JPH07261181A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device which is increased in tolerance for contamination of liquid crystals and orientation process and is free from unequal display by combining a transverse electric field system and a polymer for which a low heating temp. after applying is enough and is soluble in a solvent with active matrix elements such as thin-film transistor element. CONSTITUTION:The matrix elements are formed by having scanning electrodes 12, common electrodes 1, signal electrodes 3 intersecting with the scanning electrodes 12, active elements and pixel electrodes 4 on one substrate of a pair of substrates constituting a cell and arranging the pixel electrodes 4 and the common electrodes 1 so as to impress electric fields parallel with the substrate planes mainly on the liquid crystals. A soln. of a polymer soluble in the solvent is applied on such substrates. The solvent in the soln. of the polymer is then removed to impart liquid crystal orientability to the surfaces of the polymer. The cell is assembled by disposing a pair of the substrates having the liquid crystal molecule orientability on the surfaces via the sealing part formed in the peripheral parts of the substrates in such a manner that the surfaces having the liquid crystal molecule orientability face each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an active matrix type liquid crystal display device having high image quality without display unevenness.

[0002]

2. Description of the Related Art In a conventional active matrix type liquid crystal display device, transparent electrodes, which are formed on the interface between two substrates and face each other, are used as electrodes for driving a liquid crystal layer. This is a display method typified by a twisted nematic display method (hereinafter referred to as a vertical electric field method) that operates by making the direction of the electric field applied to the liquid crystal substantially perpendicular to the substrate interface.
By adopting. On the other hand, as a method of setting the direction of the electric field applied to the liquid crystal to a direction substantially parallel to the substrate interface (hereinafter referred to as lateral electric field method), a method using a comb-teeth electrode pair is used.
For example, it is proposed by Japanese Patent Publication No. 63-21907, but it has not been put to practical use as a display device.

[0003]

In the conventional active matrix type liquid crystal display device using the vertical electric field system, the following various problems occur due to the use of the vertical electric field system, and as a result, high display without display unevenness is achieved. It was difficult to obtain a liquid crystal display device of high image quality.

(1) Precise control of interface When a vertical electric field system is combined with a fine active matrix device such as a thin film transistor, a slight variation in interface state causes display unevenness. For example, when the surface condition of the alignment film changes, the angle (tilt angle) formed by the long axis of the liquid crystal molecule and the interface also changes, which changes the response of the liquid crystal to voltage application and changes the brightness.

The surface state of the alignment film is slightly dependent on the process conditions for forming the alignment film, and strict control of the process conditions is required. For example, in the case of a polyimide alignment film,
After a low-molecular-weight polyimide precursor solution is applied on a substrate, it is sequentially heated to dry the solvent, and a film having a high molecular weight and a dense and uniform surface state is formed by promoting the polymerization reaction. In particular, the heating temperature for promoting the polymerization reaction is extremely high, for example, 200 ° C. or higher. At this time, if the high-temperature heating condition changes, the tilt angle deviates from the designed value, causing unevenness. The tilt angle depends not only on the heating temperature but also on the rubbing conditions. Generally, when the rubbing strength is high, the inclination angle tends to decrease, but the degree of the fluctuation depends on the alignment film material used and the contamination of the alignment film surface due to rubbing. The tilt angle is not good either too high or too low for the following reasons. For example, when the tilt angle is lower than the design value, an alignment defect domain is generated particularly in a portion where a step is generated due to the presence of wiring or the like at the pixel end, and the contrast ratio is significantly reduced. vice versa,
When the tilt angle becomes higher than the design value, it becomes difficult to maintain the uniformity of the tilt angle, and uneven brightness occurs. Currently, in mass production, in order to obtain a uniform tilt angle of about 4 degrees, the materials to be used are carefully examined, and then the heating process, rubbing process, etc. are strictly controlled, but there is no display unevenness. There isn't.

(2) Maintaining high purity of liquid crystal Another physical property to be considered when combining a vertical electric field system and a fine active matrix device such as a thin film transistor is the purity of the liquid crystal composition material, and its value is 10. ¹³
It is essential to maintain an extremely high value of Ω · cm or more. This is because of the driving principle that charges must be supplied to the pixels and the charges accumulated when displaying information must be retained at least until the next information signal is supplied. Generally, this period (called one frame period)
The degree to which electric charges are retained inside is defined as a voltage retention rate, which is defined as a rate at which luminance is maintained within one frame period. This voltage holding ratio is extremely sensitive to the purity of the liquid crystal, and therefore the compounds constituting the liquid crystal composition material are currently limited to only a part of the fluorine-based compound group. In addition, there are great restrictions on the alignment film material. That is, if the purity of the alignment film material itself that is in direct contact with the liquid crystal is low, the liquid crystal composition material is gradually contaminated after the cell formation, the voltage holding ratio is significantly reduced, and the degree of the reduction is distributed depending on the location. A uniform display cannot be obtained. At present, the utmost attention is paid to the liquid crystal contamination by making the equipment used clean, but the voltage holding ratio is not 100%, and the display unevenness is not completely eliminated.

(3) Afterimage Phenomenon Although the mechanism is unknown, the so-called afterimage phenomenon in which the previous image remains even after a fixed still image is displayed and then switched to another image is strong in both the alignment film and the liquid crystal material. Depends on. Material design is extremely difficult because the mechanism is unknown.

