1. Field of the Invention
The present invention relates to a homeotropic alignment type liquid crystal display device having a liquid crystal layer in which liquid crystal molecules are vertically aligned with respect to a pair of substrates between the substrates.
2. Description of the Related Art
In a conventional liquid crystal display, a transparent type liquid crystal display device in which a backlight is set on a rear surface of the liquid crystal display device to perform illumination, a semi-transparent type liquid crystal display device in which a reflection region is partially provided or the like is extensively used as a liquid crystal display device. As alignment methods of liquid crystal molecules in these liquid crystal display devices, there are a twisted nematic (TN) mode, a homogeneous alignment mode and others. In these modes, liquid crystal molecules are arranged in substantially parallel to main surfaces or planes of the substrates in a state where a voltage is not applied, and a voltage is applied to change a long axis direction of the molecules to a direction vertical to the main surfaces of the substrates, thereby optically changing a liquid crystal layer.
In a homogeneous alignment type liquid crystal display device adopting, e.g., the above-described TN mode, liquid crystal molecules do not completely become vertical to main surfaces of substrates when a voltage is applied because of an anchoring effect or the like of a homogeneous aligning film. Therefore, birefringence in a normal direction of the substrate main surfaces does not become zero when a voltage is applied, thereby deteriorating a display grade (contrast). Thus, as an alignment method for realizing a high transmission factor and high contrast, attention is drawn to a homeotropic alignment (VA) mode by which molecules are aligned in a vertical direction (birefringence is substantially zero) with respect to the substrate main planes when no voltage is applied, and the molecules are aligned in a horizontal direction when a voltage is applied.
In the VA mode, when an electric field is applied to a liquid crystal layer, when alignment is controlled in such a manner that liquid crystal molecules are inclined in one direction in each pixel region at the time of applying an electric field to a liquid crystal layer, high contrast can be realized as described above, but viewing angle characteristics are not satisfactory. Thus, in order to improve the viewing angle characteristics, there has been proposed the following alignment control. That is, a slit or the like is provided in an electrode in the pixel region to obliquely apply an electric field. As a result, when the voltage is applied between the electrodes facing each other, alignment is controlled in such a manner that liquid crystal molecules come down in a plurality of directions in each pixel region. In the liquid crystal display device adopting this homeotropic alignment mode, however, since the falling directions of the liquid crystal molecules face many directions due to application of the voltage, light cannot be taken out when a polarization axis of a polarizing plate and an axis of the liquid crystal face the same direction as seen from a direction vertical to the substrate main surfaces, and hence a transmission factor is low.
In the liquid crystal display device adopting such a VA mode, as a device in which a plurality of retardation plates are arranged to improve contrast and viewing angle dependence (color shift) of a hue, there has been proposed a liquid crystal display apparatus in which a retardation layer having a retardation which is not smaller than approximately ½ and not greater than ¾ with respect to visible light and a retardation layer which optically has a negative refractive index anisotropy and a retardation which is approximately zero with respect to visible light are arranged in a homeotropic alignment type liquid crystal cell (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2003-015134).
According to the liquid crystal display apparatus having a plurality of retardation plates arranged therein, although contrast and a color shift are improved, the improvement is not sufficient. Further, a satisfactory transmission factor of the liquid crystal display device cannot be obtained, and high contrast cannot be acquired in a range of a wide viewing angle.