JP3301214B2 - Active matrix type color liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type active matrix type color liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as an active matrix type liquid crystal display device, a TN (twisted nematic) type is used. This active matrix type liquid crystal display device of the TN mode comprises an active matrix type liquid crystal cell in which liquid crystal molecules are twisted at a twist angle of about 90 °, and a pair of polarizing plates disposed between the liquid crystal cells. The pair of polarizing plates are provided such that their transmission axes are parallel to each other and the transmission axes are substantially parallel to the orientation direction of liquid crystal molecules on one substrate of the liquid crystal cell.

In the active matrix type liquid crystal cell, a liquid crystal is sandwiched between a pair of front and back transparent substrates.
A plurality of pixel electrodes and a plurality of active elements (for example, thin film transistors) corresponding to the respective pixel electrodes are provided on the inner surface of one substrate, and a counter electrode is provided on the inner surface of the other substrate. The orientation of the molecules is regulated by the orientation films provided on the electrode forming surfaces of both substrates, respectively.
The two substrates are twisted at a twist angle of about 90 °. Note that a nematic liquid crystal having a positive dielectric anisotropy is used as the liquid crystal.

In the TN type liquid crystal display device, the incident light from the outside is incident on the liquid crystal cell as linearly polarized light by the polarization action of one polarizing plate, and the transmission of the light passing through the liquid crystal cell is detected by the other polarizing plate. The display is controlled by optical action.In the state where no on-voltage is applied between the electrodes of both substrates of the liquid crystal cell, that is, in the state where the liquid crystal molecules are twisted, the linearly polarized light incident on the liquid crystal cell is The light exits the liquid crystal cell as linearly polarized light whose polarization direction is shifted by approximately 90 °, and this linearly polarized light is absorbed by the other polarizing plate, and the display becomes dark.

When an on-voltage is applied between the electrodes of the liquid crystal cell, the liquid crystal molecules rise and align almost perpendicularly to the substrate surface, and the linearly polarized light incident on the liquid crystal cell exits the liquid crystal cell as it is. Is transmitted through the other polarizing plate, and the display becomes bright.

[0006] The liquid crystal display devices include a transmissive liquid crystal display device and a reflective liquid crystal display device having a reflector disposed on the back surface.
In the reflection type liquid crystal display device, light incident from the front side is sequentially reflected by the reflection plate through the front side polarizing plate, the liquid crystal cell and the back side polarizing plate, and the reflected light is reflected on the back side. And the liquid crystal cell and the front-side polarizing plate sequentially emit light.

As the TN type active matrix type liquid crystal display device, there is a device which displays a multi-color image. In a color liquid crystal display device which displays this color image, a plurality of liquid crystal cells are provided on one substrate. The color of the
For example, three color filters of red, green, and blue are provided corresponding to each pixel electrode.

[0008]

However, a conventional active matrix type color liquid crystal display device uses a color filter to color light. Therefore, if a reflection type liquid crystal display device is used, the display is almost invisible. It has the problem of darkening.

This is due to the absorption of light by the color filter. The color filter not only absorbs light outside the wavelength band corresponding to the color, but also absorbs light in the wavelength band at a considerably high absorption rate. Due to absorption, the light colored by the color filter becomes light in which the amount of light is significantly reduced as compared with the light in the wavelength band before entering the color filter.

In the case of a transmission type liquid crystal display device,
Although the display can be brightened by using a large amount of backlight, the amount of incident light is limited in a reflective liquid crystal display device that displays using external light such as natural light or indoor illumination light. In the process in which light colored by the color filter is reflected and emitted to the surface side of the liquid crystal display device, the light passes through the color filter again, so that the light absorption by the color filter is further increased, and the display is almost invisible. It will be dark.

In addition, in the case of the reflection type liquid crystal display device, in the above-mentioned conventional liquid crystal display device, each of the substrates of the liquid crystal cell is moved twice before the light incident from the front side is again emitted to the front side. Since the light passes through the polarizers on both sides four times in total, and two times on each of the front and back polarizers, a large amount of light is lost due to light absorption by the substrate of the liquid crystal cell and the polarizer, which further darkens the display.

Furthermore, in the above-mentioned conventional liquid crystal display device, the display color is determined by the color of the color filter, so that a plurality of colors cannot be displayed by one pixel.

According to the present invention, as a reflection type active matrix type color liquid crystal display device, high brightness colored light is obtained by coloring light without using a color filter, and light is absorbed by a liquid crystal cell substrate and a polarizing plate. A bright color display can be obtained with less loss of light amount,
It is an object of the present invention to provide a device capable of displaying a plurality of colors with one pixel.

