Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-02-25
2001-07-10
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C349S110000, C313S505000
Reexamination Certificate
active
06259200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active-matrix display apparatus comprising a pair of insulating substrates attached to each other with a predetermined gap kept therebetween and an electro-optical material such as a liquid crystal filling the gap. More particularly, the present invention relates to the light-shielding structure of a signal line that is formed along with a thin-film transistor and its pixel electrode on the one insulating substrate.
2. Description of the Related Art
Referring to
FIG. 7
, the typical arrangement of an active-matrix display apparatus is briefly discussed. The display apparatus has a flat panel structure in which an electro-optical material such as a liquid crystal
50
is held between a lower insulating substrate
1
and an upper or top insulating substrate
60
. A pixel array and drive circuit are integrated on the insulating substrate
1
. The drive circuit is divided into a vertical scanning circuit
41
and a horizontal scanning circuit
42
. Terminal electrodes
47
for external connections are formed on a top end portion of the insulating substrate
1
. Each terminal electrode is connected to the vertical scanning circuit
41
and horizontal scanning circuit
42
via a wiring
48
. Gate lines
43
and signal lines
10
intersecting each other are formed on the pixel array. The gate lines
43
are connected to the vertical scanning circuit
41
and the signal lines
10
are connected to the horizontal scanning circuit
42
. A pixel electrode
14
and a thin-film transistor
3
for driving it are formed at each intersection where a gate line
43
intersects a signal line
10
. Although they are not shown, an opposing electrode and a black mask are formed on the inner surface of the top insulating substrate
60
. When a material having a relatively low heat resistance, such as glass, is used for the insulating substrate
1
, the thin-film transistor
3
needs to be formed on the insulating substrate
1
through a low-temperature process at 60° C. or lower. Although the thin-film transistor
3
is either of a top-gate type or a bottom-gate type, the bottom-gate type is more suited to the low-temperature process. The bottom-gate type thin-film transistor is constructed by laminating a gate electrode, a gate insulating film and then a semiconductor thin-film from bottom to top.
The pixel electrode
14
is arranged in an aperture surrounded by the signal lines
10
and the gate lines
43
, and is connected to the corresponding thin-film transistor
3
. To shade the area other than the aperture, a black mask (not shown) is formed on the top insulating substrate (opposing substrate)
60
. The black mask is typically patterned in a grid (matrix) that matches the pattern in which the signal lines
10
and the gate lines
43
intersect each other. When the active-matrix display apparatus is assembled, the bottom insulating substrate
1
and the top insulating substrate
60
need to be glued to each other in a mutually aligned position. To offset the error in alignment, the black mask formed on the top insulating substrate
60
permits a margin of extra width of 3 &mgr;m or more across the pattern against the dimension of the design requirement. This arrangement sacrifices the aperture ratio of the pixel electrode
14
, lowering the brightness of the screen of the apparatus. There is room for improvement in the arrangement of the black mask. In the manufacturing of the bottom-gate type thin-film transistor through the low-temperature process, current technology fails to provide the structure (on-chip black) in which the black mask is formed on the bottom insulating substrate
1
, and there is no choice but to form the black mask on the top insulating substrate (opposing substrate)
60
. This arrangement imposes a substantial limitation on the design of pixel, for example, on the aperture ratio of pixel.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to improve the aperture ratio of pixel.
To achieve the above object, the active-matrix display apparatus of the present invention comprises a first transparent insulating substrate supporting thereon signal lines and gate lines which intersect each other, a bottom-gate type thin-film transistor arranged at each intersection, a transparent pixel electrode arranged in an aperture surrounded by the signal lines and gate lines and connected to the corresponding thin-film transistor, and a light-shielding film which is arranged beneath the signal lines and the pixel electrode and which reaches at least the edge portion of the pixel electrode adjacent to the signal line, wherein the light-shielding film is manufactured concurrently with, and of the same material as, the gate line; a second transparent insulating substrate secured to the first transparent insulating substrate with a predetermined gap kept between the first and second transparent insulating substrates, wherein the second transparent insulating substrate is provided with a transparent opposing electrode; and an electro-optical material filling the gap.
Since the light-shielding film is arranged beneath the signal lines and the pixel electrode and extends at least to the end of the pixel electrode next to the signal line, light passing between the signal lines is prevented. Since the light-shielding film is manufactured concurrently with and of the same material as the gate line, no substantial step increase in the manufacturing process results.
The second transparent insulating substrate is preferably provided with at least a shading black mask aligned with the gate line.
Since the opposing substrate (the second transparent insulating substrate) is provided with a striped black mask, light passing around the gate lines and the thin-film transistors is prevented. Unlike conventional black masks, the black mask of the present invention needs to shade the row gate lines only, and is acceptably patterned in stripes rather than in a matrix (grid). Since one-dimensional alignment between the one insulating substrate and the other insulating substrate is acceptable in principle, the alignment operation becomes less severe accordingly. The light-shielding film formed on the thin-film transistor side substrate is also patterned in stripes. The width of the light-shielding film is slightly wider than that of the signal line. The light-shielding film is set to be wide enough to shade the edge of the pixel electrode and the domain where the liquid crystal orientation is disturbed. With this arrangement, the margin in width of the light-shielding film is still narrower than that in the black mask which is formed on the insulating substrate of the opposing electrode in the conventional art. The aperture ratio of pixel electrode is thus set to be greater accordingly. According to the present invention, the matrix-patterned black mask that was formed on the insulating substrate of the opposing electrode in the conventional art is replaced by the light-shielding film formed on the other insulating substrate on which the thin-film transistor is formed. Since the light-shielding film is manufactured of the same material as that of the gate line, the light-shielding film is produced without increasing the number of photomasks in the semiconductor process.
The gate line and the light-shielding film are preferably manufactured of a material selected from the group consisting of chromium, titanium, molybdenum, tungsten, and molybdenum-tantalum.
The signal line is manufactured of a first metal film having a first reflectance, and a second metal film, having a second reflectance lower than the first reflectance, is formed on top of the first metal film.
The signal line is preferably manufactured of a first metal film having a first reflectance, and a second metal film, having a second reflectance lower than the first reflectance, is formed on the second substrate so that the second metal film is aligned with the signal line.
The first metal film is preferably made of aluminum.
The seco
Morita Shintarou
Tashiro Yuuki
Gerike Matthew J.
Kananen Ronald P.
Patel Nimeshkumar D.
Rader Fishman & Grauer
Sony Corporation
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