JP3113593B2 - Reflective liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, application of liquid crystal display devices has been expanded from calculators to displays for word processors and personal computers (hereinafter referred to as PCs) due to the remarkable improvement in display performance due to the progress of liquid crystal display technology. More recently, personal digital assistants (hereinafter PDA: Pers)
There is a growing expectation that the market as a display of the “onal Digital Assistant” will expand.

[0003] Because of their characteristics, PDAs that are premised on mobile applications require a thin, light, and low-power display, and the most suitable seed is a reflective liquid crystal display device that does not require a backlight ( LCD). In fact, most of the PDAs that are currently commercialized adopt a reflective LCD. PDA is a mini notebook PC,
In addition, it is expected to build a huge market for new mobile PCs that will play a leading role in the multimedia era while integrating and differentiating with network PCs. In the future, reflective LCD will play an increasingly important role as its key device.

FIG. 3 shows a configuration of a conventional reflection type LCD.
FIG. 3 is a configuration diagram of a reflection type LCD using a TN liquid crystal commonly used in watches, calculators, and electronic devices in addition to a PDA. A pair of transparent electrode groups 304 sandwiching the liquid crystal layer 305
a and 304b on which substrates 304a and 304b are formed, respectively.
Polarizing plates 301a and 301b are present on the opposing outer surface of b. On the back surface of the polarizing plate 301b, a reflecting plate 307 is provided via a high refractive index layer 309. Usually, the high refractive index layer is made of an acrylic paste, and the polarizing plate 301b and the reflecting plate 307 are joined as an adhesive layer. The refractive index is about n = 1.5.

Light incident from the polarizing plate 301a passes through the liquid crystal layer 305, is reflected by the reflecting plate 307, and is emitted again to the polarizing plate 301a. By applying a voltage to the liquid crystal layer, light passing through the liquid crystal layer 305 can be modulated.

FIG. 4 shows the configuration of another conventional reflection type LCD. FIG. 4 is a configuration diagram of a reflection type LCD using an STN liquid crystal used for a PDA or the like. The basic configuration is T in FIG.
It is almost the same as N liquid crystal. The difference is that a retardation plate 402 is interposed between a polarizing plate 401a and a transparent substrate 403a on which a transparent electrode group 404a is formed in order to compensate or control coloring peculiar to the STN liquid crystal mode.

[0007] One of the problems of the reflective LCD is "color display". In order to realize color display, a method of forming a micro color filter layer of three colors of red, blue and green on the inner surface of a liquid crystal panel is usually adopted. In a transmission type LCD, a decrease in transmittance in the micro color filter layer is compensated for by a high-luminance backlight. On the other hand, it is difficult to use a micro color filter layer because there is no backlight in a reflection type LCD, and "monochrome display" is currently mainstream at present.

[0008] However, efforts are being made to achieve color display in reflective LCDs. There are two ways to achieve this: (1) a method using birefringence of liquid crystal, (2)
There are two methods of using the color filter layer by improving the transmittance of the liquid crystal panel.

Among them, (1) is to change the birefringence by controlling the voltage applied to the liquid crystal layer, thereby realizing a color display. In this method, it is difficult to increase the number of colors to five or more due to restrictions such as gradation and controllability of the thickness of a liquid crystal layer, and is not suitable for full-scale color display.

The method (2) uses a liquid crystal operation mode in which two polarizing plates are used in the current panel configuration and a liquid crystal operation mode in which only one polarizing plate is used or not used. In this method, it is possible to apply a color filter by improving the transmittance of the color filter. As one actual example, a guest / host mode is used as a liquid crystal operation mode, a color filter layer is formed on the inner surface of a panel, and a voltage from a two-terminal element is applied to the liquid crystal layer via a reflective electrode to modulate light. There is a control method (Sharp Technical Report, No. 56, 2
7, (1993)). By this method, a reflective LCD capable of displaying color is realized. In addition, as a method of using one polarizing plate, white and black light modulation can be performed by specifying the retardation of the liquid crystal layer and the optical compensating member and the optical axis of the polarizing plate and the optical compensating member in the reflection type STN liquid crystal. There is an example (JP-A-7-84252).
If this is combined with a color filter layer, color display is possible in principle.

