment film 6
And an opposing glass substrate 13 composed of a glass substrate 11 having an alignment film 9 and a transparent electrode 10 are arranged to face each other, and a liquid crystal layer 8 is sandwiched therebetween to constitute a cell.

The thickness of the liquid crystal layer 8 is kept uniform by the spacer material 7. Further, a phase plate 14 and
Polarizing beam splitter 15 also serving as polarizer and analyzer
It has a configuration with.

The reflection type active matrix substrate 12
Is an example in which a MOS transistor 2 is used as an active element for driving a liquid crystal on a single crystal silicon substrate 1. A source diffusion layer, a source electrode, a drain diffusion layer, a drain electrode, a polysilicon gate are formed on a silicon substrate and a p-type well. Thus, a MOS transistor is formed. Further, a spin-on-glass insulating layer is provided for interlayer insulation.

Examples of the material of the reflective pixel electrode 4 include metals having good reflectivity in the visible light region, for example, aluminum and silver. Here, an example using aluminum will be described.

When the reflective pixel electrode 4 is formed on a flat surface, a stable film can be formed and good reflection characteristics can be obtained. The layer is desirably planarized by surface polishing.

A dielectric film 5 is provided between the reflective pixel electrode 4 and the alignment film 6 as a protective film. As the dielectric film 5, for example, a silicon nitride film is used.

The electric signal controlled by the MOS transistor 2 is applied to the reflective pixel electrode 4 through a through-hole contact, and a voltage is applied between the reflective pixel electrode 4 and the opposing transparent electrode 10 to drive the liquid crystal layer 8.

The properties of the liquid crystal used in the present invention include that the dielectric anisotropy is positive, the refractive index anisotropy is small,
And a high nematic / isotropic phase transition temperature.

If the refractive index anisotropy is small, it is necessary to relatively increase the thickness of the liquid crystal layer in order to obtain a certain amount of retardation. Since the fluctuation of the retardation due to the fluctuation of the absolute value can be made relatively small, the tolerance to the fluctuation of the layer thickness of the liquid crystal can be widened.

In general, the refractive index anisotropy of a liquid crystal shows temperature dependence, but the higher the nematic / isotropic phase transition temperature, the smaller the rate of change of the refractive index anisotropy near room temperature with temperature. is there. Therefore, in order to reduce the change in the retardation of the liquid crystal layer due to the temperature, it is necessary that the nematic / isotropic phase transition temperature of the liquid crystal is sufficiently high.

As a liquid crystal material of the liquid crystal layer 8, a nematic liquid crystal having a refractive index anisotropy ( _ΔnLC ) of 0.09 ( _HA5109XX, manufactured by Chisso Petrochemical) was used.

The reflection type active matrix substrate 12 and the counter glass substrate 13 on which an alignment film has been applied and formed in advance by printing are provided with 45 degrees in the arrangement direction of the reflection pixel electrodes 4.
Rubbing was performed in the degree direction to give an orientation treatment.

After a spacer material 7 for maintaining the gap of the liquid crystal layer and a sealant (not shown) for the liquid crystal layer 8 are respectively arranged on the substrates, the rubbing direction of the reflection type active matrix substrate 12 and the facing glass substrate 13 Are combined so that the rubbing direction is parallel and the direction is opposite. Therefore, the twist angle of the liquid crystal in the liquid crystal layer 8 is almost 0 degrees. The thickness of the liquid crystal layer (d _LC )
Is 3.5 μm.

As the phase plate 14, a method in which a phase film is sandwiched between two glass substrates can be considered. The reason why the phase film is sandwiched between the two glass substrates is to prevent a change in the retardation of the phase film due to a strain stress caused by heat or the like, thereby increasing the retardation value of the phase film over a wide temperature range. Can be kept stable. If the cooling can be performed effectively, the phase film may be directly attached to the opposing glass substrate 13 or the polarizing beam splitter 15.

Examples of the phase film for the phase plate 14 include known polyvinyl alcohol, polycarbonate, and the like.
A film obtained by stretching a polymer film such as polysulfone to have birefringence can be used. These films are almost transparent in the visible light region. Alternatively, a polymer liquid crystal can be used.

