JPH07306408A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device capable of obtaining bright display by decreasing the loss of light quantity caused by light absorption on the base plate and the polarizing plate of a liquid crystal cell though the device is a reflection type one and preventing an external image such as the face of a display observer and the background from being reflected even when a light reflecting surface is a mirror surface. CONSTITUTION:The polarizing plate 30 is arranged on the front surface side of the liquid crystal cell 10 and a picture element electrode 13 provided on the inner surface of the back surface side base plate 11 of the liquid crystal cell 10 is made a light reflecting film M and the surface of the polarizing plate 30 is made a light diffusing surface A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, a reflection type liquid crystal display device has a structure in which a pair of front and back polarizing plates are arranged with a liquid crystal cell in between and a reflecting plate is arranged on the back surface of the back side polarizing plate. The liquid crystal cell is one in which liquid crystal is sandwiched between a pair of front and back transparent substrates, and transparent electrodes for applying a voltage to the liquid crystal layer are respectively provided on the inner surfaces of the both substrates (the surface facing the liquid crystal layer). After being formed, an alignment film is provided thereon, and the molecules of the liquid crystal are aligned in a predetermined alignment state by controlling the alignment directions on both substrates by the alignment film.

This reflection type liquid crystal display device displays by utilizing external light such as natural light or indoor illumination light, and external light incident on the liquid crystal display device from the surface side thereof is reflected by a polarizing plate on the surface side. The polarized light turns into linearly polarized light and enters the liquid crystal cell.

The alignment state of the liquid crystal molecules of the liquid crystal cell is
Since the birefringence effect of the liquid crystal layer changes depending on the alignment state of the liquid crystal molecules, the linearly polarized light incident on the liquid crystal cell changes depending on the alignment state of the liquid crystal molecules. The polarized light is incident on the back side polarizing plate.

Then, this light becomes image light due to the analyzing action of the back surface side polarizing plate, and this image light is reflected by the reflecting plate, so that the back surface side polarizing plate, the liquid crystal cell and the front surface side polarizing plate are separated. The light is emitted to the front surface side of the liquid crystal display device.

That is, the reflection type liquid crystal display device is
The polarization effect of the front side polarizing plate, the birefringence effect of the liquid crystal cell,
An optical image displayed by the back side polarizing plate is analyzed by the back side reflecting plate to be viewed from the front side of the liquid crystal display device.

In this reflection type liquid crystal display device, when the reflection surface of the reflection plate is a mirror surface, an external image such as the face of the display observer or the background thereof is reflected on the reflection plate surface and the image is displayed. Since the image appears to overlap with the image, a scattering reflection plate having a roughened surface is used as the reflection plate to eliminate the reflection of the external image.

[0008]

However, in the above-mentioned conventional reflection type liquid crystal display device, incident light from the front side thereof is reflected by the reflection plate through the front side polarizing plate, the liquid crystal cell and the back side polarizing plate. The reflected light is emitted to the front surface side of the liquid crystal display device through the back surface side substrate, the liquid crystal cell and the front surface side polarizing plate, so that the light incident from the front surface side is again output to the front surface side. In addition, both substrates of the liquid crystal cell were each passed twice, a total of 4 times, and the front and back polarizing plates were each passed twice, a total of 4 times.
Therefore, there is a problem in that the light amount loss due to light absorption in the substrate of the liquid crystal cell and the polarizing plate is large, and the display becomes dark.

According to the present invention, although it is of a reflective type, it is possible to obtain a bright display by reducing the light amount loss due to the absorption of light by the substrate of the liquid crystal cell and the polarizing plate, and moreover, the light reflecting surface is a mirror surface. Even if there is, it is an object of the present invention to provide a liquid crystal display device in which an external image such as the face of a display observer or its background is not reflected.

[0010]

A liquid crystal display device according to the present invention comprises a liquid crystal cell in which a liquid crystal is sandwiched between a pair of front and back substrates.
It consists of a polarizing plate arranged on the surface side of this liquid crystal cell,
Further, a light reflecting film is provided on the inner surface of the back side substrate of the liquid crystal cell, and one surface of the polarizing plate is a light scattering surface.

In the liquid crystal display device of the present invention, the reflection surface of the reflection film is preferably a mirror surface, and the surface of the polarizing plate is preferably a light scattering surface. In addition,
This light scattering surface may be formed by forming a transparent film having minute irregularities on the polarizing plate surface, for example.

In the liquid crystal cell, for example, a plurality of pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes are provided on the inner surface of the back side substrate, and the pixel electrodes are provided on the inner surface of the front side substrate. In the case of an active matrix type cell provided with a counter electrode facing the above, the pixel electrode may also serve as a light reflecting film.

In this case, the active element is covered with a protective insulating film, and a pixel electrode which also functions as a light reflecting film is provided so as to partially overlap the active element, and the active layer is provided in the contact hole formed in the protective insulating film. It may be connected to the device.

When the liquid crystal cell is an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the back surface side substrate, the pixel electrode is a transparent electrode, and a transparent insulating film is formed on the back surface side of the pixel electrode. A light reflection film may be provided via the light reflection film. In this case, the light reflection film also serves as a capacitor electrode, and the light retention film of the pixel in the non-selection period is provided by the light reflection film, the pixel electrode, and the insulating film therebetween. You may comprise the compensation capacity to compensate.

Further, when the liquid crystal cell is, for example, an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the front surface side substrate and a counter electrode is provided on the inner surface of the rear surface side substrate, The electrodes may also serve as the light reflecting film.

[0016]

In the liquid crystal display device of the present invention, the incident light from the front surface side enters the liquid crystal cell through the polarizing plate, and the light passing through the liquid crystal layer is reflected on the inner surface of the back side substrate of the liquid crystal cell. The light reflected by the film, again passes through the liquid crystal layer, enters the polarizing plate, and the light transmitted through the polarizing plate becomes image light and is emitted to the front surface side of the liquid crystal display device.

