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REFLECTIVE TYPE ACTIVE MATRIX
DISPLAY PANEL AND METHOD OF
MANUFACTURING SAME
BACKGROUND OF THE INVENTION 5
1. Field of the Invention
The present invention relates to a reflective type active matrix display panel used as an enlarged projection reflective type liquid crystal display, for instance, and a method of, manufacturing the same display panel. 10
2. Description of the Prior Art
In the enlarged projection type active matrix display (liquid crystal projection type display apparatus), it is possible to manufacture an active matrix display panel of less defectiveness by microminiaturizing the respective pixels of 15 the active matrix display panel for constituting the display portion, that is. by reducing the pixel area. The enlarged projection type active matrix display can be classified into two sorts of reflective type and transmissive type. At present, however, only the transmissive type has been put into 20 practice use, and the reflective type active matrix display panel has been not so far of practical use due to less available efficiency as compared with that of the transmissive type.
Hereupon, in the case of the transmissive type active ^ matrix display, since the area of a switching element occupied for each pixel increases relatively with the advance of microminiaturization, the aperture ratio is inevitably reduced, with the result that the light availability deteriorates markedly. Consequently, the transmissive type active matrix 3Q display panel is difficult to be microminiaturized, and thereby the panels less than one-inch size have been not so far put into practice. Further, the number of pixels is usually less than one hundred thousand.
Further, in the case of the enlarged projection type active 35 matrix display, the size, weight and cost of the optical system therefor increased remarkably with increasing active matrix panel size. Therefore, there exists a limit in use of the transmissive type active matrix display panel, because of the difficulty of the high resolution and microminiaturization on ^ the basis of its principle.
Accordingly, the use of the reflective type active matrix display panel has been considered. In the case of the reflective type active matrix display panel, since each pixel transistor can be formed under each pixel electrode, it is 45 possible to utilize all the pixel area other than the portion required to electrically isolate (i.e.. insulate) the respective pixels, so that the aperture ratio can be increased.
In the conventional reflective type active matrix display panel, however, the reflection factor from the panel is small 50 due to the roughness on the surfaces of the pixel electrode and the reflective layer, with the result that it has been so far impossible to obtain a brightness (light intensity) required for the practical use.
To overcome this problem, for instance, U.S. Pat. No. 55 5.056,895 discloses such a method that: after the pixel electrodes have been formed, an organic insulation substance (polyimide) is applied onto the surfaces of the pixel electrodes, and then a reflective film is formed for planarization (leveling) of the surface of the display panel. Even if a 60 liquid such as polyimide is simply applied on the surfaces of the pixel electrodes, however, since the base surface (the pixel electrodes) thereof is relatively rough, it is extremely difficult to finish the surface of the display panel into a mirror surface. 65
Further, THE JOURNAL OF THE INSTITUTE OF TELEVISION ENGINEERS OF JAPAN Vol. 44. No. 5, pp.
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544 to 549 (1990) discloses such a technology that the surfaces of the pixel electrodes are finished into mirror surface by mechanically polishing the surfaces thereof. In this method, however, since the surfaces of the pixel electrodes are very easy to be scratched, when the pixel electrodes are directly polished, there exists a possibility that the pixel electrodes are easily damaged. In addition, when the pixel electrodes are simply polished mechanically, the polished surfaces thereof are finely scratched. Therefore, when the pixels are used as the reflective type active matrix display, there exists the case where scratch noise is generated. As a result, it has been impossible to perfectly planarize the surfaces of the pixel electrodes by only the mechanical polishing process.
As described above, the transmissive type active matrix display panel is difficult to be microminiaturized, so that it has been difficult to manufacture the small-sized enlarged projection type liquid crystal display of high resolution. On the other hand, the reflective type active matrix display panel is small in reflection factor from the panel, so that it has been difficult to obtain a brightness high enough for practical use. In addition, the study of increasing the reflection factor of the reflective type active matrix display panel has not been so far made sufficiently.
SUMMARY OF THE INVENTION
Accordingly, it is the object of the present invention to provide a reflective type active matrix display panel of high reflection factor, and thereby to realize a small-sized enlarged projection type liquid crystal display of high resolution.
To achieve the above-mentioned object, the present invention provides a method of manufacturing a reflective type active matrix display panel having pixel electrodes formed on a substrate, comprising the steps of: forming an insulating film all over the substrate including the pixel electrodes; planarizing a surface of the insulating film by use of a polishing material including an etchant for etching the insulating film; and forming a reflective layer and a liquid crystal layer on the planarized insulating film.
The surfaces of the pixel electrodes may also be planarized by use of a polishing material including an etchant for etching the pixel electrodes.
The present invention further provides a method of manufacturing a reflective type active matrix display panel having pixel electrodes formed on a substrate, comprising the steps of: forming an insulating film all over the substrate including the pixel electrodes; planarizing surfaces of the pixel electrodes and the insulating film by use of a polishing material including an etchant for etching the insulating film and the pixel electrode; and forming a liquid crystal layer on the planarized pixel electrodes.
In the manufacturing methods, the etchant is may be of at least either of potassium hydroxide and ammonium hydroxide. Further, the planarizing material may be selected from the group consisting of fumed silica, colloidal silica, and cerium oxide.
The present invention provides a reflective type active matrix display panel, comprising: semiconductor pixel transistors arranged into a matrix pattern on a substrate; pixel electrodes connected to the transistors; an insulating film formed all over the substrate including the pixel electrodes, a surface of the insulating film being planarized by use of a polishing material including an etchant for etching the insulating film; a reflective layer and a liquid crystal layer formed on the planarized insulating film; wirings arranged
