The present invention relates to a semi-transmissive liquid crystal display device, and in particular relates to a semi-transmissive liquid crystal display device which employs ECB mode liquid crystals and which has little occurrence of orientation unevenness of the liquid crystals.
In recent years the application of liquid crystal display devices has rapidly spread into not only information-communication devices, but general electrical equipment as well. Since liquid crystal display devices do not themselves emit light, transmissive-type liquid crystal display devices provided with a backlight are commonly employed. However, because the backlight consumes a large amount of power, particularly for portable devices, reflective-type liquid crystal display devices which do not require a backlight are being used to reduce power consumption. Nonetheless, since reflective liquid crystal display devices utilize external light as a light source, it is difficult to view these devices in a dark room or similar environment. In view of this, in recent years development has especially been progressing into semi-transmissive-type liquid crystal display devices which combine transmissive-type and reflective-type qualities (refer to Japanese Patent Laid-Open No. 11-101992 and Japanese Patent Laid-Open No. 2005-106997).
Such a semi-transmissive liquid crystal display device comprises, in a single pixel region, a transmissive portion comprising a pixel electrode, and a reflective portion comprising both a pixel electrode and a reflective electrode. In dark places, the backlight is lit up and the pixel region transmissive portion is utilized to display an image, while in bright places, external light is utilized at the reflective portion to display an image without the backlight being lit up. This means that the backlight does not have to be lit at all times, which has the advantage that power consumption can be dramatically reduced.
One example of such a semi-transmissive liquid crystal display device will be explained with reference to
This semi-transmissive liquid crystal display device 10 comprises a matrix substrate and a color filter substrate. The matrix substrate is provided with a plurality of scanning lines 12 and signal lines 13 which are formed in a matrix pattern on a transparent insulating glass substrate 11. Here, the region enclosed by the scanning lines 12 and signal lines 13 corresponds to one pixel, wherein a TFT (Thin Film Transistor) (not shown) acting as a switching device is formed for each pixel.
Further, an interlayer film 17 comprising an organic insulating film is laminated so as to cover the scanning lines 12 and signal lines 13, wherein tiny uneven portions are formed on the surface at the reflective portion 15 and wherein the surface at the transmissive portion 16 is made flat. The interlayer film 17 is provided with a contact hole 20 at a location corresponding to the drain electrode of the TFT. For each pixel, a reflective electrode 18 comprising aluminum metal, for example, on its reflective portion 15 is formed on the contact hole 20 and the surface of the interlayer film 17, and an alignment layer 21 is formed via a transparent pixel electrode 19 comprising ITO (Indium Tin Oxide), for example, on the surface of this reflective electrode 18 and the surface of the interlayer film 17 of the transmissive portion 16.
Further the color filter substrate is provided with a color filter layer 22 on a surface of a transparent insulating glass substrate 21. A protruding portion 23 is provided on the surface of the color filter layer 22, comprising a transparent topcoat layer for narrowing the cell gap d1 at the reflective portion 15 to half that of the cell gap d2 of the transmissive portion 16. Therefore, the thickness of the layer provided on the surface of the color filter substrate glass substrate 21 varies greatly at the boundary between the reflective portion 15 and the transmissive portion 16. An alignment layer 25 is formed via a transparent opposing electrode 24 comprising ITO above the protruding portion 23, which comprises a reflective portion 15 topcoat layer, as well as above the color filter layer 22 of the transmissive portion 16. Further, an aperture 26 for making the color tone of the reflective portion 15 the same as that of the transmissive portion 16 is provided on a part of the color filter layer 22 of the reflective portion 15. The topcoat layer is also provided inside this aperture 26.
While an example has been illustrated here where the protruding portion 23 has a transparent topcoat layer for narrowing the cell gap d1 at the reflective portion 15 to half that of the cell gap d2 of the transmissive portion 16, is provided on the color filter layer substrate side, the protruding portion 23 may also be provided on the matrix substrate side. In that case, the thickness of the interlayer film of the reflective portion on the matrix substrate side is thicker than that of the transmissive portion interlayer film only by the protruding portion amount, and the thickness of the layer provided on the surface of the matrix substrate glass substrate 11 varies greatly at the boundary between the reflective portion 15 and the transmissive portion 16.
