Vertical alignment mode LCD with larger dielectric protrusions in transmissive region than in reflection region

The invention provides a liquid crystal display device having a wide viewing angle for transmissive display and reflective display. The liquid crystal display device according to the invention can include a homeotropic liquid crystal layer interposed between a pair of substrates. The liquid crystal display device has a transmissive display area and a reflective display area in each dot area. A liquid crystal layer thickness-adjustment layer can be interposed between at least the substrate of the pair of substrates and the liquid crystal layer. The liquid crystal layer thickness-adjustment layer reduces the liquid crystal layer thickness of the reflective display area in comparison with the liquid crystal layer thickness of the transmissive display area. On the substrate opposing the substrate with the liquid crystal layer thickness-adjustment layer, protrusions protruding from the inner surface of the substrate to the liquid crystal layer are formed.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a liquid crystal device and an electronic apparatus. More specifically, the invention relates to a technology for obtaining a wider viewing angle for the liquid crystal display device using homeotropic liquid crystal.

2. Description of Related Art

A liquid crystal device having a reflective mode and a transmissive mode is known as a transreflective liquid crystal device. Such a transreflective liquid crystal device has a liquid crystal layer interposed between an upper substrate and a lower substrate. A reflective film having a window for transmitting light through the film, composed of a metal plate, e.g., an aluminum plate, is disposed on the inner surface of the lower substrate. The reflective film functions as a transreflective plate. In such a case, in the reflective mode, the light entering from the upper substrate is transmitted through the liquid crystal layer and, then, is reflected at the reflective film on the inner surface of the lower substrate. The light passes through the liquid crystal layer again and is emitted out from the upper substrate to be used for displaying an image. In the transmissive mode, the light from the backlight enters from the lower substrate and passes through the window on the reflective film and then through the liquid crystal layer. Subsequently, the light is emitted to the outside from the upper substrate to be used for displaying an image.

Consequently, the area on the reflective film where the window is formed functions as a transmissive display area and the other areas functions as a reflective display area.

Known transreflective liquid crystal devices have a problem in which the viewing angle is small in transmissive display. This is because only one polarization plate disposed on the viewer's side can be used for reflective display because a transreflective plate is disposed on the inner surface of the liquid crystal cell to prevent parallax, causing the flexibility in the optical design of the device to become small. To solve this problem, Jisaki et al. proposed, in “Development of transreflective LCD for high contrast and wide viewing angle by using homeotropic alignment,” M. Jisaki et al., Asia Display/IDW′01, p. 133-136 (2001), a new liquid crystal display device using homeotropic liquid crystal. This new liquid crystal display device has three characteristics:

1) operating in a vertical alignment mode wherein liquid crystal molecules having negative dielectric anisotropy are aligned vertically relative to a substrate and, then, are tilted by applying a voltage;

2) having a multi-gap structure wherein the thickness of the liquid crystal layer (cell gap) in the transmissive display area and in the reflective display area differ (for example, refer to Japanese Unexamined Patent Application Publication No. 11-242226);

3) having a multi-domain structure wherein the transmissive display area is shaped as a regular octagon with a projection formed in the center of the regular octagon on the opposing substrate so that the liquid crystal molecules tilt in eight different directions within the transmissive display area.

SUMMARY OF THE INVENTION

Incorporating a multi-gap structure described above in a transreflective liquid crystal display device is extremely effective for balancing the electro-optical characteristics (transmittance-voltage characteristic and reflectance-voltage characteristic) in the transmissive display area and in the reflective display area. This is because, in the transmissive display area, light passes through the liquid crystal layer only once but, in the reflective display area, light passes through the liquid crystal layer twice.

However, a great difference is created in the distance between the substrates of a liquid crystal display device having a multi-gap structure and having projections for controlling the direction of tilt of the liquid crystal molecules. This is a problem because it is difficult to form projections on the substrates where the distance between the substrates differ and it is difficult to control the height of these projections. Not being able to form the projections with a predetermined height may cause a problem in that the direction of tilt of liquid crystal molecules cannot be controlled.

The object of the invention is to provide a liquid crystal display device enabling display with a wide viewing angle by solving the above-mentioned problems by providing a transreflective liquid crystal display device using homeotropic liquid crystal in which the direction of tilt of the liquid crystal molecules can be controlled easily and accurately. Another object of the invention is to provide a simply-structured transreflective liquid crystal display device using homeotropic liquid crystal. In this way, the manufacturing efficiency of the liquid crystal display device is improved and the reliability is increased in that the number of possible defects is reduced. Another object of the invention is to provide a highly reliable electronic apparatus including the liquid crystal display device.

