Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-01-28
2002-04-02
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S149000, C349S152000
Reexamination Certificate
active
06366331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix liquid-crystal display device, and more particularly to the configuration of a terminal for electrical connection to an external driving element.
2. Background of the Invention
Active matrix liquid-crystal display devices are known as flat panel displays which save space and operate on a small amount of electrical power.
FIGS.
11
(
a
)-(
b
) illustrate the concept of an active matrix liquid-crystal display device of the past, and FIG.
11
(
a
) showing the configuration thereof, and FIG.
11
(
b
) showing an equivalent circuit of a TFT substrate.
This active matrix liquid-crystal display device has a thin-film transistor (TFT) substrate
1101
and a color filter substrate (hereinafter referred to as a CF substrate)
1102
, in between which is sandwiched a twisted nematic (TN) liquid crystal.
The TFT substrate
1101
has a plurality of pixel electrodes
1106
on a matrix, these pixel electrodes
1106
being connected to thin-film transistors (TFTs)
1109
, which act as switching transistors.
Scanning lines
1107
that supply a scanning signal are connected to the gate electrodes of the TFTs, and data lines
1108
, which input a display signal, are connected to the drain electrodes, so as to drive the TFTs.
In the peripheral area around the TFT substrate
1101
are provided terminals
1110
in a terminal block
1111
for the purpose of inputting scanning and display signals, these being connected to a signal processing substrate (TAB: taped automated bonding)
1103
.
Additionally, the TAB
1103
is connected to an external printed circuit board
1104
. The CF substrate
1102
has a RGB color layers and a light-blocking layer for the purpose of blocking light, corresponding to each of the opposing electrodes and pixels.
FIG.
12
(
a
) is a plan view and FIG.
12
(
b
) is a cross-section view of a unit element in an active matrix liquid-crystal display device of the past.
In this display device, the display device is so configured in that the TFT
1203
is formed on a TFT glass substrate
1215
, and the TFT
1203
is further comprising a gate electrode
1206
connected to a scanning line
1201
, a gate insulation film
1209
formed so as to cover the gate electrode
1206
, a drain electrode
1208
connected to a signal line
1202
formed on the gate insulation film
1209
, a source electrode
1207
connected to a pixel electrode, a passivation film
1210
formed so as to cover the above-noted elements, and a pixel electrode
1205
connected to the source electrode
1207
via a contact hole
1204
provided in the passivation film. In FIG.
12
(
b
), a black matrix
1213
is shown opposite the TFT
1203
, with opposing electrodes
1214
provided therebetween.
In the above-noted active matrix liquid-crystal display device of the past, terminals are provided around the periphery of the display device for making connection between an external substrate TAB and each one of the wirings.
FIGS.
13
(
a
)-(
c
) show the gate side terminal
1303
connected to the scanning line
1301
, and the data side terminal
1304
connected to the data line
1302
, FIG.
13
(
a
) being a plan view thereof, and FIG.
13
(
b
) and FIG.
13
(
c
) being cross-section views in the directions indicated by the lines
13
(
b
)-
13
(
b
)′ and
13
(
c
)-
13
(
c
)′.
The gate side terminal
1303
is provided with a gate layer metal
1306
for forming a gate electrode or the like, onto one region of which is formed a contact hole
1312
, a transparent electrode
1310
forming a pixel electrode, for example, being formed as the uppermost layer so as to cover the gate layer metal. A gate insulation film
1307
and a passivation film
1308
are also provided.
A data side terminal
1304
is provided with a data layer metal
1311
forming a drain electrode, for example, on one region of which is formed a contact hole
1312
, a transparent electrode
1310
forming a pixel electrode, for example, being formed as the uppermost layer so as to cover the gate layer metal.
These terminals are connected to TAB lead wires by heating and applying pressure to an anisotropic conductive film (ACF) made of a thermally cured adhesive throughout which fine conductive particles are uniformed dispersed.
In a TFT substrate of the past, an inorganic film of a material such as SiN having a thickness of 200 to 400 nm is used as a passivation layer, and there was no overlap between pixel electrodes and wires.
Recently, however, there has been a disclosure, for example, in U.S. Pat. No. 5,641,974, of a technology for causing overlap between a pixel electrode and a wire and broadening the transparent region.
When this is done, in order to reduce the capacitance between the pixel electrode and the signal wires, further patterning is done of an organic film on the passivation film, this being formed to a thickness of 2 to 4 &mgr;m.
FIGS.
14
(
a
)-(
b
) show the scanning line
1401
and the data line
1402
. FIG.
14
(
a
) being a plan view thereof, and FIG.
14
(
b
) being a cross-section view in the directions indicated by the lines
14
(
b
)-
14
(
b
)′, in which the above-noted organic film is used in an interlayer insulation film.
The process up until the patterning of the passivation film
1410
is the same as in the past. a photosensitive organic film
1411
of acrylic resin or the like is spin-coated onto the passivation film
1410
, and this is exposed and developed so as to form a pattern for contact holes
1404
or the like.
When this is done, the organic film in the terminal region is removed, and post-baking is done to thermally harden the organic film.
Finally, a pixel electrode
1405
is formed, and connection is made to the source electrode
1407
of the TFT
1403
. In FIG.
13
(
b
), a black matrix
1413
is shown opposite the TFT
1403
, with opposing electrodes
1414
provided therebetween.
In the above-noted technology disclosed in U.S. Pat. No. 5,641,974, the transparent region is larger and it is possible to obtain a liquid-crystal display device with brighter and better display performance than in the past.
However, because the passivation film patterning and organic film patterning are performed in different process steps, the number of patterning steps increases, thereby complicating the process and increasing the manufacturing cost.
To solve the above-noted problems, a method was proposed in Japanese Patent Application No. 9-323423, whereby two layers of resist are used to perform organic film patterning and passivation film patterning simultaneously. FIGS.
15
(
a
)-(
d
) show the process flow using this method to form a contact hole.
Steps up until the formation of the passivation film
1507
are the same (i.e., forming a TFT on a TFT substrate
1501
having a gate electroe
1502
, a drain electrode
1505
, a source electrode
1506
, gate insulation film
1503
, an amorphous silicon layer
1504
and a passivation film
1507
) as in the prior art (FIG.
15
(
a
)). After continuous application of the organic film
1510
and the resist
1509
, exposure and developing are done to simultaneously pattern the resist and wet etch the organic film to frm contact hole
1508
(FIG.
15
(
b
)).
Then, the patterning of the passivation film
1507
is dry-etched with etching has
1511
using the resist
1509
and organic film
1510
as a mask (FIG.
15
(
c
)).
Finally, the resist
1509
only is selectively melted with a specific removing liquid so as to remove the resist (FIG.
15
(
d
)).
When this is done, because one and the same mask is used to pattern the organic film and the passivation film, it is not possible to remove the organic film on the terminal part.
FIGS.
6
(
a
)-(
b
) show how the TAB
608
and the terminal
601
are connected. In order to distribute the conductive particles
607
uniformly throughout the anisotropic conductive film
606
, the diameter of the conductive particles
607
is generally in the range of 2 to 4 &mgr;m.
On the other hand, because the thickness of the organic film is 2 to 4
Sakamoto Michiaki
Sugitani Choei
Chowdhury Tarifur R.
Sikes William L.
Sughrue & Mion, PLLC
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