As described above, it is extremely difficult to satisfy many required specifications at the same time, such as precise control of the interface (maintaining a predetermined tilt angle), maintaining high purity of the liquid crystal, and suppressing afterimages. The current situation is that the length of the manufacturing process is long and the manufacturing process is performed under extremely narrow process conditions. For example, in the heating process of the alignment film, the treatment is performed at an extremely high temperature of 200 ° C. or higher. Since the strict process conditions have to be set in this way, the selection range of other materials constituting the liquid crystal cell is narrowed, which further narrows the margin of manufacturing conditions and causes more uneven display. Making it easier.

The present invention provides means for solving these problems, and an object thereof is to provide an alignment film of a solvent-soluble polymer which can be processed by an active element, a lateral electric field method and a process at a lower temperature. By combining and
An object of the present invention is to provide a method for manufacturing an active matrix type liquid crystal display device with high image quality without display unevenness.

[0010]

In order to solve the above problems and achieve the above object, the present invention uses the following means.

[Means 1] A method for manufacturing a liquid crystal display device, which comprises the following steps.

(1) A scan electrode, a common electrode, a signal electrode intersecting with the scan electrode, an active element, and a pixel electrode are provided on one of a pair of substrates forming a cell, and the pixel electrode and the common electrode are A step of forming a matrix element arranged so as to mainly apply an electric field parallel to the substrate surface to the liquid crystal.

(2) A step of applying a solution of a polymer soluble in a solvent onto the substrate.

(3) A step of removing the solvent in the solution of the polymer.

(4) A step of imparting liquid crystal molecule aligning ability to the surface of the polymer.

(5) A cell is assembled by arranging a pair of substrates having liquid crystal molecule aligning ability on their surfaces, with spacers and a seal portion formed in the peripheral portion of the substrate so that the surfaces having liquid crystal molecule aligning ability face each other. Process.

(6) A step of injecting and sealing a liquid crystal composition into the cell to form a liquid crystal cell.

(7) A step of connecting a driving circuit and a polarizing means to the liquid crystal cell to form a module.

The means 1 is a combination of an active element, an in-plane switching method, and an alignment film of a polymer soluble in a solvent which can be processed by a process at a lower temperature, so that a high image quality active matrix liquid crystal display without display unevenness can be obtained. A method of obtaining a device is provided.

[Means 2] The method for manufacturing a liquid crystal display device according to means 1, wherein the active element is a thin film transistor element.

[Means 3] The method for manufacturing a liquid crystal display device according to means 1, wherein the solvent-soluble polymer is polyimide.

[Means 4] The method for producing a liquid crystal display device according to the means 1, wherein the solvent-soluble polymer is polyamide.

Means 2 to 4 provide more desirable means as active element and solvent soluble polymer. The thin film transistor element is excellent as an active element. Further, polyimide and polyamide are particularly excellent among dense polymer alignment films having high liquid crystal alignment ability.

[Means 5] Manufacturing of the liquid crystal display device according to means 1, wherein the substrate facing the substrate having the matrix element among the pair of substrates undergoes steps (2) to (4). Method.

[Means 6] Manufacturing of a liquid crystal display device according to means 5, characterized in that a color filter is formed on a substrate facing the substrate having the matrix element, and a plurality of color-developing capabilities are imparted to the liquid crystal cell. Method.

[Means 7] The method for manufacturing a liquid crystal display device according to means 1, wherein the substrate having the matrix element among the pair of substrates goes through the steps (2) to (4).

[Means 8] A method for manufacturing a liquid crystal display device according to means 7, characterized in that a color filter is formed on a substrate having the matrix element, and a plurality of color forming functions are provided as a liquid crystal cell.

Means 5 through 8 provide means for forming a solvent soluble polymer limited to one substrate.

[Means 9] A method for manufacturing a liquid crystal display device according to means 6 or 8, which comprises the following steps.

(1) A step of forming a film having a plurality of coloring layers.

(2) A step of irradiating a light pattern having a plurality of colors to form a color filter. [Means 10] The method for manufacturing a liquid crystal display device according to means 9, wherein the light irradiation step is performed once.

[Means 11] A film comprising the color-developing layer sandwiched between a pair of polymer protective films is irradiated with a light pattern to form a color filter, and then the film is attached onto the one substrate. Means 9 or 10
A method for manufacturing a liquid crystal display device according to item 1.

Means 9 to 11 provide a method for producing a color filter by a photographic method with a brighter color, which could not be used due to the presence of a high temperature heating process in the subsequent alignment film forming step. is there.

[Means 12] A means 6 or 8 is characterized in that a light-shielding layer for shielding the boundary between a plurality of color filters is formed on at least one of the pair of substrates when the liquid crystal cell is assembled. Liquid crystal display device manufacturing method.

[Means 13] The liquid crystal according to the means 12, wherein the light-shielding layer is formed on a substrate having the matrix element, and the plurality of color filters are formed on the substrate facing the matrix element. Manufacturing method of display device.

[Means 14] The method for manufacturing a liquid crystal display device according to means 12, wherein the light shielding layer and the plurality of color filters are formed on a substrate having the matrix element.

Means 12 to 14 provide a method of obtaining a light-shielding layer having a higher light-shielding property to obtain an active matrix type liquid crystal display device having higher image quality.

