Transflective pixel structure

Details Transflective pixel structure Transflective pixel structure

2003-01-30

2004-11-16

Chowdhury, Tarifur R. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S113000, C349S144000, C349S042000, C349S043000, C349S038000, C349S039000, C257S059000

Reexamination Certificate

active

06819385

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of Taiwan application serial No. 91134997, filed Dec. 3, 2002.
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates in general to a thin-film transistor (TFT) liquid crystal display (LCD), and more particularly, to a transflective pixel structure.
2. Related Art of the Invention
The thin-film transistor liquid crystal display is basically constructed with a thin-film transistor array substrate, a color filter array substrate, and a liquid crystal layer. The thin-film transistor array substrate includes a plurality of pixel structures arranged as an array, in which a plurality of thin-film transistors is formed, and each thin-film transistor has a corresponding pixel electrode. Each thin-film transistor has a gate, a channel layer, a drain region and a source region to be used as a switching device of the liquid crystal display.
FIG. 1
shows a top view of a conventional pixel structure, and
FIG. 2
shows a schematic cross-sectional view along the line I-I′ as shown in FIG.
1
.
Referring to
FIGS. 1 and 2
, in the fabrication method of the conventional pixel structure, a gate
102
and a scan line
101
are formed on a substrate
100
. The scan line
101
is coupled to the gate
102
. A gate dielectric layer
104
is further formed on the substrate
100
to cover the gate
102
and the scan line
101
. An amorphous silicon channel layer
106
is formed on the gate dielectric layer
104
over the gate
102
, and an Ohmic contact layer
108
is formed on the amorphous silicon channel layer
106
. A source/drain region
112
a
/
112
b
is then formed on the Ohmic contact layer
108
. Meanwhile, a data line connected to the source region
112
a
is defined on the gate dielectric layer
104
. The gate
102
, the channel layer
106
and the source/drain region
112
a
/
112
b
construct a thin-film transistor
130
. A protection layer
114
is then formed over the substrate
100
to cover the thin-film transistor
130
. The protection layer
114
is patterned to form an opening
116
therein. A pixel electrode
118
is formed on the protection layer
114
. The pixel electrode
118
is electrically connected to the drain region
112
b
via the opening
116
.
In the above pixel structure, a scan line
101
a
formed neighboring the pixel structure further comprises a pixel storage capacitor
120
. The pixel storage capacitor
120
comprises the scan line
101
a
(as a bottom electrode), a conductive layer
124
corresponding to the scan line
101
a
and the pixel electrode (as a top electrode), and the gate dielectric layer
104
formed between the bottom and top electrode. The conductive layer
124
and the pixel electrode
118
are electrically connected via an opening
126
formed in the protection layer
114
.
According to the above, the thin-film transistor
130
of the conventional pixel structure is located at a corner of the pixel structure to drive the complete pixel structure, and the pixel storage capacitor
120
is disposed on another scan line
101
a
. Therefore, the design of such a pixel structure is easy to fail due to process contamination particles. That is, if a contamination particle is attached to a part of the pixel structure to cause defects such as short circuit, the whole pixel structure cannot operate normally. Further, as the pixel storage capacitor
120
is formed on the scan line
101
a
, an additional stage of design is required for scanning waveform. Therefore, the design and fabrication process of the driving circuit are complex.
In addition, in the conventional transflective liquid crystal display, a plurality of reflective pixel structures and a plurality of transparent pixel structures are used or a semi-transparent film is formed on a substrate to obtain the transflective effect. Currently, a single pixel structure with co-existent transparent and reflective structures to attain transflective effect has not been disclosed yet.
SUMMARY OF INVENTION
The present invention provides a transflective pixel structure to resolve the problem occurring to the conventional pixel structure.
The present invention further provides a transflective pixel structure with both transparent and reflective structures coexistent in a single pixel structure.
The transflective pixel structure provided by the present invention provides is suitably formed on a substrate. The transflective pixel structure comprises a scan line, a gate dielectric layer, a data line, a protection layer, a transparent pixel electrode, a reflective pixel electrode and a double-drain thin-film transistor. The scan line is formed on the substrate. The gate dielectric layer is formed on the substrate to cover the scan line. The data line is formed on the gate dielectric layer with an extension direction different from that of the scan line. The protection layer is formed on a part of the gate dielectric layer covering the data line. The transparent pixel electrode is formed on the protection layer, and the part of the transparent pixel electrode over the scan line has a plurality of openings to reduce the parasitic capacitance between the scan line and the transparent pixel electrode. The reflective pixel electrode is formed on the exposed gate dielectric layer, with an area equal or unequal to that of the transparent pixel electrode. Further, the double-drain thin-film transistor is formed on the substrate at the center of the pixel structure. The double-drain thin-film transistor has a gate, a channel layer, a source region and two drain regions. The source region is electrically connected to the data line, and the drain regions are electrically connected to the transparent and reflective pixels, respectively. The channel is located on the gate dielectric layer on the gate, the source region and the drain regions are located on the channel layer, and the gate is electrically connected to the scan line.
In the present invention, two edges of the transflective pixel structure further include a first pixel storage capacitor and a second pixel storage capacitor. The first pixel storage capacitor includes a first common line formed on the substrate (as a bottom electrode), a conductive layer over the first common line and the transparent pixel electrode (as a top electrode), and the gate dielectric between the bottom and top electrodes. The conductive layer is electrically connected to the transparent pixel electrode via a contact window formed in the protection layer. The second pixel storage capacitor includes a second common line formed on the substrate (as a bottom electrode), the reflective pixel electrode over the second common line (as a top electrode) and the gate dielectric layer.
As the pixel structure provided by the present invention includes both a transparent pixel electrode and a reflective pixel electrode, the liquid crystal display comprising such a pixel structure has the advantages of transflective liquid crystal display such as power saving characteristic.
Further, as the thin-film transistor is formed at a center of the pixel structure, and two drain regions of the thin-film transistor simultaneously drive the pixel electrodes at two sides, so that the normal operation of the pixel structure can be maintained without being affected by the process particle.
By forming the thin-film transistor on the center of the pixel structure, the electric field on the pixel structure is more uniform and advantageous to display.
As the pixel storage capacitor is not formed on the scan line, the design of the driving circuit of the present invention is simplified.


REFERENCES:
patent: 5132819 (1992-07-01), Noriyama et al.
patent: 5132820 (1992-07-01), Someya et al.
patent: 5686976 (1997-11-01), Nishikawa
patent: 6611300 (2003-08-01), Ohkubo et al.
patent: 6697138 (2004-02-01), Ha et al.

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