[0014]

In the active matrix type color liquid crystal display device of the present invention, a liquid crystal is sandwiched between a back side substrate and a transparent front side substrate, and a plurality of pixel electrodes are provided on the inner surface of one of the substrates. And an active matrix type liquid crystal cell in which a plurality of active elements respectively corresponding to these pixel electrodes are provided, and a counter electrode is provided on the inner surface of the other substrate, and a transmission axis is formed on the surface side of the liquid crystal cell. and with respect to the alignment direction of liquid crystal molecules at the surface side substrate of the liquid crystal cell
Skewed at an angle, the polarization effect on the incident light and the front
The light whose polarization state is changed by the birefringence effect of the liquid crystal
A polarizing plate that emits light that is colored by an analyzing action to be performed , and, of the pixel electrode and the counter electrode of the liquid crystal cell, an electrode provided on the front substrate is formed of a transparent conductive film, together with the electrode provided on the back side substrate is formed of a metal layer for reflecting light, a surface of the electrode made of the metal film is intended to this and wherein forming the scattering reflective surface.

In the liquid crystal display device of the present invention, in order to make the surface of the electrode made of the metal film a scattering reflection surface, for example, the surface of the electrode may be made a fine uneven surface. Alternatively, the metal film may be formed by forming the metal film on a base surface having minute irregularities.

In the liquid crystal display device according to the present invention, for example, when the liquid crystal cell has a pixel electrode and an active element provided on a back substrate and a counter electrode provided on a front substrate, Was formed of a transparent conductive film, the pixel electrode was formed of a reflective film, and the pixel electrode was formed on the protective insulating film by covering the active element on a protective insulating film covering the active element. It is desirable to connect to the active element at a contact hole.

Further, in the liquid crystal display device of the present invention, a retardation plate may be disposed between the liquid crystal cell and the polarizing plate. In this case, the retardation plate is provided with a slow axis. The polarizing plate is disposed so as to be obliquely shifted with respect to the transmission axis of the polarizing plate.

[0018]

In the active matrix type color liquid crystal display device of the present invention, the incident light from the front side enters the liquid crystal cell through the polarizing plate, and the light passing through the liquid crystal layer is applied to the back side substrate of the liquid crystal cell. The light is reflected by the electrode made of the reflective film on the inner surface, passes through the liquid crystal layer again, is incident on the polarizing plate, and the light transmitted through the polarizing plate is emitted to the surface side of the liquid crystal display device.

In this liquid crystal display device, the light incident through the polarizing plate can be changed in the polarization state by the birefringence effect while passing through the liquid crystal layer of the liquid crystal cell, and the back side of the liquid crystal cell can be changed. The light is reflected by the inner surface of the substrate, changes its polarization state in the process of passing through the liquid crystal layer again, is incident on the polarizing plate, and the polarized component light transmitted through the polarizing plate is emitted as colored light.

That is, this liquid crystal display device uses the birefringence effect of the liquid crystal layer of the liquid crystal cell and the polarization and analysis of the polarizing plate without using a color filter to color light. In the liquid crystal display device, since the amount of colored light transmitted through the polarizing plate and emitted is almost the same as the amount of light in the wavelength band serving as the colored light of the linearly polarized light incident through the polarizing plate, A bright colored light is obtained.

Although this liquid crystal display device is of a reflection type, light is reflected by an electrode provided on the inner surface of the back side substrate of the liquid crystal cell. Since light passes through only the front substrate and only one polarizing plate, light loss due to light absorption by the liquid crystal cell substrate and the polarizing plate is small.

Therefore, according to this liquid crystal display device,
A bright color display can be obtained while being a reflection type. Further, in this liquid crystal display device, the alignment state of the liquid crystal molecules changes according to the magnitude of the voltage applied to the liquid crystal layer of the liquid crystal cell, and the birefringence of the liquid crystal layer changes accordingly. By controlling the voltage applied to the pixel, the color of the colored light can be changed, so that one pixel can display a plurality of colors.

Moreover, in this liquid crystal display device, since the surface of the electrode also serving as the reflection film is a scattering reflection surface, an external image such as a display observer's face and its background is reflected on the reflection surface and the image is displayed on the display image. There is no occurrence of so-called reflection of an external image.

Further, in this liquid crystal display device, since the electrode provided on the inner surface of the back side substrate of the liquid crystal cell also serves as a light reflection film, it is not necessary to provide a separate reflection film.
In addition, if the electrode is formed by forming a metal film on a base surface having minute irregularities, it is easy to form an electrode having a scattering reflection surface having minute irregularities, thereby manufacturing a liquid crystal cell. Since the cost can be reduced, the price of the liquid crystal display device can be reduced.

