FIELD OF THE INVENTION
This invention relates to a liquid crystal display device and a method of making the same and, more particularly, to a liquid crystal display device with excellent quality pictures in which color filters are provided on a switching element array substrate and a method of making the same with high productivity.
FIG. 5 is a cross sectional view of a conventional active-matrix type liquid crystal display device. The liquid crystal display device 100 consists primarily of an array substrate 110 on which switching elements, such as thin film transistors (TFTs) are disposed in a matrix form, a counter substrate 150 provided opposite to the array substrate 110 and a liquid crystal layer 170 held between the substrates 110 and 150.
Gate electrodes 116 of the TFTs are disposed on a glass plate substrate 111 and a gate isolation layer 112 is coated on the gate electrodes 116. The TFT 114 includes the gate electrode 116, an insulation layer 112, a semiconductor layer 115 made of amorphous silicon, for instance, and source and drain electrodes 120 and 118. The drain electrode 118 is connected to a signal line. The source electrode 120 is also connected to a transparent pixel electrode 130 covering an organic isolation film 124 and extending along an aperture 126 defined in the isolation film 124.
The counter substrate 150 includes a transparent substrate 152, a color filter layer consisting of a light blocking layer 154 and filter elements 156 disposed on the substrate 152, and a transparent common electrode 158 covering the color filter layer. The common electrode 158 may be made of Indium Tin Oxide (ITO), for instance. Further, an alignment layer (not shown in FIG. 5) is coated on the inner surface of the common electrode 158.
The liquid crystal display device shown in FIG. 5 is apt to be faced with such technical problems that electrical coupling between the pixel electrode 130 and the signal and gate lines 118 and 116 increases coupling capacitance and brings about crosstalk between pixels. In addition, since an exact position alignment must be made between each filter element 156 of the counter substrate 150 and every pixel aperture of the array substrate 110, assembling processes therefor are complicated.
In order to solve them, the structure may be modified to form the color filters on the array substrate. The organic isolation layer 124, for instance, is also used for the color filters.
In the case of the modified structure, however, the isolation layer 124 necessarily contains three-color (red, green and blue) filter elements. Thus, stripe-like patterning, for instance, is applied to make the color filters so that each pixel electrode may correspond to a filter element. The color filters are formed by processing one filter element to another in the following way, i.e., coating a filter layer material on the array substrate, and exposing and patterning it.
Where apertures are further made to connect the switching elements to the pixel electrodes at the same time of such patterning process for each filter element, the second and third filter layers are quite easy to peel off the array substrate at the end thereof.