JP2002296588A - Liquid crystal display device and method for driving the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which realizes high luminance and a small size. SOLUTION: In the structure having a liquid crystal panel in which image signals are applied on the liquid crystal by line-sequential scanning and having a surface light source disposed on the back face of the panel, an EL light emitting material is used for the surface light source. The EL light emitting material is divided into stripes and is driven to synchronize with the line-sequential scanning of the liquid crystal panel to emit light of specified colors in the respective divided regions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a method of driving the same, and more particularly, to a liquid crystal panel for displaying pixels corresponding to red (R), green (G), and blue (B), and R light, G light.
1. Field of the Invention The present invention relates to a liquid crystal display device including a planar light source that emits each color light of light and B light, and a driving method thereof.

[0002]

2. Description of the Related Art Heretofore, as a means for colorizing a liquid crystal display device, a three-panel system using three R, G, and B liquid crystal display substrates (liquid crystal display elements) and a single liquid crystal display device have been proposed. The “single-plate type” in which R, G, and B color filters are arranged on a display substrate is widely used.

However, the three-panel system literally requires three liquid crystal display substrates, and further requires an optical system for color separation / color synthesis of irradiation light and emission light. It is not suitable for such devices. Further, in the single-panel system, only one liquid crystal display substrate is required, but three pixels corresponding to R, G, and B are required to obtain one color pixel. It becomes 3.

On the other hand, recently, as a means for colorizing a new liquid crystal display device, R, G, and B video data are switched by plane-sequential scanning, and a back light that irradiates the liquid crystal display substrate surface accordingly. The light (light source) is sequentially switched in time series between R light, G light, and B light at high speed, and afterimages corresponding to the respective color lights are synthesized on a human retina to obtain a color image. )) Has been attracting attention. This screen-sequential liquid crystal display device does not require a color filter, and has a single pixel.
Since all colors of R, G and B can be displayed, higher resolution can be obtained.

FIG. 4 shows a structure of a conventional frame sequential type liquid crystal display device. The liquid crystal display device has a large liquid crystal panel 10.
0 and a planar light source 200 as a backlight. The liquid crystal panel 100 mainly includes a glass substrate 111 having thin film transistors and electrodes 112 and 113 on its surface and an alignment layer (not shown), and a common electrode 116 and an alignment layer (not shown) disposed on the surface thereof. A liquid crystal layer 1 sealed in a liquid crystal cell composed of a glass substrate 117 and these glass substrates 111 and 117 and a sealing material 114
And 15.

The planar light source 200 has three light sources of R light, G light and B light.
The light from the cold cathode tube 213 is emitted to the liquid crystal panel side via the light guide plate 212 and the diffusion layer 210. In addition, these cold cathode tubes 213
A back plate 215 provided with a mirror 214 on the surface is disposed on the back surface of the device, and reflects light emitted from the cold-cathode tube 213 to the emission side.

FIG. 5 is a diagram showing a part of a driving circuit of the liquid crystal panel 100. As shown in the figure, unit pixels are arranged in a matrix on a substrate, and each unit pixel includes a transistor 1, a charge storage capacitor 2, and a liquid crystal cell 3.
have.

[0008] Writing of pixel signals to the liquid crystal panel 100 is performed by line-sequential scanning. That is, as shown in FIG. 5, with the addition of a scanning signal to the gate electrode line Yj is a scanning line, a source electrode line X _i, X i _{+ 1,} simultaneously giving an image signal., The X direction one column An image signal is simultaneously written to the capacitor 2 of the pixel group. This operation is sequentially performed for each of the scanning lines Yj and Yj + 1. When writing to all the scanning lines (gate electrode lines) is completed, writing of a screen (one field) for monochromatic light is completed. This operation is performed for each of R, G, and B to configure one color screen. This is repeated as one frame.

On the other hand, the planar light source 200 is a liquid crystal panel.
The cold-cathode tubes of the corresponding color light are emitted in synchronization with each field, and the liquid crystal panel 100 is irradiated. During one frame, the cold-cathode tubes of the R, G, and B color lights are sequentially turned on and off, and this is repeated. In this way, the screen of the liquid crystal panel is visualized, and the visualized image is sequentially switched and displayed in three colors. Three-color images are temporally synthesized by the human eye and recognized as a color screen.

[0010]

FIG. 6 is a diagram for explaining the driving states of a liquid crystal panel and a planar light source in a conventional field sequential type liquid crystal display device. The upper part shows the driving state of the liquid crystal panel, and the lower part shows the driving state of the planar light source scanned in synchronization with the liquid crystal panel.