[0038]

[Action]

(1) Operation principle of horizontal electric field method First, the operation principle of the horizontal electric field method, which is an essential configuration of the present invention, will be described. FIG. 2 shows the definition of the angle φ _LC formed by the liquid crystal molecule major axis (optical axis) direction 10 near the interface with respect to the electric field direction 9 and the angle φ _P formed by the polarization transmission axis 11 of the polarizing plate. Since there are a pair of the polarizing plate and the liquid crystal interface above and below, respectively, they are denoted as φ _P1 , φ _P2 , φ _LC1 , and φ _LC2 as necessary. 2 corresponds to the front view of FIG. 1 described later.

1 (a) and 1 (b) are side sectional views showing the operation of the liquid crystal in the liquid crystal panel of the present invention, and FIGS. 1 (c) and 1 (d) are front views thereof. In FIG. 1, the thin film transistor element part is omitted, and a part of the wiring electrode structure is shown. Further, although the display device of the present invention is composed of a plurality of pixels, only a part within one pixel is shown here. FIG. 1A shows a cross section of the cell side when no voltage is applied, and FIG. 1C shows a front view at that time. Linear electrodes 1 and 4 are formed inside a pair of transparent substrates, and a protective insulating film 5 is applied and oriented on the linear electrodes 1 and 4. In this figure, the protective insulating film 5 is illustrated with the protective film and the orientation control film integrated, but one material may be used together or two materials may be laminated. A liquid crystal composition is sandwiched between them. The rod-shaped liquid crystal molecules 6 should have a slight angle with respect to the longitudinal direction of the electrodes 1 and 4 (front view of FIG. 1C) when no electric field is applied, that is, 45 ° ≦ | φ _LC | <90 °. It is oriented. In FIG. 1 and FIG. 2, the liquid crystal molecule major axis alignment direction (rubbing direction) 10 on the interface is indicated by an arrow. As a desirable example, the alignment directions of liquid crystal molecules on the upper and lower interfaces are parallel, that is, φ _LC1 = φ _LC2 (= φ _LC ). The dielectric anisotropy of the liquid crystal composition is assumed to be positive.

Here, when different potentials are applied to the pixel electrode 4 and the common electrode 1 and a potential difference is applied between them to apply the electric field direction 9 to the liquid crystal composition layer, the dielectric anisotropy of the liquid crystal composition is Figure 1 (b), (d) due to interaction with the electric field
As shown in, the liquid crystal molecules react and change their direction to the direction of the electric field. At this time, the brightness changes due to the interaction between the refractive index anisotropy of the liquid crystal composition layer and the polarizing plate.

(2) Freedom of Selection of Alignment Film Material and Liquid Crystal Material Next, by adopting the lateral electric field method which is an essential constitution of the present invention, the freedom of selection of the alignment film material and the liquid crystal material is increased. The operation will be described. As described in the problem to be solved by the invention, when selecting the alignment film material and the liquid crystal material, (1) precise control of the interface,
(2) Maintaining high purity of liquid crystal, (3) Suppressing afterimage phenomenon
It is necessary to consider the points. Hereinafter, effects of converting the vertical electric field method to the horizontal electric field method for these three points will be sequentially described.

In the vertical electric field system, the liquid crystal molecules that are substantially parallel to the substrate surface at the time of low electric field are converted into liquid crystal molecules by the dielectric interaction between the electric field in the direction perpendicular to the substrate surface (longitudinal electric field) and the liquid crystal molecules. The optical switching is performed by standing up. At this time, if the tilt angle is completely zero, there are two kinds of tilt directions, and the boundary between the two kinds of domains becomes an alignment defect area (referred to as a reverse tilt domain), which significantly deteriorates the image quality. . In an actual device, since there are many step structures such as wiring electrodes and thin film transistors in the vicinity of the end of the pixel, the reverse tilt domain cannot be suppressed unless there is a large inclination angle of about 4 degrees. The necessity of the tilt angle in the vertical electric field method arises from the fact that the tilt direction of the liquid crystal molecules when an electric field is applied must be determined in advance. In other words, the angle formed by the electric field direction and the initial liquid crystal molecule alignment direction must be sufficiently smaller than 90 degrees. This angle is empirically at least 88.5 degrees or less,
It is preferably 86 degrees or less. That is, when converted to a tilt angle, it is at least 1.5 degrees or more, preferably 4 degrees or more. On the other hand, also in the case of a lateral electric field, the same rule can be applied that "in order to prevent a defective alignment region, the angle between the electric field direction and the initial alignment direction of liquid crystal molecules should be sufficiently smaller than 90 degrees". Therefore, since the direction of the electric field changed from vertical to horizontal, the angle corresponding to the tilt angle in the vertical electric field method is the azimuth direction of the liquid crystal molecules in the substrate plane, and the interface between the interface and the liquid crystal molecules, which was essential in the vertical electric field method. The angle formed does not matter, and it does not matter if it is completely zero. The tilt angle is governed by the interaction between the alignment film and the liquid crystal molecules at the molecular level, whereas the azimuth direction of the liquid crystal molecules within the substrate plane can be freely determined at the design stage called the rubbing direction. It is a parameter that can be set. I briefly mentioned the interaction between the alignment film and liquid crystal molecules at the molecular level, but the phenomenon is complicated, and not only the primary structure of the material but also the secondary structure such as molecular conformation is involved. Sex cannot be avoided. Therefore, by adopting the lateral electric field method, the restriction of the tilt angle is completely released, and even with only this one point, the degree of freedom in selecting materials and processes is significantly improved. In the present invention, a process of dissolving a polymer alignment film that has already polymerized is applied by dissolving it in a solvent, and it is not necessary to cause a polymerization reaction on the substrate, and a high molecular weight and dense film quality can be obtained regardless of process variations. Further, the effect of suppressing domain and display unevenness also contributes to improvement of light use efficiency. That is, in the conventional method, the black matrix is used to shield the defective alignment portion generated near the portion having the step structure such as the thin film transistor, but in the present method, the area of the light shielding portion can be reduced. As a result, the aperture ratio and the light utilization efficiency associated therewith are improved, and a brighter display can be obtained.