Further, in the liquid crystal display device according to the present invention, the liquid crystal cell is provided with a pixel electrode and an active element on a rear substrate and a counter electrode on a front substrate.
When the counter electrode is formed of a transparent conductive film and the pixel electrode is formed of a metal film that reflects light, the pixel electrode is formed by covering the active element on a protective insulating film that covers the active element. If provided, the area of the pixel electrode can be increased and the aperture ratio can be increased.

In the liquid crystal display device of the present invention, if a retardation plate is disposed between the liquid crystal cell and the polarizing plate, light incident through the polarizing plate passes through the liquid crystal layer of the liquid crystal cell. In the process of entering the polarizing plate again, since the polarization state can be changed also by the birefringence effect of the phase difference plate, when a voltage is applied to the liquid crystal cell so that the liquid crystal molecules rise and become almost perpendicular to the substrate surface, That is, even when the birefringence effect of the liquid crystal layer is almost eliminated, the light whose polarization state has been changed by the birefringence effect of the retardation plate can be made incident on the polarizing plate to obtain colored light.

[0027]

FIG. 1 is a sectional view of a part of an active matrix type color liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device of this embodiment includes an active matrix type liquid crystal cell 10, one polarizing plate 30, and one retardation plate 40. And the retardation plate 40 is connected to the liquid crystal cell 1.
0 and the polarizing plate 30.

First, the liquid crystal cell 10 will be described. This liquid crystal cell 10 is a thin film transistor (hereinafter referred to as T
FT) is used as an active element, and in this embodiment, a liquid crystal 27 in which molecules are twisted between the substrates 11 and 12 is used.

Of the pair of substrates 11 and 12 facing each other across the liquid crystal layer of the liquid crystal cell 10, the substrate on the back side (FIG. 1)
The lower substrate 11 is an insulating substrate made of a glass plate or the like (however, it is not necessary to be transparent), and a plurality of pixels are provided on the inner surface of the rear substrate 11, that is, the surface facing the liquid crystal layer. The electrodes 13 and a plurality of TFTs 14 corresponding to each of the pixel electrodes 13 are arranged in a matrix in a row direction and a column direction, and a transparent alignment film 24 is provided thereon.

The TFT 14 includes a gate electrode 15 formed on the substrate 11, a gate insulating film 16 formed on almost the entire surface of the substrate 11 so as to cover the gate electrode 15, and a gate insulating film 16 formed on the gate insulating film 16. An i-type semiconductor film 17 made of a-Si (amorphous silicon) or the like formed to face the gate electrode 15 and an n-type semiconductor made of a-Si or the like doped with impurities on both sides of the i-type semiconductor film 17. The TFT 14 includes a source electrode 19 s and a drain electrode 19 d formed through the film 18.
Protective insulating film 2 provided over substantially the entire surface of substrate 11
Covered with 1.

Reference numeral 20 denotes a blocking insulating film formed on the channel region of the i-type semiconductor film 17. The blocking insulating film 20 protects the i-type semiconductor film 17 when patterning the n-type semiconductor film 18. It is provided for the purpose.

Although not shown, the back side substrate 11
Above, 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. .

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

The pixel electrodes 13 are provided on the protective insulating film 21 so as to cover the TFTs 14. Each pixel electrode 13 corresponds to a corresponding one of the contact holes 21a formed in the protective insulating film 21. TFT1
4 is connected to the source electrode 19s.

The pixel electrode 13 is made of a metal film which reflects light, for example, a metal film having a high reflectance such as an Al-based alloy, and the surface thereof is a scattering reflection surface A having minute unevenness. .

FIG. 2 is a plan view of a part of the pixel electrode 13. The pixel electrode 13 is formed on the protective insulating film 21 and the gate insulating film 16 thereunder by the TFT 14 part of the part where the pixel electrode 13 is provided. A large number of small holes (substantially square holes in FIG. 2) 22 are provided at small intervals over substantially the entire region except for the above (formed by photolithography) to form a base surface having minute irregularities. A metal film such as an Al-based alloy is formed on the base surface by a sputtering apparatus, and the metal film is patterned by a photolithography method.

That is, the pixel electrode 13 is formed of a metal film in which a portion (portion formed on the substrate 11) corresponding to the small hole 22 provided in the protective insulating film 21 and the gate insulating film 16 is recessed. The uneven surface of the surface is a scattering reflection surface A.

The small holes 22 are formed in the protective insulating film 2.
1 is not provided on the portion of the TFT 14, but the film surface of the protective insulating film 21 on the TFT 14 is different from the step on the surface of the TFT 14 (the portion of the source and drain electrodes 19 s and 19 d on the blocking insulating film 20 and other portions). Between the surface of the electrodes 19s and 19d and the surface of the blocking insulating film 20, etc.). The surface is also a scattering reflection surface A having minute irregularities.

