Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-03-25
2003-09-23
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S139000
Reexamination Certificate
active
06624857
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active-matrix-type liquid crystal display panel for applying driving signals to pixel electrodes through switching elements and performing a display by an electric potential difference between an opposing electrode and the pixel electrodes. The present invention also relates to a method of inspecting such an active-matrix-type liquid crystal display panel.
BACKGROUND OF THE INVENTION
A conventional liquid crystal display device includes a plurality of pixel electrodes arranged in a matrix form, an opposing electrode as a common electrode provided so as to face the pixel electrodes, and liquid crystal as display medium provided between the pixel electrode and the opposing electrode. Such a liquid crystal display device performs a display in the following manner. Namely, an electric potential is selectively written into the pixel electrode, and an optical modulation of the liquid crystal provided between the pixel electrode and the opposing electrode is taken place by the electric potential difference between the pixel electrode and the opposing electrode, and visually recognized as a display pattern.
As a method of driving the pixel electrode, a so-called active matrix driving method is known. In this method, the pixel electrodes provided in the matrix form are each connected to switching elements, and each of the pixel electrodes is driven by the switching element. General switching elements are a TFT (thin film transistor), a MIM (metal-insulator-metal) element, etc.
An active-matrix-type liquid crystal display panel provided in an active-matrix-type liquid crystal display device includes an active matrix substrate and an opposing substrate. In the active matrix substrate, a plurality of scanning lines and a plurality of data lines are provided on a transparent insulating substrate so as to cross each other, and a pixel electrode and a switching element for driving the pixel electrode are formed at each intersection of the scanning line and the data line. In the opposing substrate, an opposing electrode is formed on a transparent insulating substrate. The active matrix substrate and the opposing substrate are provided with alignment films on their surfaces where the two substrates face each other, and adhered to each other with a liquid crystal layer therebetween.
FIG. 28
shows the structure of each pixel of the active matrix substrate using the TFT as the switching element. A gate electrode of a pixel TFT
1
is connected to a scanning line
2
, and the pixel TFT
1
is driven by a scanning signal inputted to the scanning line
2
. A source electrode of the pixel TFT
1
is connected to a data line
3
, and a display signal is inputted to the data line
3
. A drain electrode of the pixel TFT
1
is connected to a pixel electrode
14
and one terminal of an auxiliary capacity, through an auxiliary capacity electrode
28
. The other terminal of the auxiliary capacity is connected to an auxiliary capacity wiring
4
, and then connected to the opposing electrode on the opposing substrate when a liquid crystal cell is constructed. The pixel TFT
1
and the pixel electrode
14
are provided in the matrix form on the insulating substrate.
FIG. 29
shows one example of the structure of the cross section of the active matrix substrate. A gate electrode
8
, a gate insulating film
9
, a semiconductor layer
10
, a n
+
-Si layer
11
to be the source and drain electrodes, a metal layer
12
to be the data line
3
, an interlayer insulating film
13
, and a transparent conductive layer to be the pixel electrode
14
are formed in this order on an insulating substrate
7
. The pixel electrode
14
is connected to the drain electrode of the pixel TFT
1
through a contact hole
15
piercing the interlayer insulating film
13
, specifically through the auxiliary capacity electrode
28
.
In the structure shown in
FIG. 29
, the interlayer insulating film
13
is formed between the scanning line
2
(the same layer as the gate electrode
8
) and the pixel electrode
14
and between the data line
3
and the pixel electrode
14
. Therefore, the pixel electrode
14
can be arranged to overlap the data line
3
. It is known that such an arrangement can improve the aperture ratio, and reduce an alignment defect of liquid crystal by shielding the electric field resulting from the data line
3
.
Next, the process thereafter will be explained with reference to FIG.
30
.
FIG. 30
is a schematic plan view of a conventional active-matrix-type liquid crystal display device. This view shows the state after a large substrate is divided into cells, each of which corresponds to a display device. In the actual process, the cells are often produced in the state where several cells are arranged in rows and columns.
On a viewing area (within the two-dot chain lines)
17
of a completed active matrix substrate
50
, an alignment film of the polyimide family is deposited, and the alignment function is added by a treatment such as rubbing. In an opposing substrate
51
, a transparent opposing electrode (not shown) such as ITO (Indium Tin Oxide) is deposited, and then the part corresponding to the viewing area
17
is subjected to the same treatment.
A sealing material (not shown) is applied to the surrounding section of the liquid crystal display panel except for a liquid crystal injection port in such a manner as to surround the panel by the printing method, etc. Further, a conductive material
19
is attached onto an opposing-substrate-use signal input terminal
27
on the active matrix substrate
50
. Thereafter, a spacer (not shown) for keeping the cell thickness of the liquid crystal layer uniform is sprayed. Then, the active matrix substrate
50
is adhered to the opposing substrate
51
, and the sealing material is fixed by adding heat.
Thereafter, liquid crystal is injected through the liquid crystal injection port, and the liquid crystal injection port is closed with an end-sealing material, thereby completing the panel section of the liquid crystal display device. Then, packaging members such as a source driver
20
a
for applying a display signal to each data line
3
, a gate driver
20
b
for applying a scanning signal to each scanning line
2
, a control circuit (not shown), and a backlight (not shown) are installed, thereby completing the liquid crystal display device. Note that the liquid crystal display device shown in
FIG. 30
is not provided with the auxiliary capacity wiring
4
.
By the way, the inspection of such a liquid crystal display device usually includes an optical inspection performed in each step of the process, an electrical inspection performed in the step where the active matrix substrate is completed, and a dynamic operating inspection and the electrical inspection, performed at the time when the panel section on which the packaging members such as the driver are not yet installed is completed.
Such inspections are performed so as to prevent materials and operations from being wasted by leaving defective parts in the subsequent process. When a deficiency exists in a device, the device is discarded at this time or repaired by means of laser, etc.
However, with the recent improvement of the production technique, the liquid crystal display panel has achieved ever higher definition, and accordingly a higher technique has been required also in the inspection process.
Specifically, since the terminals for inputting the signals to the data lines
3
and the scanning lines
2
are installed with increasingly smaller pitches, when supplying the signals by bringing the respective terminals into electric contact with pins, a prober of extremely high definition and high cost must be prepared. In addition, there is a case where existence of fine dust on the terminals in the inspection interferes with normal dynamic operations, and the defective inspection is recognized as a deficiency of the panel by mistake. In order to avoid such a case, the inspection must be performed in very clean environments. Consequently, a rise in t
Akebi Yasunobu
Nagata Hisashi
Shimada Takayuki
Tachibana Makoto
Nguyen Dung
Nixon & Vanderhye P.C.
Parker Kenneth
Sharp Kabushiki Kaisha
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