DESCRIPTION
PLASMA DISPLAY PANEL AND METHOD FOR MANUFACTURING THE SAME
[Technical Field]
[0001]
Thepresent invention relates to a plasma display panel
and a manufacturing method therefor . The present invention
relates more particularly to a plasma display panel having
a dielectric layer covered with an improved protective layer,
and a method for manufacturing the same.
[Background Art]
[0002]
A plasma display panel (hereinafter referred to as
PDP) is a flat display device that takes advantage of
radiation caused by gas discharge. The PDP has been in
practical use in many fields such as an image display device
and a public information display device, since the PDP can
achieve high-speed display and be produced in a large size.
There are two types of PDP, a direct-current (DC) type and
an alternating-current (AC) type. Especially, the AC
surface discharge PDP possesses a high technological
potential for realizing a long life and a large-screen
display, and therefore has been commercialized.
[0003]
FIG. 10 is a schematic view showing a structure of

a discharge cell (display cell), or a discharge unit, of
a general AC PDP. A PDP 1x shown in FIG. 10 is constituted
from a front panel 2 and a back panel 9 that are assembled
together. The front panel 2 includes a front panel glass
3. A plurality of display electrode pairs 6 each composed
of a scan electrode 5 and a sustain electrode 4 that are
disposed on the surface of the front panel glass 3. A
dielectric layer 7 and a surface layer 8 are layered in
the stated order to cover the display electrode pairs 6.
The scan electrode 5 and the sustain electrode 4 are
respectively composed of a transparent electrodes 51 and
41 and bus lines 52 and 42 layered thereon.
[0004]
The dielectric layer 7 is made of low-melting glass
whose softening point is approximately 550C°-600C°, and
has a current limiting function that is peculiar to the
AC PDP.
The surface layer 8 protects the dielectric layer 7
and the display electrode pairs 6 from ion bombardment as
a result of plasma discharge. The surface layer 8 also
efficiently emits secondary electrons and lowers a firing
voltage. Generally, magnesium oxide (MgO) that has high
secondary electron emission properties, high sputtering
resistance, and high optical transparency is used to form
the surface layer 8 with a thickness of approximately 0.5
µm-1 µm using the vacuum deposition method (Patent Documents

1 and 2) or the printing method (Patent Document 3) . Note
that a protective layer that has the identical structure
with the surface layer 8 may be arranged in order to have
the secondary electron emission properties and to protect
the dielectric layer 7 and the display electrode pairs 6.
[0005]
On the other hand, a back panel 9 includes a back panel
glass 10 and a plurality of data (address) electrodes 11
disposed thereon so as to intersect the display electrode
pairs 6 substantially at a right angle in plan view. The
data electrodes 11 are used for writing image data in the
discharge cells. On the back panel glass 10, a dielectric
layer 12 made of low-melting glass is disposed to cover
the data electrodes 11. Disposed on the dielectric layer
12 at a given height are barrier ribs 13 made of low-melting
glass . More specifically, the barrier ribs 13 are composed
of pattern parts 1231 and 12 3 2 that are combined to form
a grid pattern to partition a discharge space 15 into a
plurality of cells. Phosphor ink of red (R), green (G)
and blue (B) colors are applied to the surface of the
dielectric layer 12 and the lateral surfaces 13 of thebarrier
ribs, and burned to form phosphor layers 14 (phosphor layers
14R, 14G and 14B).
[0006]
The front panel 2 and the back panel 9 are sealed
together around edge portions thereof such that the display

electrode pairs 6 are orthogonal to the data electrodes
11 via the discharge space 15. In the sealed discharge
space 15, a rare gas mixture such as xenon-neon or
xenon-helium is enclosed as a discharge gas at some tens
of kilopascals. The above is the structure of the PDP 1x.
In order to display an image on the PDP, a method for
displaying gradation of the image by dividing one field
of the image into a plurality of subfields (S.F.) (e.g.
intra-field time division grayscale display method) is
used.
[0007]
In recent years, there have been demand for low-power
appliances, and similar demand is made for the PDP as well.
In a high-definition PDP, the discharge cells are
miniaturized and accordingly the number of the required
cells increases. Thus, in order to generate an address
discharge more securely, the operating voltage needs to
be risen.
A conventional PDP has the following problems.
The first problem is that, when a pulse is applied
to the display electrodes, a "discharge delay" which is
a time lag between pulse application and discharge
generation evidently occurs. Recently, in the field of
displays including the PDP, the PDP tends to have
high-definition pixels, and therefore the number of scan
lines increases. A full-high-vision TV, for example, has

