Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2001-03-16
2003-08-26
Munson, Gene M. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S306000, C257S435000, C349S043000, C349S111000
Reexamination Certificate
active
06610997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the technical field of an active matrix driving system electro-optical device. Particularly, the present invention relates to the technical field of an electro-optical device which includes a pixel electrode and a pixel switching thin film transistor (referred to as “TFT” hereinafter), which are provided with electrical conduction therebetween, and a storage capacitor and a light-shielding film which are provided in a laminated structure formed on a substrate.
2. Description of Related Art
In a conventional electro-optical device such as a TFT-driven active matrix driving system liquid crystal device, a scanning signal is supplied to a gate electrode of a TFT through a scanning line to turn the TFT on, and an image signal supplied to a source region of a semiconductor layer through a data line is supplied to a pixel electrode through the region between the source and drain of the TFT. Such an image signal is supplied to each of a plurality of pixel electrodes for only a short time through each of a plurality of TFTs. Therefore, in order to hold the voltage of the image signal supplied through a TFT over a longer time than the time of the on state, a storage capacitor is generally added to each pixel electrode.
When light is incident on at least a portion of a channel region or junction regions between the channel region and source-drain regions, and the source-drain regions adjacent to the junction regions in a semiconductor layer which constitutes the TFT, light excitation occurs to change the transistor properties of the TFT, for example, increase a leakage current in the on state. Therefore, for example, in an electro-optical device of a type in which strong light is incident, such as a transmissive electro-optical device for a projector, in order to prevent such a change in the properties of the TFT with light incidence, a light-shielding film is provided on a counter substrate on the incidence side of incident light to cover the space between the pixel electrodes including the channel region of the TFT, or an opaque wide data line which includes an Al film or the like is formed to cover the channel region. Furthermore, on the outgoing side, a light-shielding film is provided below the TFT to shield light reflected by the back, and returned light such as incident light from another electro-optical device, which passes through a synthesis optical system, in a projector that includes a combination of a plurality of electro-optical devices.
SUMMARY OF THE INVENTION
In this type of electro-optical device, improvement in quality of a display image is strongly demanded, and in order to satisfy this demand, it is important that a pixel aperture region of each pixel through which display light is transmitted is widened relative to a non-pixel aperture region through which display light is not transmitted, to increase the pixel aperture ratio while decreasing the pixel pitch, and enlarge a storage capacitor added to each pixel electrode.
The storage capacitor is generally formed by utilizing the non-pixel aperture region, and it is thus basically difficult to form the storage capacitor in the pixel aperture region. Therefore, the non-pixel aperture region where the storage capacitor can be formed is narrowed as the pixel aperture region is widened to increase the pixel aperture ratio. However, there is a problem in which the pixel aperture ratio is decreased as the non-pixel aperture region is widened to enlarge the storage capacitor.
It is also very important to sufficiently shield incident light and reflected light in a channel region of TFT or a region (referred to as the “adjacent region of channel” hereinafter) adjacent to the channel region, for example, a lightly-doped region of LDD structure TFT, as described above. Namely, a decrease in the pixel pitch causes significant deterioration in image quality resulting from only a slight change in properties of TFT.
However, a total plane region where a light-shielding film or a film having a light shielding function can be arranged is narrowed by increasing the pixel aperture ratio, thereby causing the problem of causing difficulties in completely shielding TFT from light. Furthermore, a decrease in the pixel pitch causes a problem in which even with incident light or reflected light slightly inclined with the substrate surface, light finally enters the channel region or the adjacent region of channel due to the occurrence of multiple reflection in a laminated structure after oblique incidence. Particularly, when the incidence side is covered with a data line which includes an Al film having high reflectance, shielding against incident light approaches perfection with widening of the data line, but widening the data line conversely causes a problem difficult to resolve in which reflected light is reflected by the side facing TFT or subsequently reflected by the TFT-facing surface of a light-shielding film formed below TFT, and the light is likely to be finally incident on the channel region or the adjacent region of channel. Furthermore, shielding against reflected light approaches perfection with widening of the light-shielding film formed below TFT, but widening the light-shielding film formed below TFT causes a problem difficult to resolve in which oblique incident light is reflected by the inner surface of the light-shielding film, or subsequently reflected by the inner surfaces of the data line, and is likely to be finally incident on the channel region or the adjacent region of channel. Particularly, in an electro-optical device for a projector which uses incident light or reflected light having very high intensity per unit region, the above problems are very important for improving image quality.
The present invention has been achieved at least in consideration of the above problems, and an object of the present invention is to provide an electro-optical device in which a pixel aperture ratio can be increased, a storage capacitor can be enlarged, and a high quality image can be displayed.
Another object of the present invention is to provide an electro-optical device in which a change in properties of pixel switching TFT due to incident light or reflected light can be decreased while increasing the pixel aperture ratio, and a high quality image can be displayed.
(1) In a first exemplary aspect of the present invention, an electro-optical device may include a scanning line formed above a substrate, a data line crossing the scanning line, a thin film transistor connected to the scanning line and the data line, a pixel electrode connected to a drain region of the thin film transistor, and a first storage capacitor formed by a plurality of layers between the scanning line and the data line.
In this exemplary embodiment of the present invention, the first storage capacitor is formed by a plurality of layers between the scanning line and the data line by utilizing the laminated structure to enlarge the storage capacitor, thereby providing an electro-optical device capable of displaying a high quality image.
(2) In another exemplary embodiment of the first aspect of the invention, in the electro-optical device, the first storage capacitor may include a first capacitor electrode, an insulating film facing the first capacitor electrode, and a second capacitor electrode opposed to the first capacitor electrode with the insulating film provided therebetween to serve as a relay film for electrically connecting a drain region of the thin film transistor and the pixel electrode.
In this exemplary embodiment of the present invention, the second capacitor electrode which forms the first storage capacitor is formed as the relay film for electrically connecting the drain region of the thin film transistor and the pixel electrode, whereby the problem of causing a difficulty in electrically connecting the pixel electrode and a semiconductor layer due to a long distance therebetween can be solved. Also, the second capacitor electrode can prevent etching penetra
Munson Gene M.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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