1. Field of the Invention
The present invention relates to a liquid crystal display device used for a display part of an electronic equipment, and particularly to a liquid crystal display device including a vertical alignment type liquid crystal having a negative dielectric anisotropy.
2. Description of the Related Art
A vertical alignment (VA) mode liquid crystal display device has features of a high contrast ratio and a high speed response characteristic, and in recent years, the VA mode liquid crystal display device has been actively developed. Especially, an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device has features of a wide viewing angle, a high contrast ratio and a high speed response characteristic, and receives attention as a display system most suitable for a flat panel display for a TV receiver. FIG. 7 shows a sectional structure of one pixel of the MVA mode liquid crystal display device. As shown in FIG. 7, the MVA mode liquid crystal display device includes a glass substrate 103 of a TFT substrate 102, an opposite side glass substrate 105 of an opposite substrate 104 disposed to be opposite to the TFT substrate 102, and a liquid crystal 112 sealed between both the substrates 102 and 104.
An insulating layer 106 is formed on the glass substrate 103. Plural gate bus lines and plural drain bus lines (neither of them are shown) intersecting each other through the insulating layer 106 are formed on the glass substrate 103. A not-shown thin film transistor (TFT) is formed at each of intersection parts of the gate bus lines and the drain bus lines. The gate bus lines and the drain bus lines are insulated from each other through the insulating layer 106. Besides, the insulating film 106 functions as a gate insulating film of the TFT. A pixel electrode 110 made of indium tin oxide (ITO) and patterned into a specified shape is formed on a final protection film 108. The pixel electrode 110 is connected to a source electrode of the TFT through a not-shown contact hole formed in the final protection film 108. A pixel electrode slit 116 as an alignment regulating structure for regulating an alignment direction of a liquid crystal molecule 120 is formed in the pixel electrode 110. A vertical alignment film 114 for vertically aligning the liquid crystal molecule 120 is formed on the whole surface of the pixel electrode 110 and the pixel electrode slit 116.
On the other hand, a not-shown color filter (CF) layer is formed on the opposite side glass substrate 105. An opposite electrode 124 made of ITO is formed on the CF layer and the whole surface of the substrate. A linear protrusion 118 as an alignment regulating structure protruding on the opposite electrode 124 is formed on the opposite side glass substrate 105. Similarly to the pixel electrode slit 116, the linear protrusion 118 is formed in order to regulate the alignment direction of the liquid crystal molecule 120. A vertical alignment film 122 is formed on the whole surface of the opposite electrode 124 and covers the linear protrusion 118. In the MVA mode liquid crystal display device, the linear protrusion 118 and the pixel electrode slit 116 are provided in the pixel, so that the alignment control of the liquid crystal 112 and multi-domain formation are realized.
[Patent document 1] JP-A-2001-183637
[Patent document 2] JP-A-8-122753
As a method of keeping the thickness (cell gap) of the layer of the liquid crystal 112 at a desired length, there is used a method of scattering spherical ball spacers 136 each having a diameter equal to the desired cell gap into the layer of the liquid crystal 112. The ball spacers 136 are made of plastic material or glass material. The ball spacers 136 are scattered on the TFT substrate 102 or the opposite substrate 104, and the TFT substrate 102 and the opposite substrate 104 are attached to each other through a seal material formed into a frame shape, so that the liquid crystal 112 is sealed between both the substrates 102 and 104.
For example, when the ball spacers 136 are scattered on the opposite substrate 104, there is a case where the ball spacer 136 is disposed on the linear protrusion 118. The cell gap at the position where the linear protrusion 118 is formed is narrow as compared with the other position. Thus, as shown in FIG. 7, the cell gap at the linear protrusion 118 is narrower than the diameter of the ball spacer 136. Since the ball spacer 136 is made of relatively hard material as compared with the vertical alignment films 114 and 122, when the opposite substrate 104 and the TFT substrate 102 are attached to each other, there is a case where the vertical alignment films 114 and 122 on the linear protrusion 118 and on the opposite side thereof are damaged by the pressure of the ball spacer 136.
At this state, the alignment control of the liquid crystal molecule 120 at the position becomes impossible, light leak occurs at the linear protrusion 118 and in the vicinity thereof, and a poor display occurs in the MVA mode liquid crystal display device. In general, in order to realize excellent alignment of the liquid crystal molecule 120, it is necessary that the width of the linear protrusion 118 is about 10 μm. This corresponds to several percents of the area of the pixel region. For example, in a 15-inch MVA mode liquid crystal display device with a resolution of XGA (extended Graphics Array), in the case where the linear protrusion 118 is formed to have a width of 15 μm, and 100 ball spacers per 1 mm2 are scattered, there is a case where about 7 ball spacers per 1 mm2 are scattered on the linear protrusion 118. When the vertical alignment films 114 and 122 are damaged by the ball spacer 136, the light leak occurring on the display screen becomes very noticeable.