Next, a description will be given of the second requirement, that is, the lateral electric field method has an extremely large degree of freedom in maintaining the high purity of the liquid crystal. In an active matrix type liquid crystal display device such as a thin film transistor type liquid crystal display device, an image information signal is applied to the liquid crystal only during a scanning selection time, and a pixel portion is circuit-like during a non-selection time when another line is selected. Will be open. During this time, the electric charge supplied from the signal wiring electrode must be retained until the line is next selected (one frame period). The time constant, which is the holding period of this charge, is mainly determined by the product of the electrostatic capacity and the electric resistance of the entire pixel portion. However, in the case of a vertical electric field, even the maximum value of electric resistance that can be realized by the liquid crystal is not sufficient with the electrostatic capacity of the liquid crystal itself, and a wiring portion is laid out for each pixel to add a capacitance portion. is the current situation. On the other hand, in the case of a vertical electric field, the electrodes are linear, and the cross-sectional area in the direction perpendicular to the electric field direction that determines the resistance value is significantly reduced. Therefore, even if the liquid crystal composition has the same specific resistance, the resistance value of the liquid crystal pixel portion can be significantly reduced. On the other hand, the capacitance is inversely proportional to the resistance value and decreases, which is disadvantageous in this respect. However,
The resistance value is remarkably increased (100 times or more). Therefore, the voltage can be sufficiently held by combining with the additional capacitance which has been conventionally formed. Rather, the resistance value of the liquid crystal is 1/10 to 1/100 if there is an additional capacitance element of the same level as the conventional one.
There is no problem even if it goes down. Since the contamination resistance of the liquid crystal has been remarkably improved in this way, not only the liquid crystal itself, but also the degree of freedom in selecting peripheral materials such as an alignment film, a sealant, and a sealant in contact with the liquid crystal and the process latitude for forming them. The degree increases significantly. In the step of applying the solvent-soluble polymer of the present invention in the form of a solution, it is easy to make the surface state more uniform without the need for high-temperature heating as in the conventional case. Further, even if the liquid crystal is somewhat contaminated by the residual solvent exuding or the like, the voltage holding ratio is not lowered, and in this respect, uneven display is unlikely to occur.

The present invention has a remarkable effect in suppressing the afterimage phenomenon which is the third demand. The afterimage phenomenon is also a visual recognition of the interface phenomenon. The interfacial phenomenon generally appears as a property in a direction perpendicular to the interface. In the case of the lateral electric field method, the main component of the electric field is parallel to the interface, and any such interface phenomenon is unlikely to appear. In fact, as will be described later in the examples, there is no afterimage phenomenon in any of the examples.

Due to the above three effects, various display irregularities due to the interface phenomenon and a slight amount of contamination in the liquid crystal are suppressed, and a display device having a uniform high image quality can be realized. In addition, it enables new processes that have never been possible before. That is, since the degree of freedom in selecting materials such as the alignment film, the sealant, and the sealant is increased, for example, the heating temperature is greatly reduced and the heating process time is shortened. Furthermore, color filters, light shielding materials, etc., which are peripheral agents that could not be used due to restrictions on heat resistance, pollution prevention ability, etc., can be used. As a result, it becomes possible to select a constituent material capable of further suppressing display unevenness and significantly improving the image quality. The present invention takes advantage of these characteristics of the horizontal electric field method, adopts a solvent-soluble polymer that can be applied to a low-temperature process with higher tolerance as an alignment film material, stabilizes the film quality of the alignment film, and displays uneven display. The present invention provides a method for obtaining a liquid crystal display device without a display device. In addition, the application of low-cost processes such as drastic reduction of heating temperature and shortening of heating process time leads to remarkable reduction of production power, which contributes to reduction of manufacturing cost and saving of energy resources.

[0046]

EXAMPLES The present invention will be specifically described with reference to examples.

[Example 1] A substrate having a thickness of 1.1 mm
Two transparent glass substrates whose surfaces have been polished by are used. First, a thin film transistor was formed on one of these substrates by the following procedure. The matrix element composed of the thin film transistors and the wiring electrodes may be any as long as a lateral electric field can be applied, and the manufacturing method thereof is not related to the essence of the present invention, and therefore the description will be simplified. Further, the description here regarding the manufacturing method of the matrix element is an example, and the present invention is not limited to this. 7, 8A and 8B schematically showing the cross-sectional view taken along the line CC ′ of FIG. 3 showing the structure of one pixel.
This embodiment will be described with reference to FIG.

