JP2002023145A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a liquid crystal display device with fast response and wide viewing angle. SOLUTION: The device has a liquid crystal layer 1, polarization selective layer 2 and fluorescent layer 3, and the polarization state (c) of the exciting light 4 is modulated by the liquid crystal layer 1 to generate a polarization state (b), which excites the phosphor to obtain fluorescent light 5 as the display light. Since the fluorescent light from the fluorescent layer 3 is used, display with a wide viewing angle can be obtained. Moreover, the polarizing selective layer 2 and fluorescent layer 3 can be formed inside of the liquid crystal panel, no misalignment in the view field is caused. Since the exciting light is modified into a narrow band, a fast-response liquid crystal mode such as pi liquid crystal can be used without using an optical compensator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, the development of liquid crystal displays (LCDs) has been remarkable. In particular, LC for monitor applications
In D, the screen size is steadily increasing. Along with this, many publications have alleviated the viewing angle dependency, which is a problem in large-screen LCDs. There have also been announcements that attempt to solve the problem of slow LCD display operations. As described above, in the future LCD development, there is a wide demand for improvement in image quality performance such as a wide viewing angle and moving image display.

[0003] In the above background, a wide viewing angle LCD using a fluorescent layer has been newly proposed. This example is shown in Table 9-
It can be seen in JP-A-511588 and JP-A-11-237632. FIG. 13 shows a structure disclosed in Japanese Patent Publication No. 9-511588. In this structure, two polarizing plates 4
A fluorescent layer 43 is provided on a twisted nematic (TN) liquid crystal panel 42 having 0, 41. Ultraviolet light or blue or near-ultraviolet light is incident from the back of the liquid crystal panel 42. This incident light is modulated by the TN liquid crystal panel 42. The light emitted from the TN liquid crystal panel 42 modulated as described above hits the fluorescent layer 43 and emits fluorescence. Since the fluorescent light is generated almost isotropically, a display which is visible from any direction can be obtained.

However, in the configuration of FIG. 13, since the upper glass substrate 44 is thick, the excitation light reaches the fluorescent layer 43 until the excitation light reaches the fluorescent layer 43.
It diffuses in the horizontal direction. For this reason, there is a problem that the excitation light emitted from a certain liquid crystal panel pixel reaches the adjacent fluorescent layer 43, and display blur occurs. Also,
A similar phenomenon occurs when viewed obliquely, so that the one-to-one correspondence between the liquid crystal panel pixels and the fluorescent layer pixels is shifted.

A method for solving the above-mentioned problems is disclosed in Japanese Patent Application Laid-Open No. 11-237632.
The structure of FIG. 14 in which the fluorescent layer 43 and the polarizing plate 40 are formed in 46 is exemplified. Further, a configuration shown in FIG. 15 that is easier to form in the glass substrates 45 and 46 has also been proposed. FIG.
Will be described. Of the blue light emitted from the blue light source 47, only the left circularly polarized light passes through the right-handed cholesteric liquid crystal layer 48. This left circularly polarized light becomes linearly polarized light by the λ / 4 plate 49 and enters the STN liquid crystal layer 50. If the STN liquid crystal layer 50 emits light with linearly polarized light, the λ / 4
The light is converted to right circularly polarized light by the plate 51. Further, if the right-handed cholesteric liquid crystal layer 52 is disposed, the light is reflected and does not reach the fluorescent layer 43, and does not contribute to display. On the other hand, STN
When the liquid crystal layer 50 converts the linearly polarized light into elliptically polarized light, the λ / 4 plate 51 and the right-handed cholesteric liquid crystal layer 52
Can partially pass through. Accordingly, the blue light reaches the fluorescent layer 43, and fluorescence different from the blue light is generated, which contributes to display. 14 and 15 described above, since the fluorescent layer 43 is formed inside the liquid crystal panel, the correspondence relationship between the fluorescent layer pixels of the liquid crystal panel pixels described above does not shift.

