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
2003-05-02
2004-10-19
Kang, Donghee (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, C257S066000, C257S074000, C349S124000, C349S134000, C349S138000, C349S143000
Reexamination Certificate
active
06806500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to technical fields of electro-optical devices and electronic apparatuses. More particularly, the invention relates to an electro-optical device including a pair of substrates which sandwich an electro-optical material, such as a liquid crystal, and various lines provided on the substrates, and to an electronic apparatus including such an electro-optical device.
2. Description of Related Art
The related art includes an “active matrix electro-optical device,” which includes an electro-optical material, such as a liquid crystal, pixel electrodes arrayed in a matrix, thin film transistors (hereinafter “TFTs”) connected to the respective pixel electrodes, and scanning lines and data lines which are connected to the respective TFTs, the scanning lines extending in parallel in the row direction, the data lines extending in parallel in the column direction, thus enabling active matrix driving.
In addition to a TFT array substrate having the construction described above, such an electro-optical device includes a counter substrate provided with a common electrode which is opposed to the TFT array substrate with the electro-optical material, such as a liquid crystal, therebetween. Other structures that are provided on the TFT array substrate in addition to the TFTs, scanning lines, data lines, etc., include storage capacitors connected to the TFTs in order to store electric fields applied to the pixel electrodes for a predetermined period of time, interlayer insulating films to prevent short circuiting between the individual components, and contact holes formed in the interlayer insulating films in order to provide necessary electrical connection between the individual elements.
SUMMARY OF THE INVENTION
However, the related art electro-optical device is subject to a drawback. That is, the TFT has a relatively short lifetime. The reason for this is that, if moisture enters the semiconductor layer and the gate insulating film constituting the TFT, positive charges are generated due to the diffusion of water molecules into the interface between the gate insulating film and the semiconductor layer, resulting in an increase in the threshold voltage Vth in a relatively short period of time. Such a phenomenon is more common in a p-channel TFT.
If the TFT has a relatively short lifetime as described above, the entire electro-optical device is inevitably affected, and a degradation in image quality is observed from a relatively early stage, which may result in device failure.
Such an inconvenience becomes more serious when an electro-optical device is used in a high-temperature, high-humidity environment. The reason for this is that the chance of moisture entry into TFTs increases. When an electro-optical device is used as a light valve for a liquid crystal projector, since relatively strong light emitted from a light source built in the liquid crystal projector is applied to the electro-optical device or the light valve, it is subjected to high temperature. This is a severer environment from the viewpoint of TFT life, and the problem described above easily becomes noticeable.
Additionally, although the TFT array substrate is provided with various components, such as TFTs, scanning lines, and data lines, and interlayer insulating films to isolate these components from each other, even the interlayer insulating films are not capable of sufficiently preventing moisture from entering the TFTs.
The present invention addresses the above and/or other problems, and provides an electro-optical device in which entry of moisture into TFTs is reduced or minimized to prolong the operational life. The invention also provides an electronic apparatus including such an electro-optical device.
In one aspect of the present invention, in order to address or overcome the above, an electro-optical device includes thin film transistors corresponding to intersections of scanning lines and data lines above a first substrate, pixel electrodes corresponding to the thin film transistors, and a nitride film disposed at least on the surfaces of the data lines.
In the electro-optical device of the present invention, the operation of the thin film transistors is controlled through the scanning lines, and image signals are applied to the pixel electrodes through the thin film transistors, thereby enabling so-called “active matrix driving”.
In particular, in the present invention, since the nitride film is disposed at least on the surfaces of the data lines, the following effect can be obtained. That is, it is possible to reduce or prevent moisture from entering the thin film transistors, or gate insulating films and semiconductor layers constituting the thin film transistors. The reason for this is that the nitride film has a dense structure.
Consequently, in the electro-optical device of the present invention, a stable operation can be achieved for a relatively long period of time.
In the present invention, the nitride film must be formed at least on the surfaces of the data lines, which means that the nitride film may be formed on the scanning lines, or in some cases, may be formed over the entire surface of the substrate. The “nitride film” in the present invention is represented by a silicon nitride film (SiN film, SiON film, or the like). Of course, a nitride film other than this is acceptable.
In one exemplary embodiment of the present invention, in the electro-optical device, the pixel electrodes are arrayed in a matrix, the scanning lines and the data lines intersect with each other corresponding to the matrix of the pixel electrodes, and the nitride film is disposed at least over the surfaces of the data lines and the scanning lines.
In this exemplary embodiment, since the scanning lines and the data lines are formed in a grid pattern or the like as a whole, the nitride film disposed thereon may also be formed in a grid pattern. Consequently, the effect of preventing moisture entry can be obtained more reliably.
The fact that the nitride film can be formed in such a pattern means that it is possible to have a construction in which the nitride film is not substantially placed over the entire surfaces of the pixel electrodes. In such a case, the overall transmittance of the electro-optical device can be maintained. Consequently, in this exemplary embodiment, due to the presence of the nitride film, in addition to the effect of prolonging life, it is possible to provide a brighter image with high quality. According to the research by the present inventors, it has been confirmed that the transmittance decreases by approximately 4% when the nitride film is left over the entire surface compared with the case in which no nitride film is provided.
Additionally, “being arrayed in a matrix” is a broad concept which includes a structure in which the individual pixel rows and the individual pixel columns extend straight vertically and horizontally, respectively, and also includes a structure in which the individual pixel rows and the individual pixel columns are two-dimensionally arrayed in a meandering manner or in a staggered manner. Therefore, it is to be understood that “the shape corresponding to the matrix” must be construed bearing the above in mind.
In another exemplary embodiment of the present invention, in the electro-optical device, the nitride film is formed in the periphery of an image display region that is defined by the region including the pixel electrodes, the scanning lines, and the data lines.
In this exemplary embodiment, the nitride film is also formed in the periphery of the image display region in addition to at least on the surfaces of the data lines or at least on the surfaces of the data lines and the scanning lines. Consequently, the effect of reducing or preventing moisture entry can be obtained more reliably.
In this exemplary embodiment, more preferably, the nitride film extends only on the data lines in addition to in the periphery of the image display region.
In such a case, as described above, since it is possible t
Kang Donghee
Oliff & Berridg,e PLC
Seiko Epson Corporation
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