A chromium film was formed on one side of the transparent glass substrate 7 by the sputtering method, and then the scanning electrode 12 and the common electrode 1 were patterned by the photolithography method (FIG. 7A). Thereafter, CVD thereon (C hemical V a
por D eposition) method (a gate insulating film made of SiN) (FIG. 7 (b) silicon nitride), further similarly by CVD on the surface layer is n-type amorphous silicon (a-Si) A film of a-Si13 was prepared (FIG. 7).
(C)). The signal electrode 3 and the pixel electrode 4 made of chromium were formed by sputtering and photolithography so as to cover a part of the a-Si 13 and form a thin film transistor (FIG. 7D). An insulating protective film made of SiN was formed thereon (FIG. 8E). Thereafter, a light-shielding layer 22 and a pigment color filter 23c are formed thereon, and a resin flattening film 23b is spin-coated thereon (FIG. 8).
(F)). As the light-shielding layer, an epoxy resin containing 1% by weight of carbon fine particles (MONARCH800, particle size 16 nm) manufactured by Cabot Corporation was used. As the color-developing pigments of the color filter, CR-6101, CG-5101 and CB-6101 manufactured by Fuji Hunt Co. were used for the three primary colors of red, green and blue, respectively. It was applied by spin coating, prebaked at 85 ° C., exposed and developed, and finally post-baked at 200 ° C. to form a film-like color filter. In this example, a pigment was used as the color-developing layer, but according to the present invention, since it is not necessary to heat to a high temperature in the subsequent alignment film forming process, a dye-type coloring agent having a low heat resistance and a brighter color is used. You may use it. Further, as the material for the light-shielding layer, in the present embodiment, a material such as carbon black fine particles which may become a pollution source that lowers the specific resistance of the liquid crystal was used, but there is no problem because the lateral electric field method itself is resistant to pollution. Rather, since the carbon black fine particles have an extremely high light-shielding rate, higher image quality can be realized. Of course, there is no problem even if other insulating light-shielding agents such as pigments and dyes other than carbon black fine particles are used. An epoxy resin was used as the resin for flattening the surface, but the material is not limited to this material. Next, the imidization ratio is 10
AL-105, a 0% solvent-soluble polyimide
Polymer solution 24a of No. 1 (manufactured by Japan Synthetic Rubber Co., Ltd.) was applied by spin coating (FIG. 8 (g)). In this embodiment,
The solvent used was a mixture of dimethylformamide, which is a polar solvent, and butylcellosolve, which is a nonpolar solvent, in a weight ratio of 8: 2, but N-methyl-2-pyrrolidone other than dimethylformamide can be used as long as it is a polar solvent. Or dimethylacetamide, or butyl cellosolve acetate as long as it is a nonpolar solvent. Further, although the spin coating method is adopted as the coating method in the present embodiment, various printing methods such as letterpress printing, offset printing, screen printing, roll coating method, dip method, etc. can be applied as long as they can be applied to a uniform film thickness. It is not limited to this. Then, the solution was heated to 160 ° C. and left for 30 minutes to remove the solvent. Thus, a polymer 24b which is a dense polyimide alignment film was obtained (FIG. 8 (h)). Next, this surface was subjected to rubbing treatment to impart liquid crystal aligning ability to the surface of the alignment film (FIG. 9).
(I)). In this example, as a method of imparting the orientation ability,
Although the rubbing method is adopted, other methods such as a method of forming fine grooves other than the rubbing method can also be used. Next, a substrate on the opposite side whose liquid crystal aligning ability is imparted to the surface of the alignment film by the same material and process is made to face the surfaces 24d having the aligning ability of the liquid crystal molecules, and the spacer made of polymer beads and the peripheral portion A cell was assembled with a sealant interposed (FIG. 9 (j)). Liquid crystal molecules 6 were injected into this cell in a vacuum and sealed with a sealant 28 made of an ultraviolet curable resin. After that, a driving circuit, a polarizing plate, a backlight, etc. were connected to this cell to form a module, and a liquid crystal display device was obtained.

Next, the structure of the liquid crystal display device obtained by the above process will be described in more detail.

The rubbing directions on the upper and lower interfaces are substantially parallel to each other, and the angle formed with the direction of the applied electric field is 88 degrees (φ _LC1
= Φ _LC2 = 88 °). The dielectric anisotropy Δε of the nematic liquid crystal composition sandwiched between these substrates is positive and its value is 4.5, and the refractive index anisotropy Δn is 0.072 (589n).
m, 20 ° C). Initially, the liquid crystal composition had a resistance value of 10 ¹⁴ Ω · cm or more, but was subsequently contaminated.
It fell to 6 × 10 ¹² Ω · cm. In this example, this contaminated material was used. Gap d is 3.9 μm when liquid crystal is filled with spherical polymer beads dispersed and sandwiched between the substrates.
And Therefore, Δn · d is 0.281 μm. Further, when the same alignment film material was formed on the glass substrate by the same process and the tilt angle of the liquid crystal molecule long axis was measured by the crystal rotation method, it was only 1.2 degrees. A panel is sandwiched between two polarizing plates [G1220DU manufactured by Nitto Denko Corporation], and the polarization transmission axis of one polarizing plate is slightly smaller than the rubbing direction, that is, φ _P1 = 80 ° (that is, | φ _LC1 −φ _P1 | = 8 °) and the other was orthogonal to it, that is, φ _P2 = −12 °. As a result, as the voltage V _LC applied to the pixel was gradually increased from zero, the brightness decreased and reached the minimum value (FIG. 4). In this embodiment, a normally closed characteristic is adopted in which a dark state is set at a low voltage (V _OFF ) and a bright state is set at a high voltage (V _ON ). V _OFF is 6.9V and V _ON is 9.1V.