Among the above-mentioned materials, those having retardation wavelength dispersion as close as possible to the retardation wavelength dispersion of the liquid crystal material to be used are most suitable as the phase film. This is because, in order to satisfactorily perform the black display over the entire wavelength range, R _d is required to be substantially zero over the entire wavelength range. In order to realize this, it is necessary that d _LC × _ΔnLC and d _PH × _{Δn PH} be substantially equal over the entire wavelength range, as can be seen from the above equation [1].

Next, a specific mechanism of generation of reflected light at the interface will be described with reference to FIG. The phase plate 14 uses an adhesive to fix a phase film having a refractive index of about 1.6 to a glass substrate, and the refractive index of the adhesive is approximately 1.
5 Therefore, a non-negligible reflection occurs at the interface due to the refractive index mismatch between the phase film and the adhesive. The interface reflection light on the light source side of the phase plate 14 is called A reflection light, and the interface reflection light on the liquid crystal layer side is called B reflection light.

The transparent electrode 10 is made of ITO (Indium Tin).
Oxide) was used. The refractive index of ITO is about 1.8 to 1.9, depending on the preparation conditions. On the other hand, the refractive index of the adjacent glass substrate 11 is about 1.5. Alignment film 9
Has a refractive index of about 1.6. The refractive index of the liquid crystal layer 8 differs by about 0.1 between the refractive index in the direction parallel to the molecular axis of the liquid crystal and the refractive index in the direction perpendicular thereto, but is about 1.5.

At the glass substrate / transparent electrode interface, the transparent electrode / alignment film interface, and the alignment film / liquid crystal interface which are in contact with media having different refractive indices, interface reflections which cannot be ignored (hereinafter collectively referred to as C (Referred to as reflected light).
Actually, the interfacial reflected light amount is determined in consideration of the interference effect of each interface reflected light.

As the spacer material 7, known polymer beads or silica beads can be used. Since all materials are transparent, of the incident light to the liquid crystal panel, the spacer material 7 does not pass through the liquid crystal layer without passing through the liquid crystal layer. Is different from the light passing through the liquid crystal layer (hereinafter referred to as E reflected light) and exits the liquid crystal panel without being subjected to phase modulation.

Of the reflected light at the interface between the above-mentioned phase film and the adhesive for fixing to the glass substrate, the polarization state of the reflected light (B reflected light) on the liquid crystal layer side and the polarization state of the transparent electrode and the glass substrate. The polarization state of the reflected light (C reflected light) at the interface and the reflected light (C reflected light) at the interface between the transparent electrode and the alignment film is the same as the polarization state of the light (D reflected light) that has passed through the spacer material 7. However, the polarization state of the light (E reflected light) that has passed through the liquid crystal layer is different.

Therefore, even if the liquid crystal driving voltage is set to a voltage for performing black display, the amount of light determined by the retardation of the phase film among the B, C, and D reflected lights is superimposed on the display image as an offset. This causes a decrease in contrast ratio.

As in the present invention, by setting the retardation of the phase plate to a value approximately half the center wavelength of the incident light, the phases of the B, C, D reflected light and the A, E reflected light Since the phases can be made substantially equal, it is possible to prevent the B, C, and D reflected lights from causing a decrease in the contrast ratio.

[0067] represents B are surface reflected light occurs between the phase plate 14 and the liquid crystal layer 8, C, the sum of the light intensity of the D reflected light I _r, the retardation of the phase plate 14 (d _PH × _ΔnPH )
And the light intensity I ₀ superimposed on the image light are expressed as in equation [3]. In order to minimize I ₀ , d _PH × Δ
It is understood that _nPH should be _set to λ / 2.

[0068]

Equation 4] _{I 0 = I r T p sin} 2 (2πd PH × Δ nPH / λ) ... [3] Therefore, the value of retardation of the phase plate 14, the center wavelength of light incident on the liquid crystal display device The value was set to approximately one half. That is, the phase plate 14 has a function as a half-wave plate.