In FIG. 1, the position of each scanning line is taken in the vertical direction, and the time is shown in the horizontal direction. For example, when the number of upper and lower scanning lines of a liquid crystal panel is 600, image signals are sequentially written from top to bottom for each scanning line. Therefore, it takes a certain time according to the scanning speed to write the image signal to all the scanning lines. When an image signal is written to each pixel, a voltage corresponding to the image signal is applied to the liquid crystal of each pixel.
However, the liquid crystal does not rise instantaneously, and requires a certain response time until it is stabilized in a predetermined alignment state corresponding to the image signal. Therefore, in order for the liquid crystal of all the pixels of the liquid crystal panel to actually show an alignment state corresponding to, for example, a red image signal, the time required for writing the image signal and the response time of the liquid crystal from the start of the scanning of the image signal (t0) are taken. This is after the added time (t1).

In the planar light source, red light is turned on in a state where the liquid crystals of all the pixels of the liquid crystal panel exhibit a stable orientation with respect to the red image signal. Then, when the writing of the green image signal to the liquid crystal panel starts, the light is turned off. Then, the lighting of the green light is waited until all the pixels of the liquid crystal panel show the alignment state corresponding to the stable green image signal.

For this reason, the time during which each color light of the planar light source is lit is only a part of the time (one field) spent displaying a monochromatic light image. Therefore, the effective integrated light amount emitted from the planar light source is small, which makes it difficult to increase the brightness of the liquid crystal screen.

In the above-mentioned conventional liquid crystal display device of the field sequential mode, a cold cathode tube is used as a surface light source. Therefore, for example, a small one having a diameter of 6 mm or more must be used. I can't get it. In addition, it is not desirable to increase the number of fluorescent tubes because of high power consumption. However, in order to make the light emitted from a small number of fluorescent tubes into uniform planar light, the distance between the emission surface and the cold cathode must be increased. Need to be done. For this reason, it is difficult to reduce the size of the planar light source and, consequently, the entire liquid crystal display device.

An object of the present invention is to provide a liquid crystal display device capable of achieving high luminance and miniaturization in view of the above-mentioned conventional problems.

[0016]

In order to solve the above-mentioned problems of the prior art, a liquid crystal display device according to the present invention comprises a plurality of scanning lines, a plurality of signal lines crossing the scanning lines, and a matrix at each intersection. A first transparent substrate having a pixel driving element disposed on the surface thereof; and a second transparent substrate disposed to face the surface of the first transparent substrate and having a transparent common electrode formed on the surface facing the first transparent substrate. A liquid crystal panel comprising: a substrate; a liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate; and a liquid crystal panel disposed on a back surface of the liquid crystal panel, the liquid crystal panel being disposed on the scanning line of the liquid crystal panel. It has a plurality of light-emitting regions divided into parallel bands, and each light-emitting region further has a planar light source having independent band-like EL light-emitting layers of R, G, and B.

In the method of driving a liquid crystal display device according to the present invention, the pixel driving elements of the liquid crystal panel are driven line by line for each scanning line, and the pixel driving elements corresponding to the scanning lines are synchronized with the driving. A light emitting operation is performed on the strip-shaped light emitting area at a position in a line sequential manner.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display device according to the present invention will be described with reference to the drawings.

The main feature of the liquid crystal display device according to the present embodiment is that in a configuration having a liquid crystal panel for applying an image signal to liquid crystal by line-sequential scanning and a planar light source disposed on the back thereof, In other words, a planar EL (Electro Luminescence) luminous body is used as a luminous source instead of a conventional cold cathode tube. Further, the EL luminous body is divided into bands in a plane, and is driven so as to emit predetermined color light for each divided region in synchronization with the line-sequential scanning of the liquid crystal panel. Since the EL luminous body can be composed of a thin film, the planar light source can be made thin and compact. In addition, by synchronizing the line sequential scanning of the liquid crystal panel with the operation of the planar light emitter,
More efficient lighting can be performed.

