JP2005258004A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element having excellent contrast characteristics. <P>SOLUTION: The liquid crystal display element is provided with an array substrate 1 having a color filter and a counter substrate 2 disposed opposite to and spaced a prescribed gap away from the array substrate. The counter substrate 2 has a glass substrate 31, an intermediate layer 33 formed on the glass substrate and a common electrode 34 formed on the intermediate layer. A refractive index of the intermediate layer 33 to a visible light wavelength is higher than the refractive index of the glass substrate 31 to the visible light wavelength and lower than the refractive index of the common electrode 34 to the visible light wavelength. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display element.

  In general, the demand for liquid crystal display elements is increasing as a thin, low power consumption, high-quality image display device, and the technological progress is remarkable. The above-described liquid crystal display element includes an array substrate, a counter substrate disposed opposite to the array substrate with a predetermined gap, and a liquid crystal layer sandwiched between the two substrates. One of the array substrate and the counter substrate is provided with a color filter including three colored layers of red, green, and blue.

  When the color filter is provided on the counter substrate, it is necessary to control the alignment between the array substrate and the counter substrate with high precision. In recent years, a COA (color filter on array) in which the color filter is provided on the array substrate is used. A liquid crystal display element having a structure has been developed. In recent years, in order to improve the aperture ratio of a pixel, a structure in which wiring on the array substrate and the pixel electrode are arranged in a separate layer structure to eliminate a planar gap between the two is often employed. In this case, it is necessary to form an insulating layer on the wiring on the array substrate. However, the COA structure can also serve as the insulating layer as a color filter, which is advantageous in terms of process.

  Next, a liquid crystal display element having a COA structure will be described. The array substrate includes a glass substrate, and a plurality of gate wirings and a plurality of signal wirings intersecting with the gate wirings are disposed on the glass substrate.

  A color filter composed of three colored layers of red, green, and blue and a plurality of pixel electrodes are sequentially formed on the glass substrate, the gate wiring, and the signal wiring. The gate wiring and the signal wiring are disposed so as to cover the gaps between the pixel electrodes, and have a black matrix (BM) function. For this reason, the gate wiring and the signal wiring contribute to prevention of light leakage between the pixel electrodes and improvement of contrast characteristics of the liquid crystal display element (for example, refer to Patent Document 1).

  Further, the gate wiring and the signal wiring have a width that is sufficiently wider than the gap between the pixel electrodes. For this reason, when the film thickness at the pattern edge of the colored layer becomes thicker or thinner than the film thickness at the center of the pattern, or when a driving method in which a lateral electric field is generated between the pixel electrodes is used, In addition, light leakage occurring on the pixel electrode in the vicinity of the pixel electrode can be suppressed. The material for forming the gate wiring and the signal wiring is preferably a metal from the viewpoint of suppressing the wiring resistance. However, since it is a metal, it has a characteristic of reflecting light, and the gate wiring and the signal having a sufficiently wide width. It is difficult to sufficiently suppress reflection of external light incident on the wiring.

  The above can be solved by reducing the width of the gate wiring and the signal wiring. However, when the film thickness at the pattern edge of the colored layer is thicker or thinner than the film thickness at the center of the pattern, When using a driving method in which a lateral electric field is generated between the electrodes, light leakage occurs not only between the pixel electrodes but also on the pixel electrodes in the vicinity of the pixel electrodes. For this reason, when the width of the gate wiring and the signal wiring is narrowed, the contrast characteristics are remarkably deteriorated as a result.

  The counter substrate includes a glass substrate, and a common electrode made of tin oxide or indium tin oxide (hereinafter referred to as ITO) and an alignment film made of polyimide are sequentially formed on the glass substrate. The refractive index with respect to the visible light wavelength of the material forming the common electrode is about 2.0. On the other hand, the refractive index of the glass substrate and the refractive index of the liquid crystal material are approximately 1.5, and the refractive index of polyimide as the alignment film material is approximately 1.65. Thus, the refractive index difference between the common electrode and the alignment film and between the alignment film and the liquid crystal layer is small compared to the refractive index difference between the common electrode and the glass substrate. The refractive index between the common electrode and the glass substrate is large, and Fresnel reflection occurs at this interface. For this reason, when external light enters the liquid crystal display element, strong reflection occurs at the interface between the common electrode of the counter substrate and the glass substrate, and the contrast characteristics deteriorate.