That is, in this liquid crystal display device, a light reflecting film is provided on the inner surface of the back side substrate of the liquid crystal cell so that the light incident on the front side of the liquid crystal cell is reflected on the inner surface of the back side substrate. , A single polarizing plate is provided only on the surface side of the liquid crystal cell, and the polarizing action of making the incident light from the outside into linearly polarized light and the analyzing action of making the light whose polarization state is changed into image light are provided in this polarizing plate. It has both effects of and.

In this liquid crystal display device, of both substrates of the liquid crystal cell, light passes through only the front surface side substrate and only one polarizing plate. A bright display can be obtained by reducing the light amount loss due to light absorption.

In the liquid crystal display device of the present invention,
Since a reflective film is provided on the inner surface of the back side substrate of the liquid crystal cell, it is difficult to use this reflective film as a diffuse reflective film, but since one surface of the polarizing plate is a light scattering surface, a light reflective surface is provided. That is, even if the surface of the reflective film is a mirror surface, an external image such as the face of the display observer or its background is not reflected.

Further, in the liquid crystal display device of the present invention,
If the surface of the reflection film is a mirror surface, the light whose polarization state has been changed by the birefringence effect of the liquid crystal layer can be reflected without being scattered and can be incident on the polarizing plate. Is a light-scattering surface, the light incident on the liquid crystal display device from the surface side is scattered and then becomes linearly polarized by the polarizing action of the polarizing plate, and the light reflected by the reflecting film is detected by the polarizing film. Since the image light is scattered by the light action and then scattered, the light does not scatter until the light incident through the polarizing plate passes through the polarizing plate and becomes the image light again, and therefore the quality is good. Images can be displayed.

Further, when the liquid crystal cell is, for example, an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the back side substrate and a counter electrode is provided on the inner surface of the front side substrate, the pixel electrode If you double as a light reflection film,
It is possible to simplify the structure of the liquid crystal cell and facilitate its manufacture.

Further, in this case, the active element is covered with a protective insulating film, and the pixel electrode is provided so as to partially overlap the active element and is connected to the active element through a contact hole formed in the protective insulating film. By doing so, it is possible to increase the area of the pixel electrode that also serves as the light reflection film, increase the aperture ratio of the liquid crystal display device, and make the display brighter.

When the liquid crystal cell is an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the back side substrate, the pixel electrode is a transparent electrode and a transparent insulating film is formed on the back side of the pixel electrode. Although a light reflection film may be provided via the light reflection film, in this case, the light reflection film also serves as a capacitor electrode, and the holding voltage of the pixel in the non-selected period is compensated by this light reflection film, the pixel electrode, and the insulating film between them. If the compensating capacitor is formed, the structure of the liquid crystal cell can be simplified and the manufacturing thereof can be facilitated.

Further, when the liquid crystal cell is, for example, an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the front surface side substrate and a counter electrode is provided on the inner surface of the rear surface side substrate, the counter electrode If it also serves as the light reflecting film, the structure of the liquid crystal cell can be simplified and the manufacturing thereof can be facilitated.

[0025]

【Example】

[First Embodiment] FIGS. 1 to 4 show a first embodiment of the present invention. FIG. 1 is a sectional view of a part of a liquid crystal display device.

The liquid crystal display device of this embodiment has a liquid crystal cell 1
0, one polarizing plate 30, and one retardation plate 40. The polarizing plate 30 is arranged on the front surface side of the liquid crystal cell 10, and the retardation plate 40 is the liquid crystal cell 10 and the polarization plate. Board 30
It is located between and.

First, the liquid crystal cell 10 will be described. The liquid crystal cell 10 is an active matrix type cell. In this embodiment, the molecules of the liquid crystal 26 are provided on both substrates 1.
A twisted orientation between 1 and 12 is used.

Of the pair of front and back substrates 11 and 12 which face each other across the liquid crystal layer of the liquid crystal cell 10, the back substrate (lower substrate in the drawing) 11 is an insulating substrate (such as a glass plate). However, it does not have to be transparent),
A plurality of pixel electrodes 13 and a plurality of active elements 14 respectively corresponding to the respective pixel electrodes 13 are arranged in a matrix in the row direction and the column direction on the inner surface of the rear substrate 11 that faces the liquid crystal layer. And a transparent alignment film 23 is provided thereon.

The active element 14 is, for example, a TFT (thin film transistor), and the TFT 14 includes a gate electrode 15 formed on the substrate 11, a gate insulating film 16 covering the gate electrode 15, and the gate insulating film 16. A-Si formed on top of the gate electrode 15 so as to face the gate electrode 15.
I-type semiconductor film 17 made of (amorphous silicon) or the like
And a source electrode 19s and a drain electrode 19d formed on both sides of the i-type semiconductor film 17 via an n-type semiconductor film 18 made of a-Si or the like doped with impurities. The TFT 14 is protected. It is covered with an insulating film 21.

Reference numeral 20 denotes a blocking insulating film formed on the channel region of the i-type semiconductor film 17, and the blocking insulating film 20 protects the n-type semiconductor film 18 and the i-type semiconductor film 17. It is provided to do so.

The gate insulating film 16 of the TFT 14 is S
The gate insulating film 16 is a transparent insulating film made of iN (silicon nitride) or the like, and is formed over substantially the entire surface of the substrate 11.

Although not shown, the back side substrate 11 is also provided.
A gate line (address line) for supplying a gate signal to the gate electrode 15 of the TFT 14 and a data line for supplying a data signal corresponding to image data to the drain electrode 19d of the TFT 14 are wired on the upper side. .

