JP2008293031A - Color liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase contrast of a color liquid crystal display device which has a color filter and a data line superposed on a pixel electrode. <P>SOLUTION: In the liquid crystal display device filled with liquid crystals between first and second substrates facing each other, the data line 56 is formed on the pixel electrode 58 on the first substrate. By forming the color filter 1 between the data line 56 and the pixel electrode 58, the distance between the data line 56 and the pixel electrode 58 is increased to reduce parasitic capacitance. Since sufficient voltage can be applied to the pixel electrode 58, contrast is increased. Since film thickness of a flattened film 2 is not made thick, transmittance is not lowered. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a liquid crystal display (LCD), and more particularly to an improvement in image display in a liquid crystal display formed by overlapping a source line on a pixel electrode.

  In a vertical alignment type LCD using a liquid crystal having a negative dielectric anisotropy and a vertical alignment film, for example, Japanese Patent Application Laid-Open No. 6-301036 discloses a vertical alignment having an alignment control window for controlling the alignment direction of the liquid crystal. Type LCDs have been proposed. Hereinafter, this type of LCD will be described.

  FIG. 4A is a plan view thereof, and FIG. 4B is a cross-sectional view thereof taken along the line A-A ′. A gate line 51 is formed on the first substrate 50, and a gate insulating film 52 is formed to cover the gate line 51. The gate line 51 includes a gate electrode 51a in a part of the pixel. On top of this, a polysilicon film is formed in an island shape so as to pass over the gate electrode 51a and doped with impurities to form a thin film transistor (TFT) 54 together with the gate electrode 51a. Yes. An interlayer insulating film 55 is formed so as to cover these, and a data line 56 is formed on the interlayer insulating film 55. A pixel electrode 58 made of ITO (indium tin oxide) is formed thereon via a planarizing film 57 and connected to the TFT 54 via a contact hole opened in the interlayer insulating film 55 and the planarizing film 57. . The data line 56 is formed so as to overlap below the pixel electrode 58. The data line 56 is connected to the source region of the TFT 54 and supplies charges to the pixel electrode 58 when the gate electrode 51a is turned on. A vertical alignment film 59 made of an organic material such as polyimide or an inorganic material such as cyan is formed on the pixel electrode 58. The vertical alignment film 59 is not rubbed.

  The second substrate 60 disposed to face the first substrate 50 has a color colored either red (R), green (G), blue (B), or cyan, magenta, or yellow. A filter 66 is formed at a position facing the pixel electrode 58. A common electrode 61 made of ITO or the like is formed thereon so as to cover the plurality of pixel electrodes 58. On the common electrode 61, the same vertical alignment film 62 as that on the first substrate 50 side is provided. In the common electrode 61, for example, an orientation control window 63, which is a region where no electrode is present, has a shape in which letters “Y” are connected upside down as illustrated.

  A liquid crystal 70 is sealed between the first substrate 50 and the second substrate 60, and the orientation of the liquid crystal molecules depends on the electric field strength formed by the voltage applied between the pixel electrode 58 and the common electrode 61. That is, the orientation is controlled. On the outside of the first substrate 50 and the second substrate 60, a polarizing plate (not shown) is disposed with the polarization axes orthogonal to each other. The linearly polarized light passing between these polarizing plates is modulated when passing through the liquid crystal 70 controlled to have a different orientation for each display pixel, and is controlled to a desired transmittance.

  The liquid crystal 70 has a negative dielectric anisotropy, that is, has a property of being oriented so as to tilt with respect to the electric field direction. The vertical alignment films 59 and 62 control the initial alignment of the liquid crystal 70 in the vertical direction. In this case, when no voltage is applied, the liquid crystal molecules are perpendicular to the vertical alignment films 59 and 62, and the linearly polarized light passing through one polarizing plate passes through the liquid crystal layer 70 and is blocked by the other polarizing plate. The display is recognized as black.

In this configuration, when a voltage is applied between the pixel electrode 58 and the common electrode 61, electric fields 64 and 65 are formed, and the liquid crystal molecules are inclined. At the end of the pixel electrode 58, the electric field 64 is inclined obliquely from the pixel electrode 58 toward the common electrode 61 side. Similarly, since no electrode is present at the end of the orientation control window 63, the electric field 65 is inclined toward the pixel electrode 58. The tilted electric field controls the alignment direction of the liquid crystal and tilts toward the inner side of the pixel electrode 58 and the alignment control window 63.

