WO2002005021A1

WO2002005021A1 - Liquid crystal display

Info

Publication number: WO2002005021A1
Application number: PCT/JP2001/006041
Authority: WO
Inventors: Ken Sumiyoshi
Original assignee: Nec Corporation
Priority date: 2000-07-12
Filing date: 2001-07-12
Publication date: 2002-01-17
Also published as: JP2002023145A

Abstract

A liquid crystal layer (14), a polarization selecting layer (24), and a fluorescence layer (22) are formed in this order in a path of pumping light. The polarization selecting layer (24) may be a cholesteric liquid crystal layer or an alternate multilayer structure including a layer having at least one anisotropy. A liquid crystal panel in which a polarization selecting layer and a fluorescence layer are formed may be used.

Description

Specification

Technical field

The present invention relates to a liquid crystal display device. Background art

In recent years, the development of liquid crystal displays (LCDs) has been remarkable. In particular, LCDs for monitors are steadily increasing in screen size. Along with this, many publications have alleviated the viewing angle dependency, which is an issue for large-screen LCDs. Also, there are announcements that attempt to solve the problem of slow LCD display operation. As mentioned above, in the future LCD development, image quality performance improvement such as wide viewing angle and moving image display is widely demanded.

A wide viewing angle LCD using a fluorescent layer has been proposed. An example of this can be seen in Japanese Patent Application Laid-Open No. 9-5111588 / Japanese Patent Application Laid-Open No. Hei 11-237632. Fig. 1 shows the structure disclosed in Japanese Patent Publication No. 9-51 1588. In this structure, a fluorescent layer 63 is provided on a twisted nematic (TN) liquid crystal panel 62 having two polarizing plates 60 and 61. Irradiate ultraviolet light, blue light or near-ultraviolet light from the back of the liquid crystal panel 62. This incident light is modulated by the TN liquid crystal panel 62. The light emitted from the TN liquid crystal panel 62 modulated as described above hits the fluorescent layer 63 and emits fluorescence. Since the fluorescent light is generated almost isotropically, a display that can be viewed from any direction can be obtained.

However, in the configuration of FIG. 1, since the upper glass substrate 64 is thick, the excitation light diffuses in the horizontal direction before reaching the fluorescent layer 63. For this reason, there is a problem in that the excitation light emitted from a certain liquid crystal panel pixel reaches the adjacent fluorescent layer 63, and a display droop occurs. In addition, the same phenomenon occurs when viewed from an oblique direction, so that the one-to-one correspondence between the liquid crystal panel pixels and the fluorescent layer pixels is shifted.

As a method for solving the above problems, as shown in JP-A-11-237632, a fluorescent layer 63 and a polarizing plate 60 are formed in glass substrates 65 and 66 as shown in FIG. The configuration shown in FIG. 3 has been proposed which can be easily formed in glass substrates 65 and 66.

The configuration of FIG. 3 will be described. Of the blue light emitted from the blue light source 67, only the left circularly polarized light passes through the right-handed cholesteric liquid crystal layer 68. This left circularly polarized light becomes linearly polarized light by the ΛΖ4 plate 69 and enters the STN liquid crystal layer 70. If the STN liquid crystal layer 70 emits light with linear polarization, the light is converted into right-handed circularly polarized light by the subsequent / 4 plate 71. Further, if the right-handed cholesteric liquid crystal layer 72 is disposed, the light is reflected and does not reach the fluorescent layer 63, and does not contribute to display. On the other hand, when the STN liquid crystal layer 70 converts linearly polarized light into elliptically polarized light, it can partially pass through the の / 4 plate 71 and the right-handed cholesteric liquid crystal layer 72. Accordingly, the blue light reaches the fluorescent layer 63, and fluorescence different from the blue light is generated, which contributes to display. 2 and 3 as described above, since the fluorescent layer 63 is formed inside the liquid crystal panel, the correspondence relationship between the fluorescent layer pixels of the liquid crystal panel element described above does not shift.

