Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-03-10
2004-02-10
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S044000, C349S110000, C349S138000, C345S055000, C257S059000, C257S072000
Reexamination Certificate
active
06690434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a circuit comprising thin film transistors (hereinafter referred to as TFT) over a substrate having an insulating surface, and a manufacturing method therefor. In particular, the present invention relates to an electrooptic device typified by an active matrix liquid crystal display device in which a pixel matrix circuit and driving circuits disposed around thereof are provided on one substrate and to an electronic apparatus carrying such electrooptic device. It is noted that a semiconductor device refers to devices in general which function by utilizing the semiconductive characteristics including the above stated electrooptic device and the above stated electronic apparatus carrying the electrooptic device in the present specification.
2. Description of the Related Art
The technology for fabricating thin film transistors (TFT) on a low cost glass substrate has come to be rapidly developed in these days because the demand on an active matrix liquid crystal display has been increasing. The active matrix liquid crystal display is what a thin film transistor is disposed in each of several tens to several millions of pixels disposed in a matrix to control electric charge which goes in and out of each pixel electrode by the switching function of the thin film transistor.
Each pixel TFT is controlled by a circuit TFT dispose in the driver circuit region formed in the peripheral of the pixel matrix circuit.
As such, an active matrix liquid crystal display device has an integrated circuit in which pixel TFTs disposed in matrix as pixel matrix circuit, and circuit TFTs disposed in the driver circuit region, are integrated over the same substrate.
In general, a black matrix (BM) having light shielding property is disposed over wirings and transistor where visible radiation need not to transmit when the image is displayed by driving active matrix liquid crystal display device.
This is effective for preventing the thin film transistors to deteriorate by light-induced effect in the active layer (semiconductor layer), and for preventing eyes to recognize turbulence of the displayed image that occurs when the electric field is disturbed. In particular, disposition of shielding film is indispensable for the active matrix liquid crystal display device for projector use where a light of approximately 1,000,000 lux is applied, because the deterioration by light-induced effect is a major problem.
A metal thin film having light shielding property such as titanium or chromium film, or a resin material with dispersed black pigments may be used as shielding film. Conventionally the shielding film was formed on the opposing substrate side for the ease of manufacture.
However, in the cell assembly process, the alignment accuracy with the opposing substrate has been no good heretofore, and the circumstance was such that the desired position could not be shielded unless the shielding film was formed with a large alignment margin.
Fabricating shielding film with a large alignment margin leads to the decrease in the aperture ratio of the pixel matrix circuit, and thus was not preferable.
Further, the alignment margin is too large when disposing the shielding film on the opposing substrate side when the alignment technology remains as the present is, and the fear of incapability of corresponding to the device element miniaturization that should proceed in future, is suggested.
Accordingly a “BM on TFT” structure in which the shielding film is formed on the active matrix substrate side has become the mainstream recently. In this case, a shielding film is formed either upper or lower layer of the pixel electrode by interposing an interlayer insulating film, and the desired position can be shielded from the light.
The above stated “BM on TFT” structure enables reduction of the alignment margin to the least possible when forming shielding film, and is a very effective means to increase the aperture ratio.
As stated above, while the “BM on TFT” structure has various advantages, such effectiveness is displayed only when in the pixel matrix circuits, and drawbacks are caused in the driver circuit region.
A high speed operation is required for the circuit TFT disposed in the driver circuit region compared to that of the pixel TFT for its use. However, when the shielding film is formed over the driver circuit, a problem such as decrease in the operation speed by parasitic capacitance formed between the shielding film and the circuit TFT, arises.
The image display speed becomes slow as the operation speed of the circuit TFT decreases, and various problems such as the blink or the flicker of the displayed image should arise. In other words, extremely degrading the quality as an active matrix liquid crystal display device has become a problem.
SUMMARY OF THE INVENTION
The invention disclosed in the present specification has an object to provide a technology to realize an active matrix liquid crystal display device capable of high quality image display by solving above stated problems.
The present invention provides an active matrix liquid crystal display device comprising:
a first substrate having a source signal line driver circuit and a first shielding film; and
a second substrate having a second shielding film, characterized by:
providing all or a portion of the source signal line driver circuit over all or a portion of the second shielding film; and
providing a portion of the second shielding film over a portion of the first shielding film.
The present invention provides an active matrix liquid crystal display device comprising:
a first substrate having a source signal line driver circuit, a gate signal line driver circuit, and a first shielding film; and
a second substrate having a second shielding film, characterized by:
providing all or a portion of the source signal line driver circuit over all or a portion of the second shielding film;
providing all or a portion of the gate signal line driver circuit over all or a portion of the second shielding film; and
providing a portion of the second blac matrix film over a portion of the first shielding film.
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Koyama Jun
Murakami Satoshi
Tanaka Yukio
Yamazaki Shunpei
Chowdhury Tarifur R.
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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