Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2001-07-17
2004-08-03
Tran, Thien F (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S066000, C257S072000, C257S098000, C257S294000
Reexamination Certificate
active
06770908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the technical field of an electro-optical device of an active matrix drive system, and more particularly, to the technical filed of an electro-optical device of a type having pixel switching thin film transistors (hereinafter, referred to as TFTs) disposed in a laminated layer structure on a substrate.
2. Description of Related Art
In electro-optical devices of a TFT active matrix drive system, when incident light beams are irradiated on the channel region of a pixel switching TFT associated with each pixel, a current is generated thereto by the excitation caused by the light beams so that the characteristics of the TFT are changed. In particular, in electro-optical devices used for light bulbs of projectors, since incident light beams have high intensity, it is important to shade light beams incident on the channel region and its peripheral region of a TFT. Thus, the channel region and its peripheral region are conventionally shaded by a shading film disposed at a confronting substrate to prescribe the opening region of each pixel or by a data line passing on the TFT and formed of a metal film of Al or the like. Japanese Unexamined Patent Application Publication No. 9-33944 discloses a technology for reducing light beams incident on a channel region by a shading film formed of a-Si (amorphous silicon) having a large refractive index. Further, a shading film formed of, for example, a metal having a high melting point, is sometimes disposed on a TFT array substrate at a position facing a pixel switching TFT (that is, below the TFT). The shading film also disposed below the TFT can prevent light beams reflected on the back surface of the TFT array substrate from being incident on the TFT of the electro-optical device as well as can prevent projected light beams, which have passed through a prism and the like when one optical system is constructed by a combination of a plurality of electro-optical devices through the prism and the like, from being incident on the TFT of the electro-optical device.
SUMMARY OF THE INVENTION
However, the above-mentioned various types of the shading technologies have the following problems. That is, first, according to the technology for forming the shading film on the confronting substrate and on the TFT array substrate, the shading film is considerably separated from the channel region through, for example, a liquid crystal layer, electrodes, an interlayer insulation film when observed three-dimensionally, and light beams incident obliquely between the shading film and the channel region cannot be sufficiently shaded. In particular, in small electro-optical devices used as light bulbs of projectors, light beams incident thereon are obtained by stopping light beams projected from a light source through a lens and that contain an obliquely incident light component in an amount which cannot be disregarded. Thus, it is a problem in practical use that such obliquely incident light beams are not sufficiently shaded.
In addition to the above problems, after light beams, which have traveled into an electro-optical device from a region having no shading film, and are reflected by a shading film and the inner surface of a data line (that is, the surface thereof facing a channel region), the reflected light beams, or light beams, which are created when the reflected light beams are further reflected by the shading film and the inner surface of the data line a plurality of times (hereinafter, referred to as “multipath-reflected light beams”), may finally reach the channel region of a TFT. Further, according to the technology for shading light beams by a data line, it is basically difficult for the data line to sufficiently shade light beams, because the data line is formed in a striped shape which extends perpendicularly to a scanning line when observed on a plan view. It is also necessary to dispose a thick interlayer insulation film therebetween in such a degree that the adverse affect of the capacitance coupling between the data line and the channel region can be disregarded.
Further, according to the technology described in Japanese Unexamined Patent Application Publication No. 9-33944, a relatively thick interlayer insulation film must be laminated between a gate electrode and an a-Si film to reduce the adverse affect of the capacitance coupling therebetween to form an a-Si film on a gate line. As a result, the additional formation of the a-Si film, the interlayer insulation film, and the like makes a laminated structure complex and increases its size. It is also difficult to sufficiently shade obliquely incident light beams and inner-surface reflected light beams. In particular, since electro-optical devices are miniaturized and the pixel pitches thereof are greatly narrowed to cope with a recent requirement for enhancing the quality of a displayed image, it is more difficult to sufficiently shade light beams by the various types of the above-mentioned conventional technologies. Accordingly, a problem arises in that the quality of a displayed image is lowered by flickering of the image and the like caused by the change of the characteristics of TFTs.
It should be noted that, while it is contemplated to increase a region where a shading film is formed to increase the light resistant property, an increase in the region where the shading film is formed causes a problem in that it is fundamentally difficult to increase the opening ratio of each pixel in order to enhance the brightness of a displayed image.
It is therefore an object of the present invention, which was made in view of the above-mentioned problems, to provide an electro-optical device which is excellent in its light resistant property, and which has a relatively large opening ratio of each pixel and can display an image of high quality.
To solve the above problems, an electro-optical device of the present invention includes a pair of substrates, an electro-optical substance interposed between the pair of substrates, pixel electrodes formed on one of the pair of substrates, thin film transistors connected to the pixel electrodes, a shading layer that covers at least the channel regions of the thin film transistors, and a light absorption layer interposed between the shading layer and the thin film transistors.
According to the electro-optical device of the present invention, at least the channel regions of the thin film transistors connected to the pixel electrodes are shaded by the shading layer.
When a shading layer formed of a metal film having a shading property such as an Al (aluminum) film, a Cr (chromium) film, or the like is generally used, light beams incident on the thin film transistors from a side where the shading layer is disposed basically can be sufficiently shaded by reflecting the light beams by the surface, which does not face the thin film transistors, of the shading layer (that is, by the outer surface of the shading layer in the electro-optical device). More specifically, when the shading layer is disposed on a side where light beams (for example, projected light beams when the electro-optical device is applied to a projector) are incident on the thin film transistors, the incident light beams can be shaded by the outer surface of the shading layer. Otherwise, when the shading layer is disposed on a side from which incident light beams emerge with respect to the thin film transistors, return light beams (for example, light beams reflected on a back surface when the electro-optical device is applied to the projector, light beams passing through a composite optical system from other light bulb when a plurality of electro-optical devices are used in combination as a light bulb as in a case in which the electro-optical devices are applied to a double-panel type projector) can be shaded by the outer surface of the shading layer. However, return light beams, which pass aside the thin film transistors from an opposite side of the shading layer and are oblique to the substrate (for example, when the
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