Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-03-06
2004-10-05
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S149000, C349S153000, C349S155000
Reexamination Certificate
active
06801289
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active matrix liquid crystal display device adopting switching elements such as MIM (metal insulator metal), TFT (thin film transistor).
BACKGROUND OF THE INVENTION
In recent years, a liquid crystal display device which consumes less power and has superior portability is often adopted as a display device of mobile phones. Especially, an STN-LCD (super twisted nematic-liquid crystal display) having a simple structure and of lower cost is widely adopted.
As shown in
FIG. 17
, the STN-LCD has a glass substrate
101
made of glass and a counter substrate
102
which are opposed via a liquid crystal layer (not shown). Further, a sealing section made of a sealing material for sealing the liquid crystal of the liquid crystal layer is provided so as to enclose the display area between the glass substrate
101
and the counter substrate
102
.
The glass substrate
101
includes common lines
103
which also act as pixel electrodes for applying a voltage to the liquid crystal layer. The common line
103
is connected to a reference signal driver via a COM electrode on the glass substrate
101
. The counter substrate
102
includes segment lines
104
which also act as pixel electrodes. The segment line
104
is connected to a gradation signal driver via a SEG electrode on the counter substrate
2
. Further, the common line
103
and the segment line
104
are orthogonal, and both formed by a transparent conductive film such as ITO.
Further, in a color STN-LCD, the common line
103
is formed on a color filter and on an overcoat which protects the color filter. The overcoat is easy to get a scratch. This may cause the transparent conductive film which is formed on the overcoat to be the common line
103
to cut off even by an indistinct scratch which can be made during manufacturing processes since the common line
103
and the segment line
104
are formed on different substrates. Further, adhesion between the overcoat and the transparent conductive film made of ITO or the like is exceedingly weak in comparison with, for example, adhesion between glass and a transparent conductive film. Therefore, it is almost impossible to re-mount the reference signal driver and/or the gradation signal driver in the case where mounting is failed.
On the other hand, in a small or medium sized panel used for a display of a mobile phone, commonly, an input terminal of the common line
103
is formed on the counter substrate
102
. And the input terminal and the common line
103
are electrically connected by transfer technology using conductive particles which are distributed in the sealing section. Hereinafter, this connection part is referred to as “a transfer section”. By thus electrically connecting the input terminal and the common line
103
via the transfer section, the common line
103
and the segment line
104
can exist on a single substrate (the counter substrate
102
).
As described, since the common line
103
electrically transfers to the transparent conductive film made of ITO or the like formed on the counter substrate
102
via the conductive particles distributed in the sealing section, it prevents the cutoff of the common line
103
, and also, makes it possible to re-mount the reference signal driver and/or the gradation signal driver in the mounting process. Further, since the input terminal of the common line
103
is formed on the counter substrate
102
, the common line
103
and the segment line
104
can exist on a single substrate (the counter substrate
102
). This makes it possible to adopt a segment-common integral driver, and make the mounting compact in size.
However, in the foregoing STN-LCD, variation of contact resistance between the adjacent transfer sections is perceived as non-uniform display. Therefore, when assuming the mean distribution volume of the conductive particle is D, and its distribution is &sgr;, even when the distribution density of the conductive particle is small like D-5&sgr;, it is necessary to prevent contact resistance from being perceived as non-uniform display by conserving the transfer section area as large as possible and increasing the number of the conductive particle in the transfer section.
Here, the following will explain the variation of distribution volume of the conductive particle.
As shown in
FIG. 18
, when the conductive particles are distributed, the distribution is approximated by a normal distribution around the mean distribution volume D. When the volume of the conductive particle is more than the mean volume D, it is possible to ensure stable connection in the transfer section. In contrast, when the volume of the conductive particle is less than the mean volume D, connection in the transfer section, in other words, resistance in the transfer section varies depending on the distribution volume of conductive particle. Table 1 shows separation from the mean distribution volume D and probability of existence, regarding to the distributed conductive particles. (continued)
TABLE 1
PROBABILITY OF
16%
EXISTENCE LESS
THAN (D-&sgr;)
PROBABILITY OF
2.3%
EXISTENCE LESS
THAN (D-2&sgr;)
PROBABILITY OF
0.15%
EXISTENCE LESS
THAN (D-3&sgr;)
PROBABILITY OF
6.3 × 1e
−3
%
EXISTENCE LESS
THAN (D-4&sgr;)
PROBABILITY OF
5.73 × 1e
−5
%
EXISTENCE LESS
THAN (D-5&sgr;)
If assuming that the minimum particle density to prevent the contact resistance in the transfer section from being perceived as non-uniform display is D
0
, Table 1 shows that poor contact occurs at a rate of 0.15% when D
0
=D−3&sgr;. Namely, when a panel has
160
transfer sections, at least one in 4.2 panels will show poor contact. Similarly, as shown in Table 1, poor contact occurs at a rate of 5.73e
−5
% when D
0
=D−5&sgr;. In this case, when a panel has 160 transfer sections, at least one in 10908 panels will show poor contact. Determination of the mean distribution volume D is important in the distribution of the conductive particle, because distribution &sgr; is automatically determined by the mean distribution volume D, even though the distribution &sgr; can be adjusted to some extent by using an automatic stirring device for stirring the sealing material.
The permitted limit of the STN-LCD for the contact resistance variation in the adjacent transfer sections becomes smaller, as the STN-LCD has high-precision (256 colors→4096 colors) and multi-gradation displays (6500 colors). Further, as the line width of sealing section becomes narrower in accordance with high-precision and narrower frame (narrower non-display area), the area of the transfer section becomes smaller. Accordingly, it is difficult to apply the technology of electric transfer using the conductive particles distributed in the sealing section to the STN-LCD in terms of high-precision, multi-gradation displays, and narrower frame (narrower non-display area) which are major factors for a mobile phone in next-generation.
Meanwhile, liquid crystal display devices of active driving type in which a switching element such as MIM or TFT of counter source structure have been proposed as a liquid crystal display device (LCD) having a simple structure like the STN-LCD. These liquid crystal display devices are more suitable for high-precision, multi-gradation displays, and narrower frame which are major factors for a mobile phone in next-generation, in comparison with the STN-LCD.
FIG. 19
shows an example of an equivalent circuit of the arrangement in a conventional active matrix liquid crystal display device. In this liquid crystal display device, pixel electrodes
111
are formed in a matrix manner on a transparent substrate which will be an active matrix substrate. Further, on the transparent substrate, a TFT
112
which is a switching element is provided for each pixel electrode
111
. In each TFT
112
, the pixel electrode
111
is connected to a drain electrode. And in the TFTs
112
which are horizontally (in a column direction) aligned in a display screen, respective gate elec
Fujiwara Koji
Ichioka Hideki
Inoue Naoto
Tanaka Keiichi
Yamamoto Tomohiko
Caley Michael H.
Kim Robert H.
Nixon & Vanderhye P.C.
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