In the above method, a reflective electrode is used. However, in order to achieve a performance that is bright as viewed from any angle like "paper", it is necessary to provide diffuse reflection in the panel structure. is important.

In the case of a reflecting plate, it is conceivable to form irregularities on the surface of the reflecting plate and optimize the distribution, density, height, and other factors to provide diffuse reflection. Actually, as a result of observing the reflection plate having the diffuse reflection property as described above, the reflection plate itself has extremely small angle dependency, and an appearance close to paper can be obtained.

[0013]

In a reflection type liquid crystal display device using this reflection electrode, further improvement in brightness is required in order to realize color display with high visibility by using a color filter layer.

The present invention has been made in view of the above problems, and has as its object to provide a high-quality reflective liquid crystal display device having a relatively simple configuration.

[0015]

In order to achieve the above object, a reflection type liquid crystal display device according to the present invention comprises a first substrate having a band-shaped transparent electrode group on a surface thereof, and a first substrate facing the first substrate. A second substrate, a liquid crystal layer sandwiched between opposing inner surfaces of the first substrate and the second substrate, and a reflective liquid crystal display device including a reflector on an opposing outer surface of the second substrate; Is characterized by having a strip-like reflective electrode group having a light transmitting region aligned in a direction orthogonal to the alignment direction of the first substrate.

In the above configuration, a color filter layer formed so as to have a light transmitting region in a shape corresponding to one of the transparent electrode group and the reflective electrode group may be formed between the first substrate and the second substrate. It is preferable to provide an interim.

In the above structure, it is preferable that a low refractive index layer having a refractive index n in a range of 1 ≦ n ≦ 1.4 is provided between the second substrate and the reflector. Further, in the above configuration, the low refractive index layer is made of air, water, FE,
It is preferable to include at least one selected from a P fluorocarbon resin, a tetrafluoroethylene resin, and a fluorinated silicon rubber. FEP fluorocarbon resin is a kind of fluororesin material having a low refractive index.

Further, in the above configuration, it is preferable that the constituent material of the reflecting surface of the reflecting plate contains silver. Here, “containing silver” includes a simple substance of silver or a substance obtained by laminating a transparent resin on the surface of simple silver to prevent corrosion.

In the above configuration, a white plate may be provided instead of the reflection plate. Further, in the above configuration, it is preferable that a constituent material of the white plate is at least one selected from magnesium oxide, barium sulfate, and zinc oxide.

[0020]

According to the present invention, a first substrate having a strip-shaped transparent electrode group on the surface, a second substrate facing the first substrate, a first substrate and a second substrate are provided. In a reflective liquid crystal display device having a liquid crystal layer sandwiched between opposed inner surfaces of two substrates and a reflector on the opposed outer surface of the second substrate, the second substrate is aligned in the direction in which the first substrate is aligned. By providing a strip-shaped reflective electrode group having a light transmitting region aligned in the orthogonal direction, a reflective plate is provided on the opposing outer surface of the substrate on which the reflective electrode group is formed. Accordingly, light from the gap between the electrode groups, that is, light from a region other than the pixel electrode is reflected by the reflector and reaches the observer, so that a reflective liquid crystal display device with high reflection luminance can be obtained. The reflective electrode group is formed by sputtering using aluminum or silver as a main component.

A book comprising a color filter layer formed between the first substrate and the second substrate so as to have a light transmitting region in a shape corresponding to one of the transparent electrode group and the reflective electrode group. According to the preferred configuration of the present invention, a reflective liquid crystal display device capable of bright color display can be realized by forming a color filter layer formed with a gap in a shape corresponding to the electrode group on the inner surface of the panel.

