JP3603897B2 - Transflective liquid crystal device and electronic equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transflective liquid crystal device, and further to an electronic device equipped with the transflective liquid crystal device.
[0002]
[Prior art]
Reflective liquid crystal devices with low power consumption are suitable for use in information tools such as PDAs and portable electronic devices such as mobile phones and watches. However, the conventional reflective liquid crystal device has a problem of a double image due to parallax. This is a phenomenon in which the shadow is produced by overlapping the original display because the distance between the liquid crystal layer and the reflector is equal to the thickness of the lower substrate (for example, 0.7 mm). Makes it difficult to recognize the display. Also, when a color filter is provided corresponding to each dot of the dot matrix display and the reflection type color display is performed, the vividness of the display color is also improved by the incident light and the reflected light passing through different color filters due to parallax. There was a problem of being damaged.
[0003]
In order to solve such a problem, a method of providing a metal reflective electrode in a liquid crystal cell to reduce the distance between the liquid crystal layer and the reflector and eliminate parallax is disclosed in Asia Display '95 p. In 599, it was proposed by Tatsuo Uchida and others. FIG. 7 shows an outline of the structure. 7, 701 is a light scattering plate, 702 is a polarizing plate, 703 is a retardation plate, 704 is an upper substrate, 705 is a lower substrate, 706 is a transparent electrode, and 707 is a metal reflective electrode. The light scattering plate 701 is provided to diffuse the specular reflection by the metal reflective electrode and widen the viewing angle, but a forward scattering plate is used in order not to lower the contrast. The forward scattering plate is a light scattering plate that has large scattering of transmitted light (this is called forward scattering) and little scattering of reflected light (this is called back scattering). However, it is difficult to obtain an ideal forward scattering plate, and an existing forward scattering plate involves back scattering to some extent. Therefore, a reduction in contrast is inevitable in the structure shown in FIG.
[0004]
In such a case, it is effective to dispose a light scattering plate closer to the liquid crystal cell than the polarizing plate, as disclosed in JP-A-9-113893. With this arrangement, at least half of the light scattered backward by the light scattering plate is absorbed by the polarizing plate, so that the contrast is improved. Note that Japanese Patent Application Laid-Open No. Hei 9-113893 does not mention this effect because the light scattering plate used is special.
[0005]
[Problems to be solved by the invention]
However, even if the light scattering plate is disposed below the polarizing plate, the back scattering is only halved, but never becomes zero, and a high contrast cannot be obtained.
[0006]
Accordingly, an object of the present invention is to provide a transflective liquid crystal device with high contrast by devising the position and the axial direction of the light scattering plate and preventing back scattering by the light scattering plate. It is another object of the present invention to provide a reflective color liquid crystal device capable of displaying bright colors.
[0007]
[Means for Solving the Problems]
In the transflective liquid crystal device of the present invention, a liquid crystal layer is disposed between a first substrate and a second substrate, and a reflective display using a metal reflective electrode disposed on the liquid crystal layer side of the second substrate. Alternatively, in a transflective liquid crystal device capable of performing transmissive display, a first polarizing plate is disposed on a side of the first substrate opposite to the liquid crystal layer, and a first polarizing plate and the first substrate are provided between the first polarizing plate and the first substrate. A light scattering plate is disposed, a first retardation plate is disposed between the light scattering plate and the first polarizing plate, and a second retardation plate is disposed on a side of the second substrate opposite to the liquid crystal layer. A second polarizing plate and a second polarizing plate are disposed, and light transmitted through the first polarizing plate is transmitted through the first retardation plate to be in a state of circularly polarized light, and the light scattering plate is provided. And the backscattered light by the light scattering plate that has passed through the first retardation plate is in a linearly polarized state. To be absorbed by the first polarizing plate, characterized by comprising setting the retardation and the axial direction of the first retardation plate. With this configuration, the circularly polarized light backscattered by the light scattering plate is converted into linearly polarized light perpendicular to the transmission axis of the first polarizing plate by the first retardation plate, and absorbed by the first polarizing plate. Is done. Therefore, the transflective liquid crystal device of the present invention has an effect that a high contrast can be obtained.
