JP2010156805A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element improved in numerical aperture and excelling in display quality. <P>SOLUTION: The liquid crystal element includes a plurality of thin-film transistors 13 provided in matrix shape; a plurality of connecting electrodes 17 connected to the corresponding thin-film transistors respectively; insulating layers 20, 21 provided on the plurality of thin-film transistors 13 and the plurality of the connecting electrodes 17 and having contact holes 22 at the center of every pixel; a plurality of pixel electrodes 12 provided on the insulating layer 21 and connected to the corresponding connecting electrodes 17 respectively through the contact holes 22; and a common electrode 33 disposed facing the insulating layer 21 and the plurality of pixel electrodes 12 with liquid crystal 41 held in between and having apertures 33a in conformity with the positions of the contact holes 22 for every pixel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element having an improved aperture ratio.

  The liquid crystal display element is connected to one of a pair of substrates facing each other with a plurality of pixel electrodes provided in a matrix and corresponding to the plurality of pixel electrodes. A plurality of thin film transistors and a plurality of scanning lines and a plurality of signal lines for supplying a gate signal and a data signal to each thin film transistor are provided, and a common common electrode (facing opposite to the plurality of pixel electrodes is provided on the other substrate) Electrode), an alignment film is provided on each of the opposing surfaces of the pair of substrates, and liquid crystal is sealed. The liquid crystal display element controls the orientation of the liquid crystal by applying a voltage to the pixel electrode for each pixel.

  Among them, there is a vertical alignment type liquid crystal display element using a liquid crystal having negative dielectric anisotropy with an alignment film as a vertical alignment film. When an electric field is not generated between the pixel electrode and the common electrode, the liquid crystal molecules are perpendicular to the alignment film, but when an electric field is applied between them, the major axis of the liquid crystal molecules is perpendicular to the electric field. Tilt to do. Therefore, a protrusion is provided on the common electrode side, and a vertical alignment film is also formed on the protrusion. Even when no voltage is applied between the pixel electrode and the common electrode, the liquid crystal molecules in the region of the protrusion are slightly inclined with respect to the common substrate. When a voltage is applied between the pixel electrode and the common electrode in this state, the liquid crystal molecules are tilted toward the protrusion, that is, the liquid crystal molecules are tilted in the opposite direction with respect to the apex of the protrusion, thereby obtaining a wide viewing angle. (See Patent Document 1).

Japanese Patent Laid-Open No. 11-352489

  However, even in the state where no electric field is generated between the pixel electrode and the common electrode, the liquid crystal molecules are not vertically aligned with respect to the substrate around the protrusions and are arranged with a certain inclination. Therefore, since the liquid crystal molecules around the protrusions are not vertically aligned, the backlight is transmitted. Therefore, it is necessary to provide a light shielding metal in the region of the protrusion on the TFT substrate, that is, the substrate side on which the thin film transistor is constructed, in order to prevent light leakage. When the light shielding metal is provided, the ratio of the region contributing to display is reduced with respect to the area of one pixel, and the aperture ratio is reduced.

  Since the protrusion is provided on the common substrate (counter substrate) side and the light shielding metal is provided on the TFT substrate side, when the counter substrate and the TFT substrate are bonded to each other with a gap therebetween, the protrusion and the light shielding metal may be aligned. The area of the light shielding metal needs to be increased by the amount of deviation, and the aperture ratio further decreases. In particular, in a high-definition liquid crystal display element, the aperture ratio is significantly reduced.

  An object of the present invention is to provide a liquid crystal display element having an improved aperture ratio.

  One aspect of the present invention is that a plurality of thin film transistors provided in a matrix, a plurality of connection electrodes each connected to a corresponding thin film transistor, a plurality of thin film transistors and a plurality of connection electrodes are provided on the center of each pixel An insulating layer having a contact hole, a plurality of pixel electrodes provided on the insulating layer, each connected to a corresponding connection electrode via the contact hole, and a liquid crystal facing the insulating layer and the plurality of pixel electrodes. And a common electrode having an opening corresponding to the position of the contact hole for each pixel.

