JP4082426B2 - Liquid crystal device and electronic device - Google Patents

Description

  The present invention relates to a liquid crystal device, in particular, a reflective color liquid crystal device, and further relates to an electronic apparatus equipped with the liquid crystal device.

  A reflective liquid crystal device with low power consumption is suitable for 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 double image due to parallax. This is a phenomenon in which there is a distance corresponding to the thickness of the lower substrate (for example, 0.7 mm) between the liquid crystal layer and the reflecting plate, and the shadow overlaps with the original display. Make the display difficult to recognize. In addition, when a color filter is provided corresponding to each dot of the dot matrix display and the reflective color display is performed, the vividness of the display color is also improved by passing the incident light and the reflected light which are different due to the parallax. There was a problem of being damaged.

  In order to solve these problems, Tatsuo Uchida et al. In AsiaDisplay'95 p.599 have proposed a method of reducing the distance between the liquid crystal layer and the reflector by providing a metal reflective electrode in the liquid crystal cell. was suggested. The outline of the structure is shown in FIG. In FIG. 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 in order to diffuse specular reflection by the metal reflecting electrode and widen the viewing angle, but uses a front scattering plate in order not to lower the contrast. The forward scattering plate is a light scattering plate that has a large scattering of transmitted light (referred to as forward scattering) and has little scattering of reflected light (referred to as backward scattering). However, it is difficult to obtain an ideal forward scattering plate in this way, and an existing forward scattering plate is accompanied by backscattering to some extent, so that a reduction in contrast is inevitable with the structure shown in FIG.

  In such a case, as disclosed in JP-A-9-113893, it is effective to dispose a light scattering plate closer to the liquid crystal cell than the polarizing plate. When arranged in this way, at least half of the light backscattered by the light scattering plate is absorbed by the polarizing plate, so that the contrast is improved. The above Japanese Patent Laid-Open No. 9-113893 does not mention this effect because the light scattering plate used is special.

  However, even if the light scattering plate is arranged under the polarizing plate in this way, the backscattering is only halved, never becomes zero, and there is a problem that high contrast cannot be obtained.

  Accordingly, an object of the present invention is to provide a reflective liquid crystal device having a high contrast by devising the position and axial direction of the light scattering plate and preventing back scattering by the light scattering plate. Another object of the present invention is to provide a reflective color liquid crystal device capable of displaying bright colors.

  The liquid crystal device of the present invention includes a polarizing plate, a half-wave plate, a quarter-wave plate, a light scattering plate, a first substrate provided with a transparent electrode, a liquid crystal layer, and a metal reflective electrode. The second substrate is arranged in this order, and the light incident from the polarizing plate side passes through the half-wave plate and the quarter-wave plate and is circularly polarized in the state of circular polarization. The ½ wavelength plate and the ½ wavelength plate so that back scattered light by the light scatter plate transmitted through the ¼ wavelength plate is absorbed by the polarizing plate so as to reach the light scattering plate. An axial direction of the wave plate and the quarter wave plate is set, and the light scattering plate is composed of two kinds of minute regions having different refractive indexes, and is a light scattering plate having strong forward scattering and small back scattering. Features. With this configuration, the circularly polarized light back-scattered by the light scattering plate is converted into linearly polarized light perpendicular to the transmission axis of the polarizing plate by the retardation plate and absorbed by the polarizing plate. Therefore, the liquid crystal device of the present invention has an effect that high contrast can be obtained.

  In the liquid crystal device of the present invention, it is preferable that the retardation plate is a ¼ wavelength plate and the delay axis thereof intersects with the absorption axis of the polarizing plate at an angle of approximately 45 degrees. The quarter-wave plate is preferably a retardation plate whose retardation is about ¼ of the visible light wavelength. The visible light wavelength often refers to the wavelength of green light having the highest visibility. Since it comprised in this way, it has the effect that the light which reaches | attains a light-scattering board with the simplest structure is converted into circularly polarized light, and high contrast is obtained.