  Further, immediately below the alignment control window 63, the common electrode 61 is absent, so that no electric field is formed even when a voltage is applied, and the liquid crystal molecules are fixed in the initial alignment state, that is, in the vertical direction. As a result, the alignment direction of the liquid crystal faces each other across the alignment control window 63 by the continuity of the liquid crystal, and a wide viewing angle is obtained.

  The data line 56 is formed so as to overlap the orientation control window 63. The light transmitted through the data line 56 is attenuated at a constant rate, and the liquid crystal under the alignment control window 63 maintains the initial alignment, and therefore does not transmit light even when a voltage is applied. For this reason, the transmittance of light decreases in each region, and the transmittance of the entire pixel greatly decreases. In view of this, the transmittance is prevented from being lowered by superimposing them. More details are described in Japanese Patent Application No. 10-337840.

  The means for controlling the alignment direction of the liquid crystal is not limited to the alignment control window 63, and an inclined portion may be provided on the vertical alignment films 59 and 62 facing the liquid crystal 70. This is described in Japanese Patent Application No. 6-104044.

Next, the voltage application method of the LCD will be described. FIG. 7 is a timing chart showing the voltages applied to the gate lines 51 and the data lines 56 and the voltages of the pixel electrodes driven thereby. 5A shows the voltage applied to the first gate line 51, FIG. 5B shows the voltage applied to the second gate line 51 adjacent to the first gate line, and FIG. 5C shows the voltage applied to the data line 56, respectively. (D) shows the voltage of the pixel electrode 58 controlled by the first gate line 51 and the data line 56, and (e) shows the voltage of the pixel electrode 58 controlled by the second gate line 51 and the data line 56. A voltage is applied to the first gate line 51 for one horizontal synchronization period (hereinafter referred to as 1H) and turned on. When the first gate line 51 is turned on, the TFTs of the pixel electrodes 58 in the corresponding column are turned on. A voltage corresponding to the image to be displayed is applied to each data line 56 for 1 H, and the pixel electrode 58 in this column holds the voltage. At the next 1H, the first gate electrode 51 is turned off and the second gate electrode 51 is turned on. As a result, the TFT of the pixel electrode 58 corresponding to the second gate line 51 is turned on, and similarly, the voltage of the data line 56 is held by the pixel electrode 58 of this column. Similarly, a voltage is applied to the pixel electrodes 58 in each row every 1H, and the corresponding liquid crystal is driven to display an image. Here, in order to prevent deterioration of the liquid crystal, the direction of the electric field is reversed for each adjacent row. That is, the pixel electrode 58 in the row controlled by the first gate line 51 applies a voltage V _high (10V) that is higher than the potential Vc (eg, 6V) of the common electrode 63 by a predetermined potential (eg, 4V). An inverted voltage, that is, a voltage V _low (2 V) lower than the potential Vc of the common electrode 63 is applied to the pixel electrode 58. When a voltage is applied again to the pixel electrode 58 in the row of the first gate line 51, V _low inverted from the previous time is applied. Such a voltage application method is called a line inversion method. According to the line inversion, since the applied voltage of the pixel electrode is inverted around the potential Vc of the common electrode 63, the electric field has the same shape and the direction is reversed for each row.
JP-A-6-301036 Japanese Patent Application No. 10-337840 Japanese Patent Application No. 6-104044

As described above, in the vertical alignment type LCD, since the data line 56 overlaps the pixel electrode 58, a parasitic capacitance _CSD is generated between the data line 56 and the pixel electrode 58. When line inversion is performed, a voltage such as an alternating current is applied to the data line 56 as shown in FIG. Then, due to the parasitic capacitance, the voltage of the data line 56 rides on the pixel electrode 58 as noise, and the voltage held by the pixel electrode 58 cannot maintain the applied values V _high and V _low , and FIG. As shown in (g), it is affected by the voltage applied to the data line 56. As a result, the voltages held by the pixel electrodes 58 are effectively lower than V _high or higher than V _low , respectively. That is, the potential difference between the pixel electrode 58 and the common electrode 61 is effectively reduced.

  When the potential difference between the pixel electrode 58 and the common electrode 61 becomes small, it becomes impossible to apply a sufficient electric field to the liquid crystal 70, so that the liquid crystal is insufficiently driven and the contrast of the LCD is lowered.

  In particular, since the data line 56 is superimposed on the orientation control window 63, the data line 56 and the pixel are long because the wiring length of the data line 56 in the pixel is longer than when the data line 56 is formed in a straight line. The parasitic capacitance with the electrode 58 is further increased, and the reduction of the potential difference due to the above-described noise becomes more remarkable.