Between the second substrate and the reflector, 1
According to the preferred configuration of the present invention including the low refractive index layer having the refractive index n in the range of ≦ n ≦ 1.4, the opening angle of the reflected light is reduced, and the decrease in the reflected luminance is suppressed. The light that has passed through the liquid crystal cell and reached the surface of the diffuse reflection plate reflects a large portion in the observation direction in addition to the specular reflection direction, unlike the case of the mirror reflection plate. The angles of penetration of the light reflected on the diffuse reflection plate into the liquid crystal cell are ψ1 and ψ2 for the case of the high refractive index layer such as glue and the case of the low refractive index layer such as air, respectively. Ψ1> according to Snell's law
ψ2. At this time, the refractive index n _LCD of the liquid crystal cell is n _LCD
= 1.5. The refractive index n _air of _air is n _air =
Since it is 1.0, between the emission angles ξ1 and ξ2 in each case when the liquid crystal cell is emitted, Sn is the same as before.
There is a relation of ξ1> ξ2 according to the law of ell. When the high refractive index layer is interposed between the liquid crystal cell and the diffuse reflection plate, the increase in the angle of reflection of the reflected light means a decrease in the degree of reflected light in the viewing direction. Further, when ψ1 and ψ2 are larger than the critical angle, no more light exits the liquid crystal cell due to total reflection. Also in this case, the high refractive index layer is more significantly affected. Therefore, the reflection luminance can be improved by interposing a low refractive index layer between the liquid crystal cell and the reflection plate. The present invention is effective when, for example, air having a refractive index n of 1.0 is interposed between the liquid crystal cell and the reflector.

According to the preferred structure of the present invention in which the constituent material of the reflecting surface of the reflecting plate contains silver, it is possible to realize a reflective LCD having a higher reflection luminance than when using another metal, and a paper white display. That is, a bright display can be more effectively realized from any angle, such as “paper”.

Further, by replacing the reflecting plate with a white plate, the gap between the electrode groups, that is, the area other than the pixel electrodes can be made whiter, and the paper white display performance can be improved as the panel visibility.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 shows a reflection type liquid crystal display device of this embodiment. A transparent substrate 103a on which a band-shaped transparent electrode group 104 is formed, and a transparent substrate 103 on which a band-shaped reflective electrode group 106 is formed in a direction perpendicular to the direction in which the transparent electrode group is aligned.
The liquid crystal layer 105 is sandwiched between the opposing inner surfaces b. Reflective electrode group 1
No. 06 was formed by sputtering using aluminum. The liquid crystal layer 105 was oriented parallel to the substrates 103a and 103b without twist. A retardation plate 102 and a polarizing plate 101 are arranged on the opposing outer surface of the substrate 103a. On the other hand, a reflection plate 107 is disposed on the opposing outer surface of the substrate 103b on which the reflection electrode group 106 is formed via a low refractive index layer 109. A micro color filter layer 108 was formed between the transparent electrode group 104 and the substrate 103a. Micro color filter layer 10
Reference numeral 8 denotes a band-shaped dielectric layer formed of three colors of red, green and blue to form one pixel, and is colored by a pigment.

The low-refractive-index layer 109 is made of air, and the reflection plate is a diffusion reflection plate 107 made of silver as a reflection material. In the case of the diffuse reflection plate, since the surface has irregularities, the air layer can be naturally introduced simply by placing it on the liquid crystal cell.

The retardation plate 102 has a slow axis whose liquid crystal layer 10
5 so as to be orthogonal to the liquid crystal alignment direction. Further, the retardation plate 102 and the liquid crystal layer 105 were designed so that the retardations thereof were almost equal. That is, it is in the optical compensation state. In this embodiment, the retardation of the retardation plate is 385 nm, the retardation of the liquid crystal layer is 385 nm,
The thickness d of the liquid crystal layer was 4.3 μm.

Light incident from the polarizing plate 101 passes through the phase difference plate 102 and the liquid crystal layer 105, is reflected on the reflective electrode 106 in the same linearly polarized state as the incident light, and further reaches the polarizing plate 101. At this point, the light is again emitted in the state of incident linear polarization. This is normally white
Mode.

The light that has passed through the light transmitting region of the reflective electrode group is returned to the observer side by the reflective plate bonded to the back surface of the substrate 103b, so that a bright display can be obtained. Further, by applying a voltage to the liquid crystal layer, the liquid crystal layer 105 is
Can be modulated. The effective retardation of the liquid crystal layer decreases with the applied voltage. When the retardation difference between the liquid crystal layer and the retardation plate is reduced to 1/4 of the light wavelength, the reflecting surface is in a circularly polarized state, and when the reflected light reaches the polarizing plate again, a straight line in the direction orthogonal to the incident linearly polarized light It becomes a polarization state. At this time, a dark state can be realized.

As described above, by electrically controlling the brightness in accordance with the RBG of the micro color filter, a reflective LCD of a bright color display was obtained. The integrated reflectance of this example was 15%. The integrated reflectance of the conventional example was 12%.

