JP2705652B2 - Transmissive 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 transmission type liquid crystal display device having a wide viewing angle and improved viewing angle dependency.

[0002]

2. Description of the Related Art A transmissive liquid crystal display device is a display element represented by a flat panel display, and is light, thin, and consumes low power, so that it is used for OA equipment, in-vehicle television, car navigation, and video cameras. It has been widely used as a monitor. However, a major problem is that viewing angle dependence is large. The viewing angle dependence is, for example, a display that should be displayed in black when viewed from a certain oblique direction, looks whitish or loses the gradation, thereby giving a viewer discomfort. Therefore, there is a demand for a transmissive liquid crystal display device in which black display is not whitish in any direction and gradation is not lost.

FIG. 8 is a partial sectional view of a conventional liquid crystal display device which is not a general LCD having a wide viewing angle. This transmission type liquid crystal display device includes a surface light source 201, a liquid crystal panel 210, and polarizing plates 202 and 207. The surface light source 201 includes a cold cathode fluorescent lamp, a light guide plate, and the like. The liquid crystal panel 210 has a thin film transistor (TF) formed in a matrix on a transparent glass substrate.
T) and an active matrix substrate 203 on which transparent pixel electrodes are arranged, a twisted nematic (TN) liquid crystal 204 having a twist angle of about 90 °, a color filter substrate 205 on which a transparent common electrode and a color filter are formed, and both substrates 203 and 205 The polarizing plates 202 and 207 sandwich the liquid crystal panel 210 with the transmission axes shifted by 90 ° (in the case of the normally white mode).

In the liquid crystal display device having such a configuration, a constant voltage is applied to the common electrode on the color filter substrate 205, and a voltage corresponding to pixel data to be displayed is applied to the transparent pixel electrode on the active matrix substrate 203. Is applied. As a result, the twisted state of the liquid crystal between both electrodes is changed, and the intensity of light passing through each pixel electrode portion is modulated in combination with the polarizing plates 202 and 207.

Since the properties of the liquid crystal used in the liquid crystal display device have a refractive index anisotropy, when the viewing angle is increased, the reversal of the gradation and the decrease of the contrast ratio occur, and the display quality is remarkably deteriorated. For example, in the above-described liquid crystal display device, when the angle exceeds 10 ° in the downward direction, the grayscale inversion occurs.
If the angle exceeds 50 °, the contrast ratio decreases to 10 or less. Here, the grayscale inversion means that the original grayscale order recognized from the front is reversed when viewed from a certain oblique direction, and the contrast ratio is white display / black display.

Therefore, various proposals have been made to improve the viewing angle dependence of this type of liquid crystal display device. FIG.
FIG. 1 is a cross-sectional view of a viewing angle improving liquid crystal display device proposed in Japanese Patent Application Laid-Open No. 61-284731 (hereinafter referred to as a first prior art). As shown in FIG.
The scanning electrode substrate 303 on which the first electrode 03a is formed and the signal electrode 3
And the signal electrode substrate 305 on which the liquid crystal 30 is formed.
4. They are arranged to face each other with the sealant 306 interposed therebetween, and these constitute a liquid crystal panel 310. The polarizing plates 302 and 30 are provided on the light source side and the display surface side of the liquid crystal panel 310.
7 are arranged. A collimator 311 that transmits only a light component substantially perpendicular to the surface of the liquid crystal panel 310 is disposed on the light source side of the polarizing plate 302.
A microlens 308 provided for each pixel is disposed on 7. The collimator 311 forms a louver by laminating a light transmitting portion and a blocking portion in multiple layers, and cutting the layer perpendicularly to the laminating direction.

In this liquid crystal display device, substantially parallel light among the light from the light source is extracted by a collimator 311, and a microlens 308 arranged for each pixel of the light emitted from the liquid crystal panel 310 is arranged on a polarizing plate 307. The light is diffused to increase the viewing angle.

However, the light from the light source is transmitted to the collimator 311.
When the directivity is strengthened by this, light loss due to the light shielding portion of the collimator 311 is large. Further, since the thickness of the collimator 311 is increased, it is not suitable for further reducing the thickness of the liquid crystal display device. If the number of light-shielding portions is reduced in order to reduce the loss of light or to reduce the thickness as much as possible, almost no parallel light is generated, and the following phenomenon occurs.

