JP3617520B2 - Liquid crystal device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technical field of a liquid crystal device, and more particularly to a transflective liquid crystal device capable of switching between a reflective display and a transmissive display.
[0002]
[Prior art]
Conventionally, a liquid crystal device includes a reflective liquid crystal device that performs display by reflecting external light through a liquid crystal by reflection means provided inside the device, and light source light from the light source provided inside the device via the liquid crystal. And a transflective liquid crystal device capable of switching between such a reflective display and a transmissive display.
[0003]
Of these, the reflective liquid crystal device does not use a light source, and thus consumes very little power. For this reason, it is often used for an auxiliary display part of portable devices and devices. A transflective liquid crystal device performs transmissive display using a light source in a dark place, but uses external light in a bright place in the same manner as a normal reflective liquid crystal device. small. For this reason, it is often used for an auxiliary display part of portable devices and devices.
[0004]
Such a conventional transflective liquid crystal device (see, for example, Patent Document 1) has a configuration in which a polarizing plate, a transflective plate, and a backlight are sequentially arranged on the outer surface of the liquid crystal panel opposite to the observation side. . Furthermore, in comparison with these, a transflective plate, a polarizing plate, and a backlight are sequentially arranged on the outer surface opposite to the viewing side of the liquid crystal panel, and there is no polarizing plate between the liquid crystal cell and the transflective plate. A transflective liquid crystal device in which the brightness of a reflective display is improved is known (for example, see Patent Document 2).
[0005]
In addition, with the development of portable devices and OA devices in recent years, there has been a demand for colorization of liquid crystal displays, and colorization is also necessary for devices using reflective or transflective liquid crystal devices. There are many cases. Here, when the above-described reflective or transflective liquid crystal device is used for color display, R (red), G (line), and B (on the one of the pair of substrates sandwiching the liquid crystal are used. A blue color filter having a large number of colored regions is provided (see Patent Document 3).
[0006]
In this case, in order to prevent color mixing between the colored areas in the color filter and to prevent a reduction in contrast ratio due to light leakage (white spots) in the gaps between the colored areas, a black mask is generally provided in the gaps between the colored areas. Alternatively, a light shielding film called a black matrix is provided.
[0007]
As another conventional example, a reflective color liquid crystal device (see Patent Document 3) in which a reflector is disposed so as to be in contact with a liquid crystal layer, and a transflective type in which a pixel electrode that also serves as a transflective film is provided on the inner surface of a liquid crystal cell. A liquid crystal device (see Patent Document 4) is known.
[0008]
[Patent Document 1]
Japanese Utility Model Publication No. 57-042771 [Patent Document 2]
JP-A-8-292413 [Patent Document 3]
Japanese Patent Laid-Open No. 9-258219 [Patent Document 4]
Japanese Patent Laid-Open No. 7-318929
[Problems to be solved by the invention]
However, the reflection type liquid crystal device described above has a basic problem that the display is difficult to read or cannot be read in a dark place because the display can be visually recognized using external light. For this reason, it is important to increase the reflectance of external light incident on the liquid crystal device and to increase the ratio of the portion of the incident external light that is reflected and emitted from the liquid crystal device as display light that contributes to display contrast. However, in the above-described reflective liquid crystal device, it cannot be said that the reflectance and the ratio of the portion that emits display light are sufficiently high.
[0010]
In particular, in the case of a reflective liquid crystal device that employs a configuration in which a transparent substrate is interposed between a liquid crystal layer and a reflective plate, there is a problem in that double reflection or display blurring occurs. In this case, when a color filter is further combined, there is a problem that sufficient color development cannot be obtained due to parallax. Alternatively, in this case, if a configuration in which the black mask is not provided in order to prevent light absorption by the black mask and increase the brightness of the display image, light passing through the gaps in the colored region is reflected by the reflector, The portion of the external light that does not contribute to the display contrast, that is, the portion that is emitted from the liquid crystal device regardless of the display image is relatively increased, and the contrast ratio is lowered.
