JP4454487B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a vertical alignment mode liquid crystal display device excellent in image display quality.

  In recent years, liquid crystal display devices have been widely used as display units for home appliances such as computers and televisions. The liquid crystal display device uses a liquid crystal panel in which two glass substrates are stacked and bonded together with a sealing material, and then liquid crystal is sealed in a region defined by the sealing material.

  In such a liquid crystal display device, a liquid crystal layer having negative dielectric anisotropy is arranged between a pair of glass substrates facing each other to align liquid crystal molecules vertically and to apply a voltage to the liquid crystal layer. At that time, a liquid crystal display device in a vertical alignment mode in which the tilt direction of liquid crystal molecules with respect to the glass substrate is regulated in a plurality of directions has been put into practical use.

  In this vertical alignment mode liquid crystal display device, liquid crystal molecules are aligned perpendicular to a pair of mutually opposed glass substrate surfaces in a state where no voltage is applied in a non-driven state. It passes through the liquid crystal layer with almost no change. For this reason, in a vertical alignment mode liquid crystal display device, polarizing plates are arranged on the top and bottom of the glass substrate in a crossed Nicol manner, so that almost complete black display is possible without applying voltage, and a high-contrast image is obtained. It is done.

  Even in such a vertical alignment mode liquid crystal display device, there is a viewing angle dependency problem similar to that of a conventional TN mode liquid crystal display device, and a method for solving this problem has been proposed. In order to improve viewing angle characteristics in display, it is effective to create a plurality of regions in which liquid crystal molecules aligned in the vertical direction are inclined in different directions with respect to the vertical direction in one pixel. Therefore, in order to create such a region, a convex portion is provided in the alignment film, or an opening is provided in the pixel electrode.

  FIG. 5 is an enlarged plan view schematically showing one picture element of the vertical alignment mode liquid crystal display device, and FIG. 6 is a cross-sectional view taken along the line BB of FIG. First, as shown in FIG. 6, the liquid crystal panel 100 of this liquid crystal display device has a vertical direction between a pair of mutually opposing glass substrate (TFT array substrate) 10 and glass substrate (color filter substrate) 30. A liquid crystal layer 40 having aligned liquid crystal molecules is formed. On the lower glass substrate 10, pixel electrodes 17 having openings 18 are formed in a matrix, and below the upper glass substrate 30, a common electrode 33 is formed.

  As shown in FIG. 5, a pair of gate bus lines 11 and source bus lines 12 which are parallel to each other are formed around each pixel electrode 17 so as to be orthogonal to each other. The gate bus line 11 and the source bus line 12 intersect at the intersection so that the source bus line 12 is on the upper side and the gate bus line 11 is on the lower side, and the gate bus line 11 and the source bus line are at the intersection. The line 12 is electrically insulated. A TFT (thin film transistor) 13 connected to the gate electrode 11 a that is a part of the gate bus line 11 is formed at one portion of the intersection of the gate bus line 11 and the source bus line 12 of the pixel electrode 17. .

  As shown in FIG. 6, a lower alignment film 21 is formed on the glass substrate 10 provided with the pixel electrode 17 so as to cover the pixel electrode 17. An upper alignment film 35 is formed on the glass substrate 30 on which the common electrode 33 is provided over almost the entire surface so as to cover the common electrode 33. These alignment films 21 and 35 may be subjected to a rubbing process in which a surface is rubbed in a predetermined direction using a silk cloth or the like. When the rubbing treatment is performed, the liquid crystal molecules can be aligned by forming a slight tilt angle with respect to the vertical alignment.

  As shown in FIG. 5, slit-shaped openings 18 extending in the oblique direction are formed in the pixel electrode 17, and rib-shaped convex portions 34 that also extend in the oblique direction are formed at the center position between the rows of the openings 18. It is formed on the lower side of the common electrode 33. By these liquid crystal molecule alignment regulating means, a plurality of regions in which liquid crystal molecules are inclined in different directions with respect to the vertical direction in one picture element are created, and the viewing angle characteristics in display are improved.

  The pixel electrode 17 having the opening 18 as such an alignment regulating means is usually provided via the interlayer insulating film 16, and the lower alignment film 21 is provided on the pixel electrode 17. Yes. In general, a photosensitive acrylic resin (photosensitive organic film) material is used for the interlayer insulating film 16, an ITO (indium-tin oxide) material is used for the pixel electrode 17, and a polyimide is used for the lower alignment film 21. Material is used.

