Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-12-28
2001-11-20
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S059000, C257S072000, C257S329000, C349S038000, C349S042000, C349S043000
Reexamination Certificate
active
06320221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor liquid crystal display(hereinafter “TFT-LCD”), and more particularly to a TFT-LCD having a vertical thin film transistor.
2. Description of the Related Art
Liquid crystal displays used in television and other graphic display devices have been developed for substituting the cathode ray tube(“CRT”). Particularly, the TFT-LCD has an advantage of excellent response characteristic and is appropriate for high number of pixels. Therefore, high quality and large size of display devices comparable to the CRT, is realized.
The TFT-LCD comprises a TFT array substrate in which a TFT and a pixel electrode are formed, a color filter substrate in which a color filter and a counter electrode are formed, and a liquid crystal layer sandwiched between the TFT array substrate and the color filter substrate.
FIG. 1
is a plane view showing a TFT array substrate of a conventional TFT-LCD. As shown in the drawing, a plurality of gate lines
2
are arranged in rows and a plurality of data lines
8
are arranged perpendicular to the gate lines
2
. A pixel electrode
7
made of transparent metal layer, for example an ITO metal layer, is disposed within a pixel area defined by a pair of gate lines
2
and a pair of data lines
8
. A TFT
10
is disposed at a portion of intersection of the gate line
2
and the data line
8
. The TFT
10
includes a gate electrode, i.e. a part of the gate line
2
, a drain electrode
8
b
withdrawn from the data line
8
, and a source electrode
8
a
opposed to the drain electrode
8
b
and in contact with the pixel electrode
7
.
FIG. 2
is a cross-sectional view taken along the line II-II′ of FIG.
1
. As shown in the drawing, a transparent insulating substrate, for example a glass substrate
1
is provided and a gate electrode
2
a
is formed on the glass substrate
1
. A gate insulating layer
3
is deposited on the glass substrate
1
to cover the gate electrode
2
a,
and an etch stopper
4
is formed on the gate insulating layer portion of an upper portion of the gate electrode
2
a.
A semiconductor layer
5
and an ohmic contact layer
6
of a stacked structure are formed to extend at both sides of the etch stopper
4
. The semiconductor layer
5
is made of an undoped amorphous silicon and the ohmic contact layer
6
is made of a doped amorphous silicon. A pixel electrode
7
is formed on the gate insulating layer portion corresponding to the pixel area. Source and drain electrodes
8
a,
8
b
made of an opaque metal are formed on the ohmic contact layer
5
, thereby forming a TFT
10
. The source electrode
8
a
is formed in contact with the pixel electrode
7
.
The TFT-LCD having the TFT array substrate of the foregoing structure has shortcomings as follows.
First of all, the semiconductor layer of the TFT is made of the undoped amorphous silicon as previously described. However, since the amorphous silicon has low mobility, it is suitable for applying in the small size TFT-LCD, and it is not suitable for applying in the large size and high quality TFT-LCD. Meanwhile, a technique to use polysilicon having relatively high mobility instead the amorphous silicon, has been under development. However, in order to utilize this technique, already established production line should be changed thereby requiring further cost for investing the equipment.
Next, the source and the drain electrodes of the TFT are formed within the pixel area. However, since the source and the drain electrodes made of an opaque metal, the aperture ratio is degraded.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a TFT-LCD having a vertical TFT capable of obtaining enhanced aperture ratio and suitable for the manufacturing of large size and high quality display device.
To accomplish the object, the TFT-LCD of the present invention comprises: a transparent insulating substrate; a plurality of gate lines and data lines arranged on the transparent insulating substrate perpendicular to each other, wherein the gate line comprises a recess at a portion toward a corresponding pixel area; a pixel electrode disposed within a pixel area defined by a pair of gate lines and a pair of data lines, wherein the pixel electrode comprises a protrusion disposed within the recess without contacting the gate line; and a thin film transistor disposed at a portion of intersection of the gate line and the data line, wherein the thin film transistor comprises a gate electrode including the recess; a protrusion of the pixel electrode functioning as a source electrode; a first ohmic contact layer, a semiconductor layer and a second ohmic contact layer all stacked on the protrusion; and a drain electrode withdrawn from the data line and disposed on the second ohmic contact layer, wherein channel regions in the semiconductor layer are formed in a vertical direction at each portion adjacent to the gate electrode.
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Choi Gyo Un
Kim Sung Kon
Sung Nak Hyun
Dickey Thomas L.
Hyundai Electronics Industries Co,. Ltd.
Selitto Behr & Kim
Tran Minh Loan
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