[0011]
On the other hand, in the case of the reflective color liquid crystal device in which the reflector is disposed so as to be in contact with the liquid crystal layer described in Patent Document 3, each colored region of the color filter is used to brighten the display as described above. If a configuration without a black mask is used, the external light that has entered through the gaps in the colored area without the black mask is reflected by the reflector and is emitted outside the liquid crystal device with a part of the display light. As a result, color mixing occurs, causing the color to blur or blur, and the contrast ratio to decrease.
[0012]
As described above, the conventional reflective liquid crystal device has a problem that it is difficult to display a bright and high-contrast image.
[0013]
On the other hand, in the transflective liquid crystal device described in Patent Document 2, since a transmissive substrate is interposed between the liquid crystal layer and the transflective plate, double reflection or display blurring occurs. There is also a problem that sufficient color development cannot be obtained by parallax when a color filter is further combined.
[0014]
On the other hand, as described above, Patent Document 4 proposes a transflective liquid crystal device in which a pixel electrode that also serves as a transflective film is provided on the inner surface of a liquid crystal cell. A configuration in which a pixel electrode made of an ITO (Indium Tin Oxide) film is superimposed on a reflective film via an insulating film is disclosed. However, in this liquid crystal device, first, a fine defect portion such as a hole defect or a concave defect or a fine opening portion is formed on the pixel electrode that also serves as the semi-transmissive reflective film or the semi-transmissive reflective film on which the pixel electrode is superimposed. Therefore, it is difficult to manufacture a reliable pixel electrode or transflective film because the device configuration is complicated and a special process is additionally required in the manufacturing process.
[0015]
In particular, when a pixel electrode that also serves as a transflective film is employed, the liquid crystal portion through which the light source light that passes through the opening during transmissive display passes is obliquely distorted by the pixel electrode portion in the non-opening portion. Since it must be driven, the display quality deteriorates due to the disorder of the liquid crystal alignment as compared with the case where the liquid crystal is driven by a vertical electric field.
[0016]
Furthermore, when a configuration in which pixel electrodes are stacked on a semi-transmissive reflective film made of a metal film via an insulating film is adopted, each pixel electrode, insulating film, and semi-transmissive reflective film are provided between adjacent pixel electrodes. Capacitive coupling is caused through the constructed capacitor and the semi-transmissive reflective film. For this reason, signals such as image signals supplied to the plurality of pixel electrodes are mixed with each other or cross-talked to generate a so-called waveform rounding, which ultimately leads to deterioration of the quality of the display image. In addition, when the pixel electrode is used as a data line or a segment electrode to which an image signal having a complicated waveform and a high driving frequency is used as compared with a scanning signal or the like, such quality deterioration becomes more serious.
[0017]
As described above, the conventional transflective liquid crystal device has a problem that it is difficult to display a bright and high-contrast image.
[0018]
The present invention has been made in view of the above-described problems. In a transflective liquid crystal device, a liquid crystal device that does not cause double reflection due to parallax or blurring of display, and can display a bright and high-contrast image. It is an object to provide a device and an electronic device using the liquid crystal device.
[0019]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a pair of first and second substrates, a liquid crystal layer sandwiched between the first and second substrates, and a surface of the second substrate on the liquid crystal layer side. A plurality of transparent electrodes formed apart from each other, a reflection film formed between the plurality of transparent electrodes and the second substrate, and having a surface provided with irregularities, the reflection film, and the A liquid crystal device comprising: a color filter formed between a plurality of transparent electrodes and having a colored region facing each of the plurality of transparent electrodes; and a backlight disposed behind the second substrate. The region where the reflective film that transmits light from the backlight to the liquid crystal layer side is not provided is provided corresponding to the gap between the plurality of transparent electrodes, and the colored region of the color filter Is provided with the reflective film To provide a liquid crystal device according to claim disposed in overlapping regions and the reflective film of the transparent electrode and the region without.