Further, a capacitor electrode 23 is provided on the back side substrate 11 so as to oppose each pixel electrode 13 with the gate insulating film 16 and the protective insulating film 21 interposed therebetween. And pixel electrode 1
3 and the insulating films 16 and 21 therebetween constitute a compensation capacitance (storage capacitor) Cs for compensating the holding voltage of the pixel during the non-selection period. Although not shown, a capacitor line formed integrally with the capacitor electrode 23 is wired on the back-side substrate 11, and each capacitor electrode 23 is connected to a reference potential via the capacitor line. You.

On the other hand, the front side substrate (upper substrate in FIG. 1) 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 or the like.
On the inner surface of the front-side substrate 12, that is, the surface facing the liquid crystal layer, a single-film transparent opposing electrode 25 facing all of the pixel electrodes 13 disposed on the back-side substrate 11 is provided. A transparent alignment film 26 is provided thereon.

Although not shown, the back side substrate 11 and the front side substrate 12 are joined at their outer peripheral edges via a frame-shaped sealing material.
The area between the first and second sealing materials is filled with the sealing material.

The liquid crystal 27 is a nematic liquid crystal having a positive dielectric anisotropy.
The alignment directions on the substrates 11 and 12 are regulated by the alignment films 24 and 26 provided on the substrates 1 and 12, respectively.
It is twist-oriented between 1 and 12. Each of the alignment films 24 and 26 is a horizontal alignment film made of polyimide or the like, and its film surface is subjected to an alignment process by rubbing.

The retardation plate 40 is made of a uniaxially stretched film such as polycarbonate. The retardation plate 40 is formed by the polarizing plate 30 disposed on the surface of the liquid crystal cell 10 and the liquid crystal cell 10. The polarizing plate 30 is disposed such that the slow axis (stretching axis) of the retardation plate 40 and the transmission axis of the polarizing plate 30 are obliquely shifted 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), and the polarizing plate 30 is adhered to the surface of the retardation plate 40.

In the liquid crystal display device of this embodiment,
The alignment direction of liquid crystal molecules on both substrates 11 and 12 of the liquid crystal cell 10 (rubbing direction of alignment films 24 and 26);
The direction of the transmission axis of the polarizing plate 30 and the direction of the slow axis of the phase difference 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 set to an azimuth of 0 °.
And the liquid crystal molecule alignment direction on the front substrate 12 of the liquid crystal cell 10 and the polarizing plate 30 based on this direction.
And the slow axis direction of the phase difference plate 40 are set.

That is, FIG. 3 is a plan view showing a liquid crystal molecule alignment direction of the liquid crystal cell 10, a slow axis of the retardation plate 40, and a transmission axis of the polarizing plate 30 in the liquid crystal display device.
In the figure, reference numeral 11a denotes an alignment direction of liquid crystal molecules on the rear substrate 11 of the liquid crystal cell 10, and 12a denotes an alignment direction of liquid crystal molecules on the front substrate 12 of the liquid crystal cell 10.

As shown in FIG. 3, the liquid crystal molecule orientation direction 12a on the front substrate 12 of the liquid crystal cell 10 is different from the liquid crystal molecule orientation direction 11a on the rear substrate 11, that is, the azimuth angle is 0 °. Almost 9 counterclockwise as seen from the side
The liquid crystal molecules are twisted at a twist angle of about 90 ° between the substrates 11 and 12 by 0 °.

In FIG. 3, reference numeral 30a denotes the polarizing plate 30.
The transmission axis 30a of the polarizing plate 30 is shown.
Is approximately 45 ° counterclockwise as viewed from the front side with respect to the direction of the azimuth angle of 0 °. That is, the polarizing plate 30
The transmission axis 30a is obliquely shifted by approximately 45 ° with respect to the liquid crystal molecule alignment direction 12a on the front substrate 12 of the liquid crystal cell 10.

Further, in FIG. 3, reference numeral 40a denotes a slow axis of the phase difference plate 40. The slow axis 40a of the phase difference plate 40 is viewed from the front side with respect to the azimuth angle of 0 °. It is almost 140 ° counterclockwise. In other words, the slow axis 40a of the retardation plate 40 is obliquely displaced approximately 95 ° counterclockwise from the transmission axis 30a of the polarizing plate 30 when viewed from the front side.