  When external light is incident on a liquid crystal display element provided with a color filter on the counter substrate, Fresnel reflection occurs due to a difference between the refractive index of the color filter and the refractive index of the common electrode. However, the refractive index of the color filter is often between the refractive index of the common electrode and that of the transparent electrode, and external light reflected at the interface due to Fresnel reflection at the interface between the common electrode and the color filter. Passes through the color filter twice. For this reason, the incident external light is considerably absorbed by the color filter, and in reality, it is hardly a problem.

  However, since the above-described liquid crystal display element has a COA structure in which a color filter is provided on the array substrate side, Fresnel reflection at the interface between the common electrode and the glass substrate is large and the reflected light is hardly absorbed. Therefore, when the COA structure is used, the contrast characteristics are remarkably deteriorated.

  In the case of a liquid crystal display element having a COA structure in which the width of the gate wiring and the signal wiring is reduced and the BM layer overlapping the gate wiring and the signal wiring is provided on the counter substrate side, the metal on the gate wiring and the signal wiring Since reflection can be prevented, a reduction in contrast can be reduced to some extent. However, since Fresnel reflection at the interface between the common electrode and the glass substrate cannot be prevented, sufficient contrast characteristics cannot be obtained.

  Further, the provision of the BM layer causes a step on the surface of the counter substrate. Thereby, in the region near the edge of the BM layer, the tilt angle of the liquid crystal molecules at the liquid crystal layer interface close to the common electrode is different from the other regions. For this reason, light leakage occurs in the region near the edge of the BM layer, and the contrast characteristics are deteriorated. This problem is more likely to occur as the BM layer is thicker.

Note that in the case where the BM layer is provided on the counter substrate side, the BM layer does not have to have other functions such as wiring, and therefore needs only to have excellent light shielding properties. For this reason, if the BM layer is formed of a metal having a low reflectance, the thickness can be sufficiently reduced. However, in this case, a photoresist is required for pattern formation of the BM layer. For this reason, the BM layer is often formed directly using a resist material, and the film thickness of the BM layer inevitably increases, leading to a decrease in contrast characteristics.
JP 2000-137242 A

As described above, the liquid crystal display element having the COA structure has the following three problems. (1) When the width of the gate wiring and the signal wiring is widened, the incident external light is reflected by these wirings, so that the contrast characteristics of the liquid crystal display element are deteriorated. (2) Since the Fresnel reflection at the interface between the common electrode and the glass substrate of the counter substrate is large and the reflected light is hardly absorbed, the contrast characteristics are remarkably deteriorated. (3) When the BM layer is provided on the counter substrate side, the tilt angle of the liquid crystal molecules at the liquid crystal layer interface near the common electrode is different from the region near the end of the BM layer due to the step on the surface of the counter substrate caused by the BM layer. Since it is different from the region, light leakage occurs in the region near the end of the BM layer, and the contrast characteristics are deteriorated.
The present invention has been made in view of the above points, and an object thereof is to provide a liquid crystal display element having excellent contrast characteristics.

  In order to solve the above problems, a liquid crystal display element according to an aspect of the present invention includes an array substrate having a color filter, and a counter substrate disposed facing the array substrate with a predetermined gap therebetween, The counter substrate has a substrate, a transparent intermediate layer formed on the substrate, and a common electrode formed on the intermediate layer, and the refractive index of the intermediate layer with respect to the visible light wavelength is visible light It is characterized by exceeding the refractive index of the substrate with respect to the wavelength and less than the refractive index of the common electrode with respect to the visible light wavelength.

  According to the present invention, a liquid crystal display element excellent in contrast characteristics can be provided.

Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIGS. 1 and 2, the liquid crystal display element is sandwiched between the array substrate 1, the counter substrate 2 disposed opposite to the array substrate with a predetermined gap, and the array substrate and the counter substrate. Liquid crystal layer 3.

  The array substrate 1 has a glass substrate 11 as a transparent insulating substrate. On this glass substrate 11, an insulating film 12 is formed as an undercoat film. On the insulating film 12, a plurality of gate lines 15 as first lines and signal lines 17 as second lines are provided. The plurality of gate lines 15 and the plurality of signal lines 17 are arranged in a matrix. A thin film transistor (hereinafter referred to as TFT) 21 is provided as a switching element at each intersection of the gate wiring 15 and the signal wiring 17.

  Next, the configuration of the TFT 21 will be described. A channel layer (active layer) 13 is formed on the glass substrate 11 on which the insulating film 12 is formed, and a gate insulating film 14 is formed on the glass substrate and the channel layer. On the gate insulating film 14, a gate wiring 15 overlapping the channel layer 13 is disposed, and an interlayer insulating film 16 is formed on the gate insulating film and the gate wiring.