Hereinafter, the liquid crystal display device according to the present embodiment will be described in more detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of the liquid crystal display device of the present embodiment. As shown in FIG. 1, the liquid crystal display device includes a liquid crystal panel 10 and a planar light source 20 serving as a backlight. The liquid crystal panel 10 having the same configuration as the conventional liquid crystal panel can be used. For example,
On the surface, a glass substrate 1 having thin film transistors and electrodes 12, 13 as pixel driving elements and an alignment layer (not shown)
1, a glass substrate 17 having a common electrode 16 and an alignment layer (not shown) on its surface, and a liquid crystal cell comprising these glass substrates 11, 12 and a sealing material 14. And a liquid crystal layer 15. In addition,
Although not shown in this sectional view, a thin film transistor and a charge storage capacitor are formed on the glass substrate 11. Each pixel has a basic electric circuit shown in FIG. 5 and writes an image signal by line-sequential scanning. As the liquid crystal layer 15, a general nematic liquid crystal material can be used.

On the other hand, a planar light source 20 using an EL luminous body
Are arranged on the back surface of the liquid crystal panel 10, and the size thereof can be substantially the same as that of the liquid crystal panel. The EL luminous body includes a dispersion type in which a fluorescent material powder is dispersed in a dielectric binder and a vapor-deposited thin film type. Further, the thin film type is classified into an inorganic type and an organic type according to the luminescent material. Any of the planar light sources 20 can be used. Various structures can be used for the EL luminous body. FIG. 1 illustrates a three-layer structure including a hole transport layer, a light emitting layer, and an electron transport layer.

As shown in FIG. 1, a planar light source 20 includes, for example, an anode 23 and a hole transport layer 2 on a glass substrate 21.
4. An EL luminous body having a luminescent layer 25, an electron transport layer 26, and a cathode 27 is formed. The light from the EL illuminator is applied to the liquid crystal panel 10 as more uniform light via the glass substrate 21 and the diffusion layer 22 formed on the light emission surface of the glass substrate 21.

In the EL luminous body, as shown in FIG. 1, an anode 23 is formed in a strip shape on a glass substrate 21, and a hole transport layer 24 is formed so as to cover the anode. On the hole transport layer 24, band-shaped light-emitting layers 25 of R, G, and B light are formed so as to correspond to the band-shaped pattern of the anode 23.
Are formed. These components are covered with a sealing material 28 made of a resin material.

It should be noted that the above-mentioned band-shaped pattern of the anode 23 and the light emitting layer of each color light is arranged so as to be parallel to a scanning line serving as a unit for writing an image signal on the liquid crystal panel 10. The width of the band-shaped pattern is not particularly limited.
The width of the light-emitting layer of a set of three colors G and B is set to a size that divides the pixel region of the liquid crystal panel into a plurality of regions, and preferably divides the pixel region into three or more regions. FIG. 1 shows an example in which the width of each monochromatic light emitting layer is set to a width corresponding to the unit pixel width of the liquid crystal panel.

In this EL luminous body, when a forward voltage is applied between the cathode 27 and the anode 23 of the planar light source 20,
Electrons accumulate near the interface between the light emitting layer 25 and the hole transport layer 24 and recombine with holes injected from the anode to generate excitons. When the exciton disappears, light emission depending on the light emitting material is generated.

The predetermined color light emitted from the planar light source 20 enters the liquid crystal panel 10 from the lower glass substrate 11 and is emitted from the upper glass substrate 17. In the course of passing through the liquid crystal layer 15 on the way, the light is modulated and emitted according to the alignment state of the liquid crystal according to the pixel signal.

The liquid crystal panel is driven by line-sequential scanning basically similar to the conventional one. That is, as shown in FIG.
For example, a scan signal is applied to a gate electrode line Yj, which is a scanning line, and source electrode lines X _i , X
_The image signals are simultaneously applied to _{i + 1} ,..., and the image signals are simultaneously written to the capacitors 2 of the pixel group in one column in the X direction.
This signal scanning is performed for each scanning gate electrode line.
j, Yj + 1,... When the scanning of all the gate electrode lines is completed, the writing of the screen with respect to the monochromatic light (one field) is completed.

FIG. 2 shows that the planar light source 20 is divided into three parts.
It is a time series showing a light emitting state of a light emitting surface when three sets of band-shaped regions each including a light emitting layer of three colors G and B are formed. Note that, on the corresponding liquid crystal panel, first, an image signal corresponding to the R color is written from top to bottom in the drawing,
Next, it is assumed that writing proceeds line-sequentially in the order of B color and G color.