[0006]

However, it is practically difficult to build the structures shown in FIGS. 14 and 15 inside a liquid crystal panel. For example, in the configuration of FIG. 14, it is necessary to form a polarizing plate inside a liquid crystal panel. After forming this polarizing plate layer, it is necessary to form an electrode layer and an alignment film as shown in FIG. Japanese Patent Application Laid-Open No. 11-237632 describes an STN liquid crystal mainly. However, a thin film transistor (TFT) driven LC
In D, it is required to form each layer of the TFT in addition to the above-mentioned electrode layer and alignment film.

Generally, a polarizing plate is produced by dyeing a uniaxially stretched polymer with a dichroic dye. Therefore, the upper limit of the heat resistance is about 100 ° C. However, the above T
The formation of each layer of FT, the electrode layer, and the alignment film requires a high temperature of 200 ° C. or more, and it is almost impossible to form them. Further, in the configuration of FIG. 15, λ / 4 plates 49 and 51 and cholesteric liquid crystal layers 48 and 52 are used instead of the polarizing plate.
Must be built inside the LCD panel. Both layers may have higher heat resistance than the above-mentioned polarizing layers. However, it is practically difficult to form each of the TFT layers, electrode layers, and alignment films that require even higher temperatures for formation. Accordingly, the present invention provides a liquid crystal display device capable of obtaining a display screen with a wide viewing angle, high-speed response, and high brightness.

[0008]

According to the liquid crystal display device of the present invention, the excitation light passes through at least the liquid crystal layer 1, the polarization selection layer 2, and the fluorescent layer 3, as shown in FIG. Be composed. The operation will be described below.
Has the function of reflecting light of a certain polarization state (a) at a certain wavelength and transmitting light of the same polarization and another polarization state (b).
Excitation light 4 in a certain polarization state (c) enters the liquid crystal layer 1 and is converted into a polarization state (a). At this time, since the polarization selection layer 2 reflects this light, it does not reach the fluorescent layer 3 and does not contribute to display. When a voltage is applied to the liquid crystal, its birefringence changes. At this time, when the excitation light 4 having a certain polarization state (c) enters the liquid crystal layer 1 and is converted into the polarization state (b), the excitation light 4 passes through the polarization selection layer 2 and the fluorescent layer 3 generates the fluorescent light 5. I do. As described above, according to the first aspect of the present invention, the display operation can be performed with a simple configuration in creation.

The polarization selection layer 2 can be realized by the following two configurations. The invention according to claim 2 is a liquid crystal display device, wherein the polarization selection layer 2 according to claim 1 is formed of a cholesteric liquid crystal layer. This includes a cholesteric liquid crystal layer 6 having a helical structure as shown in FIG. When the cholesteric liquid crystal layer 6 is twisted right, it reflects right circularly polarized light 8 and transmits left circularly polarized light 7.
The wavelength at this time is determined by the helical pitch of the cholesteric liquid crystal.

A third aspect of the present invention is a liquid crystal display device, wherein the polarization selective layer 2 of the first aspect has an alternating multilayer structure 9 including at least one layer having anisotropy. . This operation will be described with reference to FIG. In this case, the multilayer structure is two types (x, y) of alternately laminated structures. The refractive indexes of the x layer 10 and the y layer 11 are different in the p-polarized light 12 direction and the s-polarized light 13 direction. If the x layer 10 in the p polarization direction
When the refractive index of the y-layer 11 is the same as that of the y-layer 11, the p-polarized light 12 can pass. On the other hand, the x layer 10 and the y layer
When the refractive index of the layer 11 is different, the s-polarized
3 is reflected. This wavelength is determined by the cycle of the alternate lamination. The matching / mismatching of the refractive indices in the polarization direction as described above can be realized when at least either the x layer 10 or the y layer 11 is anisotropic. As described above, linearly polarized light (p-polarized light 1
When 2 or s-polarized light 13) is incident, it is possible to reflect only specific linearly polarized light of a specific wavelength.

According to a fourth aspect of the present invention, there is provided a liquid crystal display device wherein the polarization selection layer 2 and the fluorescent layer 3 are formed inside the liquid crystal panel of the first aspect. It is possible to form the above-described polarization selection layer 2 and fluorescent layer 3 on a glass substrate. If a liquid crystal panel is subsequently formed, the polarization selection layer 2 and the fluorescent layer 3 can be easily formed inside the liquid crystal panel.

