1. Field of the Invention
The present invention relates to a liquid crystal display panel (LCD panel), and more particularly, to an active device array substrate.
2. Description of Related Art
The market today requires a thin film transistor liquid crystal display (TFT-LCD) to have high contrast ratio, no gray scale inversion, less color shift, high luminance, high chroma, high color saturation, fast response and wide viewing angle. It is available for a TFT-LCD to provide a wide viewing angle nowadays that a technology of twisted nematic liquid crystal (TN liquid crystal) plus wide viewing film, in-plane switching LCD (IPS LCD), fringe field switching LCD (FFS LCD) and multi-domain vertically alignment LCD (MVA LCD), wherein with an MVA LCD, since alignment protrusions or slits formed on a color filter substrate (CFS) or on a TFT array substrate are used to make the liquid crystal molecules arranged in multi-directions alignment so as to obtain a plurality of different-alignment domains, therefore, an MVA LCD is capable of wide viewing.
FIG. 1 is a graph showing relationship curves of the normalized transmittance vs. gray level of a conventional MVA LCD. Referring to FIG. 1, the abscissa herein represent gray level, while ordinate represents normalized transmittance. It can be seen from FIG. 1, although a MVA LCD has achieve the wide viewing angle requirement, but the wide viewing effect is varied with angles of viewing, where the curvatures of the curves of the normalized transmittance vs. gray level corresponding to different angles of viewing (φ, θ) are different. Specifically, φ is an azimuth, while θ is an elevation angle. In other words, when an angle (φ, θ) of viewing is changed, the frame luminance of a conventional NVA LCD varies, which further leads to color shift or color washout problem.
In order to solve the above-mentioned color shift problem, various conventional techniques have been provided, a solution herein is to form an additional capacitor in every single pixel, where different pixel electrodes in a single pixel respectively produce electrical field with different intensities by using capacitor coupling effect so as to make the liquid crystal molecules over different pixel electrodes have different arrangements. Although the above-mentioned technique is able to improve color shift, but an additional transistor is usually employed so as to stabilize the data voltage produced by the above-mentioned capacitor coupling effect, but the added transistors would decrease the aperture ratio of the liquid crystal display panel.
Another conventional solution is to add a transistor in each pixel, thus, a single pixel has two transistors. Since different transistors would make two pixel electrodes in a single pixel produce different electrical fields, and accordingly the liquid crystal molecules over the different pixel electrodes have different arrangements, color shift can be improved. However, such a solution requires two transistors formed in a single pixel, which causes a loss of aperture ratio as well.
Although the above-mentioned conventional techniques work to improve color shift phenomena for middle or small size LCDs, but they bring a loss of aperture ratio with the pixel design, so that a middle or small size LCD with an improved color shift suffers a drawback of insufficient luminance.