In-plane switching type liquid crystal display devices having improved aperture ratio and methods of fabrication therefor using nonuniform spacing between pixel and common electrodes

[0002] The present invention relates to liquid crystal display (LCD) devices and methods of fabrication therefor, more particularly, to in-plane switching (IPS) type LCD devices and methods of fabrication therefor.

[0003] Liquid crystal display (LCD) devices are commonly used flat panel display devices. LCD devices include twisted-nematic (TN) type devices, which may have switching elements such as thin-film transistors (TFTs) for controlling respective pixels, and super-twisted-nematic (STN) type devices. TN and STN devices typically include first and second substrates which have opposing transparent common and pixel electrodes formed thereon, respectively, with a liquid crystal material being sandwiched between the substrates. Unfortunately, TN and STN type LCD devices typically have narrow viewing angles, especially in an up-down direction. Furthermore, since the common electrode and the pixel electrodes are formed on separate substrates, and the two substrates may connected in order to convey signals therebetween, numerous and difficult process steps may be required to produce a display device.

[0004] To avoid these problems, in-plane switching (IPS) type LCD devices have been developed. In an IPS LCD device, a plurality of pixel electrodes and common electrodes are formed on the same substrate, as described in European Patent Application No. 93307154.0. The electric field developed between the pixel electrode and the common electrode, which affects the orientation of the molecules of the liquid crystal, is aligned parallel to the substrate, in contrast to the perpendicular electric fields produced by the electrodes of a typical TN or STN LCD device. Unfortunately, however, conventional IPS LCD devices may have an undesirably small aperture ratio, especially when all the electrodes are formed on one substrate.

[0005] In light of the foregoing, it is an object of the present invention to provide an in-plane switching (IPS) type liquid crystal display (LCD) device with improved aperture ratio.

[0006] This and other objects, features and advantages are provided according to the present invention by IPS type LCD devices in which common electrodes and pixel electrodes of a pixel have a width minimized according to a design rule such as a maximum resistance, and are spaced to provide the same maximum gap therebetween, except for a different gap separating an outlying electrode from an adjacent electrode. This nonuniform gap may be located on only one side of the pixel, separating an outlying electrode nearest a data line from an adjacent pixel, with the outlying electrode being separated from the data line by a gap which is minimized according to a design rule such as a photolithographic margin and/or a maximum coupling capacitance. Alternatively, the pixel may have two non-uniform gaps which separate two respective outlying electrodes from respective adjacent electrodes. By providing the nonuniform gaps, increased aperture ratio may be achieved over pixels in which common and pixel electrodes are uniformly spaced.

[0007] In particular, according to the present invention, a panel for a liquid crystal display device includes a substrate and a data line on the substrate, extending along a first direction. A pixel is formed on the substrate, disposed adjacent the data line, and includes a plurality of spaced apart elongate pixel electrodes extending parallel to the data line, and a plurality of spaced apart elongate common electrodes extending parallel to the data line and interspersed among the pixel electrodes such that a respective pixel electrode is disposed adjacent a respective common electrode. The common and pixel electrodes define a plurality of gaps, a respective one of the gaps separating a common electrode and a pixel electrode, the plurality of gaps having nonuniform widths. Preferably, the plurality of gaps includes a first group of gaps having a first width and a second group of gaps having a second width. According to one embodiment, the first group of gaps includes all of the plurality of gaps except a gap between one common electrode nearest the data line and a pixel electrode nearest the one common electrode. According to another embodiment, the first group of gaps includes all of the plurality of gaps except a gap between a first common electrode nearest the data line and a pixel electrode nearest the first common electrode, and a gap between a second common electrode furthest from the data line and a pixel electrode nearest the second common electrode.

[0008] Preferably, the common electrodes and the pixel electrodes have a minimum width according to a first design rule, and the data line has a minimum width according to a second design rule; the first and second design rules may include a resistance, for example. The first gap width preferably is a maximum width according to a third design rule such as a driving voltage, while the second gap width preferably is a minimum width according to a fourth design rule such as a photolithographic margin and/or a coupling capacitance. The data line and a nearest one of the pixel electrodes and the common electrodes preferably define a gap therebetween having a minimum width according to a fifth design rule such as a photolithographic margin and/or a coupling capacitance.

