JP5315117B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device having a simple matrix type electrode structure.

  FIG. 4 is a sectional view of a vertical alignment type liquid crystal display device showing an example of a liquid crystal display device having a simple matrix type electrode structure. The vertical alignment type liquid crystal display device 1 includes a liquid crystal panel 2 and displays an image using the liquid crystal panel 2.

  As shown in FIG. 4, in the liquid crystal panel 2, a first strip-shaped transparent electrode 3a made of ITO (indium tin oxide) or the like is formed on a plate surface on one side, and the first strip-shaped transparent electrode 3a is formed on the first strip-shaped transparent electrode 3a. And a first transparent substrate 5a made of a glass plate or the like obtained by rubbing the first alignment film 4a, and ITO (indium tin oxide) or the like on the same plate surface. A glass plate in which a second strip-shaped transparent electrode 3b is formed, a second alignment film 4b is formed on the second strip-shaped transparent electrode 3b, and the second alignment film 4b is rubbed. And the second transparent substrate 5b made of a polymer sphere 6 or the like as a spacer material and bonded in such a direction that the first and second alignment films 4a and 4b face each other. The perimeter is sealed and a panel book 2a is formed. In the case of the liquid crystal panel 2, the first transparent substrate 5 a on the upper side in FIG. 4 is the front substrate 5 a on the display surface side, and the second transparent substrate 5 b on the lower side in FIG. 4 is the backlight (light source) side. The rear side substrate 5b is of a transmissive type.

  A liquid crystal layer 8 is formed by sealing liquid crystal in a gap (cell gap) between the first and second transparent substrates 5a and 5b by a vacuum injection method, a dropping method, or the like. In the case of the liquid crystal panel 2, nematic liquid crystal (negative type liquid crystal) having negative dielectric anisotropy is used as the liquid crystal, which is a vertical alignment type.

  Further, a first polarizing plate 9a is attached to the plate surface opposite to the side in contact with the liquid crystal layer 8 of the first transparent substrate 5a, and the side in contact with the liquid crystal layer 8 of the second transparent substrate 5a The second polarizing plate 9b is attached to the opposite plate surface, and the liquid crystal panel 2 is completed.

  As shown in FIG. 5, among the first and second strip-shaped transparent electrodes 3a and 3b, for example, a plurality of first strip-shaped transparent electrodes 3a are arranged in the lateral direction of the first transparent substrate 5a (the front and back directions in FIG. 4). Are formed in a horizontal stripe pattern as a whole, and are used as scanning electrodes connected to the scanning side drive circuit 10, and a plurality of second strip-shaped transparent electrodes 3b are provided. The second transparent substrate 5b is formed in parallel to the vertical direction (left and right direction in FIG. 4 and vertical direction in FIG. 5), and is formed in a vertical stripe pattern as a whole and connected to the signal side drive circuit 11. The first and second strip-shaped transparent electrodes 3a and 3b form a simple matrix type electrode structure. In the liquid crystal panel 2, the intersection of the first and second transparent electrodes 3a and 3b formed in parallel in the horizontal direction (horizontal direction) and the vertical direction (vertical direction) is defined as one pixel. In other words, the liquid crystal panel 2 arranges pixels in a grid pattern, and arranges the first and second strip-shaped transparent electrodes 3a and 3a in the horizontal and vertical directions with respect to the pixels arranged in the grid pattern. A voltage is applied by selecting the required first and second transparent electrodes 3a and 3a in the horizontal and vertical directions. As a result, the liquid crystal layer 8 (liquid crystal cell) of the pixel at the intersection of the first and second strip-shaped transparent electrodes 3a and 3b in the selected horizontal and vertical directions is driven. That is, the liquid crystal panel 2 has a simple matrix type electrode structure and performs simple matrix driving (duty driving). However, when the number of display pixels is large, the driving is time-division multiplex driving.

  As shown in FIG. 6, of the first and second polarizing plates 9a and 9b, the first polarizing plate 9a has an absorption axis in the direction indicated by the arrow 9a ′, and the second polarizing plate 9b The absorption axis is in the direction indicated by the arrow 9b '. That is, the first polarizing plate 9a and the second polarizing plate 9b are arranged so that the absorption axes 9a ′ and 9b ′ are orthogonal to each other (crossed Nicols arrangement), and the display mode of the liquid crystal panel 2 is no Mari black.

