JPH1138410A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep excellent display quality under various environments from a bright place to a dark place and to reduce power consumption. SOLUTION: A backlight unit 11 provided with a diffusion plate 5, a light guide plate 4, a white reflection plate 3 and an edge light system cold cathode tube 1 is arranged on a back surface side of a guest host liquid crystal display panel 10. It is used as a transmission type liquid crystal display device by turning the edge light system cold cathode tube 1 on in the dark place. It is used as a reflection type liquid crystal display device by reflecting peripheral light with the white reflection plate 3 without turning the edge light system cold cathode tube 1 on in the bright place.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable information terminal device, a video camera with an LCD monitor, and a portable O such as a notebook personal computer.
The present invention relates to a liquid crystal display device which is suitably used for an A (Office Automation) device or the like and can be switched between a transmissive type and a reflective type according to the surrounding environment.

[0002]

2. Description of the Related Art The above-mentioned liquid crystal display device has a liquid crystal display panel in which liquid crystal is sandwiched between a pair of substrates. Since this liquid crystal display panel is a non-light emitting type and does not emit light by itself, some kind of lighting means is required for use as a display device. According to this illumination means, the conventional liquid crystal display device is divided into the following three types: a transmissive type, a reflective type and a transflective type.

In a transmissive liquid crystal display device, an illuminating device called a backlight is arranged on the back side (far away from an observer) of the liquid crystal display panel, and the backlight irradiates the liquid crystal display panel with light. . This transmissive liquid crystal display device has an advantage that it can be used even in a dark place and the brightness of the display screen can be adjusted by the strength of the lighting device. On the other hand, since the power consumption of the backlight increases, it is difficult to reduce the power consumption of the liquid crystal display device.

In a reflection type liquid crystal display device,
A reflector is disposed on the back side of the liquid crystal display panel, and ambient light such as sunlight or indoor lighting applied to the liquid crystal display is reflected by the reflector. This reflective liquid crystal display device
Since ambient light can be used as the lighting means, a liquid crystal display device with low power consumption can be realized and can be used outdoors. However, the brightness of the illuminating means is greatly affected by the environment in which the liquid crystal display device is used, so that the display screen is dark and difficult to see in a dark place.

[0005] In a transflective liquid crystal display device, a transflective plate such as a magic mirror is disposed between the liquid crystal display panel and a lighting device on the rear side thereof.

FIG. 9 is a sectional view of a conventional transflective liquid crystal display device. This liquid crystal display device has an active matrix substrate 3 on which TFTs (thin film transistors) and the like are formed in a matrix as switching non-linear elements.
A liquid crystal display panel 310 in which a twisted nematic liquid crystal 303 is sandwiched between a liquid crystal display panel 310 and a counter substrate 302, and polarizing plates 304, 304 are provided on both sides thereof. A transflective plate 305 is provided on the back side (lower side in the figure) of the liquid crystal display panel 310, and further a prism sheet 306 / diffusion plate 307 / light guide plate 308 for backlight.
/ White reflector 309 is provided. On the side surface (left side in the figure) of the light guide plate 308, an edge-light type cold cathode tube 311 installed on the holder 312 is arranged. This transflective liquid crystal display device does not turn on the edge-light type cold cathode fluorescent lamp 311 in a bright environment, and the transflective plate 30
5 is used as a reflection type by reflecting ambient light. In a dark environment, the edge-light type cold cathode fluorescent lamp 31 may be used.
1 is turned on, and the light is transmitted through a semi-transmissive reflection plate to be used as a transmission type.

[0007]

Among the above-mentioned conventional liquid crystal display devices, the transmissive type can be used even in a dark place and can adjust the brightness of the display screen, but has the problem of increasing power consumption. is there.

[0008] The reflection type can be used outdoors,
Although the power consumption of the lighting means can be reduced, there is a problem that it cannot be used in a dark place.

Furthermore, the transflective type has a problem that its characteristics are greatly affected by the transmittance and the reflectance of the material used for the transflective plate. In general, in a semi-transmissive reflection plate, if a loss such as light scattering is subtracted,
The relationship between the transmittance and the reflectance is almost a trade-off relationship. Therefore, when a transflective plate having a high transmittance and a low reflectance is used, a transmissive liquid crystal display device that requires an illumination device is mainly used, and power consumption is increased. In addition, when a transflective plate having a low transmittance and a high reflectance is used, the liquid crystal display device is mainly of a reflection type that can be used in a bright environment, and the display is difficult to see in a dark place.

The present invention has been made to solve the problems of the prior art, and can maintain good display quality under various environments from a bright place to a dark place, and has low power consumption. It is an object of the present invention to provide a liquid crystal display device capable of achieving a high degree of performance.