As shown in FIG. 10, light emitted from the signal electrode 305a at a certain converging angle is reflected on the signal electrode substrate 3
05 and spread by the polarizing plate 307. Therefore, originally,
The light to be observed at part c spreads to the range of d,
Refraction occurs on the curved surface of the microlens 308, and scattering occurs if the surface is not a mirror surface. This display blur increases as the distance L from the signal electrode 305a to the microlens 308 increases.

FIG. 11 is a cross-sectional view of a viewing angle improving liquid crystal display device proposed in Japanese Patent Application Laid-Open No. Sho 62-56930 (hereinafter referred to as a second prior art). This is the first
The conventional collimator 311 is provided on the display surface side. A collimator 311 is disposed on a polarizing plate 307, and a microlens 30 provided for each pixel is disposed thereon.
8 are arranged.

In principle, similarly to the first prior art, substantially parallel light out of light from a light source is extracted by a collimator 311 and a micro lens 308 is provided on the front surface of the collimator 311.
The light is diffused to increase the viewing angle.

In the second prior art, as in the first prior art, light loss and display blur occur, and there is a problem in making the liquid crystal display device thinner. In this case, as shown in FIG. 12, since the collimator 311 is included in the distance L ′, the display blur becomes more remarkable than in the first related art.

[0013]

The conventional liquid crystal display device shown in FIG. 8, which is not a general LCD having a wide viewing angle, has a narrow viewing angle, and the gradation deviates from the normal line of the liquid crystal panel 210 due to the difference in retardation. There is a drawback that the display performance is lost, the contrast ratio is reduced, and a display with a wide viewing angle cannot be obtained.

The first and second prior arts, which are the viewing angle dependency improvement plans of FIGS. 9 and 11, have a problem that display blur occurs because the distance between the display position and the microlens 308 is large. . Since the display blur is emitted at a certain angle, the light is spread according to the distance from the display position to the lens surface, is scattered on the lens surface, and is recognized by refraction to the viewpoint. Further, the collimator 311 hinders the thinning of the liquid crystal display device.

The present invention has been made to solve these problems, and an object of the present invention is to provide a transmission type liquid crystal display device having excellent display quality.

[0016]

According to the present invention, in order to achieve the above object, according to the present invention, a pair of a surface light source and a transparent light conductive electrode formed on a surface opposite to the surface light source with a gap therebetween. A liquid crystal panel including a glass substrate and liquid crystal injected into the gap; a polarizing plate disposed on a light source side and a display side of the liquid crystal panel; and a light diffusing unit disposed on a display surface side of the liquid crystal panel And a total reflection light guide path is provided in the glass substrate on the display surface side of the pair of glass substrates. Further, according to the present invention, a surface light source, a pair of glass substrates having a transparent conductive film electrode formed on the opposite surface side, which are disposed to face each other via a gap, and a liquid crystal injected into the gap are provided. A liquid crystal panel; a polarizing unit disposed on a light source side and a display surface side of the liquid crystal panel; a light diffusing unit disposed on a display surface side of the liquid crystal panel; and a light diffusing unit disposed on the surface light source side of the liquid crystal panel. And a condensing means, wherein a total reflection light guide path is provided in the glass substrates on the display surface side of the pair of glass substrates, thereby obtaining a transmission type liquid crystal display device.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG. 1 shows a partial cross-sectional view of the first embodiment of the present invention. This transmission type liquid crystal display device has a surface light source 101.
, A liquid crystal panel 110, polarizing plates 102 and 107, and a light diffusion layer 108. The surface light source 101 includes a cold cathode fluorescent lamp and a light guide plate for making the light uniform on the surface. In addition, the liquid crystal panel 1
Reference numeral 10 denotes an active matrix substrate 103 in which thin film transistors (TFTs) and transparent pixel electrodes are arranged in a matrix on a transparent glass substrate, a twisted nematic (TN) liquid crystal 104 having a twist angle of approximately 90 °, a total reflection light guide path 109 and a transparent It is composed of a color filter substrate 105 on which a common electrode and a color filter are formed, and a sealant 106 for bonding the two substrates 103 and 105 and sealing the liquid crystal. The light diffusion layer 108 may be formed of a microlens sheet having a fine lens, a lenticular sheet, a sheet mixed with fine particles, a diffusion sheet having a random irregular surface, an internal refractive index distribution type sheet, a diffraction grating layer, or the like. Is a sheet that refracts and scatters light. Polarizing plate 10
Reference numerals 2 and 107 denote a liquid crystal panel 110 and a light diffusion layer 108 by shifting the transmission axis by 90 ° (in the case of a normally white mode).
Is sandwiched between. Here, the polarizing plate 107 is a light diffusion layer 108.
It is better to have a direct view than to. The fact that the polarizing plate 107 is a direct view surface means that external light reflection is suppressed to half or less, and the display is not whitened by scattering of the light diffusion layer 108,
Good display quality can be obtained.