more than twice as many scan lines as a conventional NTSC
TV. Thus, as the higher-def inition PDP has been developed,
the PDP needs to be driven at a higher speed. For the
high-speed drive, it is necessary for a width of a data
pulse applied to the address period to be narrowed down.
However, when the PDP is driven at the high speed by applying
the narrowed width of data pulse, there is a smaller chance
that the discharge is completed in duration of the narrowed
pulse. Therefore, there is a risk that some of the discharge
cells are not addressed properly thereby failing to light.
[0008]
The second problem is that the temperature dependency
on discharge delay increases with increase in Xe gas
concentration in the discharge gas. More specifically,
a high content of the Xe gas causes the discharge delay
to be more dependent on temperatures, especially at a low
temperature. Thus, the occurrence of the discharge delay
becomes more problematic . This problem is actually crucial
in the initial stage of driving the PDP.
The third problem is that the higher the concentration
of Xe gas in the discharge gas is, the more dependent on
the number of sustain pulses the discharge delay is
(dependence of discharge delay on space charges). The
discharge delay occurs more frequently when the number of
pulses is small. For example, when the number of pulses
in a sub fieldis relatively small, the discharge delay occurs

more frequently.
[0009]
To solve the above problems, several approaches have
been made to reform the MgO, for example, by changing the
crystal structure of the MgO protective layer or adding
(i) Fe, Cr and V, or (ii) Si and Al to the MgO.
Patent Document 5 discloses the following to reduce
the discharge delay. The MgO protective layer is formed
with use of a gas-phase method on the dielectric layer or
on the MgO deposition layer that is formed by a vapor
deposition method or sputtering method. Alternatively,
MgO powder that is formed by the gas-phase method is arranged
on the dielectric layer.
[0010]
Other approaches have been made to solve problems
associated with the dependence of discharge delay on
temperatures (discharge delay especially in a low
temperature range) as follows. Patent Document 6 discloses
an attempt to optimize an amount of Si that is added to
MgO, and Patent Document 7 discloses another attempt such
as adding Fe, Ca, Al, Ni and K as well as Si.
[Patent Document 1] Japanese Laid-Open Patent Application
Publication No. H5-234519
[Patent Document 2] Japanese Laid-open Patent Application
Publication No. H8-287833
[Patent Document 3] Japanese Laid-Open Patent Application

Publication No. H7-296718
[Patent Document 4] Japanese Laid-open Patent Application
Publication No. H10-125237
[Patent Document 5] Japanese Laid-open Patent Application
Publication No. 2006-54158
[Patent Document 6] Japanese Laid-Open Patent Application
Publication No. 2004-134407
[Patent Document 7] Japanese Laid-Open Patent Application
Publication No. 2004-273452
[Disclosure of the Invention]
Problems the Invention is Attempting to Solve
[0011]
However, none of the above conventional techniques
duly solves all the problems of the "discharge delay,"
"dependence of discharge delay on temperatures (especially
at low temperatures)", and the "dependence on the number
of pulses (dependence of discharge delay on space charges) ,"
both occurred as a result of the high Xe content.
Having these problems, the state-of-the-art PDP still
has room for improvement.
[0012]
The present invention is conceived in view of the above
problems, and aims to solve both problems of the "discharge
delay" and the "dependence of discharge delay on
temperatures" by reforming the protective layer.

