TFT-LCD (thin film transistor liquid crystal display) is an important flat panel display device. Depending on the direction of the electric field driving the liquid crystal, TFT-LCD can be classified into a vertical electric field type and a horizontal electric field type. The vertical electric field type TFT-LCD requires pixel electrodes formed on an array substrate, and common electrodes formed on a substrate to be aligned and assembled with the array substrate (e.g. a color filter substrate), as in the commonly used TN mode; the horizontal electric field type TFT-LCD requires pixel electrodes and common electrodes respectively formed on the array substrate, as in the ADS mode (advanced ultra-dimensional field switching mode) or in the IPS mode.
As shown in FIG. 1, a new type of TFT-LCD is currently developed on the basis of the conventional horizontal electric field type TFT-LCD, the new TFT-LCD comprising a strip-shaped pixel electrode 103 and a strip-shaped second common electrode 104 formed on an array substrate 102 as well as a plate-shaped first common electrode 105 formed on a color filter substrate 101. In the conventional horizontal electric field type TFT-LCD, a phenomenon of liquid crystal phase error would occur in the liquid crystal molecules due to the electric field formed between the strip-shaped pixel electrode and the strip-shaped second common electrode on the array substrate, i.e. a black line (caused by the liquid crystal phase error) appears between the strip-shaped pixel electrode 103 and the strip-shaped second common electrode 104 as shown in FIG. 3, while in the structure of the TFT-LCD shown in FIG. 1, the plate-shaped first common electrode 105 is formed on the color filter substrate 101, therefore the phenomenon of the liquid crystal phase error can be avoided. The array substrate 102 in the above mentioned TFT-LCD is similar to the IPS mode, the solution is also possible if the array substrate 102 is implemented in the ADS mode wherein the second common electrode is a plate-shaped electrode and the pixel electrode is a stripe-shaped electrode; or the pixel electrode is a plate-shaped electrode and the second common electrode is a strip-shaped electrode.
As shown in FIG. 2, on the basis of the TFT-LCD having the structure as shown in FIG. 1, a dielectric layer (over coater) 106 is formed on the first common electrode 105 of the color filter substrate 101, wherein the dielectric layer 106 is typically made of insulating material such as acrylic resin. By comparing the distribution diagram of the electric field equipotential lines as shown in FIG. 1 and FIG. 2, it can be seen in the structure of the TFT-LCD of FIG. 2 that, lateral equipotential lines are substantially distributed in the dielectric layer 106, and the amount of vertical equipotential lines distributed in the liquid crystal layer is also increased, thus the TFT-LCD having the structure shown in FIG. 2 may facilitate transition of the liquid crystal molecules from an upright state to an inclined state, thereby improving the transmittance of the TFT-LCD having the structure shown in FIG. 2. In addition, comparing the display screens shown in FIGS. 3 and 4, it can be seen that the brightness of the TFT-LCD having the structure shown in FIG. 2 is increased as compared to the conventional horizontal electric field type TFT-LCD.
Brightness of a liquid crystal display device is related to the angle between the liquid crystal molecule and light. When a liquid crystal molecule has a certain orientation, the brightness of a same location on the liquid crystal display device as observed from different positions outside the liquid crystal display device is different, this is because the light output angles from a same location on the liquid crystal display device as observed from different positions outside the liquid crystal display device are different, so that the angles between the liquid crystal molecules and light are different. For this reason, if the liquid crystal molecules within a pixel unit have a single orientation or the difference among the orientation is rather small, the brightness of the pixel unit observed from different positions outside the liquid crystal display device is different, that is, a phenomenon of color shift occurs. Although the liquid crystal molecules in the liquid crystal display device have different deflection directions under the influence of electric field, the liquid crystal molecule have few orientations, so that color shift occurs.