JP2003167224A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device being bright and showing high contrast in respective reflection and transmission modes. <P>SOLUTION: In the liquid crystal display device formed by sticking one member formed by successively laminating a stripe-shaped transparent electrode group and an alignment layer on a transparent substrate and the other member formed by forming a stripe-shaped laminated electrode group formed by arranging a laminated body of a transparent conductive layer and a light reflection layer in a stripe shape on the principal surface of a substrate and laminating an alignment layer on the stripe- shaped laminated electrode group to each other via a super twisted nematic liquid crystal to arrange pixels in a matrix shape, providing light transmission parts at every pixel to the light reflection layer to be made to be in a transmission mode and providing a light reflection parts to be made to be in a reflection mode, the light transmission parts and the light reflection parts satisfy relational formulas 0.2≤Δn.dt-Δn.dr≤0.4 and 0.70≤Δn.dr≤0.85 (wherein Δn.dt denotes the product of refraction index anisotropy Δn of the liquid crystal and the cell gap dt corresponding to the light transmission parts and Δn.dr denotes the product of refraction index anisotropy Δn of the liquid crystal and the cell gap dr corresponding to the light reflection parts). <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device called a transflective type having both functions of a reflection type and a transmission type. 2. Description of the Related Art In recent years, liquid crystal display devices have been used in a wide range of applications from large devices used for televisions and personal computers to small and medium devices used for portable information terminals. The liquid crystal display devices are properly used depending on the intended use. For example, a transmission type liquid crystal display device is mainly used for a television used indoors, and a reflection type or a reflection type is used for a portable information terminal used outdoors. What is called a transflective type is used. Among them, the demand for a transflective liquid crystal display device for mobile phones tends to increase year by year. According to this transflective liquid crystal display device,
When used as a reflection type that uses light from the outside world such as sunlight or fluorescent light (reflection mode), and when a backlight is mounted as internal illumination on the back side and used as a transmission type that uses the light for display (transmission) Mode), and a semi-transmissive film is adhered to a polarizing plate in order to have both functions (see Japanese Patent Application Laid-Open No. 61-260202). FIG. 1 is a schematic sectional view showing the structure of a simple matrix type transflective liquid crystal display device. A large number of transparent electrodes 4 are arranged in parallel on the inner surface of a glass substrate 3 to form an alignment film 5. On the inner surface of the other glass substrate 11, a semi-permeable film 10, a color filter 9, an overcoat 7, a transparent electrode 4, and an alignment film 5 are sequentially laminated. [0006] Both substrates are connected to both parallel transparent electrode groups 4.
Are arranged so as to be orthogonal to each other, and the nematic liquid crystal molecules 8 are interposed in a twist arrangement of 180 ° to 270 °. 6 is a seal member. A polarizing plate 1 and a phase difference plate 2 are stacked on one main surface of the liquid crystal panel having such a configuration, and a polarizing plate 13 and a phase difference plate 12 are stacked on the other main surface. A backlight unit including a light guide plate 14 and a light guide plate 15 is provided. The transflective liquid crystal display device is designed so that it can be used in a wide range of environments from a dark place to a bright place. However, according to the reflective transflective liquid crystal display device, since the reflective mode and the transmissive mode are used in combination, the conventional semi-transmissive film 10 causes an optical loss in the reflective mode and in the transmissive mode, respectively. This causes a problem that light use efficiency is reduced. Further, in the transflective liquid crystal panel, the color reproducibility in the transmissive mode using the light from the backlight is lower than the color reproducibility in the reflective mode mainly using the light from the outside. It was remarkably low. In order to solve such a problem, instead of the semi-transmissive film, a completely reflective film is patterned into a specific pattern by an etching method or the like, and a transmission hole for transmitting light from a backlight is provided. Accordingly, a technique has been proposed in which a region in a pixel is divided into a reflective region and a transmissive region, thereby increasing light use efficiency during transmission (see Japanese Patent No. 2878231). In an active matrix type liquid crystal display device using a TFT element, a cell gap in a region through which light from a backlight is transmitted is made larger than a cell gap in a region which reflects external light, thereby reducing external light. By making the retardation (Δn · dt) of the area that transmits light from the backlight larger than the retardation (Δn · dr) of the reflective area, the optical characteristics of the liquid crystal panel in the reflection mode and the transmission mode are