The gate line is formed integrally with the gate electrode 15 of the TFT 14 on the substrate 11,
The gate line is covered with the gate insulating film 16 except for its terminal portion. Also, the above data line is
It is formed on the gate insulating film 16, and this data line is connected to the drain electrode 19d of the TFT 14.

Further, the pixel electrode 13 is formed on the gate insulating film 16 while avoiding the TFT 14, and each pixel electrode 13 is connected to the source electrode 19s of the corresponding TFT 14 at one end thereof. ing.

Each of the pixel electrodes 13 also serves as a light reflecting film M. The pixel electrode 13 is formed of a metal film having a high light reflectance made of Al (aluminum) or an Al alloy. The surface, that is, the light reflection surface, is almost a mirror surface.

On the back side of each pixel electrode 13, the pixel electrode 13 is sandwiched with the gate insulating film 16 interposed therebetween.
Is provided with the capacitor electrode 22 and the pixel electrode 13 and the gate insulating film 16 between them to form a compensation capacitance Cs for compensating the holding voltage of the pixel in the non-selected period.

The capacitor electrode 22 is formed on the back side substrate 1
The capacitor electrode 20 and T
The gate electrode 15 and the gate line of the FT 14 are simultaneously formed by forming a metal film of Al-based alloy or the like on the substrate 11 by a sputtering apparatus or the like and patterning this metal film by photolithography.

In this embodiment, the capacitor electrode 22 is formed to have substantially the same size as the pixel electrode 13, and the facing area between the capacitor electrode 22 and the pixel electrode 13 is increased to increase the compensation capacitance Cs. The capacity value is increased.

Further, the capacitor electrode 22 is the gate line of the TFT corresponding to the pixel electrode in the previous row (row selected before) of the pixel electrode 13 facing the capacitor electrode 22, or the back side substrate 11 Capacitor line (parallel to the gate line) (not shown,
The capacitor electrode 22 is formed of the same metal film as that of the capacitor electrode 22), and each capacitor electrode 22 is connected to the reference potential via the gate line or the capacitor line.

On the other hand, the front side substrate (upper side substrate in the figure) 12 of the liquid crystal cell 10 is a transparent substrate (glass plate in the figure) made of a glass plate or a transparent resin film, and the inner surface of the front side substrate 12 On the surface facing the liquid crystal layer,
A transparent counter electrode 24 made of an ITO film or the like is provided, and a transparent alignment film 25 is provided thereon. The counter electrode 24 is a single film electrode that faces all of the pixel electrodes on the back substrate 11.

Although not shown, the back-side substrate 11 and the front-side substrate 12 are bonded to each other via a frame-shaped sealing material at the outer peripheral edge thereof, and the liquid crystal 26 is provided on both substrates 1.
The region surrounded by the sealing material between 1 and 12 is filled.

The liquid crystal 26 is a nematic liquid crystal having a positive dielectric anisotropy, and the molecules of the liquid crystal 26 are formed on both substrates 1.
Orientation directions on the substrates 11 and 12 are regulated by the orientation films 23 and 25 provided on the substrates 1 and 12, respectively.
The twist orientation is provided between the first and the second portions. The alignment films 23 and 25 are horizontal alignment films made of polyimide or the like, and the film surfaces thereof are subjected to an alignment treatment by rubbing.

Further, the polarizing plate 30 is a polarizing plate whose one surface, for example, the surface, is a light scattering surface A, and this light scattering surface A is shown in FIG. As described above, the transparent film 31 having minute irregularities is formed on the surface of the polarizing plate 30.

The transparent film 31 is made of a resin having a high light transmittance such as acrylic resin, and the transparent film 31 is transferred and printed on the surface of the polarizing plate 30 by using a printing plate having a minute unevenness made of a resin material. Curing, a method in which the resin material is applied to the surface of the polarizing plate 30 to a uniform thickness, and then unevenness is formed by embossing, followed by curing, or transparent fine particles such as silica are mixed in the resin material. It is formed by any of the methods of applying an object to the surface of the polarizing plate 30 and curing it.

The average height h of the irregularities of the transparent film 31 (the difference between the heights of the concave surface and the convex surface) h is 1 to 5 μm, the average pitch p of the irregularities is 5 to 40 μm, and the haze value of the light scattering surface A is Is 9 to 14%.

The haze value is measured according to JIS K 67.
It is a value measured by an integrating sphere type light transmittance measuring device (haze meter) according to 14. This haze value is calculated by the following formula.

Total light transmittance; Tt (%) = T2 / T1 parallel light transmittance; Tp (%) = Tt-Td diffuse transmittance; Td (%) = [T4-T3 * (T2 / T1)]
/ T1 haze value; H (%) = (Td / Tt) x 100 T1; Incident light amount T2; Total light transmitted light amount T3; Measuring device diffused light amount T4; Test piece (transparent film 31) and diffused light amount by measuring device Further, the retardation plate 40 is made of a uniaxially stretched film such as polycarbonate, and the retardation plate 40 is provided between the liquid crystal cell 10 and the polarizing plate 30 disposed on the surface side of the liquid crystal cell 10. The retardation plate 40 is arranged with the slow axis (stretching axis) and the transmission axis of the polarizing plate 30 obliquely displaced by a predetermined angle. The retardation plate 40 is adhered to the surface of the liquid crystal cell 10 (the outer surface of the front substrate 12),
The polarizing plate 30 is adhered to the surface of the retardation plate 40.

In the liquid crystal display device of this embodiment,
An alignment direction of liquid crystal molecules on both substrates 11 and 12 of the liquid crystal cell 10 (rubbing direction of the alignment films 23 and 25),
The direction of the transmission axis of the polarizing plate 30 and the direction of the slow axis of the retardation plate 40 are set as follows.