[0009] According to method aspects of the present invention, a panel of a liquid crystal display device is fabricated by forming a data line on a substrate, extending along a first direction. A pixel is formed on the substrate adjacent the data line, the pixel including a plurality of spaced apart elongate common electrodes extending parallel to the data line and a plurality of spaced apart elongate pixel electrodes extending parallel to the data line and interspersed among the common electrodes such that a respective one of the pixel electrodes is disposed adjacent a respective common electrode. The common and pixel electrodes define a plurality of gaps, a respective one of the gaps separating a common electrode and a pixel electrode, the plurality of gaps having nonuniform widths. Preferably the plurality of gaps includes a first group of gaps having a first width and a second group of gaps having a second width. Preferably, the common electrodes and the pixel electrodes have a minimum width according to a first design rule, the data line has a minimum width according to a second design rule, the first width is a maximum width according to a third design rule, the second width is a minimum width according to a fourth design rule, and the data line and a nearest one of the pixel electrodes and the common electrodes define a gap therebetween having a minimum width according to a fifth design rule. Improved IPS type LCD devices may thereby be formed.

[0010] Some of the objects and advantages of the present invention having been stated, others will be more fully understood from the detailed description that follows and by reference to the accompanying drawings in which:

[0011] FIGS. 1 and 2 are plan views illustrating alternative configurations of a panel for IPS type LCD device;

[0012] FIG. 3 is a plan view illustrating an embodiment of a panel for an IPS type LCD device according to the present invention; and

[0013] FIG. 4 is a plan view illustrating another embodiment of a panel for an IPS type LCD device according to the present invention.

[0014] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. Those skilled in the art will appreciate that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, sizes and thickness of regions may be exaggerated for clarity, and like numbers refer to like elements throughout.

[0015] FIG. 1 shows a pixel 30aof a panel of an IPS type LCD device. A gate line 1 and a data line 2 are formed on a substrate 20 in a transverse direction and a longitudinal direction, respectively. Common electrode lines 3 are formed parallel to the gate line 1, and a plurality of common electrodes 4, 5, 6 are formed parallel to the data line 2, connected to the common electrode lines 3. A plurality of pixel electrodes 7, 8, 9 are formed interspersed among the common electrodes 4, 5, 6, parallel to the data line 2. The pixel electrodes 7,8,9 are connected to drain electrode 11 of a thin-film transistor TFT. A portion of the gate line 1 serves as a gate electrode of the thin-film transistor TFT, and a source electrode 12 of the thin-film transistor TFT is connected to the data line 2. One common electrode 4 is disposed at the left side of the pixel 30a, while one pixel electrode 9 is disposed at the right side of the pixel, nearest to the data line 2. The pixel electrodes 7, 8, 9 may be formed from the same material layer as the data line 2.

[0016] The common electrodes 4, 5, 6 and the pixel electrodes 7, 8, 9 preferably have a width W which is a first minimum width W_min1according to a design rule such as a photolithographic margin and/or a maximum resistance. The gaps S between the common electrodes 4, 5, 6 and the pixel electrodes 7, 8, 9 preferably have a first maximum width S_max1according to a design rule such as a maximum driving voltage. Similarly, the data line 2 has a width D which is a second minimum width W_min2according to a design rule such as a photolithographic margin and/or a maximum resistance.