  In addition to the above-mentioned LCD having an alignment control window, for example, even in an LCD having an inclined portion in an alignment film in contact with the liquid crystal for controlling the alignment, the data line is superimposed on the pixel electrode. If they are formed, they occur in exactly the same way.

  Accordingly, an object of the present invention is to provide an LCD having a high contrast in an LCD in which data lines are formed so as to overlap pixel electrodes.

  The present invention has been made in order to solve the above-described problem, and includes a first pixel electrode formed with a plurality of pixel electrodes that are spaced apart from each other and a data line that applies a voltage to the pixel electrode. A substrate, a second substrate on which a common electrode facing the plurality of pixel electrodes is formed; a color filter; and a liquid crystal sealed between the first and second substrates. In the liquid crystal display device, the data line is formed so as to overlap with the pixel electrode, the color filter is formed between the data line and the pixel electrode, a thin film transistor that connects the pixel electrode and the data line, a thin film transistor, The color liquid crystal display device further includes a contact for electrically connecting the pixel electrode, and the color filter does not overlap the contact.

  Further, the liquid crystal has a negative dielectric anisotropy, having an alignment control window formed by opening a region facing the pixel electrode of the common electrode.

  In addition, the liquid crystal display device further includes a vertical alignment film that makes the initial alignment of the liquid crystal substantially vertical on the pixel electrode, and an alignment control inclined portion provided in the vertical alignment film, and the liquid crystal has negative dielectric anisotropy. Features.

  Further, a part of the end portion of the color filter is located outside the end portion of the pixel electrode by at least 1 μm.

According to the present invention, since the color filter is formed between the data line and the pixel electrode in the LCD in which the data line is formed so as to overlap the pixel electrode, the interval between the data line and the pixel electrode is secured, The capacity can be reduced.
Therefore, a sufficient voltage can be applied to the pixel electrode, and an LCD with high contrast can be obtained.

  In particular, according to the invention described in claim 4, since the color filter does not overlap the contact, the connection between the pixel electrode and the data line is reliable.

Particularly, according to the fifth aspect of the present invention, a part of the end portion of the color filter is located at least 1 μm outside the pixel electrode from the end portion of the pixel electrode. The light transmitted by the liquid crystal can also be colored.

  FIG. 1A is a plan view of a first embodiment of the present invention, and FIG. 1B is a sectional view thereof. A gate line 51 having a gate electrode 51a is formed on the first substrate 50, and a gate insulating film 52 is formed to cover the gate line 51. On top of this, a polysilicon film is formed in an island shape so as to pass over the gate electrode 51a, and doped with impurities to form the TFT 54 together with the gate electrode 51a. An interlayer insulating film 55 is formed so as to cover these, and a data line 56 is formed on the interlayer insulating film 55. A color filter 1 is formed so as to cover the data line 56 and colored in either red (R), green (G), blue (B), or cyan, magenta, or yellow. A pixel electrode 58 made of ITO is formed through and is connected to the TFT 54 through a contact hole opened in the interlayer insulating film 55 and the planarizing film 2. The data line 56 is formed so as to overlap below the pixel electrode 58. The data line 56 is connected to the source region of the TFT 54 and supplies charges to the pixel electrode 58 when the gate electrode 51a is turned on. A vertical alignment film 59 made of an organic material such as polyimide or an inorganic material such as cyan is formed on the pixel electrode 58. The vertical alignment film 59 is not rubbed.

  A common electrode 61 made of ITO or the like is formed on the second substrate 60 disposed so as to face the first substrate 50 so as to cover the plurality of pixel electrodes 58. On the common electrode 61, the same vertical alignment film 62 as that on the first substrate 50 side is provided.

  A liquid crystal 70 having negative dielectric anisotropy is sealed between the first substrate 50 and the second substrate 60, and an electric field formed by a voltage applied between the pixel electrode 58 and the common electrode 61. The orientation is controlled according to the strength. On the outside of the first substrate 50 and the second substrate 60, a polarizing plate (not shown) is disposed with the polarization axes orthogonal to each other. The linearly polarized light passing between these polarizing plates is modulated when passing through the liquid crystal 70 controlled to have a different orientation for each display pixel, and is controlled to a desired transmittance.

  The orientation control window 63 has, for example, a shape in which the letters “Y” are connected upside down as shown in the figure, and the data line 56 is formed so as to overlap the orientation control window 63.