In this embodiment, the orientation direction of the liquid crystal molecules on the rear substrate 11 of the liquid crystal cell 10 is 0 °.
Of the liquid crystal cell 10 on the front side substrate 12 of the liquid crystal cell 10 and the polarizing plate 30.
The transmission axis direction and the slow axis direction of the retardation plate 40 are set.

That is, FIG. 3 shows the alignment direction of the liquid crystal molecules of the liquid crystal cell 10 and the retardation plate 40 in the liquid crystal display device.
11 is a plan view showing the slow axis of the liquid crystal cell 10 and the transmission axis of the polarizing plate 30. In FIG.
Alignment direction of liquid crystal molecules in the upper part, 12a is liquid crystal cell 10
3 shows the alignment direction of liquid crystal molecules on the front surface side substrate 12.

As shown in FIG. 3, the liquid crystal molecule alignment direction 12a on the front surface side substrate 12 of the liquid crystal cell 10 is different from the liquid crystal molecule alignment direction 11a direction on the back surface side substrate 11, that is, the azimuth angle of 0 °. The molecules of the liquid crystal 26 are shifted by 90 ° counterclockwise as viewed from the front side, and the molecules of the liquid crystal 26 are on both substrates 11, 1.
The two are twist-oriented with a twist angle of approximately 90 °.

Further, in FIG. 3, reference numeral 30a denotes a polarizing plate 30.
, 40a denotes the slow axis of the retardation plate 40, and the transmission axis 30a of the polarizing plate 30 has a direction of approximately 45 ° counterclockwise when viewed from the surface side with respect to the direction of the azimuth angle of 0 °. The slow axis 40a of the retardation plate 40 is in the direction of approximately 140 ° counterclockwise when viewed from the surface side with respect to the direction of the azimuth angle of 0 °, and therefore, the slow axis 40a of the retardation plate 40 is the polarizing plate. Thirty
With respect to the transmission axis 30a of FIG.

This liquid crystal display device is of a reflection type which displays by utilizing light (natural light or room illumination light) incident from the surface side thereof. In this liquid crystal display device,
The incident light (external light) from the front surface side enters the liquid crystal cell 10 through the polarizing plate 30 and the retardation plate 40, and the light that has passed through the liquid crystal layer is the inner surface of the rear substrate 11 of the liquid crystal cell 10. In the liquid crystal display, the light reflected by the pixel electrode 13 also serving as the reflection film M, passes through the liquid crystal layer and the retardation plate 40 and enters the polarizing plate 30, and the light that passes through the polarizing plate 30 becomes image light. The light is emitted to the surface side of the device.

That is, in this liquid crystal display device, the light reflection film M (also used as the pixel electrode 13 in this embodiment) is provided on the inner surface of the back side substrate 11 of the liquid crystal cell 10 so that the liquid crystal cell 10 is exposed from the front surface side. The incident light is reflected on the inner surface of the back-side substrate 11, and the liquid crystal cell 10
One polarizing plate 30 is provided only on the front surface side of the polarizing plate 30, and the polarizing plate 30 has a polarizing action of making incident light from the outside into linearly polarized light and an analyzing action of making light whose polarization state is changed into image light. It has both effects of.

The display operation of the liquid crystal display device will be described. In this liquid crystal display device, since the slow axis 40a of the retardation plate 40 is obliquely displaced from the transmission axis 30a of the polarizing plate 30, the polarization The linearly polarized light that has entered through the plate 30 changes its polarization state due to its birefringence effect in the process of passing through the retardation plate 40 to become elliptically polarized light. This elliptically polarized light passes through the liquid crystal layer of the liquid crystal cell 10 and The polarization state can be further changed by the birefringence effect, and the light is reflected by the light reflection film M (pixel electrode 13) on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 and is passed through the liquid crystal layer and the retardation plate 40 again. The polarization state is further changed by the birefringence effect of (1) and enters the polarizing plate 30.

The reflected light that has entered the polarizing plate 30 is non-linearly polarized light whose polarization state is changed by the birefringence effect of the retardation plate 40 and the liquid crystal layer. Only the wavelength light of the polarization component that passes through 30 passes through the polarizing plate 30 and is emitted, and this emitted light becomes colored light corresponding to that wavelength.

That is, this liquid crystal display device includes the retardation plate 4
0 and the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 and the polarizing plate 3
Light is colored by utilizing the polarization of 0 and the analysis function. According to this liquid crystal display device, a very bright colored light is obtained as compared with a liquid crystal display device using a commonly used color filter. Can be obtained.

That is, the color filter absorbs light having a wavelength other than the wavelength range corresponding to the color and colors the light.
Since this color filter also absorbs light in the wavelength range corresponding to that color with a considerably high absorptivity, in a liquid crystal display device that colors light with the color filter, the wavelength that becomes colored light of the light that enters the display device. The amount of colored light passing through the color filter is considerably reduced as compared with the amount of light in the band.

In this respect, since the color liquid crystal display device of the above-described embodiment colors transmitted light without using a color filter, light absorption by the color filter does not occur, and the retardation plate 40 and the liquid crystal layer do not. Since the polarization state of the transmitted light is changed but the light is hardly absorbed, the polarization state can be changed by these birefringence effects, and the light amount of the colored light transmitted through the polarizing plate 30 and emitted therefrom passes through the polarizing plate 30. Since the amount of light in the wavelength band that becomes the colored light in the linearly polarized light that has entered is substantially the same, colored light with high brightness can be obtained.

Further, in the liquid crystal display device in which light is colored by the color filter, the display color is determined by the color of the color filter, so that one pixel cannot display a plurality of colors. According to the liquid crystal display device, one pixel can display a plurality of colors.