The basis for setting Δ _nd to １ ／ of the central wavelength λ ₀ of the incident light will be described. FIG. 5 shows the relationship between the retardation of the phase plate and the off-reflectance. Off reflectance is
This is the ratio of the light intensity during black display to the light intensity during white display. The smaller the value, the better the contrast ratio. The relationship with the contrast ratio is as follows: contrast ratio =
It is expressed as 100 / (off reflectance).

In the figure, black circles indicate measured values, and solid lines indicate calculated values. Note that the retardation of the phase plate is a value with respect to the central wavelength λ ₀ = 550 nm of the incident light. At this time, λ _0/2
Is 275 nm and is indicated by an arrow.

[0071] The calculated values in the formula (3) representing the light intensity to be superimposed on the image light, which is the result of fitting the experimental data as parameters I _r T _p.

The calculated values shown by the curves well explain the experimental results. Conversely, the retardation of the phase plate was λ ₀ /
It can be seen that the effect of setting to 2 is well exhibited in the experimental results. Therefore, by setting the retardation of the phase plate and lambda _0/2, off reflectance is greatly reduced, it is possible to significantly improve the contrast ratio.

In FIG. 5, when the retardation of the phase plate is 265 nm, the contrast ratio of the liquid crystal display device is 250: 1.

Further, in the embodiment of the liquid crystal display device of the present invention, the reflection type active matrix substrate 12 is constituted by the MOS transistor array formed on the single crystal silicon substrate 1, but the polycrystalline silicon or the A thin film transistor array formed of amorphous silicon may be used as an active matrix substrate.

In this embodiment, the reflection pixel electrode 4 which also serves as a reflection mirror and a pixel electrode is used. However, the present invention is not limited to this. A reflection mirror formed of a dielectric multilayer film is placed on the pixel electrode. It may be provided. These are the same in the following embodiments.

Further, in order to keep the thickness of the liquid crystal layer 8 constant in the plane, silica beads or polymer beads having the same particle size as a spacer are dispersed in the liquid crystal layer or a sealant for sealing the liquid crystal layer. Good to put. In addition, a pillar made of silicon oxide, silicon nitride, or an organic polymer material formed by a photoetching process may be provided as a spacer. This is the same in the following embodiments.

[Embodiment 2] FIG. 6 is a diagram showing a configuration of a liquid crystal projector of the present invention. The liquid crystal projector of the present invention includes a light source 28 for white light 30, an ultraviolet and infrared cut filter 29, and dichroic mirrors 31 and 32 for separating the white light 30 into red, green and blue primary color lights 33, 35 and 34. , Polarizing beam splitters 15R, 15
G, 15B and the separated three primary color lights 33, 34, 35
Liquid crystal display device 22 of the present invention which modulates light to give image information
R, 22G, 22B and field lenses 36, 37,
38, dichroic mirrors 42 and 43 for synthesizing the modulated three primary color lights 39, 40 and 41 again, and a projection lens system 45 for projecting the synthesized light 44 onto a screen (not shown). As the white light source 28, a metal halide lamp, a xenon lamp, or the like is preferable.

The white light 30 emitted from the light source 28 is
Unnecessary ultraviolet rays and infrared rays are removed by an ultraviolet ray and infrared ray cut filter 29. First, the red light 33 and the other light (green and blue) are emitted by the dichroic mirror 31.
And the latter light is transmitted to the next dichroic mirror 3
2 separates the light into blue light 34 and green light 35. The separated three primary color lights 33, 34, 35 enter the polarization beam splitters 15R, 15B, 15G, respectively.

The three primary color lights 33, 34, and 35 are reflected by the polarizing beam splitters 15R, 15B, and 15G at the interface of the polarizing beam splitter, and the p-polarized light is transmitted at the interface of the polarizing beam splitter. The p-polarized light undergoes image modulation by each of the liquid crystal display elements 22R, 22B, and 22G.

