Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-03-25
2003-05-27
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S139000
Reexamination Certificate
active
06570630
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display panel such as a liquid crystal display panel used in television sets, personal computers, word processors, OA (Office Automation) apparatuses, or the like.
2. Description of the Related Art
Such a liquid crystal display panel has a structure where a pair of substrates are provided so as to oppose each other with a liquid crystal layer being interposed therebetween as a display medium. One of the pair of substrates is an active matrix substrate, in which a plurality of signal lines and a plurality of scanning lines are provided so as to cross each other via an insulation film. A pixel electrode is provided in the vicinity of an intersection between the signal line and the scanning line and is connected to the signal lines and the scanning lines via a TFT (Thin Film Transistor) as a switching element. Each of the pixel electrodes is provided with a signal from the corresponding signal line via the TFT, which is switched by a signal from the corresponding scanning line. Thus, a voltage is applied to the liquid crystal layer between the pixel electrode and an opposing counter electrode, thereby changing the optical characteristics of the corresponding portion of the liquid crystal layer between the electrodes. This change in the optical characteristics is visually perceived as a display pattern.
When a voltage of, for example, about 100 V or more generated by an electrostatic charge, or the like, is applied to the signal line or the scanning line, the characteristics of the TFT may deteriorate, or the insulation film between the signal line and the scanning line may be broken. In such a case, a linear defect or a display non-uniformity may appear in a displayed image, thus lowering the display quality. Since an electrostatic charge of such a magnitude often occurs during a step of producing the active matrix substrate or a step of rubbing an alignment film for aligning the liquid crystal layer, it is impossible to completely avoid such problems as described above.
In view of this, an active matrix substrate provided with a short-circuiting line, as shown in
FIGS. 7 and 8
, has been conventionally used.
FIG. 7
shows an equivalent circuit of such a conventional active matrix substrate
101
. The active matrix substrate
101
includes a transmissive substrate
1
made of a glass plate, or the like, as well as a plurality of signal lines
2
and a plurality of scanning lines
3
provided to cross each other via an insulation film. The active matrix substrate
101
further includes TFTs
4
in the vicinity of the intersection between the signal lines
2
and the scanning lines
3
as switching elements, and pixel electrodes
5
. A display region is defined by the plurality of pixel electrodes
5
arranged in a matrix. Each of the pixel electrodes
5
is connected to a corresponding TFT
4
. The signal lines
2
and the scanning lines
3
extend beyond the display region. A signal input terminal
6
is provided at one end of each signal line
2
while a signal input terminal
7
is provided at one end of each scanning line
3
. Furthermore, a short-circuiting line
8
is formed around the display region. Until a certain point in the production process, the short-circuiting line
8
is connected to both ends of the signal lines
2
and the scanning lines
3
.
FIG. 8
is a plan view illustrating another conventional active matrix substrate
111
. Elements in
FIG. 8
which are functionally the same as those in
FIG. 7
are denoted by the same reference numerals and will not be further described. In
FIG. 8
, for simplicity, elements provided inside a display region
20
and some of the lines and terminals provided around the display region
20
are not shown. In this active matrix substrate, the short-circuiting line
8
is connected to one end of each signal line
2
at which the signal input terminal
6
is not provided and to one end of each scanning line
3
at which the signal input terminal
7
is not provided.
Such an active matrix substrate is attached to a counter substrate having a transmissive substrate and counter electrodes provided thereon. Then, a liquid crystal material is injected between the substrates, thereby completing the liquid crystal display panel. Herein, the panel cannot be driven with the signal lines
2
and the scanning lines
3
being short-circuited by the short-circuiting line
8
. Therefore, the short circuit is removed before the liquid crystal panel is completed by severing the substrate
111
along a severance line
10
.
As described above, the short-circuiting line
8
is provided to connect the signal lines
2
and the scanning lines
3
to one another, whereby the signal lines
2
and the scanning lines
3
are always kept at the same potential. Thus, it is possible to prevent the deterioration of the TFT characteristics and the insulation breakdown between the signal lines
2
and the scanning lines
3
, even if an electrostatic charge is applied during a step of producing the liquid crystal display panel.
However, in the structures illustrated in
FIGS. 7 and 8
, the signal lines
2
and the scanning lines
3
are electrically isolated from one another after the active matrix substrate is severed. Thus, it is not possible to prevent the deterioration of the TFT characteristics and the insulation breakdown between the signal lines
2
and the scanning lines
3
due to an electrostatic charge generated during steps after the severance step. Moreover, even after the liquid crystal display panel is completed, the TFT, whose characteristics can deteriorate even by an applied voltage of about 100 V, is always subject to an influence of an electrostatic charge until it is incorporated in a shield case. For example, the TFT is subject to the influence of an electrostatic charge during steps of connecting drivers to the panel, attaching a polarizer thereto, and incorporating the panel into a shield case. Thus, it is very difficult in practice to completely prevent an electrostatic charge of such a magnitude from being generated and influencing the TFTs.
Furthermore, in the structure illustrated in
FIG. 7
, after the severance, each edge of the substrate
101
includes severed sections of the signal lines
2
or the scanning lines
3
. In the structure illustrated in
FIG. 8
, two edges of the counter substrate (e.g., the upper and left edges, as in FIG.
8
), along which the signal input terminals
6
or
7
are not provided, will have severed sections of either the signal lines
2
or the signal lines
3
after the severance. An electrostatic charge entering the panel through these severed sections often causes a problem, thereby significantly lowering the product yield.
Moreover, in the structures illustrated in
FIGS. 7 and 8
, until the active matrix substrate is severed and the short circuit by the short-circuiting line
8
is removed, all the signal lines
2
and the scanning lines
3
are short-circuited, whereby it is not possible to conduct a test for detecting a short circuit between the signal lines
2
and the scanning lines
3
or for detecting a disconnection of the lines.
In view of this, another type of conventional active matrix substrate
121
is known, which includes elements
12
and inner short-circuiting line
13
, as shown in FIG.
9
.
FIG. 9
shows an equivalent circuit of such a conventional active matrix substrate
121
. Elements in
FIG. 9
which are functionally the same as those in
FIG. 7
are denoted by the same reference numerals and will not be further described. In this active matrix substrate
121
, the inner short-circuiting line
13
is separately provided inside the short-circuiting line
8
, where the signal lines
2
and the scanning lines
3
are connected to the inner short-circuiting line
13
via the elements
12
. As the element
12
, a high resistance element made of a semiconductor thin film, or the like, or a non-linear element which exhibits non-linear resistance values for different applied voltages may be u
Nakajima Kazuko
Nakajima Mutsumi
Nixon & Vanderhye P.C.
Parker Kenneth
Sharp Kabushiki Kaisha
LandOfFree
Display panel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display panel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display panel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3030334