  The liquid crystal device of the present invention is a laminate in which the retardation plate is arranged in the order of a half-wave plate and a quarter-wave plate from the polarizing plate side, and the retardation axis of the half-wave plate and the transmission of the polarizing plate. When the angle formed with the axis is θ, the angle formed between the delay axis of the quarter-wave plate and the transmission axis of the polarizing plate is preferably approximately 2θ + 45 degrees. A half-wave plate is a retardation plate whose retardation is about ½ of the visible light wavelength. Since it comprised in this way, it has the effect that the light of the wide wavelength range which reaches | attains a light-scattering plate is converted into circularly polarized light, a high contrast is obtained and the coloring of a display is small.

  In the liquid crystal device of the present invention, when no voltage is applied to the liquid crystal layer, the retardation of the liquid crystal layer is such that light incident from the polarizing plate side reaches the metal reflective electrode in a linearly polarized state. It is preferable to set a twist angle. With this configuration, a bright display can be obtained 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 the backscattering of the light scattering plate as well as all other interface reflections are removed by the phase difference plate arrangement. Therefore, a display with a very high contrast can be obtained.

  An electronic apparatus according to the present invention includes the liquid crystal device as a display unit. With such a configuration, the electronic device of the present invention can obtain a high-quality display with low power consumption.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
FIG. 1 is a diagram showing a main part of the structure of a liquid crystal device according to the present invention. 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 bonded to each other with glue. Also, the upper and lower substrates are drawn widely apart, but this is for clarity of illustration, and in reality, they face each other with a narrow gap of several μm to several tens of 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 part, a driver IC, and a drive circuit are indispensable, but these are not particularly necessary for explaining the present invention. However, it is omitted because it may complicate the figure and make it difficult to understand.

  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 prepared by adsorbing a halogen substance such as iodine or a dichroic dye onto a polymer film such as poly, vinyl, or petital.

  The phase difference plate 102 is a uniaxially stretched film of a poly / vinyl / alcohol resin. The retardation is 0.14 μm, which is about ¼ of the green light wavelength with the highest visibility of visible light, and functions as a ¼ wavelength plate.

  The light scattering plate 103 is preferably a film composed of two kinds of minute regions having different refractive indexes. By being configured in this way, a light scattering plate with strong forward scattering and low backscattering can be obtained. Specifically, a plastic film in which fine beads are dispersed in a transparent binder having a refractive index different from that of the beads can be used. Alternatively, a plastic film in which two kinds of micro regions having different refractive indexes form a layer structure and scatter only light incident from a specific angle may be used.

  As the liquid crystal layer 105, a nematic liquid crystal composition twisted from 0 degree to 270 degrees can be used. The twist angle is determined by the direction of alignment treatment on the upper and lower glass substrate surfaces and the amount of chiral agent added to the liquid crystal.

  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 made of ITO, and the metal reflective electrode 108 was made of an Al—Nd alloy.

  Next, specific liquid crystal cell conditions are 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 of each axis, 201 is a polarization axis (transmission axis) of the polarizing plate 101, 202 is a slow axis (stretching axis) of the retardation plate 102, 203 is a rubbing axis of the upper substrate 104, Reference numeral 204 denotes a rubbing shaft of the lower substrate 106. Here, the angle 211 formed by 202 with 201 is set to 45 degrees to the left, the angle 212 formed with 203 to the left is 101 degrees, and the angle formed with 204 to 203, that is, the twist angle 213 of the liquid crystal is set to 70 degrees left. Note that the angle 211 only needs to be set to approximately 45 degrees, and there is no problem with some deviation.

  In the liquid crystal device of Example 1 configured as described above, a display with very high contrast was obtained. The principle will be briefly described with reference to FIG.

  In FIG. 3, 301 is a polarizing plate, 302 is a retardation plate, 303 is a light scattering plate, 304 is an upper substrate, 305 is a lower substrate, 306 is a liquid crystal layer to which no voltage is applied, and 307 has a sufficiently high voltage. It is the applied liquid crystal layer. Each component is drawn widely apart to illustrate the polarization state. 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 light that vibrates in all directions.