  As shown in FIG. 7A, the liquid crystal panel 2 configured as described above is in a non-driven state in which no voltage is applied between the first and second strip-shaped transparent electrodes 3a and 3b. The liquid crystal molecules 8a in the liquid crystal layer 8 (liquid crystal cell) sandwiched between the second strip-shaped transparent electrodes 3a and 3b have the molecular long axis direction of the first and second alignment films 4a and 4b due to the action of the first and second alignment films 4a and 4b. Although the light is aligned substantially along the optical axis perpendicular to the second transparent substrates 5a and 5b, it is aligned with a slight tilt (pretilt) to control the alignment direction, etc., and the polarization state of light passing therethrough Hardly changes. Therefore, the light (linearly polarized light) transmitted through the second polarizing plate 9b on the backlight side of the liquid crystal panel 2 is almost directly incident on the first polarizing plate 9a on the display surface side of the liquid crystal panel 2 and is mostly absorbed there. And dark display (black display).

  On the other hand, in a driving state in which a voltage is applied between the first and second strip transparent electrodes 3a and 3b, as shown in FIG. 7B, the first and second strip transparent electrodes 3a and 3b. The liquid crystal molecules 8a in the liquid crystal layer 8 sandwiched between them are in a direction substantially orthogonal to the electric field due to the negative dielectric anisotropy, that is, substantially parallel to the first and second transparent substrates 5a and 5b. To change the polarization state of light passing therethrough. For this reason, since the light transmitted through the second polarizing plate 9b on the backlight side of the liquid crystal panel 2 changes the polarization state and exits the liquid crystal layer 8, the first polarizing plate 9a on the display surface side of the liquid crystal panel 2 is used. The polarization component of the transmission axis perpendicular to the absorption axis 9a ′ increases, resulting in bright display (white display).

  As described above, the vertical alignment type liquid crystal display device 1 includes the first and second transparent substrates 5a and 5b arranged opposite to each other at a predetermined interval, and the second transparent substrate 5b of the first transparent substrate 5a. The first strip-shaped transparent electrode 3a and the second transparent substrate 5b arranged in parallel on the opposite surface of the first transparent substrate 5b are opposed to the first transparent substrate 5a in a direction orthogonal to the first strip-shaped transparent electrode 3a. A liquid crystal molecule having a negative dielectric anisotropy and being arranged between the second strip-like transparent electrode 3b arranged in parallel and the opposing surfaces of the first and second transparent substrates 5a and 5b The liquid crystal molecules 8a are aligned when a voltage is applied between the first and second strip-shaped transparent electrodes 3a and 3b, and the liquid crystal molecules 8a are aligned with the first and second transparent substrates 5a and 5b. On the first and second transparent substrates 5a and 5b The first liquid crystal layer 8 that is substantially parallel to the first transparent substrate 5a and the first transparent substrate 5a that has an absorption axis 9a 'in a predetermined direction disposed on the surface of the second transparent substrate 5a opposite to the surface facing the second transparent substrate 5a. The absorption axis in the direction orthogonal to the absorption axis 9a ′ of the first polarizing plate 9a is disposed on the surface of the polarizing plate 9a and the second transparent substrate 5b opposite to the surface facing the first transparent substrate 5a. And a second polarizing plate 9b having 9b 'for simple matrix driving (duty driving).

  Incidentally, the first and second strip-shaped transparent electrodes 3a and 3b used in such a vertical alignment type liquid crystal display device 1 (an example of a liquid crystal display device having a simple matrix electrode structure) are generally shown in FIG. As shown, the electrode ends are tapered with respect to the opposing surfaces of the first and second transparent substrates 5a and 5b (the taper angle with respect to the opposing surfaces of the first and second transparent substrates 5a and 5b is smaller than 90 °). The entire electrode is trapezoidal with the opposing surfaces of the first and second transparent substrates 5a and 5b as the bottom.