However, it is practically difficult to build the configurations shown in FIGS. 2 and 3 inside a liquid crystal panel. For example, in the configuration of FIG. 2, 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, in a thin-film transistor (TFT) -driven LCD, in addition to the above-mentioned electrode layer and alignment film, it is necessary to further form each TFT layer.

Generally, a polarizing plate is produced by dyeing a dichroic dye in a uniaxially stretched polymer. For this reason, the upper limit of heat resistance is about 100 ° C. However, the formation of each layer, electrode layer and alignment film of the above-mentioned TFT requires a high temperature of 200 ° C or more, and it is almost impossible to make them. Further, in the configuration of FIG. 3, the quarter-wave plates 69 and 71 and the cholesteric liquid crystal layers 68 and 72 must be formed inside the liquid crystal panel instead of the polarizing plate. Both layers may have higher heat resistance than the above-mentioned polarizing layers. However, it is practically difficult to create TFT layers, electrode layers, and alignment films that require even higher temperatures.

Therefore, an object of the present invention is to provide a liquid crystal display device capable of obtaining a display screen with a wide viewing angle, high-speed response, and high brightness. Disclosure of the invention

According to the present invention, there is provided a liquid crystal display device comprising a liquid crystal layer, a polarization selection layer, and a fluorescent layer in this order in a path of excitation light.

The polarization selection layer may include a cholesteric liquid crystal layer.

The polarization selection layer may have an alternating multilayer structure including at least one layer having anisotropy.

A liquid crystal panel having the polarization selection layer and the fluorescent layer formed therein may be provided.

The liquid crystal panel may include an active element array and a counter substrate facing the active element array via the liquid crystal layer, and the counter substrate may include the polarization selection layer and the fluorescent layer.

The opposing substrate may include a flattening layer between the fluorescent layer and the polarization selection layer. The counter substrate may include an alignment layer between the fluorescent layer and the polarization selection layer. The counter substrate may have a wavelength selection layer between the fluorescent layer and the polarization selection layer.

The counter substrate may have a lens array.

The opposing substrate may have a waveguide array.

A light-reducing layer may be provided on the downstream side of the fluorescent layer.

The light-reducing layer may include a counter substrate having the polarization selection layer and the fluorescent layer, and the light-reducing layer may be disposed on a surface of the counter substrate. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of an example of a conventional liquid crystal display device.

FIG. 2 is a cross-sectional view of another example of the conventional liquid crystal display device.

FIG. 3 is a cross-sectional view of still another example of the conventional liquid crystal display device.

FIG. 4 is a sectional view of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of the liquid crystal display device of FIG.

FIG. 6 is a diagram for explaining an example of a deflection selection layer included in the liquid crystal display device of FIG. FIG. 7 is a diagram for explaining a modification of the deflection selection layer included in the liquid crystal display device of FIG.

FIG. 8 is a diagram for explaining a modification of the liquid crystal display device of FIG.

FIG. 9 is a diagram for explaining another operation of the liquid crystal display device of FIG.

FIG. 10 is a diagram for explaining another modification of the liquid crystal display device of FIG.

FIG. 11 is a sectional view of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 12 is a diagram for explaining a method of manufacturing the liquid crystal display device of FIG. BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 4, a liquid crystal display device according to a first embodiment of the present invention will be described. The liquid crystal display device shown in FIG. 4 includes a liquid crystal panel 10 having an array plate 13 and a facing plate 5 facing each other via a known liquid crystal layer 14.

The array plate 13 includes a rectangular glass plate 17, a plurality of active elements 18 mounted on one surface of the glass plate 17, that is, an upper surface, and an alignment film covering the glass plate 17 together with the active elements 18. 19 and has. Each active element 18 is, for example, an amorphous silicon thin film transistor, and can be formed on the glass plate 17 by repeatedly performing a film forming step and a photolithography step. The alignment film 19 is subjected to a well-known rubbing treatment.

The opposing substrate 15 includes a rectangular glass plate 21, a plurality of fluorescent layers 22 formed on one surface, that is, a lower surface of the glass plate 21, and an organic layer whose lower surface is planarized by covering the fluorescent layer 22. A planarization layer 23 made of resin, a deflection selection layer 24 covering the lower surface of the planarization layer 23, a plurality of light shielding layers 25 formed on the lower surface of the deflection selection layer 24, and a light shielding layer 25 And an alignment film 26 covering the lower surface of the deflection selection layer 24.