[0008]
Further, the present invention is characterized in that the first retardation plate is a quarter-wave plate, and its delay axis intersects the absorption axis of the first polarizing plate at an angle of approximately 45 degrees. A 波長 wavelength plate is a retardation plate whose retardation is about ４ of the wavelength of visible light. Further, the visible light wavelength often indicates the wavelength of green light having the highest visibility. With such a configuration, the liquid crystal device of the present invention has an effect of converting light reaching the light scattering plate into circularly polarized light with the simplest configuration, and obtaining a high contrast.
[0009]
Further, the first retardation plate is a laminate in which a １ ／ wavelength plate and a 波長 wavelength plate are arranged in this order from the first polarizing plate side, and the retardation axis of the 波長 wavelength plate and the polarization plate Assuming that the angle between the transmission axis and the transmission axis is θ, the angle between the delay axis of the 板 wavelength plate and the transmission axis of the polarizing plate is approximately 2θ + 45 degrees. A half-wave plate is a retardation plate whose retardation is about half the wavelength of visible light. With such a configuration, the liquid crystal device of the present invention converts light of a wide wavelength range reaching the light scattering plate into circularly polarized light, and has an effect that high contrast is obtained and display coloring is small.
[0010]
In addition, the present invention provides a liquid crystal layer with a retardation such that when no voltage is applied to the liquid crystal layer, light incident from the first polarizing plate reaches the metal reflective electrode in a state of linearly polarized light. It is characterized in that the phase and the twist angle are set. With such a configuration, the transflective liquid crystal device of the present invention can obtain a bright display when no voltage is applied to the liquid crystal layer. Further, when a sufficient voltage is applied to the liquid crystal layer, the retardation of the liquid crystal layer becomes zero, so that a dark display can be obtained. This dark display state is very black because, due to the arrangement of the first retardation plate, not only the back scattering of the light scattering plate but also all other interface reflections are removed. Therefore, the transflective liquid crystal device of the present invention can provide a display with a very high contrast.
[0011]
According to another aspect of the invention, an electronic apparatus includes the above-described liquid crystal device as a display unit. With such a configuration, the electronic device of the present invention can obtain high-quality display with low power consumption.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, reference examples and embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
(Reference Example 1)
FIG. 1 is a diagram illustrating a main part of a structure of a liquid crystal device according to Reference Example 1. First, the configuration will be described. In FIG. 1, 101 is a polarizing plate, 102 is a retardation plate, 103 is a light scattering plate, 104 is an upper substrate, 105 is a liquid crystal layer, 106 is a lower substrate, 107 is a transparent electrode, and 108 is a metal reflective electrode. 101 and 102, 102 and 103, and 103 and 104 are adhered to each other with glue. Although the upper and lower substrates are drawn widely apart, this is for the sake of clarity of the drawing, and they are actually opposed to each other with a narrow gap of several μm to several tens μm. In addition to the components shown in the figure, elements such as a liquid crystal alignment film, an insulating film, a spacer ball, a seal portion, a driver IC, and a drive circuit are indispensable, but they are not particularly necessary for describing the present invention. However, it is omitted because it may complicate the figure and make it difficult to understand.
[0014]
Next, each component will be described in order. The polarizing plate 101 has a function of absorbing a predetermined linearly polarized light component and transmitting other polarized light components. This is the most commonly used type of polarizing plate at present, and is produced by adsorbing a halogen substance such as iodine or a dichroic dye onto a polymer film such as polyvinyl butyral.
[0015]
The retardation plate 102 is a uniaxially stretched film of a polyvinyl alcohol resin. The retardation is 0.14 μm, which is about １ ／ of the wavelength of green light having the highest visibility of visible light, and thus functions as a 波長 wavelength plate.
[0016]
The light scattering plate 103 is preferably a film composed of two types of minute regions having different refractive indexes. With this configuration, a light scattering plate having strong forward scattering and small back scattering can be obtained. Specifically, a plastic film in which fine beads are dispersed in a transparent binder having a different refractive index from the fine beads can be used. Alternatively, a plastic film may be used in which two types of minute regions having different refractive indices form a layer structure, and scatter only light incident from a specific angle.
[0017]
For the liquid crystal layer 105, a nematic liquid crystal composition twisted from 0 degrees to 270 degrees can be used. The twist angle is determined by the direction of the alignment treatment on the upper and lower glass substrates and the amount of the chiral agent added to the liquid crystal.