According to a fifth aspect of the present invention, in the liquid crystal display device of the fourth aspect, the polarization selection layer 2 and the fluorescent layer 3 are provided on a counter substrate of a liquid crystal panel having an active element array. A liquid crystal display device characterized by the following. This will be described with reference to FIG. FIG. 4 shows a thin film transistor (T
It comprises an active element array substrate 14 such as FT) or diode (MIM), and a counter substrate 15 having the polarization selection layer 2 and the fluorescent layer 3. In the present invention, the active element array substrate 14 can follow a conventional substrate manufacturing method. The only point to be changed is the counter substrate 15, which can be manufactured without greatly changing the manufacturing process of the conventional liquid crystal panel.

According to a sixth aspect of the present invention, there is provided a liquid crystal display device comprising at least a flattening layer between the fluorescent layer 3 and the polarization selection layer 2 on the counter substrate 15 according to the fifth aspect. The fluorescent layer 3 can be roughly made of either an inorganic substance or an organic substance. After the fluorescent layer 3 is formed, it is necessary to sequentially stack the polarization selection layer, the electrode layer, and the liquid crystal alignment layer. For this reason, since the fluorescent layer 3 experiences a relatively high temperature, the fluorescent layer 3 made of an inorganic material having excellent heat resistance is advantageous. However, the inorganic fluorescent substance is often particles of about several microns, and the surface of the inorganic fluorescent substance has an uneven structure. This concavo-convex structure adversely affects the polarization selection layer and the liquid crystal alignment later. Such an adverse effect can be solved by forming a flattening layer on the surface of the inorganic fluorescent substance.

According to a seventh aspect of the present invention, there is provided a liquid crystal display device having at least an alignment layer between the fluorescent layer 3 and the polarization selection layer 2 on the counter substrate 15 according to the fifth aspect. When forming the above-described polarization selection layer 2, its azimuth axis must be set. For example, in FIG. 2, the orientation direction of the cholesteric liquid crystal layer 6 must be defined. In the anisotropic alternating multilayer structure shown in FIG. 3, the direction of anisotropy must be determined. The setting of the azimuth axis as described above is performed by forming an alignment layer immediately before forming the polarization selection layer 2 and performing a subsequent alignment process.

According to an eighth aspect of the present invention, there is provided a liquid crystal display device having at least a wavelength selection layer between the fluorescent layer 3 and the polarization selection layer 2 on the counter substrate 15 according to the fifth aspect. This will be described with reference to FIG. Wavelength selection layer 1
The excitation light 4 transmitted through 6 enters the fluorescent layer 3. The fluorescent layer 3 emits fluorescent light 5 isotropically. Therefore, the fluorescence 5 emitted in the direction of the display surface is roughly half or less. The remaining fluorescent light 5 goes to the wavelength selection layer 16 again. Since the wavelength of the fluorescence 5 is different from the wavelength of the excitation light, the fluorescence 5 passes through the wavelength selection layer 16. For this reason, only less than half of the total fluorescence is obtained as display light. In order to solve this, FIG.
As shown in the figure, the wavelength selection layer 16 is made up of the fluorescent layer 3 and the polarization selection layer 2.
It is inserted between. The wavelength selection layer 16 can be formed using a high refractive index layer and a low refractive index layer while controlling the thickness of each layer. This design technique is widely performed using numerical calculations. If the wavelength selection layer 16 is designed using the above-described design method, the wavelength selection layer 16 is designed to transmit the excitation light wavelength.
Further, it is possible to reflect fluorescence having a wavelength longer than the wavelength of the excitation light. For this reason, the fluorescence 5 that is going to return to the polarization selection layer 2 is
The light is reflected by the wavelength selection layer 16 and can contribute to display. As described above, according to the present invention, the display can be made brighter.

