Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-12-09
2003-07-01
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000, C349S039000, C349S042000, C349S139000, C349S143000
Reexamination Certificate
active
06587162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device which is improved in yield factor by preventing disconnection from occurring in a layered line portion or a lead terminal portion in a liquid crystal display device of an active matrix type such as a thin-film transistor (TFT) type.
2. Description of the Related Art
Liquid crystal display devices are widely used as display devices for notebook personal computers, desktop personal computers and other electronic equipment because the liquid crystal display devices have advantages such as thin size, light weight, high contrast, fast response and the capability to reproduce moving images as well as high resolution which compares with cathode ray tubes.
Liquid crystal display devices are basically classified into two types: the type in which a liquid crystal layer is interposed between two substrates at least one of which is made of transparent glass or the like, and predetermined pixels are turned on or off by selectively applying voltage to various kinds of pixel-forming electrodes formed over the substrates (this type is called the simple matrix type); and the type in which such various kinds of electrodes and pixel-selecting switching elements are formed and predetermined pixels are turned on or off by selectively driving these switching elements (this type is called the active matrix type in which so-called thin-film transistors (TFTs) or so-called MIM diodes are used as the switching elements).
The latter active matrix type of liquid crystal display device has become a leading liquid crystal display device because of its contrast performance and its high-speed display performance.
In general, the active matrix type of liquid crystal display device is a vertical electric field type which includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: an active matrix substrate over which gate lines, a gate insulating layer, a semiconductor layer, a contact layer, source and drain lines, a passivation layer and a pixel electrode layer are formed on one substrate in that order; a color filter substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer on the other insulative substrate; and a liquid crystal layer sealed in the gap between the active matrix substrate and the color filter substrate. The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed over the active matrix substrate and the color filter substrate. In the vertical electric field type, an electric field for changing the direction of alignment of liquid crystal molecules which constitute the liquid crystal layer is applied between the electrodes formed over the active matrix substrate and the electrodes formed over the other substrate.
In recent years, a lateral electric field type (In-Plane Switching Mode: IPS type) of liquid crystal display device has been put into practice, in which a direction in which to apply an electric field to its liquid crystal is made nearly parallel to the surface of a substrate. In this lateral electric field type of liquid crystal display device, a common electrode to be formed on the other substrate (color filter substrate) in the vertical electric field type of liquid crystal display device is formed on an active matrix substrate as a counter electrode, and a pixel electrode and the counter electrode are arrayed in a comb-tooth-like shape to control the direction of alignment of liquid crystal molecules in a plane parallel to the substrate.
In this type of liquid crystal display device, since the intersections of gate lines and drain lines are formed between adjacent pixels over the active matrix substrate, it is important that the breakdown voltage of the passivation layer (CVD insulating layer) between the gate lines and the drain lines be sufficiently high.
FIG. 14
is a plan view illustrating the essential portion of one example of the construction of an intersection of a gate line and a drain line in a pixel area of a related-art liquid crystal display device which uses thin-film transistors as switching elements, and
FIG. 15
is a cross-sectional view taken along line A-A′ of FIG.
14
.
As shown in
FIG. 15
taken along line A-A′ of
FIG. 14
, in the intersection of a gate line and a drain line, a gate line
2
, a gate insulating layer
3
, a semiconductor layer
4
, a contact layer
5
, a drain layer
6
, a source electrode
7
and a passivation layer
8
are formed over a lower transparent insulative substrate
1
which is an active matrix substrate.
In
FIG. 14
, reference numeral
9
denotes a contact hole for connecting a pixel electrode
10
and the source electrode
7
, and reference numeral
11
denotes a light shield layer.
In addition, the surfaces of terminal lead lines, which are formed outside the pixel area of a liquid crystal panel in which a liquid crystal is sealed, are covered with an insulating material such as a resin so that the terminal lead lines are isolated from external impact or moisture contained in the air.
FIG. 16
is a diagrammatic cross-sectional view illustrating an example of the construction of an outside portion of the pixel area of the liquid crystal panel, and
FIG. 17
is an enlarged cross-sectional view of the essential portion of FIG.
16
. In
FIGS. 16 and 17
, reference numeral
1
denotes an active matrix substrate, reference numeral
14
an upper transparent insulative substrate which is a color filter substrate, reference numeral
15
denotes a liquid crystal layer, reference numeral
16
a sealing material, reference numeral
17
a driver chip, reference numeral
18
an epoxy resin, reference numeral
19
a conductor layer, and reference numeral
20
a bump.
As shown in
FIGS. 16 and 17
, the liquid crystal layer
15
is interposed between the active matrix substrate
1
and the color filter substrate
14
, and is sealed along its periphery by the sealing material
16
. The driver chip
17
is disposed in the periphery of the active matrix substrate
1
, and is connected to a terminal line which is led from the pixel area inside the sealing material
16
.
The liquid crystal panel is covered with the epoxy resin
18
on its sealing-material side and on the side on which the driver chip
17
is disposed, whereby the pixel area and the driver chip are isolated from external impact and moisture contained in the air.
As shown in
FIG. 15
, in case that a minute defect is present in the gate insulating layer
3
at the intersection of the gate line
2
and the drain line
6
in an individual pixel of the pixel area, the gate line
2
and the drain line
6
will be electrically shorted or a leak current will flow therebetween when a voltage is applied to both lines as indicated by an arrow C, because the breakdown voltage of the gate insulating layer
3
is low. This defect frequently occurs in an edge portion in which the drain line
6
passes over the gate line
2
.
At this time, in case that a defect is present in the passivation layer
8
as indicated by an arrow A, there will occur the problem that moisture contained in the air penetrates through the portion of the detect of the passivation layer
8
and the drain line
6
breaks down by an electrolytic corrosion action as indicated by an arrow B.
Another problem is that, in the peripheral portion of the liquid crystal panel, as shown by the left-hand one of arrows A in
FIG. 17
, a crack is formed in the passivation layer
8
at the edge portion of the epoxy resin
18
by the stress thereof and moisture contained in the air penetrates through the crack and an electrolytic corrosion occurs in the drain line
6
, thus leading to the disconnection of the drain line
6
. A similar problem occurs on a lead-terminal side of th
Kaneko Toshiki
Ono Kikuo
Antonelli Terry Stout & Kraus LLP
Chung David Y.
Hitachi , Ltd.
Parker Kenneth
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