As shown in FIG. 2, the planar light source 2 in this case is
0, at T1, R light is emitted in the upper one-third band region at the light-emitting surface, the light emitter in the middle band region is in the OFF state, and the lower one-third.
B light is emitted in the band region of. At T2, top 1
The R light is emitted in the three regions and the intermediate region, and the light emitter is turned off in the lower third region. Further, at T3, the upper 1/3 region is turned off, and the R light is emitted in the middle region and the lower 1/3 region. Similarly, G light from T4 to T9,
The B light is illuminated line-sequentially. As described above, in the planar light source 20 of the present embodiment, the light emitting layer of the color light corresponding to the line-sequential line-by-line is turned on and off in accordance with the writing scan of the line-sequential image signal on the liquid crystal panel. Is R,
The liquid crystal panel 10 is irradiated with three-color light by repeating each of the G and B color lights.

As described above, when a plurality of sets of band-shaped light-emitting layers including light-emitting layers of at least three colors of R, G, and B are formed, unlike a conventional planar light-emitting layer using a cold-cathode tube, In synchronization with the line-sequential scanning of the panel, light can be emitted for each light-emitting layer in the strip-shaped region of the light-emitting layer at the corresponding location. Therefore, it is not necessary to wait for the completion of the writing of the image signal to all the pixels of the liquid crystal panel in performing the light emission of the planar light source 20, so that the light-off time loss of the light emitting source can be shortened as compared with the related art.

If the light emitting layer is divided into finer band-like regions, light emission can be further performed in accordance with the writing scan of the liquid crystal panel. FIG. 3 shows a planar light source 20 (EL light source).
FIG. 3 is a diagram for explaining respective driving states of the liquid crystal panel and the planar light source 20 when a band-shaped light emitting layer of each color light is formed with an accuracy substantially equivalent to the pixel density of a liquid crystal panel (LCD). The driving state of the liquid crystal panel 10 is shown on the upper side of FIG.
4 illustrates a driving state of an L light source. The position of the scanning line is taken in the vertical direction and time is taken in the horizontal direction.

As shown in the figure, the basic operation of the LCD is as follows.
The operation is basically the same as the operation of the conventional liquid crystal panel shown in FIG. The image signal is written on the screen line-sequentially as described above. As in the related art, there is a time loss due to the response time of the liquid crystal between screen displays for each color light.

On the other hand, the EL light source emits each color light in a line-sequential manner in synchronization with the line-sequential drive of the LCD, so that the EL light source shows a driving state almost similar to the figure showing the driving state of the liquid crystal panel. Accordingly, the effective lighting time in one field becomes longer, and more efficient irradiation to the liquid crystal panel becomes possible. Further, it is possible to increase the brightness of the screen by increasing the effective lighting time of the light source. Further, when the planar light source is ON / OFF driven in units of planes as in the related art, it is necessary to increase the driving scanning speed of the liquid crystal panel and shorten the scanning time loss. In the case of the embodiment, since the operation of the EL light source is synchronized with the line-sequential scanning of the LCD, the problem of scanning time loss is small. As a result, it is possible to further reduce the demand for the operation speed of the transistor mounted on the liquid crystal panel. Also, 1
Since the scanning time per field has a margin, it is easy to increase the number of scanning lines of the liquid crystal panel. Therefore, it can be applied to a higher definition liquid crystal panel and a larger liquid crystal panel.

Next, a method of manufacturing a planar light source using an EL luminous body will be described. Although a general-purpose EL manufacturing method can be used, for example, the following method may be used. Hereinafter, description will be made with reference to FIG.

First, a glass substrate 2 having a thickness of 0.5 to 1 mm
A transparent electrode (for example, ITO (Indium Tin Oxide)) is formed on the substrate 1 by using sputtering or vacuum evaporation. Thereafter, the transparent electrode is etched using a photolithography process to form a strip electrode. For example, a striped anode 23 having a line width of several hundred μm and a line interval of several tens μm is formed. Note that patterning may be performed by performing mask evaporation during direct sputtering.

Next, a hole transport layer 24 made of a diamine derivative having a thickness on the order of μm is formed by vapor deposition so as to cover the surface on which the anode 23 is formed. Further, on the hole transport layer 24, a light emitting layer 25 having each of R, G, and B emission colors is separately applied in accordance with the pattern of the strip electrode. For example, when a red light emitting layer is first formed, ZnS: Sm (light emitting center Sm (samarium)) which is a light emitting center was added.
ZnS (hydrogen sulfide)) is formed by a method such as vapor deposition or the like, and thereafter, this is patterned into a belt shape. Next, ZnS: Tb (Zn added with emission center Tb (terbium)) which is a green light emitting layer
S) is formed by vapor deposition. At this time, a resist pattern is formed in advance, and an unnecessary portion of the film is removed by a lift-off method after the vapor deposition. Further, as a blue light emitting layer, Sr
S: Ce (Ce (cerium) to which luminescence center SrS (strontium sulfide) is added) is also formed by vapor deposition using a lift-off method, and then unnecessary portions of the film are removed together with the resist.
Thus, a band-shaped pattern of the light emitting layer 25 for each of the R, G, and B light is formed.

