JP2005107373A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element which makes high display quality and satisfactory contrast characteristics compatible by suppressing a display defect and reduction of image quality caused by disclination and avoiding reduction of contrast characteristics. <P>SOLUTION: A first alignment layer 1 is formed in an inner side region and a second alignment layer 2 having alignment regulating force stronger than that of the first alignment layer is formed in a peripheral region. A pre-tilt angle θ2 in the peripheral region in each pixel electrode 101 is oriented and regulated to be an angle larger than the pre-tilt angle θ1 in the inner side region to be the region the most seriously concerning image display. The display defect and the reduction of image quality caused by disclination are suppressed in the peripheral region and the reduction of contrast characteristics of image display is avoided in the inner side region which is inner side of the peripheral region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display element having an alignment film such as an inorganic alignment film and suitably used as, for example, a light valve of a liquid crystal projector.

  Conventionally, a TN (Twisted Nematic) type liquid crystal display element (liquid crystal display panel) is used in a projection type liquid crystal display device called a so-called liquid crystal projector. In the TN type liquid crystal display element, an organic alignment film is used. It was used.

  However, the amount of light incident on the light valve tends to become stronger due to the recent increase in brightness and cost reduction of liquid crystal projectors. There is concern about deterioration and deterioration of the film. Therefore, in recent years, it has been proposed to use an inorganic alignment film formed by vapor-depositing an inorganic material such as SiO2 particularly for a liquid crystal display element for a liquid crystal projector.

  However, since the inorganic alignment film tends to have a weak chemical interaction with the TN liquid crystal, the alignment stability is low, and it is not necessarily said that the stage has yet reached a stage sufficient for practical use.

  On the other hand, it is known that when an inorganic vapor deposition film formed by oblique deposition of SiO2 is used as the alignment film, the vertical alignment type can be stably aligned. However, also in this case, the alignment regulating force of the liquid crystal molecules tends to be weaker than the alignment regulating force of the liquid crystal molecules due to the molecular interaction between the alignment polymer and the liquid crystal molecules in the organic vertical alignment film such as polyimide.

  Moreover, in a liquid crystal display element such as a light valve, a TFT switching element, a scanning line, a signal line, etc. are arranged with high definition on the active element substrate side called a so-called TFT substrate, so that a pixel potential is applied. In this case, a so-called lateral electric field is generated in the direction parallel to the substrate surface in the vicinity of adjacent pixels. Due to this lateral electric field, the tilt direction of liquid crystal molecules is disturbed when a voltage is applied, so-called disclination occurs, and this appears in the display screen as a noticeable unevenness of brightness and darkness, a decrease in contrast ratio or an afterimage, It will be visually recognized as an unsightly display defect.

  As a countermeasure to suppress the occurrence of such disclination, a method of inclining the director of liquid crystal molecules from the normal direction of the substrate to give a so-called pretilt angle, in other words, increasing the alignment regulating force has been proposed. , Also actually adopted.

  However, if the pre-tilt angle is increased by increasing the alignment regulating force as much as possible, the so-called vertical alignment type liquid crystal display element may cause a decrease in contrast ratio (characteristic).

Therefore, in order to achieve both suppression of disclination and avoidance of deterioration of contrast characteristics, the pre-tilt angle is increased in the alignment film on the TFT substrate side, which is easily affected by the lateral electric field, and the alignment film on the counter substrate side Then, a method of setting a slight pretilt angle has been devised (Patent Document 1).
JP-A-10-161127

  However, in the conventional method as described above, a liquid crystal of a driving method that tends to generate a strong lateral electric field such as a one-line inversion driving method that is generally applied to a transmissive liquid crystal light valve. In the case of a display element, there is a problem that disclination may occur even when a large pretilt angle is uniformly given to the TFT (Thin Film Transistor) substrate side.

  Another effective method is to prevent the disclination from being seen by concealing the area between adjacent pixels, which is likely to generate such a strong lateral electric field, with a shading band provided on the TFT substrate. However, this method still does not change that a large pretilt angle is given to the TFT substrate side, so that the contrast ratio is lowered as in the conventional method as described above. There is a problem that cannot be avoided.

  The present invention has been made in view of such problems, and the object thereof is to suppress display defects and image quality deterioration due to the occurrence of disclination and to avoid deterioration of contrast characteristics, and to achieve high display quality and good quality. An object of the present invention is to provide a liquid crystal display element capable of achieving both contrast characteristics.