[0011]

The liquid crystal display device of the present invention has a backlight unit on the back side of a liquid crystal display panel in which liquid crystal is sandwiched between a pair of substrates, and the backlight unit is a diffusion plate. A light guide plate and a reflection plate in this order from the liquid crystal display panel side, and a light source.The light from the light source of the backlight unit is guided by the light guide plate, and the light is diffused by the diffusion plate. It is used as a transmission type by being incident on the liquid crystal display panel from the back side, and light incident from the front side of the liquid crystal display panel is reflected by the reflector of the backlight unit and returned to the liquid crystal display panel side. It is configured to be used also as a reflection type, thereby achieving the above object.

[0012] The liquid crystal may be a guest-host liquid crystal in which a dichroic dye is mixed in a homogeneously aligned nematic liquid crystal, a guest-host liquid crystal in which a dichroic dye is mixed in a cholesteric liquid crystal, or a twisted nematic liquid crystal.
It may be made of a guest-host liquid crystal mixed with a coloring dye.

A plurality of scanning wirings and a plurality of signal wirings are provided on one of the pair of substrates so as to intersect with each other, and a switching wiring provided near an intersection of each scanning wiring and each of the signal wirings is provided. And a pixel electrode connected to the nonlinear element.

The operation of the present invention will be described below.

In the present invention, the light from the light source of the backlight unit is guided by the light guide plate, diffused by the diffusion plate, and incident on the liquid crystal display panel from the back side, so that it can be used as a transmission type. It is possible. Further, the light incident from the front side of the liquid crystal display panel is reflected by the reflector of the backlight unit and returned to the liquid crystal display panel side, so that it can be used as a reflection type. Therefore, when the surroundings are sufficiently bright, the light source of the backlight unit is not turned on and the reflection type liquid crystal display device is used. When the surroundings are dark, the light source of the backlight unit is turned on and the transmission type liquid crystal display device is used. Can switch.

The liquid crystal may be a guest-host liquid crystal in which a dichroic dye is mixed in a homogeneously aligned nematic liquid crystal, a guest-host liquid crystal in which a dichroic dye is mixed in a cholesteric liquid crystal, or a twisted nematic liquid crystal.
Guest host liquid crystal or the like mixed with a coloring dye can be used. In particular, when a twisted nematic liquid crystal mixed with a dichroic dye is used, a polarizing plate is not required, so that a brighter display can be obtained and a gradation display can be performed.

On one substrate constituting the liquid crystal display panel,
An active matrix type configuration in which a plurality of scanning wirings and a plurality of signal wirings intersecting with each other are provided, and a switching non-linear element such as a TFT is provided near an intersection of the two wirings, and the non-linear element is connected to a pixel electrode. This makes it possible to actively drive the guest-host liquid crystal by using a TFT or the like, and it becomes possible to perform multicolor display by combining with a color filter.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a schematic structure of the liquid crystal display device of the present embodiment.

This liquid crystal display device has a liquid crystal display panel 6 in which a guest-host liquid crystal 10 is sandwiched between an active matrix substrate 7 on which TFTs and the like are formed in a matrix as switching nonlinear elements and a counter substrate 8. . On the back side (lower side in the figure) of the liquid crystal display panel 6, a backlight unit 11 having a diffusion plate 5, a light guide plate 4, a white reflector 3, and an edge light type cold cathode tube 1 is provided. The edge light type cold cathode tube 1 as a light source is disposed on the side surface (left side in the figure) of the light guide plate 4, and the diffusion plate 5, the light guide plate 4, the white reflector 3 and the edge light type cold cathode tube 1 are attached to the holder 2. is set up.

FIG. 2 is a sectional view showing the structure of the liquid crystal display panel 6.

The liquid crystal display panel 6 is provided with alignment films 9a and 9b on an active matrix substrate 7 and a counter substrate 8 on which TFTs and the like are provided in a matrix, and is subjected to a rubbing treatment. Are disposed opposite each other via a silica spacer. The rubbing direction at this time is set so that the liquid crystal molecules are twisted by about 45 ° or about 240 ° between the upper and lower substrates. In this embodiment, the rubbing direction is 240 °. A guest-host liquid crystal 10 in which a dichroic dye is mixed in a twisted nematic liquid crystal is sandwiched between the two substrates. In the present embodiment, a nematic liquid crystal having a positive dielectric anisotropy and a refractive index anisotropy of 0.1 is mixed with an azo-based and anthraquinone-based black dichroic dye by several wt%,
The ratio d / p between the cell thickness d and the helical pitch p of the liquid crystal is 0.5
It was adjusted to be 5. In the guest-host liquid crystal 10, as shown in FIG. 2, the two-color dye is oriented along the twist of the liquid crystal molecules, and thus becomes transparent when no voltage is applied.