JP 2000-47217 A

  As shown in FIGS. 7A to 7C, generally, the coating of the lower alignment film 21 on the pixel electrode 17 is performed by previously applying a surfactant 20 on the pixel electrode 17. Is going from. This is to prevent the occurrence of repelling and unevenness in thickness when the lower alignment film 21 is coated. Since this surfactant 20 is hydrophilic, it easily comes into contact with the ITO material, which is an inorganic material, and bonds chemically and firmly.

  However, as shown in FIG. 7B, in the opening 18 formed in the pixel electrode 17, in the portion where the underlying interlayer insulating film 16 is exposed, the interlayer insulating film 16 is Since it is a photosensitive acrylic resin of an organic material, the surfactant 20 is difficult to contact and the bond is weak, so that the surfactant 20 is not sufficiently applied. As a result, as shown in FIG. 7C, the alignment film 21 is repelled in the vicinity of the opening 18, and there is a problem that alignment failure of liquid crystal molecules occurs in this portion. Furthermore, in the worst case, the alignment film 21 near the opening 18 triggers the alignment film to be repelled in one pixel unit, resulting in a poor alignment in one pixel unit. It has occurred.

  Accordingly, the problem to be solved by the present invention is to provide a liquid crystal display device capable of preventing repelling of an alignment film in an opening formed in a pixel electrode as liquid crystal molecule alignment regulating means.

  In order to solve the above problems, a liquid crystal display device according to the present invention includes a first substrate having a switching element provided in the vicinity of an intersection of a scanning line and a signal line, and having a pixel electrode connected to the switching element. And a second substrate having a common electrode disposed opposite to the first substrate, wherein the liquid crystal is sealed between the substrates, and the pixel electrode is interposed via an interlayer insulating film An orientation film is provided on the surface of the pixel electrode on the liquid crystal side, and a plurality of openings are formed in the pixel electrode, and a floating island-like orientation film is prevented from repelling in the opening. The gist is that the portion is formed of the same material as that of the pixel electrode. Incidentally, the “floating island shape” which is a constituent requirement of the present invention refers to a state where it is separated from surrounding pixel electrodes in the opening.

  In this case, it is preferable that a plurality of alignment film repellency preventing portions are provided in the opening. The plurality of openings may be slit-shaped.

  According to the liquid crystal display device having the above-described configuration, the alignment film is provided on the liquid crystal side surface of the pixel electrode provided through the interlayer insulating film, and a plurality of openings are formed in the pixel electrode. At the same time, a floating island-like alignment film repellency prevention portion is formed of the same material as that constituting the pixel electrode in the opening, so that the bonding force with the above-described surfactant is weak in the opening. The exposed area of the interlayer insulating film is reduced by the alignment film repellency prevention part, and the area of the same material as the pixel electrode having a strong binding force with the surfactant is expanded, so that the alignment film is repelled. Is prevented. In addition, since the same material as that of the pixel electrode is used, the formation of the alignment film repellency prevention portion can be included in the step of forming the pixel electrode, thereby preventing an increase in the number of steps.

  In this case, if a plurality of alignment film repellency prevention portions are provided in the opening, alignment film repellency can be sufficiently prevented without forming the alignment film repellency prevention portion on almost the entire surface of the opening. In addition, the material used for the alignment film repellency prevention portion can be reduced. Further, if the plurality of openings have a slit shape, it can be applied to a pixel electrode having a slit-shaped opening that is widely used.

  Embodiments of a liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged plan view schematically showing one picture element of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG. FIG. 3 is a diagram showing a procedure for forming an alignment film at the position of the opening of the pixel electrode.

  As shown in FIG. 2, the liquid crystal panel 1 of this liquid crystal display device is vertically aligned between a pair of mutually opposing glass substrate (TFT array substrate) 10 and glass substrate (color filter substrate) 30. A liquid crystal layer 40 having liquid crystal molecules is formed, and pixel electrodes 17 are formed in a matrix on the lower glass substrate 10.

  First, the glass substrate (TFT array substrate) 10 will be described. As shown in FIG. 1, a gate bus line 11 and a source bus line 12 made of a pair of aluminum and the like that are parallel to each other are formed around each pixel electrode 17 so as to be perpendicular to each other. ing. The gate bus line 11 and the source bus line 12 intersect at the intersection so that the source bus line 12 is on the upper side and the gate bus line 11 is on the lower side, and the gate bus line 11 and the source bus line are at the intersection. The line 11 is electrically insulated.

