The present invention relates to liquid crystal display devices.
Liquid crystal display devices are display devices utilizing a liquid crystal composition to display images. In a typical display mode thereof, a liquid crystal panel containing a liquid crystal composition between a pair of substrates is irradiated with light from a backlight and voltage is applied between pixel electrodes and a counter electrode (common electrode) arranged on the substrate(s) to change the alignment of liquid crystal molecules, whereby the amount of light passing through the liquid crystal panel is controlled. Such liquid crystal display devices have advantageous features such as thin profile, light weight, and low power consumption, and are therefore used in electronic devices such as televisions, smartphones, tablet PCs, and automotive navigation systems.
Techniques of controlling the alignment of liquid crystal molecules to improve the viewing angle characteristics of a liquid crystal panel have been considered. One of the techniques is to use comb electrodes, which are provided with openings (slits) formed between linear electrodes, as pixel electrodes. For example, a method of producing a liquid crystal display device disclosed in WO 2010/131495 enables production of a liquid crystal display device having excellent display properties owing to reduction in alignment defects of liquid crystal molecules which may occur around the tips of an electrode is a vertical alignment liquid crystal display device using a comb electrode for voltage application to liquid crystal molecules (WO 2010/131495, FIG. 1). JP 2010-117737 A discloses a technique of forming slits in a pixel electrode and forming, at the slit side ends of the pixel electrode, quadrangular projections that project from the pixel electrode in a substrate plane, thereby controlling the positions of nodes (singular points) of the liquid crystal alignment formed (JP 2010-117737 A, FIG. 2).
Comb electrodes, which are provided with openings between linear electrodes, may be a cause of low production yield because the linear electrodes have a small electrode width and thus the linear electrodes are easily disconnected during production. Here, the production yield can be increased by closing the slits such that the electrode portions at the outer edges of the closed slits conduct, electricity even when the linear electrodes are disconnected. Meanwhile, studies made by the present inventor show that the alignment of liquid crystal molecules may be instable at the ends of closed slits to generate a dark line during display of images, causing a decrease in transmittance and response speed. Also, an afterimage may be generated when a specific image is displayed.
In response to the above issues, an object of the present invention is to provide a liquid crystal display device that reduces generation of afterimages while increasing the transmittance and the response speed.
(1) One embodiment of the present invention is directed to a liquid crystal display device including: a plurality of gate bus lines arranged on a substrate; a plurality of source bus lines crossing the gate bus lines; and a pixel electrode arranged in a pixel region surrounded by the gate bus lines and the source bus lines, the pixel electrode including a linear first electrode portion arranged along the gate bus lines in a plan view and a plurality of linear second electrode portions that are electrically connected to the first electrode portion and are parallel to each other, at least one slit between the linear second electrode portions being open on a source bus line side.
(2) In an embodiment of the present invention, the liquid crystal display device includes the structure (1), and every slit is open on the source bus line side.
(3) In an embodiment of the present invention, the liquid crystal display device includes the structure (1), and a slit open on the source bus line side and a slit closed on the source bus line side are formed alternately.
(4) In an embodiment of the present invention, the liquid crystal display device includes the structure (1), (2), or (3), and further includes an auxiliary storage capacitor electrode that overlaps the pixel electrode in a plan view.
(5) In an embodiment of the present invention, the liquid crystal display device includes the structure (4), and the auxiliary storage capacitor electrode is superposed on a contact hole in a plan view and crosses, along the gate bus lines, the pixel region surrounded by the gate bus lines and the source bus lines.
(6) In an embodiment of the present invention, the liquid crystal display device includes the structure (4), and the second electrode portions each extend to a position where the second electrode portion is superposed on the auxiliary storage capacitor electrode and is not superposed on a contact hole.
(7) In an embodiment of the present invention, the liquid crystal display device includes the structure (1), (2) or (3), and further includes a planar common electrode that is arranged between the substrate and the pixel electrode and is formed from a transparent conductive material, and a metal line that is arranged in a layer different from the gate bus lines and electrically connected to the planar common electrode as being superposed on part of the planar common electrode.
The present invention can provide a liquid crystal display device that reduces generation of after images while increasing the transmittance and the response speed.
Hereinafter, a liquid crystal display device according to an embodiment of the present invention is described. The embodiment, however, is not intended to limit the scope of the present invention. The design may be modified as appropriate within the range satisfying the configuration of the present invention.
The liquid crystal display device according to the embodiment of the present invention includes: a plurality of pate bus lines arranged on a substrate; a plurality of source bus lines crossing the gate bus lines; and a pixel electrode arranged in a pixel region surrounded by the gate bus lines and the source bus lines, the pixel electrode including a linear first electrode portion arranged along the gate bus lines in plan view and a plurality of linear second electrode portions that are electrically connected to the first electrode portion and are parallel to each other, at least one slit between the linear second electrode portions being open on a source bus tine side.
