Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-18
2003-03-18
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S040000
Reexamination Certificate
active
06535261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to liquid crystal display devices of the active matrix type and, more particularly, to a liquid crystal display device with avoidability of on-screen image display irregularities such as line defects occurring due to cutting failure and/or re-attachment of melt components during cut-away processes of electrode leads for use in driving picture elements or “pixels”.
2. Description of the Related Art
In recent years, active-matrix liquid crystal display devices with thin-film transistors used as its switching elements are widely employed as those liquid crystal display devices adaptable for use as monitor units of various types in image visualization equipment and/or information processing apparatus.
A typical liquid crystal display device of this type is arranged to include an active matrix substrate with a plurality of (multiple) thin-film transistors for pixel selection formed on an electrically insulating or dielectric substrate and a color filter substrate having thereon a common electrode and color filter, which substrates are bonded together to define therebetween a thin gap space in which a layer of liquid crystals is sealed to thereby provide a liquid crystal panel with requisite driver circuitry assembled together.
While the liquid crystal display device of this type has traditionally been designed to employ so-called “tape automated bonding (TAB)” techniques for using a flexible printed circuit board tape carrier package (TCP) with built-in driver circuits mounted thereon to electrically connect between on-board electrical leads, such as image signal electrode leads and scanning electrode leads, and the driver circuits operatively associated therewith, the trend of modern LCD industry is to employ chip-on-glass (COG) architectures for directly mounting the driver circuits of a liquid crystal panel on one of the substrates thereof as the requirements are becoming more strict to further increase the effective display screen area while reducing the panel thickness when assembling into portable personal computers and the like.
These conventional liquid crystal display devices are designed to be equipped with an electrostatic protective lead (anti-static lead) for protecting the thin-film transistors or the like thereof from static damages during manufacturing processes of an active matrix substrate thereof. The electrostatic protective lead is electrically connected to an image signal electrode lead as provided inside of the liquid crystal panel at an extra portion of a mother board which will be removed from the liquid crystal panel during a cut-out process thereof from the mother board. The image signal electrode lead and electrostatic protective lead are formed of a thin film made typically of indium-tin-oxide (ITO), respectively.
FIGS. 8A and 8B
are diagrams for explanation of an image signal electrode lead extension portion of a liquid crystal panel constituting one of conventional liquid crystal display devices, wherein
FIG. 8A
illustrates a plan view of main part corresponding to a single image signal electrode driving circuit whereas
FIG. 8B
depicts in cross-section an image signal electrode lead thereof.
As shown in
FIG. 8A
, this liquid crystal panel is structured from an active matrix substrate
1
and a color filter substrate
10
as bonded together to define a gap space therebetween in which a layer of liquid crystals is sealed. At the periphery of the active matrix substrate
1
, a common lead
5
for electrostatic protection is formed outside of a cut line
7
to be cut during manufacturing. This electrostatic protective common lead
5
is formed with an electrostatic protective lead
4
while a plurality of image signal electrode leads
2
that are extended from the side of an effective display area AR are connected to this electrostatic protective lead
4
.
Reference numeral “
3
” designates external connection terminals each serving as an input terminal of an image signal electrode driver circuit (IC)
6
, to which an output of external circuitry, not shown, is coupled. A separation section
8
is formed between a respective one of the image signal electrode leads
2
and its associated electrostatic protective lead
4
, wherein irradiation of laser light on a laser scan region
9
of this separator section
8
may enable cut-away for separation between the image signal electrode lead
2
and electrostatic protective lead
4
from each other.
As better shown in
FIG. 8B
, the separator section
8
, which couples the image signal electrode leads
2
and the electrostatic protective lead
4
, is comprised of an ITO layer
80
in the form of a transparent conductive film. The ITO separator section
8
extending between the image signal electrode leads and the electrostatic protective lead is cut by a laser beam before or after the active matrix substrate is cut into a product size, while letting the driver circuit (IC)
6
be mounted at this cut portion.
SUMMARY OF THE INVENTION
Unfortunately, in view of the fact that the ITO material is inherently high in electrical resistivity and also has a wide lead width splashy fragments or particles can badly behave to again attach or re-adhere to those portions between neighboring ones of the image signal electrode leads
2
during the cutaway processes using laser light, resulting in creation of undesired electrical short-circuiting therebetween. In addition, while a YAG laser that is widely used today to effect such a cutaway process of this kind measures 1.065 micrometers (&mgr;m) in wavelength, ITO material exhibits a high transmissivity of those rays of light with wavelength values greater than or equal to that of visible light, so that the laser light cutting processes are less efficient. Due to this inefficiency, several ITO portions in the cutting area fail to be removed away and remain thereat, which sometimes results in a failure to adequately separate the image signal electrode leads
2
and electrostatic protective lead
4
from each other.
While swarf being blown up and reattached and/or remaining at cut portions causes electrical short circuits on the active matrix substrate, line defects take place on the display screen of the liquid crystal display panel, cause product defects thereof, and thus reduce the manufacturing yield and reliability thereof.
One of objects of the present invention is to avoid the aforementioned problems in the prior art and to provide a liquid crystal display device suitable for improving the manufacturing yield and product reliability thereof.
To attain the foregoing object, the present invention provides a specific device structure wherein a separator section for use in cutting away by laser light for separation of those electrode leads formed on an active matrix substrate—specially, image signal electrode leads and electrostatic protective lead—is arranged to have a laminated structure including a low-resistivity metal layer and a high-melting-point metal layer (e.g. a refractory metal layer). In addition, this laminated structure is coated with an insulating film.
(1) One of typical structures of the liquid crystal display devices in accordance with the invention is defined as follows.
The liquid crystal display device comprises:
a color filter substrate having a common electrode and color filters of multiple colors on an insulating substrate;
an active-matrix substrate having a plurality of scan electrode leads formed on an insulating substrate, a plurality of image signal electrode leads formed to cross over or intersect the scan electrode leads, a plurality of thin-film transistors as two-dimensionally laid out to connect to the scan electrode leads and the image signal electrode leads for forming an effective display area, picture element electrodes connected to the thin film transistors respectively, more than one additional capacitance element connected to the picture element electrodes, a common electrode lead terminal for connection to the common electrode as formed
Anno Kouichi
Kawamura Tetsuya
Matsuda Masaaki
Okawara Hiroshi
Tanaka Takeshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Parker Kenneth
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