JPH0943586A - Liquid crystal display element - Google Patents

Abstract

(57) Abstract: A liquid crystal display element having a large aperture ratio and a bright display is provided. SOLUTION: TF of liquid crystal display element of white tailor type
A TFT 21, a white underlayer 22 formed on the TFT 21, a phosphor layer 23 formed on the white underlayer 22, and a TFT on the phosphor layer 23 in each pixel region of the T substrate 11.
21 and a pixel electrode 24 connected to the end of each pixel region and formed on the entire surface of each pixel region. Since the pixel electrode 24 is formed on the entire surface of each pixel region on the TFT 21, the area contributing to display is wide. Therefore, the display becomes bright.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a large aperture ratio,
The present invention relates to a liquid crystal display device having a bright display.

[0002]

2. Description of the Related Art In a TN type liquid crystal display device, incident light from the outside is linearly polarized by one polarizing plate and is incident on a liquid crystal layer, and out of light passing through the liquid crystal layer, the other polarizing plate transmits the light. Only the polarization component parallel to the axis is emitted. Therefore, there is a problem that a large amount of light is lost due to light absorption in the polarizing plate and the display is dark.

This problem is particularly noticeable in a reflection type liquid crystal display element in which a reflection plate is arranged on the back side of the liquid crystal display element. More specifically, the reflective liquid crystal display element is
The display is performed using natural light or indoor illumination light, and the available light itself is weak. Further, the light incident from the front surface side of the liquid crystal display element passes through the pair of polarizing plates twice each before being reflected by the reflection plate and emitted to the front surface side. For this reason,
The light loss is large and the display is extremely dark.

In a transmissive liquid crystal display device in which a backlight is arranged on the back surface side, light that enters from the back surface side and exits to the front surface side passes through a pair of polarizing plates once. Therefore, the loss of light in the polarizing plate is smaller than that in the reflective liquid crystal display element. However, the brightness of the display is less than half the brightness of the illumination light from the backlight.

Further, the conventional color display element displays a color image by using a color filter to color the transmitted light by absorbing the light in the predetermined wavelength range of the transmitted light. However, the color filter absorbs a large amount of light, and particularly in a reflective liquid crystal display element, light passes through the color filter twice, so that the display becomes considerably dark. Therefore, the TN type liquid crystal display device using the color filter has a problem that the display is particularly dark.

As a liquid crystal display element for displaying a bright color image, a birefringence control type liquid crystal display element utilizing the birefringence of liquid crystal is known. The birefringence control type liquid crystal display element deforms the alignment of the liquid crystal molecules by applying an electric field to the liquid crystal, and utilizes the change in the birefringence of the liquid crystal cell at that time to perform color display. However, the birefringence control type liquid crystal display device has a problem that it is difficult to realize full color.

[0007]

In order to solve these problems, a liquid crystal display in which light is colored by using a phosphor layer and incident light is reflected by using a white base layer formed under the phosphor layer. Devices have been proposed. However, in this liquid crystal display element, as shown in a sectional view of FIG. 6, a TFT 21 as an active element that does not contribute to display and a pixel electrode 24 are formed on the same substrate (TFT substrate 11), and a plan view of FIG. As shown, the TFT 21 was formed so as to occupy a partial area of the pixel electrode 24. Therefore, the liquid crystal display device having such a structure has a problem that the aperture ratio is not sufficient and the display image is not sufficiently bright.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal display element having a large aperture ratio and a bright display image.

[0009]

In order to achieve the above object, a liquid crystal display element according to the present invention comprises an active element arranged in each pixel region, a white base layer arranged on the active element, A first substrate formed by stacking a phosphor layer disposed on the white underlayer and a first electrode disposed on the entire surface of each pixel region and connected to the active element; A second substrate which is disposed so as to face the first substrate and has a second electrode which faces the first electrode on a surface which faces the first substrate;
And a liquid crystal to which a dichroic dye is added, the liquid crystal being sealed in a twist alignment state between the second substrate and the second substrate.

According to the liquid crystal display element having the above structure, the first electrode is formed over the entire pixel area on each active element. Therefore, the area that contributes to display is wider than in the conventional example in which the active element and the first electrode are formed on the same substrate. Therefore, the aperture ratio becomes larger than that of the conventional example, and the displayed image becomes brighter.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
A white-tailor type TFT liquid crystal display device will be described as an example with reference to the drawings. 1 shows a sectional structure of a liquid crystal display element according to the present embodiment, FIG. 2 shows a planar structure of a TFT substrate, FIG. 3 shows an enlarged sectional structure of a liquid crystal display element, and FIG. 4 shows a planar structure of a counter substrate. Show.