Hereinafter, an exemplary structure of the liquid crystal display device according to the embodiment of the present invention is described with reference to
As shown in
As shown in
The pixel electrode 20 has a structure in which pixel electrode ends are connected along the gate bus lines 1 since the linear first electrode portions 21 are each. arranged along the gate bus lines 1. In a state where the TFTs 30, which are switching elements, are, turned OFF, large negative voltage is applied to the gate bus lines 1. Liquid crystal molecules present near the gate bus lines 1 may therefore be affected by the negative voltage. This may lead to instable alignment, causing defects such as light leakage. In contrast, the liquid crystal display device according to the embodiment of the present invention has the structure in which the pixel electrode ends are connected along the gate bus lines I. The liquid crystal display device therefore can stabilize the alignment of liquid crystal molecules present near the gate bus lines 1 and reduce defects such as light leakage.
Also, at least one slit 23 between the linear second electrode portions 22 of the pixel electrode 20 is open on the source bus line 2 side. A slit 23 is an opening between the linear second electrode portions 22 and is a portion where no electrode is arranged. The expression “open on the source bus line side” means that the ends of the linear second electrode portions 22 arranged side by side with a slit 23 in between are not connected on the source bus line 2 side. In the pixel electrode 20, the electrode may be removed at a position corresponding to a contact hole 33 and an opening 24 may be formed at the position.
In the case of a liquid crystal display device using a pixel electrode with a slit closed on the source bus line side, a dark line may be generated along the source bus line due to instable alignment of liquid crystal molecules at the end of the closed slit. This may decrease the response speed of the liquid crystal molecules. Also, parasitic capacitance is formed between a source bus line and a pixel electrode. Here, a pixel electrode with a slit closed on the source bus line side has a large area superposed on the source bus line, which changes the effective value of the voltage to be actually applied to the corresponding pixel region 10 upon polarity inversion in the next frame. As a result, when the background of the display portion of the liquid crystal display device is set to have an intermediate grayscale value and a quadrangular image having a white or another single color is displayed at the center of the display portion, an afterimage of a straight line may be observed in the display portion.
In contrast, in the liquid crystal display device according to the embodiment of the present invention, at least one slit 23 is open on the source bus line 2 side. The liquid crystal display device therefore can stabilize the alignment of liquid crystal molecules around the end of the open slit 23 and around the end on the source bus line 2 side of the linear second electrode portion. 22. Thereby, the liquid crystal display device can reduce generation of dark lines due to alignment defect of liquid crystal molecules and increase the transmittance of the pixel regions 10 and the response speed of liquid crystal molecules. Furthermore, as the slit 23 is opened, the area of the pixel electrode 20 along the source bus line 2 is reduced and parasitic capacitance formed between the source bus line 2 and the pixel electrode 20 is decreased. This structure can reduce the change in effective value of the voltage to be applied to the pixel region 10 in each frame after polarity inversion and can reduce generation of an afterimage.
Hereinafter, exemplary structures other than the pixel electrodes are described with reference to
As shown in
The substrate 3 may be any transparent substrate such as a glass substrate or a transparent resin substrate. The entire substrate, including the components such as the TFTs 31 on the substrate 3, may also be referred to as the TFT substrate 70.
The semiconductor layer 31 is not particularly limited, and can be an amorphous silicon semiconductor or an oxide semiconductor containing indium (In), gallium (Ga), and/or zinc (Zn), such as an indium gallium zinc oxide (In—Ga—Zn—O) semiconductor.
A common electrode 50 may, for example, be superposed on the pixel electrode 20 with the insulating films 40 and 41 in between. Also, an insulating film 42 may be arranged between the gate bus lines 1 and the common electrode 50. One common electrode 50 may be arranged in each pixel region 10 or may be arranged in the entire display region over a plurality of the pixel regions 10.
The common electrode 50 is preferably a transparent electrode, and can be formed using, for example, a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).
The structures such as the composition and film thickness of each of the insulating films 40, 41, and 42 are not particularly limited, and may be structures typically used in the field of liquid crystal display devices.
The counter substrate 90 may be a color filter substrate including color filters. The color filter substrate may have a structure such as one including a black matrix in a region facing the gate bus lines 1 and the source bus lines 2 and color filters in regions partitioned by the black matrix. The color filters are of colors such as red (R), green (G), and blue (B).
The liquid crystal layer 80 contains liquid crystal molecules. The liquid crystal display device according to the embodiment of the present invention displays an image by changing the alignment azimuth of liquid crystal molecules in the liquid crystal layer 80. The liquid crystal molecules are not particularly limited and may be formed from a material typically used in the field of liquid crystal display devices.
An alignment film defining the initial alignment of liquid crystal molecules may be disposed between the liquid crystal layer 80 and the TFT substrate 70 and between the liquid crystal layer 80 and the counter substrate 90. The liquid crystal display device shown in
One example of the display method in the liquid crystal display device according to the embodiment of the present invention is described. When source voltage is applied to the source bus line 2, electricity is conducted through the semiconductor layer 31 (TFT is turned ON), and then voltage is applied to the pixel electrode 20 through the drain electrode 32. In the example shown
Hereinabove, an exemplary fringe field switching (FES) mode liquid crystal display device has been described. The display mode, however, is not limited to FES. The liquid crystal display device according to the embodiment of the present invention may be is the in-plane switching (IPS) mode. Examples of the IPS mode include a mode in which pixel electrodes and a common electrode face each other in the same plane. The common electrode also preferably includes a linear electrode portion.
