Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1997-06-30
2001-07-17
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000
Reexamination Certificate
active
06262784
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to display devices and methods of forming display devices, and more particularly to liquid crystal display devices and methods of forming liquid crystal display devices.
BACKGROUND OF THE INVENTION
In order to minimize the space required by display devices, research into the development of various flat panel display devices such as LCD display devices, plasma display panels (PDP) and electro-luminescence displays (EL), has been undertaken to displace larger cathode-ray tube displays (CRT) as the most commonly used display devices. Particularly, in the case of LCD display devices, liquid crystal technology has been explored because the optical characteristics of liquid crystal material can be controlled in response to changes in electric fields applied thereto. As will be understood by those skilled in the art, a thin film transistor liquid crystal display (TFT LCD) typically uses a thin film transistor as a switching device and the electrical-optical effect of liquid crystal molecules to display data visually.
At present, the dominant methods for fabricating liquid crystal display devices and panels are typically methods based on amorphous silicon (a-Si) thin film transistor technologies. Using these technologies, high quality image displays of substantial size can be fabricated using low temperature processes. As will be understood by those skilled in the art, conventional LCD devices typically include a transparent (e.g., glass) substrate with an array of thin film transistors thereon, pixel electrodes, orthogonal gate and data lines, a color filter substrate and liquid crystal material between the transparent substrate and color filter substrate. The use of a-Si TFT technology typically also requires the use of separate peripheral integrated circuitry to drive the gates and sources (i.e., data inputs) of the TFTs in the array. In particular, gate driving signals from a gate driving integrated circuit are typically transmitted to the gate electrodes of TFTs in respective rows and data driving signals from a data driving integrated circuit are typically transmitted to the source electrodes of TFTs in respective columns. A display is typically composed of a TFT substrate in which a plurality of liquid crystal pixels are formed. Each pixel typically has at least one TFT and a pixel electrode coupled to the drain of the respective TFT. Accordingly, the application of a gate driving signal to the gate of a TFT will electrically connect the pixel electrode of a respective TFT to the data line connected thereto.
Referring now to
FIGS. 1-3
, an active matrix substrate of a conventional TFT LCD with a light blocking film will be described. This and other TFT LCDs are more fully described in U.S. Pat. No. 5,426,523 to Shimada et al. In particular,
FIG. 1
is a plan view showing a conventional active matrix display device.
FIG. 2
is a cross-sectional view of the active matrix display device of
FIG. 1
, taken along line A—-A′ and
FIG. 3
is a cross-sectional view of the active matrix display device of
FIG. 1
, taken along line B-B′. As illustrated by
FIG. 1
, a gate line
130
is formed in a horizontal direction, and a data line
150
crosses the gate line
130
. A light blocking film
8
, with a width larger than that of the data line
150
, is formed on each data line
150
. Each of the side excess portions over the data line
150
in the transverse direction is set to a length “d”. In each region defined by the gate and data lines, a pixel electrode
7
is formed so that both sides of the pixel electrode
7
overlap the neighboring blocking films and data lines by a constant length. In each pixel region, a TFT is formed. Specifically, the region of a silicon film
110
under the branch of the gate
130
forms a gate of the TFT, the region of the silicon film
110
connected to the data line
150
by way of a contact hole
4
a
forms a source of the TFT, and the region of the silicon film
110
connected to the pixel electrode
7
by way of a contact hole
4
b
forms a drain of the TFT. If a turn-on voltage is applied to the gate line
130
, a conduction path between source and drain becomes active due to the ON state of the TFT, and, therefore a video signal from the data line
150
can be transmitted to the pixel electrode
7
via the silicon film
110
.
Referring now to
FIG. 2
, a silicon film
110
is formed on a
10
transparent substrate
100
, and serves as a source electrode, a drain electrode and a semiconductor active layer of the TFT. A gate insulating film
120
is formed on the silicon film
110
and the transparent substrate
100
so as to cover the entire surface. On a certain region of the gate insulating film
120
, a gate electrode
130
is formed. Moreover, an insulating film
140
is formed on the entire surface of the gate electrode
130
and the gate insulating film
120
. A contact hole
4
a is formed through the gate insulating film
120
and the insulating film
140
. On the insulating film
140
, the data line
150
is formed and connected to the silicon film
110
via the contact hole
4
a.
On the entire surface of the insulating film
140
and the data line
150
, a passivation film
160
is formed, and a contact hole
4
b
is formed through the gate insulating film
120
, the insulating film
140
and the passivation film
160
. A pixel electrode
7
, made of an indium-tin-oxide (ITO) film, is formed on the passivation film
160
and connected to the silicon film
110
via the contact hole
4
b
. A video signal received from the data line
150
passes through the silicon film
110
via the contact hole
4
a
, and, then, is transmitted to the ITO pixel electrode
7
via the contact hole
4
b
. The TFT with such a structure where the gate electrode
130
is located on the semiconductor layer is called a top gate type TFT.
A cross-sectional structure of the prior active matrix substrate coupled with a liquid crystal layer and a counter substrate will now be described with reference to FIG.
3
. Here, a gate insulating film
120
is formed on a transparent substrate
100
, and a data line
150
is formed thereon. A passivation film
160
is formed on the entire film of the gate insulating film
120
and the data line
150
, and a light blocking film
8
is formed on the passivation film so as to cover a certain region of the passivation film over the data line
150
. An insulating film
180
is formed on the entire surface of the light blocking film
8
and the passivation film
160
, and an ITO pixel electrode
7
is formed thereon. In the above mentioned structure of the prior active matrix substrate, the data line
150
has a thickness of 500 nm, and is usually formed of aluminum (Al). The passivation film
160
is formed of silicon oxide (SiOx) having a thickness of 400 nm. Furthermore, the light blocking film
8
having a thickness of 100 nm is formed of the same material as the data line
150
, and each of the lengths “d” of the side excess portions of the light blocking film
8
over the data line
150
in the transverse direction, is set to be 5 &mgr;m.
A counter substrate
200
, including a transparent counter electrode
210
formed on the surface thereof, is attached to the active matrix substrate. Into a space between the two substrates, liquid crystal is injected to form the liquid crystal layer
190
, and the thickness of the liquid crystal layer
190
is set to be about 5 &mgr;m. Here, even though abnormal light leakage occurs due to the orientation disorder of the liquid crystal molecules in the edge regions of the data line
150
(caused by a step of the data line
150
), the light leakage can be blocked considerably since the light blocking film
8
is broader than the data line
150
and is formed to cover the data line
150
. In these circumstances, the orientation disorder of the liquid crystal molecules by a step of the light blocking film
8
can be negligible, since the thickness of the light blocking film
8
is very small than that of the data line
150
.
Howev
Malinowski Walter J.
Myers Bigel & Sibley & Sajovec
Samsung Electronics Co,. Ltd
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