Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-09-17
2002-05-14
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S151000
Reexamination Certificate
active
06388723
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention includes a liquid crystal display device, for example, used for a VTR (Video Tape Recorder) with a camera integrated thereto, a liquid crystal projector and the like, and particularly to a liquid crystal display device having a so-called on chip black matrix (optically compensated birefringence or OCB) structure in which a metal light shielding layer referred to as a black mask is provided on the driving substrate side.
In recent years, as an electronic apparatus with a liquid crystal display device, such as a liquid crystal projector, has been popularized, the liquid crystal display device has increasingly been required to have high performance, and improvement to achieve a liquid crystal display device having higher definition and higher luminance has progressed. Such a liquid crystal display device conventionally comprises a substrate (referred to as a “driving substrate” hereinafter) on which pixel electrodes, thin film transistors (TFTs) for controlling the respective electrodes, auxiliary capacitor or capacitance Cs etc. are formed, a substrate (referred to as a “counter substrate” hereinafter) on which a color filter (in the case of a color liquid crystal panel), a metal light shielding layer (black mask), etc. are formed, and a liquid crystal layer held between both substrates.
Although the liquid crystal display device having the above construction requires precise alignment between the driving substrate and the counter substrate which are spaced, precise alignment becomes difficult as the definition of pixels increases. Therefore, a so-called on chip color filter structure is proposed in which a color filter is formed on the driving substrate side (refer to Japanese Patent Unexamined Publication No. 254217). In this on chip color filter structure, since the color filter is overlapped with each of the pixel electrodes, no parallax occurs between the pixel electrodes and the color filter, and the effective opening ratio of the pixel portion can be increased, as compared with a conventional structure in which a color filter is provided on the counter substrate side. There is also the advantage that since substantially no error occurs in alignment between the pixel electrodes and the color filter, a high opening ratio can be maintained even if the pixel portion becomes fine. Besides the on chip color filter structure, in order to increase the effective opening ratio of the display device having a so-called on chip black matrix structure has recently been proposed in which a metal light shielding layer (black mask) is also formed on the driving substrate.
FIG. 6
shows a sectional structure of the peripheral circuit portion (including a horizontal driving circuit, a vertical driving circuit, etc.) around the effective pixel portion in a liquid crystal display
100
having the above structure. Like the conventional effective pixel portion, the conventional peripheral circuit portion comprises a liquid crystal layer
118
held between a driving substrate
110
and a counter substrate
120
. On the driving substrate
110
is formed a pattern of a polycrystalline silicon film
111
as a semiconductor thin film which constitutes the TFTs, and an insulating film (SiO2)
112
is formed on the polycrystalline silicon film
111
. On the insulating film
112
is formed a metal interconnecting layer
113
comprising aluminum (Al). The potential of this metal interconnecting layer
113
is set to potential Vss. On the metal interconnecting layer
113
are laminated in turn interlayer insulating films
114
a
and
114
b
. On the interlayer insulating film
114
b
is formed a metal light shielding layer (black mask)
115
having a pattern reverse to the metal interconnecting layer
113
, and a flattening layer
116
is formed on the pattern of the metal light shielding layer
115
. On the other hand, on the counter face of the counter substrate
120
is formed a counter electrode
119
. The liquid crystal layer
118
is held between the counter electrode
119
and the driving substrate
110
.
In the liquid crystal display device
100
, the metal light shielding layer
115
on the driving substrate side is set to the same potential as the potential of the counter electrode
119
on the counter substrate side and an auxiliary capacitor or capacitance Cs of the pixel portion. This is a measure for preventing application of a DC voltage to the liquid crystal layer
118
held between the driving substrate
110
and the counter substrate
120
. However, not only the effective pixel potion, but also the metal light shielding layer
115
on the peripheral circuit portion are set to the same potential. Therefore, a strong electric field occurs due to a potential difference between the metal light shielding layer
115
and the metal interconnecting layer (Al wiring layer)
113
at potential Vss, and impurity ions present in the periphery are attracted. As a result, water chemically reacts with aluminum (Al) on the cathode (the metal interconnecting layer
113
) side, thereby causing disconnection due to corrosion of aluminum. The metal light shielding layer
115
on the peripheral circuit portion is formed in a pattern reverse to the metal interconnecting layer
113
under the metal light shielding layer
115
, i.e., so that both layers do not overlap each other, as viewed from the upper side. Therefore, in a portion where the pattern of the metal light shielding layer
115
is absent, incident light is cut off by the metal interconnecting layer
113
. Thus, in a portion where the pattern of the metal interconnecting layer
113
is large, large quality of light is incident, and the above chemical reaction of aluminum is accelerated by light and heat, thereby more easily causing disconnection. Further, this disconnection allows light irradiation of the active layer
11
of the thin film transistors (TFTs) provided under the metal interconnecting layer
113
, and thus has an adverse effect on the operation, such as variation in operation points of the TFTs. Particularly, when the liquid crystal display device
100
is used for a projector or the like, this brings about a large problem with respect to reliability. When electrical leakage from the metal interconnecting layer
113
of the peripheral circuit portion occurs, the liquid crystal display device
100
becomes defective regardless of the position of leakage.
SUMMARY OF THE INVENTION
The present invention has been achieved in consideration of the above problems, and an object of the invention is to provide a liquid crystal display device which is capable of suppressing occurrence of an electric field between a metal light shielding layer and a metal interconnecting layer in the peripheral circuit portion to prevent disconnection of the metal interconnecting layer, and which has improved reliability under conditions where light and heat are present.
In order to achieve the object, in accordance with an aspect of the present invention, there is provided a liquid crystal display device comprising a first substrate in which a pixel portion having a plurality of pixel electrodes, and a peripheral circuit portion disposed around the pixel portion are formed, and which comprises a metal interconnecting layer provided in the peripheral circuit portion and set to a second potential, and a metal light shielding layer which is selectively provided in a pattern reverse to the metal interconnecting layer in each of regions of the pixel portion and the peripheral circuit portion, and which is set to a first potential in a region corresponding to the pixel portion and set to the second potential in a region corresponding to the peripheral circuit portion; a second substrate disposed opposite to the first substrate with a predetermined space and having a counter electrode set to the first potential; and a liquid crystal layer held between the first and second substrates. The liquid crystal display device further comprises a transparent electrode formed on the metal light shielding layer of the peripheral ci
Iida Masayuki
Koike Satofumi
Parker Kenneth
Sonnenschein Nath & Rosenthal
Sony Corporation
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