  A liquid crystal display element according to the present invention includes a plurality of pixel electrodes arranged in a matrix on one of a pair of substrates, a plurality of switching means for driving each of the plurality of pixel electrodes, and the plurality of the plurality of pixel electrodes. A plurality of data lines and a plurality of scanning lines respectively connected to the switching means are provided, a counter electrode is provided on the other substrate of the pair of substrates, and at least a pixel electrode is provided of the pair of substrates. An alignment film is provided in the effective display area of one of the substrates, and the alignment film has a pretilt angle that is an angle formed between the substrate normal and the director of the liquid crystal molecules in the peripheral area of each pixel electrode. The angle is set larger than the pretilt angle in the area inside the peripheral area.

  In the liquid crystal display device according to the present invention, the peripheral region of each pixel electrode (a region having a predetermined width at the peripheral portion of the pixel electrode) is likely to generate disclination due to a lateral electric field between adjacent pixel electrodes. ) By controlling the pretilt angle by the alignment film to an angle larger than the pretilt angle by the alignment film in the region inside the peripheral region, that is, the region most important in image display. A large pre-tilt angle in the area suppresses display defects and image quality degradation due to disclination, and a small pre-tilt angle in such an area inside the peripheral area prevents a decrease in image display contrast characteristics. Is done.

  The alignment film is set so that the alignment regulating force in the peripheral region of each pixel electrode is stronger than the alignment regulating force in the inner region. You may make it make an angle larger than the pretilt angle in the area | region inside it. In addition, a first alignment film may be formed in the inner region, and a second alignment film having an alignment regulating force stronger than that of the first alignment film may be formed in the peripheral region. Alternatively, by making the first alignment film and the second alignment film have different film thicknesses, the alignment regulating force of the second alignment film is made stronger than the alignment regulating force of the first alignment film. You may do it. In the inner region, the first alignment film is laminated on the second alignment film so that the first alignment film faces the liquid crystal layer, and in the peripheral region, the second alignment film faces the liquid crystal layer. It is also possible to set to do so.

  According to the liquid crystal display element of the present invention, the peripheral region of each pixel electrode (predetermined width of the peripheral portion of the pixel electrode) in which disclination is likely to occur due to a lateral electric field between adjacent pixel electrodes. In the peripheral region, the pretilt angle by the alignment film in the region) is set larger than the pretilt angle by the alignment film in the region inside the peripheral region, that is, the region most important in image display. A large pretilt angle suppresses display defects and image quality degradation due to the occurrence of disclination, and a decrease in contrast characteristics of image display is avoided by a small pretilt angle in an area inside such a peripheral area. As a result, display defects and image quality degradation due to disclination are suppressed, and contrast characteristics are degraded. Avoided by, it is possible to achieve both high display quality and good contrast characteristics.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of a liquid crystal display element according to an embodiment of the present invention. In order to avoid complication of illustration, in the following description, there is a direct relationship with the alignment film and its pretilt angle and alignment regulating force, such as a scanning line, a signal line, and a TFT switching element in a so-called TFT substrate. Detailed description of the low part is omitted or simplified.

  The liquid crystal display element is formed by sandwiching a liquid crystal layer 300 between a pair of TFT substrates 100 and a counter electrode substrate 200 (cell gap), which are arranged to face each other and whose periphery is sealed with a sealing material. is there.

  As shown in FIG. 2, the counter electrode substrate 200 is provided with the counter electrode 201 on the surface of the glass substrate 210 over almost the entire surface of the effective display area. The TFT substrate 100 includes a plurality of TFTs provided with a plurality of pixel electrodes 101 arranged in a matrix on the surface of a glass substrate 110, a gate 102, a source 103, a drain 104, and the like for driving the pixel electrodes 101, respectively. A switching element 105, a plurality of signal lines 105 and a plurality of scanning lines 106 respectively connected to the plurality of TFT switching elements 105, a pixel potential capacitor dielectric layer 107 for forming a so-called storage capacitor, a planarization layer 108, etc. Is provided.

  Further, on the TFT substrate 100 side, the pretilt angle θ2 in the peripheral region of each pixel electrode 101 is larger than the pretilt angle θ1 in the inner region (referred to as an inner region) of the peripheral region. It has become. Here, the “pretilt angle” is an angle formed by the normal direction of the substrate and the director of the liquid crystal molecules 301 (shown as θ1 and θ2 in FIG. 1).

  More specifically, on the TFT substrate 100 side, the first alignment film 1 is laminated on the second alignment film 2 in the inner region, and the first alignment film 1 faces the liquid crystal layer 300. The second alignment film 2 is directly formed on the surface of the glass substrate 110 in the peripheral region where the disclination is likely to occur due to the alignment regulating force of the first alignment film 1. The two alignment films 2 face the liquid crystal layer 300, and the liquid crystal molecules 301 are set so as to regulate the alignment at a pretilt angle θ2 larger than the pretilt angle θ1 by the first alignment film 1.