FIG. 3 is a plan view of the active matrix substrate 7, and FIG. 4 is a sectional view taken along line AA 'of FIG.

As shown in FIG. 3, the active matrix substrate 7 is made of Ta, Mo, Al, C
A scanning wiring (gate wiring) 102 made of a single layer or a multilayer of a metal such as r is provided. This gate wiring 102
So as to intersect with ITO (Indium Tin O
xide) layer 108a and metal layer 1 such as Ti or Ta
10 are provided. Near the intersection of each gate line and each source line,
A TFT and a pixel electrode 108 are provided.

As shown in FIG. 4, the TFT has a gate electrode 102a branched from a gate wiring 102 provided on a glass substrate 101, and a first gate insulating layer formed by anodizing the gate electrode 102a so as to cover the surface thereof. A film 103 is provided, on which a second gate insulating film 104 made of silicon nitride (SiN _x ) is provided. Second
Of the intrinsic amorphous silicon (a-Si) so as to partially overlap the gate electrode 102a on the gate insulating film 104 of FIG.
The semiconductor layer 105 composed of (i)) is formed, the etching stopper layer 106 made of SiN _X on the center of the semiconductor layer 105 is provided. Note that the formation of the etching stopper layer 106 can be omitted. Etching stopper layer 106 on semiconductor layer 105
Is divided into two on the etching stopper layer 106 with n ⁺ -type amorphous silicon (a-Si
Contact layers 107a and 107b made of (n ⁺ )) are provided. On the contact layer 107a, the above-described I
A source wiring composed of a TO layer 108a and a metal layer 110 is provided, and the ITO layer 10a is formed on the contact layer 107b.
8b and a drain wiring composed of the metal layer 109 are provided. The ITO layer 108b of the drain wiring is connected to the ITO layer of the pixel electrode 108. On top of that, TF
T, the drain wiring, a protective film 111 made of SiN _X covering the opening of the source wiring and the pixel is provided.

FIG. 5 is a plan view showing a color filter pattern of the counter substrate 8, and FIG. 6 is a sectional view taken along line BB 'of FIG.

As shown in FIG. 5, the opposite substrate 8 is provided with a black matrix layer 202 made of a metal such as Cr on a glass substrate 203. An opening (pixel portion) 201 is formed in a pattern on the black matrix 202 by a photolithography method. A color filter layer 204 of each color of red, green, and blue obtained by dyeing an organic film made of gelatin or the like is provided thereon. Each color filter 204 is separated from each other on the black matrix 202 as shown in FIG. An overcoat layer (protective film) made of acrylic or urethane resin that covers it
205 is provided. Note that the formation of the overcoat layer 205 can be omitted. A transparent electrode film (counter electrode) 206 for driving the liquid crystal is provided thereon.

As shown in FIG. 2, the active matrix substrate 7 and the counter substrate 8 are provided with alignment films 9a and 9b, and the pixel electrodes 108 and the black matrix 202 are provided.
Color filter layer 20 provided in opening 201 of
4 are opposed to each other. In order to hold the guest-host liquid crystal 10 between the two substrates,
In-cell spacers of about μm are scattered, and the spacers are also scattered in a sealing material used for bonding both substrates. A guest host liquid crystal 10 is injected and sealed between the two substrates, and a driver (not shown) necessary for driving the TFT is provided around the liquid crystal display panel 6.

In the liquid crystal display device according to the present embodiment thus configured, in a dark environment, as shown in FIG.
The edge light type cold cathode tube 1, which is the light source of the backlight unit, is turned on, and the light from there is guided by the light guide plate 4 and diffused by the diffusion plate 5 so as not to be evenly distributed on the entire screen. The light enters from the back of the panel 6. At this time, light from the edge light type cold cathode tube 1 toward the white reflector 3 is reflected by the white reflector 3 and is incident on the liquid crystal display panel 6 side via the light guide plate 4 and the diffusion plate 5. Thereby, a display as a transmissive liquid crystal display device is obtained. In a bright environment where ambient light can be used, such as outdoors, the ambient light transmitted through the liquid crystal display panel 6 is reflected by the white reflector 3 without turning on the edge-lit cold-cathode tube 1 which is the light source of the backlight unit. The light is reflected, uniformly scattered by the light guide plate 4 and the diffusion plate 5 over the entire screen, and is incident on the liquid crystal display panel 6. Thereby, a display as a reflective liquid crystal display device is obtained. According to this liquid crystal display device, since a transflective reflector or a polarizing plate as in a conventional transflective liquid crystal display device is not required, a brighter display can be obtained.

