Abstract
A liquid crystal display panel is provided and includes a pair of substrates arranged face to face so as to sandwich a liquid crystal layer, a lower electrode formed on a lower substrate, an upper electrode formed on the lower substrate through an insulating layer, in which plural slits are formed in each sub-pixel, wherein each of the plural slits is formed as an aperture in which both ends thereof in the longitudinal direction are closed, and an alignment film formed so as to cover a surface of the upper electrode and the insulating layer. The plural slits have different widths at both ends of slits in a longitudinal direction, and a rubbing direction of the alignment film is a direction crossing longitudinal edges of each of the slits.
Claims
1. A liquid crystal display panel comprising: a pair of substrates arranged face to face so as to sandwich a liquid crystal layer; a lower electrode formed on one of the pair of substrates; and an upper electrode that has a rectangular shape and is formed on a surface of a lower electrode through an insulating layer, in which plural slits are formed in each sub-pixel, wherein the plural slits have different shapes at both ends of the slits, wherein the plural slits include slits each of which has a tip portion and a remaining portion other than the tip portion, the tip portion having a tapered shape, and the remaining portion having a constant width, and wherein the tip portions of the slits are arranged along a long side of the upper electrode.
2. The liquid crystal display panel according to claim 1, further comprising: an alignment film provided to cover a surface of the upper electrode and the insulating layer.
3. The liquid crystal display panel according to claim 2, wherein a rubbing direction of the alignment film is different from a direction in which each of the slits extend.
4. The liquid crystal display panel according to claim 1, further comprising: a plurality of scanning lines; a plurality of signal lines each crossing each of the scanning lines; wherein the lower electrode is arranged to cover a sectioned region by each of the scanning line and each of the signal lines.
5. The liquid crystal display panel according to claim 1, wherein the lower electrode includes a transparent electrode.
6. The liquid crystal display panel according to claim 1, wherein the upper electrode includes a transparent electrode.
7. The liquid crystal display panel according to claim 1, wherein the plural slits include slits each of which has a first portion and a second portion other than the first portion, the first portion having a reverse tapered shape, and the second portion having a constant width, and wherein the slit having the tip portion and the remaining portion, and the slit having the first portion and the second portion, are arranged alternately.
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) FIG. 1 is a schematic cross-sectional view for explaining the operation principle of a liquid crystal display according to an embodiment;
(2) FIG. 2A is a plan view of an upper electrode of one pixel according to a first embodiment and FIG. 2B is an enlarged view for explaining angles made by one slit and a rubbing direction of FIG. 2A;
(3) FIG. 3 is a graph showing VT curves of long edges of the slit according to the first embodiment;
(4) FIG. 4A is a plan view of an upper electrode of one pixel according to a second embodiment and FIG. 4B is an enlarged view for explaining angles made by one slit and the rubbing direction of FIG. 4A;
(5) FIG. 5A is a plan view of an upper electrode of one pixel according to a third embodiment and FIG. 5B is an enlarged view for explaining angles made by one slit and the rubbing direction of FIG. 5A;
(6) FIG. 6 is a graph showing VT curves of long edges of the slit according to the third embodiment;
(7) FIG. 7A is a plan view of an upper electrode of one pixel according to a fourth embodiment and FIG. 7B is an enlarged view for explaining angles made by a pair of slits and the rubbing direction of FIG. 7A;
(8) FIG. 8 A is a plan view of an upper electrode of one pixel according to a fifth embodiment and FIG. 8B is an enlarged view for explaining angles made by a pair of slits and the rubbing direction of FIG. 8 A;
(9) FIG. 9 is a graph showing VT curves of long edges of the slit according to the fifth embodiment; and
(10) FIG. 10 is a schematic plan view showing arrangement of electrodes and rubbing directions in one sub-pixel of a horizontal-electric field liquid crystal display panel in related art.
DETAILED DESCRIPTION
(11) Hereinafter, embodiments will be explained with reference to the drawings. In respective drawings used for explanation in the specification, respective layers and respective members are displayed with different scale ratios in order to allow respective layers and respective members to be sizes recognizable on the drawings, therefore, they are not displayed with the size corresponding to actual sizes.