In order to achieve the above-mentioned object, a liquid crystal display device according to the invention can include a liquid crystal layer interposed between an upper and a lower substrate and a dot area including both a transmissive display area and a reflective display area. The liquid crystal layer is composed of liquid crystal that is vertically aligned at an initial alignment state and has negative dielectric anisotropy. Interposed between at least the lower substrate and the liquid crystal layer is a liquid crystal layer thickness-adjustment layer for reducing the thickness of the liquid crystal layer in the reflective display area in comparison with the thickness of the liquid crystal layer in the transmissive display area. On the upper substrate without the liquid crystal layer thickness-adjustment layer, protrusions protruding from the inner surface of the substrate to the liquid crystal layer are formed. In the invention, the inner surface of the substrate refers to the surface of the substrate adjacent to the liquid crystal layer. Moreover, the protrusions protruding from the surface of the substrate refers to protrusions protruding from the inner surface of the liquid crystal layer thickness-adjustment layer when there is a liquid crystal layer thickness-adjustment layer formed on the inner surface of the substrate.

As described above, the liquid crystal display device according to the invention is a transreflective liquid crystal display using homeotropic liquid crystal. Furthermore, the liquid crystal display device has the liquid crystal layer thickness-adjustment layer for substantially equalizing the retardation in the reflective display area and the transmissive display area. In other words, the liquid crystal display device has a multi-gap structure. In this way, the alignment direction of the liquid crystal molecules is controlled effectively.

More specifically, a homeotropic liquid crystal display device tilts the liquid crystal molecules, which are vertically aligned at an initial alignment state, with respect to the substrate surface by applying an electrical field. Without inducing a pre-tilt, the turning direction of the liquid crystal molecules cannot be controlled. Thus, disarrangement (disclination) of the alignment of the liquid crystal molecules occurs, causing a failure in display such as leakage of light. As a result, the quality of the display can be reduced. Thus, in a homeotropic liquid crystal, it is important to control the alignment direction of the liquid crystal molecules when an electric field is applied.

In the liquid crystal display device according to the invention, the protrusions protruding from the inner surface of the substrate into the liquid crystal layer are formed to control the alignment direction of the liquid crystal molecules. Due to this structure, the liquid crystal molecules are vertically aligned at an initial alignment state and have a pre-tilt according to the shape of the protrusions. As a result, the direction of tilt of the liquid crystal molecules can be restricted or controlled. In this way, disarrangement (disclination) of the alignment of the liquid crystal molecules hardly occur and failures of display such as leakage of light can be prevented. Consequently, failures of display such as residual images and smear-like unevenness are suppressed, and a liquid crystal display device with a wide viewing angle is provided.

Since in the liquid crystal display device according to the invention has a multi-gap structure, the liquid crystal layer thickness of the transmissive display area is greater than that of the reflective display area. For this reason, the electro-optical characteristics (transmittance-voltage characteristic and reflectance-voltage characteristic) in the transmissive display area and the reflective display area are balanced.

Since the protrusions are formed on the substrate without the liquid crystal layer thickness-adjustment layer for the multi-gap structure, the formation of the protrusions and the setting of the height of the protrusions are easy. More specifically, since the liquid crystal layer thickness-adjustment layer on the substrate obviously causes a difference in the distance between the substrates (which forms the multi-gap structure), it is extremely difficult to form protrusions where there is a difference in the distance between the substrate. In other words, it is difficult to form the protrusions on the substrate where the distance between the substrates is small. Also the height of the protrusions may differ depending on whether they are formed on the substrate where the distance between the substrate is large or small. Contrarily, by adopting the structure of the invention, the protrusions can be formed on a relatively flat surface. Accordingly, the above-mentioned problems do not occur and the protrusions can be formed extremely easily. Moreover, the setting of the height of the protrusions is also extremely easy.

The protrusions of the liquid crystal display device according to the invention function as a device for controlling the alignment of the liquid crystal molecules. The protrusions have inclined surfaces having a slope of a predetermined angle with respect to the inner surface of the substrate. The inclined surfaces of the protrusions enable control of the direction of the liquid crystal molecules in which they tilt along the inclined surface. The protrusions can be formed on dot areas, which are display areas. The protrusions are preferably formed on the transmissive display area instead of the reflective display area.

Electrodes for driving the liquid crystal are formed on the inner surface of the upper and lower substrates. The protrusions are formed on at least the electrodes on the inner surface of the upper substrate. In this case, an alignment film for vertically aligning the liquid crystal molecules is disposed on the inner surfaces of the protrusions and/or the electrodes. On each outer surface of the upper and lower substrates, circular polarization plates for emitting circularly polarized light into the liquid crystal layer may be disposed. As the circular polarization plates, a combination of a polarization layer and a retardation layer may be used.

The liquid crystal display device according to the invention includes the upper substrate and the lower substrate. On the outer surface of the lower substrate, a backlight for transmissive display is disposed. On the inner surface of the lower substrate, a reflective layer is disposed selectively in the reflective display area. In this case, the light from the backlight entering from the lower substrate is used for the transmissive display, and the outside light such as lighting or sunlight entering from the upper substrate is reflected at the reflective layer and used for the reflective display.

On the lower substrate with the liquid crystal layer thickness-adjustment layer, a color filter layer may be disposed. The color filter layer may be composed of a plurality of color layers in which the color layers are stacked on the areas between the dots. In this case, the stacked color layers are capable of displaying the color black. Thus, the stacked color layer can be used as a black matrix in the areas between the dots. Accordingly, it is unnecessary to form another black matrix, and the structure of the liquid crystal display device becomes simple and the production efficiency is improved.