  Natural light 311 and 312 are converted into linearly polarized light by the polarizing plate 301, further converted into counterclockwise 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 into clockwise circularly polarized light, and returns to linearly polarized light again by the phase difference plate 302. This linearly polarized light oscillates in a direction perpendicular to the transmission axis of the polarizing plate 301. Therefore, it is absorbed by the polarizing plate. Similarly, the light reflected backward at the interface between the upper substrate and the transparent electrode is also absorbed by the polarizing plate. Since all of the light reflected backward does not contribute to the display, high contrast can be obtained by absorbing such light.

  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 reflection plate. This is because the retardation and twist angle of the liquid crystal layer are set in advance so as to do so. The reflected light follows exactly the same path and is returned to the original left-handed circularly polarized light. Such conversion is generally applicable to a liquid crystal layer that performs conversion so as to be linearly polarized light on the reflecting plate, and is described in detail in JP-A-3-223715. The counterclockwise 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.

  Of the light scattered forward by the light scattering plate, the light incident on the liquid crystal layer 307 reflects the metal as left-handed circularly polarized light because the liquid crystal is aligned almost in parallel with the incident light and has no birefringence. It 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 previous light scattering plate and is absorbed by the polarizing plate, resulting in dark display.

  As described above, the liquid crystal device according to the first embodiment absorbs the light back-scattered by the light-scattering plate and the light reflected from each interface by the combination of the retardation plate and the polarizing plate, so that high contrast can be obtained. In addition, by providing a dark display in a state where a sufficient voltage is applied to the liquid crystal layer, a high contrast that could not be realized in the conventional single-polarization-type liquid crystal display mode was obtained.

(Example 2)
FIG. 4 is a diagram showing a main part of the structure of the liquid crystal device according to the present invention. First, the configuration will be described. In FIG. 4, 401 is a polarizing plate, 402 is an upper retardation plate, 403 is a lower retardation plate, 404 is a light scattering plate, 405 is an upper substrate, 406 is a liquid crystal layer, 407 is a lower substrate, and 408 is a color filter. , 409 are scanning lines using transparent electrodes, 410 is a signal line, 411 is a metal reflective electrode, and 412 is an MIM element. 401 and 402, 402 and 403, 403 and 404, and 404 and 405 are bonded to each other with glue. Also, the upper and lower substrates are drawn widely apart, but this is for clarity of illustration, and in reality, they face each other with a narrow gap of several μm to several tens of μm. 4 shows a part of the liquid crystal device, only a 3 × 3 matrix formed by the intersection of three scanning lines 409 and three signal lines 410, that is, only nine dots is shown. In fact, it has 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 part, a driver IC, and a drive circuit are indispensable, but these are not particularly necessary for explaining the present invention. However, it is omitted because it may complicate the figure and make it difficult to understand.

  The retardation plates 402 and 403 are both uniaxially stretched films of polycarbonate resin. The color filter 408 used has a higher transmittance and a lighter color than those used in conventional transmission type color liquid crystal devices. The signal line 410 was made of metal Ta, and the metal reflective 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. In addition, the same components as those in Example 1 were used for the constituent elements such as the liquid crystal and the light scattering plate.

  Next, specific liquid crystal cell conditions are 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. The retardation of the upper retardation plate functions as a ½ wavelength plate because it is about ½ of the green light wavelength with the highest visibility of visible light. Similarly, the lower retardation plate functions as a quarter wavelength plate.

  FIG. 5 is a diagram showing the relationship between the axes of the liquid crystal device of Example 2. Reference numeral 501 denotes a polarization axis (transmission axis) of the polarizing plate 401, 502 denotes a slow axis (stretching axis) of the upper retardation plate 402, and 503. Is the slow axis (extension axis) of the lower retardation plate 403, 504 is the rubbing axis of the upper substrate 405, and 505 is the rubbing axis of the lower substrate 406. Here, the angle 511 between 502 and 501 is 17 degrees to the left, the angle 512 between 503 and 501 is 79 degrees to the left, the angle 513 between 504 and 501 is 135 degrees to the left, and the angle between 505 and 504, The twist angle 514 of the liquid crystal was set to 70 degrees to the left. If the angle formed 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. JP-A-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. The angle 512 may be set to approximately 2θ + 45.