optimized respectively. (See Japanese Patent Application Laid-Open Nos. 11-101992 and 2001-33754). [0013] However, a simple matrix type liquid crystal display device using a super twisted nematic liquid crystal has the above-described structure in consideration of the d / p margin of the liquid crystal material. It was difficult to adopt. Accordingly, the present invention has been completed in view of the above description, and maintains the d / p margin at a level practical for mass production, furthermore, the cell gap in the area for reflecting external light and the light from the backlight. An object of the present invention is to provide a liquid crystal display device which exhibits bright and high contrast in each of the reflection and transmission modes by optimizing a cell gap in a region where light is transmitted and optimizing an optical compensation film. A liquid crystal display device according to the present invention comprises a member formed by sequentially laminating a stripe-shaped transparent electrode group and an alignment layer on a transparent substrate, and one member formed on one main surface of the substrate. A stripe-shaped laminated electrode group formed by arranging a laminate of a transparent conductive layer and a light-reflecting layer in a stripe pattern is formed. The laminated electrode group and the striped transparent electrode group are bonded together via a super twisted nematic liquid crystal so as to intersect, and the pixels are arranged in a matrix, and a light transmitting portion is provided for each pixel with respect to the light reflecting layer. A backlight is provided outside the other member of the liquid crystal panel in the reflection mode by providing a light reflection portion by further providing a light reflection portion, and the light transmission portion and the light reflection portion are defined by the following relational expression. It is characterized by having done. 0.2 ≦ Δn · dt−Δn · dr ≦ 0.4 and 0.70 ≦ Δn · dr ≦ 0.85 where Δn · dt is the refractive index anisotropy Δn of the liquid crystal corresponding to the light transmitting portion and the cell gap. dt and Δn · d
r is the product of the refractive index anisotropy Δn of the liquid crystal corresponding to the light reflecting portion and the cell gap dr. According to the liquid crystal display device of the present invention, as described above, a light transmitting portion is provided for each pixel in the light reflecting layer to achieve a transmission mode, and a light reflecting portion is provided to provide a reflection mode. As a result, the pixel region is divided into a region that reflects light from the outside and a region that transmits light from the backlight, thereby improving light use efficiency in both the transmission mode and the reflection mode. Also, a cell gap in the light reflecting portion;
By optimizing the cell gap in the light transmitting portion that transmits light from the backlight and further optimizing the optical compensation film, excellent visibility can be obtained in both the reflection mode and the transmission mode. FIG. 2 is a schematic sectional view of a liquid crystal display device according to the present invention. The same parts as those of the conventional transflective liquid crystal display device shown in FIG. First, the structure of the color liquid crystal display device shown in FIG. 2 will be described. For the one member, the glass substrate 3
A color filter 9 and an overcoat 7 made of an acrylic resin are formed on the inner surface of the substrate, and a plurality of transparent electrodes 4 made of ITO are arranged on the overcoat 7 in a stripe pattern. An orientation film 5 made of polyimide resin rubbed in the direction is covered. Note that a resin or SiO 2 is disposed between the transparent electrode 4 and the alignment film 5.
_An insulating film made of ₂ or the like may be interposed, and the overcoat layer 7 may not be provided. The color filters 9 are arranged for each pixel on the inner surface of the glass substrate 3. These color filters 9 are of a pigment dispersion type, that is, the pigments (red, green, blue)
Is coated on a substrate and formed by photolithography. A black matrix of chromium metal or a photosensitive resist may be formed between the color filters 9. As for the other member, the glass substrate 11
On the inner surface of the substrate, a transparent electrode 4 made of ITO, which is arranged in a stripe pattern in a large number of parallel, is formed. 5 are sequentially stacked. Since the reflection films 16 are formed on the transparent electrode 4, a large number of the reflection films 16 are arranged in stripes in parallel. Although the alignment film 5 is formed directly on the patterned reflective film 16, an insulating film made of resin or SiO ₂ is interposed between the oriented film 5 and the patterned reflective film 16. You may. The reflection film 16 and the transparent electrode 4 may be turned upside down to form an insulating film and an alignment film 5 on the transparent electrode 4. Then, the one member and the other member of the above configuration are bonded together by a seal member 6 via a liquid crystal 8 made of a chiral nematic liquid crystal twisted at an angle of, for example, 200 ° to 260 °. A large number of spacers are arranged between the two members to keep the thickness of the liquid crystal 8 constant. Further, a forward scattering plate 17 and a retardation plate 2 made of polycarbonate or the like are provided outside the glass substrate 3 as one member.