(12) FIG. 1 is a schematic cross-sectional view for explaining the operation principle of a liquid crystal display panel according to an embodiment. FIG. 2A is a plan view of an upper electrode of one pixel according to a first embodiment and FIG. 2B is an enlarged view for explaining angles made by one slit and a rubbing direction of FIG. 2A. FIG. 3 is a graph showing VT characteristics of long edges of the slit according to the first embodiment. FIG. 4A is a plan view of an upper electrode of one pixel according to a second embodiment and FIG. 4B is an enlarged view for explaining angles made by one slit and the rubbing direction of FIG. 4A. FIG. 5A is a plan view of an upper electrode of one pixel according to a third embodiment and FIG. 5B an enlarged view for explaining angles made by one slit and the rubbing direction of FIG. 5A. FIG. 6 is a graph showing VT characteristics of long edges of the slit according to the third embodiment. FIG. 7A is a plan view of an upper electrode of one pixel according to a fourth embodiment and FIG. 7B is an enlarged view for explaining angles made by a pair of slits and the rubbing direction of FIG. 7A. FIG. 8A is a plan view of an upper electrode of one pixel according to a fifth embodiment and FIG. 8B is an enlarged view for explaining angles made by a pair of slits and the rubbing direction of FIG. 8A. FIG. 9 is a graph showing VT characteristics of long edges of the slit according to the fifth embodiment.
(13) First, the operation principle of an FFS-mode liquid crystal display panel common to respective embodiments will be explained with reference to FIG. 1. An FFS-mode liquid crystal display device 10 includes an array substrate AR and a color filter substrate CF. In the array substrate AR, plural scanning lines and common wiring are respectively provided in parallel to a surface of a first transparent substrate 11 and plural signal lines (all lines are not shown) are provided in a direction crossing these scanning lines and the common wiring. A lower electrode 15 made of a transparent material such as ITO, IZO or the like connected to the common wiring so as to cover respective regions sectioned by the scanning lines and the signal lines is provided. Therefore, the lower electrode 15 operates as a common electrode. On a surface of the lower electrode 15, upper electrodes 18 made of a transparent material such as ITO in which plural slits 17 are formed in a stripe shape are provided through an insulating film 16. The surface of the upper electrodes 18 and the plural slits 17 are covered with an alignment layer 20. The upper electrodes 18 are connected to switching elements such as not-shown TFTs (Thin Film Transistors) and operate as pixel electrodes.
(14) The color filter substrate CF has a structure in which a color filter layer 23, an overcoat layer 24 and an alignment film 25 are provided on a surface of a second transparent substrate 22. The array substrate AR is placed so as to face the color filter substrate CF to allow the upper electrodes 18 and the lower electrode 15 of the array substrate AR to face the color filter layer 23 of the color filter substrate CF. Next, liquid crystal LC is sealed between the array substrate AR and the color filter substrate CF as well as polarizing plates 26, 27 are arranged outside both substrates AR, CF respectively to thereby form the FFS-mode liquid crystal display device 10.
(15) In the FFS-mode liquid crystal display device 10, when the electric field is formed between the upper electrode 18 and the lower electrode 15, the electrode field is directed to the lower electrode 15 at both sides of the upper electrodes 18 as shown in FIG. 1. Accordingly, it is possible to drive not only liquid crystal existing in the slit 17 but also liquid crystal existing on the upper electrodes 18. Therefore, the FFS-mode liquid crystal display device 10 has characteristics that it has a wide viewing angle as well as high contrast, further, it can perform bright display because of high transmittance. Additionally, there is an advantage that the FFS-mode liquid crystal display device 10 generates high storage capacitance collaterally because the overlapping area of the upper electrodes 18 and the lower electrode 15 in plan view is large, which eliminates the need for an auxiliary capacitance line separately.
(16) [First Embodiment]
(17) A structure of an upper electrode 18a of one sub-pixel in the liquid crystal display panel 10A in the first embodiment will be explained with reference to FIGS. 2A and 2B. The upper electrode 18a has a rectangular shape, which is depicted in landscape in FIG. 2A. In the upper electrode 18a, plural slits 17a having the same shape are formed. The slit 17a is substantially longer than is wide, in which opposite short edges are called a first short edge 31, a second short edge 32, and in which a first long edge is called a long edge 33 and a right long edge is called a second long edge 34 in a pair of long edges connecting to the short edges. The first and second long edges 33, 34 of the slit 17a and a rubbing direction R (which is equal to an alignment direction of liquid crystal when the electric field is not applied) cross each other. When an angle made by the left long edge 33 and the rubbing direction R is Θ1 and an angle made by the right long edge 34 and the rubbing direction R is Θ2 as shown in FIG. 2B, angles made by the first and second long edges 33, 34 of the slit 17a and the rubbing direction R are arranged to be Θ1≠Θ2. Additionally, the slit 17a is made to be symmetrical with respect to a central axis Ya in a long edge direction. That is, when a perpendicular bisector of the second short edge 32 of the slit 17a is the central axis Ya and lengths of portions of the first short edge 31 positioned at both sides of the central axis Ya are respectively X1 and X2, the relation of X1=X2 is satisfied.