[0018]
Both the upper substrate 104 and the lower substrate 106 are transparent glass substrates. The lower substrate may be an opaque substrate, such as a silicon wafer. The transparent electrode 107 was formed of ITO, and the metal reflective electrode 108 was formed of an Al-Nd alloy.
[0019]
Next, specific conditions of the liquid crystal cell will be introduced. First, the retardation of the liquid crystal layer 105 in FIG. 1 was set to 0.25 μm. FIG. 2 is a diagram showing the relationship between the axes, 201 is the polarization axis (transmission axis) of the polarizing plate 101, 202 is the slow axis (stretching axis) of the retardation plate 102, 203 is the rubbing axis of the upper substrate 104, 204 is a rubbing axis of the lower substrate 106. Here, the angle 211 between 202 and 201 is set at 45 degrees to the left, the angle 212 between 203 and 201 is set at 101 degrees to the left, and the angle between 204 and 203 is set at 70 degrees to the left. Note that the angle 211 may be set to approximately 45 degrees, and there is no problem with a slight shift.
[0020]
In the liquid crystal device of Reference Example 1 configured as described above, a display with a very high contrast was obtained. The principle will be briefly described with reference to FIG.
[0021]
3, reference numeral 301 denotes a polarizing plate, 302 denotes a phase difference plate, 303 denotes a light scattering plate, 304 denotes an upper substrate, 305 denotes a lower substrate, 306 denotes a liquid crystal layer to which no voltage is applied, and 307 denotes a sufficiently high voltage. The applied liquid crystal layer. The components are drawn widely apart to illustrate the state of polarization. Reference numerals 311 and 312 denote external light incident on the liquid crystal layer 306 and the liquid crystal layer 307, respectively, which are natural lights vibrating in all directions.
[0022]
The natural lights 311 and 312 are converted to linearly polarized light by the polarizing plate 301, further converted to left-handed circularly polarized light by the phase difference plate 302, and reach the light scattering plate 303. The light scattered backward by the light scattering plate is converted to clockwise circularly polarized light and returned to linearly polarized light again by the phase difference plate 302. This linearly polarized light vibrates in a direction orthogonal to the transmission axis of the polarizing plate 301. Therefore, it is absorbed by the polarizing plate. Light reflected backward at the interface between the upper substrate and the transparent electrode is also absorbed by the polarizing plate. Since all the light reflected backward does not contribute to display, high contrast can be obtained by absorbing such light.
[0023]
On the other hand, of the light scattered forward by the light scattering plate, the light incident on the liquid crystal layer 306 is converted into linearly polarized light by the liquid crystal layer and reaches the metal reflector. This is because the retardation and the twist angle of the liquid crystal layer are set in advance so as to be the same. The reflected light follows exactly the same path and is returned to its original counterclockwise circular polarization. Such a conversion can be generally applied to a liquid crystal layer that performs conversion so as to become linearly polarized light on a reflection plate, and is described in detail in JP-A-3-223715. The left-handed circularly polarized light returns to the original linearly polarized light by the phase difference plate 302 and passes through the polarizing plate 301, so that a bright display is obtained.
[0024]
Also, of the light scattered forward by the light scattering plate, the light incident on the liquid crystal layer 307 is reflected in the metal as left-handed circularly polarized light because the liquid crystal is substantially parallel to the incident light and has no birefringence. The light reaches the plate and is reflected to become clockwise circularly polarized light. This light follows the same path as the light scattered backward by the light scattering plate and is absorbed by the polarizing plate, so that a dark display is obtained.
[0025]
As described above, in the liquid crystal device of Reference Example 1, high contrast is obtained because the light scattered backward by the light scattering plate and the light reflected at each interface are absorbed by the combination of the retardation plate and the polarizing plate. In addition, by setting a state in which a sufficient voltage is applied to the liquid crystal layer as a dark display, a high contrast that could not be realized in the conventional single-polarizer type liquid crystal display mode was obtained.