  On the interlayer insulating film 16, a signal wiring 17, a source wiring 18 extending a part of the signal wiring, and a drain wiring 19 are formed. The source wiring 18 is connected to the source region of the channel layer 13 through a contact hole formed in the gate insulating film 14 and the interlayer insulating film 16. The drain wiring 19 is connected to the drain region of the channel layer 13 through a contact hole formed in the gate insulating film 14 and the interlayer insulating film 16.

  A passivation film 20 is formed on the interlayer insulating film 16, the signal wiring 17, the source wiring 18, and the drain wiring 19. On the passivation film 20, striped red colored layers 22R, green colored layers 22G, and blue colored layers 22B are arranged adjacently and alternately. The colored layer 22R, the colored layer 22G, and the colored layer 22B constitute a color filter. Here, the peripheral edges of the colored layer 22R, the colored layer 22G, and the colored layer 22B are formed, for example, so as to overlap the gate wiring 15 and the signal wiring 17, respectively.

  On the colored layers 22R, 22G, and 22B surrounded by the two adjacent gate wirings 15 and two signal wirings 17, a pixel electrode 23 is formed of a transparent conductive film such as ITO (indium tin oxide). Are formed respectively. Each pixel electrode 23 is connected to the drain wiring 19 through a contact hole formed in the colored layer and the passivation film 20. The peripheral edge of the pixel electrode 23 is positioned so as to overlap the gate wiring 15 and the signal wiring 17. The gate wiring 15 and the signal wiring 17 have a light shielding function as a black matrix (BM). An alignment film 24 is formed on the coloring layers 22R, 22G, 22B and the pixel electrode 23.

  The counter substrate 2 has a glass substrate 31 as a transparent insulating substrate. On this glass substrate 31, a common electrode 34 is sequentially formed by an intermediate layer 33 as a transparent insulating layer and a transparent conductive film such as ITO. Here, the intermediate layer 33 is formed directly on the surface of the glass substrate 31. Similarly, the common electrode 34 is directly formed on the surface of the intermediate layer 33. An alignment film 35 is formed on the common electrode 34. The intermediate layer 33 may be transparent, and may be almost transparent or completely transparent.

  The gap between the array substrate 1 and the counter substrate 2 is held by a plurality of columnar spacers (not shown) disposed on one of these substrates. The array substrate 1 and the counter substrate 2 are bonded to each other by a sealing material (not shown) arranged at the peripheral edge of both the substrates. The alignment films 24 and 35 are rubbed in a predetermined direction so that the twist angle of the liquid crystal molecules in the liquid crystal layer 3 is 90 °. Polarizing plates (not shown) are arranged on the outer surfaces of the array substrate 1 and the counter substrate 2, respectively.

Next, a more detailed configuration of the liquid crystal display element will be described together with its manufacturing method.
First, the glass substrate 11 is prepared. After the insulating film 12 is formed on the glass substrate 11, the TFT 21 is formed on the insulating film by a normal manufacturing process such as repeating the film formation and patterning. On the glass substrate 11, the gate wiring 15, the signal wiring 17, and the passivation film 20 are formed.

Subsequently, using a spinner, as a red resist, for example, a negative ultraviolet curable acrylic resin resist in which a red pigment is dispersed is applied on the glass substrate 11. Thereafter, a pattern is exposed to the red resist using a photomask that irradiates light to a region to be colored red. At the time of exposure, the red resist is irradiated with ultraviolet rays with a wavelength of 365 nm and an exposure amount of 100 mJ / cm ² .

  Next, the exposed red resist is developed with a 1% aqueous solution of potassium hydroxide (KOH) for 10 seconds and then baked at 230 ° C. for 1 hour to form a red colored layer 22R having a thickness of 2.0 μm. . Thereafter, the same process as that of the colored layer 22R is repeated, and a green colored layer 22G and a blue colored layer 22B having a thickness of 2.0 μm are sequentially formed on the glass substrate.

  Subsequently, the passivation film 20 and the colored layer overlapping the drain wiring 19 are removed using a photoetching method to form a through hole. Thereafter, an ITO film having a thickness of 1500 mm is deposited on the through holes and the colored layers 22R, 22G, and 22B by sputtering. Next, a plurality of pixel electrodes 23 are formed by patterning ITO using a photoetching method. Subsequently, for example, a polyimide resin having a thickness of 700 mm is applied on the entire surface of the glass substrate 11, and then the alignment film 24 is formed by performing a rubbing process.