According to a ninth aspect of the present invention, there is provided the liquid crystal display device according to the first aspect, wherein the liquid crystal display device has a light reducing layer. This will be described with reference to FIG. Generally, a display device is used under room lighting. For this reason, in the case of the present invention, the user's eyes simultaneously see the influence of the room light 17 in addition to the display fluorescence. More specifically, it is as follows. As described above, the surface of the inorganic fluorescent layer has an uneven structure. For this reason, when the room light 17 is incident on the back surface of the fluorescent layer 3, it is scattered, and the user sees the scattered light at the same time. In addition, the room light 17 becomes excitation light, enters from the back surface of the fluorescent layer 3, and newly generates fluorescence. Due to the influence of the room light 17 as described above, even if there is no display fluorescence, the user perceives a certain amount of light, and the contrast ratio of the displayed image is reduced. The above problem can be solved by disposing the dimming layer 18 between the fluorescent layer 3 and the user as shown in FIG. That is, the room light 17 passes through the light-reducing layer 18 and enters the fluorescent layer 3, and scattered light from the room light 17 passes through the light-reducing layer 18 again. That is, it must pass through the dimming layer 18 twice to get into the eyes of the user. On the other hand, the display fluorescence passes through the dimming layer 18 once and reaches the user's eyes. For this reason, the display fluorescence is slightly darkened, but the contrast of the room light 17 is dramatically improved because the effect of the light reducing layer 18 is effective twice.

According to a tenth aspect of the present invention, there is provided a liquid crystal display device according to the ninth aspect, wherein the dimming layer is disposed on the surface of the counter substrate. FIG. 8 shows the simplest configuration for realizing the above-described invention. According to this structure, the dimming layer 18 may be formed on the liquid crystal panel surface in addition to the configuration described in claim 5. In the simplest case, it is only necessary to attach the film-like light reducing layer 18 to the liquid crystal panel surface. Therefore, the contrast can be more easily improved. In the drawing, 19 indicates a light shielding layer, 20 indicates a light distribution film, and 21 indicates a polarized light excitation light source.

According to an eleventh aspect of the present invention, there is provided a liquid crystal display device having a lens array or a waveguide array on the counter substrate 15 according to the fifth aspect. This will be described with reference to FIG. It has already been described that the fluorescent light 5 from the fluorescent layer 3 is generated almost isotropically. Among them, only fluorescent light that can be emitted from the glass substrate can be display light.
However, of the light incident on the glass substrate-air interface, only light within a certain angle can be emitted into the air. This angle is determined by the refractive index of the glass substrate. Therefore,
As shown in FIG. 9, a lens 22 is formed for each pixel unit, the optical path is bent, and the fluorescent light 5 is emitted in the air. Thereby, it is possible to improve the brightness of the display screen. Although the case where the lens array is used has been described, the same effect can be obtained by using the waveguide array.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. In FIG. 10, an amorphous silicon thin film transistor array substrate 23 is used as an active element array substrate. As is well known, the amorphous silicon thin film transistor array substrate 23 can be formed by repeating a film formation and a photolithography process on a glass substrate. An alignment film 20 is formed on the substrate, and a rubbing process is performed. As described above, the amorphous silicon thin film transistor array substrate 23 is completed. Further, the counter substrate 15 can be formed as follows. A resin containing a phosphor is printed on a glass substrate. At this time, if printing is performed three times while changing the type of the phosphor 3, the phosphor layer 3 corresponding to the R, G, and B color pixels is completed. The above fluorescent layer 3 is excellent in heat resistance, but is in a rough surface state. Therefore, the surface unevenness is filled by covering the flattening layer 24 made of an organic resin.

The surface of the flattening layer 24 is subjected to a known rubbing treatment. Thereafter, a UV-curable cholesteric liquid crystal solution is applied. The pitch of the cholesteric liquid crystal is adjusted to be about twice the wavelength of the excitation light. Thereafter, the cholesteric liquid crystal layer 6 is cured by irradiating ultraviolet rays so that a stable structure is obtained. As described above, a polarization selective layer can be obtained. Thereafter, the light shielding layer 19 is formed by a photolithography process. This light-shielding film prevents fluorescence from the fluorescent layer 3 from entering the thin film transistor. Further, an alignment film 20 is formed and a rubbing process is performed. As described above, the counter substrate 15 is completed.

