Liquid crystal display device

Details Liquid crystal display device Liquid crystal display device

2000-11-15

2003-02-04

Dudek, James (Department: 2871)

Liquid crystal cells, elements and systems

Particular excitation of liquid crystal

Plasma excitation

Reexamination Certificate

active

06515718

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, in particular, to a plasma addressed liquid crystal display device of a flat panel structure including a liquid crystal cell and a plasma cell arranged in layers.
Development of plasma addressed liquid crystal display devices (hereinafter, abbreviated as PALCD devices) is in progress for realization of large and thin flat displays. For example, a PALCD device is disclosed in Japanese Laid-Open Patent Publication No. 1-217396.
FIG. 20
schematically illustrates a conventional PALCD device
200
. The PALCD device
200
has a layered structure composed of a liquid crystal cell
201
and a plasma cell
202
with a dielectric sheet
203
interposed therebetween. A pair of polarizing plates
213
and
214
sandwich the liquid crystal cell
201
and the plasma cell
202
. Typically, a backlight (not shown) is disposed on the back of the plasma cell
202
.
The plasma cell
202
includes: an insulating substrate
204
having a plurality of parallel stripe grooves
205
formed therein; and the dielectric sheet
203
that serves as part of the liquid crystal cell
201
as will be described later. Each of the plurality of grooves
205
formed in the substrate
204
is sealed with the dielectric sheet
203
. The sealed space of the groove is filled with gas ionizable with discharge, forming a plasma channel
205
(denoted by the same reference numeral as the groove). A pair of plasma electrodes
206
and
207
are placed on the bottom of each groove
205
. A voltage is applied to the confined gas through the plasma electrodes that serve as an anode A and a cathode K, to ionize the gas and thus generate plasma discharge. The ionization of the gas in the plasma channel
205
under the plasma discharge is also called “activation” of the plasma channel
205
in some cases.
The liquid crystal cell
201
includes a substrate
208
, the dielectric sheet
203
, and a liquid crystal layer
209
interposed between the substrate
208
and the dielectric sheet
203
. A plurality of parallel stripe electrodes (column electrodes)
210
are formed on the surface of the substrate
208
facing the liquid crystal layer
209
. The electrodes
210
extend to cross the plasma channels
205
. Also formed on the surface of the substrate
208
facing the liquid crystal layer
209
are colored layers (not shown) formed at positions corresponding to the respective electrodes
210
and a black matrix
212
filling spaces between the colored layers. The colored layers typically include red, green, and blue layers (see FIG.
22
A).
Pixel regions are formed in the respective crossings of the electrodes
210
and the plasma channels
205
. The portion of the liquid crystal layer
209
located in each of the pixel regions changes its orientation state depending on the voltage applied between the electrode
210
and the plasma channel
205
, thereby changing the amount of light passing through the pixel region. By applying video signals to the portions of the liquid crystal layer
209
located in the respective pixel regions arranged in a matrix as a whole, the amounts of light passing through the respective pixel regions are controlled, whereby an image is displayed. As used herein, the minimum display unit is referred to as a “pixel”, and the region of an LCD device that corresponds to each “pixel” is referred to as a “pixel region”. Each pixel region exists in each crossing of the plasma channel
205
and the electrode
210
. In a typical conventional LCD device having a black matrix, each pixel region exists in each opening of the black matrix. In other words, the opening of the black matrix defines the outline of the pixel region. In principle, pixel regions as well as pixels do not overlap each other. However, as will be described later in detail, if a crosstalk phenomenon occurs in a PALCD device, a “pixel” and a “pixel region” as defined in actual display operation overlap at least part of the adjacent “pixel” and “pixel region”, respectively. That is, the “pixel region” in actual display operation does not match the “pixel region” in design (structure). Herein, the “pixel region in display” and the “pixel region in design” are often used to distinguish one from the other.
In the conventional PALCD device
200
, the plasma channels
205
serve as row scanning units while the electrodes
210
serve as column scanning units, for example. Linear sequential scanning is carried out by activating the plasma channels
205
selectively in succession. In synchronization with this scanning, a video signal is applied to the electrodes
210
constituting the column drive units. The selectively activated plasma channel
205
, which is filled with ionized gas, is entirely turned to an anode potential (also called a “reference potential”). In this state, when a drive voltage (corresponding to a video signal voltage) is applied between the plasma channel
205
and the electrode
210
facing each other via the dielectric sheet
203
and the liquid crystal layer
209
, charges of the amount corresponding to the potential difference between the anode potential and the drive potential are induced to and accumulated on the bottom surface
203
S of the dielectric sheet
203
(the surface facing the plasma channel
205
, which is hereinafter called a “dielectric bottom surface
203
S). Next, when this plasma channel
205
is made non-selected (plasma discharge is stopped), the plasma channel
205
is put in an insulated state. Thus, the charges are kept accumulated on the dielectric bottom surface
203
S until the plasma channel
205
is selected and activated next time. As a result, the potential difference (voltage) between the dielectric bottom surface
203
S and the electrode
210
is maintained. In other words, the voltage corresponding to the drive voltage that had been applied to the corresponding electrode
210
when the plasma channel
205
was selected (the drive voltage itself if the anode voltage was the ground voltage) is sample-held by the existence of capacitances formed by the dielectric bottom surface
203
S/dielectric sheet
203
/liquid crystal layer
209
/electrode
210
. In this way, the plasma channel
205
functions as a switching element that controls electrical connection/disconnection between the dielectric bottom surface
203
S and the anode electrode
207
. The dielectric bottom surface
203
S serves as a virtual electrode. The rows and the columns may be reversed so that the drive voltage is applied to the anode electrodes
207
of the plasma channels
205
while the scanning voltage is applied to the electrodes
210
.
The pixel region of the PALCD device
200
can be represented by an equivalent circuit shown in FIG.
21
. Referring to
FIG. 21
, one pixel region of the PALCD device
200
is essentially composed of: a capacitance C
G
(dielectric sheet capacitance) including the dielectric bottom surface
203
S and the dielectric sheet
203
; a capacitance C
LC
(liquid crystal capacitance) including the liquid crystal layer
209
serially connected to the capacitance C
G
; and the anode electrode
207
connected to the dielectric bottom surface
203
S via a switch S (plasma channel
205
). A drive voltage V
D
is externally applied to the electrode
210
. When the switch S is turned ON, the drive voltage V
D
(AC voltage; V
D
is absolute) is applied between the dielectric bottom surface
203
S and the electrode
210
. At this time, it is a voltage V
LC
applied to the liquid crystal capacitance C
LC
that directly influences the display state of the pixel region (the orientation state of liquid crystal molecules in the liquid crystal layer
209
). The voltage V
LC
is given by expression (1) below.
V
LC
=V
D
×{C
G
/(
C
LC
+C
G
)}  (1)
In other words, the drive voltage is divided between the serially connected capacitance C
LC
and capacitance C
G
. Assuming that the thickness of the liquid crystal layer
209
is d
LC
, that of the dielectric sheet
203
is d
G
, and the relat

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