The directions in which the total reflection light guide path 109 embedded in the color filter substrate 105 extends are vertical and vertical directions depending on the viewing angle. This is the light diffusion layer 1
08 corresponds to the case where light is diffused in the vertical direction.

FIG. 4 is a partial perspective view of the total reflection light guide path 109. As the material, a metal having a high melting point, such as silver, chromium, tungsten, tantalum, or titanium is used. As another material, an alloy based on aluminum having high reflectivity may be used in order to minimize light loss. In molding, first, these metals which become the total reflection light guide path 109 are formed on a glass substrate by sputtering.

When the total reflection light guide 109 is made of chromium or silver,
Silicon oxide film as a mask, for example, plasma CVD
The film is formed by the method. Next, a photoresist is applied, developed in the form of a light guide path, and the silicon oxide film is dry-etched with a fluorine gas, for example, CF ₄ . Thereafter, the photoresist is removed, and chromium and silver metals are dry-etched using chlorine gas, for example, Cl ₂ to form light guide paths.

When the total reflection light guide path 109 is made of tungsten, tantalum or titanium, an aluminum film is formed as a mask by sputtering. Next, a photoresist is applied, developed into the shape of a light guide path, and the aluminum film is dry-etched using a chlorine gas, for example, Cl ₂ . Thereafter, the photoresist is removed, and a metal such as tungsten is dry-etched using a fluorine gas, for example, CF ₄ to form a light guide path.

When the total reflection light guide path 109 is made of tungsten, tantalum or titanium, an aluminum film is formed by sputtering as a mask. Next, a photoresist is applied, developed into the shape of a light guide path, and the aluminum film is dry-etched using a chlorine gas, for example, Cl ₂ . Thereafter, the photoresist is removed, and a metal such as tungsten is dry-etched using a fluorine gas, for example, CF ₄ to form a light guide path.

As a method of embedding the completed total reflection light guide path 109 in the color filter substrate 105, molten glass was flowed on a stage with a frame, the total reflection light guide path 109 was immersed together with the glass substrate, and the glass substrate was melted again. rear,
Allow to cool and solidify. The thickness of the glass serving as the color filter substrate 105 is 1 to 2 mm in order to maintain strength. After hardening, polishing is performed. Thereafter, in order to align the total reflection light guide path 109 with a black matrix described later, a photoresist marker is formed by photolithography at a position other than where the black matrix portion is formed. The substrate thus manufactured does not have surface irregularities, and has no deformation due to a temperature change by making the coefficient of expansion of the total reflection light guide 109 as close as possible to that of the color filter substrate 105.

The thickness X, which is the metal part of the light guide path in the vertical direction depending on the viewing angle, is within the range covered by the black matrix 115 as shown in FIG.
μm. The black matrix 115 is applied to the color filter substrate 105,
The purpose of the present invention is to hide the total reflection light guide path 109 in the black matrix 115 that originally existed, for the purpose of suppressing leakage current, preventing backlight light leakage, and preventing color deterioration. As a result, the aperture ratio does not decrease. Black matrix 1
15 to hide the total reflection light guide path 109,
After embedding 09 in the color filter substrate 105, a black matrix 115 is formed in accordance with the mark provided for alignment.