And an iodine-based polarizing plate 1 are sequentially formed. In this example, the liquid crystal display device employs an external scattering method, and a forward scattering plate 17 is provided between the retardation plate 2 and the glass substrate 3. Further, a retardation plate 12 made of polycarbonate or the like and an iodine-based polarizing plate 13 are sequentially formed outside the glass substrate 11 as the other member. These arrangements are performed by applying an adhesive made of an acrylic material. Then, the backlight unit including the light source unit 14 and the light guide plate 15 is disposed in close contact with the polarizing plate 13. The patterned reflective film 16 is formed of an inorganic material, for example, Al, Ag, Cr, Ti,
Pure metals containing at least one of the elements W, Mo, Ta, In, Fe, Co, Ni, and Si, or intermetallic compounds (AlNd, AlTi, AgPd, AgPdC)
u), oxides (TiO ₂ , SiO ₂ or a laminate of these materials), nitrides (SiN), carbides (AlMgC)
There is. A between the reflective film 16 and the transparent electrode 4
1, Ag, Cr, Ti, W, Mo, Ta, In, Fe,
A pure metal containing at least one of Co, Ni, and Si elements, or an intermetallic compound, an oxide, a nitride, or a carbide may be formed, thereby improving the adhesion of the reflective film 16 or Heat resistance may be improved. Alternatively, A between the reflection film 16 and the alignment film 5
1, Ag, Cr, Ti, W, Mo, Ta, In, Fe,
A pure metal containing at least one of Co, Ni, and Si elements, or an intermetallic compound, an oxide, a nitride, or a carbide may be formed, whereby the heat resistance and the chemical resistance of the reflection film 16 may be reduced. May be increased. Moreover, when the thickness of the reflective film 16 is increased, the reflected light becomes yellowish, and when the thickness is reduced, the reflected light becomes bluish. However, the color due to the reflective film 16 at the time of such reflection or transmission is also reduced. It can be adjusted by a layer between the reflection film 16 and the color filter 9. As an example of such a structure, a 350 ° -thick Cr
A layer, an Al layer having a thickness of 1000 ° as the reflective film 16 and the alignment film 5 may be sequentially laminated. As another example, a 1000 mm thick silver alloy (Ag alloy) layer as the reflection film 16, the transparent electrode 4, and the alignment film 5 may be sequentially laminated on the glass substrate 11. The patterning of the reflection film 16 is performed by a photolithography method in a light transmitting portion for transmitting light from the backlight unit. That is, a photosensitive resist is applied to the film surface on which the metal film is formed, exposed using a photolithography mask, and then formed through development, etching, and peeling steps. Further, between the reflective film 16 and the alignment film 5, Al,
Ag, Cr, Ti, W, Mo, Ta, In, Fe, C
When a pure metal containing at least one of the elements of o, Ni, and Si, or an intermetallic compound, an oxide, a nitride, or a carbide is formed, the reflection film 16 is patterned by a photolithography method after forming the film. Alternatively, the above film may be formed after patterning the reflective film 16. According to the laminated structure of the reflection film 16 and the transparent electrode 4 as described above, a light transmission portion is provided for each pixel in the reflection layer 16 to perform a transmission mode, and further, a light reflection portion is provided to provide reflection. In the mode, the ratio between the reflectance and the transmittance of the liquid crystal panel can be adjusted by adjusting the area ratio between the reflection region and the transmission region in the pattern of the transmission region. In the liquid crystal display device having the above-described structure, incident light from external illumination such as sunlight or fluorescent light passes through the polarizing plate 1, the phase difference plate 2 and the glass substrate 3, and is reflected through the color filter 9, the liquid crystal 8 and the like. Reaching the film 16, the reflection film 1
The light is reflected by the reflection region 6 and the reflected light is emitted as a reflection mode. Light emitted from the backlight unit passes through the polarizing plate 13, the phase difference plate 12, the forward scattering plate 17, and the glass substrate 11, and further passes through the transmission region of the reflection film 16, and the liquid crystal 8 and the color The light passes through the filter 9, the glass substrate 3, the retarder 2, and the polarizing plate 1 and is emitted in a transmission mode. In the above structure, the cell gap dt in the region through which light from the backlight is transmitted is different from the cell gap dr in the region through which external light is reflected, as shown in the sectional view of the main part of FIG. The thickness is increased by dm (dt-dr) corresponding to the thickness of 16. Therefore, by arbitrarily changing the thickness dm (dt-dr) of the reflective film 16, the difference between the cell gap dr of the area that reflects external light and the cell gap dt of the area that transmits light from the backlight is adjusted. Which is the optimum retardation in both the reflection and transmission modes
Set n · dr and Δn · dt. Next, Δn · dr and Δn · dt are optimized. (Optimization of Δn · dr) In order to optimize Δn · dr, first, Δn · dr = 0.6, 0.65, 0.7,
Cells were manufactured under the conditions of 0.75, 0.8, 0.85, and 0.9, and the polarizing plate 1 and the retardation plate 2 were optimized at each Δn · dr. The liquid crystal used in the cell used for optimization had a twist angle of 240 ° and Δn = 0.18.