The above-mentioned amorphous silicon thin film transistor array substrate 23 and counter substrate 15 are bonded so that the rubbing directions are antiparallel. Thereafter, a nematic liquid crystal (homogeneous liquid crystal layer 25) is injected in a vacuum to seal the hole. At this time, the product Δnd of the distance d between the two substrates and the refractive index anisotropy Δn of the liquid crystal is set so that switching can be performed in the wavelength range of the excitation light. Thereafter, the polarizing plate 26 is attached to the back surface of the amorphous silicon thin film transistor array substrate 23. Further, the film-shaped light-reducing layer 18 is formed on
Paste on the back of 5. The above liquid crystal panel is disposed on a planar excitation light source including a black light source 28 and a light guide plate 27.

Next, a second embodiment will be described with reference to FIG. The amorphous silicon thin film transistor array substrate 23 can be formed by the method described above. On the other hand, the counter substrate 15 is formed as shown in FIG. A high refractive index layer 29 is formed on the counter substrate 15 (a). A photoresist layer 30 is formed thereon, and is exposed using a mask 31 (b). The obtained photoresist pattern can be deformed into a lens shape by performing an appropriate heat treatment and reflowing (c). Using this deformed photomask layer as a mask,
The high refractive index layer 29 is formed and processed (d). This is obtained by etching. At this time, if the photoresist layer 30 and the high refractive index layer 29 can be made to have the same etching rate, the shape of the photoresist layer 30 can be dug into the high refractive index layer 29 as it is (e).
Thereafter, an ultraviolet curable low refractive index layer 32 is applied, and a focal length adjusting substrate 33 is adhered to form a lens array (f). If the thickness of the focal length adjusting substrate 33 can be maintained at the focal length of the lens array,
Fluorescence from the fluorescent layer can be more efficiently collected.

Thereafter, as shown in FIG.
And G and B three times. Further, a flattening film 24 is applied to flatten the surface of the fluorescent layer 3. Thereafter, the wavelength selection layer 35 is formed by a vacuum evaporation method. For example, a desired wavelength selection layer 35 can be formed by stacking a large number of silicon oxide films and titanium oxide films. An alignment film 20 is applied to this surface, and a rubbing process is performed. The cholesteric liquid crystal polymer 34 is applied on the alignment film while heating the substrate. The pitch of the cholesteric liquid crystal polymer 34 is adjusted to be twice the wavelength of the excitation light. Thereafter, when the temperature is rapidly returned to room temperature, the cholesteric liquid crystal polymer 34 freezes and becomes stable at room temperature. Further, a light shielding film 19 is formed and molded. This light shielding film 19
Light is prevented from entering the thin film transistor. An alignment film 20 is further formed on the light-shielding film, and a rubbing process is performed. The manufacture of the counter substrate 15 is completed as described above.

The substrates 15, 2 obtained as described above
3 are bonded so that the rubbing directions are antiparallel.
By injecting the nematic liquid crystal into the gap between the two substrates, a display operation based on the pi-type liquid crystal can be performed. A quarter-wave plate 37 and a polarizing plate 26 are attached to one surface of the liquid crystal panel, and the dimming layer 18 is attached to the other surface. Blue light source 3
This is completed by arranging a backlight light source composed of the light guide plate 6 and the light guide plate 27. Further, when a ferroelectric liquid crystal or an antiferroelectric liquid crystal is used as the liquid crystal, higher-speed operation can be performed.

[0025]

As described above, according to the present invention, a wide-field liquid crystal display device using fluorescence can be obtained. In particular, in nematic liquid crystals, high-speed response and high contrast ratio,
It has been conventionally difficult to achieve both high-speed response and high transmittance.

That is, it has been known that a homogeneous liquid crystal or a pie-type liquid crystal having no twist structure in a liquid crystal layer operates at a high speed, but cannot display black by itself.
In order to obtain a black display, a combination with an optical compensator is required. However, as described above, it is necessary to exactly match the birefringence of the optical compensator and the liquid crystal layer, the production margin is narrow, and it has been practically difficult to obtain a high contrast ratio. For this reason, even if the liquid crystal response was fast, it was not compatible with a high contrast ratio. However, according to the present invention, since the excitation light has almost a single wavelength, the excitation light can be turned on and off without using an optical compensator. Therefore,
High-speed response and high contrast ratio of liquid crystal can be compatible.

