Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal writing tablet
Reexamination Certificate
2000-03-03
2002-10-29
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal writing tablet
C349S113000
Reexamination Certificate
active
06473140
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display (LCD) and, in particular, to an active matrix LCD integrated with a pen input apparatus. Description of the Related Art
FIG. 1
is a cross-sectional view briefly showing structure of an example of an active matrix LCD of a twisted nematic (TN) mode driven or addressed by thin-film transistors (TFTs). As can be seen from
FIG. 1
, the active matrix LCD of the prior art includes a substrate
10
a
with pixel electrodes
8
and a substrate
10
b
with a common electrode
6
. Each glass substrate
10
a
,
10
b
has a thickness of about 0.6 millimeter (mm) to 1.1 mm.
Disposed on the glass substrate
10
b
is a common electrode layer
6
. For a color panel, there is further arranged a color filters. On the other side, there are disposed on the glass of the substrate
10
a
a plurality of gate and drain bus lines in a matrix shape. In association with the gate and drain bus lines, thin-film transistors (TFTs)
9
are connected to pixel electrodes
8
. Consequently, both heat resisting characteristic and flatness are required for the glass substrate employed as the substrate
10
a
for fabrication of these TFTs
9
. The glass substrates
10
a
and
10
b
are separated from each other by spacers having a diameter of about several micrometers (&mgr;m). Sealed in the gap therebetween is liquid crystal to form a liquid crystal layer
7
so as to form a liquid crystal panel. On each of two outside surfaces, there are arranged polarizing plates
2
. For an LCD of a transmission type, a back light layer
11
is provided as shown in FIG.
1
. For an LCD of a reflective or reflection type, a polarizer plate of a reflection type is disposed on one of the outside surfaces in place of one of the transmission-type polarizing plates
2
. Additionally, electrodes for pen input operation
4
are formed on the opposing glass substrate
10
b
. This allows use of data input facilities such as a screen input apparatus in which data is inputted to the liquid crystal display when a surface of the apparatus is depressed, for example, by a pen
1
.
In addition to the liquid crystal display above, there exists an active matrix LCD of phase-change guest-host (PCGH) mode driven by thin-film transistors. Although the glass substrates of the LCD are the same as those of the TN-type LCD, the liquid crystal includes dichroic dye mixture; moreover, the polarizer plates are dispensed with. As a consequence, when the GH-mode LCD is produced as a reflection-type display, metallic electrodes of aluminum or the like are employed as the pixel electrodes to function also as reflection plates. An LCD having the configuration above has been described, for example, in pages 437 to 440 of the SID 92 Digest entitled “Bright Reflective Multicolor LCDs Addressed by a-Si TFTs” written by S. Mitsui, Y. Shimada, K. Yamamoto, T. Takamatsu, N. Kimura, S. Kozaki, S. Ogawa, H. Morimoto, M. Matsuura, M. Ishii, K. Awane, and T. Uchida.
There has been known an apparatus to input images in a computer in which an input device is integrated with a display including a screen such that when the screen is directly touched, for example, by a finger, the touched position is presented on the screen.
For example, as shown in
FIG. 2
, there exists an apparatus including a display
12
and a tablet
13
separated from the display
12
, which are fixedly attached onto each other. In this constitution, for example, a liquid crystal display is adopted as the display
12
and a resistive-film-type tablet is used as the tablet in which, for example, small openings are disposed between two resistive films connected to a power source. When the resistive films are brought into contact with each other, an electric current resultantly flowing through the contract point is sensed so as to detect the position of the contact point. In this regard, a reference numeral
14
designates a pen for designating the indication point in FIG.
2
. Subsequently,
FIG. 3
shows a cross-sectional view of a display with integrated tablet constructed as shown in FIG.
2
. The display of
FIG. 3
includes a tablet
15
, polarizer layers
16
and
17
, glass substrates
18
and
19
keeping liquid crystal therebetween, twisted nematic (TN) liquid crystal
20
, and a back light layer
21
as a light source.
Conventionally, according to an active matrix LCD in the field of the present invention, a glass substrate having a thickness of about 0.6 mm to about 1.1 mm is utilized for each of the substrates. In consideration of mechanical strength of the glass substrate, it is difficult to further reduce the thickness thereof. In the case where a screen input apparatus such as a pen input device is combined with the LCD of this kind, when a pen of the pen input device is brought into contract with a surface of the LCD to input data such as characters and letters, the thickness of the glass substrate, i.e., the distance between an end point of the pen placed on the surface and an image formed by the liquid crystal is observed as parallax, leading to difficulty in input operation.
On the other hand, the thickness of each film substrate of the LCD is set to about 0.1 mm to remove parallax, when other films are accumulated on the substrate on the pixel electrode side to construct switching elements, the substrate may be warped or cambered by stress of the accumulated thin films because of the reduced thickness of the substrate. In addition, there also exists a problem in which when handling the substrate, the substrate is bent and hence switching elements thus formed are damaged.
Generally, moreover, in a display using the TN liquid crystal, when the gap thickness of liquid crystal is changed, the angle of twist of the liquid crystal is also varied in the pertinent portion, resulting in considerable alteration in transmittivity. Consequently, in the case where a display with integrated tablet is formed using the liquid crystal of TN mode as shown in
FIG. 2
, when the operator pushes a pen
14
against the tablet
13
to input data in the display, the gap thickness of liquid crystal is altered at the contact point of the pen
14
and in the periphery thereof. Consequently, the value of transmittivity at the position varies from the inherent value thereof in the display operation. This accordingly leads to the problem that quality of the image displayed therein is deteriorated when compared with that of the image in other areas of the screen.
To solve this problem, there has been proposed a method in which, as shown in
FIG. 4
, a transparent protective layer
23
formed of glass, plastic, or the like is inserted between the tablet
13
and the LCD
12
to prevent pressure of the pen
14
from exerting influence upon the LCD
12
. However, when this method is employed, in order to keep the gap thickness of the LCD
12
unchanged, it is necessary to guarantee that the protective layer
23
is not deformed by pressure. For this purpose, a considerably thick and strong protective layer is required to be provided between the tablet
13
and the LCD
12
. This inevitably results in of increase in weight and thickness when producing the display with integrated tablet. Additionally, since the end point of the pen
14
is separated from the liquid crystal by several millimeters or more, there also occurs a problem of parallax, namely, the image is displayed at a position displaced from the position indicated by the end point of the pen
14
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an active matrix LCD in which warping of the substrates and damage of switching elements are prevented and parallax between the end point of the pen of the pen input device and the image formed by the liquid crystal is eliminated.
In accordance with the present invention, to achieve the above object, there is provided a liquid crystal display (LCD) with integrated tablet comprising an upper substrate on a viewing side on which electrodes are formed to drive liquid crystal, a lower substrate o
Hirai Yoshihiko
Ikeda Naoyasu
Mizobata Eishi
Hayes & Soloway P.C.
Nguyen Dung
Ton Toan
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