3. Then, for the liquid crystal display device thus optimized, under three conditions (condition 1, condition 2, and condition 3) considered to be particularly excellent in visibility, the dependence of the reflection optical characteristics on Δn · dr depends on each condition. When the properties were evaluated, results as shown in Tables 1 to 3 were obtained. Further, when the contrast characteristics were also measured, the results are as shown in Tables 1 to 3. [Table 1] [Table 2] [Table 3] When the reflectance and contrast of the liquid crystal panel using the conventional technique were measured in the same manner, the results shown in Table 4 were obtained. This prior art device is the liquid crystal display device shown in FIG. 1 and optimizes the polarizing plate 1 and the retardation plate 2 when Δn · d = 0.80. [Table 4] The results are shown in FIGS. 4 and 5. The evaluation in the reflection mode was obtained by a measuring method as shown in FIG. According to the reflection mode measuring method shown in the figure, light (C light source) is incident on the liquid crystal panel from above, and the reflectance and contrast (white) when the liquid crystal panel is driven when white display is performed. (Reflectance during white display / reflectance during black display) was measured. As is clear from the results shown in FIGS. 4 and 5, in the panel structure using the present invention, the reflectance is improved, and thereby the contrast is also improved.
From this result, it is understood that the improvement effect is large under the conditions 2 and 3. In condition 2, Δn · dr = 0.
At 78, the contrast shows the maximum value, and under the condition 3, the contrast shows the maximum at Δn · dr = 0.81. (Optimization of Δn · dt) Next, optimization of Δn · dt was examined using conditions 2 and 3. In each of the values where the contrast in the reflection mode takes the maximum value, that is, Condition 2: Δn · dr = 0.78 Condition 3: Δn · dr = 0.81, the film thickness dm of the reflective film 16 is 0.1 μm ≦ dm ≦ 0.25. μm
When the transmittance and the contrast characteristics were measured in the range of 変 化, the results shown in Tables 5 and 6 were obtained, and dm was optimized. The results are shown in FIGS. 6 and 7, and the method for measuring the transmission optical characteristics is shown in FIG. [Table 5] [Table 6] With respect to the prior art, the results shown in Table 7 were obtained. [Table 7] In the case of the transmission mode, as shown in FIG. 9, light (C light source) is incident from the lower part of the liquid crystal display device to be measured, and when this device is driven, the transmittance during white display and the contrast ( (Transmittance during white display / transmittance during black display) was measured. As is clear from FIGS. 6 and 7, under condition 2, the maximum values of the transmittance and the contrast were obtained at dm = 0.17. In condition 3, dm =
At 0.12, maximum values were obtained for both transmittance and contrast. It was confirmed that the optical characteristics were superior to the optical characteristics of the panel manufactured by using the conventional technology under any conditions. From the above results, 0.70 ≦ Δn · dr ≦
At 0.85, reflective optical properties were obtained that exceeded the prior art. In particular, when Δn · dr = 0.78, the contrast in the reflection mode became the maximum. When Δn · dr = 0.78, 0.2
In the range of ≦ Δn · dt−Δn · dt ≦ 0.4, transmission optical characteristics superior to the conventional technology were obtained. Furthermore, dm = 0.1
7, that is, Δn · dt−Δn · dt = 0.17, the contrast in the transmission mode became the maximum. As described above, according to the liquid crystal display device of the present invention, one member formed by sequentially laminating a stripe-shaped transparent electrode group and an alignment layer on a transparent substrate, and one principal surface of the substrate A stripe-shaped laminated electrode group formed by arranging a stacked body of a transparent conductive layer and a light-reflecting layer in a stripe shape on the other side, and the other member formed by laminating an orientation layer on the stripe-shaped laminated electrode group, The stripe-shaped laminated electrode group and the stripe-shaped transparent electrode group are pasted together via a super-twisted nematic liquid crystal so as to intersect, and the pixels are arranged in a matrix. A backlight is provided outside the other member of the liquid crystal panel in a reflection mode by providing a light reflection portion by providing a light transmission portion and a light reflection portion.