  However, in the first and second strip-shaped transparent electrodes 3a and 3b having tapered ends, the liquid crystal in the liquid crystal layer 8 (liquid crystal cell) sandwiched between the first and second strip-shaped transparent electrodes 3a and 3b. The orientation of the molecules 8a is as shown in FIG. That is, the tilt angle of the liquid crystal molecules 8a is equal to a predetermined pretilt angle at the center of the electrode (pixel center), but becomes smaller or larger than the predetermined pretilt angle at the tapered portion (pixel peripheral portion) at the electrode end. The alignment of the liquid crystal molecules 8a is disturbed. For this reason, there is a problem that light leakage occurs in the periphery of the pixel, the OFF transmittance increases, and the contrast decreases.

  In order to solve such a problem, for example, Patent Document 1 discloses that the second transparent substrate 5b has a pixel peripheral portion in a portion where the second transparent electrode 3b is not provided on the surface facing the first transparent substrate 5a. A liquid crystal display device provided with a light shielding film called a black mask for preventing light leakage and improving contrast is disclosed. However, in the liquid crystal display device described in Patent Document 1, a black mask for improving the contrast must be additionally manufactured, which causes an increase in manufacturing steps and an increase in manufacturing cost. there were.

JP-A-5-2161

  The present invention has been made in view of the above-described problems of the background art, and suppresses light leakage from the periphery of a pixel without using a black mask and the like, and does not cause an increase in manufacturing steps and an increase in manufacturing cost. An object of the present invention is to provide a liquid crystal display device capable of improving the above.

In order to achieve the above object, a liquid crystal display device according to the present invention includes first and second transparent substrates 5a and 5b that are arranged to face each other at a predetermined interval, and a second transparent substrate of the first transparent substrate 5a. A direction perpendicular to the first strip-shaped transparent electrode 30a on the first transparent substrate 5a facing the first strip-shaped transparent electrode 30a and the second transparent substrate 5b arranged in parallel on the facing surface to 5b In the liquid crystal display device, the second strip-shaped transparent electrode 30b disposed in parallel with the liquid crystal layer 8 disposed between the opposing surfaces of the first and second transparent substrates 5a and 5b. The ends of the first and second strip-shaped transparent electrodes 30a and 30b are reversely tapered with respect to the opposing surfaces of the first and second transparent substrates 5a and 5b, and the first and second strip-shaped transparent electrodes The electrodes are connected to each other. Shape, and is characterized in that it is inverted trapezoidal shape with the bottom facing surfaces of said first and second transparent substrates.

As in the present invention, it has a reverse-tapered shape with respect to the opposing surface of the first and second strip-shaped end portions of the transparent electrodes 30a and 30b the first and second transparent substrates 5a and 5b, the first And the second strip-shaped transparent electrodes 30a and 30b, when the entire cross-sectional shape is an inverted trapezoidal shape with the opposing surfaces of the first and second transparent substrates 5a and 5b as the bottom , Since the surfaces of the first and second strip-shaped transparent electrodes 30a and 30b on the liquid crystal layer 8 side are in a plane parallel to the first and second transparent substrates 5a and 5b from end to end, the first and second strip-shaped transparent electrodes 30a and 30b The orientation of the liquid crystal molecules 8a in the liquid crystal layer 8 (liquid crystal cell) sandwiched between the transparent electrodes 30a and 30b is as shown in FIG. That is, the tilt angle of the liquid crystal molecules 8a is substantially equal to a predetermined pretilt angle at both the electrode central portion (pixel central portion) and the electrode end portion (pixel peripheral portion), and the alignment disorder of the liquid crystal molecules 8a is reduced. Therefore, light leakage at the pixel peripheral portion can be suppressed.

  According to the present invention, it is possible to provide a liquid crystal display device capable of suppressing light leakage from the peripheral portion of a pixel without using a black mask or the like and improving the contrast without causing an increase in manufacturing steps and an increase in manufacturing cost. Is possible.