As shown in FIG. 1, this liquid crystal display device has a pair of transparent substrates 11 and 12 joined by a sealing material SC.
And the liquid crystal 13 sealed between the pair of transparent substrates 11 and 12.
It is composed of The liquid crystal 13 is composed of a nematic liquid crystal to which a chiral agent is added, and contains, for example, about 0.5 to 10% by weight of a black dichroic dye having positive absorption anisotropy.

The transparent substrates 11 and 12 are made of glass, transparent resin or the like. Lower transparent substrate (hereinafter TFT substrate)
As shown in FIG. 1, TFTs (thin film transistors) 21 as active elements are arranged in a matrix 11 at 11. In each pixel region, a white base layer 22 that covers the TFT 21 and phosphor layers 23 (23R, 23G, 23B) are arranged in a matrix. Further, as shown in FIG. 2, a transparent electrode (pixel electrode) 24 connected to a part of the TFT 21 is arranged on each phosphor layer 23. Further, on the TFT substrate 11, the pixel electrodes 2 of each row are
4 and a plurality of compensation capacitance electrodes 26 facing each other.

The TFT 21 is a TFT as shown in FIG.
A gate electrode 211 formed on the substrate 11, a gate insulating film 212 covering the gate electrode 211, and a gate insulating film 2
A- formed on the upper surface 12 to face the gate electrode 211.
It is composed of an intrinsic semiconductor layer 213 made of Si (amorphous silicon) or the like, and a source electrode 215 and a drain electrode 214 formed on both ends of the intrinsic semiconductor layer 213. The intrinsic semiconductor layer 213 and the source electrode 21
5 and the drain electrode 214 to obtain ohmic contact, the intrinsic semiconductor layer 213 and the source electrode 215
And an n-type high concentration layer may be formed between the intrinsic semiconductor layer 213 and the drain electrode 214.

The source electrodes 215 of the TFTs 21 in each column are connected to the corresponding data lines DL, and the TFTs 21 in each row are connected.
The gate electrode 211 of each TFT 21 is connected to the corresponding gate line GL, and the drain electrode 214 of each TFT 21 is the pixel electrode 2
4 is connected.

The compensation capacitance electrode 26, as shown in FIG.
It is formed of a conductor that faces a plurality of pixel regions in the row direction, and is connected to a counter electrode 31 described later via an electrode terminal 27. The compensation capacitance electrode 26 forms a compensation capacitance with the pixel electrode 24 facing each other and the phosphor layer 23 and the white base layer 22 between them.

The white base layer 22 is made of an insulating material such as synthetic resin, and is formed over almost the entire pixel region so as to cover the TFT 21 and the compensation capacitance electrode 26. The phosphor layer 23 includes a plurality of phosphor layers emitting fluorescence of different colors, for example, a phosphor layer 23R emitting red fluorescence, a phosphor layer 23G emitting green fluorescence, and a phosphor layer emitting blue fluorescence. 23B and. The phosphor layers 23R, 23G, and 23B are arranged in a predetermined order on the white base layer 22 so that full-color display is possible.

Each phosphor layer 23 is composed of a transparent resin base material and granular fluorescent materials mixed in the resin base material in a scattered state. Resin base material is acrylic resin, vinyl chloride resin,
It is composed of an alkyd resin, an aromatic sulfonamide resin, a urea resin, a melamine resin, a benzoquaminan resin, and a transparent resin composed of a copolycondensate thereof.

The fluorescent substance is obtained by pulverizing a fluorescent material obtained by dyeing the same resin as the resin base material or another transparent resin with a fluorescent dye into fine particles. The fluorescent substance has a wavelength conversion function of absorbing light other than a specific wavelength region (a wavelength region of fluorescence emitted by the fluorescent substance) and emitting light in the specific wavelength region by the energy of the absorbed light. Therefore, the light emitted from the phosphor layer 23 becomes the light colored with the color of the fluorescence emitted by the fluorescent substance.