After the formation of the light emitting layer 25, an aluminum chelate complex having a thickness of the order of μm is formed on the entire surface of the light emitting layer 25 as an electron transport layer 26 thereon. Furthermore, with a thickness of several hundred
1 of the cathode 27 is formed.

Finally, these laminates are covered with a sealing material 28 made of plastic or glass material, and the gap is sealed with an adhesive resin such as epoxy or acrylic resin, so that the laminates are shielded from the outside air. . When the diffusion layer 22 is attached to the back surface of the glass substrate 21, the planar light source 20 is completed.

Thereafter, by disposing the planar light source 20 on the back surface of the liquid crystal panel manufactured by using a conventional method or the like, the liquid crystal display device according to the present embodiment can be formed.

Since the EL luminous body is formed of a thin film, fine patterning is possible, and the above-mentioned band shape can be obtained relatively easily. Also, since each layer forming the EL luminous body is a thin film on the order of μm, the thickness can be greatly reduced as compared with a conventional planar light source using a cold cathode tube, and the entire liquid crystal display device can be made compact. Can be achieved. Further, since the EL luminous body is planar, unevenness in brightness and uneven color is less likely to occur as compared with the case where a conventional cold cathode tube is used.

Although the liquid crystal display device of the present invention has been described in connection with the present embodiment, the present invention is not limited to the description of the embodiment, and various modifications and improvements are possible. Some will be obvious to those skilled in the art.

[0043]

As described above, according to the liquid crystal display device of the present invention, since the EL light emitting layer is used as the planar light source, it is possible to provide a thin and compact display device with less uneven brightness and color. Since the surface light source can emit light by line-sequential scanning in synchronization with the scanning of the liquid crystal panel, higher luminance can be achieved by more efficient light emission. Response is also possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 illustrates an EL of a liquid crystal display device according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating a light emitting state of a light source.

FIG. 3 is a diagram for explaining a driving state of a liquid crystal panel and an EL light source of the liquid crystal display device according to the embodiment of the present invention.

FIG. 4 is a sectional view of a conventional liquid crystal display device.

FIG. 5 is a diagram showing an equivalent electric circuit of each pixel of the liquid crystal panel.

FIG. 6 is a diagram for explaining a driving state of a liquid crystal panel and a planar light source of a conventional liquid crystal display device.

[Explanation of symbols]

 Reference Signs List 10 liquid crystal panel 11, 17, 21 glass substrate 12, 13 electrode 14 sealant 15 liquid crystal layer 16 common electrode 20 planar light source (EL light source) 22 diffusion layer 23 anode 24 hole transport layer 25 light emitting layer 26 electron transport layer 27 Cathode 28 Sealant

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/34 G09G 3/34 J 3/36 3/36 F term (Reference) 2H091 FA44Z GA13 LA17 LA18 2H093 NA43 NC16 NC34 NC35 NC43 NC44 ND04 ND09 ND17 ND42 5C006 AA22 AF42 AF71 BB15 BB29 FA16 FA41 5C080 AA06 AA10 BB05 CC03 DD01 DD22 EE30 FF11 JJ01 JJ06 5G435 AA04 BB05 BB12 BB15 CC09 CC12 EE23 EE26

Claims (2)

[Claims] A first transparent substrate having, on its surface, a plurality of scanning lines, a plurality of signal lines intersecting the plurality of scanning lines, and pixel driving elements arranged in a matrix at each intersection; A second transparent substrate disposed so as to oppose the surface of the substrate and having a transparent common electrode formed on the opposing surface; and a liquid crystal sandwiched between the first transparent substrate and the second transparent substrate. A liquid crystal panel having a plurality of layers; a plurality of light emitting regions arranged on a back surface of the liquid crystal panel and divided into strips parallel to the scanning lines of the liquid crystal panel; B. A liquid crystal display device comprising: a planar light source having an independent band-shaped EL light-emitting layer. 2. The method for driving a liquid crystal panel according to claim 1, wherein the pixel driving elements of the liquid crystal panel are driven line by line for each scanning line, and the scanning is performed in synchronization with the driving. A driving method of a liquid crystal display device, wherein a light emission operation is performed in a line-sequential manner on the strip-shaped light-emitting area at a position corresponding to a line.