Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2000-12-20
2002-09-17
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S072000, C349S043000, C349S046000, C349S106000
Reexamination Certificate
active
06452210
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thin film transistor substrate, and more particularly to a thin film transistor substrate that has a structure in which a thin film transistor array is formed on color filters. Also, the present invention is directed to a method of fabricating such a thin film transistor substrate.
2. Description of the Related Art
Generally, in a liquid crystal display (LCD) having a thin film transistor array provided on color filters, a thin film transistor substrate includes color filters formed on a transparent substrate; and switching devices of thin film transistors (TFT's) consisting of gate electrodes, a gate insulating film, an active layer, an ohmic contact layer and source and drain electrodes, and pixel electrodes, each of which is provided on the color filters.
FIG. 1
is a section view showing a structure of a conventional thin film transistor substrate having a thin film transistor array provided on color filters. Referring to
FIG. 1
, the thin film transistor substrate includes a black matrix
4
formed in a lattice shape on a transparent substrate
2
to divide the substrate
2
into a plurality cell areas in which color filter is to be formed and to prevent a color interference between the cell areas. On the transparent substrate
2
divided into cell units by means of the black matrix
4
, red, green and blue color filters
6
for transmitting the respective red, green and blue color lights are provided. The color filters
6
are made from an acrylic or polyimide resin dispersed with pigments, and formed on the black matrix
4
to be separated from each other for the purpose of preventing a color mixture. On the surfaces of the color filters
6
is coated a smoothing layer
8
for preventing a contamination in the color filters
6
and for compensating for a step coverage or morphological difference between the red, green and blue color filters
6
formed separately to smooth the substrate. A gate electrode
10
is formed on the smoothing layer
8
. The gate electrode
10
is formed by depositing a gate metal material, that is, any one of metal materials such as Al, Mo, Cr, Ta and an Al alloy or building a double layer of the metal materials on the smoothing layer
8
and thereafter patterning it. On the smoothing layer formed with the gate electrode
10
, a gate insulating film
11
made from SiN
x
or SiO
x
, etc. is provided. A semiconductor layer
12
and an ohmic contact layer
14
are formed by disposing amorphous silicon (a-Si) and amorphous silicon (n
+
a-Si) doped with an impurity on the gate insulating film
11
and then patterning it. Source and drain electrodes
16
and
18
are formed by depositing a metal such as Al, Mo, Cr, Ta or an Al alloy, etc. and then pattering it. A pixel electrode
22
is made by forming a protective film from a material of SiN
x
or SiO
x
, etc. and a transparent electrode material (e.g., indium tin oxide (ITO)) and thereafter patterning them.
As described above, the conventional thin film transistor substrate inevitably requires the smoothing layer
8
so as to compensate for step coverage between the red, green and blue color filters
6
. However, the smoothing layer
8
does not make a little effect to a step coverage removal in the thin film transistor formed at the upper portion of the smoothing layer
8
. In the thin film transistor, a badness may occur at the layers (i.e., the semiconductor layer and the source and drain electrodes) disposed in the post process due to a step coverage in the gate electrode. Upon manufacturing of a large-dimension panel, it is necessary to form the gate electrode into a double metal layer for the sake of a good signal transmission. However, since a step coverage in the gate electrode is enlarged in the case of forming the gate electrode into a double metal layer, it becomes difficult to form a double layer of gate electrode and a material selection of the gate electrode is limited.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a thin film transistor substrate wherein a gate electrode is provided within a smoothing layer so as to compensate for step coverage in a thin film transistor.
A further object of the present invention is to provide a method of fabricating a thin film transistor substrate wherein a gate electrode is provided within a smoothing layer so as to compensate for step coverage in a thin film transistor.
In order to achieve these and other objects of the invention, a thin film transistor substrate according to one aspect of the present invention includes a thin film transistor formed on color filters; and a smoothing layer compensating for a step coverage between the color filters and being provided with a recess in which a gate electrode of the thin film transistor is to be formed.
A method of fabricating a thin film transistor substrate according to another aspect of the present invention includes the steps of forming color filters on a transparent substrate; forming a smoothing layer on the color filters and then pattering it to thereby define a recess in which a gate electrode of the thin film transistor is to be formed; and forming the thin film transistor on the smoothing layer.
REFERENCES:
patent: 5085973 (1992-02-01), Shimizu
patent: 5757451 (1998-05-01), Miyazaka et al.
patent: 6023307 (2000-02-01), Park
Birch & Stewart Kolasch & Birch, LLP
Flynn Nathan J.
LG. Philips LCD Co. Ltd.
Mandala Jr. Victor A.
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