On the inner surface of the color filter layer, the liquid crystal layer thickness-adjustment layer is disposed so that it covers the area with stacked color layers. The upper substrate without the color filter layer and the liquid crystal layer thickness-adjustment layer has second protrusions protruding from the inner surface of the substrate to the liquid crystal layer formed on at least the area opposing the area with the stacked color layers. In this case, the second protrusions function as substitutes of spaces or, in other words, as substitutes of the device for controlling the thickness of the liquid crystal layer (the distance between the substrates, i.e., the cell gap). The area with the stacked color layers protrudes into the liquid crystal layer more than the other areas by the thickness of the stack of color layers. Therefore, when the second protrusions are formed at least on the area opposing the stacked color layers, the thickness of the liquid crystal layer is minimized in the area with the second protrusions. Consequently, the second protrusions can be used as the device for controlling the thickness of the liquid crystal layer.

The second protrusions are preferably formed in a same process as the above-mentioned protrusions (which are hereinafter referred to as the first protrusions) for controlling the direction of tilt of the liquid crystal molecules in order to improve the production efficiency. In this case, the first and the second protrusions formed in the transmissive display area and/or the reflective display area are composed of the same material. Moreover, the second protrusions have a substantially identical height as the first protrusions formed in the transmissive display area and/or the reflective display area. Since the first and the second protrusions in the transmissive display area and/or the reflective display area have a substantially identical height, the first protrusions are prevented from contacting the opposing substrate. Thus, the alignment of the liquid crystal molecules is sufficiently controlled.

An electronic apparatus according to the invention can include the above-mentioned liquid crystal display device. Such an electronic apparatus has both a transmissive mode and a reflective mode. The electronic apparatus has a display capable of displaying images with a wide viewing angle in both modes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments according to the invention are described below by referring to drawings. The sizes of the layers and parts depicted in the drawings do not represent the actual proportions since the sizes are altered so that the layers and parts are viewable in the drawings.

A liquid crystal display device according to this embodiment described below is an embodiment of an active matrix liquid crystal display device using a thin-film diode (TFD) as a switching element and, in particular, is a transreflective liquid crystal display device enabling reflective display and transmissive display.

FIG. 1is an equivalent circuit diagram of a liquid crystal display device100according to this embodiment. The liquid crystal display device100includes a scanning signal driving circuit110and a data signal driving circuit120. The liquid crystal display device100has signal lines, i.e., a plurality of scanning lines13and a plurality of data lines9that intersect with the scanning lines13. The scanning lines13are driven by the scanning signal driving circuit110and the data lines9are driven by the data signal driving circuit120. In each pixel area150, a TFD element40and a liquid crystal display element160(liquid crystal layer) is serially connected between a scanning line13and a data line9. InFIG. 1, the TFD element40is connected to the scanning line13and the liquid crystal display element160is connected to the data line9. Contrarily, the TFD element40may be connected to the data line9and the liquid crystal display element160may be connected to the scanning line13.

By referring toFIG. 2, the planar structure of electrodes included in the liquid crystal display device according to this embodiment is described. As shown inFIG. 2, the liquid crystal display device according to this embodiment has pixel electrodes31, which are rectangular in the plan view, arranged in a matrix and connected to the scanning lines13via the TFD elements40. Common electrodes9are arranged in a stripe pattern perpendicular to the pixel electrodes31and the vertical direction of the drawing. The common electrodes9are composed of the data lines arranged in a stripe pattern intersecting with the scanning lines13. In this embodiment, each area with a pixel electrode31forms a dot area. Each of the dot areas arranged in a matrix are activated.

The TFD element40is a switching element connecting the scanning line13and the pixel electrode31. The TFD element40has a MIM structure including a first conductive film essentially composed of Ta, an insulating film essentially composed of Ta2O3 and disposed on the surface of the first conductive film, and a second conductive film essentially composed of Cr and disposed on the surface of the insulating film. The first conductive film of the TFD element40is connected to the scanning line13, and the second conductive film is connected to the pixel electrode31.

The pixel structure of the liquid crystal display device100according to this embodiment is described by referring toFIG. 3.FIG. 3(a) illustrates the pixel structure of the liquid crystal display device100. In particular, the drawing illustrates the planar structure of the pixel electrodes31.FIG. 3(b) is a cross-sectional view taken along line A-A′ ofFIG. 3(a). The liquid crystal display device100according to this embodiment has dot areas including pixel electrodes31inside the area surrounded by the data lines9and the scanning lines13, as shown inFIG. 2. As shown inFIG. 3(a), each dot area has a color layer that corresponds to one of the three primary colors. The three dot areas D1, D2, and D3each form a pixel including a blue color layer22B, a green color layer22G, and a red color layer22R.

As shown inFIG. 3(b), the liquid crystal display device100according to this embodiment can include a liquid crystal layer50interposed between an upper substrate (element substrate)25and a lower substrate (opposing substrate)10. The liquid crystal layer50is composed of liquid crystal having molecules that are vertically aligned at an initial alignment state and have negative dielectric anisotropy.

