1. Field of the Invention
The present invention relates to an active matrix type liquid crystal display apparatus with a high aperture ratio of a pixel portion.
2. Description of the Related Art
Liquid crystal display apparatuses have been widely used as display devices for TV sets and graphics display devices due to their advantageous features of thin structure and low power consumption. Among liquid crystal display, an active matrix type liquid crystal display apparatus using thin film transistors (referred to as TFTS) as switching devices has high speed response characteristic and high precision characteristics, making it an attractive choice for high picture quality, large size, and color pictures.
Each display device portion of such an active matrix type liquid crystal display apparatus is generally composed of a switching active device (such as a TFT), an active device array substrate, an opposite substrate, a liquid crystal material, and polarizing plates. The active device array substrate has a pixel electrode connected to the switching active device. The opposite substrate has an opposite electrode disposed opposite to the active device array substrate. The liquid crystal material is disposed between the active device array substrate and the opposite substrate. The polarizing plates are disposed outside of the two substrates. In the active matrix type liquid crystal display apparatus, each liquid crystal pixel cell corresponding to each pixel is composed of the pixel electrode, the opposite electrode, and the liquid crystal layer.
By varying a voltage supplied to each pixel electrode, the optical state of liquid crystal molecules in the liquid crystal pixel cell is changed and thereby a picture is displayed on the screen. An electric field corresponding to a picture signal voltage is not supplied to a liquid crystal layer disposed outside the pixel electrodes (namely, the non-pixel region). Thus, the non-pixel region is optically shielded. By varying an electric field of a pixel portion in which a pixel electrode is formed, the optical state of the liquid crystal layer of the pixel portion is changed and thereby a picture is displayed.
To reduce the entire power consumption of the liquid crystal display apparatus, the non-pixel region that is optically shielded should be minimized and thereby the aperture ratio of the pixel portion should be maximized to improve the optical use efficiency of the display apparatus.
As a related art reference, a technology for improving the aperture ratio of a pixel portion has been disclosed as Japanese Patent Laid-Open Publication No. 1-73324. In this related art reference, one auxiliary capacitor line is disposed between two adjacent pixel electrodes. The auxiliary capacitor line is shared by the two adjacent pixel electrodes.
However, the liquid crystal pixel cell corresponding to each pixel tends to be affected by the electric field that takes place between signal lines and scanning lines disposed on pixel electrodes and the vicinity thereof. As a result, the liquid crystal molecules in the vicinity of a peripheral portion of the pixel electrode are reversed. (This situation is referred to as edge reverse phenomenon.) In other words, the liquid crystal molecules in the vicinity of the peripheral portion of the pixel electrode are affected by the electric field that takes place between signal lines and scanning lines as well as by the electric field that precisely corresponds to a picture signal voltage of a picture signal supplied from the pixel electrode. As a result, the optical state of each pixel portion does not precisely correspond to the picture signal. Consequently, light leaks out at the peripheral portion of each pixel portion, thereby decreasing the contrast of the picture. Thus, the display quality of the screen is remarkably deteriorated.