Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Plasma excitation
Reexamination Certificate
1998-07-24
2001-05-01
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Plasma excitation
Reexamination Certificate
active
06226056
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, in particular to a plasma addressed liquid crystal display device (PALC). The present invention also relates to a dielectric sheet for separating a plasma switching section from a liquid crystal cell section of a PALC, and a method for producing the same.
2. Description of the Related Art
FIG. 26
is a perspective view of a conventional plasma addressed liquid crystal display device (PALC), and
FIG. 27
is a cross sectional view thereof. The conventional plasma addressed liquid crystal display device will now be described with reference to
FIGS. 26 and 27
.
The plasma addressed liquid crystal display device includes two sections: a plasma switching section
1
a
and a liquid crystal cell section
1
b.
The plasma switching section (also referred to as a plasma cell substrate)
1
a
includes a glass substrate
4
, a dielectric sheet
6
, and a plurality of partition walls
5
formed between the glass substrate
4
and the dielectric sheet
6
, and a plurality of plasma discharge channels (i.e., plasma generating region, plasma channel, or plasma cell) surrounded by the glass substrate
4
, the dielectric sheet
6
, and the plurality of partition walls
5
. The liquid crystal section
1
b
includes a liquid crystal layer
7
and a counter substrate (also referred to as a color filter substrate in the case where it includes a color filter layer)
1
b′.
The liquid crystal layer
7
is interposed between the dielectric sheet
6
and the counter substrate
1
b′.
The counter substrate includes a glass substrate
10
and a plurality of strip electrodes
8
on a side of the liquid crystal layer
7
. The counter substrate
1
b′
may include a color filter layer
9
having R, G and B color filters for conducting a color display.
In the plasma cell substrate
1
a,
alternating strips of anode electrodes
14
and cathode electrodes
12
are formed on the glass substrate
4
having a thickness of about 2 mm. The partition wall
5
for separating a plasma discharge channel
17
are formed on each of the anode electrodes
14
. Prior to the formation of the anode electrodes
14
and the cathode electrodes
12
, an underlying film
13
of, for example, an SiO
2
-type material is formed on that surface of the glass substrate
4
on which the anode electrodes
14
and the cathode electrodes
12
are to be formed.
The dielectric sheet
6
for separating the plasma discharge channels
17
from the liquid crystal layer
7
is formed on the partition walls
5
. Conventionally, a thin plate of glass is used as the dielectric sheet
6
. After being evacuated into a vacuum state, each plasma discharge channel
17
between the partition walls
5
is filled with a rare gas (such as He and Ne) containing a small amount of Hg, in order to cause a plasma discharge in the plasma discharge channel
17
.
In the counter substrate
1
b′,
a black matrix
9
a
and a color filter layer
9
are formed on a glass substrate
10
. On the color filter layer
9
, strips of signal electrodes
8
of indium tin oxide (ITO) are formed substantially perpendicular to the partition walls
5
.
Alignment films
15
and
16
(not shown in
FIG. 26
) are respectively applied on the opposing surfaces of the dielectric sheet
6
and the color filter layer
9
having the signal electrode
8
thereon. Then, the alignment films
15
and
16
are rubbed. The plasma cell substrate
1
a
and the counter substrate
1
b′
are attached to each other with a spacer (not shown) being provided either on the plasma cell substrate
1
a
or on the counter substrate
1
b′
for maintaining a prescribed cell gap (i.e., a thickness of a liquid crystal layer). At this time, the plasma cell substrate
1
a
and the counter substrate
1
b′
are attached to each other so that the respective rubbing directions are substantially perpendicular to each other. The gap between the plasma cell substrate
1
a
and the counter substrate
1
b′
is filled with a liquid crystal material, whereby the liquid crystal layer
7
is formed. Polarizing plates
3
and
11
are provided to the respective outer surfaces of the glass substrates
4
and
10
such that their polarization axes correspond to the respective rubbing directions. Accordingly, the polarization axes of the polarizing plates
3
and
11
are substantially perpendicular to each other. A surface-emitting backlight
2
is provided on the plasma cell substrate
1
a
side.
(Operation principle of plasma switching section)
The operation principle of the plasma switching section will now be described with reference to FIGS.
28
and
29
. It should be noted that time periods (
1
) to (
6
) in
FIG. 29
correspond to (
1
) to (
6
) in
FIG. 28
, respectively.
In the plasma addressed liquid crystal display device (PALC), the plasma discharge channels
17
in which a plasma discharge is caused are subjected to switched line-sequential scanning, and a data signal or an image signal is applied to the signal electrodes
8
in synchronization with the scanning, whereby display driving is conducted. When the anode electrodes
14
are connected to the ground and a negative pulse voltage is applied to the cathode electrodes
12
, a plasma discharge occurs within the corresponding plasma discharge channel
17
(
FIG. 28
, (
1
)), and carriers (space charges) (ions/electron pairs) for writing data are produced. Accordingly, the plasma discharge channel
17
is rendered at the same potential as that of the anode electrode
14
. Furthermore, an interface potential is produced at that surface of the dielectric sheet
6
which faces the plasma discharge channel
17
, whereby a virtual electrode (not shown) is formed. When the application of the negative pulse voltage is discontinued after a prescribed time period, the plasma discharge is finished. However, the virtual electrode still remains at the same potential as that of the anode electrodes
14
. When a data voltage corresponding to the data signal or the image signal is applied to the signal electrodes
8
, the data voltage is divided according to the capacitance division ratio of the dielectric sheet
6
to the liquid crystal layer
7
, whereby a prescribed image signal is applied (written) to the liquid crystal layer
7
(
FIG. 28
, (
2
)). When the plasma discharge is finished, the carriers will disappear over time, and the plasma discharge channel
17
will return to an insulating state. The accumulated charges corresponding to the image signal applied (written) to the liquid crystal layer
7
are retained until the next discharge occurs in response to the application of a negative pulse voltage (
FIG. 28
, (
3
)). By conducting the series of operations described above, display data corresponding to a single line is output from a liquid crystal driver to the signal electrodes
8
on a plasma discharge channel by plasma discharge channel basis. Thus, the data corresponding to a single line is written to the liquid crystal layer
7
at one time. In order to prevent degradation of the life of the liquid crystal material, the write operation to the liquid crystal layer
7
is conducted by alternating-current driving of the anode potential. Accordingly, data is written to the liquid crystal layer
7
with a polarity of the data voltage being inverted on a line by line basis.
FIG. 28
further shows a plasma discharge (
4
), a data write operation (
5
) and a data retaining operation (
6
) in the case of the write operation conducted with polarity inversion. The operation principle in the case of (
4
), (
5
) and (
6
) is the same as that in the case of (
1
), (
2
) and (
3
) except that the polarity of the data voltage is inverted in (
4
), (
5
) and (
6
). The series of operations described above is sequentially conducted on the plasma discharge channel by plasma discharge channel basis, whereby an image corresponding to a single frame is displayed.
(Dielectric sheet)
The dielectric sheet
6
will now be d
Malinowski Walter J.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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