This liquid crystal display device uses an external light such as natural light or indoor illumination light to display an image. External light incident from the surface of the liquid crystal display passes through the polarizing plate 30 and the phase difference plate 40. Light incident on the liquid crystal cell 10 and passing through the liquid crystal layer is reflected by the pixel electrode 13 serving also as a reflection film provided on the inner surface of the backside substrate 11 of the liquid crystal cell 10, and the liquid crystal layer and the retardation plate 40 are again formed. The light passes through the polarizing plate 30 and passes through the polarizing plate 30 to be emitted to the front surface side of the liquid crystal display device.

That is, in this liquid crystal display device, the pixel electrode 13 provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 is formed of a metal film that reflects light, and is incident on the liquid crystal cell 10 from the front surface side. Light is reflected by the pixel electrode 13 on the inner surface of the backside substrate 11 of the liquid crystal cell 10, and one polarizing plate 30 is provided only on the front surface of the liquid crystal cell 10. It has a polarizing action to make it linearly polarized light and an analyzing action to control the emission of light.

The display operation of the liquid crystal display device will be described. In this liquid crystal display device, the slow axis 40a of the retardation plate 40 is obliquely shifted with respect to the transmission axis 30a of the polarizing plate 30; The linearly polarized light incident through the plate 30 is changed in polarization state by the birefringence effect in the process of passing through the phase difference plate 40 to become elliptically polarized light, and this elliptically polarized light is changed in the process of passing through the liquid crystal layer of the liquid crystal cell 10. While the polarization state can be further changed by the birefringence effect, the light is reflected by the pixel electrode 13 on the inner surface of the backside substrate 11 of the liquid crystal cell 10, and further passes through the liquid crystal layer and the retardation plate 40. The polarization state is changed and the light enters the polarizing plate 30.

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

That is, this liquid crystal display device has a phase difference plate 4
0 and the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 and the polarizing plate 3
The light is colored by utilizing the polarization of 0 and the light analyzing function. According to this liquid crystal display device, a very bright colored light is produced compared to a conventional color liquid crystal display device using a color filter. Obtainable.

That is, the color filter absorbs light having a wavelength other than the wavelength range corresponding to the color to color the light.
Since this color filter also absorbs light in a wavelength range corresponding to the color with a considerably high absorptivity, in a liquid crystal display device in which light is colored by a color filter, a wavelength that becomes a colored light of light incident on the display device is used. Compared with the light amount in the band, the light amount of the colored light passing through the color filter is considerably reduced.

In this regard, since the liquid crystal display device of the above embodiment colors transmitted light without using a color filter, light is not absorbed by the color filter, and the retardation plate 40 and the liquid crystal layer are Since almost no light is absorbed merely by changing the polarization state of the transmitted light, the amount of the colored light that passes through the polarizing plate 30 and exits after the polarization state is changed by these birefringence effects passes through the polarizing plate 30. And the amount of light in the wavelength band that becomes the colored light out of the linearly polarized light incident on the light source is high, so that colored light with high luminance can be obtained.

Further, in a liquid crystal display device in which light is colored by a 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 is between the pixel electrode 13 and the counter electrode 25. It changes as the state of alignment of the liquid crystal molecules changes according to the magnitude of the voltage applied to the liquid crystal molecules.

When a voltage is applied between the electrodes 13 and 25 of the liquid crystal cell 10 so that the liquid crystal molecules rise and orient substantially perpendicular to the surfaces of the substrates 11 and 12, the birefringence effect of the liquid crystal layer is almost apparent. Although it disappears, even at that time, the polarizing plate 3
The light incident through 0 can change the polarization state by the birefringence effect of the retardation plate 40.

Therefore, by controlling the voltage applied to the liquid crystal cell 10 to change the birefringence effect of the liquid crystal layer,
Accordingly, the polarization state of light passing through the phase difference plate 40 and the liquid crystal layer of the liquid crystal cell 10 changes, so that the color of the colored light transmitted through and emitted from the polarizing plate 30 can be changed. A plurality of colors can be displayed by one pixel.

The display driving of this liquid crystal display device is basically performed in the same manner as the display driving of a generally known active matrix liquid crystal display device (one using a TFT as an active element). A reference signal having a waveform synchronized with the synchronization signal is supplied to the electrode 25, and a gate signal is sequentially supplied to each gate line in synchronization with the synchronization signal. This may be performed by supplying a data signal. If the potential of the data signal is controlled in accordance with image data, a data signal of a potential corresponding to the image data is supplied to the pixel electrode via the TFT 14 during a selection period of a pixel in each row. 1
3 and the charge is stored in the compensation capacitor Cs.
A voltage corresponding to the amount of charge stored in the compensation capacitance Cs is applied between the pixel electrode 13 and the counter electrode 25 during the non-selection period.