  Similarly, on the counter electrode substrate 200 side, the first alignment film 1 is laminated on the second alignment film 2 in a region facing the inner region of each pixel electrode 101 of the TFT substrate 100, In the region where the first alignment film 1 faces the liquid crystal layer 300 and directly faces the peripheral region, the second alignment film 2 is formed directly on the surface of the glass substrate 210, and the second alignment film 2. Is set so as to face the liquid crystal layer 300.

  The first alignment film 1 and the second alignment film 2 are so-called inorganic oblique vapor deposition films.

  The second alignment film 2 formed in the peripheral region has a stronger alignment regulating force than the first alignment film 1 formed in the inner region. As a result, the alignment regulating force in the peripheral region of each pixel electrode 101 becomes a stronger regulating force than the alignment regulating force in the inner region mainly involved in image display inside the peripheral region, and the pretilt angle in the peripheral region θ2 is larger than the pretilt angle θ1 in the inner region. That is, between the pretilt angle θ1 imparted to the liquid crystal molecules 301 of the liquid crystal layer 300 by the first alignment film 1 and the pretilt angle θ2 imparted to the liquid crystal molecules 301 of the liquid crystal layer 300 by the second alignment film 2. , Θ1 <θ2 is established.

  Such strength of the alignment regulation force (and thus the pretilt angle) is realized by forming the second alignment film 2 thinner than the first alignment film 1. Has been. That is, as shown in FIG. 1, when the film thickness of the first alignment film 1 is d1, and the film thickness of the second alignment film 2 is d2, d1> d2.

  The TFT substrate 100 is provided with a light shielding band 111 that covers a region between adjacent pixel electrodes 101 so that a part of the peripheral region near the inner periphery is exposed without being covered with the light shielding band 111. Is set. That is, the light shielding band 111 is provided so as to extend inward from the outer peripheral edge of each pixel electrode 101 and is provided so as to partially overlap the peripheral edge of the pixel electrode 101 as shown in FIG. Thus, when the width of the light shielding band 111 overlapping is WB and the width of the second alignment film 2 is W1, W1> WB.

  Next, the operation of the liquid crystal display element of this embodiment will be described.

  In a so-called TFT active matrix type liquid crystal display element having a configuration as shown in FIG. 2, in general, fine TFT switching elements 105, signal lines 105, scanning lines 106, etc. are formed with high density, Since the pixel arrangement is high-definition, the distance between adjacent pixel electrodes 101 is as narrow as several μm. For this reason, a horizontal electric field is generated between adjacent pixel electrodes 101, and disclination (alignment failure) is likely to occur due to this.

  Therefore, in the liquid crystal display element of the present embodiment, in order to suppress the occurrence of disclination in the peripheral region of each pixel electrode 101, the second peripheral region having a strong alignment regulating force is provided in the peripheral region of each pixel electrode 101. By disposing the alignment film 2, the pretilt angle θ2 of the liquid crystal molecules 301 is increased.

  On the other hand, a liquid crystal display element originally provided with a vertically oriented inorganic oblique vapor deposition film as an alignment film is originally provided in the main area involved in image display inside the peripheral area, in other words, near the center of the pixel electrode 101. In order to avoid a decrease in the contrast ratio (good contrast characteristics) of the wrinkles that are present, by arranging the first alignment film 1 having a lower alignment regulating force than the second alignment film 2 disposed in the peripheral region, The pretilt angle θ1 of the liquid crystal molecules 301 is reduced.

  As a result, the occurrence of disclination can be suppressed and an image display with a high contrast ratio can be realized.

  3 and 4 show the main flow of the formation process of the first alignment film 1 and the second alignment film 2.

  First, the TFT substrate 100 or the counter electrode substrate 200 in a state before forming the first alignment film 1 and the second alignment film 2 (A in FIG. 3) is maintained at an angle inclined by φ from the substrate normal direction. Then, a second alignment film 2 is formed by depositing a SiO2 film on the surface (B in FIG. 3).

  Subsequently, the periphery of the second alignment film 2 is covered with the photoresist 401 over the width W1 on the pixel electrode 101 by a photolithography method using the patterning mask 400 or the like (D in FIG. 3) (FIG. 3). 3C to A in FIG. 4, and SiO2 is deposited (B in FIG. 4). Then, the photoresist 401 is peeled off to form the first alignment film 1 (C in FIG. 4).

  Then, the TFT substrate 100 and the counter electrode substrate 200 are arranged to face each other, and both substrates are bonded by a sealant (not shown) including a spacer (not shown), and a space (cell gap) between the two substrates is opposed. 2), a liquid crystal display device as shown in FIG. 2 is completed.