In each liquid crystal display device, the voltage corresponding to the image signal is applied to the liquid crystal for each pixel, so that the incident p-polarized light is converted from linearly polarized light to arbitrary elliptically polarized light for each pixel. Out of each liquid crystal display element.

The s-polarized light component is reflected at the interface between the polarization beam splitters 15R, 15B, and 15G. on the other hand,
The remaining p-polarized light components are again polarized beam splitters 15R,
15B and 15G, and returns to the light source direction.

The light emitted from each of the liquid crystal display elements 22R, 22B, and 22G is output from the polarization beam splitters 15R, 15B, and 15G.
The p-polarized light component that has passed through G is converted to a dichroic mirror 4
The images are combined by the projection lens 2 and the projection lens 43 and projected on a screen via a projection lens 45.

By setting the retardation of the phase plate in each liquid crystal display element to approximately half the center wavelength (λ ₀ ) of the white light 30, unnecessary interface reflected light between the phase plate and the liquid crystal layer is obtained. And the polarization directions of the image lights 39, 40, and 41 of the respective colors are different from each other by 90 degrees, so that unnecessary interface reflected light returns to the light source direction and is not superimposed on the image light. Therefore, a liquid crystal projector that displays an image with a good contrast ratio can be realized.

FIG. 5 shows that the contrast ratio of 250: 1 was obtained when the retardation of the phase plate in the liquid crystal display element was 265 nm. In this case, the contrast ratio of the projector was 150: 1. be able to.

On the other hand, in the conventional reflection type liquid crystal display device, the contrast ratio is 30: 1 (JP-A-3-2761).
No. 22). In a transmissive liquid crystal display element, the contrast ratio can be increased up to about 150: 1 by increasing the drive voltage. However, the contrast ratio at a practical drive voltage is about 100: 1, Contrast ratio from 70: 1 to 10
0: 1 is a realistic value.

Although the present embodiment uses three liquid crystal display elements corresponding to the three primary color lights, the retardation of the phase plate in each liquid crystal display element is determined by the central wavelength of the incident light to each liquid crystal display element ( λ _R , λ _G , and λ _B ) can be expected to further improve the contrast ratio by making them approximately half.

In general, the retardation of a phase film used for a phase plate tends to increase at a short wavelength and decrease at a long wavelength. Therefore, for example, when green light is selected as the center wavelength, the retardation of the phase plate in the region of blue light and red light is ２ of each center wavelength.
And part of the unnecessary interface reflected light is superimposed on the image light. In order to solve this, the retardation of the phase plate in each liquid crystal display element corresponding to each of the three primary colors is determined by the central wavelength (λ) of the light incident on each liquid crystal display element.
_R , λ _G , λ _B ), which are approximately λ of the retardation at λ _R / 2, λ _G / 2, λ _B / 2.

In this embodiment, the center wavelengths of red light, green light and blue light are 610 nm, 540 nm and 480 n, respectively.
m.

The retardation of the phase plate in the liquid crystal display device corresponding to each of the three primary color lights is set to a value that is approximately half the center wavelength of each of the three primary color lights incident on each liquid crystal display element. That is, the retardation of the phase plate in the liquid crystal display element for red light was set to 305 nm, which is almost half the value of red light having a wavelength of 610 nm.

Similarly, the retardation of the phase plate in the liquid crystal display device for green light is 270 nm for green light having a wavelength of 540 nm, and the retardation of the phase plate in the liquid crystal display device for blue light is 2 nm for blue light of 480 nm.
40 nm. Thereby, unnecessary reflection light at the time of black display can be further reduced, and the contrast ratio is further improved, as compared with the case where a phase plate having the same retardation is used in each liquid crystal display element.

In this embodiment, a prism type polarizing beam splitter is used as a polarizer, but a mirror type polarizing beam splitter may be used. Also, since the extinction ratio of a polarizing beam splitter is generally low, in order to improve the contrast ratio, it is necessary to place the polarizing beam splitter between a white light source, between the polarizing beam splitter and a projection lens, or inside or outside the projection lens. It is effective to provide a polarizing plate.