A part of the lower substrate10includes an insulating film24interposed between a substrate body10A composed of a transparent material, such as quartz or glass, and a reflective film20composed of a metal, such as silver with a high reflectance. The area with the reflective film20is a reflective display area R. The area without the reflective film20, i.e., the area where an opening21is formed on the reflective film20, is a transmissive display area T. The liquid crystal display device100according to this embodiment is a homeotropic liquid crystal display device having a homeotropic liquid crystal layer50. Moreover, it is a transreflective liquid crystal display device capable of reflective display and transmissive display.

The insulating film24disposed on the substrate body10A has a bumpy surface24a. Accordingly, the surface of the reflective film20attached to the bumpy surface24ais also bumpy. The reflected light is dispersed by the bumpy surface of the reflective film20. In this way, light from outside is prevented from forming reflections in the reflective display and a wide viewing angle is obtained.

A color filter22(the red color layer22R inFIG. 3(b)) is disposed across the reflective film20in the reflective display area R and on the substrate body10A in the transmissive display area T. The periphery of the red color layer22R is surrounded by a black matrix BM composed of chromium metal. The black matrix BM forms the borders of the dot areas D1, D2, and D3(cf.FIG. 3(a)).

On the color filter22, an insulating film26can be formed on the position corresponding to the reflective display area R. More specifically, the insulating film26is formed selectively above the reflective film20with the color filter22interposed therebetween. Because of the insulating film26, the thickness of the liquid crystal layer50differs in the reflective display area R and the transmissive display area T. The insulating film26is composed of, for example, an organic acrylic resin film with a thickness of about 0.5 to 2.5 mm. The insulating film26has an inclined surface, in order that the film thickness gradually changes, on the border of the reflective display area R and the transmissive display area T. The thickness of the liquid crystal layer50, without any insulating film26is about 1 to 5 mm. The thickness of the liquid crystal layer50in the reflective display area R is about half the thickness of the liquid crystal layer50in the transmissive display area T.

The insulating film26functions as a liquid crystal layer thickness-adjustment layer (liquid crystal layer thickness-controlling layer) for varying the thickness of the liquid crystal layer50in the reflective display area R and the transmissive display area T. In this embodiment, the edge of the flat surface of the upper surface of the insulating film26and the edge of the reflective film20(reflective display area) substantially match. Thus, the inclined surface is partly or entirely included in the transmissive display area T.

On the surface of the lower substrate10including the surface of the insulating film26, common electrodes9composed of indium tin oxide (ITO) are disposed. On the common electrodes9, an alignment film27composed of polyimide is disposed. The alignment film27functions as a homeotropic alignment film for aligning the liquid crystal molecules vertically relative to the film surface. Alignment processing, such as rubbing is not performed on the alignment film27. InFIG. 3, the common electrodes9are formed in a stripe pattern in which the stripes extend in the longitudinal direction of the drawing. Each of the common electrodes9are used for each of the dot areas arranged in a row in the longitudinal direction of the drawing. The common electrodes9have slits91formed by cutting off parts of the common electrodes9. In this embodiment, the reflective film20and the common electrodes9are formed separately before they are stacked. In the reflective display area R, however, the reflective film composed of a metal film may be used as part of the common electrodes.

In the upper substrate25, a matrix of the pixel electrodes31composed of an ITO transparent conductive film is disposed on the inner surface (adjacent to the liquid crystal layer) of the substrate body25A composed of a transparent material such as glass or quartz. On the pixel electrodes31, protrusions28and29composed of a dielectric material are formed. More specifically, the protrusions28and29are formed on the inner surface (adjacent to the liquid crystal layer) of the pixel electrodes31in the transmissive display area T and the reflective display area R, respectively. Moreover, on the pixel electrodes31including the protrusions28and29, a homeotropic alignment film33, similar to the one on the lower substrate10composed of polyimide, is disposed.

The outer surface (not adjacent to the liquid crystal layer50) of the lower substrate10has a retardation plate18and a polarization plate19. Also, the outer surface of the upper substrate25has a retardation plate16and a polarization plate17. In this way, circularly-polarized light enters the inner surface (adjacent to the liquid crystal layer50) of the substrate. The combinations of the retardation plate18and the polarization plate19, and the retardation plate16and the polarization plate17each function as a circularly-polarization plate. The polarization plate17(19) transmits only linearly-polarized light polarized in a predetermined direction. The retardation plate16(18) can be a λ/4 retardation plate. On the outer surface of the polarization plate19on the lower substrate10, a backlight15is formed as a light source for transmissive display.

In the liquid crystal display device100according to this embodiment, the protrusions28and29composed of dielectric material can be formed on the inner surface (adjacent to the liquid crystal layer) of the electrode. The protrusions28and29can control the alignment of the liquid crystal molecules of the liquid crystal layer50or, in other words, can control the direction of tilt of the liquid crystal molecules vertically aligned at an initial alignment state when a voltage is applied to the electrodes. InFIG. 3, on the inner surface (adjacent to the liquid crystal layer) of the pixel electrodes31disposed on the inner surface of the upper substrate25, the protrusions28and29are formed on the transmissive display area T and the reflective display area R, respectively.

