JPH07104256A - Active matrix liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide an active matrix liquid crystal display element with which a very bright screen can be obtd. compared to a TN type element. CONSTITUTION:A first transparent substrate 1 on which plural transparent picture element electrodes 3 and plural active elements (TFT) 4 corresponding to the picture element electrodes 3, respectively are formed and a second transparent substrate 2 having a transparent counter electrode 10 facing to the picture element electrodes 3 are disposed with the electrode forming surfaces faced each other. A liquid crystal/polymer composite film 20 formed by dispersion of a liquid crystal in a polymer layer is interposed between these substrates 1, 2. Further, a phosphor film 11 is formed on the first transparent substrate 1 corresponding to the picture element electrodes 3.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a TN type liquid crystal display element has been used as an active matrix liquid crystal display element. This T
The N-type active matrix liquid crystal display device includes a first transparent substrate on which a plurality of transparent pixel electrodes and a plurality of active devices corresponding to the respective pixel electrodes are arranged, and a transparent counter electrode facing the pixel electrodes. A second transparent substrate on which the electrode forming surfaces are opposed to each other, a nematic liquid crystal layer is provided between the two substrates, and a polarizing plate is disposed on the outer surface side of each of the two substrates. Is.

Alignment films for controlling the alignment direction of liquid crystal molecules are provided on the electrode formation surfaces of both substrates, and the liquid crystal molecules are twist-aligned between the substrates at a twist angle of about 90 °. ing. Further, the pair of polarizing plates respectively arranged on the outer surface sides of both substrates are provided with their transmission axes substantially parallel to each other.

[0004]

By the way, an active matrix liquid crystal display element is generally used with a backlight disposed on the back surface side thereof. However, the above-mentioned TN type active matrix liquid crystal display element has a backlight. Incident light is linearly polarized by one of the polarizing plates and is incident on the liquid crystal layer. Of the light that has passed through the liquid crystal layer, an area in which liquid crystal molecules are vertically aligned by the application of an electric field between the pixel electrode and the counter electrode is selected. Since the light passing therethrough passes through the other polarizing plate and is emitted, there is a large amount of light loss due to the absorption of light in the polarizing plate, and therefore the screen is dark. The brightness of the screen of this liquid crystal display element is 1/2 or less of the brightness of the illumination light from the backlight. An object of the present invention is to provide an active matrix liquid crystal display device capable of obtaining a very bright screen as compared with the TN type.

[0005]

An active matrix liquid crystal display device of the present invention comprises: a first transparent substrate having a plurality of transparent pixel electrodes and a plurality of active devices corresponding to the respective pixel electrodes; A second transparent substrate provided with a transparent counter electrode in which the pixel electrodes face each other is disposed with their electrode forming surfaces facing each other, and a liquid crystal / high liquid crystal in which a liquid crystal is dispersed in a polymer layer between the both substrates. It is equipped with a molecular composite membrane,
Further, a phosphor film is provided on the first transparent substrate so as to correspond to the pixel electrodes.

[0006]

In other words, the active matrix liquid crystal display element of the present invention displays by utilizing the scattering and transmission of light in the liquid crystal / polymer composite film, and is dispersed in the polymer layer of this composite film. The molecules of the liquid crystal are oriented in various directions when no electric field is applied, and in this state,
Light incident from one substrate side is scattered by the composite film, so that the display observed from the other substrate side is in a dark state. Further, when an electric field is applied between the pixel electrode and the counter electrode of both substrates, the liquid crystal molecules are vertically aligned, so that the incident light from the one substrate side passes through the composite film without being scattered and the other The light is emitted to the substrate side, and the display becomes bright.

Therefore, this liquid crystal display element does not require a polarizing plate, which is indispensable for a TN type liquid crystal display element, and therefore there is no loss of light quantity due to light absorption by the polarizing plate. Moreover, in this liquid crystal display element, since the phosphor film is provided on the first transparent substrate on which the pixel electrode is arranged so as to correspond to the pixel electrode, when the transmitted light passes through the phosphor film, Since fluorescence is generated in the phosphor film, the bright display becomes brighter due to the fluorescence.