[0020]
According to the liquid crystal device of the present invention, the portion of the external light incident from the first substrate side that has passed through the transparent electrode is reflected to the liquid crystal layer side by the reflective film formed in the region facing the transparent electrode, and reflected. Type display is performed. At this time, since the reflective film is disposed on the liquid crystal layer side of the second substrate, there is almost no gap between the reflective film and the liquid crystal layer. Does not occur. On the other hand, when the portion of the external light incident from the first substrate side that passes through the gap between the transparent electrodes is reflected to the liquid crystal layer side, so-called light omission (white omission) is caused and the contrast ratio is lowered.
[0021]
However, in the liquid crystal device of the present invention, the portion of the external light incident from the first substrate side that passes through the gap between the transparent electrodes passes through the region that is not provided with the reflective film facing the gap. In this region, the reflection film does not reflect the liquid crystal layer. Accordingly, it is possible to reduce image quality deterioration due to the light passing through the gap between the transparent electrodes reflected by the reflective film and mixed with the display light emitted to the outside.
[0022]
In one aspect of the liquid crystal device of the present invention, the reflective film includes a plurality of reflective films that are spaced apart from each other corresponding to the plurality of transparent electrodes. According to this aspect, the plurality of reflective films that are spaced apart from each other corresponding to the plurality of transparent electrodes can reflect the outside light that passes through the transparent electrodes, and the outside light that passes through the gap between the transparent electrodes. Can be passed through the gap between the reflecting films to prevent reflection.
[0023]
In another aspect of the liquid crystal device of the present invention, the liquid crystal device further includes a color filter formed on at least one of the first and second substrates and having a colored region facing the plurality of transparent electrodes, The color filter does not have a light shielding region in a region facing at least a part of a gap between the plurality of transparent electrodes. According to this aspect, the light that passes through the transparent electrode through the colored region of the color filter is reflected by the reflective film, and a color reflective display is performed.
[0024]
At this time, the color filter does not have a light-shielding region at least in a region where the reflective film is not provided facing the gap between the transparent electrodes. Therefore, although external light passes through the region between the colored regions that do not have the light-shielding region, no reflective film is formed in this region, so the external light is reflected by the reflective film and between adjacent colored regions. Therefore, it is possible to prevent the situation where the color image is mixed and the display is blurred or blurred.
[0025]
In another aspect of the liquid crystal device of the present invention, an insulating film is interposed between the transparent electrode and the reflective film. In this aspect, since the insulating film is interposed between the transparent electrode and the reflective film, even if the reflective film is made of a conductive material such as Al, a plurality of transparent electrodes may leak through the reflective film. The possibility of short-circuiting can be reduced, and the degree of freedom with respect to the planar pattern of the reflective film is increased.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a liquid crystal device according to the present invention will be described based on examples with reference to the drawings.
[0027]
An embodiment of a liquid crystal device according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic longitudinal sectional view showing the structure of an embodiment of a liquid crystal device according to the present invention. This embodiment basically relates to a simple matrix type liquid crystal display device, but can be applied to an active matrix type device, other segment type devices, and other liquid crystal devices with the same configuration. .
[0028]
In the transflective liquid crystal device according to the embodiment, a liquid crystal cell in which a liquid crystal layer 403 is sealed with a frame-shaped sealing material 404 is formed between two transparent substrates 401 and 402. The liquid crystal layer 403 is composed of nematic liquid crystal having negative dielectric anisotropy. A plurality of striped transparent electrodes 409 are formed of ITO or the like on the inner surface of the upper transparent substrate 401, and an alignment film 410 for vertically aligning liquid crystals is formed on the surface of the transparent electrode 409. The direction is rubbed.
[0029]
By this rubbing treatment, the liquid crystal molecules have a pretilt angle of about 85 degrees in the rubbing direction. In the case of an active matrix type device including a TFT element or a TFT element, the transparent electrode 409 is formed in a rectangular shape and connected to a wiring through the active element.