It is sectional drawing which shows the shape of the electrode of the liquid crystal display device concerning this invention. It is a figure which shows the mode of the inclination of the liquid crystal molecule at the time of the non-drive of the liquid crystal display device concerning this invention. It is a figure which shows the preparation methods of the electrode of the liquid crystal display device concerning this invention. It is sectional drawing of the vertical alignment type liquid crystal display device as an example of the liquid crystal display device which has a simple matrix type electrode structure. FIG. 5 is a diagram showing a simple matrix type electrode structure of the vertical alignment type liquid crystal display device of FIG. 4. It is a figure which shows the arrangement structure of the polarizing plate of the vertical alignment type liquid crystal display device of FIG. FIGS. 5A and 5B are diagrams for explaining driving of the vertical alignment type liquid crystal display device of FIG. 4, in which FIG. FIG. 5 is a cross-sectional view showing a conventional shape of electrodes of the vertical alignment type liquid crystal display device of FIG. 4. FIG. 5 is a diagram illustrating a state of tilt of liquid crystal molecules when the electrodes of the vertical alignment type liquid crystal display device of FIG. 4 are not driven in a conventional shape.

  Embodiments of the present invention will be described below with reference to the drawings. In the display device according to the embodiments of the present invention, the first and second strip-shaped transparent electrodes constituting a simple matrix electrode structure have a specific shape. The first and second alignment films are formed on the opposing surfaces of the first and second transparent substrates, and the first and second alignment films are formed on the first and second strip-shaped transparent electrodes along the specific shape. Other than the above, it is the same as the vertical alignment type liquid crystal display device as an example of the liquid crystal display device having the simple matrix type electrode structure shown in FIG. The shape of the 1st and 2nd strip | belt-shaped transparent electrode formed in this opposing surface, its effect, and a preparation method are demonstrated.

  FIG. 1 is a sectional view showing an electrode shape of a liquid crystal display device according to an embodiment of the present invention. As shown in FIG. 1, the first and second strip-shaped transparent electrodes 30a and 30b have opposite end taper shapes (first and second) with respect to the opposing surfaces of the first and second transparent substrates 5a and 5b. The taper angle with respect to the opposing surfaces of the second transparent substrates 5a and 5b is greater than 90 ° and less than 180 °). It has an inverted trapezoidal shape at the bottom. Further, with respect to such a taper angle, it is 95 ° in consideration of effectively suppressing light leakage from the pixel peripheral portion so as not to cause cracks at the end portions of the first and second strip-shaped transparent electrodes 30a and 30b. The range of ˜170 ° is preferable, and 110 ° to 150 ° is more preferable.

  The first and second alignment films 40a and 40b are formed along the shape of the first and second strip-shaped transparent electrodes 30a and 30b.

  FIG. 2 is a diagram showing a state of inclination of liquid crystal molecules when the liquid crystal display device according to the embodiment of the present invention is not driven. As shown in FIG. 2, the end portions of the first and second strip-shaped transparent electrodes 30a and 30b are inversely tapered with respect to the opposing surfaces of the first and second transparent substrates 5a and 5b. Since the surface on the liquid crystal layer 8 side of the second strip-shaped transparent electrodes 30a and 30b is in a plane parallel to the first and second transparent substrates 5a and 5b from end to end, the first and second strip-shaped transparent electrodes The orientation of the liquid crystal molecules 8a in the liquid crystal layer 8 (liquid crystal cell) sandwiched between the electrodes 30a and 30b is such that the tilt angle of the liquid crystal molecules 8a is either at the electrode center (pixel center) or at the electrode end (pixel periphery). The alignment of the liquid crystal molecules 8a is less disturbed substantially at a predetermined pretilt angle. As a result, light leakage at the periphery of the pixel can be suppressed, and the OFF transmittance is lowered. Therefore, it is possible to provide a liquid crystal display device that can suppress light leakage from the peripheral portion of the pixel without using a black mask and improve the contrast without causing an increase in manufacturing steps and an increase in manufacturing cost.