Each protrusion28and29is a generally circular cone or a polygonal pyramid protruding from the inner surface of the upper substrate25(main surface of the electrodes) to the inner part of the liquid crystal layer50. The protrusions28and29have an inclined surface (including a mildly curved surface) having a slope of a predetermined angle with respect to the inner surface of the substrate (the main surface of the electrode) for controlling the direction of tilt of the liquid crystal molecules LC along the inclined surface.

The common electrodes9disposed on the inner surface of the lower substrate10have slits91formed by cutting off parts of the common electrodes9. These slits91generate a distorted electric field between the electrodes9and31in the area where the slits are formed. According to the distorted electric field, the direction of tilt of the liquid crystal molecules vertically aligned at an initial alignment state when a voltage is applied is controlled. As shown inFIG. 3(a), the slits91of the common electrodes9surround the protrusions28and29formed on the pixel electrodes31. As a result, the direction of tilt of the liquid crystal molecules LC are controlled so that the liquid crystal molecules are arranged in a radial pattern around the protrusions28and29.

The liquid crystal display device100described above have the advantages described below.

In general, when a voltage is applied to liquid crystal molecules having negative dielectric anisotropy aligned on an unrubbed homeotropic alignment film, since the direction of the liquid crystal molecules is not controlled, the liquid crystal molecules tilt in random directions and, thus, the molecules fail to align. In this embodiment, however, the protrusions28and29are formed on the inner surface of the pixel electrodes31and, in addition, the slits91are formed to planarly surround the common electrodes9. In this way, the direction of tilt of the liquid crystal molecules vertically arranged at an initial alignment state are controlled by the inclined surface of the protrusions28and29and/or by the distorted electric field generated by the slits91. Consequently, disclination due to alignment failure of the liquid crystal molecules is prevented. In this way, a high quality image, which does not have any residual images caused by disclination and smear-like unevenness that appear when viewed from an oblique direction, can be obtained.

The liquid crystal display device100has a multi-gap structure since the reflective display area R is formed on the insulating film26. More specifically, the thickness of the liquid crystal layer50in the reflective display area R is substantially half the thickness of the liquid crystal layer50in the transmissive display area T. In this way, the retardation of the reflective display is substantially equal to the retardation of the transmissive display. As a result, the contrast of the display can be improved.

Since the protrusions28and29are formed on the upper substrate25and not on the lower substrate10having the insulating film26making up the multi-gap structure, forming the protrusions28and29and setting their height is easy.

In other words, the surface of the lower substrate10adjacent to the liquid crystal layer50including the insulating film26has a difference in thickness, which forms the multi-gap structure. Forming the protrusions28and29on the portion where the thickness is small is extremely difficult. This difference in thickness may cause a difference in height of the protrusions28and29, which are each formed on a portion with different thicknesses. Contrarily, as in this embodiment, by forming the protrusions28and29on the substrate without the insulating film26, the protrusions28and29can be formed on a relatively flat surface. In this way, the above-mentioned problems concerning the formation of the protrusions28and29do not occur. Thus, the protrusions28and29can be formed extremely easily and their height can be set extremely easily.

As shown inFIG. 4c, the protrusion28on the transmissive display area T can be formed so that the height is relatively larger than the height of the protrusion29. Since the thickness of the liquid crystal layer of the transmissive display area T is relatively larger than that of the reflective display area R due to the multi-gap structure, in the transmissive display area T, the alignment of the liquid crystal molecules must be controlled with even greater force. Therefore, it is desirable to set the height of the protrusions as described above.

A liquid crystal display device200according to a second embodiment is described below by referring to a drawing.FIG. 4illustrates a liquid crystal display device200according to a second embodiment whereinFIG. 4(a) is a plane view andFIG. 4(b) is cross-sectional view.FIG. 4is equivalent toFIG. 3illustrating the first embodiment. The basic structure of the liquid crystal display device200according to the second embodiment is substantially the same as the liquid crystal display device100illustrated inFIG. 3except that the structure of the color filter differs. Therefore, for the parts inFIG. 4that are indicated by the same reference numerals that were used inFIG. 3are the same as those inFIG. 3unless otherwise specified and their descriptions are omitted.

The liquid crystal display device200according to the second embodiment is an active matrix transreflective liquid crystal display device including a TFD as a switching element. The liquid crystal display device200includes a liquid crystal layer50interposed between an upper substrate (element substrate)25and a lower substrate (opposing substrate)10. The liquid crystal layer50is composed of a liquid crystal having molecules that are vertically aligned at an initial alignment state and have negative dielectric anisotropy.

A part of the lower substrate10includes a substrate body10A composed of a transparent material, such as quartz or glass, and a reflective film20composed of a metal, such as aluminum and silver, with a high reflectance. The reflective film20is formed in a predetermined pattern or, in other words, formed selectively on a reflective display area R. The lower substrate10also has a bumpy surface similar to the structure of the first embodiment formed of an insulating film24interposed between the substrate body and the reflective film.