Dt−Δn · dr ≦ 0.4 and 0.70 ≦ Δn · d
By setting r ≦ 0.85, a light transmitting portion is provided for each pixel with respect to the light reflecting layer to form a transmission mode, and a light reflecting portion is further provided to form a reflection mode, so that the pixel region is exposed from the outside. Is divided into a region that reflects the light from the backlight and a region that transmits the light from the backlight, thereby improving the light use efficiency in both the transmission mode and the reflection mode. According to the present invention, the reflection mode is optimized by optimizing the cell gap in the light reflection section and the cell gap in the light transmission section that transmits light from the backlight, and further optimizing the optical compensation film. Excellent visibility was obtained in both the transmission mode and the transmission mode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a conventional transflective liquid crystal display device. FIG. 2 is a schematic sectional view of the liquid crystal display device of the present invention. FIG. 3 is an enlarged sectional view of a pixel portion in the liquid crystal display device of the present invention. FIG. 4 is a diagram showing a relationship between Δn · dr and reflectance. FIG. 5 is a diagram showing a relationship between Δn · dr and contrast. FIG. 6 is a diagram showing a relationship between Δn · dm and transmittance. FIG. 7 is a diagram showing a relationship between Δn · dm and contrast. FIG. 8 is an explanatory diagram showing a measurement method for evaluating a reflection mode. FIG. 9 is an explanatory diagram illustrating a measurement method for evaluating a transmission mode. [Description of Signs] 1, 13 ... Polarizing plate 2, 12 ... Phase plate 3, 11 ... Glass substrate 4 ... Transparent electrode 5 ... Alignment film 6 ... Seal agent 7 ... ..Overcoat 8 liquid crystal 9 color filter 10 transflective film 14 light source unit 15 light guide plate 16 patterned reflective film 17 forward scattering plate

   ────────────────────────────────────────────────── ─── Continuation of front page    F-term (reference) 2H089 QA16 RA10 SA04 TA02 TA04                       TA12 TA17 TA18                 2H090 HB08 KA08 LA01 LA05 LA16                       LA20 MB01                 2H091 FA02Y FA14Y FA41Z GA02                       GA03 GA06 HA10 KA02 LA17                 2H092 GA11 HA03 HA04 HA05 NA01                       PA02 PA08 PA12 PA13 QA10

Claims (1)

Claims: 1. A member formed by sequentially laminating a stripe-shaped transparent electrode group and an orientation layer on a transparent substrate, and a transparent conductive layer and a light reflection layer on one main surface of the substrate. A stripe-shaped laminated electrode group formed by arranging the laminate in a stripe shape is formed, and the other member formed by laminating the alignment layer on the stripe-shaped laminated electrode group is formed by the stripe-shaped laminated electrode group and the stripe-shaped transparent electrode group. And superimposed through super twisted nematic liquid crystal so that the pixels are arranged in a matrix, and a light transmission section is provided for each pixel with respect to the light reflection layer, and the light reflection section is formed. A liquid crystal display device in which a backlight is provided outside the other member of the liquid crystal panel provided to be in the reflection mode, and the light transmitting portion and the light reflecting portion have the following relational expression. 0.2 ≦ Δn · dt−Δn · dr ≦ 0.4 and 0.70 ≦ Δn · dr ≦ 0.85 where Δn · dt is the refractive index anisotropy Δn of the liquid crystal corresponding to the light transmitting portion and the cell gap. dt and Δn · d
r is the product of the refractive index anisotropy Δn of the liquid crystal corresponding to the light reflecting portion and the cell gap dr.