  An example of a method for manufacturing the first and second strip-shaped transparent electrodes 30a and 30b shown in FIG. 1 will be described with reference to FIG. In addition, since the preparation method of the 1st strip | belt-shaped transparent electrode 30a and the fabrication method of the 2nd strip | belt-shaped transparent electrode 30b are the same, the preparation method of the 1st strip | belt-shaped transparent electrode 30a is demonstrated and the 2nd strip | belt-shaped transparent electrode Description of the manufacturing method of 30b is omitted.

First, in the step (a), an ITO film 31 as a transparent electrode is formed by sputtering, for example, on a plate surface on one side of the first transparent substrate 5a according to a conventional method.
Next, in the step (b), a photoresist is applied on the ITO film 31 (coat), the first transparent substrate 5a coated with the photoresist is heated, and the photoresist is solidified (prebaked). A photoresist film 32 is formed on the ITO film 31.
Next, in step (c), the photoresist film 32 is irradiated with light to react. At this time, the photomask 33 depicting the striped pattern of the first strip-shaped transparent electrode 30a is used to control the striped pattern of the first strip-shaped transparent electrode 30a on the photoresist film 32 by controlling the portion irradiated with light. (Exposure).
Next, in the step (d), the exposed first transparent substrate 5a is immersed in a developing solution, and the excess photoresist film 32 other than the pattern portion is removed (development).
Next, in step (e), the excess ITO film 31 other than the pattern portion is removed with an etching solution (etching). Since the remaining portion of the photoresist film 32 is not removed by the etching solution, a striped pattern of the first strip-shaped transparent electrode 30a is formed on the plate surface on one side of the first transparent substrate 5a. Further, since the ITO film 31 has a property that the crystallinity in the vicinity of the first transparent substrate 5a is low and the film surface is high in crystallinity, the ITO film 31 in the vicinity of the first transparent substrate 5a has a property that the crystallinity is high in the etching process. The etched ITO film 31 has an inverted trapezoidal shape with the opposing surfaces of the first and second transparent substrates 5a and 5b as the bottom, where the shape of the end of the first strip-shaped transparent electrode 30a, That is, a reverse taper shape is obtained with respect to the opposing surface of the first transparent substrate 5a.
Finally, in the step (f), the photoresist film 32 in the pattern portion is peeled off.

  Thus, on the first transparent substrate 5a, the first strip-shaped transparent electrode 3a having an end portion reversely tapered with respect to the opposing surface of the first transparent substrate 5a is formed, and the first strip-shaped transparent electrode is formed. The electrodes 3a are formed in parallel to form a first strip-shaped transparent electrode 3a having a striped pattern as a whole.

  As described above, this embodiment describes one embodiment of the liquid crystal display device according to the present invention as a vertical alignment type (VA type). However, the present invention is not limited to a simple matrix drive type (for example, a twisted nematic type). The present invention can be applied to electrodes used in liquid crystal display devices of TN type or super twisted nematic type (STN type), and is not limited to the present embodiment, and various modifications can be made without departing from the scope of the present invention. Is something that can be done.

DESCRIPTION OF SYMBOLS 1 Vertical alignment type liquid crystal display device 2 Liquid crystal panel 2a Panel main body 3a, 3b, 30a, 30b Strip | belt-shaped transparent electrode 4a, 4b, 40a, 40b Alignment film | membrane 5a, 5b Transparent substrate 8 Liquid crystal layer 8a Liquid crystal molecule 9a, 9b Polarizing plate

Claims (1)

A first strip-shaped transparent electrode disposed in parallel on the opposing surfaces of the first and second transparent substrates opposed to each other at a predetermined interval and the second transparent substrate of the first transparent substrate; A second transparent electrode disposed on the surface of the second transparent substrate facing the first transparent substrate in a direction perpendicular to the first transparent electrode; and the first and second transparent substrates And a liquid crystal layer disposed between the opposing surfaces, wherein the ends of the first and second strip-shaped transparent electrodes are opposite to the opposing surfaces of the first and second transparent substrates. Each of the first and second strip-shaped transparent electrodes has a tapered shape, and the entire cross-sectional shape of each of the first and second strip-shaped transparent electrodes is an inverted trapezoidal shape with the opposing surfaces of the first and second transparent substrates as the bottom. A liquid crystal display device characterized by the above.

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