[0030]
On the other hand, unevenness having a height difference of about 8 μm is formed on the inner surface of the lower transparent substrate 402 by a photosensitive acrylic resin, and Al added with 1.0 wt% Nd on the surface has a thickness of 25 nm. A reflective film 411 is formed by sputtering with a thickness and then patterning into an island shape (see FIG. 2A) or a stripe shape (see FIG. 2B).
[0031]
Here, FIGS. 2A and 2B referred to as the formation example of the reflective film 411 of the present invention will be briefly described. FIG. 2A is a schematic front view of a lower transparent substrate when the present invention is applied to an active matrix type liquid crystal device using a TFD element. The reflective film 503 is formed on an island-shaped Al reflective film 503. The figure shows that an island-like ITO transparent electrode 504 having a larger area than that is laminated. Reference numeral 501 denotes a scanning line and 502 denotes a TFD element.
[0032]
FIG. 2B is a schematic front view of an example of a lower transparent substrate when the present invention is applied to a simple matrix type liquid crystal device, and a striped ITO transparent formed on the inner surface of the upper transparent substrate of the liquid crystal cell. In this example, a striped transparent electrode 603 is formed on the inner surface of the lower transparent substrate so as to intersect with the electrode 601. The striped transparent electrode 603 is slightly wider than the Al reflective film 602.
[0033]
In FIG. 1, a color filter 414 is formed on a reflective film 411 through a protective film 412, and three color layers of R, G, and B are arranged in a predetermined pattern on the color filter 414. A transparent protective film 415 is coated on the surface of the color filter 414, and a plurality of striped transparent electrodes 416 are formed on the surface of the protective film 415 by an ITO film or the like. Each is formed so as to intersect with the transparent electrode 409. An alignment film 417 is formed on the surface of the transparent electrode 416. Note that the alignment film 417 is not rubbed.
[0034]
A polarizing plate 405 is disposed on the outer surface of the upper transparent substrate 401, and a retardation plate (¼ wavelength plate) 406 is disposed between the polarizing plate 405 and the transparent substrate 401. Further, a retardation plate (¼ wavelength plate) 408 is disposed behind the transparent substrate 402 below the liquid crystal cell, and a polarizing plate 407 is provided behind the retardation plate (¼ wavelength plate) 408. Has been placed. A backlight having a fluorescent tube 419 that emits white light and a light guide plate 418 having an incident surface along the fluorescent tube 419 is disposed behind the polarizing plate 407.
[0035]
The light guide plate 418 is a transparent body such as an acrylic resin plate on which a rough surface for scattering is formed on the entire back surface or a printed layer for scattering is formed. The light guide plate 418 receives light from the fluorescent tube 419 as a light source on the surface. Thus, almost uniform light is emitted from the upper surface of the figure. As the other backlight, LED (light emitting diode), EL (electroluminescence), or the like can be used.
[0036]
In this embodiment, in order to prevent light from leaking from the region between the dots in the transmissive display, the black matrix layer 413 that is a light shielding portion formed between the colored layers of the color filter 414 is planarly formed. Almost correspondingly provided. The black matrix layer 413 is formed by depositing a Cr layer or a photosensitive black resin layer.
[0037]
Here, as shown in FIG. 3A, the transmission axes Pl and P2 of the polarizing plate 405 and the polarizing plate 407 are set in the same direction, and the retardation plate is set with respect to the transmission axes P1 and P2 of these polarizing plates. The directions of the slow axes Cl and C2 of the (¼ wavelength plates) 406 and 408 are set to the direction rotated clockwise by θ = 45 degrees. Further, the rubbing treatment direction R1 of the alignment film 410 on the inner surface of the transparent substrate 401 is also applied in a direction that coincides with the directions of the slow axes C1 and C2 of the phase difference plates (¼ wavelength plates) 406 and 408. ing.