  The major difference between the present embodiment and the prior art is that the color filter 1 is formed between the pixel electrode 58 of the first substrate 50 and the data line 56. The conventional planarization film has a thickness of about 1 μm, and the distance between the conventional pixel electrode 58 and the data line 56 is 1 μm. The color filter has a thickness of about 1.7 μm. On the other hand, the distance between the pixel electrode 58 and the data line 56 of the present embodiment is the total thickness of these two films by forming the color filter 1 between the pixel electrode 58 and the data line 56. It becomes about 2.7 μm. Further, since the color filter is made of an acrylic resin containing a pigment, the dielectric constant ε is almost equal to the dielectric constant ε of the planarizing film, and the capacitance is inversely proportional to the distance between the electrodes. Therefore, since the distance between the pixel electrode 58 and the data line 56 is increased by the thickness of the color filter 1, this parasitic capacitance can be reduced.

The parasitic capacitance between the data line and the pixel electrode is proportional to S · ε / d, where S is the area where the pixel electrode and the data line overlap, d is the distance, and ε is the dielectric constant between them. Decreasing the overlapping area S means reducing the line width of the data line. However, if the line width is reduced, there is a problem that the electrical resistance of the data line increases and the voltage responsiveness of the data line decreases. Arise. Therefore, in order to reduce the parasitic capacitance, it is only necessary to increase the distance between the data line and the pixel electrode.

  However, when the thickness of the planarization film separating the data line and the pixel electrode is increased, the planarization film itself has a certain transmittance, so that the light transmittance of the screen is lowered. Further, the planarizing film made of acrylic resin is slightly yellowish, and if the thickness of the planarizing film is increased, the entire screen is yellowed.

  On the other hand, since the thickness of the color filter 1 is indispensable in order to surely color transmitted light, it is necessary to ensure the distance between the pixel electrode 58 and the data line 56 by the color filter 1. This is convenient because it does not cause a decrease in transmittance.

  In addition, when the color filter 1 is formed on the first substrate 50 on which the pixel electrode 58 is formed, the pixel electrode 58 and the color are caused by an alignment error in bonding the first substrate 50 and the second substrate 60. No positional deviation from the filter 1 occurs, which is convenient for downsizing and high definition of the LCD.

  By the way, it is desirable that the color filter 1 be formed so as not to overlap the contact connecting the TFT 54 and the pixel electrode 58. The reason is described below. In manufacturing the configuration of the present embodiment, the TFT 54 formation, the interlayer insulating film 55 formation, the contact hole formation for connecting the TFT 54 and the pixel electrode 58 to the interlayer insulating film 55, the color filter formation, and the inside of the contact hole are included. Although a process of forming ITO and forming a pixel electrode is performed, if a color filter is formed on a contact hole, the color filter material enters the contact hole. The color filter material is removed by immersing it in an organic alkaline solution. However, it is difficult to completely remove the color filter material in the contact hole because the chemical solution does not easily enter the contact hole. If the color filter material remains in the contact hole, the contact between the pixel electrode 58 and the TFT 54 becomes poor.

  Note that the color filter in the region above the data line 56 is thinner than the other region by the thickness of the data line 56. In general, it is not desirable that the thickness of the color filter is not uniform. However, since the data line is made of metal, this region becomes a light-shielding region, so that there is no problem.

  In the LCD of this embodiment, the orientation of the liquid crystal is controlled by the inclination of the electric field 64 at the pixel electrode end 58, and the electric field 64 by the pixel electrode 58 is formed to bulge outward from the pixel electrode 58. Accordingly, the liquid crystal molecules aligned by the voltage applied to the pixel electrode 58 are not only those positioned immediately above the pixel electrode 58 but also the liquid crystal on the outer side of about 1 μm. Therefore, the formation region of the color filter 1 is formed to be 1 μm or more wider than the formation region of the pixel electrode 58. Of course, the color filter 1 may be formed without providing a gap in the row direction as shown in FIG.