Each pixel electrode 24 is formed of a transparent conductive film made of ITO (oxide of indium and tin) or the like, and the TFT 21 is formed at the end of each pixel region through a contact hole formed in the white base layer 22. Connected to the drain electrode 214 of the above, and is arranged on almost the entire surface of each pixel region including on the TFT 21. A signal voltage (writing voltage) is applied to the pixel electrode 24 via the TFT 21.

An alignment film 25 made of polyimide or the like is formed on each pixel electrode 24 so as to entirely cover the pixel electrode 24.

On the other hand, the upper transparent substrate (hereinafter referred to as the counter substrate)
As shown in FIGS. 1 and 4, one transparent electrode (counter electrode) 31 is provided on the entire surface of the region 12 facing the pixel electrode 24.
Are formed. The counter electrode 31 is made of ITO or the like. The counter electrode 31 is connected to the electrode terminal 37, and a predetermined reference voltage (common voltage) is applied.

An alignment film 36 made of polyimide or the like is formed on the counter electrode 31. The alignment film 36 on the upper side in FIG. 1 is subjected to an alignment treatment such as rubbing in the direction shown by the solid line in FIG. 5 (direction of 0 °), and the alignment film 25 on the lower side is processed in the direction indicated by the broken line in FIG. The orientation treatment is applied to the (90 ° direction).

The liquid crystal 13 and the dichroic dye added to the liquid crystal 13 are counterclockwise as shown in FIG. 5 from the counter substrate 12 side toward the TFT substrate 11 side according to the alignment treatment of the alignment films 36 and 25. Oriented by twisting (0 ° to -90 °).

In the liquid crystal display device having such a structure,
When no voltage is applied between the pixel electrode 24 and the counter electrode 31, that is, when no electric field is applied to the liquid crystal 13, the molecules of the liquid crystal 13 and the molecules of the dichroic dye added to the liquid crystal 13 are It is oriented substantially parallel to the substrate and maintains an orientation state in which it is twisted by about 90 ° from one substrate to the other substrate. Therefore, the light incident on the liquid crystal display element is absorbed by the dichroic dye. The light not absorbed by the dichroic dye is reflected by the white underlayer 22 and is again absorbed by the dichroic dye. Therefore, almost no light is emitted to the outside, and the display is in a dark state.

On the other hand, when a sufficiently large electric field is applied to the liquid crystal 13, the liquid crystal 13 and the dichroic dye are aligned substantially perpendicular to the substrate. Therefore, the light incident on the liquid crystal display element passes through the liquid crystal 13 without being absorbed by the dichroic dye. The light that has passed through the liquid crystal 13 is the white underlayer 2.
The light is reflected at 2, passes through the liquid crystal 13 again, and is emitted to the outside. Therefore, the display is in a bright state.

When an intermediate electric field is applied to the liquid crystal 13, the liquid crystal 13 and the dichroic dye are twisted and aligned at a tilt angle according to the magnitude of the electric field. Therefore, the amount of light incident on the liquid crystal display element is equal to the amount of the liquid crystal 13 depending on the tilt angle.
Is reflected by the white base layer 22, and only an amount of the reflected light according to the tilt angle passes through the liquid crystal 13 and is emitted to the outside. Therefore, the display is in a halftone state according to the magnitude of the electric field.

In this way, by controlling the electric field applied to the liquid crystal 13, the display gradation can be controlled.

The incident light is red in the red phosphor layer 23R, green in the green phosphor layer 23G, and blue in the blue phosphor layer 23B.
Are colored blue respectively. Therefore, the display is full color.

The liquid crystal display device having such a structure is composed of the liquid crystal 1
It is a white-tailor type that controls the absorption and transmission of light by the dichroic dye added to 3, and since a polarizing plate is not used, the displayed image is bright.

Further, as shown in FIGS. 2 and 3, the pixel electrode 24 is formed on the entire surface of the pixel region above the TFT 21, the data line DL, and the compensation capacitance electrode 26. Therefore,
The area of the pixel electrode 24 that contributes to display is larger and the aperture ratio is larger than when the TFT 21 and the pixel electrode 24 are formed on the same substrate. Therefore, the display becomes brighter than that of the liquid crystal display element using the phosphor layer of the conventional example.

A white base layer 22 is provided under the phosphor layer 23.
Is formed, the intensity of the reflected light is increased and the display is brightened.