That is, in the liquid crystal display device of the above embodiment, the birefringence effect of the retardation plate 40 does not change, but the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 does not change.
Since the voltage applied between the electrodes 13 and 24 of the liquid crystal changes as the alignment state of the liquid crystal molecules changes, the voltage applied to the liquid crystal cell 10 is controlled to control the liquid crystal of the retardation plate 40 and the liquid crystal cell 10. By changing the polarization state of light that has passed through the layers, it is possible to change the color of the colored light that passes through the polarizing plate 30 and is emitted, and thus one pixel can display a plurality of colors. it can.

The display drive of this liquid crystal display device is basically the same as the display drive of a generally known active matrix type liquid crystal display device (those using TFTs as active elements). A reference signal having a waveform synchronized with a synchronization signal is supplied to the counter electrode 24, a gate signal is sequentially supplied to each gate line in synchronization with the synchronization signal, and a potential corresponding to image data is supplied to each data line in synchronization with the reference signal. Of the data signal is controlled by controlling the potential of the data signal in accordance with the image data, the data signal of the potential corresponding to the image data is supplied to the pixel through the TFT 14 during the selection period of the pixel in each row. The charge supplied to the electrode 13 is accumulated in the compensation capacitance Cs, and a voltage corresponding to the amount of accumulated charge in the compensation capacitance Cs is applied to the pixel electrode during the non-selection period. It is applied between 13 and the counter electrode 24.

The display color of the above liquid crystal display device will be described. For example, as described above, the liquid crystal cell 10 is one in which liquid crystal molecules are twist-aligned between the substrates 11 and 12 at a twist angle of about 90 °. Both substrates 11,
Alignment directions 11a and 12a of liquid crystal molecules on 12;
The transmission axis 30a of the polarizing plate 30 and the slow axis 4 of the retardation plate 40
0a are in the directions shown in FIG. 3, and the value of Δn · d (the product of the refractive index anisotropy Δn of the liquid crystal 26 and the liquid crystal layer thickness d) of the liquid crystal cell 10 is about 1000 nm, and the retardation plate 40
If the retardation value of is about 600 nm, then 1
One pixel can display red, green, blue, and white colors.

FIG. 4 is a CIE chromaticity diagram showing a color change of emitted light with respect to an applied voltage of the liquid crystal display device. The liquid crystal display device has a direction of 30 ° with respect to its normal line (direction may be arbitrary). The result of observing the emitted light from the normal direction of the liquid crystal display device is shown by allowing white light to enter.

As shown in FIG. 4, in the above liquid crystal display device, the color of the emitted light is changed to P as the voltage value applied between the electrodes 13 and 24 of the liquid crystal cell 10 is increased.
The color changes from point S to point Pe as shown by the arrow, and in the middle of that, the colors become green G, blue B, red R, and white W with high light intensity and good color purity.

The x coordinate value and y coordinate value of each of the colors G, B, R and W are x = 0.299, y for green G.
= 0.396, blue B x = 0.247, y = 0.23
3, red R x = 0.399, y = 0.402, white W x
= 0.332, y = 0.351, and both have sufficiently satisfactory color purity.

In the above liquid crystal display device, as shown in FIG.
As described above, the color of the emitted light becomes a color close to white W even while the color of the emitted light changes from green G to blue B.
Since the color change with respect to the voltage change is large and the voltage control for displaying this color is troublesome, the white W
It is desirable that the display of (1) is performed with a voltage higher than the voltage for obtaining the display color of red R.

As described above, in the above liquid crystal display device, the colors of the emitted light are green G, blue B, red R, and white W according to the applied voltage, so that red, green, and blue are formed in one pixel. It is also possible to display a white color, or by displaying different colors in a plurality of adjacent pixels, it is possible to display a mixed color of a plurality of colors of red, green, blue, and white.

The liquid crystal display device of the above-mentioned embodiment is red,
Green, blue, and white colors are displayed. The display colors of this liquid crystal display device are the applied voltage and both substrates 1 of the liquid crystal cell 10.
Alignment direction 11a, 12a of liquid crystal molecules on 1, 12
And the twist angle of the liquid crystal molecules and the transmission axis 3 of the polarizing plate 30.
Since it is determined by the direction of 0a and the direction of the slow axis 40a of the retardation plate 40, the display color of the liquid crystal display device can be arbitrarily selected by selecting these conditions.

Although the liquid crystal display device is of a reflection type, the pixel electrode 13 provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 also serves as the light reflection film M, and the back surface side substrate 11 of Since the light is reflected on the inner surface,
Of the two substrates 11 and 12 of the liquid crystal cell 10, light passes through only the front substrate 12, and since only one polarizing plate 30 is provided, the amount of light due to light absorption by the substrate of the liquid crystal cell and the polarizing plate is large. A bright display can be obtained with less loss.

In this liquid crystal display device, light also passes through the phase difference plate 40 and the liquid crystal layer of the liquid crystal cell 10, but since the phase difference plate 40 and the liquid crystal layer absorb little light as described above, There is almost no light loss due to these.

In the above liquid crystal display device, the pixel electrode 13 provided on the inner surface of the rear substrate 11 of the liquid crystal cell 10.
Since the pixel electrode 13 is also extremely thin, it is difficult to use the light reflection film M as a diffuse reflection film, but the surface of the polarizing plate 30 is the light scattering surface A. Since the incident light and the outgoing light to the liquid crystal display device can be scattered by the light scattering surface A, even if the light reflecting surface, that is, the surface of the pixel electrode 13 is a mirror surface, No external image such as the observer's face or its background is reflected.