A preferred mode of the liquid crystal display device according to the embodiment is described below.
Preferably, every slit is open on the source bus line side. This structure can further stabilize the alignment of liquid crystal molecules around the end of the open slit 23 and around the end on the source bus line 2 side of the linear second electrode portion 22, further increasing the transmittance of the pixel region. 10 and the response speed. The structure can also further reduce the area of the pixel electrode to reduce parasitic capacitance between the source bus line and the pixel electrode, further reducing generation of an afterimage.
Preferably, a slit open on the source bus line side and a slit closed on the source bus line side are formed alternately. Another exemplary structure of the liquid crystal display device according to the embodiment of the present invention is described below with reference to
As shown in
The liquid crystal display device preferably further includes an auxiliary storage capacitor electrode that overlaps the pixel electrode in a plan view. The auxiliary storage capacitor electrode may be arranged at any position, and may be arranged at the center of a pixel region or at a position where the auxiliary capacitor electrode is superposed on another conductive line such as a gate bus line or a source bus line. With the auxiliary storage capacitor electrode not arranged at the center of a pixel region, the transmittance of the pixel region can be increased. The auxiliary storage capacitor electrode may have any shape and may have a linear shape, a quadrangular shape, a shape obtained by combining these shapes, or a planar shape. Examples of the auxiliary storage capacitor electrode include transparent electrodes such as ITO and IZO. As described below, in the case of being arranged in a region where a dark line is likely to be generated, ne auxiliary storage capacitor electrode is preferably a metal electrode formed from a metal such as chrome (Cr), molybdenum (Mo), aluminum (Al), titanium (Ti), or nickel (Ni), or an alloy material of these metals.
As shown in
Preferably, the auxiliary storage capacitor electrode is superposed on a contact hole in a plan view and crosses, along the gate bus lines, the pixel region surrounded by the gate bus lines and the source bus lines. The contact hole port on has a concave shape and thus is a region where the alignment of liquid crystal molecules is instable, easily generating a dark line. With the auxiliary storage capacitor electrode arranged in the region where a dark line is easily generated, generation of an afterimage can be reduced, and the display quality can be improved.
As shown in
As shown in
As shown in
Preferably, the second electrode portions each extend to a position where the second electrode portion is superposed on the auxiliary storage capacitor electrode and is not superposed on the contact hole.
extending to a position where the linear second electrode portion 22 is superposed on the auxiliary storage capacitor electrode 60 and is not superposed on the contact hole 33, the slits 23 can also be extended to positions near the contact hole 33. Thereby, a dark line generated at the closed end of a slit 23 can be transferred to a region where the linear second electrode portion 22 is superposed on the auxiliary storage capacitor electrode 60. Thereby, the transmittance and the response speed can be increased. Also, extending the slit 23 leads to reduction of the area of the pixel electrode 20, reducing parasitic capacitance between the source bus line 2 and the pixel electrode 20. This reduces generation of an afterimage.
Meanwhile, the liquid crystal display device may not include an auxiliary storage capacitor electrode from the viewpoint of increasing the transmittance of pixels.
Preferably, the liquid crystal display device further includes a planar common electrode that is arranged between the substrate and the pixel electrode and is formed from a transparent conductive material, and a metal line that is arranged in a layer different from the gate bus lines and electrically connected to the planar common electrode as being superposed on part of the planar common electrode.
Examples of the transparent conductive material include indium tin oxide (ITO) and indium zinc oxide (IZO).
A metal line 51 may be any metal that has a lower resistance than the transparent conductive material, and examples thereof include copper titanium (Ti), and silver (Ag).
Materials such as ITO and. IZO have a high resistance. Thus, the resistance of the common electrode 50 can be decreased by arranging the metal line 51 such that the metal line 51 is superposed on part of the planar common electrode 50 as shown in
Preferably, the metal line 51 is superposed on the contact hole 33 in a plan view. Since the contact hole 33 has a concave shape and the alignment of liquid crystal molecules therearound is instable, the region is preferably shielded from light. Superposing the metal line 51 on the contact hole 33 enables the region around the contact hole 33 to be shielded from light without decreasing the pixel aperture ratio as compared with the case where the metal line 51 is arranged at a different position. Although, the metal line 51 is arranged in the lower layer (on the substrate 3 side) of the common electrode 50 in
The present invention will be described in more detail based on the following examples. The examples, however, are not intended to limit the scope of the present invention.
Example 1 is one specific example of the liquid crystal display device according to the embodiment shown in
Example 2 is one specific example of the liquid crystal display device according to the embodiment shown in
Example 3 is one specific example of Modified Example 2 of the liquid crystal display device according to the embodiment shown in
The present application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 62/892,210 filed on Aug. 27, 2019, the contents of which are incorporated herein by reference in their entirety.
Number | Date | Country | |
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62892210 | Aug 2019 | US |