The phosphor layer 22 is formed by printing a resin containing a phosphor on the glass plate 21. At this time, if the printing is performed three times while changing the kind of the phosphor, the phosphor layer 22 can be made to correspond to the R (red), G (green), and B (blue) color pixels. Since the fluorescent layer 3 experiences a relatively high temperature, it is desirable that the fluorescent layer 3 be made of an inorganic material having excellent heat resistance. Phosphors composed of inorganic substances are usually particles of a few micron squares.

The phosphor layer 22 thus produced is excellent in heat resistance, but is often in a rough surface state. Therefore, the unevenness on the surface of the fluorescent layer 22 is filled by providing the flattening layer 24. Rubbing treatment is performed on the surface of the planarization layer 24.

The deflection selection layer 24 can be made as follows. On the surface of the flattening layer 24, a solution of a UV-curable cholesteric liquid crystal 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 is cured by irradiating ultraviolet rays so that a stable structure is obtained. Thus, the polarization selection layer 24 can be obtained.

The light-shielding layer 25 can be formed by one photolithography process. The light shielding layer 25 is for preventing fluorescence from the fluorescent layer 22 from being incident on the active element 18. Further, the orientation film 26 is subjected to a rubbing treatment.

When assembling the liquid crystal panel 10, the above-described array plate 13 and opposing plate 15 are attached to each other so that the rubbing directions are antiparallel. Thereafter, a nematic liquid crystal (homogeneous liquid crystal layer) is injected in a vacuum to seal the liquid crystal, thereby forming a liquid crystal layer 14. At this time, the product of the distance between the array plate 13 and the opposing plate 15 and the refractive index anisotropy of the liquid crystal is set so that switching can be performed in the wavelength range of the excitation light. Thereafter, the polarizing plate 27 is attached to the lower surface of the array plate 13. Further, a light-attenuating film is stuck on the back surface of the counter substrate 15 to form a light-attenuating layer 28. This liquid crystal panel 10 is arranged on a planar excitation light source 33 composed of a light source 31 and a light guide plate 32. Note that a black light is used as the light source 31.

The operation of the liquid crystal display device of FIG. 4 will be described with reference to FIG.

The excitation light from the planar excitation light source 33 passes through at least the liquid crystal layer 14, the polarization selection layer 24, and the fluorescent layer 22. The polarization selection layer 24 has a function of reflecting light of a certain polarization state (a) having a certain wavelength and transmitting light of the same wavelength and another polarization state (b). The excitation light 34 in a certain polarization state (c) enters the liquid crystal layer 14 and is converted into a polarization state (a). At this time, since the polarization selection layer 24 reflects this light, it does not reach the fluorescent layer 22 and does not contribute to display. When a voltage is applied to the liquid crystal layer 14, its birefringence changes. At this time, when the excitation light 34 in a certain polarization state (c) enters the liquid crystal layer 14 and is converted into the polarization state (b), the excitation light 34 passes through the polarization selection layer 24. Fluorescence is generated from 35. Therefore, the liquid crystal display device can perform a display operation with a simple configuration in terms of production. As an example of the polarization selection layer 24, a cholesteric liquid crystal layer 36 having a helical structure as shown in FIG. 6 can be used. When the cholesteric liquid crystal layer 36 is twisted to the right, it reflects right circularly polarized light 37 and transmits left circularly polarized light 38. The wavelength at this time is determined by the helical pitch of the cholesteric liquid crystal. The azimuthal axis of the cholesteric liquid crystal layer 36 is set by forming an alignment layer immediately before forming the polarization selection layer 24 and performing a subsequent alignment process.