Further, in the above liquid crystal display device, since the surface of the pixel electrode 13 which also serves as the light reflection film M is a mirror surface, the light whose polarization state is changed by the birefringence effect of the liquid crystal layer is reflected without being scattered. And the light is incident on the polarizing plate 30, and when the surface of the polarizing plate 30 is the light scattering surface A, the light incident on the liquid crystal display device from the surface side is scattered before the polarization of the polarizing plate 30. The light reflected by the pixel electrode 13 becomes a linearly polarized light by the action, and the light reflected by the pixel electrode 13 becomes an image light by the analysis action of the polarizing plate 30 and is scattered. The light is not scattered until it becomes the image light through the polarizing plate 30, so that a high-quality image can be displayed.

The scattering effect of the light-scattering surface A is determined by the above-mentioned haze value. If this haze value is 25% or more, the light that has become image light due to the analyzing action of the polarizing plate 30 is also largely scattered. When the haze value is 6% or less, the external image is reflected, but when the haze value of the light scattering surface A is in the range of 9 to 14%, a clear display is obtained. It is possible to obtain an image and eliminate the reflection of an external image.

In addition, in the above liquid crystal display device, since the pixel electrode 13 provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 also serves as the light reflecting film M, it is formed on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10. Although it has a light reflection film,
The structure of the liquid crystal cell 10 can be simplified and its manufacture can be facilitated.

In the liquid crystal display device of the above-described embodiment, the pixel electrode 13 provided on the inner surface of the backside substrate 11 of the liquid crystal cell 10 also serves as the light reflecting film M. Since the provided capacitor electrode 22 has nothing to do with the aperture ratio of the liquid crystal display device, the capacitor electrode 22 can be formed large and a sufficient capacitance value of the compensation capacitance Cs of the pixel can be secured.

[Second Embodiment] In the first embodiment, the pixel electrode 13 also serving as the light reflecting film M is formed avoiding the TFT 14 which is an active element. Alternatively, a part thereof may be formed on the TFT 14 in an overlapping manner.

FIG. 5 is a sectional view of a part of a liquid crystal display device showing a second embodiment of the present invention. In the liquid crystal display device of this embodiment, a protective insulating film 21 covering the TFT 14 is provided on a substrate 1.
1, a pixel electrode 13 is provided on the protective insulating film 21 so as to partially overlap the TFT 14, and the pixel electrode 13 is formed in the contact hole formed in the protective insulating film 21. 21a is connected to the source electrode 19s of the TFT 14.

The present embodiment is the same as the above-described first embodiment except for the formation state of the protective insulating film 21 covering the TFT 14 and the pixel electrode 13, and therefore the duplicate description will be omitted. The same symbols are attached to the drawings and omitted. However, in this embodiment, the insulating film of the compensation capacitance Cs (the insulating film between the pixel electrode 13 and the capacitor electrode 22) is a two-layer film including the gate insulating film 16 and the protective insulating film 21.

As in this embodiment, the TFT 14 is covered with the protective insulating film 21, and the pixel electrode 13 is partially covered by the TFT.
The pixel electrode 1 that also functions as the light reflection film M if it is provided so as to overlap 14
It is possible to increase the area of 3 and increase the aperture ratio of the liquid crystal display device to make the display brighter.

[Third Embodiment] In the first and second embodiments, the pixel electrode 13 provided on the inner surface of the backside substrate 11 of the liquid crystal cell 10 also serves as the light reflecting film M. The pixel electrode 13 may be a transparent electrode made of an ITO film or the like, and a light reflecting film may be provided on the back surface side of the pixel electrode 13 via a transparent insulating film.

In this case, the light-reflecting film has a structure shown in FIGS.
If the light-reflecting film and the pixel electrode 13 and the insulating film between them also serve as the capacitor electrode 22 shown in FIG. 2 to form a compensation capacitance Cs for compensating the holding voltage of the pixel in the non-selected period, the structure of the liquid crystal cell 10 is It is possible to simplify and facilitate its manufacture.

In this way, the capacitor electrode 22 is formed on the light reflecting film.
In the case of also serving as the above, the capacitor electrode 22 of the liquid crystal display device shown in FIGS. 1 and 5 may be formed of a light reflecting film, and the pixel electrode 13 may be a transparent electrode. However, in the case of the liquid crystal display device shown in FIG. 5, the protective insulating film 21 is also a transparent insulating film. Further, in this case, the area of the capacitor electrode 22 formed of the light reflecting film becomes the size of the display pixel.

[Fourth Embodiment] In the first to third embodiments, the pixel electrode 13 and the TFT 14 are provided on the rear substrate 11 of the liquid crystal cell 10.
Alternatively, the pixel electrode 13 and the TFT 14 may be provided on the front substrate 12.

FIG. 6 is a sectional view of a part of a liquid crystal display device showing a fourth embodiment of the present invention. In this embodiment, a liquid crystal cell 10 is provided on a front surface side substrate 12 with a plurality of pixel electrodes 13.
And a plurality of TFTs respectively corresponding to these pixel electrodes
(Active element) 14 is provided, and the counter electrode 24 facing the pixel electrodes 13 is provided on the inner surface of the backside substrate 11 to form an active matrix type cell, and the pixel electrode 13 is used as a transparent electrode. The electrode 24 is formed of a metal film having a high light reflectance made of Al or an Al-based alloy or the like, and the counter electrode 24 also serves as the light reflecting film M.

Incidentally, the liquid crystal cell 10 in this embodiment.
Is used as the front side substrate 12 of the liquid crystal cell 10 shown in FIG. 1 and the pixel electrode 1 provided on this substrate.
3 is a transparent electrode, the front side substrate 12 of the liquid crystal cell 10 shown in FIG. 1 is the back side substrate 11, and the counter electrode 24 provided on this substrate is also an electrode also serving as the light reflection film M. The structure of the TFT 14 and the like is the same as that shown in FIG. 1, and the arrangement of the polarizing plate 30 and the retardation plate 40 is also the same as that of the above-described first embodiment, and therefore, the overlapping description is the same as that in the drawing. A reference numeral is attached and omitted.

