Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-02-27
2004-03-09
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S152000
Reexamination Certificate
active
06704068
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal device, a projection type display device and a method of manufacturing the liquid crystal device. Particularly, the present invention relates to a light shielding structure in a liquid crystal device comprising a thin film transistor (referred to as “TFT” hereinafter) as a pixel switching element.
2. Description of Related Art
For a conventional active matrix driving system liquid crystal device a configuration is brought into practical use in which pixel electrodes are formed in a matrix on a glass substrate and a pixel switching TFT comprising a semiconductor layer of an amorphous silicon film or a polysilicon film is formed in correspondence with each of the pixel electrodes so that a voltage is applied to each pixel electrode through the TFT to drive a liquid crystal. In a liquid crystal device comprising pixel switching polysilicon TFT, TFT'S for driving circuits comprising peripheral driving circuits such as a shift register circuit, etc. for driving and controlling a screen display portion can be formed in substantially the same process as the pixel switching TFT, and thus the liquid crystal device attracts attention because it is suitable for high integration.
In such an active matrix system liquid crystal device, in order to achieve high definition of the display, a light shielding film referred to as a black matrix (or black stripes) or the like and made of a chromium film, aluminum film, or the like is formed on an opposite substrate. The light shielding film is also formed to overlap with the pixel switching TFT so as to prevent the light incident on the opposite substrate from entering the channel region and junctions of the pixel switching TFT and prevent a leak current from flowing through the pixel switching TFT. (This light shielding film is referred to as “third shielding film hereinafter.)
However, the leak current due to light is not only due to the light incident on the opposite substrate side but also irradiation of the channel region of the pixel switching TFT with the light reflected by a polarizing plate or the like disposed on the back side of the liquid crystal device substrate.
As a method of preventing the leak current due to such reflected light (return light), Japanese Examined Patent Publication No. 3-52611 discloses an invention in which a light shielding film is also provided on the lower layer side of the channel region of the pixel switching TFT. However, in the disclosed invention, the potential of the light shielding film is not fixed, and there is thus a problem in which TFT characteristics vary or deteriorate due to the parasitic capacitance between the semiconductor layer of the TFT and the light shielding film.
On the other hand, the peripheral driving circuits are increasingly demanded to be highly integrated with an increase in the number of pixels and miniaturization of an electronic apparatus containing the liquid crystal device. Particularly, in a liquid crystal device containing the peripheral driving circuits provided on the same substrate, as a technology for achieving high integration of circuits, a multilayer wiring technology is used in which wiring is provided by forming metallic films of aluminum or the like in multiple layers with insulating films between the respective layers. However, this technology has a problem in that the number of steps and production cost are increased by forming the multilayer wiring structure.
Also, as the speed of the operation frequency of the active matrix driving system liquid crystal device increases, attempts are made to improve the quality of the semiconductor film by employing a SOI technology, a recrystallization technology using laser annealing, or the like in order to improve TFT characteristics. However, such a method of improving TFT characteristics has the problem of increasing the variations in characteristics and the problem of complicating the manufacturing process.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a technology for suppressing a leak current due to the influence of the light reflected by a polarizing plate or the like in pixel switching TFTs of a liquid crystal device and a projection type display device comprising the liquid crystal device, to stabilize the characteristics of the pixel switching TFTs.
Another object of the present invention is to provide a technology for achieving high integration of driving circuits provided in the periphery of a display region in a liquid crystal device without increasing the number of the steps of the manufacturing process.
A further object of the present invention is to provide a technology for improving TFT characteristics in a liquid crystal device without increasing the number of the steps of the manufacturing process.
In order to solve the above problems, the present invention provides a liquid crystal device comprising a liquid crystal device substrate including a display region in which pixels are formed in a matrix by a plurality of data lines and a plurality of scanning lines, peripheral driving circuits connected to at least one of the data lines and the scanning lines on the outside of the display region, and a plurality of thin film transistors connected to the data lines and the scanning lines; and a liquid crystal held between the liquid crystal device substrate and an opposite substrate;
wherein the liquid crystal device substrate has a first conductive light shielding film provided on at least the lower layer side of the channel regions of the thin film transistors so that the light shielding film and the channel regions overlap each other with an interlayer insulation film therebetween, and a constant voltage is applied to the first light shielding film.
In the liquid crystal device in accordance with the present invention, since the first light shielding film is formed to overlap with the channel regions of the thin film transistors, i.e., the pixel switching TFTs, connected to the data lines and the scanning lines, even if light is reflected from the back side of the liquid crystal device substrate, the reflected light does not enter the channel regions of the pixel switching TFTs. Therefore, no leak current occurs in the pixel switching TFTs due to the light reflected from the back side of the liquid crystal device substrate. In addition, since the potential of the first light shielding film is fixed at the constant voltage power source on the low-potential side of a scanning line driving circuit, the TFT characteristics neither change nor deteriorate due to the influence of the parasitic capacitance between the semiconductor layers of the TFTs and the first light shielding layer.
In the present invention, in order to apply a constant voltage to the first light shielding film, the first light shielding film may comprise channel shielding portions which respectively overlap with the channel regions, and wiring portions extended from the channel shielding portions in order to apply a constant voltage to the channel shielding portions.
In this case, the wiring portions of the first light shielding film are respectively extended from the channel shielding portions to the outside of the display region along the signal lines of at least either of the scanning lines and the data lines, and are connected to constant potential wiring formed between layers different from the first light shielding film at least through contact holes of the interlayer insulation film in the outside of the display region.
In some cases, the wiring portions of the first light shielding film are respectively extended from the channel shielding portions to the outside of the display region along both signal lines of the scanning lines and the data lines, and are connected to constant potential wiring formed between layers different from the first light shielding film at least through contact holes of the interlayer insulation film on the outside of the display region.
In the present invention, eac
Seiko Epson Corporation
Ton Toan
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