On the reflective film20selectively formed on the reflective display area R and on the substrate body10A of the transmissive display area T, a color filter22(22R,22G, and22B) is disposed across the reflective display area R and the transmissive display area T. The color filter22includes color layers22R,22G, and22B that are red, green, and blue, respectively. The color layers22R,22G, and22B make up dot areas D1, D2, and D3, respectively (cf.FIG. 4(a)).

In this embodiment, a black matrix BM forming the borders of the dot areas D1, D2, and D3is not composed of the generally-used chromium metal, but instead is composed of a stack of the color layers22R,22G, and22B. More specifically, the color layers22R,22G, and22B are stacked in the areas between dots adjacent to the reflective display area R. The stacked layers display a black color. As a result of stacking the color layers, the thickness of the color filter22in the areas between dots becomes larger.

Covering the stacked color layers22R,22G, and22B in the color filter22is an insulating film26functioning as a liquid crystal layer thickness-adjustment layer disposed across the reflective display area R. On the surface of the lower substrate10including the surface of the insulating film26, common electrodes9composed of ITO are disposed. On the common electrodes9, a homeotropic alignment film27composed of polyimide is disposed. As a result of stacking the color layers22R,22G, and22B, as described above, the color filter22protrudes into the liquid crystal layer50by the thickness of the stack of color layers. The insulating film26disposed on the color filter22also has protrusions having the same shape as the color filter22. The common electrode9has slits91formed by cutting off portions of the electrodes.

In the upper substrate25, on the inner surface of the substrate body25A composed of a transparent material, such as glass or quartz, a matrix pixel electrodes31composed of transparent conductive film such as ITO and an alignment film33composed of a material such as polyimide having a homeotropic alignment as same as the lower substrate10are disposed. Similar to the first embodiment, the pixel electrodes31in the transmissive display area T has protrusions28protruding from the inner surface of the electrode to the liquid crystal layer50. Also, in the area between dots, protrusions29aprotrude from the inner surface of the substrate body25A to the liquid crystal layer50in the area corresponding to the area where the insulating film26protrudes. The protrusions29aare formed of the same material as the protrusion28in the transmissive display area T and have substantially the same height as the protrusions28.

In the liquid crystal display device200according to the invention, the protrusions29aprotrude from the substrate body25A in the upper substrate25to the liquid crystal layer50and oppose the area defined by disposing the insulating film26on stacked color layers22R,22G,22B in the lower substrate10. The protrusions29afunction to control the thickness of the liquid crystal layer50(in place of spacers). More specifically, the area with the stacked color layers22R,22G,22B protrudes from the other areas to the liquid crystal layer50by the thickness of the stack of color layers. The insulating film26is disposed on the stacked color layers. The thickness of the liquid crystal layer in the area provided with the protrusions29ais almost zero. As a result, the protrusions29acan define the thickness of the liquid crystal layer. Thus, the thickness of the liquid crystal layer can be maintained uniformly on the surface without disposing spacers. The protrusions29are formed by the same process as the protrusions28formed on the transmissive display area T for improving the efficiency of production. The protrusions29ahave the same height as the protrusions28.

In addition to the advantages of the liquid crystal display device100according to the first embodiment, the liquid crystal display device200described above has the advantages of improved production efficiency and reduced production costs since the black matrix BM is formed without using chromium metal. Moreover, the problem of environmental destruction caused by disposition of chromium metal can be prevented. Furthermore, since the thickness of the liquid crystal layer can be controlled without using spacers, the production efficiency can be improved and production costs can be reduced. In the lower substrate10, in addition to the insulating film26, color layers22R,22G,22B are stacked. Therefore, the difference in the thickness of the lower substrate10becomes greater. By forming protrusions28and29aon the upper substrate25such as described in this embodiment the production efficiency and the setting of the height of the protrusions becomes even easier.

The liquid crystal display device according to the second embodiment was described above. Structures such as the one illustrated inFIG. 5may be added. More specifically, the embodiment described above only has the protrusions28in the transmissive display area T. In the liquid crystal display device300illustrated inFIG. 5, however, protrusions29bare formed in a reflective display area R to control the direction of tilt of the liquid crystal molecules. The protrusions29bformed in the reflective display area R are preferably formed so that they have substantially the same height as the protrusions29aformed in the area between dots. In this way, the problem of the protrusions29btouching the inner surface of the opposite substrate can be prevented. As a result, the alignment of the liquid crystal molecules can be controlled accurately.

A liquid crystal display device according to a third embodiment is described by referring to a drawing.FIG. 6illustrates a liquid crystal display device400according to a third embodiment, whereinFIG. 6(a) is a plane view andFIG. 6(b) is cross-sectional view.FIG. 6is equivalent toFIGS. 4 and 5illustrating the second embodiment. The basic structure of the liquid crystal display device400according to the third embodiment is substantially the same as the liquid crystal display device200illustrated inFIG. 4and the liquid crystal display device300illustrated inFIG. 5except that, in comparison with the second embodiment, a color filter22including color layers22R,22G, and22B and an insulating film26are disposed on an upper substrate25and protrusions28,29a, and29bare formed on a lower substrate10. Therefore, for the parts inFIG. 6that are indicated by the same reference numerals that were used inFIGS. 4 and 5are the same as those inFIGS. 4 and 5unless otherwise specified and their descriptions are omitted.