FIG. 3A is a plan view of the second embodiment of the present invention, and FIG. 3B is a sectional view thereof. In the present embodiment, the alignment control means for controlling the alignment direction of the liquid crystal is not the alignment control window, but the alignment control inclined portion 10 is provided in the vertical alignment film, and other configurations are the same as those in the first embodiment. It is almost the same. A gate line 51 having a gate electrode 51 a is formed on the first substrate 50, a TFT 54 is formed through a gate insulating film 52, and a data line 56 is formed through an interlayer insulating film 55. The color filter 1 is formed so as to cover the data line 56, the pixel electrode 58 is formed thereon via the planarizing film 2, and the TFT 54 is connected via the interlayer insulating film 55 and the contact hole opened in the planarizing film 2. It is connected to the. The data line 56 is formed to overlap with the pixel electrode 58, is connected to the source region of the TFT 54, and supplies charges to the pixel electrode 58 when the gate electrode 51a is turned on. A vertical alignment film 59 is formed on the pixel electrode 58.

  A common electrode 61 made of ITO or the like is formed on the second substrate 60 disposed so as to face the first substrate 50 so as to cover the plurality of pixel electrodes 58. On the common electrode 61, the same vertical alignment film 62 as that on the first substrate 50 side is provided.

  A liquid crystal 70 having negative dielectric anisotropy is sealed between the first substrate 50 and the second substrate 60, and an electric field formed by a voltage applied between the pixel electrode 58 and the common electrode 61. Depending on the strength, the orientation of the liquid crystal molecules, ie the orientation, is controlled. On the outside of the first substrate 50 and the second substrate 60, a polarizing plate (not shown) is disposed with the polarization axes orthogonal to each other. The linearly polarized light passing between these polarizing plates is modulated when passing through the liquid crystal 70 controlled to have a different orientation for each display pixel, and is controlled to a desired transmittance.

  The difference of this embodiment from the above embodiment is that the end portion of the pixel electrode 58 is raised, and the alignment control inclined portions 10a and 10b are formed on the vertical alignment film 59 covering the end portion. The initial alignment of the liquid crystal molecules is tilted to the right in the drawing by the alignment control tilt portion 10a, and is tilted to the left in the drawing by the alignment control tilt portion 10b. The alignment direction of the liquid crystal molecules in the center of the pixel is controlled even when a voltage is applied due to the continuum effect from the liquid crystal molecules around the inclined portion.

  Also in this embodiment, since the color filter 1 is formed between the pixel electrode 58 and the data line 56, the parasitic capacitance between them can be reduced, and the same effects as in the first embodiment can be obtained. can get.

  As described above, in the LCD formed by overlapping the pixel electrode and the data line, since the color filter is formed between the pixel electrode and the data line, the interval between the pixel electrode and the data line can be secured, The parasitic capacitance during this period can be reduced. In the above embodiment, as an example of the alignment control means, the LCD having the method having the alignment control window 63 and the LCD having the alignment control inclined portion 10 are described as examples. However, the present invention is not limited to this. In addition, any LCD can be used as long as it is an LCD in which pixel electrodes and data lines are overlapped.

1A is a plan view of a liquid crystal display device according to a first embodiment of the present invention, and FIG. It is the top view of other embodiment of this invention, and its sectional drawing. It is the top view of other embodiment of this invention, and its sectional drawing. It is the top view of the conventional liquid crystal display device, and its sectional drawing. It is a timing chart of the voltage application by a line inversion system.

Explanation of symbols

1 Color Filter 2 Planarization Film 51 Gate Line 56 Data Line 58 Pixel Electrode 61 Common Electrode 63 Orientation Control Window

Claims (4)

A first substrate on which a plurality of pixel electrodes formed to be spaced apart from each other and driving a liquid crystal and a data line for applying a voltage to the pixel electrodes are formed;
A second substrate on which a common electrode facing the first substrate and facing the plurality of pixel electrodes is formed;
A color filter,
In a liquid crystal display device comprising a liquid crystal sealed between the first and second substrates,
The data line is formed to overlap the pixel electrode,
The color filter is formed between the data line and the pixel electrode,
A thin film transistor connecting the pixel electrode and the data line;
A contact for electrically connecting the thin film transistor and the pixel electrode;
The color liquid crystal display device, wherein the color filter does not overlap the contact. An alignment control window formed by opening a region facing the pixel electrode of the common electrode;
The color liquid crystal display device according to claim 1, wherein the liquid crystal has negative dielectric anisotropy. A vertical alignment film that makes the initial alignment of the liquid crystal substantially vertical on the pixel electrode;
An alignment control inclined portion provided on the vertical alignment film;
The color liquid crystal display device according to claim 1, wherein the liquid crystal has a negative dielectric anisotropy. 5. The color liquid crystal display device according to claim 1, wherein a part of the end portion of the color filter is located at least 1 μm outside the pixel electrode from the end portion of the pixel electrode.

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