[0017] For the configuration shown in FIG. 1, a pixel electrode 9 is the nearest electrode to the data line 2. As the pixel electrode 9 and the data line 2 may be formed from the same material layer in the same process step, the coupling capacitance between them can reduce the image quality. In contrast, a common electrode may be formed laterally closer to the data line in comparison to a pixel electrode, allowing a pixel in which a common electrode is neighbors the data line 2 (as illustrated in FIG. 2) to have a greater aperture ratio. However, for the configuration illustrated in FIG. 1, if the size of the pixel results in a gap M between the data line 2 and the neighboring pixel electrode 9 which has a minimum value S_min1according to a design rule such as a photolithographic margin and/or a maximum coupling capacitance, then the pixel may achieve an optimal aperture ratio. If a common electrode 6 is the nearest electrode to the data line 2, as illustrated in FIG. 2, and the gap between the data line 2 and the neighboring pixel electrode 6 has a minimum value S_min2according to a design rule such as a photolithographic margin and/or a maximum coupling capacitance, then the LCD may achieve an optimal aperture ratio.

[0018] Referring to FIG. 1, because pixel size typically is determined without consideration of minimum electrode widths and maximum and minimum gaps between electrodes, a case may arise in which the gap M, which does not contribute to the effective display area, is smaller than S_max1+S_min2+W_min1but larger than S_min2. In other words, the gap M is too narrow to allow another common electrode to be placed between the rightmost pixel electrode 9 and the data line 2 while maintaining the maximum separation S_max1from the pixel electrode 9, but is wider than the minimum width S_min2which would maximize aperture ratio. FIG. 2 illustrates a pixel 30bof an IPS type LCD device which can avoid this problem by putting a common electrode 6 nearest to the data line 2, corresponding to the pixel configuration illustrated in FIG. 1 with the rightmost pixel electrode 9 removed and the gaps S between the electrodes maintain the same width S_max1as in the configuration of FIG. 1. However, to fill the pixel area and provide a gap M₂between the rightmost common electrode 6 and the data line 2 which has the minimum width S_min2, the width W of the electrodes is increased in comparison to those in the configuration of FIG. 1. Consequently, the aperture ratio may be reduced in comparison to the structure of FIG. 1.

[0019] According to one embodiment of the present invention illustrated in FIG.3, improved aperture ratio may be achieved by arranging electrodes of a pixel 30csuch that an electrode nearest a bordering data line is spaced apart from an adjacent electrode by a gap which has a width which differs from the maximized gaps separating other electrodes in the pixel. As shown in FIG. 3, respective common electrodes 4, 5, 6 are spaced from respective pixel electrodes 7, 8, 9 by gaps S which are maximized according to a design rule such as a maximum driving voltage. However, a common electrode 10, formed between a pixel electrode 9 and a data line 2, is spaced apart from the pixel electrode 9 by a gap L which differs from the gaps S. The width of the common electrode 10 preferably is the same as that of the other electrodes, i.e., a width which is a maximum according to a design rule such as a maximum resistance. The gap M₁between the common electrode 10 and the data line 2 preferably has a minimum width according to a design rule such as a photolithographic margin and/or a maximum coupling capacitance. A gap L between the common electrode 10 and the neighboring pixel electrode 9 is smaller than the gap S between the other electrodes, but can help contribute to the effective display area and improve aperture ratio.

[0020] According to another embodiment of the present invention illustrated in FIG. 4, electrodes which are disposed at outer portions of a pixel 30dare spaced from adjacent electrodes by gaps which differ from the maximized gaps separating other electrodes in the pixel. As illustrated in FIG. 4, respective common electrodes 5, 6 are spaced from respective pixel electrodes 7, 8, 9 by gaps S which are maximized according to a design rule such as a maximum driving voltage. However, a common electrode 10, formed between the pixel electrode 9 and the data line 2, and a common electrode 4, formed adjacent the pixel electrode 7, are spaced apart from pixel electrode 9 and pixel electrode 7, respectively, by gaps L1 which differ from the gaps S. Preferably, the outlying common electrodes 4, 10 have the same width as the other electrodes, i.e., a width minimized according to a design rule such as a maximum resistance, while the gap M₂preferably has a width which is a minimum according to a design rule such as a photolithographic margin and/or a maximum coupling capacitance. The gaps L1 between the outlying common electrodes 4, 10 preferably have the same width, smaller than the gaps S, and can contribute to the effective display area and increase aperture ratio.

[0021] In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.