  In particular, the contact hole formed for each pixel in the insulating layer and the opening formed in the common electrode are preferably arranged coaxially. The common electrode preferably has an opening having a diameter larger than that of a contact hole formed for each pixel in the insulating layer. A first vertical alignment film formed over the pixel electrode, a second vertical alignment film formed over the common electrode, and a negative dielectric anisotropy interposed between the first and second vertical alignment films And a liquid crystal having properties. The connection electrode may be formed of a transparent conductive material.

  According to the present invention, since the contact hole that contacts the pixel electrode and the connection electrode and the opening of the common electrode are aligned, when no electric field is generated between the pixel electrode and the common electrode, the vicinity of the contact hole Light leakage due to the inclination of the liquid crystal molecules is suppressed by the liquid crystal molecules due to the opening of the common electrode. Therefore, a liquid crystal display element with improved contact ratio and excellent display quality can be obtained.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.
1 is a plan view of a TFT substrate 10 of the liquid crystal display element 1 according to the embodiment of the present invention, FIG. 2 is a plan view of a common substrate 30 of the liquid crystal display element 1, and FIG. 3 is a line III-III in FIG. 4 is a sectional view taken along line IV-IV shown in FIG. 1, and FIG. 5 is a sectional view taken along line VV shown in FIG.

  The liquid crystal display element 1 according to the embodiment of the present invention is an active matrix liquid crystal display element, in which a TFT substrate 10 and a counter substrate (also referred to as “common substrate”) 30 are provided in front of each other with a predetermined interval therebetween, Liquid crystal is sealed between the TFT substrate 10 and the counter substrate 30 to form a liquid crystal layer 40.

  The TFT substrate 10 includes a transparent substrate 11, a plurality of pixel electrodes 12 provided so as to be arranged in a matrix on the transparent substrate surface, and a plurality of thin film transistors (TFTs) provided so as to correspond to the plurality of pixel electrodes 12, respectively. Thin Film Transistor) 13, a plurality of gate lines 14 and a plurality of signal lines 15 respectively provided in the row direction and the column direction so as to supply a gate signal and a data signal to each of the plurality of thin film transistors 13, and a plurality of pixel electrodes A plurality of auxiliary capacitance electrodes 16 provided for each of 12, a connection electrode 17 for connecting the pixel electrode 12 and the thin film transistor 13, and an alignment film 18 provided on the surface of the TFT substrate including the pixel electrode 12. Yes.

  On the other hand, the counter substrate 30 is opposed to a transparent substrate 31, a color filter 32 provided on the surface of the transparent substrate 31, and a common electrode (counter electrode) 33 provided on the color filter 32 and having an opening 33a for each pixel. An alignment film 34 provided on the surface of the substrate 30, that is, on the surface of the common electrode 33 and the color filter 32 is included. As shown in FIG. 2, R, G, and B color filters are provided in order.

The configuration of the TFT substrate 10 will be described in detail.
A plurality of gate lines 14 are arranged side by side in the column direction on a transparent substrate 11 such as a glass substrate, and each gate line 14 is arranged in the row direction. Each gate line 14 has a gate electrode 13a for each pixel region. The gate line 14 is formed of a metal such as Cr, for example.

A first insulating layer 19 is formed so as to cover the transparent substrate 11 and the gate line 14.
On the first insulating layer 19, a plurality of signal lines 15 are provided side by side in the row direction, and each signal line 15 is arranged in the column direction. As shown in FIG. 5, the signal line 15 is composed of a stacked layer of a semiconductor layer 15a, an ohmic contact layer 15b, and a metal layer 15c, and is formed by the same process as a partially stacked layer of a thin film transistor 13 described later.

  Each region surrounded by adjacent gate lines 14 and 14 and signal lines 15 and 15 constitutes one pixel region, and a thin film transistor 13 is provided for each pixel region. In the thin film transistor 13, a predetermined position in each pixel region, in the example shown in FIG. 1, a part of the lower gate line 14 becomes a gate electrode 13a, and a portion of the first insulating layer 19 covering the gate electrode 13a is a gate. A semiconductor layer 13c is provided so as to cover the gate insulating film 13b, and an etching stopper layer 13d is provided on the surface of the semiconductor layer 13c in the region of the gate electrode 13a, and a part of the surface of the etching stopper layer 13d is covered. A pair of ohmic contact layers 13e and 13f extending opposite to each other in the column direction, and a drain electrode 13g and a source electrode 13h are provided so as to cover the pair of ohmic contact layers 13e and 13f, respectively.