As shown inFIG. 6, the liquid crystal display device400according to the third embodiment is an active matrix transreflective liquid crystal display device including a thin-film transistor (TFT) as a switching element. The liquid crystal display device400includes a liquid crystal layer50interposed between a lower substrate (element substrate)10and an upper substrate (opposing substrate)25. The liquid crystal layer50is composed of a liquid crystal having molecules that are vertically aligned at an initial alignment state and have negative dielectric anisotropy.

A part of the lower substrate10includes a substrate body10A and a reflective film20acomposed of a metal, such as aluminum or silver, with a high reflectance on the substrate body10A. The reflective film20ais formed in a predetermined pattern or, in other words, formed selectively on a reflective display area R. In the area without the reflective film20a, i.e., a transmissive display area T, transparent electrodes9aare formed with a predetermined pattern. The reflective film20aand the transparent electrodes9aare combined to form a matrix of pixel electrodes.

On the reflective film20aand the transparent electrodes9aforming the pixel electrodes, protrusions28,29a, and29bare formed in the transmissive display area T, the reflective display area R, and the area between dots, respectively. The protrusions28,29a, and29bare structured as same as the above-mentioned second embodiment. On the reflective film20aand the transparent electrodes9aincluding the protrusions28,29a, and29b, a homeotropic alignment film27is disposed.

On the upper substrate25, the color filter22including an area formed by stacking color layers22R,22G,22B onto the surface of a substrate body25A is disposed. On the color filter22, an insulating film26functioning as a liquid crystal layer thickness-adjustment layer and a common electrodes31acovering the entire surface are disposed. Slits91are formed on the common electrodes31aby cutting off portions of the electrodes to generate a distorted electric field. On the common electrodes31a, a homeotropic alignment film33ais disposed.

In this embodiment, the black matrix BM composed of the stacked color layers22R,22G,22B is disposed in the area between dots of the color filter22between the pixel electrodes. More specifically, in the areas between the dots adjacent to the reflective display area R, the color layers22R,22G, and22B are stacked. The stacked layers display a black color. As a result of stacking the color layers, the thickness of the color filter22in the areas between dots becomes larger. The protrusions29afunction to control the thickness of the liquid crystal layer, and the protrusions28, and29bfunction to control the direction of tilt of the liquid crystal molecules turn.

As described above, the liquid crystal display device400according to the third embodiment having the color filter22including the black matrix composed of the stacked color layers22R,22G,22B in the upper substrate25can also have the advantages of the liquid crystal display device100according to the first embodiment and the liquid crystal display devices200and300according to the second embodiment.

A liquid crystal display device according to a fourth embodiment is described below by referring to a drawing.FIG. 7illustrates a liquid crystal display device500according to a fourth embodiment whereinFIG. 7(a) is a plane view andFIG. 7(b) is cross-sectional view.FIG. 7is equivalent toFIGS. 4 and 5illustrating the second embodiment. The basic structure of the liquid crystal display device500according to the fourth embodiment is substantially the same as the liquid crystal display devices200and300illustrated inFIGS. 4 and 5except that the shape of the protrusions formed for controlling the alignment of the liquid crystal molecules differs. Therefore, for the parts inFIG. 7that are indicated by the same reference numerals that were used inFIGS. 4 and 5are the same as those inFIGS. 4 and 5unless otherwise specified, and their descriptions are omitted.

As shown inFIG. 7, in the liquid crystal display device500according to this embodiment, protrusions28, and29bfor controlling the alignment of the liquid crystal molecules are formed linearly on dot areas, which are display areas. More specifically, in the first to third embodiments, the protrusions for controlling the direction of tilt of the liquid crystal molecules were shaped as cones or polygonal pyramids. In this embodiment, however, projections extending linearly within each of the dots control the direction of tilt of the liquid crystal molecules. In this case, the alignment of the liquid crystal molecules can be controlled even more effectively.

A liquid crystal display device according to a fifth embodiment is described below by referring to a drawing.FIG. 9illustrates a liquid crystal display device600according to a fifth embodiment whereinFIG. 9(a) is a plane view andFIG. 9(b) is cross-sectional view.FIG. 9is equivalent toFIG. 3illustrating the first embodiment. The basic structure of the liquid crystal display device600according to the fifth embodiment is substantially the same as the liquid crystal display device100illustrated inFIG. 3except that the structures of a switching element and a pixel electrode differ. Therefore, for the parts inFIG. 9that are indicated by the same reference numerals that were used inFIG. 3are the same as those inFIG. 3unless otherwise specified and their descriptions are omitted.

The liquid crystal display device600according to the fifth embodiment is an active matrix transreflective liquid crystal display device including a thin-film transistor (TFT) as a switching element. The liquid crystal display device600includes a liquid crystal layer50interposed between a lower substrate (element substrate)610and an upper substrate (opposing substrate)625. The liquid crystal layer50is composed of a liquid crystal having molecules that are vertically aligned at an initial alignment state and have negative dielectric anisotropy.