The display color of the 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 approximately 90 °. The two substrates 11,
Orientation directions 11a and 12a of liquid crystal molecules on
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, respectively, and the value of Δn · d (the product of the refractive index anisotropy Δn of the liquid crystal 27 and the liquid crystal layer thickness d) of the liquid crystal cell 10 is about 1000 nm; 40
When the retardation value of is about 600 nm, 1
One pixel can display red, green, blue, and white colors.

FIG. 4 is a CIE chromaticity diagram showing the color change of the emitted light with respect to the applied voltage of the liquid crystal display device. The liquid crystal display device has a direction of 30 ° with respect to its normal line (the direction may be arbitrary). The figure shows the result of observation of emitted light from the normal direction of the liquid crystal display device when white light is incident on the liquid crystal display device.

As shown in FIG. 4, in the above-described liquid crystal display device, the color of the emitted light changes to P as the voltage applied between the electrodes 13 and 25 of the liquid crystal cell 10 increases.
From point S to point Pe, the color changes as indicated by arrows, and in the middle, the colors of green G, blue B, red R, and white W have high light intensity and good color purity.

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

In the above liquid crystal display device, FIG.
As shown in the figure, while the color of the emitted light is changing from green G to blue B, the color becomes close to white W.
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
Is desirably displayed with a voltage higher than the voltage for obtaining the display color of red R.

As described above, in the above-mentioned liquid crystal display device, the color of the emitted light becomes green G, blue B, red R, and white W in accordance with the applied voltage. , White, and different colors are displayed on a plurality of adjacent pixels, so that a mixed color of a plurality of colors among the red, green, blue, and white can be displayed.

Note that the liquid crystal display device of the above embodiment has red,
The liquid crystal display device displays green, blue, and white colors. The display colors of the liquid crystal display device include the applied voltage and both substrates 1 of the liquid crystal cell 10.
Orientation directions 11a and 12a of liquid crystal molecules on
And the twist angle of the liquid crystal molecules and the transmission axis 3 of the polarizing plate 30
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.

Further, the liquid crystal display device is of a reflection type, but the pixel electrode 13 provided on the inner surface of the backside substrate 11 of the liquid crystal cell 10 is used as an electrode also serving as a reflection film, and the liquid crystal cell 1
0, the light is reflected by the pixel electrode 13 on the inner surface of the back side substrate 11 of the liquid crystal cell 10.
Of the two substrates 11 and 12, light passes through the front substrate 1
2 and only one polarizing plate 30,
Light amount loss due to light absorption by the substrate of the liquid crystal cell and the polarizing plate can be reduced.

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. However, since the phase difference plate 40 and the liquid crystal layer hardly absorb light as described above, There is almost no light quantity loss due to these.

As described above, since the above-mentioned liquid crystal display device is for coloring transmitted light without using a color filter, a high-luminance colored light can be obtained, and a liquid crystal cell substrate and a polarizing plate can be used. Since there is little light loss due to light absorption,
Although it is a reflection type, a bright color display can be obtained, and a plurality of colors can be displayed by one pixel.

Further, in the above-mentioned liquid crystal display device, since the surface of the pixel electrode 13 also serving as a reflection film is formed as the scattering reflection surface A, an external image such as the face of the display observer or its background is reflected on the reflection surface. Does not appear on the display image, that is, so-called reflection of an external image.

That is, the liquid crystal display device is for coloring light without using a color filter, and has a high light transmittance. Therefore, if the light reflecting surface is a mirror surface, the display observer's face or An external image such as the background is reflected on the reflection surface and the image overlaps with the display image and is seen. However, if the surface of the pixel electrode 13 serving also as the reflection film is the scattering reflection surface A as described above, No reflection of the external image occurs.

If the scattering effect of the scattering reflection surface A is too large, light is scattered largely and the displayed image becomes unclear, and if the scattering effect is small, an external image is reflected. The size of the unevenness, that is, the width of the concave and convex surfaces and the pitch of the unevenness are set so as to obtain an appropriate scattering effect that can prevent the reflection of an external image without making the displayed image unclear.

In the above liquid crystal display device, the TFT 14 disposed on the inner surface of the back substrate 11 of the liquid crystal cell 10 is provided.
Is covered with a protective insulating film 21, and the pixel electrode 13 also serving as a reflective film
Is provided on the protective insulating film 21 so as to cover the TFT 14, so that the area of the pixel electrode 13 can be increased and the aperture ratio can be increased.

Further, in the above-mentioned liquid crystal display device, the pixel electrode 1 provided on the inner surface of the back side substrate 11 of the liquid crystal cell 10 is provided.
3 is also used as a light reflection film, it is not necessary to provide a separate reflection film, and if the pixel electrode 13 is formed by forming a metal film on a base surface having minute irregularities. ,
Pixel electrode 13 whose surface is a scattering reflection surface having minute irregularities
Can be easily formed and the manufacturing cost of the liquid crystal cell 10 can be reduced, so that the cost of the liquid crystal display device can be reduced.

