The liquid crystal display (LCD) has been broadly used in various applications in the daily life with the improvement and popularity of the digital network technology. Nowadays, the image quality of the LCD is nip and tuck with that of the cathode ray tube (CRT) display. However, there are still some problems for the LCD needed to be improved and solved, such as the small viewing angle and the non-uniform displaying.
Many techniques are developed for obtaining a wider viewing angle for the LCD, among which the in-plane switching (IPS) mode is regarded as an excellent technique to achieve the mentioned purpose. It is known that, however, the IPS LCD is disadvantageous in lower aperture ratio and color shift. In order to resolve the color shift of the IPS LCD, various improved LCD structures, e.g. the super IPS LCD (S-IPS LCD) and the advanced super IPS LCD (AS-IPS LCD), are respectively developed to enhance the aperture ratio.
Please refer to FIGS. 1A and 1B, relating to a plan view and a cross-sectional view schematically showing the structure of an S-IPS LCD disclosed in U.S. Pat. No. 6,839,115 B2. As shown in FIGS. 1A and 1B, gate lines 111 and data lines 112 are respectively arranged in longitudinal and transverse directions on a first transparent substrate 11 so as to define a pixel area of the S-IPS LCD. The pixel area includes plural first common electrode 113 and plural pixel electrodes 114, wherein some of the pixel electrode 114 and some of the first common electrode 113 are overlapped in the peripheral region A of the pixel area, which is further enlarged for a clear description in FIG. 1B. A second common electrode 115 is positioned to overlap some of the pixel electrode 114 that overlaps some of the first common electrode 113, and is connected to the first common electrode 113 through a contact hole 116. On a second substrate 12 facing to the first substrate 11, a black matrix 121 is arranged, so as to prevent the light from leaking. In this case, the first common electrodes 113 as well as the second common electrode 115 adjacent thereto operate for shielding the pixel electrodes 114 from the effects of a data voltage on an adjacent one of the data lines 112. However, such a structure of the S-IPS LCD still needs to be improved since it is difficult to suppress the local crosstalk caused by the capacitive coupling between the pixel electrodes 114 and the data lines 112.
On the other hand, it is possible for the AS-IPS LCD to achieve a higher aperture ratio. Please refer to FIG. 2, which is a cross-sectional view schematically showing the layer sequence of the AS-IPS LCD disclosed in U.S. Pat. No. 6,693,687 B2. The AS-IPS LCD includes a first substrate 21 and a second substrate 22 having a black matrix 221 which are faced to each other, while a liquid crystal layer 23 is disposed therebetween. The orientation films 24 and 25 are mounted on respective surfaces of the inner sides of the substrates 21 and 22.
On the first substrate 21, the drain lines 211 composed of a conductive layer are arranged and corresponded to the black matrix 221, which operate as image signal lines for the display. The common electrodes comprises a first portion 212 and a second portion 214.The first portion 212 made of a transparent conductive layer is formed for shielding and completely covers the drain line 211, so as to completely eliminate the leakage electric field from the drain line 211 and thus the crosstalk. Beside, the pixel electrodes 213, 215 as well as the second portion 214 are disposed for controlling the display. In this case, an overcoat layer 26 made of a transparent resin material is provided between the orientation film 24 and the first substrate 21, so as to reduce the capacitance between the drain line 211 and the first portion 212 which is overlapped on the drain line 211.
Through the overcoat layer in the AS-IPS LCD, the improvement of the aperture ratio and the estimation of the crosstalk are achievable. However, the application of the overcoat layer results in a significant increase in the manufacturing cost.
In order to overcome the mentioned drawbacks in the prior art, a novel in-plane switching liquid crystal display with an improved cell transmittance and a reduced production cost is provided in the present invention.