As described above, the liquid crystal display element of the present invention has T
There is no light amount loss due to light absorption in a polarizing plate such as an N-type element, and the bright display becomes brighter due to the fluorescence emitted by the phosphor film, so a very bright screen can be obtained compared to the TN type. it can.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a part of an active matrix liquid crystal display device showing a first embodiment of the present invention.

In FIG. 1, reference numerals 1 and 2 denote a pair of transparent substrates made of a glass plate or the like, and a plurality of substrates arranged in a row direction and a column direction are arranged on a lower substrate (hereinafter referred to as a lower substrate) in the figure. A transparent pixel electrode 3 and a plurality of active elements 4 corresponding to the respective pixel electrodes 3 are provided, and a substrate (hereinafter, referred to as an upper substrate) 2 on the upper side in the drawing is almost entirely covered with the above-mentioned lower substrate. All pixel electrodes 3 on substrate 1
A transparent counter electrode 10 facing each other is provided.

The active element 4 is, for example, a TFT (thin film transistor), and the TFT 4 includes a gate electrode 5 formed on the lower substrate 1, a gate insulating film 6 covering the gate electrode 5, and the gate insulating film 6. A semiconductor film 7 made of a-Si (amorphous silicon) or the like formed so as to face the gate electrode 5, and a source electrode 8 and a drain electrode 9 formed on both sides of the semiconductor film 7.
It consists of and.

Although not shown, a gate line (address line) for supplying a gate signal to the TFT 4 and a data line for supplying a data signal corresponding to image data to the TFT 4 are wired on the lower substrate 1. And T
The gate electrode 5 of the FT 4 is formed integrally with the gate line, and the drain electrode 9 is connected to the data line.

The gate insulating film 6 of the TFT 4 is
The gate insulating film 6 is a transparent film made of Si N (silicon nitride) or the like, and is formed over almost the entire surface of the lower substrate 1. The pixel electrode 3 has the gate insulating film 6
Is provided on top of the corresponding T at one end
It is connected to the source electrode 8 of FT4.

Further, the lower substrate 1 is provided with a phosphor film 11 corresponding to each pixel electrode 3 arranged on the substrate 1 and emitting fluorescence when exposed to light. This phosphor film 11 is a transparent resin base material in which granular phosphor substances are mixed in a scattered state, and the phosphor film 11 corresponding to each pixel electrode 3 is formed on almost the entire surface of the pixel electrode 3. It is formed in the opposing area.

In this embodiment, as the phosphor film 11, a plurality of phosphor films emitting fluorescence of different colors, for example,
A phosphor film that emits red fluorescence, a phosphor film that emits green fluorescence, and a phosphor film that emits blue fluorescence are used, and these phosphor films are arranged alternately.

Also, in this embodiment, the phosphor film 11 is used.
Is provided between the lower substrate 1 and the gate insulating film 6, and the phosphor film 11 and the pixel electrode 3 are opposed to each other with the gate insulating film 6 interposed therebetween.

The lower substrate 1 and the upper substrate 2 are joined to each other at their outer peripheral edges via a frame-shaped sealing material (not shown), and are surrounded by the sealing material between the substrates 1 and 2. A liquid crystal / polymer composite film 20 is provided in the region.

The liquid crystal / polymer composite film 20 is one in which liquid crystal is dispersed in a polymer layer.
A liquid crystal is confined in each void of the polymer layer 21 polymerized so as to have a cross section like a sponge. In FIG. 1, reference numeral 22 denotes a liquid crystal part (a part in which the liquid crystal is confined) in the composite film 20.

In this embodiment, a nematic liquid crystal having a positive dielectric anisotropy is used as the liquid crystal, and a black dichroic dye is mixed in the liquid crystal. FIG. 2 shows the composite membrane 2
FIG. 3 is an enlarged cross-sectional view of one liquid crystal portion 22 of 0 in a non-electric field state and an electric field applied state. In the figure, A indicates a liquid crystal molecule and B indicates a dichroic dye molecule.