In the liquid crystal display of the above embodiment, the retardation plate 40 is disposed between the liquid crystal cell 10 and the polarizing plate 30, but the retardation plate 40 may not be provided. If the transmission axis of the polarizing plate 30 is obliquely shifted with respect to the alignment direction of the liquid crystal molecules on the front substrate 12 of the liquid crystal cell 10, light incident through the polarizing plate 30 will The polarization state can be changed by the birefringence effect in the process of passing through, and the reflection state is reflected by the pixel electrode 13 on the inner surface of the backside substrate 11 of the liquid crystal cell 10, and the polarization state can be further changed in the process of passing through the liquid crystal layer again. Since the light is incident on the polarizing plate 30, the light of the polarization component transmitted through the polarizing plate 30 can be emitted as colored light, and the colored light can be emitted by controlling the voltage applied to the liquid crystal cell 10. It is possible to change the color.

However, as in the above embodiment, the liquid crystal cell 1
If the retardation plate 40 is disposed between the first polarizer 30 and the polarizing plate 30, the light incident through the polarizing plate 30 passes through the liquid crystal layer of the liquid crystal cell 10 and is incident on the polarizing plate 30 again. Since the polarization state can also be changed by the birefringence effect of the retardation plate 40, when a voltage is applied to the liquid crystal cell 10 so that the liquid crystal molecules rise and become almost perpendicular to the surfaces of the substrates 11 and 12, that is, the birefringence effect of the liquid crystal layer. Even when apparently disappears, the light whose polarization state has been changed by the birefringence effect of the phase difference plate 40 can be made incident on the polarizing plate 30 to obtain colored light. In this case, two or more retardation plates may be arranged in an overlapping manner.

In the above embodiment, in order to increase the aperture ratio of the liquid crystal display device, the rear substrate 11 of the liquid crystal cell 10
The protective insulating film 21 covering the TFT 14 provided on the substrate 1
1 is formed over substantially the entire surface, and the pixel electrode 13 serving also as a reflection film is provided on the protective insulating film 21 so as to cover the TFT 14. However, when it is not necessary to particularly increase the aperture ratio, the pixel electrode 13 is used. May be provided on the sides avoiding the TFT 14, in which case the protective insulating film 21
May be provided only on the TFT 14, the pixel electrode 13 may be formed on the gate insulating film 16, and this pixel electrode may be connected to the source electrode 19s of the TFT 14 at one side edge thereof.

In this case, the gate insulating film 16
A plurality of small holes 22 are provided as a base surface having minute irregularities, and a metal film is formed thereon to form the pixel electrode 13 having a scattering reflection surface A having minute irregularities. Good.

Further, in the above embodiment, the liquid crystal cell 10 is provided with the pixel electrode 13 and the TFT 14 provided on the back substrate 11, but the liquid crystal cell 10 is provided with the pixel electrode and the TFT on the inner surface of the front substrate. May be provided, and a counter electrode may be provided on the inner surface of the back side substrate, in which case,
The pixel electrode provided on the front substrate may be formed of a transparent conductive film, the counter electrode provided on the rear substrate may be formed of a metal film that reflects light, and the surface of the counter electrode may be a scattering reflection surface.

In this case, the counter electrode is formed, for example, by roughening and etching the inner surface of the back-side substrate to make the substrate surface a base surface having minute irregularities, and forming a metal film thereon. I just need.

In the above embodiment, an active matrix type cell having a TFT 14 as an active element is used as the liquid crystal cell 10, but this liquid crystal cell uses a two-terminal non-linear resistance element such as an MIM or a thin film diode as an active element. The twist angle of liquid crystal molecules is not limited to 90 °, and may be, for example, 180 to
270 °, and the liquid crystal cell 10
Liquid crystal molecules are aligned homogeneously, homeotropically,
The alignment may be performed in an alignment state such as a hybrid alignment.

[0084]

According to the active matrix type color liquid crystal display device of the present invention, high brightness colored light is obtained by coloring light without using a color filter, and light is absorbed by a liquid crystal cell substrate and a polarizing plate. Therefore, a bright color display can be obtained in spite of the reflection type, and a plurality of colors can be displayed by one pixel.

Further, in this liquid crystal display device, since the surface of the electrode also serving as the reflection film is a scattering reflection surface, an external image such as a display observer's face and its background is reflected on the reflection surface and the image is displayed on the display image. There is no occurrence of so-called reflection of an external image.