A semi-transmissive liquid crystal display device is fabricated by aligning the above-described matrix substrate and the color filter substrate so that they oppose each other, then laminating around the periphery with a sealant and enclosing liquid crystals into the interior. Injection of liquid crystals into a liquid crystal display device is usually conducted by dipping a liquid crystal injection inlet provided in the liquid crystal display device into a liquid crystal bath that is filled with liquid crystals. Methods for injecting the liquid crystals include an injection method which subjects an empty cell interior to vacuum suction; an injection method illustrated in Japanese Patent Laid-Open No. 11-101992, which provides a secondary injection inlet to thereby generate a pressure difference between the two injection inlets; and an injection method which utilizes capillary action based on the fact that an empty cell is a fine gap.
For example, for the liquid crystal display device 50 described in Japanese Patent Laid-Open No. 6-180457, as illustrated in
Japanese Patent Laid-Open No. 5-61054 discloses a liquid crystal display device which has a liquid crystal injection inlet provided in the center region of one side face of a substrate. Liquid crystal display devices which have an injection inlet provided in the center region of one side face of the substrate, such as the above-described, can attain the best liquid crystal injection efficiency, as such devices have the shortest leading distance for the liquid crystals into the empty cells in the liquid crystal injection step.
However, for a liquid crystal display device comprising such a structure, it is necessary to align (orient) the liquid crystal molecules of the liquid crystals enclosed in the interior in a fixed array. Thus, the above-described matrix substrate and color filter substrate are respectively formed with alignment layers 21 and 25 (refer to
The process for forming this alignment layer is generally, conducted by coating a solution, in which the alignment layer forming material has been dissolved in a solvent, onto a substrate by a certain method, heating the substrate to cause only the solvent to volatize off (pre-heating), then heating the alignment layer forming material from which the solvent has been volatized off at an even higher temperature to harden (heat) the alignment layer forming material and thereby form an alignment layer. The alignment layer is subsequently subjected to a rubbing treatment (as disclosed in Japanese Patent Laid-Open No. 5-203953 and 10-161078).
As used here, the “rubbing treatment” brings the alignment layer formed on the substrate surface into contact with a rubbing roller, around which is wound a rubbing fabric made from cloth or the like. This roller is rotated so as to rub against the surface of the alignment layer in one direction, whereby the nap on the alignment layer surface is made to stand up and form grooves, thereby conferring a certain energy directivity which controls the alignment direction of the liquid crystal molecules in the rubbing direction.
For example, when using TN mode, it is necessary to offset the orienting direction with respect to one substrate 90° from the orienting direction with respect to the other substrate. Therefore, if the rubbing treatment is conducted with the angle φ with respect to one substrate equaling 0°, i.e. so that the relative movement direction 69 of the rubbing roller 63 is parallel to the longitudinal direction X of the substrate to be treated 60, the angle φ with respect to the other substrate must equal 90°, i.e. the rubbing treatment must be conducted so that the longitudinal direction X of the substrate to be treated 60 is at right angles (parallel to the width direction Y) to the relative movement direction 69 of the rubbing roller 63.
In contrast, two kinds of treatment exist for ECB mode; one in which the initial orientation of the liquid crystal molecules is a horizontal orientation (homogeneous alignment), and another in which the initial orientation of the liquid crystal molecules is a perpendicular orientation (homeotropic alignment). Of these, and especially for a liquid crystal display device which employs the former ECB mode, the liquid crystal display device is a “normally white” type wherein the liquid crystal molecules enclosed in between the pair of glass substrates are orientated horizontally with respect to the two substrates when voltage is not applied, so that the display can be activated by applying voltage. Thus, for this ECB mode, the rubbing direction in the rubbing treatment applied to the matrix substrate and color filter substrate pair are opposite directions rotated 180° from each other.