  On the other hand, the counter substrate 2 uses a glass substrate 31. The glass substrate 31 has a refractive index ng with respect to a visible light wavelength of 1.5, for example. After printing the RTZ film (Catalytic Chemical Industry Co., Ltd.) on the glass substrate 31 by the transfer method, the RTZ film is dried at 90 ° C. for 5 minutes. Thereafter, UV light is irradiated to cure the RTZ film. In the present embodiment, the material of the RTZ film is a material whose solvent concentration is adjusted to a film thickness of 10,000 mm. By baking the RTZ film at 200 ° C. for 20 minutes, an intermediate layer 33 having a refractive index nm at a wavelength of 550 nm of 1.75 was obtained.

  Thereafter, using a sputtering method, ITO having a thickness of 1000 mm is deposited on the intermediate layer 33 to form the common electrode 34. For example, the common electrode 34 has a refractive index ni with respect to a visible light wavelength of 2.0. Subsequently, after an alignment film is formed on the entire surface of the common electrode 34 and the glass substrate 31, an alignment film 35 is formed by performing a rubbing process.

  The array substrate 1 and the counter substrate 2 formed as described above are arranged to face each other with a predetermined gap held by a plurality of columnar spacers, and the two substrates are bonded together by a sealing material arranged on the peripheral edge thereof. Then, after injecting positive nematic liquid crystal between both substrates by a liquid crystal injection port (not shown) formed in the sealing material, the liquid crystal injection port is sealed with a sealing material such as an ultraviolet curable resin. As a result, the liquid crystal is sealed between the array substrate 1 and the counter substrate 2 to form the liquid crystal layer 3. With the manufacturing method described above, a TN liquid crystal display element is completed.

  According to the liquid crystal display element configured as described above and the method for manufacturing the liquid crystal display element, in the counter substrate 2, the refractive index nm of the intermediate layer 33 is the refractive index ng of the glass substrate 31 and the refractive index ni of the common electrode 34. It is almost equal to the average value. For this reason, the refractive index difference at each interface between the glass substrate 31 and the intermediate layer 33 and the intermediate layer and the common electrode 34 is as small as 0.25. Thereby, even when external light is incident from the outer surface side of the counter substrate 2, Fresnel reflection occurring at each interface can be reduced. As described above, the contrast can be improved. The effect of reducing Fresnel reflection is more effective as the largest refractive index difference among the refractive index differences at each interface is small. For this reason, the effect of reducing Fresnel reflection is maximized when the intermediate layer 33 having a refractive index nm of the average value of the refractive index ng and the refractive index ni is used.

  From the above, even when the film thickness at the pattern edge of the colored layer is thicker or thinner than the film thickness at the center of the pattern, or when using a driving method in which a lateral electric field is generated between the pixel electrodes, the contrast is increased. It will not lead to a decline. Further, even when the gate wiring 15 and the signal wiring 17 are formed using any material such as metal, or when the width of these wirings is formed wider than the gap between the pixel electrodes 23, the contrast is not reduced.

  The refractive index nm can be adjusted by optimizing the film thickness. Thereby, the optical display performance of the liquid crystal display element can be improved. Further, if the refractive index nm exceeds the refractive index ng and is lower than the refractive index ni (ng <nm <ni), Fresnel reflection can be reduced.

  The film thickness of the intermediate layer 33 for having a specific refractive index nm can be obtained by calculating multiple reflections using the Jones matrix method. For example, when the refractive index ng is 1.5, the refractive index ni is 2.0, and the refractive index nm is 1.6, the thickness of the intermediate layer 33 is 1000 mm. According to this embodiment, when the contrast characteristic of the liquid crystal display element is measured in an environment with an illuminance of 5000 lux (lx), a very good value of 150: 1 is obtained. For this reason, it can be seen that the contrast characteristic 15: 1 of the liquid crystal display element without the intermediate layer 33 is greatly exceeded.

Next, a liquid crystal display element and a method for manufacturing the liquid crystal display element according to another embodiment of the present invention will be described.
As shown in FIG. 3, the counter substrate 2 uses a glass substrate 31. On the glass substrate 31, as a light-shielding material, for example, a black resist material (hereinafter referred to as a black resist) manufactured by JSR is applied by spin coating. Next, a photomask is disposed to face the black resist layer. Then, the black resist layer is exposed by irradiating ultraviolet rays through a photomask. Here, the photomask has a gradation pattern, has a first region that overlaps the gate wiring 15 and the signal wiring 17 of the array substrate 1, and a second region other than that, and transmits light only in the first region. It is configured to

  Subsequently, the exposed black resist layer is developed and unnecessary portions are removed, whereby a BM layer 32 having a thickness of 1.0 μm is formed as a cross-stripe-shaped light shielding layer. Thereafter, as in the above-described embodiment, the intermediate layer 33, the common electrode 34, and the alignment film 35 are sequentially formed on the glass substrate 31 on which the BM layer 32 is formed. The refractive index nm is adjusted to be higher than the refractive index ng and lower than the refractive index ni.