A connection electrode 17 is provided on the source electrode 13 h and the first insulating layer 19.
The connection electrode 17 includes a rectangular central portion 17a disposed in a substantially intermediate region between the adjacent gate lines 14 and 14 and the adjacent signal lines 15 and 15, and a source electrode extending thinly from the central portion 17a in the column direction. And an elongated portion 17b that partially overlaps 13h. The row width of the elongated portion 17b is shorter than the row width of the source electrode 13h.

  The laminated structure of the semiconductor layer 13c, the etching stopper layer 13d, the pair of ohmic contact layers 13e and 13f, the drain electrode 13g and the source electrode 13h of the thin film transistor 13 is formed on the surface of the first insulating layer 19, and the signal line 15 described above is also formed. Since it is formed on the surface of the first insulating layer 19, the signal line 15 also has a stacked structure of the semiconductor layer 15a, the ohmic contact layer 15b, and the metal layer 15c, and is formed simultaneously with the process of the thin film transistor 13.

A second insulating layer 20 is formed on the signal line 15, the first insulating layer 19, and the thin film transistor 13 in each pixel region.
On the second insulating layer 20, the auxiliary capacitance electrodes 16 are provided in the regions of the gate lines 14 and the signal lines 15, respectively. The auxiliary capacitance electrodes 16 adjacent in the row direction and the column direction form a frame shape. Yes.
A third insulating layer 21 is provided on the auxiliary capacitance electrode 16 and the second insulating layer 20. In the second insulating layer 20 and the third insulating layer 21, a contact hole 22 is formed so as to penetrate almost the center of each pixel region, and a part of the central portion 17 a of the connection electrode 17 is exposed. The center of the contact hole 22 is formed substantially coaxially with the center of the central portion 17 a of the connection electrode 17.
On the third insulating layer 21, the pixel electrode 12 is formed over the entire pixel region and on the opening edge 22 a of the contact hole 22 and the connection electrode 17.

  In the example shown in FIGS. 4 and 5, the pixel electrode 12 has edge portions 12 a and 12 b in the column direction of the pixel electrode 12 partially overlapping with the auxiliary capacitance electrode 16 instead of partially overlapping with the signal lines 15 and 15. Edges 12 c and 12 d in the row direction of the pixel electrode 12 do not partially overlap the gate lines 14 and 14 but partially overlap the auxiliary capacitance electrode 16. Note that the column-direction edges 12a and 12b of the pixel electrode 12 partially overlap the signal lines 15 and 15, and one or both of the row-direction edges 12c and 12d of the pixel electrode 12 are partially connected to the gate line 14. It may be formed so as to overlap. The pixel electrode 12 and the connection electrode 17 are formed of a transparent conductive material such as ITO.

  A vertical alignment film 18 as a first alignment film is provided on the plurality of pixel electrodes 12 and the third insulating layer 21. The vertical alignment film 18 may or may not be rubbed.

The structure of the counter substrate 30, particularly the CF substrate will be described.
RGB color filters 32 are provided on the surface of the transparent substrate 31, and a common electrode 33 is formed on the color filter 32. The common electrode 33 has an opening 33a on the central axis of the bottom 22b connected to the connection electrode 17 via the contact hole 22 at the center of the pixel electrode 12 for each pixel region. As shown in FIG. 2, the opening 33a is circular, for example. The center of the bottom 22b of the contact hole 22 and the center of the opening 33a are substantially coaxial. Here, the diameter of the opening 33 a is larger than the dimension of the contact hole 22. The reason for this will be described later.

  A vertical alignment film 34 as a second alignment film is formed on the common electrode 33 and the color filter 32. The vertical alignment film 34 may or may not be rubbed.

  As described above, the TFT substrate 10 and the counter substrate 30 are arranged at a predetermined interval so that the central axis of the contact hole 22 and the central axis of the opening 33a are substantially coaxial in each pixel region. Liquid crystal molecules having negative dielectric anisotropy are filled between the alignment films 18 and 34 to form the liquid crystal layer 40.

