Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-09-02
2001-01-09
Malinowski, Walter (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S149000
Reexamination Certificate
active
06172733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) which includes thin film transistors (TFTs) and to a method of manufacturing the same and more specifically, to a method of manufacturing LCDs which has a reduced number of masking steps.
2. Description of the Related Art
Among display devices for showing visual images on a screen, thin film flat panel display devices are highly favored because of their light weight and easy adaptability. Recent research activities have focused on the development of liquid crystal display devices because of their high resolution and fast response time suitable for display of motion picture images.
A liquid crystal display device works by using polarization and optical anisotropy of a liquid crystal. By controlling the orientation of rod-shaped liquid crystal molecules via a polarization technique, transmission and interception of a light through the liquid crystal molecules are achieved due to the anisotropy of the liquid crystal. This principle is utilized in liquid crystal display devices. Active matrix liquid crystal displays (or AMLCDs) having TFTs arranged in a matrix pattern and pixel electrodes connected to the TFTs provide high quality images and are now widely used. An active panel of a conventional LCD will now be described with reference to FIG.
1
.
The conventional LCD comprises two panels
3
and
5
on which a plurality of elements are placed, and liquid crystal (not shown) is located between the two panels
3
,
5
. One panel of the LCD includes elements reproducing colors, which panel is called a color filter panel
3
. The color filter panel
3
has color filters
7
including red (R), green (G) and blue (B) filters, which are sequentially arranged on a first transparent substrate
81
and correspond to pixels formed in a matrix pattern. Among these color filters
7
, black matrixes
9
are arranged in a lattice pattern so as to prevent mixture of colors at boundaries between the color filters. A common electrode
85
covers the color filters
7
and functions as one electrode for generating an electric field applied to the liquid crystal.
The other panel is an active panel
5
which includes switch elements and bus lines, which generate the electric field for driving the liquid crystal. The active panel
5
has a pixel electrode
41
which is disposed on a second transparent substrate
83
. The pixel electrode
41
is located opposite to the common electrode
85
disposed on the color filter panel
3
and functions as the other electrode for generating the electric field applied to the liquid crystal. Signal bus lines
13
extend along the column direction of the array of the pixel electrodes
41
and data bus lines
23
extend along the row direction of the array of the pixel electrode
41
. A TFT
89
which functions as a switch element for driving the pixel electrode
41
is formed on the substrate
83
. A gate electrode
11
of the TFT
89
is connected with the signal bus line
13
(“gate bus line”), a source electrode
21
is connected with the data bus line
23
(“source bus line”). A drain electrode
31
of the TFT
89
is connected with the pixel electrode
41
.
Between the source electrode
21
and the drain electrode
31
, a semiconductor layer
33
is formed as seen in FIG.
2
. The source electrode
21
and the drain electrode
31
are in ohmic contact with the semiconductor layer
33
. A gate pad
15
and a source pad
25
, which function as terminals receiving external signals, are disposed at the end portions of the gate bus line
13
and the source bus line
23
, respectively. A gate pad terminal
57
and a source pad terminal
67
are formed on the gate pad
15
and the source pad
25
, respectively.
When an external electric signal, which is applied to the gate pad
15
, is sent to the gate electrode
11
through the gate bus line
13
, electrical picture data, which is applied to the source pad
25
, is sent to the source electrode
21
through the source bus line
23
and to the drain electrode
31
. If the electric signal is not applied to the gate bus line
13
, the drain electrode
31
is electrically isolated from the source electrode
21
. Accordingly, whether the data signal is applied to the drain electrode
31
is determined by controlling the signal to the gate electrode
11
. Therefore, application of the data signal to the pixel electrode
41
, which is connected with the drain electrode
31
, is artificially controlled. In other words, the TFT
89
functions as a switch for selectively driving the pixel electrode. A gate insulating layer
17
is formed between the gate bus line
13
and the source bus line
23
in order to electrically isolate the gate bus line
13
and the source bus line
23
and a passivation layer
37
covers the source bus line
23
in order to protect the elements as shown in FIGS.
3
a
-
3
f
described below.
These two panels, i.e. the color filter panel
3
and the active panel
5
, are arranged to face each other with a certain distance or “cell gap” disposed therebetween. In between the spaced panels
3
,
5
in the cell gap, liquid crystal is injected. In order to keep the cell gap between the two panels
3
and
5
constant and to prevent the liquid crystal from leaking outside, the edges of the joined panels are sealed with epoxy or similar material. The liquid crystal panel is now completed as described above.
Many complicated processes for manufacturing the liquid crystal panel are required, especially, many masking processes for manufacturing the active panel including TFTs. Because the active panel includes the elements which mainly affect the performance of the LCD, it is important for manufacturing high quality LCD products to simplify the processes for manufacturing the active panel. In general, the manufacturing processes are determined by the types of materials used to form each element, the structure thereof and methods for solving the problems such as static electricity which occur during the forming processes.
Although a resistance of a material used to form gate bus lines rarely affects the picture quality when manufacturing the conventional miniature liquid crystal display device, the resistance affects the picture quality when manufacturing a large area liquid crystal display, i.e. computer monitor of 12 inches or more. In other words, a metal which has a good surface-stability when the metal is formed into a thin film, such as tantalum, tungsten and molybdenum, is used for forming gate elements (gate bus lines, gate electrodes and gate pads) of the conventional miniature LCD. For forming the gate elements of the large area LCD, a metal which has a low resistance, such as aluminum, is preferably used.
However, there are many problems with forming the gate elements of aluminum or aluminum alloy. Hillocks, which are formed on the surface of the aluminum, are the most serious problem. After depositing aluminum, minute particles of the aluminum exist on the aluminum film. During the manufacturing process, the particles are growing so much that they break an insulating layer because of a high temperature condition, resulting in the deterioration of the LCD. Furthermore, if the gate elements are formed of aluminum, the contact-resistance between the gate elements and ITO increases. In other words, Al
2
O
3
film is unintentionally formed between the aluminum and the ITO when the ITO is deposited on the aluminum, and consequently, the contact-resistance increases. As a result, transmission of the electric signal to the gate is significantly delayed.
In order to enhance the surface-stability of the aluminum film, the conventional art includes a step of anodizing the surface of the aluminum. When anodizing the aluminum, a portion of the aluminum, which should be electrically connected with an external element such as the gate pad, is not anodized. Instead, an interim electrode is formed with a metal such as chromium in order to maintain the contact-resistance in a normal state. This convent
Hong Chan Hee
Kim Hye Young
Kim Jong Woo
Lim Byoung Ho
LG.Philips LCD Co. , Ltd.
Malinowski Walter
LandOfFree
Liquid crystal display including conductive layer passing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display including conductive layer passing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display including conductive layer passing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449149