  As an example, as a specification of the liquid crystal display device manufactured by the above manufacturing process, the exposure width W1 is made larger than the overlap width WB, and the pretilt angle θ1 provided by the first alignment film 1 is 2 °. For each of the cases where the pretilt angle θ1 applied by the second alignment film 2 was changed from 8 ° to 14 ° while being fixed, the change in disclination and the contrast ratio were simulated.

  As a comparative example, the change in disclination and the contrast ratio in the case where only the second alignment film 2 is provided on almost the entire surface of the effective display area without providing the first alignment film 1 are also shown by simulation. Asked.

  As a result, as shown in FIG. 5, in the case of the liquid crystal display element of each of the above embodiments, the disclination is small enough to be hidden in the light shielding band 111 of the TFT substrate 100 without reducing the contrast ratio. It was possible to suppress or eliminate the following, and as a result, it was confirmed that the display quality was successfully prevented from deteriorating. On the other hand, as shown in FIG. 6, in the case of the above-described comparative example, the disclination becomes so large that it cannot be concealed by the light shielding band 111, and the light shielding band 111 is included in the image display of the pixel electrode 101. It was confirmed that it would be in a state of being noticed prominently.

  In addition, a simulation was also performed on the relationship between the occurrence of disclination, the contrast ratio, and the pretilt angle in a liquid crystal display device according to a conventional method as disclosed in, for example, Japanese Patent Laid-Open No. 10-161127.

  As a result, as shown in FIG. 7, according to the liquid crystal display element of the present embodiment, a large pretilt angle is imparted by the second alignment film 2 in the peripheral region, and the first alignment film 1 in the inner region. It was confirmed that both the suppression of disclination and the achievement of a high contrast ratio (avoidance of a decrease in contrast characteristics) can be realized by providing a small pretilt angle by.

  On the other hand, as shown in FIG. 8, in the case of the liquid crystal display device disclosed in Japanese Patent Laid-Open No. 10-161127 as the prior art, the disclination is so large that it cannot be hidden by the light shielding band 111. It has been confirmed that the image is developed from 111 to the image display of the pixel electrode 101 and is remarkably visually recognized.

  Here, in the above embodiment, an inorganic oblique vapor deposition film formed by vapor deposition at an angle of 50 ° from the substrate normal direction is used as the second alignment film 2. In this case, however, the disclination is reduced. The pretilt angle θ2 is preferably θ2 ≧ 8 °. In order to give such a pretilt angle θ2 to the liquid crystal molecules 301, the film thickness d2 of the second alignment film 2 is set to d2 ≦ 70 [nm].

  Focusing on the contrast characteristics, it is desirable that θ1 be as small as possible within a range in which random disclination does not occur in the inner region. In the case of the above embodiment, it is desirable that θ1 ≦ 6 °. In order to give such a pretilt angle θ1 to the liquid crystal molecules 301, the film thickness d1 of the first alignment film 1 is set based on the correlation between the film thickness d and the pretilt angle θ shown in FIG. It can be seen that 100 [nm] ≦ d1. However, more practically, since the pretilt angle θ1 is approximately θ1 = 0 at a film thickness of 250 [nm], it is desirable that 100 [nm] ≦ d1 ≦ 250 [nm].

  As described above, in the liquid crystal display element according to this embodiment, the light resistance and heat resistance of the liquid crystal display element can be improved by using the inorganic alignment film.

  In addition, by increasing the pretilt angle in the peripheral region where the probability of occurrence of a lateral electric field is high, the occurrence of disclination is suppressed, and by increasing the pretilt angle in the inner region mainly involved in image display It is possible to avoid deterioration of display characteristics such as a decrease in contrast ratio and an afterimage. Furthermore, since the pretilt angle is controlled by the film thickness of the oblique vapor deposition film, the pretilt angle can be controlled by the vapor deposition film thickness management by a crystal resonator or the like in the manufacturing process. Stabilization of the alignment characteristics of the alignment film can be achieved.

  The liquid crystal display element according to the present embodiment as described above includes, for example, a projection display device that includes a light source, a light valve, and an enlarged projection optical system that enlarges and projects light modulated by the light valve onto a projection surface. And can be suitably used as the light valve.

  In the above embodiment, the case where the pretilt angle is controlled by the film thickness of the first alignment film 1 and the second alignment film 2 has been described. However, the pretilt angle is controlled by changing the deposition angle. You may make it do.