[0026]
(Reference Example 2)
FIG. 4 is a diagram illustrating a main part of the structure of the liquid crystal device according to Reference Example 2. First, the configuration will be described. 4, reference numeral 401 denotes a polarizing plate, 402 denotes an upper retardation plate, 403 denotes a lower retardation plate, 404 denotes a light scattering plate, 405 denotes an upper substrate, 406 denotes a liquid crystal layer, 407 denotes a lower substrate, and 408 denotes a color filter. , 409 are scanning lines of transparent electrodes, 410 is a signal line, 411 is a metal reflection electrode, and 412 is a MIM element. Reference numerals 401 and 402, 402 and 403, 403 and 404, and 404 and 405 are bonded to each other with glue. Although the upper and lower substrates are drawn widely apart, this is for the sake of clarity of the drawing, and they are actually opposed to each other with a narrow gap of several μm to several tens μm. Although FIG. 4 shows a part of the liquid crystal device, only a 3 × 3 matrix formed by crossing three scanning lines 409 and three signal lines 410, that is, nine dots, is illustrated. Actually have more dots. In addition to the components shown in the figure, elements such as a liquid crystal alignment film, an insulating film, a spacer ball, a seal portion, a driver IC, and a drive circuit are indispensable, but they are not particularly necessary for describing the present invention. However, it is omitted because it may complicate the figure and make it difficult to understand.
[0027]
Each of the retardation plates 402 and 403 is a uniaxially stretched film of a polycarbonate resin. The color filter 408 used had a higher transmittance and a lighter color than those used in the conventional transmission type color liquid crystal device. The signal line 410 was made of metal Ta, and the metal reflection electrode 411 was made of Al-Nd alloy. The MIM element 412 has a structure in which an insulating film Ta2O5 is sandwiched between metal Ta and an Al-Nd alloy. Other components such as a liquid crystal and a light scattering plate were the same as those in Reference Example 1.
[0028]
Next, specific conditions of the liquid crystal cell will be introduced. First, the retardations of the upper retardation plate 402, the lower retardation plate 403, and the liquid crystal layer 406 in FIG. 4 were set to 0.27 μm, 0.25 μm, and 0.14 μm, respectively. Since the retardation of the upper retardation plate is about の of the green light wavelength having the highest visibility of visible light, it functions as a 波長 wavelength plate. Similarly, the lower retardation plate functions as a quarter-wave plate.
[0029]
FIG. 5 is a diagram showing the relationship between the axes of the liquid crystal device of Reference Example 2. Reference numeral 501 denotes a polarization axis (transmission axis) of the polarizing plate 401; 502, a slow axis (stretching axis) of the upper retardation plate 402; Denotes a slow axis (stretch axis) of the lower retardation plate 403, 504 denotes a rubbing axis of the upper substrate 405, and 505 denotes a rubbing axis of the lower substrate 406. Here, an angle 511 that 502 forms with 501 is 17 degrees to the left, an angle 512 that 503 forms with 501 is 79 degrees to the left, an angle 513 that 504 forms 501 is 135 degrees to the left, and an angle 505 forms 504. The twist angle 514 of the liquid crystal was set to 70 degrees left. If an angle between the delay axis of the half-wave plate and the transmission axis of the polarizing plate is θ, the angle 511 corresponds to θ. Since θ = 17, the angle 512 was set to 2θ + 45 = 2 × 17 + 45 = 79 degrees. Japanese Patent Application Laid-Open No. 5-100114 discloses that such a laminate of a polarizing plate and a retardation plate functions as a circular polarizing plate over a wide wavelength range. Note that the angle 512 may be set to approximately 2θ + 45.
[0030]
Since the liquid crystal device of Reference Example 2 manufactured as described above has a reflector inside the liquid crystal cell, a vivid color display was obtained. Moreover, high contrast was obtained because the light that was backscattered by the light scattering plate and the light that was reflected at each interface were absorbed by the combination of the retardation plate and the polarizing plate. The adoption of the MIM active matrix method was also effective in obtaining high contrast.
[0031]
(Example 1)
Three examples of the transflective liquid crystal device of the present invention and an electronic device using the same are shown. The transflective liquid crystal device of the present invention is suitable for portable equipment used in various environments and requiring low power consumption.
