Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-09-11
2003-02-25
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S110000, C349S111000
Reexamination Certificate
active
06525787
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and particularly relates to a liquid crystal display device suitable for a projection-type display apparatus.
In a liquid crystal display device using a polycrystalline silicon thin film transistor (hereinafter referred to as “polycrystalline Si-TFT”) having a top gate structure or a planer structure as a switching element for a pixel electrode, since the active layer of the polycrystalline Si-TFT is formed in the undermost layer of the driving substrate in which the polycrystalline Si-TFT is formed, light incident from the side of the driving substrate is incident directly on the active layer of the polycrystalline Si-TFT.
In general, light incident from a counter substrate is shielded by a black matrix for shielding the part other than pixel openings, which is provided on the counter substrate or as a layer in the driving substrate upper than the polycrystalline Si-TFT (i.e., the counter substrate side with respect to the polycrystalline Si-TFT), so as to simultaneously shield incident light to the polycrystalline Si-TFT. Furthermore, because the light from a light source is generally incident from the counter substrate side, the light incident from the driving substrate is so-called stray light such as return light of the light passing through the panel.
The polycrystalline silicon has less light sensitivity than the amorphous silicon. However, the recent liquid crystal display device is often used under a large amount of light such as a projector, and thus a light leakage current cannot be ignored in the polycrystalline Si-TFT.
SUMMARY OF THE INVENTION
The present invention is a liquid crystal display device for solving the above-described problems.
That is, the invention relates to a liquid crystal display device comprising a driving substrate having thereon a pixel electrode and a pixel transistor for driving the pixel electrode, the pixel transistor comprising a top gate type or planer type thin film transistor, wherein a light-shielding layer is provided as an underlayer of the pixel transistor. At least edge parts of a source/drain of the pixel transistor are shielded from light by the light-shielding layer.
In the liquid crystal display device of the invention comprising a driving substrate having thereon a pixel electrode and a pixel transistor for driving the pixel electrode, because the light-shielding layer is provided as an underlayer of the pixel transistor comprising a top gate type or planer type thin film transistor, stray light, i.e., return light of the light passing through the panel and incident on the pixel transistor from the side of the driving substrate, is shielded by the light-shielding layer and is not incident on the pixel transistor. The generation of a light leakage current is suppressed. This effect of suppression of a light leakage current can be obtained when at least the edge parts of the source/drain of the pixel transistor are shielded from light.
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Duong Tai
Kananen, Esq. Ronald P.
Rader & Fishman & Grauer, PLLC
Sikes William L.
Sony Corporation
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