In the present embodiment, a guest-host liquid crystal in which a dichroic dye is mixed into a twisted nematic liquid crystal is used. However, a nematic liquid crystal in which a twist angle of liquid crystal molecules is about 0 ° between upper and lower substrates is homogeneously aligned. 2 on the liquid crystal
Heilmeier-type guest-host liquid crystal mixed with a chromatic dye, or 2 between a pair of substrates subjected to a vertical alignment process.
The present invention is also applicable to a liquid crystal display device using a white tailor type guest-host liquid crystal or the like utilizing a nematic-cholesteric phase transition by injecting a cholesteric liquid crystal mixed with a coloring dye. However, when a guest-host liquid crystal in which a dichroic dye is mixed into a twisted nematic liquid crystal is used as in the present embodiment, a polarizing plate is not required unlike the case where a Heilmeier-type guest-host liquid crystal is used. The display is obtained. Further, when a guest-host liquid crystal in which a dichroic dye is mixed into a twisted nematic liquid crystal is used, there is no hysteresis in the voltage-transmittance characteristic as in the case of using a white tailor type, so that gradation display is also possible.

[0031]

As is apparent from the above description, according to the present invention, it can be used as a transmission type or a reflection type according to the environment, and a good display can be obtained even in a bright environment or a dark environment. Can be. In addition, since it is possible to use a reflection type using ambient light without using a lighting device according to the environment, power consumption can be reduced. Further, a good display can be obtained without being affected by the characteristics of the transflective plate unlike the conventional transflective liquid crystal display device.

In the present invention, the use of a guest-host liquid crystal in which a dichroic dye is mixed in a twisted nematic liquid crystal eliminates the need for a polarizing plate, so that a bright display can be obtained, and a liquid crystal display capable of gradation display. It can be a device.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of a liquid crystal display panel in the liquid crystal display device of the embodiment.

FIG. 3 is a plan view of an active matrix substrate in the liquid crystal display device of the embodiment.

FIG. 4 is a sectional view taken along line A-A ′ of FIG. 3;

FIG. 5 is a plan view showing a color filter pattern of a counter substrate in the liquid crystal display device of the embodiment.

6 is a sectional view taken along line B-B 'of FIG.

FIG. 7 is a cross-sectional view for describing a case where the liquid crystal display device of the embodiment is used as a transmission type.

FIG. 8 is a cross-sectional view for describing a case where the liquid crystal display device of the embodiment is used as a reflection type.

FIG. 9 is a cross-sectional view showing a schematic structure of a conventional transflective liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Edge light type cold cathode tube 2 Holder 3 White reflector 4 Light guide plate 5 Diffusion plate 6 Liquid crystal display panel 7 Active matrix substrate 8 Opposite substrate 9a, 9b alignment film 10 Guest host liquid crystal 101 Glass substrate 102 Gate wiring 102a Gate electrode 103 First gate insulating film 104 Second gate insulating film 105 a-Si (i) semiconductor layer 106 Etching stopper layer 107 a, 107 b Contact layer 108 a, 108 b ITO layer 108 Pixel electrode 109, 110 Metal layer 111 Protective film 201 Black matrix Opening 202 Black matrix layer 203 Glass substrate 204 Color filter layer 205 Overcoat layer 206 Transparent electrode film

Claims (3)

[Claims] 1. A backlight unit is provided on the back side of a liquid crystal display panel in which liquid crystal is sandwiched between a pair of substrates. The backlight unit includes a diffusion plate, a light guide plate, and a reflection plate on the liquid crystal display panel side. And a light source. The light from the light source of the backlight unit is guided by the light guide plate and diffused by the diffusion plate to be incident on the liquid crystal display panel from the back side. Is used as a transmission type, and light incident from the front side of the liquid crystal display panel is reflected by a reflector of the backlight unit and returned to the liquid crystal display panel side to be used as a reflection type. Liquid crystal display device. 2. The liquid crystal according to claim 1, wherein the liquid crystal is a guest-host liquid crystal in which a dichroic dye is mixed in a homogeneously aligned nematic liquid crystal, a guest-host liquid crystal in which a dichroic dye is mixed in a cholesteric liquid crystal, or a twisted nematic liquid crystal.
2. A guest-host liquid crystal mixed with a coloring dye.
3. The liquid crystal display device according to 1. 3. One of the pair of substrates includes:
A plurality of scanning wirings and a plurality of signal wirings provided so as to intersect with each other; a switching nonlinear element provided near an intersection of each scanning wiring and each signal wiring; and a pixel electrode connected to the nonlinear element. 3. The method according to claim 1, wherein
3. The liquid crystal display device according to 1.