  The intermediate layer 33 has a function of flattening the surface of the counter substrate 2 having a step formed by the BM layer 32, and the surface of the intermediate layer facing the array substrate 1 is formed flat. When the array substrate 1 and the counter substrate 2 are bonded together, the gate wiring 15, the signal wiring 17, and the BM layer 32 are stacked and bonded together. Here, the BM layer 32 has a width wider than that of the gate wiring 15 and the signal wiring 17.

  According to the liquid crystal display element and the method of manufacturing a liquid crystal display element according to another embodiment configured as described above, the refractive index nm is adjusted to be higher than the refractive index ng and lower than the refractive index ni. , Fresnel reflection can be reduced. Further, the surface of the intermediate layer 33 is formed flat, and the alignment film in contact with the liquid crystal layer is also formed flat. For this reason, even when the BM layer 32 is formed on the counter substrate 2 side, it is a region overlapping the outer periphery of the BM layer, and light leakage that occurs in the vicinity of the periphery of the pixel electrode 23 can be suppressed. . As described above, the contrast can be improved.

  According to this embodiment, when the contrast characteristic of the liquid crystal display element is measured in an environment with an illuminance of 5000 lx, a very good value of 200: 1 is obtained. For this reason, it can be seen that the contrast characteristic 20: 1 of the liquid crystal display element without the intermediate layer 33 is greatly exceeded. The other configuration of the liquid crystal display element is the same as that of the above-described embodiment, and the detailed description thereof is omitted.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention. For example, in the above-described embodiment, the first wiring is described as the gate wiring 15. However, the first wiring may be an auxiliary capacitance line (not shown) extending in parallel with the gate wiring. In this case, the colored layers 23R, 24G, and 25B and the pixel electrodes 23 are arranged in a region surrounded by the auxiliary capacitance line and the signal wiring 17, and the peripheral edge thereof overlaps with a part of the auxiliary capacitance line and the signal wiring. Is provided.

1 is a cross-sectional view of a liquid crystal display element according to an embodiment of the present invention. FIG. 2 is a plan view of the array substrate shown in FIG. 1. Sectional drawing of the liquid crystal display element which concerns on other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Array substrate, 2 ... Counter substrate, 11 ... Glass substrate, 31 ... Glass substrate, 32 ... BM layer, 33 ... Intermediate layer, 34 ... Common electrode, ng ... Refractive index of glass substrate, nm ... Refractive index of intermediate layer , Ni ... the refractive index of the common electrode

Claims (5)

An array substrate having a color filter, and a counter substrate disposed facing the array substrate with a predetermined gap therebetween,
The counter substrate includes a substrate, an intermediate layer formed on the substrate, and a common electrode formed on the intermediate layer,
The liquid crystal display element, wherein a refractive index of the intermediate layer with respect to a visible light wavelength exceeds a refractive index of the substrate with respect to a visible light wavelength and is less than a refractive index of the common electrode with respect to a visible light wavelength. A substrate constituting the array substrate, a plurality of first wirings formed on the substrate, and a plurality of second wirings intersecting with the plurality of first wirings;
A light shielding layer disposed between the substrate and the intermediate layer of the counter substrate and facing the plurality of first wirings or the plurality of second wirings,
The liquid crystal display element according to claim 1, wherein a surface of the intermediate layer on the counter electrode side is flat. The color filter has a plurality of colored layers formed side by side on the array substrate,
The liquid crystal display element according to claim 2, wherein a peripheral edge of each colored layer is formed so as to overlap the first wiring or the second wiring.   The array substrate includes a plurality of switching elements connected to the first wiring and the second wiring, respectively, and a plurality of pixel electrodes connected to the switching elements and formed on the colored layer. The liquid crystal display element according to claim 3, wherein the liquid crystal display element is a liquid crystal display element.   The refractive index of the intermediate layer with respect to a visible light wavelength is substantially equal to an average value of a refractive index of the substrate with respect to a visible light wavelength and a refractive index of the common electrode with respect to a visible light wavelength. The liquid crystal display element as described.

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