However, for a semi-transmissive liquid crystal display device employing ECB mode liquid crystals such as that described above, it was found that due to the differences in production conditions of the semi-transmissive liquid crystal display device, partial disarray in the orientation of the liquid crystal molecules (domain) might occur. The inventors of the present invention learned from wide-ranging investigation into the causes of domain in semi-transmissive liquid crystal display devices employing such ECB mode liquid crystals, that, essentially, as illustrated in
That is, it is an object of the present invention to provide a semi-transmissive liquid crystal display device which employs ECB mode liquid crystals that has little unevenness in the orientation of the liquid crystals.
The present invention can achieve the above-described object with the following constitution. Namely, a semi-transmissive liquid crystal display device, which employs ECB mode liquid crystals according to one aspect of the present invention, comprises a pair of substrates, and provides a protruding portion extending in a first direction used for adjusting a cell gap on a reflective portion of each pixel in one of the substrates, and when an orienting direction of an alignment layer formed on said one of the substrates intersects with the protruding portion extending in said first direction, a liquid crystal injection inlet is provided at a position such that a tangent of a circular arc drawn with said liquid crystal injection inlet as a center and the orienting direction of the alignment layer on the side comprising said protruding portion are never at a right angle, or is provided at a position such that a contact point of the tangent where said tangent of a circular arc and the orienting direction of the alignment layer of said one of the substrates are at a right angle is on an edge of said substrate.
Further, the semi-transmissive liquid crystal display device, which employs ECB mode liquid crystals according to the above aspect, may comprise a topcoat wherein said protruding part is provided on a reflective portion of a color filter substrate.
Further, the semi-transmissive liquid crystal display device, which employs ECB mode liquid crystals according to the above aspect, may comprise an interlayer film wherein said protruding part is provided on a reflective portion of a matrix substrate side.
Further, when the orienting direction of the alignment layer of said one of the substrates is inclined with respect to the semi-transmissive liquid crystal display device, said semi-transmissive liquid crystal display device, which employs ECB mode liquid crystals according to the above aspect, may provide said liquid crystal injection inlet at any one of a periphery of an opposite side to the orienting direction of said alignment layer, or three corners intersecting in this periphery vicinity.
Further, when the orienting direction of the alignment layer of said one of the substrates is in a longitudinal direction of the semi-transmissive liquid crystal display device, said semi-transmissive liquid crystal display device which employs ECB mode liquid crystals according to the above aspect, may provide said liquid crystal injection inlet at any one of a periphery, or periphery both sides thereof, of an opposite side to the orienting direction of said alignment layer, or at any of the corners.
The present invention can also achieve the above-described object with the following constitution. Namely, a semi-transmissive liquid crystal display device, employs ECB mode liquid crystals according to another aspect of the present invention, comprises a pair of substrates, and provides a protruding portion extending in a first direction used for adjusting a cell gap on a reflective portion of each pixel in one of the substrates, a liquid crystal injection inlet being provided so that an orienting direction of an alignment layer formed on said one of the substrates is parallel to the protruding portion extending in said first direction.
As will now be described in more detail in the following examples, according to the above constitutions the present invention provides a semi-transmissive liquid crystal display device employing ECB mode liquid crystals which comprises a protruding portion used for adjusting a cell gap on a reflective portion, wherein a good display quality can be obtained since domain essentially no longer occurs due to the presence of the protruding portion.
The most preferred embodiment for carrying out the present invention will now be explained in detail with reference to the drawings. Although the below embodiment illustrates a semi-transmissive type liquid crystal display employing ECB mode liquid crystals in order to describe the technical ideas behind the present invention in more detail, this embodiment is in no way intended to limit the present invention. The present invention can equally be applied to other embodiments, which are contained within the scope of claims.
First, an active matrix substrate and a color filter substrate the same as in the related art illustrated in
Next, semi-transmissive liquid crystal display devices were fabricated that employed ECB mode liquid crystals in which the orienting direction of the alignment layer for the substrate on which the protruding portion was formed, and the position of the liquid crystal injection inlet, were variously altered, whereby domain occurrence was investigated. The results are shown in
The following can be understood by referring to
Similarly, the following can be understood by referring to
Similarly, in
Thus, taking all of what is illustrated in
Therefore, as illustrated in
Number | Date | Country | Kind |
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2005-218545 | Jul 2005 | JP | national |