  A gate which is a part of the gate bus line 11 is formed at the intersection between the lower side of the pair of laterally extending gate bus lines 11 surrounding the pixel electrode 17 and the left side of the pair of longitudinally extending source bus lines 12. A TFT (thin film transistor) portion 13 as a switching element connected to the electrode 11a is formed.

  The gate bus line 11 and the gate electrode 11a are formed in the same wiring layer (first wiring layer). That is, the gate bus line 11 and the gate electrode 11a are formed by patterning the same conductive film. The gate bus line 11 and the gate electrode 11a are covered with a gate insulating film 14 made of silicon nitride or the like (see FIG. 2).

  A semiconductor layer (not shown) made of amorphous silicon or the like is formed on the gate insulating film 14 at the TFT 13 so as to overlap the gate electrode 11a. On the gate insulating film 14, a source electrode 13a and a drain electrode 13b of the TFT 13 are formed. The source electrode 13a and the drain electrode 13b are formed on both sides of the semiconductor layer on the gate electrode 11a so as to be separated from each other. The source electrode 13 a is connected to the source bus line 12, and the drain electrode 13 b is connected to the pixel electrode 17 through the contact hole 15. Although not shown in FIG. 2, the source bus line 12, the source electrode 13 a, and the drain electrode 13 b are formed in the same wiring layer (second wiring layer) on the gate insulating film 14.

  The source bus line 12 and the TFT 13 are covered with an interlayer protective film 16 formed on the gate insulating film 14. The interlayer insulating film 16 is made of a photosensitive acrylic resin (photosensitive organic film) material, and includes the TFT 13, the first and second wiring layers (gate bus line 11, source bus line 12, etc.), the pixel electrode 17, and the like. Between the two conductors (see FIG. 2).

  On the interlayer insulating film 16, a pixel electrode 17 is formed for each pixel region. The picture element electrode 17 is formed of a transparent conductor such as an ITO (indium-tin oxide) material. The pixel electrode 17 is electrically connected to the drain electrode 13 b of the TFT 13 through a contact hole 15 formed in the interlayer insulating film 16.

  A slit-shaped opening 18 extending in the oblique direction is formed in the pixel electrode 17. This opening 18 is for improving the viewing angle characteristics as described above. In this embodiment, the openings 18 are arranged so as to be vertically symmetrical within one picture element electrode 17. The width of the opening 18 is about 10 μm.

  In the opening 18, a plurality of alignment film repelling prevention portions 19 formed in a floating island shape are formed side by side in the longitudinal direction of the opening 18. This is for preventing the lower alignment film 21 from being repelled in the opening 18 of the pixel electrode 17 as shown in FIG. In the present embodiment, the alignment film repellency prevention unit 19 is also formed of the same ITO material as the pixel electrode 17. Therefore, the formation of the alignment film repellency prevention unit 19 can be included in the process of forming the pixel electrode 17, thereby preventing an increase in the number of processes.

  Next, the glass substrate (color filter substrate) 30 will be described. As shown in FIG. 2, a black matrix 31 is formed under the glass substrate 30. The black matrix 31 shields light from a region outside the region where the gate bus line 11, the source bus line 12, and the TFT 13 on the glass substrate 10 side are formed. In addition, a color filter 32 of any one of red (R), green (G), and blue (B) is formed for each picture element under the glass substrate 30. In this embodiment, red (R), green (G), and blue (B) color filters are repeatedly arranged in order in the horizontal direction, and color filters of the same color are arranged in the vertical direction.

  Under the color filter 32, a common electrode 33 common to each pixel is formed. The common electrode 33 is also formed of a transparent conductor such as an ITO material. A convex portion 34 is formed under the common electrode 33. As shown in FIG. 1, the convex portion 34 is disposed so as to be at the center position between the columns of the opening portions 18 provided in the pixel electrode 17 on the glass substrate (TFT array substrate) 10 side. The convex portions 34 are for improving the viewing angle characteristics by aligning the liquid crystal molecules so as to be in a predetermined tilt direction with respect to the vertical direction.

  An upper alignment film 35 is formed below the common electrode 33. The upper alignment film 35 covers the surfaces of the common electrode 33 and the convex portion 34. The upper alignment film 35 is made of, for example, a polyimide material.