[0032]
FIG. 6A shows a mobile phone, in which a display unit 602 is provided at an upper front portion of a main body 601. Mobile phones are used in all environments, both indoors and outdoors. Especially, it is often used in cars, but the inside of cars at night is very dark. Therefore, as a display device used for a mobile phone, a transflective liquid crystal device capable of performing a transmissive display using auxiliary light as necessary, mainly a reflective display with low power consumption, is desirable. In the transflective liquid crystal device of the present invention, for example, in FIG. 1, the thickness of the metal reflective electrode 108 is reduced so that several percent of the light is transmitted, and a retardation plate and a polarized light are disposed outside the lower substrate 106. By arranging the plates, it is possible to easily change to a transflective liquid crystal device. The liquid crystal device of the present invention has a feature that the contrast ratio is higher than that of the conventional liquid crystal device in both the reflection type display and the transmission type display.
[0033]
FIG. 6B shows a watch in which a display unit 604 is provided at the center of the main body 603. An important aspect in watch applications is luxury. The liquid crystal device of the present invention not only has a high contrast but also has no double image due to parallax, so that a very high-quality display can be obtained as compared with the conventional liquid crystal device.
[0034]
FIG. 6C illustrates a portable information device in which a display unit 606 is provided above a main body 605 and an input unit 607 is provided below. Conventionally, such portable information devices often use a reflection type monochrome liquid crystal device. This is because a transmissive color liquid crystal device always uses a backlight, consumes a large amount of power, and has a short continuous use time. Even in such a case, if the reflective color liquid crystal device as in the first embodiment of the present invention is used, color display can be performed with low power consumption, so that an easy-to-use portable information device can be obtained.
[0035]
【The invention's effect】
As described above, according to the present invention, a transflective liquid crystal device having high contrast can be provided. Further, it is possible to provide a reflective color liquid crystal device capable of displaying a vivid color.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a main part of a structure of a liquid crystal device according to a reference example 1.
FIG. 2 is a diagram illustrating a relationship between axes of the liquid crystal device according to Reference Example 1.
FIG. 3 is a diagram for explaining the principle of display of the liquid crystal device in Reference Example 2.
FIG. 4 is a diagram illustrating a main part of a structure of a liquid crystal device according to a reference example 2.
FIG. 5 is a diagram illustrating a relationship between axes of the liquid crystal device according to Reference Example 2.
FIG. 6 is a diagram illustrating an appearance of the electronic device according to the first embodiment of the present invention. (A) a mobile phone, (b) a watch, and (c) a portable information device.
FIG. 7 is a diagram showing a main part of a structure of a conventional liquid crystal device.
[Explanation of symbols]
Reference Signs List 101 polarizing plate 102 retardation plate 103 light scattering plate 104 upper substrate 105 liquid crystal layer 106 lower substrate 107 transparent electrode 108 metal reflective electrode 201 polarization axis of polarizing plate (transmission axis)
202 Slow axis (stretch axis) of retardation plate
203 Upper substrate rubbing axis 204 Lower substrate rubbing axis 211 202 Angle 201 formed with 201 Angle 203 203 formed with 201 Angle 213 204 formed with 203, that is, twist angle of liquid crystal

Claims (4)

A transflective liquid crystal device having a liquid crystal layer disposed between a first substrate and a second substrate and capable of performing a reflective display or a transmissive display using a metal reflective electrode disposed on the liquid crystal layer side of the second substrate. At
A first polarizing plate is disposed on a side of the first substrate opposite to the liquid crystal layer, and a light scattering plate is disposed between the first polarizing plate and the first substrate. A first retardation plate is disposed between the first substrate and the first polarizing plate, and a second retardation plate and a second polarizing plate are disposed on the side of the second substrate opposite to the liquid crystal layer. Has been
The light transmitted through the first polarizing plate is transmitted through the first retardation plate to be in a state of circular polarization, is incident on the light scattering plate, and is transmitted through the first retardation plate. The retardation and the axial direction of the first retardation plate are set such that the back scattered light by the light scattering plate becomes linearly polarized and is absorbed by the first polarizing plate. Transflective liquid crystal device. The transflective liquid crystal device according to claim 1,
A transflective liquid crystal device, wherein the first retardation plate is a quarter-wave plate. The transflective liquid crystal device according to claim 1,
A transflective liquid crystal device, wherein the first retardation plate is a laminate in which a half-wave plate and a quarter-wave plate are arranged in this order from the first polarizing plate side. An electronic apparatus comprising the transflective liquid crystal device according to any one of claims 1 to 3 as a display unit.

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