In addition to the solutions for the above problems,
the present invention also aims toprovide a PDP that exhibits
excellent display performance by suppressing the
"dependence of discharge delay on space charges."
Means for Solving the Problems
[0013]
To solve the above problems, the present invention
provides a plasma display panel having a first substrate
and a second substrate that oppose each other with a discharge
space therebetween and are sealed together around edge
portions thereof, the first substrate including electrodes
and a dielectric layer that are disposed thereon_in the
stated order, wherein on or above a surface of the dielectric
layer that faces the discharge space, powder substantially
made of magnesium oxide particles eachhavinga (100) crystal
face and a (111) crystal face is disposed.
[0014]
Herein, the powder may be disposed directly on the
surface of the dielectric layer. In addition, a surface
layer made of a metallic oxide may be disposed on the surface
of the dielectric layer. The metallic oxide is at least
one selected from magnesium oxide, calcium oxide, barium
oxide, and strontium oxide. In addition, the powder may
be disposed on a surface of the surface layer that faces
the discharge space. The magnesium oxide particles may

include particles that are partially embedded in the surface
layer so that each magnesium oxide particle is exposed to
the discharge space.
[0015]
The magnesium oxide particles may include particles
each having a hexahedral structure with at least one
truncated surface. Herein, each hexahedral particle has
a main surface which is the (100) crystal face and the
truncated surface which is the (111) crystal face.
The magnesium oxide particles may include particles each
having an octahedral structure with at least one truncated
surface. In this case, each octahedral particle may have
a main surface which is the (111) crystal face and the
truncated surface which is the (100) crystal face.
[0016]
The magnesium oxide particles may include particles
each having a sodium chloride type crystal structure, and
each sodium chloride particle is a tetrakaidecahedron that
has six surfaces each of which is the (100) crystal face
and eight surfaces each of which is the (111) crystal face.
Each tetrakaidecahedral magnesium oxide particle may have
a main surf ace which is the (100) crystal face and a truncated
surface which is the (111) crystal face. Alternatively,
each tetrakaidecahedral magnesium oxide particle may have
a main surf ace which is the (111) crystal face and a truncated
surface which is the (100) crystal face. Note that it is

desirable that the powder has been formed by burning a
magnesium oxide precursor.
[Effects of the Invention]
[0017]
According to the present invention with the above
structure, the MgO powder is characterized by the Mgo
particles having the (100) crystal face and the (111) crystal
face (hereinafter, referred to as "two specific crystal
faces").
The (10 0) crystal face, with its lowest surface free
energy, barely absorbs impurity gas (water, hydrocarbon,
carbon dioxide, etc.) in a wide temperature range from a
low temperature to a temperature equal to or higher than
a normal temperature. Thus, the (100) crystal face stably
emits secondary electrons at a low temperature at which
impurity gas is easily absorbed. Furthermore, the (111)
crystal face has a large secondary electron emission
coefficient, and therefore smoothly emits secondary
electrons at a temperature equal to or higher than a normal
temperature. Thus, disposing the MgO particles with the
two specific crystal faces on the dielectric layer ensures
a synergistic effect between the properties of each crystal
face, enabling the two specific crystal faces efficiently
and stably to emit secondary electrons in the wide
temperature range. Consequently, the PDP in accordance

with the embodiments of the present invention is able to
suppress the "discharge delay," "dependence of discharge
delay on temperatures" and in the wide temperature range,
and therefore can be expected to display high-definition
images.
[0018]
Note that the MgO powder in accordance with the present
invention may include MgO particles each having the (100)
crystal face, the (110) crystal face and the (111) crystal
face (hereinafter, referred to as "three specific crystal
faces") besides the MgO particles having the two specific
crystal faces . The MgO particles having the three specific
crystal faces are expected to produce similar effects as
the MgO particles having the two specific crystal faces.
In addition to the effects, the MgO particles having the
three specific crystal faces are expected to improve
dependence of discharge delay on space charges.
[Brief Description of the Drawings]
[0019]
FIG. 1 is a cross-sectional view showing the structure
of a PDP in accordance with Embodiment 1 of the present
invention;
FIG. 2 is a schematic view showing a relation between
electrodes and drivers;
FIG. 3 shows an example waveform when the PDP is driven;