Further, in this liquid crystal display device, since the electrode provided on the inner surface of the back substrate of the liquid crystal cell also serves as a light reflection film, it is not necessary to provide a separate reflection film.
In addition, if the electrode is formed by forming a metal film on a base surface having minute irregularities, it is easy to form an electrode having a scattering reflection surface having minute irregularities, thereby manufacturing a liquid crystal cell. Since the cost can be reduced, the price of the liquid crystal display device can be reduced.

Further, in the liquid crystal display device according to the present invention, the liquid crystal cell is provided with a pixel electrode and an active element on a rear substrate and a counter electrode on a front substrate.
When the counter electrode is formed of a transparent conductive film and the pixel electrode is formed of a metal film that reflects light, the pixel electrode is formed by covering the active element on a protective insulating film that covers the active element. If provided, the area of the pixel electrode can be increased and the aperture ratio can be increased.

In the liquid crystal display device of the present invention, if a retardation plate is disposed between the liquid crystal cell and the polarizing plate, light incident through the polarizing plate passes through the liquid crystal layer of the liquid crystal cell. In the process of entering the polarizing plate again, since the polarization state can be changed also by the birefringence effect of the phase difference plate, when a voltage is applied to the liquid crystal cell so that the liquid crystal molecules rise and become almost perpendicular to the substrate surface, That is, even when the birefringence effect of the liquid crystal layer is almost eliminated, the light whose polarization state has been changed by the birefringence effect of the retardation plate can be made incident on the polarizing plate to obtain colored light.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a part of an active matrix type color liquid crystal display device showing one embodiment of the present invention.

FIG. 2 is a plan view of a part of a pixel electrode also serving as a reflection film.

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 shows CIE showing color change of emitted light with respect to applied voltage.
Chromaticity diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal cell 11 ... Back side substrate 12 ... Front side substrate 13 ... Pixel electrode (reflection film) A ... Scattering / reflection surface 14 ... TFT (active element) 21 ... Protective insulating film 21a ... Contact hole 24 ... Alignment film 25 ... Opposite Electrode 26 ... Alignment film 27 ... Liquid crystal 30 ... Polarizer 40 ... Phase plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-71081 (JP, A) JP-A-4-243226 (JP, A) JP-A-1-156720 (JP, A) JP-A-6-1994 11711 (JP, A) JP-A-4-97121 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1335 510 G02F 1/1335 520 G02F 1/1343

Claims (5)

(57) [Claims] 1. A reflective active matrix color liquid crystal display device, comprising: a liquid crystal sandwiched between a back substrate and a transparent front substrate; and a plurality of pixel electrodes formed on an inner surface of one of the substrates. An active matrix type liquid crystal cell in which a plurality of active elements respectively corresponding to the pixel electrodes are provided, and a counter electrode is provided on the inner surface of the other substrate, and on the surface side of the liquid crystal cell,
And with respect to the alignment direction of liquid crystal molecules are arranged offset at an angle to the transmission axis of the surface side substrate of the liquid crystal cell, the incident light
Polarization state due to the polarization action on the liquid crystal and the birefringence effect of the liquid crystal
Light colored by the analysis of the light that has been changed
And a polarizing plate that emits light, and of the pixel electrode and the counter electrode of the liquid crystal cell, an electrode provided on the front substrate is formed of a transparent conductive film, and an electrode provided on the back substrate is formed of light. An active matrix type color liquid crystal display device comprising a metal film that reflects light and a surface of an electrode made of the metal film forming a scattering reflection surface. 2. A comprising electrodes of a metal film has minute irregularities
A scattering reflection surface formed by depositing a metal film on the lower ground
2. The active matrix type color liquid crystal display device according to claim 1, comprising: 3. An electrode made of a metal film has a number of small holes in a booth.
Formed by depositing a metal film on the underlying surface
2. The active matrix type color liquid crystal display device according to claim 1, further comprising a scattering reflection surface . 4. A liquid crystal cell wherein a pixel electrode and an active element are provided on a back side substrate, and a counter electrode is provided on a front side substrate. The counter electrode is formed of a transparent electrode, and the pixel electrode is formed of a light emitting element. And the pixel electrode is provided on the protective insulating film covering the active element so as to cover the active element, and the pixel electrode is formed in a contact hole formed in the protective insulating film. 4. The active matrix type color liquid crystal display device according to claim 1, wherein the active matrix type color liquid crystal display device is connected to an element. 5. A retardation plate is provided between a liquid crystal cell and a polarizing plate, and a slow axis of the retardation plate is obliquely shifted with respect to a transmission axis of the polarizing plate. Claim 1
4. An active matrix type color liquid crystal display device according to item 1.