(18) In the FFS-mode liquid crystal display panel, the VT characteristics vary according to the angle made by the long edge of the slit and the rubbing direction, the width of the slit and the distance between adjacent slits. Accordingly, one slit 17a of the upper electrode 18a will have both VT characteristics by the left long edge 33 (displayed as Θ1) and VT characteristics by the right long edge 34 (displayed as Θ2) as shown in FIG. 3. Accordingly, the liquid crystal display panel 10A according to the first embodiment is observed by an observer as the panel which has VT characteristics represented by an envelope of both VT characteristics as shown in FIG. 3. If a tinge of yellow is added in respective VT characteristics, the color is compensated with one another in respective characteristics such that, when some region has a tinge of yellow, yellow does not appear in other regions of VT characteristics, as a result, coloring phenomenon can be suppressed.
(19) In the above case, the left edge and the right edge of the slit incline to the same side with respect to the rubbing direction to make crossing angles as shown in FIGS. 2A and 2B, however, the left edge and the right edge may incline to the reverse side with respect to the rubbing direction as the embodiment. In that case, a rotating direction of liquid crystal differs in the vicinity of the left edge and in the vicinity of the right edge, therefore, large effect can be obtained on compensation for color variations depending on the viewing angle, in addition to the effect of color compensation by different VT characteristics as in the embodiment. Also in the following embodiments, the same effect can be obtained by setting the rubbing angle in the same manner.
(20) [Second Embodiment]
(21) A structure of an upper electrode 18b of one sub-pixel in the liquid crystal display panel 10B in the second embodiment will be explained with reference to FIGS. 4A and 4B. In FIGS. 4A and 4B, the same reference numerals and signs are given to the same components as the liquid crystal display panel 10A according to the first embodiment and the detailed explanation thereof is omitted. The upper electrode 18b is the same as in the case of the liquid crystal display panel 10A according to the first embodiment in a point that angles made by the first and second long edges 33, 34 of a slit 17b and the rubbing direction R are arranged to be Θ1≠Θ2 when the angle made by the left long edge 33 and the rubbing direction R is Θ1 and the angle made by the right long edge 34 and the rubbing direction R is Θ2 as shown in FIG. 4B. However, the slit 17b of the upper electrode 18b has a different structure from the case of the liquid crystal display panel 10A according to the first embodiment in a point that the slit 17b is formed to be asymmetrical with respect to a central axis Yb in the long edge direction.
(22) That is, when a perpendicular bisector of the second short edge 32 of the slit 17b is the central axis Yb and lengths of portions positioned at both sides of the central axis Yb of the first short edge 31 are respectively X1 and X2, the relation of Θ1≠Θ2 is satisfied. According to the structure, respective angles 81, 82 made by the long edges 33, 34 at both sides of the slit 17b along the longitudinal direction and the rubbing direction R can be set to be optional plural values, therefore, plural VT characteristics fixed by these angles can be optionally set. The VT characteristics having a similar tendency as the upper electrode 18a in the liquid crystal display panel 10A of the first embodiment can be obtained also by applying the above structure. Accordingly, the same effect as the liquid crystal display panel 10A according to the first embodiment can be obtained also in the liquid crystal display panel 10B according to the second embodiment.