  In the liquid crystal display element 1, although not shown, a polarizing plate is provided on the lower side of the TFT substrate 10, a polarizing plate is provided on the upper side of the common substrate 31, and the two polarizing plates are orthogonal to each other.

6 schematically shows the state of the liquid crystal molecules 41 between the pixel electrode 12 and the common electrode 33, where (A) shows a case where no electric field is generated, and (B) shows a case where an electric field is generated. FIG.
When no potential difference is generated between the pixel electrode 12 and the common electrode 33, that is, when an electric field is not generated, the pixel electrode 12 side and the common electrode 33 side also have liquid crystal molecules as shown in FIG. The long axis 41 is aligned so as to be perpendicular to the alignment films 18 and 34. In particular, the liquid crystal molecules 41 are inclined toward the central axis of the contact hole 22 at the edge on the contact hole 22 side. As a result, the backlight from the back side of the TFT substrate 10 may slightly leak. However, since the liquid crystal molecules 41 on the common substrate 30 side are vertically aligned in the opening 33a of the common substrate 30, and the diameter of the opening 33a is larger than the dimensions (width and length) of the contact hole 22, the leakage is small. .
In this state, when a potential difference is generated between the pixel electrode 12 and the common electrode 33, the common electrode 33 and the pixel electrode are shown on the surface of the common electrode 33 and the pixel electrode 12 as indicated by a dotted line in FIG. While an electric field is generated so as to be orthogonal to any of 12, an electric field curved toward the pixel electrode 12 is generated at the end of the opening 33 a of the common electrode 33. Since the liquid crystal molecules 41 have negative dielectric anisotropy, the liquid crystal molecules 41 are aligned so that their long axes are orthogonal to the electric field. Accordingly, the liquid crystal molecules 41 are inclined around the central axis of the opening 33a around the opening 33a of the common electrode 33, and the liquid crystal molecules 41 in one pixel region are symmetric with respect to the central axis of the opening 33a. A corner is obtained.

  In the embodiment of the present invention, one pixel region is defined by the gate lines 14 and 14 adjacent in the column direction and the signal lines 15 and 15 adjacent in the row direction, and the pixel electrode 12 extends over the entire pixel region. The contact hole 22 is formed at the approximate center of the diagonal line of each pixel region, and the central portion 17a of the connection electrode 17 is formed under the contact hole. On the other hand, the center of the opening 33 a of the common electrode 33 is arranged substantially coaxially with the center of the contact hole 22. Therefore, black is displayed when no electric field is generated between the pixel electrode 12 and the common electrode 33, but the backlight leaks light even when the liquid crystal molecules 41 are inclined at the opening edge 22a of the contact hole 22. hard. When an electric field is generated from this state, the liquid crystal molecules 41 are tilted around the opening 33a and white display is performed. At that time, the liquid crystal molecules 41 can be tilted so as to surround the opening 33a and the alignment can be controlled. In the present embodiment, each connection electrode 17 is formed of a transparent conductive material such as ITO and extends to the center region of each pixel region. Therefore, the contrast ratio is not lowered by the connection electrode 17. Therefore, a decrease in aperture ratio can be prevented, and a high-definition liquid crystal display element can be provided.

  Embodiments of the present invention are not limited to those described above, and various modifications can be applied within the scope of the gist of the present invention.

  For example, in the above-described example, the auxiliary capacitance electrode 16 is made of a metal in a frame shape for each pixel region. However, if only the inner part is made of a transparent electrode material such as ITO, it is possible to avoid a decrease in the aperture ratio. it can.

  FIG. 7 is a plan view showing the positional relationship between the connection electrode 17, the pixel electrode 52, and the common electrode in one region surrounded by adjacent gate lines and adjacent signal lines, according to another embodiment of the present invention. When one pixel electrode 52 is long in the column direction as shown in FIG. 1, as shown in FIG. 7, slits 52a are provided in the row direction so as to divide the pixel electrode 52 into, for example, three regions. The pixel electrode 52 is divided into three regions, a common electrode opening 63 is provided at the center of each of the subdivided regions, contact holes are provided so as to face the openings 63, and the pixel electrode 52 is connected to the connection electrode 17. Good.

  Further, the drain electrode 13g and the source electrode 13h of the thin film transistor 13 may be formed of a transparent conductive material such as ITO. In this case, the connection electrode 17 is integrated with the drain electrode 13g and the source electrode 13h in the same process. It may be formed.

