This invention relates to a black coloring composition which is excellent in coloring property, in adhesivity and in long-term storage stability. This invention also relates to a light-shielding component (or member) excellent in heat resistance and in electric resistance, and in particular to a high heat resistance light-shielding component which is suited for use as a light-shielding film or a black matrix of electronic parts. Further, this invention also relates to a black coloring composition which is useful for the manufacture of a high heat resistance light-shielding component. This invention also relates to an array substrate provided with a light-shielding film formed of the aforementioned high heat resistance light-shielding component and to a method of manufacturing the array substrate. Furthermore, this invention also relates to a liquid crystal display device provided with the array substrate.
In recent years, an active matrix type liquid crystal display element (LCD) wherein a thin film transistor (TFT) employing an amorphous silicon (.alpha.-Si) is utilized as a switching element has been taken noticed of and extensively and increasingly employed as a display element of a personal computer, etc. If this .alpha.-Si which is capable of forming a film at a low temperature is employed for the manufacture of a TFT array and formed on a cheap glass substrate, a large panel display (a flat type television) which is excellent in fineness and in image quality can be manufactured at a low cost, and a further development of such a TFT array is expected.
If a color liquid crystal display device is to be completely substituted for a CRT (cathode ray tube), the cost for manufacturing a color liquid crystal display device has to be further reduced. However, there is still a great gap in price between a color liquid crystal display device and the CRT. One of main causes for the high price of color liquid crystal display device is the cost for an array substrate. Therefore, it is required for the array substrate, in addition to an improvement of the performance thereof, to reduce the number of manufacturing steps of the array substrate so as to reduce the manufacturing cost thereof.
The conventional color liquid crystal display device is constructed as illustrated in FIG. 1 for instance. Namely, a gate line 72 and a capacity line 79 are formed on a glass substrate 71 and are covered by a gate insulating film 73. On this gate insulating film 73 is formed a TFT comprising an .alpha.-Si layer 74, n.sup.+ .alpha.-Si layers 75a and 75b, a source electrode 76a and a drain electrode 76b. The drain electrode 76b is connected with a pixel electrode 78a made of ITO. A passivation film 77 is formed on the pixel electrode 78a in such a manner that a portion of the pixel electrode 78a is exposed therefrom.
On the other hand, on the surface of a substrate 80 which faces to the glass substrate 71, there are successively formed a black matrix 81, a color filter 82 and a counter electrode 83 formed of ITO. Furthermore, a liquid crystal layer 84 is interposed between these substrates 71 and 80, thus forming the color liquid crystal display device. However, when a black matrix is formed on a color filter substrate as in the case of liquid crystal display device shown in FIG. 1, the opening ratio of the display device is restricted thereby making it difficult to realize a high opening ratio. With a view to minimize the matching margin between the array substrate and the color filter substrate so as to increase the opening ratio, there has been recently developed a black matrix-on array substrate where a black matrix is formed on an array substrate.
On the other hand, a liquid crystal display device provided, as a switching element, with a TFT employing a polycrystalline silicon (p-Si) film, which is capable of prominently improving the performance as compared with the conventional .alpha.-SiTFT has been proposed.
There are known two kinds of .alpha.-SiTFT, i.e. a stagger structure (FIG. 2A) and a reverse-stagger structure (FIG. 2B), which have been utilized as a switching element for a liquid crystal display device. It is reported that the TFT of stagger structure shown in FIG. 2A is more advantageous in reducing the number of manufacturing steps of the array substrate as compared with that of the reverse-stagger structure. However, the .alpha.-SiTFT of stagger structure is accompanied with the following problems. Namely, in the case of the .alpha.-SiTFT of reverse-stagger structure, a gate electrode 91a and a gate line 91b are disposed below a semiconductor layer 89 with a gate insulating film 90 being interposed therebetween, so that the channel region of TFT between a source electrode 87 and a drain electrode 88 is shielded from a back light, etc. Whereas, in the case of the .alpha.-SiTFT of stagger structure, the gate electrode 91a and the gate line 91b are disposed over the semiconductor layer 89, so that the channel region of TFT cannot be shielded from a back light, thus allowing the back light to reach the channel region to thereby generate a photo-leak current in the TFT.
On the other hand, there are known two kinds of structure in the TFT employing a polycrystalline silicon (p-Si) film, i.e. a coplanar structure (FIG. 2C) and a reverse-coplanar structure (FIG. 2D), the TFT of coplanar structure (FIG. 2C) being commonly employed among them. This TFT of coplanar structure is also accompanied with the problem of a photo-leak current due to a leakage of light into the channel region of TFT as in the case of the TFT of stagger structure, since the gate electrode 91a and the gate line 91b are disposed over the semiconductor layer 93.
The aforementioned problem of a photo-leak current in the TFT of stagger structure or of coplanar structure may be overcome by constructing the structure of these TFT elements in such a manner that a black matrix is disposed below the channel region after the black matrix functioning also as a light-shielding film has been formed on a transparent substrate. However, such a light-shielding film which is currently available is accompanied with various problems as illustrated below.
The TFT is generally manufactured through a process involving a high temperature treatment. The temperature involved in the process is 300.degree. C. or more in the case of .alpha.-SiTFT and 600.degree. C. or more in the case of p-SiTFT. Therefore, the black matrix (light-shielding film) is required to be heat-resistive to such a high temperature and at the same time to have a high electric resistance (10.sup.9 .OMEGA..multidot.cm). Although the employment of materials such as metals (chromium, etc.) and semiconductors (silicon) as a black matrix may be satisfactory as far as the heat resistance is concerned, but these materials are low in electric resistance, so that the following problems would be raised. Namely, if a black matrix is formed by making use of a material which is low in electric resistance, an electric capacitive coupling is generated between the black matrix and a signal line or a source electrode, thus generating a crosstalk in a liquid crystal display device thereby inducing an increase in power consumption and a deterioration in quality of picture image. On the other hand, a black pigment-dispersed resist is high in electric resistance, but a black matrix formed by making use of this black pigment-dispersed resist is defective in that the heat resistance thereof too poor to withstand the processing temperature in the manufacture of a TFT. Namely, a light-shielding film which is high in both electric resistance and heat resistance is not available as yet.
By the way, a black paint or a black ink containing carbon black dispersed therein is now extensively employed. Since carbon black is a highly hydrophobic pigment, a large quantity of a dispersant is required in order to disperse the carbon black in a solvent. Specifically, the quantity of the dispersant required may be no less than that of carbon black in terms of weight or volume, thus limiting the concentration of black color. In particular, when the colorant is to be used as a thin film, a desired black color concentration may not be achieved. Moreover, carbon black is defective in that it is vulnerable to an oxidative decomposition at a high temperature in air atmosphere, thus resulting in a discoloration of carbon black.
Accordingly, an object of the present invention is to provide a black coloring composition which is excellent in coloring property, in adhesivity and in long-term storage stability.
Another object of this invention is to provide a light-shielding component which is high in electric resistance and excellent in heat resistance, and hence suited for use as a light-shielding film or a black matrix of an array substrate.
Another object of this invention is to provide a black coloring composition which is useful for the manufacture of a high-heat resistance light-shielding component.
Another object of this invention is to provide an array substrate which is high in opening ratio and low in power consumption and can be manufactured at a low cost.
Further object of this invention is to provide a liquid crystal display device provided with such an array substrate as mentioned above.
Still another object of this invention is to provide a method of manufacturing an array substrate which is high in opening ratio and low in power consumption at a low cost.