In the above liquid crystal display element, for example, a pair of substrates 1 and 2 are joined together via a sealing material, and then the substrates 1 and 2 are joined together.
Injecting a mixed solution of a polymer material that polymerizes by light and a liquid crystal to which a dichroic dye is added, by a vacuum injection method from an injection port formed by removing a part of the sealing material between the two. It can be manufactured by a method of filling and filling the filling solution with ultraviolet rays from the outer surface side of the upper substrate 2 on which the counter electrode 10 is formed to photopolymerize the polymer material. The injection port is sealed after filling the solution or after photopolymerization of the polymer.

As described above, when the mixed solution filled between the substrates 1 and 2 is irradiated with ultraviolet rays, the polymer material in a monomer or oligomer state is radicalized by the dissolution of its double bond, and adjacent molecules are adsorbed. The radicals are combined with each other to form a polymer by radical polymerization reaction, and the liquid crystal is phase-separated by polymerizing the polymer material.

Therefore, the polymerized polymer layer 21 has a cross section like a sponge, and the liquid crystal is confined in the gaps of the polymer layer 21, and the liquid crystal / polymer composite film 20 having the above-described structure is formed. Is formed. The method for forming the composite film 20 is a method called a photopolymerization phase separation method.

In the active matrix liquid crystal display device, a backlight is arranged on the back side of one of the substrates, for example, the lower substrate 1, and light from this backlight is scattered or transmitted by the liquid crystal / polymer composite film 20. As shown in FIG. 2A, the molecules A of the liquid crystal of the liquid crystal part 22 dispersed in the polymer layer 21 of the composite film 20 are various as shown in FIG. 2A. Since the molecules B of the dichroic dye are also oriented in various directions, when the light incident from the lower substrate 1 side passes through the composite film 20 in this electric fieldless state. , Its liquid crystal part 2
The light is scattered by the light scattering action of the liquid crystal of the liquid crystal part 22 and the interface between the polymer layer 21 and the polymer layer 21, and most of the scattered light is absorbed by the dichroic dye.

Therefore, in the non-electric field state, the light emitted to the upper substrate 2 side through the composite film 20 is very small, and therefore the display observed from the upper substrate 2 side is in a dark state of almost black. become.

On the other hand, when an electric field is applied between the pixel electrode 3 and the counter electrode 12 of both substrates 1 and 2, the liquid crystal molecule A of the liquid crystal part 22 of the composite film 20 is, as shown in FIG. 2B. Of the dichroic dye are uniformly oriented so as to be substantially perpendicular to the surfaces of the substrates 1 and 2, and the molecules B of the dichroic dye are also oriented accordingly. The emitted light passes through the composite film 20 and is emitted to the upper substrate 2 side with almost no light scattering effect in the composite film 20 and almost no absorption by the dichroic dye. Become.

Further, since the incident light from the lower substrate 1 side passes through the phosphor film 11 provided on the lower substrate 1 so as to correspond to each pixel electrode 3, a certain amount of this incident light is generated. , Fluorescence is generated by hitting the fluorescent substance scattered in the phosphor film 11.

Therefore, in the above electric field applied state,
Of the incident light, the light that has passed through the phosphor film 11 without hitting the fluorescent substance and the fluorescence emitted by the phosphor film 11 upon receiving the incident light pass through the composite film 20 to the upper substrate 2 side. A bright display of the color of the fluorescence emitted and emitted by the phosphor film 11 is obtained.

The fluorescent substance in the phosphor film 11 is
Since fluorescence is emitted not only by visible light but also by light having a wavelength outside the visible light band, the fluorescence emitted from the phosphor film 11 is high-intensity light. Therefore, high-intensity light is emitted from the upper substrate 2 when an electric field is applied. Since the light is emitted to the side, a high-contrast display having a large contrast ratio between the dark display and the bright display can be obtained.

That is, the above-mentioned liquid crystal display element is for displaying by utilizing the scattering and transmission of light in the liquid crystal / polymer composite film 20, and therefore the polarizing plate which is indispensable for the TN type liquid crystal display element is used. Since it is unnecessary, there is no light amount loss due to light absorption by the polarizing plate.

Moreover, in this liquid crystal display device, since the phosphor film 11 is provided corresponding to the pixel electrode 3 on the lower substrate 1 on which the pixel electrode 3 is arranged, the transmitted light is the phosphor film 11. Since fluorescent light is generated in the phosphor film 11 when passing through, the bright display becomes brighter due to the fluorescent light.