  In the illustrated example, since the light shielding metal is not disposed below the contact hole 22 in the TFT substrate 10, the aperture ratio is further improved. However, when there is no size limitation, the light shielding metal is disposed. It doesn't matter. Further, the opening 33a of the common electrode 33 may be a polygonal shape instead of a circle in a plan view, and the contact hole 22 may be a circle or a polygonal shape in a plan view. In addition, the contact hole 22 has been described in the case where it is formed at substantially the center of the diagonal line of each pixel region. However, the contact hole 22 may be formed at any position in each pixel region as long as the liquid crystal orientation can be controlled, such as widening the viewing angle. In this case, the pixel regions may be arranged at different positions. Further, in the present embodiment, the vertical alignment type liquid crystal display element having negative dielectric anisotropy has been described. However, the vertical alignment type liquid crystal display element having positive dielectric anisotropy or the vertical alignment type liquid crystal display element Can be applied to different liquid crystal display elements.

It is a top view of a TFT substrate among liquid crystal display elements concerning an embodiment of the present invention. It is a top view of a common board | substrate among the liquid crystal display elements which concern on embodiment of this invention. It is sectional drawing which follows the III-III line | wire of FIG. 2 regarding the liquid crystal display element which concerns on embodiment of this invention. It is sectional drawing which follows the IV-IV line | wire of FIG. 1 regarding the liquid crystal display element which concerns on embodiment of this invention. It is sectional drawing which follows the VV line | wire shown in FIG. 1 regarding the liquid crystal display element which concerns on embodiment of this invention. The state of the liquid crystal molecules between the pixel electrode and the common electrode is schematically shown. (A) shows a case where no electric field is generated, and (B) shows a case where an electric field is generated. It is a top view which shows the positional relationship of a connection electrode, a pixel electrode, and a common electrode about one area | region enclosed by the adjacent gate line and the adjacent signal line about another embodiment of this invention.

Explanation of symbols

1: liquid crystal display element 10: TFT substrate 11: transparent substrate 12, 52: pixel electrode 12c, 12d: edge of pixel electrode 13: thin film transistor 13a: gate electrode 13b: gate insulating film 13c: semiconductor layer 13d: etching stopper layer 13e , 13f: ohmic contact layer 13g: drain electrode 13h: source electrode 14: gate line 15: signal line 15a: semiconductor layer 15b: ohmic contact layer 15c: metal layer 16: auxiliary capacitance electrode 17: connection electrode 17a: central portion 17b: The elongated portions 18 and 34: the alignment film 19: the first insulating layer 20: the second insulating layer 21: the third insulating layer 22: the contact hole 22a: the opening edge 22b: the bottom 30: a common substrate (counter substrate)
31: Transparent substrate 32: Color filter 33: Common electrode 33a, 63a: Opening of common electrode 34: Alignment film 40: Liquid crystal layer 41: Liquid crystal molecule 52a: Slit

Claims (5)

A plurality of thin film transistors provided in a matrix;
A plurality of connection electrodes each connected to the corresponding thin film transistor;
An insulating layer provided on the plurality of thin film transistors and the plurality of connection electrodes and having a contact hole in the center of each pixel;
A plurality of pixel electrodes provided on the insulating layer, each connected to the corresponding connection electrode via the contact hole;
A common electrode disposed opposite to the insulating layer and the plurality of pixel electrodes with a liquid crystal in between, and having an opening corresponding to the position of the contact hole for each pixel;
A liquid crystal display element comprising:   The liquid crystal display element according to claim 1, wherein a contact hole formed in the insulating layer for each pixel and an opening formed in the common electrode are arranged coaxially.   The liquid crystal display element according to claim 1, wherein the common electrode has the opening having a diameter larger than a contact hole formed in the insulating layer for each pixel.   A first vertical alignment film formed over the pixel electrode; a second vertical alignment film formed over the common electrode; and a negative intervening between the first and second vertical alignment films. The liquid crystal display element according to claim 1, comprising the liquid crystal having dielectric anisotropy.   The liquid crystal display element according to claim 1, wherein the connection electrode is formed of a transparent conductive material.

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