The structures of the thin film transistor and various electrodes are shown in FIG. 3 and will be described in detail. FIG. 3A is a front view seen from a direction perpendicular to the substrate surface, and FIGS. 3B and 3C are side sectional views. The thin film transistor element 14 is composed of a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, a scan electrode (gate electrode) 12, and amorphous silicon 13. The common electrode 1 and the scan electrode 12, and the signal electrode 3 and the pixel electrode 4 are formed by patterning the same metal layer. The capacitive element 16 is formed as a structure in which the gate insulating film 2 is sandwiched between the pixel electrode 4 and the common electrode 1 in a region (indicated by a dotted line in FIG. 3) connecting the two common electrodes 1. The pixel electrode 4 is arranged between the two common electrodes 1 in the front view (FIG. 3A). One pixel pitch 15 is 69 μm in the lateral direction (that is, between signal electrodes),
The vertical direction (that is, between the scanning electrodes) is 207 μm. The electrode width is the scanning electrode, which is a wiring electrode extending over a plurality of pixels, the signal electrode, the common electrode wiring portion (parallel to the scanning electrode (see FIG.
The lateral extension) was widened to avoid line defects. Each width is 10 μm. On the other hand, in order to improve the aperture ratio, the widths of the pixel electrode formed independently for each pixel and the part of the common electrode extending in the longitudinal direction of the signal wiring electrode are slightly narrowed to 5 μm and 8 μm, respectively. By narrowing the width of these electrodes, the possibility of disconnection due to the inclusion of foreign matter or the like increases, but in this case, a partial defect of one pixel does not lead to a line defect. In addition, the common electrode and the signal electrode were slightly overlapped (1 μm) with an insulating film interposed therebetween in order to achieve the highest possible aperture ratio. As a result, the black matrix in the direction parallel to the signal wiring becomes unnecessary. Therefore, FIG. 3 (c)
As shown in (1), a black matrix structure that shields light only in the scanning electrode direction is adopted. Thus, the gap between the common electrode and the pixel electrode was 20 μm, the length of the opening in the longitudinal direction was 157 μm, and a high aperture ratio of 44.0% was obtained. The number of pixels was 320 × 160 with 320 signal electrodes and 160 scanning electrodes. A panel portion composed of a plurality of pixels is shown in FIGS. In FIG. 5, the black matrix is omitted, and in FIG. 6, the black matrix is used to block light.

Next, the circuit configuration and drive waveform will be described. A signal electrode drive circuit 18 and a scan electrode drive circuit 19 were connected to each scan electrode 12 and each signal electrode 3. Further, the common electrode drive circuit 20 is also provided for the common electrode 1.
Were connected (Fig. 13). A signal waveform having information is applied to the signal electrode 3, and a scanning waveform is applied to the scanning electrode 12 in synchronization with the signal waveform. An information signal is transmitted from the signal electrode 3 to the pixel electrode 4 through the thin film transistor element 14, and a voltage is applied to the liquid crystal portion between the signal electrode 3 and the common electrode 1. FIG. 14 shows a specific example of the drive voltage waveform. The amplitudes in this embodiment are V _D-CENTER = 14.0, V _GH = 28.0, V _GL = 0, V _DH
= 15.1, V _DL = 12.9, V _CH = 20.4, V _CL = 4.
39, and as a result, the jump voltages ΔV _GS (+) and ΔV _GS (-) due to the parasitic capacitance between the gate electrode and the source electrode, the voltage V _S applied to the pixel electrode, and the voltage V _LC applied to the liquid crystal are shown in the table below. It became like. In addition, the unit of voltage is volt after this.

[0053]

[Table 1]

V _ON and V _OFF shown in FIG. 4 are 9.16 respectively.
It became 6.85 volts. In this embodiment, the process for forming the alignment film is performed at a temperature sufficient to remove the solvent.
The temperature was 0 ° C, which is much lower than the conventional temperature. The tilt angle was 1.2 degrees, which was low enough to cause alignment defects in the conventional longitudinal electric field method, but alignment defects such as reverse tilt domains did not occur at all. Further, as an effect of reducing the tilt angle, the nonuniformity of the alignment is eliminated, and the uniformity of the display is improved. When the display performance was measured with a luminance meter, a sufficiently high contrast ratio of 80 was obtained. Further, no display unevenness due to contamination of the liquid crystal was observed, and a highly uniform display was obtained. Furthermore, when the fixed pattern was displayed for one hour and then switched to another pattern, the afterimage (burn-in) phenomenon was not visually recognized at all, and the pattern was immediately switched to a new pattern.

[Embodiment 2] In this embodiment, a solvent-soluble polyamide HTX-670 is used as the polyimide alignment film of Embodiment 1.
Changed to 0 (manufactured by Hitachi Chemical). As in Example 1, after coating the polyamide in a solution state, the solution was heated to 150 ° C. and left for 30 minutes to remove the solvent, thereby obtaining a dense polyamide alignment film. The tilt angle was 1.0 degree. Other configurations are the same as those in the first embodiment. As a result of modularization and evaluation of characteristics, a sufficiently high contrast ratio of 100 was obtained, and no unevenness of alignment, misalignment such as reverse tilt domain, display unevenness due to liquid crystal contamination, etc. were observed at all, and uniformity was observed. High display was obtained. When the fixed pattern was displayed for one hour and then switched to another pattern, the afterimage (burn-in) phenomenon was not visually recognized at all, and the pattern was immediately switched to a new pattern.