On the other hand, it has been known that the thickness of the liquid crystal layer is reduced as an effective means for responding the nematic liquid crystal at high speed. However, when the thickness of the liquid crystal layer is reduced, the amount of birefringence decreases. For this reason, there has been a problem that the maximum amount of light during transmission cannot be secured. As described above, the conventional nematic liquid crystal cannot achieve both high-speed response and high transmittance. However, in the present invention, the amount of birefringence of the liquid crystal layer only needs to be about the short wavelength of the excitation light, and a large amount of fluorescence can be obtained with a thin liquid crystal layer. As described above, by using the liquid crystal display device of the present invention, a display screen having a wide viewing angle, high-speed response, and high luminance can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating the invention described in claim 1;

FIG. 2 is a diagram illustrating an optical operation of a cholesteric liquid crystal layer, which is a main part of claim 2.

FIG. 3 is a diagram illustrating an optical operation of an anisotropic alternating multilayer structure, which is a main part of claim 3;

FIG. 4 is a configuration diagram for explaining the invention described in claim 5;

FIG. 5 is a configuration diagram for explaining the invention described in claim 8;

FIG. 6 is a schematic diagram showing the influence of room light for explaining the invention described in claim 9;

FIG. 7 is a configuration diagram for explaining the invention described in claim 9;

FIG. 8 is a configuration diagram for explaining the invention described in claim 10;

FIG. 9 is a configuration diagram for explaining the invention described in claim 11;

FIG. 10 is a configuration diagram of a first embodiment of the present invention.

FIG. 11 is a configuration diagram of a second embodiment of the present invention.

FIG. 12 is a schematic diagram of a creation method according to the second embodiment.

FIG. 13 is a configuration diagram illustrating a conventional technique.

FIG. 14 is a configuration diagram illustrating a conventional technique.

FIG. 15 is a configuration diagram illustrating a conventional technique.

[Explanation of Symbols] 1 ... liquid crystal layer 2 ... polarization selection layer 3 ... fluorescent layer 4 ... excitation light 6 ... cholesteric liquid crystal layer 9 ... alternating multilayer structure 14 ... active element array substrate 15 ... counter substrate 16 ...・ Wavelength selection layer 18 ・ ・ ・ Darkening layer 22 ・ ・ ・ Lens 24 ・ ・ ・ Planarization layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA05 BA43 BB64 BC22 2H091 FA07Y FA29X FA41Z FA50X FB02 FB06 FC12 FC22 FD06 GA01 GA06 HA07 HA10 LA19 LA30 5C094 AA06 AA08 AA10 AA12 AA13 BA03 BA12 BA32 DA04 ED01 ED03 ED20 5G435 AA00 AA02 AA03 AA04 BB12 BB15 CC09 DD11 EE25 FF05 FF08 FF11 GG02 GG11 HH06

Claims (11)

[Claims] 1. A liquid crystal display device in which excitation light passes through at least a liquid crystal layer, a polarization selection layer, and a fluorescent layer. 2. The liquid crystal display device according to claim 1, wherein the polarization selection layer comprises a cholesteric liquid crystal layer. 3. The liquid crystal display device according to claim 1, wherein the polarization selection layer has an alternating multilayer structure including at least one layer having anisotropy. 4. The liquid crystal display device according to claim 1, wherein at least a polarization selection layer and a fluorescent layer are formed inside the liquid crystal panel. 5. The liquid crystal panel has an active element array, and has at least a polarization selection layer on a counter substrate of the liquid crystal panel.
The liquid crystal display device according to claim 4, further comprising a fluorescent layer. 6. The device according to claim 5, wherein at least a flattening layer is provided between the fluorescent layer and the polarization selection layer on the counter substrate.
3. The liquid crystal display device according to 1. 7. The liquid crystal display device according to claim 5, further comprising at least an alignment layer between the fluorescent layer and the polarization selection layer on the counter substrate. 8. The liquid crystal display device according to claim 5, further comprising at least a wavelength selection layer between the fluorescent layer and the polarization selection layer on the opposing substrate. 9. The liquid crystal display device according to claim 1, further comprising a dimming layer. 10. The liquid crystal display device according to claim 5, wherein the light reducing layer according to claim 9 is disposed on a surface of the counter substrate. 11. The liquid crystal display device according to claim 5, wherein a lens array or a waveguide array is provided on the opposing substrate.