The thickness Y of the light guide path in the normal direction of the liquid crystal panel is
Considering light leakage, it is best that the thickness is the same as the thickness of the color filter substrate 105. However, the total reflection light guide 10
By providing 9 in the color filter substrate 105, the strength of the substrate itself is reduced. Therefore, the thickness Y of the light guide path
Is set smaller than the thickness of the color filter substrate 105 so that the entire surface of the color filter substrate 105 on the direct viewing side and the entire surface light source side is continuously connected.

The operation of the transmission type liquid crystal display device of the present invention will be described with reference to FIG. FIG. 3 without total reflection light guide path 109
In the case of (a), light emitted from the color filter 112 formed on the color filter substrate 105 spreads on the color filter substrate 105. Therefore, the light that should be originally observed in the portion “a” spreads to the range “b” and is visually recognized in the range “b” by scattering, refraction, diffraction, and the like in the light diffusion layer 108. For example, when the portion a is 300 μm and the thickness of the glass is 1 mm, when the light diffusion layer 108 is not provided, 3
Although visible with a width of 00 μm, the light diffusion layer 108 is provided,
When the light emission angle is 30 °, the range of b is 1455 μm
(Approximately 4.8 times). This can be easily calculated by trigonometric function calculation. In the actual observation state, although the grayscale inversion that occurs when viewed in an oblique direction is mitigated, the display becomes blurred, lowering the resolution and giving discomfort.

In the case of FIG. 3B in which the total reflection light guide path 109 is provided, the light emitted from the color filter 112 is reflected by the total reflection light guide path 109 and proceeds. The light to be observed in the portion a does not spread because of the total reflection light guide path 109,
The original width of 300 μm can be visually recognized by scattering, refraction, diffraction and the like in the light diffusion layer 108. Because of total reflection, light loss is small, display blur does not occur, resolution degradation is suppressed, and good display with reduced gradation inversion is obtained. Since the total reflection light guide path 109 is inserted into the color filter substrate 105, the liquid crystal display device does not become thicker.

FIG. 2 shows a second embodiment of the present invention in which a light-condensing layer 111 is provided between a surface light source 101 and a liquid crystal panel 110. The condensing layer 111 has a function of making the diffused light of the surface light source 101 parallel light as much as possible. For example, there are a prism lens film and a louver. In addition, there are also those in which the function of the light condensing layer 111 is included in the surface light source 101,
For example, a prism lens is formed on the liquid crystal panel 110 side of the light guide plate constituting the surface light source 101, or a groove is formed on the light guide plate on the side opposite to the liquid crystal panel 110 so that light is efficiently directed to the front. And so on. These light guide plates are formed by a mold. In the liquid crystal display device including the light-condensing layer 111, the amount of light vertically transmitted through the liquid crystal panel 110 increases.
A good display with a high contrast ratio, a wider viewing angle, and no degraded gradation can be obtained. However, the light collecting layer 111
However, perfect collimated light cannot be obtained even when the light beam enters, so that the present invention is effective due to the phenomenon described with reference to FIG.

FIG. 5 shows a total reflection light guide 113 of a liquid crystal display device according to a third embodiment of the present invention. The configuration of the entire apparatus is the same as FIG. 1 or FIG. In this embodiment, a total reflection light guide is provided in the left-right direction in addition to the vertical total reflection light guide in the first embodiment. Therefore, the shape becomes like the eyes of a go board. The total reflection light guide path 113 described in the vertical direction
Has a thickness Z of 10 to 50 μm in the left-right direction. Therefore, it is effective when the viewing angle also depends on the left and right direction. The third embodiment is based on the premise of a stripe-type pixel array structure. In the stripe type, filters of each color of R, G, and B are formed in a straight line in a vertical direction, and one pixel includes three colors of R, G, and B linearly arranged in a horizontal direction. . Pixels containing these three colors are arranged in a straight line in the vertical and horizontal directions.

FIG. 6 shows a total reflection light guide path 114 of a liquid crystal display device according to a fourth embodiment of the present invention. The configuration of the entire apparatus is the same as FIG. 1 or FIG. This is the same as the effect of the third embodiment. This mode is based on a mosaic-type pixel array structure. In the mosaic type, one pixel has a configuration in which R, G, and B are arranged in the horizontal direction, and the pixels are linearly arranged in the horizontal direction, and are shifted by half a pixel in the vertical direction in a staggered manner. Are located.