In this embodiment, the case where air is most effective as the low refractive index layer has been described. Water (n = 1.33) instead of air, FEP fluorocarbon resin (n
= 1.34), ethylene tetrafluoride resin (n = 1.3)
The same result can be obtained when 5) or using silicon fluoride rubber (n = 1.38).

Also, the case where color display is realized by using a micro color filter has been described. Naturally, even in the case of monochrome display without using a micro color filter, this method is an effective means for increasing the reflection luminance. It is.

(Embodiment 2) FIG. 4 shows a reflection type liquid crystal display device of this embodiment. The basic configuration is almost the same as that of the reflection type liquid crystal display of FIG. The difference is that the external reflection plate is replaced with a white plate 407 made of magnesium oxide.
Light that has passed through the light transmission region of the reflective electrode group is diffusely reflected by the white plate toward the observer. As a result, it was possible to improve the whitening of the reflected light.

Similar effects could be obtained with any of magnesium oxide, barium sulfate, and zinc oxide as constituent materials of the white plate. In the above embodiments, the electric field control birefringence effect is used as the liquid crystal operation mode. However, the same applies to the operation mode in which the reflective electrode is used and the number of polarizing plates used is one or less as described above. Can be implemented. Furthermore, the content of the present invention is simple matrix driving,
The present invention can be applied to any driving by a switching element such as a TFT.

[0035]

As described above, according to the present invention, it is possible to obtain a reflection type liquid crystal display device which has a high reflection luminance by a relatively simple method and can perform color display by combining with a micro color filter layer. Effects can be obtained.

Further, if air is used as the low refractive index layer interposed between the liquid crystal cell and the reflection plate, productivity and repairability are reduced as compared with the case of using a paste which is a conventional general method. This has the effect of significantly increasing the cost and enabling a reduction in cost, and is extremely practical.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a reflective liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a reflective liquid crystal display device according to another embodiment of the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional reflective liquid crystal display device.

FIG. 4 is a configuration diagram showing another example of a conventional reflective liquid crystal display device.

[Explanation of symbols]

101, 201, 301a, 301b, 401a, 40
1b: polarizing plates 102, 202, 402 ... retardation plates 103a, 103b, 203a, 203b, 303a,
303b, 403a, 403b... Transparent substrate 104, 204, 304a, 304b, 404a, 40
4b ·· Transparent electrode group 105, 205, 305, 405 ··· Liquid crystal layer 106, 206 ··· Reflective electrode group 107, 307, 407 ··· Reflector 207 ··· White plate 108, 208 ··· Micro Color filter layer 109, 209: low refractive index layer 309, 409: high refractive index layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1335 520 G02F 1/1343

Claims (7)

(57) [Claims] 1. A first substrate having a band-shaped transparent electrode group on the surface, a second substrate facing the first substrate, and sandwiched between opposed inner surfaces of the first substrate and the second substrate. Liquid crystal layer and a reflection type liquid crystal display device provided with a reflection plate on an opposing outer surface of the second substrate, wherein the second substrate is aligned in a direction orthogonal to the alignment direction of the first substrate. A reflective liquid crystal display device comprising a belt-like reflective electrode group having the following. 2. A color filter layer formed between the first substrate and the second substrate so as to have a light transmitting region in a shape corresponding to one of the transparent electrode group and the reflective electrode group. The reflective liquid crystal display device according to claim 1. 3. The method according to claim 1, wherein a distance between the second substrate and the reflection plate is 1.
The reflective liquid crystal display device according to claim 1, further comprising a low refractive index layer having a refractive index n in a range of ≦ n ≦ 1.4. 4. The low refractive index layer includes at least one selected from the group consisting of air, water, FEP fluorocarbon resin, ethylene tetrafluoride resin, and silicon fluoride rubber.
4. The reflection type liquid crystal display device according to 1. 5. The reflection type liquid crystal display device according to claim 1, wherein a constituent material of a reflection surface of said reflection plate contains silver. 6. The reflection type liquid crystal display device according to claim 1, further comprising a white plate in place of said reflection plate. 7. The reflection type liquid crystal display device according to claim 6, wherein the constituent material of said white plate is at least one selected from magnesium oxide, barium sulfate, and zinc oxide.