As a modification of the deflection selection layer 24, a liquid crystal layer 39 having an alternating multilayer structure including at least one layer having anisotropy as shown in FIG. 7 may be used. In this case, the liquid crystal layer 39 has two types (x, y) of alternately laminated structures. The refractive indices of the X layer 41 and the y layer 42 differ between the p-polarization direction 43 and the s-polarization direction 44. If the refractive index of the X layer 41 and the refractive index of the y layer 42 are the same in the p-polarization direction 43, the p-polarized light can be transmitted. On the other hand, when the refractive index of the X layer 41 and the refractive index of the y layer 42 are different in the s-polarized direction 44, the s-polarized light of a certain wavelength is reflected. This wavelength is determined by the cycle of the alternate lamination. The above-described agreement or mismatch of the refractive indices in the polarization direction can be realized when at least one of the X layer 41 and the y layer 42 is anisotropic. As described above, when linearly polarized light (p-polarized light or s-polarized light) is incident, it is possible to reflect only specific linearly polarized light of a specific wavelength. The azimuth axis of the liquid crystal layer 39 having the alternating multilayer structure is set by forming an alignment layer immediately before forming the polarization selection layer 24 and performing alignment processing thereafter.

A modified example of the liquid crystal display device of FIG. 4 will be described with reference to FIG.

As shown in FIG. 8, it is preferable to interpose a wavelength selection layer 46 between the fluorescent layer 22 and the polarization selection layer 24 on the counter substrate 15. The wavelength selection layer 46 can be formed by using a high refractive index layer and a low refractive index layer and controlling the thickness of each layer. If the wavelength selection layer 16 is designed using this design method, it is possible to transmit the excitation light wavelength and reflect the fluorescence having a longer wavelength than the excitation light wavelength. For this reason, the fluorescent light 5a returning to the polarization selection layer 24 can be reflected by the wavelength selection layer 46 and contribute to display. Therefore, the display can be made brighter.

Generally, a display device is used under room lighting. For this reason, in addition to the display fluorescent light, the indoor light 47 affects the user's eyes. More specifically, since the surface of the fluorescent layer 22 has an uneven structure, when the room light 47 enters the fluorescent layer 22, it is scattered and becomes scattered light. The user also sees the scattered light at the same time. It is also assumed that the room light 47 becomes excitation light and enters the fluorescent layer 22 to generate new fluorescence. Due to the influence of the room light 47, the user perceives a certain amount of light even if there is no display fluorescence, so that the contrast ratio of the displayed image is reduced.

This problem is solved as described below by disposing the light-extinguishing layer 28 between the fluorescent layer 22 and the user as shown in FIGS. The room light 47 passes through the dimming layer 28 and is incident on the fluorescent layer 22, and the scattered light therefrom passes through the dimming layer 28 again. That is, in order for the room hole 47 to enter the user's eyes, it has to pass through the dimming layer 28 twice. On the other hand, the display fluorescence passes through the dimming layer 28 once and reaches the user's eyes. As a result, the display fluorescence is slightly darkened, but the contrast of the room light 47 is dramatically improved because the light-attenuating layer 28 operates twice.

A modification of the liquid crystal display device of FIG. 4 will be described with reference to FIG.

The fluorescent light 35 from the fluorescent layer 22 is generated almost isotropically. Of these, only fluorescent light that can exit the glass plate 21 can be display light. Of the light incident on the interface between the glass plate 21 and the air, only light within a predetermined angle can be emitted into the air. The predetermined angle is determined by the refractive index of the glass plate 21.

Therefore, as shown in FIG. 10, a lens 48 is formed on the glass plate 21 for each pixel unit, and the optical path is bent by the lens 48 to emit the fluorescent light 35 into the air. This makes it possible to improve the brightness of the display screen. Similar effects can be obtained by using a waveguide array in which a waveguide is formed in the glass plate 21 instead of using the lens array in which the lens 48 is formed in the glass plate 21. In short, it is preferable to provide a lens array or a waveguide array on the opposing plate 15.

Next, a liquid crystal display device according to a second embodiment of the present invention will be described with reference to FIG. 11 and FIG. The same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. The array plate 13 can be prepared by the method described above. Here, the fabrication of the opposing plate 15 will be described with reference to FIGS.