As described above, the liquid crystal display element has no light amount loss due to light absorption in the polarizing plate like the TN type element,
In addition, since the bright display becomes brighter due to the fluorescence emitted from the phosphor film, an extremely bright screen can be obtained as compared with the TN type.

In the above display example, light is made incident from the lower substrate 1 side, but even if light is made incident from the upper substrate 2 side and the display is observed from the lower substrate 1 side, it is possible to obtain the above-mentioned emergency. You can get a bright screen.

Further, in the above embodiment, the lower substrate 1 and the TFT
4 is provided between the gate insulating film 6 and the phosphor film 11, and the phosphor film 11 and the pixel electrode 3 are opposed to each other with the gate insulating film 6 interposed therebetween. It may be provided so as to overlap with the electrode 3.

FIG. 3 is a sectional view of a part of an active matrix liquid crystal display device showing a second embodiment of the present invention. In this embodiment, a phosphor film 11 is provided on a pixel electrode 3. .

FIG. 4 is a sectional view of a part of an active matrix liquid crystal display device showing a third embodiment of the present invention. In this embodiment, a transparent protective insulating film covering the TFT 4 on the lower substrate 1 is shown. 12 is provided, the phosphor film 11 corresponding to each pixel electrode 3 is provided on the protective insulating film 12, the pixel electrode 3 is provided on the phosphor film 11, and the pixel electrode 3 is protected. The contact hole 13 formed in the insulating film 12 is connected to the source electrode 8 of the TFT 4.

The second and third embodiments shown in FIGS. 3 and 4 are different only in the formation state of the phosphor film 11 and the pixel electrode 3, and other configurations are the same as those shown in FIG. 1
Since it is the same as the embodiment of FIG.

In the above embodiment, the nematic liquid crystal is used as the liquid crystal of the liquid crystal / polymer composite film 20, but this liquid crystal may be a cholesteric liquid crystal, and this cholesteric liquid crystal is a molecule in a non-electric field state. Since the array structure has a spiral structure, it has a high light scattering property, so that dark display can be made darker and the display contrast can be further increased.

Further, in the above-mentioned embodiment, the liquid crystal / polymer composite film 20 is formed by mixing the dichroic dye in the liquid crystal, but the composite film 20 contains the dichroic dye in the liquid crystal. The display may be performed by scattering light in a non-electric field state and transmitting light in an electric field application state. In addition, the active element is a TFT
However, it may be MIM or the like.

[0039]

According to the active matrix liquid crystal display element of the present invention, the first transparent substrate provided with a plurality of transparent pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes and the pixel electrodes face each other. And a second transparent substrate provided with a transparent counter electrode, the electrode forming surfaces of which face each other, and a liquid crystal / polymer composite film in which a liquid crystal is dispersed in a polymer layer between the two substrates. Provided, and the first
Since the phosphor film is provided on the transparent substrate corresponding to the pixel electrode, a very bright screen can be obtained as compared with the TN type.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view of one liquid crystal part of the liquid crystal / polymer composite film in a non-electric field state and an electric field applied state.

FIG. 3 is a sectional view of a part of a liquid crystal display element showing a second embodiment of the present invention.

FIG. 4 is a partial cross-sectional view of a liquid crystal display element showing a third embodiment of the present invention.

[Explanation of symbols]

 1, 2 ... Transparent substrate 3 ... Pixel electrode 4 ... Active element (TFT) 10 ... Counter electrode 11 ... Fluorescent substance film 20 ... Liquid crystal / polymer composite film 21 ... Polymer layer 22 ... Liquid crystal part A ... Liquid crystal molecule B ... Dichroic dye molecule

Claims (1)

[Claims] 1. A first transparent substrate having a plurality of transparent pixel electrodes and a plurality of active elements corresponding to the respective pixel electrodes, and a second transparent substrate having a transparent counter electrode facing the pixel electrodes. And a transparent substrate of which the electrode forming surfaces are opposed to each other, and a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer layer is provided between the both substrates, and the first substrate An active matrix liquid crystal display device, characterized in that a phosphor film is provided on a transparent substrate so as to correspond to the pixel electrodes.