Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-08-30
2003-11-25
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S138000
Reexamination Certificate
active
06654073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor (TFT) type liquid crystal display and a method of fabricating the same. In particular, the present invention relates to a high-resolution liquid crystal display which has an improved aperture ratio and high reliability as well as is simple in structure and capable of low-cost and high-yield fabrication, and a method of fabricating the same.
2. Description of the Related Art
An active matrix type liquid crystal display using thin film transistors (hereinafter, referred to as TFTs) as its switching elements comprises a TFT array substrate, a light shielding film (so-called black matrix), and a color filter substrate which are opposed to one another across liquid crystal. Pixel regions each having an independent TFT and a pixel electrode are arranged on the TFT array substrate in a matrix. On the color filter substrate are laminated a color layer and a transparent common electrode.
FIG. 1
is a circuit diagram showing the circuit configuration of a single pixel region in a conventional liquid crystal display. In
FIG. 1
, this liquid crystal display comprises a plurality of address lines
110
a
,
110
b
, . . . , a plurality of address lines
120
a
,
120
b
, . . . , a liquid crystal element
130
, a TFT section
140
, and a storage capacitance section
150
. The address lines
110
a
,
110
b
, . . . are formed on an insulative substrate. The data lines
120
a
,
120
b
, . . . are formed thereon across a gate insulating film so as to cross the address lines
110
a
,
110
b
, . . . . The liquid crystal element
130
is formed in a pixel region P
1
that is enclosed with the address lines
110
a
,
110
b
and the data lines
120
a
,
120
b
. The TFT section
140
drives the liquid crystal element
130
. The storage capacitance section
150
stores capacitance in parallel with the liquid crystal element
130
.
The address lines
110
a
,
110
b
, . . . are driven by an address line driver (not shown), so that a signal for forming a scanning line on the screen of the liquid crystal display is transmitted to the TFT section
140
in the pixel region P
1
.
The data lines
120
a
,
120
b
, . . . are driven by a data line driver (not shown), so as to transmit an image signal to the TFT section
140
in this pixel region P
1
.
The liquid crystal element
130
consists of a pixel electrode
131
, liquid crystal
132
, and a counter electrode
133
. The pixel electrode
131
and the liquid crystal
132
spread throughout the pixel region P
1
. The counter electrode
133
, opposed to the pixel electrode
131
across the liquid crystal
132
, is common to the entire screen of the liquid crystal display. This counter electrode
133
is connected to a con potential COM. Both the pixel electrode
131
and the counter electrode
133
are formed of an ITO (indium-tin oxide) or other transparent conductive film.
The TFT section
140
consists of a gate
141
extended from the address line
110
a
, an electrode (hereinafter, referred to as drain electrode)
142
extended from the data line
120
a
, and an electrode (hereinafter, referred to as source electrode)
143
connected to the pixel electrode
131
. The scanning line signal applied to the gate
141
selectively connects the drain electrode
142
and the source electrode
143
to each other so that the image signal supplied through the data line
120
a
is transmitted to the pixel electrode
131
.
The storage capacitance section
150
is provided so that when the address line
110
b
becomes non-selected, a liquid crystal driving potential applied to the pixel electrode
131
at that moment is retained until a next scanning line signal is applied to the gate
141
. This prevents the liquid crystal driving potential from leaking to drop through the TFT section
140
and the like and shifting the liquid crystal
132
into an inactive mode to cause a change in color density. In the example of
FIG. 1
, the storage capacitance section
150
is formed between the address line
110
b
of an adjacent pixel region P
2
and the storage capacitance electrode
151
in this pixel region P
1
. While a scanning line signal is applied to the pixel region P
1
the address line
110
b
in the adjacent pixel region P
2
is non-selected, and is supplied with a constant potential of the order of −10 V from a driver IC (not shown). This makes it possible to use the address line
110
b
as a common electrode
152
in the storage capacitance section
150
.
In some other examples of the liquid crystal display, the common electrode to be opposed to the storage capacitance electrode
151
is not extended from the address line
110
b
in the adjacent pixel region P
2
. In such cases, auxiliary capacitance common wiring is additionally laid between the address lines
110
a
and
110
b
, and this auxiliary capacitance cannon wiring is used as the common electrode
152
opposed to the storage capacitance electrode
150
.
FIGS. 2 and 3
show the typical constitution of a pixel region in a conventional liquid crystal display, the pixel region having the circuit configuration shown in FIG.
1
.
FIG. 2
is a plan view showing the pixel region in a conventional liquid crystal display.
FIG. 3
is a sectional view taken along the line I—I of FIG.
2
.
In
FIGS. 2 and 3
, this liquid crystal display comprises address lines
110
b
and
110
b
formed on an insulative substrate
101
. A gate insulating film
102
is formed thereon. Moreover, data lines
120
a
and
120
b
cross the address lines
110
a
and
110
b
are formed thereon. A pixel electrode
131
is arranged in a pixel region P
1
enclosed with the address lines
110
a
,
110
b
and the data lines
120
a
,
120
b
. Also formed in this pixel region P
1
is a TFT section
140
which includes a gate
141
extended from the address line
110
a
, a drain electrode
142
extended from the data line
120
a
, and a source electrode
143
connected to the pixel electrode
131
. The connection between the source electrode
143
and the pixel electrode
131
is established by a conductive through hole
135
piercing through an upper insulating film
103
. In this liquid crystal display, one end of the pixel electrode
131
is extended until it overlaps the address line
110
b
, so as to form a storage capacitance electrode
151
. Accordingly, a storage capacitance section
150
is constituted with the address line
110
b
as a common electrode
152
.
In the liquid crystal display shown in
FIGS. 2 and 3
, however, the storage capacitance electrode
151
and the can electrode
152
sandwiched both the gate insulating film
102
and the upper insulating film
103
, i.e., dielectric layers of greater thickness. Therefore, per-area capacitance was small. On this account, a method has been devised in which a part of the address line
110
b
is extended into the pixel region as the common electrode
152
to increase the area of the storage capacitance section
150
. Nevertheless, the non-transparent storage capacitance section made it difficult to secure both a sufficient aperture ratio and capacitance within the given pixel region, producing a problem of darker images.
FIG. 4
is a sectional view showing a pixel region in another conventional liquid crystal display. To solve the problem, the following structure has been proposed. That is, as shown in
FIG. 4
, the storage capacitance electrode
151
was formed over the address line
110
b
across the gate insulating film
102
by using the same metal film that constitutes the source electrode
143
. This storage capacitance electrode
151
was connected to the pixel electrode
131
via a conductive through hole
136
piercing through the upper insulating film
103
.
Recently, increased demand for high-resolution liquid crystal displays has shifted the dimensions of the pixel regions from a conventional order of e.g. 100 &mgr;m×300 &mgr;m to a latest order of 40 &mgr;m×120 &mgr;m. This not only demands higher working precision, but also requires that factors d
Hidehira Masanobu
Horie Yoshitaka
Kikkawa Hironori
Maruyama Muneo
Nakata Shinichi
Hayes & Soloway P.C.
NEC LCD Technologies Ltd.
Schechter Andrew
Ton Toan
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