[0038]
The rubbing direction R1 defines the direction in which the major axis of the liquid crystal molecules tilts when an electric field is applied to the liquid crystal layer 403. A negative nematic liquid crystal is used for the liquid crystal layer 403. FIG. 3B shows the drive voltage characteristic of the reflectance in the reflective display according to this embodiment and the drive voltage characteristic of the transmittance in the transmissive display. The display state when no electric field is applied is dark (black). When this liquid crystal cell is used, it is not necessary to form the black matrix layer 413.
[0039]
Next, referring to FIG. 1, the operation of the reflective display and the transmissive display in the present embodiment configured as described above will be described. First, in the case of reflective display, external light incident on the liquid crystal device from the upper side in FIG. 1 is transmitted through the polarizing plate 405 and the phase difference plate 406, passes through the liquid crystal layer 403, passes through the color filter 414, and is reflected on the reflective film. The light is reflected by 411 and emitted from the polarizing plate 405 again. At this time, the bright state, the dark state, and the intermediate brightness are controlled by the voltage applied to the liquid crystal layer 403.
[0040]
In the case of transmissive display, light from the backlight is converted into predetermined polarized light by the polarizing plate 407 and the retardation plate 408 and is introduced into the liquid crystal layer 403 through the gaps of the reflective film 411 and passes through the color filter 414 and the liquid crystal layer 403. Thereafter, the light passes through the retardation plate 406. At this time, according to the voltage applied to the liquid crystal layer 403, the state of light transmitted through the polarizing plate 405 (bright state), the state of absorption (dark state), and the intermediate brightness can be controlled.
[0041]
2A and 2B referred to in the above description of the reflective film 411 of the present invention, in the case of transmissive display, the reflective film 503 or the reflective film 602 out of the light incident on the liquid crystal cell from the backlight. Only the light source light from the backlight that enters the transparent electrode 504 or the transparent electrode 603 portion through the gap is introduced into the liquid crystal layer.
[0042]
According to the configuration of the present embodiment as described above, a color liquid crystal device capable of switching and displaying a reflective display and a transmissive display that do not have double projection or display blur is realized.
[0043]
The reflective film 411 of this embodiment uses a metal layer containing Al as a main component, the surface is covered with a protective film 412, and a color filter 414, a protective film 415, and a transparent electrode 416 are formed thereon. For this reason, since the Al metal layer does not come into direct contact with the ITO developer or the color filter developer, the A1 metal layer is not dissolved by the developer. Furthermore, it is possible to easily handle an Al metal layer that is easily damaged. For example, Al having a thickness of 25 nm to which 1.0% by weight of Nd is added exhibits values of a reflectance of 80% and a transmittance of 10%, and functions sufficiently as the reflective film 411.
[0044]
Further, the reflective film 411 provided with unevenness can reflect the reflected light at a wide angle, so that a liquid crystal device with a wide viewing angle is realized. In this embodiment, instead of forming a protective film on the reflective film, the reflective film is anodically oxidized or thermally oxidized, or in addition to the oxide film obtained by anodizing, an organic substance is formed by spin coating. An insulating film may be formed on the reflective film by applying and laminating.
[0045]
The colored layer of the color filter 414 used in the embodiment described above will be described with reference to FIG. FIG. 4 is a characteristic diagram showing the transmittance of each colored layer of the color filter 414.
[0046]
In this embodiment, when performing reflective display, incident light once passes through one of the colored layers of the color filter 414, then passes through the liquid crystal layer, is reflected by the reflective film, and passes through the colored layer again. Released from. Therefore, unlike a normal transmissive liquid crystal device, the color filter 414 passes twice, so the display becomes dark and the contrast decreases with the normal color filter.