  Further, in the inner region, the first alignment film 1 and the second alignment film 2 are laminated in two steps in total, but three steps having different film thicknesses so that the film thickness changes more gradually. Multi-level steps may be provided by stacking alignment films in the above multilayer. Furthermore, in the above-described embodiment, the case where the technique of forming SiO2 by the oblique vapor deposition method is adopted as the alignment film for imparting the pretilt angle has been described, but the most commonly used organic alignment film is used. The technique described in this embodiment can also be applied to an alignment film formed by rubbing a certain polyimide polymer film. However, in that case, it is possible to control the pretilt angle by changing the rubbing intensity between the peripheral region and the inner region, for example.

  Needless to say, the method described in the above embodiment can be applied to a vertical alignment type liquid crystal display element of a reflection type in addition to a transmission type liquid crystal display element.

  The liquid crystal display element of the present invention can be used as a transmissive liquid crystal display panel having an inorganic alignment film, for example, used as a light valve of a liquid crystal projector.

It is a figure showing the schematic structure of the liquid crystal display element which concerns on one embodiment of this invention. It is sectional drawing showing the structure for 1 pixel of the transmissive liquid crystal display element formed by forming the 1st alignment film and the 2nd alignment film. It is a figure showing the main flow of the formation process of a 1st alignment film and a 2nd alignment film. FIG. 4 is a diagram illustrating a main flow of a process of forming a first alignment film and a second alignment film following FIG. 3. It is a figure showing the simulation result about the disclination generation | occurrence | production in the case of the liquid crystal display element of each Example. It is a figure showing the simulation result about the disclination generation | occurrence | production in the case of the liquid crystal display element of a comparative example. It is a figure showing the relationship between generation | occurrence | production of disclination, a contrast ratio, and a pretilt angle in an Example and a prior art. It is a figure showing the simulation result about the disclination generation | occurrence | production in the case of the liquid crystal display element by a prior art. It is a figure showing the correlation between the film thickness d and the pretilt angle θ.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st alignment film, 2 ... 2nd alignment film, 100 ... TFT substrate, 101 ... Pixel electrode, 111 ... Shading zone, 200 ... Counter electrode substrate, 300 ... Liquid crystal layer, 301 ... Liquid crystal molecule

Claims (9)

A liquid crystal display element having a liquid crystal layer sandwiched between a pair of substrates disposed opposite to each other and sealed around with a sealing material,
A plurality of pixel electrodes arranged in a matrix on one of the pair of substrates, a plurality of switching means for driving the plurality of pixel electrodes, respectively, and connected to the plurality of switching means, respectively. A plurality of data lines and a plurality of scanning lines are provided, a counter electrode is provided on the other of the pair of substrates, and at least the pixel electrode of the pair of substrates is provided. An alignment film is provided in the effective display area of
The alignment film is set such that a pretilt angle, which is an angle formed by a substrate normal and a director of liquid crystal molecules, in a peripheral region of each pixel electrode is larger than a pretilt angle in a region inside the peripheral region. A liquid crystal display element characterized by the above. 2. The alignment film according to claim 1, wherein an alignment regulating force in a peripheral region of each pixel electrode is a stronger regulating force than an alignment regulating force in a region inside the peripheral region. Liquid crystal display element. A first alignment film is formed in the inner region, and a second alignment film having an alignment regulating force stronger than that of the first alignment film is formed in the peripheral region. The liquid crystal display element according to claim 2. By making the first alignment film and the second alignment film have different film thicknesses, the alignment regulating force of the second alignment film is stronger than the alignment regulating force of the first alignment film. The liquid crystal display element according to claim 3, wherein: The first alignment film is laminated on the second alignment film in the inner region, the first alignment film faces the liquid crystal layer, and the second alignment in the peripheral region. The liquid crystal display element according to claim 3, wherein the film is set so as to face the liquid crystal layer. The second alignment film is formed by depositing an inorganic alignment film at a thickness of 10 nm to 100 nm at an angle of 40 ° to 60 ° from the normal direction of the substrate,
The first alignment film is formed by depositing an inorganic alignment film at a film thickness of 100 [nm] to 250 [nm] at the same angle as the second alignment film. 3. The liquid crystal display element according to 3. The liquid crystal display element according to claim 1, wherein the alignment film is an inorganic oblique vapor deposition film. It is incorporated in a projection type liquid crystal display device having a light source, a light valve, and an enlarged projection optical system that enlarges and projects light modulated by the light valve onto a projection surface, and is used as the light valve. Item 2. A liquid crystal display device according to item 1. A light-shielding band is provided to cover a region between adjacent pixel electrodes;
The liquid crystal display element according to claim 1, wherein at least a part of the peripheral region is set to be exposed without being covered with the light shielding band.

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