A lower substrate610includes a substrate body10A composed of a transparent material, such as quartz or glass. Also, similar to the first embodiment, an insulating film (liquid crystal layer thickness-adjustment layer)26is selectively disposed in the area corresponding to a reflective display area R. In this way, the thickness of the liquid crystal layer50differs in the reflective display area R and a transmissive display area T. The inner surface of the insulating film26has a bumpy surface26a.

On the inner surface of the insulating film26having the bumpy surface26a, a reflective film620is selectively disposed. The area of the reflective film620is the reflective display area R, and the area without the reflective film620, i.e., the opening on the reflective film620, is the transmissive display area T. The reflective film620is attached to the bumpy surface26aof the reflective film20and, accordingly, has a bumpy surface. Consequently, light from outside is prevented from forming reflections in the reflective display and a wide viewing angle is obtained.

On the inner surface of the substrate body10A in the transmissive display area T, electrodes609composed of indium tin oxide are formed. The electrodes609are selectively formed in the transmissive display area T and are electrically connected to the reflective films620in the reflective display area R (cf.FIG. 9(a)). On the inner surface of the lower substrate610of this embodiment, the electrodes609composed of indium tin oxide are disposed in the transmissive display area T, and the reflective film620composed of a metal such as aluminum with a high reflectance is disposed in the reflective display area R. The electrodes609and the reflective film620form a matrix of pixel electrodes. The pixel electrodes composed of the electrodes609and the reflective film620have slits91on the electrodes609in the transmissive display area T and on the border of the electrodes609and the reflective film620.

On the inner surface of the pixel electrodes609composed of the electrodes609and the reflective film620, an alignment film27composed of polyimide is disposed. The alignment film27functions as a homeotropic alignment film for vertically aligning the liquid crystal molecules with respect to the film surface. Alignment processing such as rubbing is not performed on the alignment film27.

The upper substrate625has a substrate body25A composed of a transparent material such as quartz or glass. On the inner surface of the substrate body25A, a color filter22is disposed. Then, on the entire inner surface of the color filter22, common electrodes631are disposed. On the inner surface of the common electrodes631, an alignment film33composed of a material such as polyimide is disposed. The alignment film33functions as a homeotropic alignment film for vertically aligning the liquid crystal molecules relative to the film surface. Alignment processing such as rubbing is not performed on the alignment film33.

On the inner surface of the common electrode631, protrusions28protruding from the inner surface of the electrodes to the liquid crystal layer50are formed in the transmissive display area T. More specifically, as shown inFIG. 9(a), the protrusions28are formed in the center of the area surrounded by substantially rectangular slits91. On the inner surface of the substrate body25A of the upper substrate625, spacers (not shown in the drawing) formed together with the protrusions28are disposed outside the pixel areas. In this embodiment, the height of the protrusions28and the spacers are substantially the same. Therefore, both the protrusions28and the spacers can be formed from protrusions composed of dielectric material, such as resin in a single photo-process.

In this way, the protrusions28in the pixel areas function to control the direction of tilt of the liquid crystal molecules when an electrical voltage is applied so that the molecules align along the inclined surface of the protrusions. The spacers disposed outside the pixel areas function as means for controlling the liquid crystal layer thickness (liquid crystal cell thickness). In this way, the generation of disclination and smear-like unevenness that appear when the liquid crystal display device is viewed from an oblique direction can be prevented or suppressed. In this embodiment, a plurality of protrusions is formed on the substrate opposing the substrate including the insulating film26. The protrusions in the pixel area are the protrusions28for controlling the alignment of the liquid crystal molecules. On the other hand, the protrusions in areas except the pixel areas are spacers for controlling the thickness of the liquid crystal layer. In this way, the production efficiency can be improved. As described in the second embodiment, the protrusions28may be formed in the reflective display area R to control the alignment of the liquid crystal molecules.

Subsequently, an embodiment of an electronic apparatus having a liquid crystal display device of an above-mentioned embodiment according to the invention is described.

FIG. 8is a perspective view of an embodiment of a cellular phone. InFIG. 8, the reference numerals1000and1001indicate a cellular phone body and a display including the liquid crystal display device, respectively. Such an electronic apparatus has a display including the liquid crystal display device according to an above-mentioned embodiment. Therefore, an electronic apparatus including a liquid crystal display with high brightness and contrast and with a wide viewing angle, regardless of the environment, may be produced.

Embodiments of the invention have been described above. The technical scope of the invention, however, is not limited to the above-mentioned embodiments and may be modified in various ways to an extent that does not deviate from the object of the present invention. For example, in the above-mentioned embodiments, the retardation plate was formed of a single plate. The retardation plate, however, may be formed by layering a ½wavelength plate and a ¼wavelength plate. The layered plates function as a wide-range circular polarization plate for achromatizing the black display. The shapes of the protrusions and the electrode slits formed in the embodiments are not limited to the shapes of the above-mentioned embodiments. Any type of protrusion or slit may be acceptable providing that the direction of tilt of the vertically aligned liquid crystal molecules can be controlled.