(23) [Third Embodiment]
(24) A structure of an upper electrode 18c of one sub-pixel in the liquid crystal display panel 10C in the third embodiment will be explained with reference to FIGS. 5A and 5B. In FIGS. 5A and 5B, the same reference numerals and signs are given to the same components as the liquid crystal display panel 10A according to the first embodiment and the detailed explanation thereof is omitted. A slit 17c formed in the upper electrode 18c has a portion in which the long edges 33, 34 of both sides in the longitudinal direction are parallel to each other or a portion in which the long edges 33, 34 extend in different directions, which is formed to be symmetrical with respect to a central axis Yc in the long edge direction. When such structure is applied, respective long edges 33, 34 cross the rubbing direction at three different angles of Θ1, Θ2 and Θ3 as shown in FIG. 5B. As a result, the liquid crystal display panel 10C of the third embodiment is observed by an observer as the panel which has the VT characteristics represented by an envelope of three VT characteristics as shown in FIG. 6. If a tinge of yellow is added in respective VT characteristics, the color is compensated with one another in respective characteristics such that, when some region has a tinge of yellow, yellow does not appear in other regions of VT characteristics, as a result, coloring phenomenon can be more suppressed.
(25) [Fourth Embodiment]
(26) A structure of an upper electrode 18d of one sub-pixel in the liquid crystal display panel 10D in the fourth embodiment will be explained with reference to FIGS. 7A and 7B. In FIGS. 7A and 7B, the same reference numerals and signs are given to the components as the liquid crystal display panel 10A according to the first embodiment and the detailed explanation thereof is omitted. The upper electrode 18d includes plural pairs of slits 17d1, 17d2, in which slits in each pair have the same shape and arranged to be inverted with respect to each other. The slit 17d1 as one of the slits has the same shape as the slit 17a of the liquid crystal display panel 10A of the first embodiment, whereas the other slit 17d2 has a structure in which the slit 17d1 is inverted in the vertical direction at a central axis Xd in the direction orthogonal to the longitudinal direction of the slit, for example, in FIG. 7B.
(27) When the above structure is applied, many pairs of slits 17d1, 17d2 having different shapes from each other can be arranged symmetrically with respect to the central axis Xd within one sub-pixel. Additionally, many slits can be arranged within one sub-pixel, and a light emitting state of liquid crystal will be symmetrical with respect to the central axis Xd in the direction orthogonal to the longitudinal direction of the slits 17d1, 17d2. According to the liquid crystal display 10D of the fourth embodiment, viewing-angle characteristics become good as well as the transmittance is improved, thereby realizing the liquid crystal display panel having good display quality and less coloring.
(28) [Fifth Embodiment]
(29) A structure of an upper electrode 18e of one sub-pixel in the liquid crystal display panel 10E in the fifth embodiment will be explained with reference to FIGS. 8A and 8B. In FIGS. 8A and 8B, the same reference numerals and signs are given to the same components as the liquid crystal display panel 10D according to the fourth embodiment and the detailed explanation thereof is omitted. The upper electrode 18e includes plural pairs of slits 17e1, 17e2, in which slits in each pair have different shapes from each other. The slit 17e1 as one of the slits has the same shape as the slit 17c of the liquid crystal display 10C of the third embodiment, however, the other slit 17e2 is formed so that a left long edge 33′ and a right long side 34′ are parallel to the right long edge 34 and the left long edge 33 of one slit 17e1 respectively.
(30) In the above structure, the slits have shapes which are commonly called complementary shapes. The slits 17e1, 17e2 are asymmetrical with respect to a central axis Xe in the direction orthogonal to the longitudinal direction of the slits, and many slits 17e1, 17e2 can be arranged in each one sub-pixel. Moreover, the slits can cross the rubbing direction with at least three angles of Θ1 to Θ3 in each pair of slits as shown in FIG. 8B. As a result, the liquid crystal display panel 10E will have three VT characteristics of Θ1 to Θ3 as shown in FIG. 9, which is observed by an observer as the penal which has the VT characteristics represented by an envelope of three VT characteristics. For example, when the long edges 33, 34 and the long edges 33′, 34′ forming the slits 17e1, 17e2 are not formed to be parallel in the same slit respectively, angles made by the long edges 33, 34 as well as the long edges 33′, 34′ and the rubbing direction R will have four VT characteristics of Θ1 to Θ4. If a tinge of yellow is added in respective VT characteristics, the color is compensated with one another in respective characteristics such that, when some region has a tinge of yellow, yellow does not appear in other regions of VT characteristics, as a result, coloring phenomenon can be more suppressed.
(31) The slits according to the embodiments have shapes in which widths of both ends of slits are different. When applying the structure, the VT characteristics vary according to the width difference, therefore, plural VT characteristics can be obtained not only by angles made by the rubbing angle but also by the slit width, which enables of the reduction of coloring with each other and suppression of the coloring phenomenon. As a result, the high-quality liquid crystal display panel can be provided.
(32) It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