Further, in place of the polarizing plate provided between the polarizing beam splitter and the white light source, it is possible to provide a polarization conversion element having a characteristic of aligning incident non-polarized light with specific polarized light.
This is effective not only for improving the contrast ratio but also for improving the light use efficiency.

Although the dichroic mirror is used for the color separating and synthesizing element in the liquid crystal projector of the present invention, a dichroic prism may be used instead of the dichroic mirror.

[Embodiment 3] FIG. 7 shows an example of a structure when the liquid crystal display device of the present invention is used as a liquid crystal display.

This liquid crystal display has a light source 5 for white light.
0, a polarizing beam splitter 51, a liquid crystal display element 52 of the present invention, and a magnifying lens system 53.

The light emitted from the light source 50 is radiated by the polarizing plate 57 and the polarizing beam splitter 51 to the liquid crystal display element 52 only with the polarized light component parallel to the plane of the drawing.
2 undergoes image modulation and the polarization beam splitter 51
Of the light reflected in the direction, only the polarized light component perpendicular to the paper surface is reflected by the polarizing beam splitter 51 in the direction of the magnifying lens system 53, and the image is visually recognized by the observer 54 by the magnifying lens system 53.

Depending on the application, the image on the liquid crystal display element 52 and the scenery 55 are switched by using the shutter 56, or the combined image of both images is configured to be visible to the observer 54. That is, when the shutter 56 is closed, only the image of the liquid crystal display
, The shutter 56 is opened, and the liquid crystal display element 52 is opened.
Is displayed in black, only the landscape 55 is
Is visually recognized.

When the shutter 56 is opened and the liquid crystal display element 52 displays an image, a composite image of the image of the liquid crystal display element 52 and the image of the landscape 55 is displayed by the observer 54.
Is visually recognized.

As an application example of this liquid crystal display,
A view finder, a head mounted display, and the like are given.

[0100]

The reflection type liquid crystal display device using the electric field birefringence display mode using the conventional phase plate can cover almost the entire area of the pixel with the reflection pixel electrode. Although a high aperture ratio can be obtained, there has been a problem that interface reflection between members constituting the element is superimposed on an image at the time of black display, and the contrast ratio tends to decrease.

However, by setting the retardation of the phase plate to approximately one half of the center wavelength of the incident light as in the present invention, the scattered light due to the spacer beads of the liquid crystal panel and the phase plate and ITO and other element members can be prevented. Can be prevented from being superimposed on the image at the time of black display, and a display image with a high contrast ratio can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device of the present invention.

FIG. 2 is an explanatory view (during black display) of a relative relationship between optical elements of the liquid crystal display element of the present invention.

FIG. 3 is an explanatory diagram (at the time of white display) of a relative relationship of each optical element of the liquid crystal display element of the present invention.

FIG. 4 is an explanatory view of interface reflected light.

FIG. 5 is a graph showing a relationship between retardation of a phase plate and off-reflectance.

FIG. 6 is a configuration diagram of a liquid crystal projector of the present invention.

FIG. 7 is a configuration diagram of a liquid crystal display using the liquid crystal display element of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Single crystal silicon substrate, 2 ... MOS transistor, 3
... Wiring layer, 4 reflective pixel electrode, 5 dielectric film, 6 alignment film, 7 spacer material, 8 liquid crystal layer, 9 alignment film, 10
Transparent electrode, 11: glass substrate, 12: reflection type active matrix substrate, 13: counter glass substrate, 14: phase plate, 15: polarization beam splitter, 16: interface, 17 ...
Incident light, 18 s-polarized light, 19 p-polarized light, 22 liquid crystal display element, 23 liquid crystal alignment axis, 26 outgoing light, 28 light source,
29: UV and infrared cut filters, 31: Dichroic mirror, 32: Dichroic mirror, 3
3 red light, 34 blue light, 35 green light, 36 field lens, 37 field lens, 38 field lens, 39 red image light, 40 blue image light, 4
1: green image light, 42: dichroic mirror, 43:
Dichroic mirror, 45: projection lens system, 50: light source, 51: polarizing beam splitter, 52: liquid crystal display element, 53: magnifying lens system, 54: observer, 55: landscape,
56 ... Shutter.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02F 1/1343 G02F 1/1343 1/136 500 1/136 500 1/137 1/137 G09F 9/00 331 G09F 9/00 331G (72) Inventor Osamu Ito 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi R & D Co., Ltd. Hitachi, Ltd. (72) Inventor: Kazuo Takemoto 3300 Hayano, Mobara-shi, Chiba Electronic Device Division, Hitachi, Ltd.