  A liquid crystal layer 40 having negative dielectric anisotropy is formed between the glass substrate (TFT array substrate) 10 and the glass substrate (color filter substrate) 30 having such a configuration. For example, a columnar spacer (not shown) is disposed between the two substrates, and the distance between the two substrates (cell gap) is maintained constant. In addition, polarizing plates (not shown) are disposed on the lower side of the glass substrate 10 and the upper side of the glass substrate 30, respectively.

  Next, the alignment film repellency prevention unit 19 formed in a floating island shape in the opening 18 of the pixel electrode 17 which is a characteristic part of the present invention will be described. As shown in FIG. 3, when the lower alignment film 21 made of polyimide material is coated on the pixel electrode 17 made of ITO material, a surfactant 20 is applied on the pixel electrode 17 in advance ( FIG. 3 (a) → FIG. 3 (b)). This is because repelling and uneven thickness are less likely to occur when the lower alignment film 21 is coated.

  Since this surfactant 20 is hydrophilic, it can easily come into contact with the ITO material, which is an inorganic material, and can be chemically and firmly bonded. However, in the opening 18, the underlying photosensitive acrylic resin (photosensitive Since the interlayer insulating film 16 made of an organic film) material is exposed, the bonding force of the surfactant 20 is weaker in this portion than the ITO material as described in the prior art (see FIG. 6C). ).

  In the present invention, since the floating island-shaped alignment film repellency prevention portion 19 is formed in the opening 18 with the same ITO material as the pixel electrode 17, the bonding force with the surfactant 20 in the opening 18. Therefore, the exposed area of the underlying interlayer insulating film 16 is weakened, and the area of the ITO material having a strong bonding force with the surfactant 20 is enlarged. Thereby, as shown in FIG. 3C, the lower alignment film 21 can be prevented from being repelled, thickness unevenness does not occur, and the problem of poor alignment of liquid crystal molecules in this portion is eliminated. Furthermore, the repelling of the lower alignment film 21 at the opening 18 is a trigger, and the repelling of the alignment film is prevented from expanding and reaching one pixel unit.

  Note that the gap h between the alignment film repellency prevention unit 19 and the opening 18 shown in FIG. 3A is preferably set to a level that ensures sufficient insulation.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to such Embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in a various aspect. For example, although the opening as the liquid crystal molecular alignment regulating means of the pixel electrode has been described as an oblique slit shape, it is needless to say that the opening can be applied to openings having various shapes. For example, even in the case of the opening 22 having a circular opening as shown in FIG. 4, the opening 22 can be applied in a configuration in which the alignment film repellency prevention unit 23 divided into four is filled.

It is a top view which expands and shows the outline of 1 picture element of the liquid crystal display device which is one Embodiment of this invention. It is sectional drawing in the AA of FIG. It is the figure which expanded and showed the procedure of formation of the alignment film in the opening part position of the pixel electrode of FIG. It is the figure which showed the modification of FIG. It is a top view which expands and shows the outline of one picture element of the liquid crystal display device used conventionally. It is sectional drawing in the BB line of FIG. It is the figure which expanded and showed the procedure of formation of the alignment film in the opening part position of the pixel electrode of FIG.

Explanation of symbols

1 Liquid crystal panel 10 Glass substrate (TFT array substrate)
11 Gate bus line 11a Gate electrode 12 Source bus line 13 TFT
13a Source electrode 13b Drain electrode 14 Gate insulating film 15 Contact hole 16 Interlayer insulating film 17 Pixel electrodes 18, 22 Openings 19, 23 Alignment film repelling prevention part 20 Surfactant 21 Lower alignment film 30 Glass substrate (color filter substrate) )
31 Black matrix 32 Color filter 33 Common electrode 34 Convex part 35 Upper alignment film 40 Liquid crystal layer

Claims (3)

  A switching element is provided in the vicinity of the intersection of the scanning wiring and the signal wiring, and a first substrate having a picture element electrode connected to the switching element, and a first substrate having a common electrode disposed opposite to the first substrate. In the liquid crystal display device in which liquid crystal is sealed between the substrates, the pixel electrode is provided via an interlayer insulating film, and the liquid crystal side surface of the pixel electrode is aligned on the liquid crystal side surface. A film is provided, and a plurality of openings are formed in the pixel electrode, and a floating island-shaped alignment film repellency prevention portion is formed in the opening from the same material as that constituting the pixel electrode. A liquid crystal display device.   The liquid crystal display device according to claim 1, wherein a plurality of the alignment film repellency prevention portions are provided in the opening.   The liquid crystal display device according to claim 1, wherein the plurality of openings have a slit shape.

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