Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-07-16
2004-09-07
Wilson, Allan R. (Department: 2815)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S069000, C349S070000, C349S122000, C349S125000, C349S138000, C349S140000
Reexamination Certificate
active
06788373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a protective film for protecting a dielectric layer of a plasma display panel from discharge, a method of forming the same, a plasma display panel and a method of manufacturing the same, and more particularly, to a protective film of which a discharge characteristic is improved, a method of forming the same, a plasma display panel and a method of manufacturing the same.
2. Description of the Related Art
Generally, a plasma display panel (PDP) has a thin structure, no flicker and a great display contrast ratio. Also, the PDP has a large number of features that it can be manufactured as a relatively large screen, its response speed is fast, a multicolor light emission is possible by using a fluorescent material because it is a spontaneous light emission type, and the like. Therefore, recently, the PDP has been widely used for the display device field related to the computer and the color image display field.
In the plasma display according to an operating method, there are AC driving type where electrodes are coated with a dielectric and operated indirectly in AC discharge state and DC driving type where electrodes are exposed to a discharge space and operated in DC discharge state. Further, in the AC driving type plasma display, there are a memory operating type to use memory of discharge cell as a driving method and a refresh operating type not to use it. And, brightness of the AC driving type plasma display is proportional to the number of discharge times. In case of the above refresh operating type, it is mainly used in the plasma display having small display capacity because brightness decreases when display capacity increases.
FIG. 1
is an exploded view schematically showing a structure of the AC driving memory operating type color plasma display.
In PDP, two isolation substrates
101
and
102
made of glass are provided. The isolation substrate
101
becomes a rear substrate, and the isolation substrate
102
becomes a front substrate.
On the isolation substrate
102
, transparent electrodes
103
and
104
are provided on a face side opposite to the isolation substrate
101
. The transparent electrodes
103
and
104
are extended in a horizontal direction (transverse direction) of the panel. Also, trace electrodes
105
and
106
are arranged to overlap the transparent electrodes
103
and
104
, respectively. The trace electrodes
105
and
106
are made of, for example, metal material and provided in order to lower electrode resistance value between each electrode and external driving device. Further, there are formed a dielectric layer
112
covering the transparent electrodes
103
and
104
, a plurality of black stripe layers
108
formed on the dielectric layer
112
and extended in a vertical direction (longitudinal direction) of the panel, color filter layers
110
R,
110
G and
110
B of red color R, green color G and blue color B formed between the black stripe layers
108
, and a protective film
114
for protecting the dielectric layer
112
and the transparent electrode
103
from discharge.
Also, because PDP emits each visible light of R, G and B by exciting the fluorescent material with emitted ultraviolet light, the color filter layers are not necessarily needed. The color filter layers are to collect spectrum of luminescent colors by the fluorescent material.
On the isolation substrate
101
, data electrodes
107
perpendicular to the transparent electrodes
103
and
104
are provided on a face side opposite to the isolation substrate
102
. Therefore, the data electrodes
107
are extended in the vertical direction. Further, a partition wall
109
is provided to divide a display cell in the horizontal direction. The partition wall
109
is opposite to the black stripe layers
108
. Further, a dielectric layer
113
covering the data electrodes
107
is formed, and a fluorescent layer
111
to transform ultraviolet light generated by discharging of discharge gas into visible light is formed on a side surface of the partition wall
109
and a surface of the dielectric layer
113
. Further, a discharge gas space is secured by means of the partition wall
109
in the space between the isolation substrates
101
and
102
, and the discharge gas space is filled with a discharge gas consisting of helium, neon, xenon or mixture of gases thereof.
The protective film
114
is provided in order to protect the dielectric layer
112
, the transparent electrode
103
and the like, from sputtering by ion bombardment during discharge as mentioned above, and because the protective film
114
comes in contact with the discharge gas space, its material and film quality affect greatly the discharge characteristic. Further, in AC driving type PDP, low consuming power, simplification of driving circuit, high precision and larger screen are important factors.
Therefore, generally, magnesium oxide MgO is used as a material of the protective film
114
. MgO is an insulator having excellent sputtering resistance and a large secondary electron emission coefficient. The driving of PDP becomes possible with lowering discharge starting voltage by using MgO.
Subsequently, a conventional method of forming the protective film in the PDP will be described. The protective film is generally formed by a vacuum deposition method.
FIG. 2
is a schematic diagram showing a conventional film forming apparatus of the protective film.
In the conventional film forming apparatus, a deposition chamber
121
is provided. In an upper part of the deposition chamber
121
, a substrate
124
in which a dielectric layer, etc. have already been formed and MgO film is formed is mounted. Also, in lower part of the deposition chamber
121
, a deposition source
125
composed of MgO as a raw material of the protective film is mounted. Further, in the deposition chamber
121
, a heater
132
heating the substrate
124
and a gas inlet (not shown) for O
2
gas are formed.
In case of manufacturing the protective film using the conventional film forming apparatus configured as mentioned above, first, the substrate
124
is fixed in the upper part of the deposition chamber
121
, and the substrate
124
is heated by the heater
132
, and simultaneously, the deposition chamber
121
is exhausted. Subsequently, in order to arrange crystal orientation of MgO film, while oxygen gas is introduced into the deposition chamber
121
, an electron beam
133
is irradiated to the deposition source
125
so that the MgO film is formed as the protective film on the opposite side to the deposition source
125
of the substrate
124
.
Further, in order to improving an orientation property of the MgO film, the method of forming the MgO film in an atmosphere including hydrogen atom in excited or ionized state is disclosed (Japanese Patent Laid-Open No. Hei 9-295894 Publication).
Further, in order to lower a discharge voltage by improving the secondary electron emission coefficient of the protective film, the PDP in which an orientation of the protective film is in (n00) or (mm0) orientation and a surface roughness is 30 nm or more is disclosed (Japanese Patent Laid-Open No. Hei 11-3665 Publication).
However, in the display operation of the conventional AC memory operating type PDP, first, a discharge is generated in a discharge space by applying a discharge voltage pulse to the transparent electrodes
103
and
104
. By this discharge, on the surface of the discharge space side of the protective film
114
, a charge having opposite polarity to the polarities applied to each electrode is accumulated at the position where the transparent electrodes
103
and
104
face each other (wall charge forming step).
Then, a discharge is generated once more in the discharge space by applying a voltage having opposite polarity to the above discharge voltage pulse to the transparent electrodes
103
and
104
. The accumulated charge (wall charge) is erased by this discharge so that the wall charge does not exist in the entire surface of PDP (erasing step
Hirano Toshiaki
Ito Ken
Kokura Takeshi
Ueda Kentaro
NEC Corporation
Ortiz Edgardo
Sughrue & Mion, PLLC
Wilson Allan R.
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