Comparative Example 1 An alignment film was formed on the conventional vertical electric field type thin film transistor matrix substrate in the same manner as in Example 2. The color filter was formed under the transparent conductive film formed on the counter substrate. The display system was a twisted nematic system. As the liquid crystal material, a material which was not contaminated and had a resistance value of 10 ¹⁴ Ω · cm was used. Except for these points, the same procedure as in Example 2 was performed.

As a result, a misalignment domain due to insufficient tilt angle was generated at the pixel edge, a light scattering phenomenon occurred, and the contrast ratio was lowered to 25: 1. In addition, display unevenness that occurs when a contaminated liquid crystal is used also occurs.

[Embodiment 3] In this embodiment, a color filter is formed on the counter substrate side. A schematic sectional view of the liquid crystal display device of this embodiment is shown in FIG. Color filters 23c having a plurality of colors are stacked on the substrate 7 on the opposite side, and boundaries of the plurality of colors are arranged right above the light shielding layer 22 on the matrix substrate. The width of the light-shielding portion is 50 μm, which is 3 to 10 μ which is the alignment accuracy between the substrates of a general liquid crystal panel assembling apparatus.
Since it is much wider than m, it is extremely easy to assemble. In addition, the color filter of this embodiment is a positive type film FUJICHROME, PROVIA, 100DAY manufactured by Fuji Photo Film Co., Ltd.
A pattern of multiple colors was formed on the LIGHT and RDPII135 by one irradiation. The film has a plurality of color-developing layers between two protective films in advance. Therefore, if light is irradiated through a photomask corresponding to a color pattern required for a liquid crystal display device, the color filter can be irradiated by one light irradiation. can get. The color filter was adhered onto the counter substrate at room temperature while being pressed with an epoxy adhesive, and then the cells were formed into cells through the same alignment film forming process as in the example. At this time, the solvent was removed at 80 ° C. under a reduced pressure of 10 mmHg for 5 hours. Other conditions are the same as those in the second embodiment.

When the characteristics were evaluated by modularizing,
A sufficiently high contrast ratio of 100 was obtained, and display with high uniformity was obtained without any non-uniformity of alignment, alignment failure such as reverse tilt domain, and display unevenness due to liquid crystal contamination. When the fixed pattern was displayed for one hour and then switched to another pattern, the afterimage (burn-in) phenomenon was not observed at all, and the pattern was immediately switched to a new pattern. In addition, the color tone of the color filter made from such a positive type film is very vivid, and the color of the liquid crystal display device of the present invention using it is also vivid.

In this embodiment, a color-developing layer sandwiched between protective films was used and bonded to a glass substrate after forming a color filter pattern. However, even if the color-developing layer is formed on the glass substrate from the beginning. I do not care. Also,
The light exposure is preferably performed once, but it may be performed multiple times.

Example 4 In this example, a color filter was produced by using the positive type film EKTACHROME DYNA 100 manufactured by Kodak Company in the same process as in Example 3. In addition, the light shielding layer was provided in the color filter pattern, and the light shielding layer was not formed in the active element. FIG. 12 shows the arrangement of the light shielding layers in the color filter of this embodiment. FIG. 12A shows a pattern when the side cross section is viewed from the front of FIG. 12B.

Similarly, when the characteristics were evaluated by modularization, a sufficiently high contrast ratio 90 was obtained, and there was no display unevenness due to alignment nonuniformity, reverse tilt domains such as reverse tilt domains, and liquid crystal contamination. It was not seen, and a highly uniform display was obtained. Also, when the fixed pattern was displayed for one hour and then switched to another pattern, the afterimage (burn-in) phenomenon was not observed at all, and the pattern was immediately switched to a new pattern. As in Example 3, the color tone of the color filter made from such a positive type film was very vivid, and the color of the liquid crystal display device of this example using it was also vivid.

According to Examples 1 to 4 described above, in the active element such as the thin film transistor element, the lateral electric field method and the polymer soluble in the solvent are used as the alignment film, so that the tolerance against liquid crystal contamination and the alignment film varnish can be improved. Since the heating temperature after coating is low and the tolerance for the equi-orientation process is increased, a high quality liquid crystal display device without display unevenness was obtained.

[0064]

According to the present invention, in an active matrix device such as a thin film transistor device, by combining a lateral electric field system and a polymer soluble in a solvent which can be heated at a low heating temperature after coating, liquid crystal contamination and alignment can be achieved. A high-quality liquid crystal display device with no display unevenness can be obtained because of increased process margin.

[Brief description of drawings]

FIG. 1 is a diagram showing an operation of liquid crystal in a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing an angle formed by a molecular long-axis orientation direction (rubbing direction) φ _LC on the interface and a polarizing plate polarization transmission axis direction φ _P with respect to an electric field direction.

FIG. 3 is a diagram showing a structure of a thin film transistor, an electrode, and a wiring of the liquid crystal display device of the present invention. [(A) Front view, (b),
(c) Side sectional view. ]

FIG. 4 is a diagram showing electro-optical characteristics of the liquid crystal display device of the present invention.

FIG. 5 is a diagram showing an arrangement of a plurality of pixels of the liquid crystal display device of the present invention.