[0031]

As described above, the transmission type liquid crystal display device of the present invention uses a light diffusion layer by providing a total reflection light guide path in a color filter substrate to suppress the spread of light. The display blur which has occurred in the wide-viewing-angle liquid crystal display device in which the light-collecting layer is added thereto is almost eliminated.

For example, when a display having a width of 300 μm is displayed, the liquid crystal display device having a wide viewing angle using a light diffusion layer is visually recognized at a width of 1455 μm. , Approximately 300 μm wide. Therefore, it is possible to obtain a pixel having a high resolution and a wide viewing angle. In addition, since the total reflection light guide path is placed in the color filter substrate, the liquid crystal display device does not become thicker.

[Brief description of the drawings]

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

FIG. 2 is a partial sectional view of a liquid crystal display device according to a second embodiment of the present invention.

FIGS. 3A and 3B are partial cross-sectional views illustrating the effect of the present invention.

FIG. 4 is a diagram showing a total reflection light guide path of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a total reflection light guide path according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating a total reflection light guide path according to a fourth embodiment of the present invention.

FIG. 7 is a partial cross-sectional view illustrating a black matrix.

FIG. 8 is a partial cross-sectional view of a conventional liquid crystal display device without a wide viewing angle.

FIG. 9 is a partial cross-sectional view of a liquid crystal display device showing a configuration of a first conventional technique.

FIG. 10 is a diagram showing an optical path of a first related art.

FIG. 11 is a partial cross-sectional view of a liquid crystal display device showing a configuration of a second conventional technique.

FIG. 12 is a diagram showing an optical path according to a second conventional technique.

[Explanation of symbols]

101, 201 Surface light source 102, 107, 202, 207, 302, 307
Polarizers 103, 203 Active matrix substrate 303 Scan electrode substrate 303a Scan electrode 104, 204 TN liquid crystal 304 Liquid crystal 105, 205 Color filter substrate 305 Signal electrode substrate 305a Signal electrode 106, 206 Sealant 306 Sealant 108 Light diffusion layer 308 Micro Lens 109 Total reflection light guide 110, 210, 310 Liquid crystal panel 111 Light collecting layer 311 Collimator 112 Color filter 113 Stripe type total reflection light guide 114 Mosaic type total reflection light guide

Claims (5)

(57) [Claims] 1. A liquid crystal panel comprising: a surface light source; a pair of glass substrates oriented and disposed with a gap therebetween, a transparent conductive film electrode formed on an opposing surface thereof; and a liquid crystal injected into the gap; In a transmission type liquid crystal display device having a polarizing plate disposed on a light source side and a display surface side of the liquid crystal panel, respectively, and a light diffusing unit disposed on a display surface side of the liquid crystal panel, A transmission type liquid crystal display device, wherein a total reflection light guide path is provided in a glass substrate on a display surface side. 2. A liquid crystal panel comprising: a surface light source; a pair of glass substrates disposed opposite to each other via a gap, having a transparent conductive film electrode formed on the opposite surface side; and a liquid crystal injected into the gap. Polarizing means disposed on the light source side and the display surface side of the liquid crystal panel, light diffusing means disposed on the display surface side of the liquid crystal panel, and light condensing disposed on the surface light source side of the liquid crystal panel, respectively. Means, wherein a total reflection light guide path is provided in the glass substrate on the display surface side of the pair of glass substrates. 3. The transmission type liquid crystal display device according to claim 1, wherein said total reflection light guide path is incorporated in parallel, and a direction in which said parallel reflection optical path is incorporated is perpendicular to a direction depending on a viewing angle. A transmission type liquid crystal display device characterized by the above-mentioned. 4. The transmissive liquid crystal display device according to claim 1, wherein said total reflection light guide is of a stripe type corresponding to a pixel array arranged in a vertical and horizontal straight line. . 5. The transmissive liquid crystal display device according to claim 1, wherein the total reflection light guide path is a mosaic type corresponding to a pixel array that is vertically arranged in a staggered manner. Display device.