A high refractive index layer 49 is formed on a glass plate 21 (a). A photoresist layer 50 is formed thereon, and is exposed using a mask 51 (b). The obtained photoresist pattern is subjected to an appropriate heat treatment, and is transformed into a lens shape by closing the riff. (C :). Using the deformed photoresist pattern 52 as a mask, the high refractive index layer 49 is formed (d). This is obtained by etching. At this time, if the photoresist pattern 52 and the high refractive index layer 49 can be made to have the same etching rate, the shape of the photo resist pattern 52 can be dug into the high refractive index layer 49 as it is. it can.残存 The remaining portion of the refractive index layer 49 is indicated by reference numeral 49 '(e). Thereafter, a UV-curable low refractive index layer 53 is applied, and a focal length adjusting substrate 54 is bonded to form a lens array (f). The thickness of the focal length adjusting substrate 54 is kept at the focal length of the lens array. Thereby, the fluorescence from the fluorescent layer 22 can be more efficiently collected.

Thereafter, as shown in FIG. 11, the fluorescent layer 22 is printed and applied three times for R, G, and B. Further, a flattening film 23 is applied to flatten the surface of the fluorescent layer 22. Thereafter, a wavelength selection layer 55 is formed by a vacuum evaporation method. For example, a desired wavelength selection layer 55 can be formed by laminating a large number of silicon oxide films and titanium oxide films. An alignment film 56 is applied to this surface, and rubbing is performed.

Further, a cholesteric liquid crystal polymer is applied on the alignment film 56 while heating. The pitch of the cholesteric liquid crystal polymer is adjusted to be twice the excitation light wavelength. Thereafter, when the temperature is rapidly returned to room temperature, the cholesteric liquid crystal polymer freezes and becomes stable at room temperature, forming the deflection selection layer 24.

Further, a light shielding film 25 is formed and molded. The light shielding film 25 serves to prevent light from entering the active element 18 such as a thin film transistor. An orientation film 26 is further formed on the light-shielding film 25, and rubbing is performed. As described above, the manufacture of the facing plate 15 is completed.

The obtained array plate 13 and opposing plate 15 are stuck so that the rubbing directions are antiparallel. By injecting a nematic liquid crystal into the gap between the array plate 13 and the opposing plate 15, a display operation based on the pi-type liquid crystal can be performed.

Further, a quarter-wave plate 57 and a polarizing plate 27 are attached to the lower surface of the array plate 13. Also, a dimming layer 28 is stuck on the upper surface of the facing 15. Then, a backlight light source composed of the light source 31 and the light guide plate 32 is arranged to complete the operation. Note that a ferroelectric liquid crystal or an antiferroelectric liquid crystal is used as the liquid crystal layer 14, and a blue light source is used as the light source 31. Industrial applicability

The liquid crystal display device of the present invention is suitable for a display device such as a computer and a mobile phone.

Claims

The scope of the claims

1. A liquid crystal display device comprising a liquid crystal layer, a polarization selection layer, and a fluorescent layer in this order in a path of excitation light.

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, comprising a liquid crystal panel in which the polarization selection layer and the fluorescent layer are formed.

5. The liquid crystal panel includes an active device array and a counter substrate facing the active device array via the liquid crystal layer, and the counter substrate includes the polarization selection layer and the fluorescent layer. The liquid crystal display device according to claim 4.

6. The liquid crystal display device according to claim 5, wherein the counter substrate has a flattening layer between the fluorescent layer and the polarization selection layer.

7. The liquid crystal display device according to claim 5, wherein the counter substrate has an alignment layer between the fluorescent layer and the polarization selection layer.

8. The liquid crystal display device according to claim 5, wherein the counter substrate has a wavelength selection layer between the fluorescent layer and the polarization selection layer.

9. The liquid crystal display device according to claim 5, wherein the counter substrate has a lens array.

10. The liquid crystal display panel according to claim 5, wherein the counter substrate has a waveguide array.

11.The method according to claim 1, further comprising a light-attenuating layer disposed downstream of the fluorescent layer.

12. The liquid crystal display device according to claim 11, further comprising a counter substrate having the polarization selection layer and the fluorescent layer, wherein the dimming layer is disposed on a surface of the counter substrate.