Further, the source electrode 215 and the data line D
L and the like are formed under the pixel electrode 24 and the white base layer 22. Therefore, the light incident on the liquid crystal display element does not reach the source electrode 215 and the wiring portion such as the data line DL.
Therefore, the line width of the wiring such as the source electrode 215 and the data line DL can be increased without taking the aperture ratio into consideration.
The resistance value can be reduced. Similarly, since the size of the compensation capacitance electrode 26 can be set without considering the aperture ratio, the compensation capacitance having an optimum value can be configured.

Since the pixel electrode 24 and the drain electrode 214 are connected to each other at the end of the pixel region, the phosphor layer 23 and the white underlayer 22 can be made into a uniform layer, and the unevenness of the fluorescence intensity can be prevented. You can

Since the pixel electrode 24 is formed on an insulating layer such as the white base layer 22 and the phosphor layer 23, the pixel electrode 24
It is possible to prevent a situation where the drive voltage is stepped down in the insulating layer when is formed under the insulating layer, and the drive voltage can be reduced.

Since the TFT 21 having many irregularities is covered with the white underlayer 22, the alignment film 25 can be made relatively flat. Therefore, poor alignment of the liquid crystal 13 can be prevented.

The present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, in the above-described embodiment, the pixel electrode 24 is formed on the phosphor layer 23, but the pixel electrode 24 made of a transparent conductive film is formed on the entire pixel region on the white base layer 22. You may form the fluorescent substance layer 23 on it.

In the above embodiment, the present invention has been described by taking the liquid crystal display element having the TFT as the active element as an example, but the present invention can be applied to the liquid crystal display element having the MIM as the active element.

The present invention is not limited to the white Taylor type liquid crystal display element in which the liquid crystal 13 is twisted by 90 °, and
The present invention is also applicable to a white tailor type liquid crystal display device having a twist orientation of 0 ° or more.

Further, the pixel electrode 24, the phosphor layer 23, and the white base layer 22 are laminated and arranged on a reflective liquid crystal display device of TN or STN mode using a polarizing plate, not limited to the white-tailor type. Good. In this case, a polarizing plate is arranged outside the counter substrate 12.

[0041]

As described above, according to the present invention, the white underlayer is formed on the active element, and the phosphor layer and the pixel electrodes arranged on the entire surface of each pixel region are formed on the white underlayer. By doing so, a liquid crystal display device having a large aperture ratio and a bright display image can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a white-tailor type TN liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a TFT substrate.

FIG. 3 is an enlarged sectional view showing a configuration of one pixel of a liquid crystal display element.

FIG. 4 is a plan view showing a configuration of electrodes of a counter substrate.

FIG. 5 is a diagram showing an alignment treatment direction and a liquid crystal twist direction.

FIG. 6 is a cross-sectional view showing a configuration of a conventional liquid crystal display element.

FIG. 7 is a plan view showing a configuration of a TFT substrate of a conventional liquid crystal display element.

[Explanation of symbols]

11 ... TFT substrate, 12 ... counter substrate, 13 ... liquid crystal,
21 ... TFT, 211 ... Gate electrode, 212 ... Gate insulating film, 213 ... Intrinsic semiconductor layer, 214 ... Drain electrode, 215 ... Source electrode, 22 ... White base layer , 23
R ・ 23G ・ 23B ... Phosphor layer, 24 pixel electrodes, 25 ・
..Alignment film, 26 ... Compensation capacitance electrode, 31 ... Counter electrode, 3
6 ... Alignment film, 37 ... Electrode terminal, SC ... Sealing material, G
L: Gate line, DL: Data line

Claims (4)

[Claims] 1. An active element disposed in each pixel region, a white underlayer disposed on the active element, a phosphor layer disposed on the white underlayer, and an entire surface of each pixel region. A first substrate formed by laminating a first electrode connected to the active element, and a first substrate formed so as to face the first substrate, and the first substrate being provided on a surface facing the first substrate. A second substrate on which a second electrode facing the first electrode is formed; and a liquid crystal which is sealed between the first and second substrates in a twist alignment state and to which a dichroic dye is added, A liquid crystal display device comprising: 2. The phosphor layer is formed on the white underlayer, and the first electrode is composed of a transparent conductive film formed on the phosphor layer. The liquid crystal display element according to claim 1. 3. The first electrode is composed of a transparent conductive film formed on the white underlayer, and the phosphor layer is formed on the first electrode. The liquid crystal display element according to claim 1. 4. The phosphor layer is made of a resin to which a fluorescent substance emitting fluorescence of at least one of red, green and blue is added. The liquid crystal display element according to any one of the above.