[0047]
Therefore, in this embodiment, as shown in FIG. 4, the color filter 414 is formed in a light color so that the minimum transmittance 61 in the visible region of each colored layer of R, G, B is 25 to 50%. Yes. The colored layer is lightened by reducing the thickness of the colored layer or reducing the concentration of the pigment or dye mixed in the colored layer. Thus, it is possible to configure so that the brightness of the display is not lowered when performing the reflective display.
[0048]
This lightening of the color filter 414 causes a lightening of the display because it is transmitted only once through the color filter 414 in the case of transmissive display, but in this embodiment, a large amount of backlight light is blocked by the reflective film. In many cases, it is rather convenient for ensuring the brightness of the display.
[0049]
The liquid crystal device of the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit or concept of the invention that can be read from the claims and the entire specification. Such a liquid crystal device is also included in the technical scope of the present invention.
[0050]
【The invention's effect】
The liquid crystal device according to the present invention can be used as various display devices capable of displaying a bright and high-contrast image, and can be used as a liquid crystal device constituting a display unit of various electronic devices. An electronic device according to the present invention includes a liquid crystal television, a viewfinder type or a monitor direct-view type video tape recorder, a car navigation device, an electronic notebook, a calculator, a word processor, a workstation, It can be used as a mobile phone, a video phone, a POS terminal, a touch panel and the like.
[0051]
In particular, when the liquid crystal device according to the present invention is used as a display unit of a portable information device, a portable information device with a bright display can be obtained regardless of whether it is a reflective type, a transflective type, or a transmissive type.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing a schematic structure of an embodiment of a liquid crystal device according to the present invention.
2A is a plan view showing an example of a semi-transmissive reflective film made of a reflective film arranged with a gap in an embodiment of a liquid crystal device according to the present invention, and FIG. It is a top view which shows the other example of the semi-transmissive reflective film which consists of a reflective film arrange | positioned at the gap | interval in the Example of the liquid crystal device which concerns.
FIG. 3A is an explanatory diagram showing a relationship between a rubbing direction of a polarizing plate, a retardation plate, and a liquid crystal cell in an embodiment of a liquid crystal device according to the present invention. (B) is a characteristic diagram showing a driving voltage-one reflectance / transmittance characteristic of the liquid crystal device having the relationship of (a).
FIG. 4 is a graph showing the light transmittance of each color layer of the color filter in the example of the liquid crystal device according to the present invention.
[Explanation of symbols]
401, 402 Transparent substrate 403 Liquid crystal layer 404 Sealing material 406, 408 Phase difference plate (1/4 wavelength plate)
407 Polarizing plate 409, 416, 504, 601, 603 Transparent electrode 410, 417 Alignment film 411, 503, 602 Reflective film 412, 415 Protective film 414 Color filter 418 Light guide plate 419 Fluorescent tube

Claims (3)

A pair of first and second substrates;
A liquid crystal layer sandwiched between the first and second substrates;
A plurality of reflective films used for reflective display formed in an island shape on the surface of the second substrate on the liquid crystal layer side;
And island-like transparent electrodes formed on the island-shaped reflection film corresponding to each of the plurality of reflecting films formed on the island,
A backlight disposed behind the second substrate;
A liquid crystal device comprising:
Together with the island-like transparent electrodes formed on the island-shaped reflection film and the island-shaped reflection film is formed to have a region where mutually becomes heavy, the island-like transparent electrodes are shaped the island It is also formed in a part between the plurality of reflective films formed in the area from the backlight in the region where the part of the transparent electrode is formed between the plurality of reflective films formed in the island shape. A liquid crystal device which performs transmissive display using the light of the above . The liquid crystal according to claim 1, wherein the liquid crystal layer is a liquid crystal having negative dielectric anisotropy, and an alignment film for vertically aligning the liquid crystal is formed on a surface of the transparent electrode. apparatus. A resin having unevenness is formed on the surface of the second substrate on the liquid crystal layer side, and the island-like reflective film is formed on the resin so that the surface has unevenness. The liquid crystal device according to claim 1, wherein the liquid crystal device is a liquid crystal device.

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