FIG. 6 is a diagram showing an arrangement of a plurality of pixels in the liquid crystal display device of the present invention.

FIG. 7 is a diagram showing a manufacturing process of the liquid crystal display device of the present invention.

FIG. 8 is a diagram showing a manufacturing process of the liquid crystal display device of the present invention.

FIG. 9 is a diagram showing a manufacturing process of the liquid crystal display device of the present invention.

FIG. 10 is a side sectional view of a liquid crystal display device of the present invention equipped with a color filter.

FIG. 11 is a diagram showing a method for manufacturing a color filter of the liquid crystal display device of the present invention.

FIG. 12 is another embodiment of the color filter of the liquid crystal display device of the present invention.

FIG. 13 is a diagram showing a circuit of a liquid crystal display device of the present invention.

FIG. 14 is a diagram showing another drive waveform of the liquid crystal display device of the present invention.

[Explanation of symbols]

1 ... Common electrode (common electrode), 2 ... Gate insulating film, 3 ...
Signal electrode (drain electrode), 4 ... Pixel electrode (source electrode), 5 ... Protective insulating film, 6 ... Liquid crystal molecules in liquid crystal composition layer, 7 ... Substrate, 8 ... Polarizing plate, 9 ... Electric field direction, 10 ... Interface Upper molecular long axis alignment direction (rubbing direction), 11 ... Polarizing plate polarization transmission axis direction, 12 ... Scan electrode (gate electrode), 13
... amorphous silicon, 14 ... thin film transistor element, 15 ... 1 pixel pitch, 16 ... additional capacitance element section, 17
... Control circuit, 18 ... Signal electrode drive circuit, 19 ...
Scan electrode drive circuit, 20 ... Common electrode drive circuit, 21 ... Display area, 22 ... Light-shielding layer, 23a ... Coloring layer, 23b ... Flattening film, 23c ... Color filter, 23d ... Polymer protective film, 24a ... Polymer solution, 24b ... Polymer, 24c ... Rubbing roller, 24d ... Alignment film, 25 ... Photomask,
26 ... Light, 27 ... Sealing agent, 28 ... Sealing agent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keikazu Araya 7-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (14)

[Claims] 1. A method of manufacturing a liquid crystal display device, comprising the following steps. (1) A scan electrode, a common electrode, a signal electrode intersecting with the scan electrode, an active element, and a pixel electrode are provided on one of a pair of substrates forming a cell, and the pixel electrode and the common electrode are mainly liquid crystals. A step of forming matrix elements arranged so as to apply an electric field parallel to the substrate surface. (2) A step of applying a solution of a polymer soluble in a solvent onto the substrate. (3) A step of removing the solvent in the solution of the polymer. (4) A step of imparting liquid crystal molecule aligning ability to the surface of the polymer. (5) A step of assembling a cell in which a pair of substrates having liquid crystal molecule aligning ability on their surfaces are opposed to each other with surfaces having liquid crystal molecule aligning ability facing each other through a spacer and a seal portion formed around the substrate. (6) A step of injecting and sealing a liquid crystal composition into the cell to form a liquid crystal cell. (7) A step of connecting a driving circuit and a polarizing means to the liquid crystal cell to form a module. 2. The method for manufacturing a liquid crystal display device according to claim 1, wherein the active element is a thin film transistor element. 3. The method of manufacturing a liquid crystal display device according to claim 1, wherein the solvent-soluble polymer is polyimide. 4. The method of manufacturing a liquid crystal display device according to claim 1, wherein the solvent-soluble polymer is polyamide. 5. The method of manufacturing a liquid crystal display device according to claim 1, wherein the substrate facing the substrate having the matrix element among the pair of substrates undergoes steps (2) to (4). . 6. The method for manufacturing a liquid crystal display device according to claim 5, wherein a color filter is formed on a substrate facing the substrate having the matrix element, and a plurality of color forming functions are provided as a liquid crystal cell. . 7. The method of manufacturing a liquid crystal display device according to claim 1, wherein the substrate having the matrix element among the pair of substrates undergoes steps (2) to (4). 8. The method of manufacturing a liquid crystal display device according to claim 7, wherein a color filter is formed on the substrate having the matrix element, and a plurality of color forming functions are provided as a liquid crystal cell. 9. The method for manufacturing a liquid crystal display device according to claim 6, which comprises the following steps. (1) A step of forming a film having a plurality of coloring layers. (2) A step of forming a color filter by irradiating a light pattern having a plurality of colors. 10. The method for manufacturing a liquid crystal display device according to claim 9, wherein the light irradiation step is performed once. 11. A film comprising the color-forming layer sandwiched between a pair of polymer protective films is irradiated with a light pattern to form a color filter, and then the film is attached onto the one substrate. The method for manufacturing a liquid crystal display device according to claim 9 or 10. 12. The liquid crystal according to claim 6, wherein a light-shielding layer that shields a boundary between a plurality of color filters when forming the liquid crystal cell is formed on at least one of the pair of substrates. Manufacturing method of display device. 13. The liquid crystal display according to claim 12, wherein the light shielding layer is formed on a substrate having the matrix element, and the plurality of color filters are formed on a substrate facing the matrix element. Device manufacturing method. 14. The method of manufacturing a liquid crystal display device according to claim 12, wherein the light shielding layer and the plurality of color filters are formed on a substrate having the matrix element.