However, in this embodiment, since the front surface side substrate 12 of the liquid crystal cell 10 has the capacitor electrode 22 constituting the compensation capacitance CS, the counter electrode 2 on the inner surface of the rear surface side substrate 11 is provided.
Since the light reflected at 4 is blocked by the capacitor electrode 22, the capacitor electrode 22 is formed so as to face one side edge portion of the pixel electrode 13 to reduce the decrease in the aperture ratio due to the capacitor electrode 22. .

In the liquid crystal display device of this embodiment, the incident light (external light) from the surface side thereof enters the liquid crystal cell 10 through the polarizing plate 30 and the retardation plate 40, and passes through the liquid crystal layer. The light is reflected on the inner surface of the backside substrate 11 of the liquid crystal cell 10 by the counter electrode 24 which also serves as the reflective film M, passes through the liquid crystal layer and the retardation plate 40 again, and enters the polarizing plate 30. The light transmitted through 30 becomes image light and is emitted to the front surface side of the liquid crystal display device.

The liquid crystal display device of this embodiment is also one which colors light by utilizing the birefringence effect of the retardation plate 40 and the liquid crystal layer of the liquid crystal cell 10 and the polarization and analysis of the polarizing plate 30. Therefore, it is possible to obtain very bright colored light and to control the voltage applied between the electrodes 13 and 24 of the liquid crystal cell 10 as compared with a liquid crystal display device using a commonly used color filter. By doing so, one pixel can display a plurality of colors.

The liquid crystal display device of this embodiment is also of a reflection type, but the counter electrode 24 provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 also serves as the light reflection film M, and this back surface side Since the light is reflected on the inner surface of the substrate 11, only the front substrate 12 of the two substrates 11 and 12 of the liquid crystal cell 10 allows the light to pass therethrough, and only one polarizing plate 30 is provided. Therefore, light quantity loss due to light absorption by the substrate and the polarizing plate of the liquid crystal cell can be reduced, and bright display can be obtained.

Further, in this liquid crystal display device, the counter electrode 24 provided on the inner surface of the rear substrate 11 of the liquid crystal cell 10.
Since the counter electrode 24 is extremely thin, it is difficult to use the light reflection film M as a diffuse reflection film, but the surface of the polarizing plate 30 becomes the light scattering surface A. Therefore, incident light and outgoing light to the liquid crystal display device can be scattered by the light scattering surface A. Therefore, even if the light reflecting surface, that is, the surface of the pixel electrode 13 is a mirror surface, display observation is possible. The external image of the person's face or its background is not reflected.

Further, in this liquid crystal display device, since the surface of the counter electrode 24 which also serves as the light reflection film M is a mirror surface, the light whose polarization state has been changed by the birefringence effect of the liquid crystal layer is reflected without being scattered. And the surface of the polarizing plate 30 is a light scattering surface (light scattering surface having a haze value of 9 to 14%) A.
The light incident on the surface of the liquid crystal display device is scattered and then linearly polarized by the polarizing action of the polarizing plate 30, and the light reflected by the pixel electrode 13 is reflected by the polarizing plate 30.
Since it is scattered after it becomes image light due to the analysis effect of
Light is not scattered until the light incident through the polarizing plate 30 passes through the polarizing plate 30 and becomes image light again.
Therefore, a high quality image can be displayed.

Further, in the liquid crystal display device of this embodiment, the counter electrode 24 provided on the backside substrate 11 of the liquid crystal cell 10 also serves as the light reflecting film M, so that the structure of the liquid crystal cell is simplified and Manufacturing can be facilitated.

[Other Embodiments] The above-mentioned first to fourth embodiments
In any of the liquid crystal display devices of the above examples, a color liquid crystal display device that colors light by utilizing the birefringence effect of the liquid crystal layer of the retardation plate 40 and the liquid crystal cell 10 and the polarization and analysis function of the polarizing plate 30. However, in the present invention, the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 and the polarizing plate 30 are not provided with the retardation plate 40.
ECB that colors light by utilizing the polarization and analysis of the light
It can be applied to a (birefringence effect) type color liquid crystal display device, and can also be applied to a TN type or STN type liquid crystal display device.

In each of the above embodiments, the active matrix type cell having the TFT 14 as an active element is used as the liquid crystal cell 10. However, this liquid crystal cell has a two-terminal nonlinear resistance element such as an MIM or a thin film diode. It may be an active matrix type cell used as an element, a simple matrix type cell, a segment display type cell, or the like.

Furthermore, in each of the above embodiments, the surface of the polarizing plate 30 is the light scattering surface A, but this polarizing plate 30 may have either the front surface or the back surface as the light scattering surface A, or a liquid crystal cell. The light reflection film provided on the back side substrate 11 of 10 is the pixel electrode 13, the capacitor electrode 22, or the counter electrode 24.
You may form with a metal film different from.

[0097]

According to the liquid crystal display device of the present invention, a light reflecting film is provided on the inner surface of the back side substrate of the liquid crystal cell, so that the light incident from the front side of the liquid crystal cell is reflected on the inner surface of the back side substrate. At the same time, a polarizing plate is provided only on the front surface side of the liquid crystal cell, and the polarizing action that makes the incident light from the outside into linearly polarized light and the light whose polarization state is changed are detected as image light. According to this liquid crystal display device, light passes through only the front surface side substrate of both substrates of the liquid crystal cell and only one polarizing plate is used. Therefore, it is possible to reduce the light amount loss due to the light absorption in the substrate of the liquid crystal cell and the polarizing plate and obtain a bright display.