Claims (3)

[Claims] An active matrix substrate in which a plurality of pixels each having a reflection mirror and a pixel electrode (or a pixel electrode serving also as a reflection mirror) and a switching element are arranged in rows and columns, and an alignment film is provided on the reflection mirror. (A first support substrate), a transparent substrate (a second support substrate) comprising a counter transparent electrode provided with an alignment film and disposed opposite to the first support substrate at a predetermined gap, and A liquid crystal layer filled between the two supporting substrates, a phase plate, a polarizer, and an analyzer, wherein the liquid crystal layer has an orientation axis substantially parallel to the substrate and a twist angle of approximately 0 degrees. A reflection type liquid crystal display device in which the slow axis of the phase plate is substantially orthogonal to the alignment axis of the liquid crystal layer, wherein the thickness (d _PH ) of the phase plate and the refractive index anisotropy (delta _nph) product of _{(d PH} · Δ nPH) incident light Center wavelength (lambda ₀₎ of approximately 2 minutes 1 (λ _0/2) and the reflecting type liquid crystal display element characterized by the. 2. A liquid crystal projector comprising: a white light source; a reflective liquid crystal display device for modulating light from the white light source based on image information; and a projection lens system for projecting the modulated light. An active matrix substrate (first element) in which a plurality of pixels each having a reflection mirror and a pixel electrode, or a pixel electrode serving as a reflection mirror, and a switching element are arranged in rows and columns and an alignment film is provided on the reflection mirror. And a transparent substrate (second support substrate) including a counter transparent electrode provided with an alignment film and facing the first support substrate at a predetermined gap, and the first and second supports. A liquid crystal layer filled between the substrates, a phase plate, a polarizer, and an analyzer, wherein the alignment axis of the liquid crystal layer is substantially parallel to the substrate, and the twist angle is substantially zero degrees;
The retardation axis of the phase plate is disposed so as to be substantially orthogonal to the alignment axis of the liquid crystal layer. The product (d _PH ·) of the thickness (d _PH ) of the phase plate and the refractive index anisotropy (Δ _nPH ) is obtained. nearly half of 1 (λ _0/2) and to a liquid crystal projector, wherein a All delta _nph) the center wavelength of the incident light (λ _0). 3. A white light source, a color separation element for separating light from the white light source into three primary colors of red, green and blue, and a plurality of reflective liquid crystal displays for modulating each of the separated three primary colors based on image information. In a liquid crystal projector comprising an element and a projection lens system for projecting the modulated light, the reflection type liquid crystal display element forms a reflection mirror and a pixel electrode, or a pixel electrode serving also as a reflection mirror, and a pixel having a switching element. And an active matrix substrate (first support substrate) provided with an alignment film on the reflection mirror, and an opposing transparent electrode provided with an alignment film, and a predetermined gap with the first support substrate. A transparent substrate (a second support substrate) disposed opposite to the above, a liquid crystal layer filled between the first and second support substrates, a phase plate, a polarizer, and an analyzer. The axis is the substrate Substantially parallel against, and twist angle are oriented substantially 0 degrees,
The retardation axis of the phase plate is arranged so as to be substantially orthogonal to the alignment axis of the liquid crystal layer. The thickness (d _PH ) and the refractive index of each phase plate used for each of the plurality of reflective liquid crystal display elements The product (d _PH · _{Δn PH} ) with the anisotropy ( _{Δn PH} ) is set to approximately one half of the center wavelength of the light incident on each reflection type liquid crystal display element.
2. The liquid crystal projector according to 1.