  Since the liquid crystal device of Example 2 produced as described above has a reflector inside the liquid crystal cell, a vivid color display was obtained. In addition, since the light back scattered by the light scattering plate and the light reflected by each interface are absorbed by the combination of the phase difference plate and the polarizing plate, a high contrast is obtained. Employing the MIM active matrix method is also effective in obtaining high contrast.

(Example 3)
Three examples of the electronic apparatus of the present invention are shown. The liquid crystal device of the present invention is suitable for portable devices that are used in various environments and require low power consumption.

  FIG. 6A shows a mobile phone, in which a display unit 602 is provided in the upper front portion of the main body 601. Mobile phones are used in all environments, indoors and outdoors. Although it is often used in automobiles, it is very dark at night. Therefore, it is desirable that the display device used for the mobile phone is a transflective liquid crystal device capable of performing transmissive display using auxiliary light as necessary, mainly reflective display with low power consumption. In the 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 light is transmitted, and a retardation plate and a polarizing plate are disposed outside the lower substrate 106. Thus, the transflective liquid crystal device can be easily changed. 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 reflective display and the transmissive display.

  FIG. 6B shows a watch, and a display portion 604 is provided in the center of the main body 603. An important aspect in watch applications is luxury. Since the liquid crystal device of the present invention has high contrast and does not have a double image due to parallax, a very high-quality display can be obtained as compared with a conventional liquid crystal device.

  FIG. 6C illustrates a portable information device, in which a display unit 606 is provided on the upper side of the main body 605 and an input unit 607 is provided on the lower side. Conventionally, a reflective monochrome liquid crystal device is often used for such portable information equipment. This is because the transmissive color liquid crystal device uses a backlight at all times and consumes a large amount of power and has a short continuous use time. Even in such a case, if a reflective color liquid crystal device as in the third embodiment of the present invention is used, color display can be performed with low power consumption, and an easy-to-use portable information device can be obtained.

〔The invention's effect〕
As described above, according to the present invention, a reflective liquid crystal device with high contrast can be provided. In addition, it is possible to provide a reflective color liquid crystal device that can display bright colors.

It is a figure which shows the principal part of the structure of the liquid crystal device in Example 1 of this invention. It is a figure which shows the relationship of each axis | shaft of the liquid crystal device in Example 1 of this invention. It is a figure for demonstrating the principle of a display of the liquid crystal device in Example 1 of this invention. It is a figure which shows the principal part of the structure of the liquid crystal device in Example 2 of this invention. It is a figure which shows the relationship of each axis | shaft of the liquid crystal device in Example 2 of this invention. It is a figure which shows the external appearance of the electronic device in Example 3 of this invention. (A) a mobile phone, (b) a watch, (c) a portable information device. It is a figure which shows the principal part of the structure of the conventional liquid crystal device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Polarizing plate 102 Phase difference 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 (transmission axis) of polarizing plate
202 Slow axis (stretching axis) of retardation plate
203 rubbing axis of upper substrate 204 rubbing axis of lower substrate 211 angle formed by 202 212 angle formed by 203 203 angle formed by 203 213 204, that is, twist angle of liquid crystal

Claims (3)

A polarizing plate, a half-wave plate, a quarter-wave plate, a light scattering plate, a first substrate provided with a transparent electrode, a liquid crystal layer, and a second substrate provided with a metal reflective electrode A liquid crystal device arranged in this order,
The light incident from the polarizing plate side passes through the half-wave plate and the quarter-wave plate and reaches the light scattering plate in a circularly polarized state, and the half-wave plate And set the axial direction of the half-wave plate and the quarter-wave plate so that backscattered light from the light-scattering plate that has passed through the quarter-wave plate is absorbed by the polarizing plate,
The light scattering plate is a light scattering plate which is composed of two kinds of minute regions having different refractive indexes, and is a light scattering plate having strong forward scattering and small back scattering. The liquid crystal device according to claim 1,
The retardation of the half-wave plate is about ½ wavelength of the green light wavelength, and the retardation of the ¼ wavelength plate is about ¼ of the green light wavelength. An electronic apparatus comprising the liquid crystal device according to claim 1 as a display unit.

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