In the liquid crystal display device of the present invention,
Since a reflective film is provided on the inner surface of the back side substrate of the liquid crystal cell, it is difficult to use this reflective film as a diffuse reflective film, but since one surface of the polarizing plate is a light scattering surface, a light reflective surface is provided. That is, even if the surface of the reflective film is a mirror surface, an external image such as the face of the display observer or its background is not reflected.

Furthermore, in the liquid crystal display device of the present invention,
If the surface of the reflection film is a mirror surface, the light whose polarization state has been changed by the birefringence effect of the liquid crystal layer can be reflected without being scattered and can be incident on the polarizing plate. Is a light-scattering surface, the light incident on the liquid crystal display device from the surface side is scattered and then becomes linearly polarized by the polarizing action of the polarizing plate, and the light reflected by the reflecting film is detected by the polarizing film. Since the image light is scattered by the light action and then scattered, the light does not scatter until the light incident through the polarizing plate passes through the polarizing plate and becomes the image light again, and therefore the quality is good. Images can be displayed.

In the case where the liquid crystal cell is, for example, an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the back surface side substrate and a counter electrode is provided on the inner surface of the front surface side substrate, the pixel electrode If you double as a light reflection film,
It is possible to simplify the structure of the liquid crystal cell and facilitate its manufacture.

Further, in this case, the active element is covered with a protective insulating film, and the pixel electrode is partially overlapped with the active element and is connected to the active element through a contact hole formed in the protective insulating film. By doing so, it is possible to increase the area of the pixel electrode that also serves as the light reflection film, increase the aperture ratio of the liquid crystal display device, and make the display brighter.

When the liquid crystal cell is an active matrix type cell in which the pixel electrode and the active element are arranged on the inner surface of the back surface side substrate, the pixel electrode is a transparent electrode and a transparent insulating film is formed on the back surface side of the pixel electrode. Although a light reflection film may be provided via the light reflection film, in this case, the light reflection film also serves as a capacitor electrode, and the holding voltage of the pixel in the non-selected period is compensated by this light reflection film, the pixel electrode, and the insulating film between them. If the compensating capacitor is formed, the structure of the liquid crystal cell can be simplified and the manufacturing thereof can be facilitated.

Further, when the liquid crystal cell is, for example, an active matrix type cell in which a pixel electrode and an active element are arranged on the inner surface of the front surface side substrate and a counter electrode is provided on the inner surface of the rear surface side substrate, the counter electrode If it also serves as the light reflecting film, the structure of the liquid crystal cell can be simplified and the manufacturing thereof can be facilitated.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a liquid crystal display device showing a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a light scattering surface of a polarizing plate.

FIG. 3 is a plan view showing a liquid crystal molecule alignment direction of a liquid crystal cell, a slow axis of a retardation plate, and a transmission axis of a polarizing plate.

FIG. 4 is a CIE showing a color change of emitted light with respect to an applied voltage.
Chromaticity diagram.

FIG. 5 is a sectional view of a part of a liquid crystal display device showing a second embodiment of the present invention.

FIG. 6 is a partial cross-sectional view of a liquid crystal display device showing a fourth embodiment of the present invention.

[Explanation of symbols]

 10 ... Liquid crystal cell 11 ... Back side substrate 12 ... Front side substrate M ... Light reflection film 13 ... Pixel electrode 14 ... TFT (Active element) 15 ... Gate insulating film 21 ... Protective insulating film 21a ... Contact hole 22 ... Capacitor electrode Cs ... Compensation capacity 23 ... Alignment film 24 ... Counter electrode 25 ... Alignment film 30 ... Polarizing plate 31 ... Transparent film A ... Light scattering surface 40 ... Retardation plate

Claims (9)

[Claims] 1. A reflective liquid crystal display device comprising a liquid crystal cell in which a liquid crystal is sandwiched between a pair of front and back substrates, and a polarizing plate disposed on the front surface side of the liquid crystal cell. A liquid crystal display device, wherein a light reflecting film is provided on the inner surface of the back side substrate of the cell, and one surface of the polarizing plate is a light scattering surface. 2. The liquid crystal display device according to claim 1, wherein the reflecting surface of the light reflecting film is a mirror surface. 3. The liquid crystal display device according to claim 1, wherein the surface of the polarizing plate is a light scattering surface. 4. The liquid crystal display device according to claim 1, wherein the light-scattering surface of the polarizing plate is formed by forming a transparent film having minute irregularities on the polarizing plate surface. 5. A liquid crystal cell is provided with a plurality of pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes on the inner surface of a back surface side substrate, and faces the respective pixel electrodes on the inner surface of the front surface side substrate. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an active matrix type cell provided with a counter electrode, and the pixel electrode also serves as a light reflecting film. 6. The active element is covered with a protective insulating film, and the pixel electrode is partially overlapped with the active element.
The liquid crystal display device according to claim 5, wherein the liquid crystal display device is connected to the active element through a contact hole formed in the protective insulating film. 7. A liquid crystal cell is provided with a plurality of pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes on the inner surface of a back surface side substrate, and faces the respective pixel electrodes on the inner surface of a front surface side substrate. An active matrix type cell provided with a counter electrode, wherein the pixel electrode is a transparent electrode, and a light reflection film is provided on the back surface side of the pixel electrode via a transparent insulating film. The liquid crystal display device according to claim 1. 8. The light reflecting film also serves as a capacitor electrode,
The liquid crystal display device according to claim 7, wherein the light reflection film, the pixel electrode, and the insulating film between them constitute a compensation capacitor for compensating the holding voltage of the pixel in the non-selection period. 9. A liquid crystal cell is provided with a plurality of pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes on the inner surface of a front surface side substrate, and faces the respective pixel electrodes on the inner surface of a back surface side substrate. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an active matrix type cell provided with a counter electrode, and the counter electrode also serves as a light reflection film.