FIGs. 4A and 4B are schematic enlarged views showing
the structure of a protective layer in accordance with each
embodiment of the present invention;
FIGs. 5A, 5B, 5C and 5D are views each showing the
shape of each magnesium oxide particle;
FIGs. 6A, 6B, 6C, 6D, 6E and 6F are views showing
variations of the shape of each magnesium oxide particle;
FIG. 7 is a cross-sectional view showing the structure
of a PDP in accordance with Embodiment 2 of the present
invention;
FIGs. 8A, 8B, 8C and 8D each show a photo of the shape
of the magnesium oxide particle;
FIG. 9 is a graph showing waveforms obtained by
observing the magnesium oxide particles by
Cathodoluminescence measurement;
FIG. 10 is a cross-sectional view showing the structure
of a conventional PDP.
Reference Numerals
[0020]
1, 1a, 1x PDP
2 front panel
3 front panel glass
4 sustain electrode
5 scan electrode
6 display electrode pair
2
7, 12 dielectric layer
8 surface layer
9 back panel
10 back panel glass
11 data (address) electrode

13 barrier rib
14 phosphor layer
15 discharge space
16a MgO particle having two specific crystal faces
16b MgO particle having two specific crystal faces
16c MgO particle having three specific crystal
faces
16d MgO particle having three specific crystal
faces
16a1, 16a2 variation of MgO particle having two specific
crystal faces
16b1, 16b2 variation of MgO particle having two specific
crystal faces
16c1 variation of MgO particle having three specific
crystal faces
16d1 variation of MgO particle having three specific
crystal faces
16 MgO powder
17 protective layer
[Best Mode for Carrying Out the Invention]

[0021]
The following describes preferred embodiments and
examples of the present invention. Note that the present
invention is never limited to these and various changes
may be made as necessary without departing from the technical
scope of the present invention.

(Structure of PDP)
FIG. 1 is a schematic sectional view of a PDP 1 in
accordance with Embodiment 1 of the present invention, the
section being taken along the x-z plane. The structure
of the PDP 1 is basically identical with that of a
conventional PDP (FIG. 10) except for the structure in the
vicinity of the protective layer.
[0022]
The PDP 1 is an AC PDP with a 42 - inch screen in conformity
with the NTSC specification. The present invention may
be, of course, applied to other specifications such as XGA
and SXGA. The applicable specifications of the
high-definition PDP that is able to display images at a
higher resolution than an HD (high-definition) PDP are PDPs
with a size of 37, 42 , and 5 0 inches having 1024x720 (pixels) ,
1024 x 768 (pixels) , and 1366 x 768 (pixels) , respectively.
In addition, such a PDP is also applicable to display images
at higher resolution than the PDP 1. Examples of a PDP
having higher-definition pixels than the HD PDP include

a full HD PDP with 1920 x 1080 (pixels).
[0023]
As shown in FIG. 1, the PDP 1 is composed of
substantially two members that are a first substrate (front
panel 2) and a second substrate (back panel 9) that oppose
each other in face-to-face relationship.
The front panel 2 includes a front panel glass 3 as
its substrate. On one main surface of the front panel glass
3, a plurality of electrode pairs 6 (each composed of a
scan electrode 5 and a sustain electrode 4) are each disposed
at a given discharge gap (75 µm) therebetween. Each
electrode is composed of transparent electrode 51 or 41
and bus line 52 or 42 layered thereon. The transparent
electrodes 51 and 41 in a stripe pattern (each transparent
electrode is 0.1 µm thick, 150 µm wide) are made of
transparent conductive materials such as indium tin oxide
(ITO), zinc oxide (ZnO) , and tin oxide (SnO2) . The bus lines
52 and 42 (7 µm thick, 95 µm wide) are made of an Ag thick
film (2 pun-10 µm thick) , an Al thin film (0.1 µm-1 µm thick) ,
a Cr/Cu/Cr layered thin film (0.1 µm-1 µm thick) or the
like. These bus lines 52 and 42 reduce the sheet resistance
of the transparent electrodes 51 and 41.
[0024]
The term, "thick film," is a film that is formed with
various kinds of thick-film processing. In the thick-film
processing, a film is formed by applying a paste and the

like containing the conductive materials and burning the
paste. The term, "thin film," is a film that is formed
by various kinds of thin-film processing using vacuum
processing such as a sputtering method, ion plating method,
or electron-beam deposition method.
On the entire surface of the front panel glass 3 where
the display electrode pairs 6 are disposed, a dielectric
layer 7 is formed with use of a screen printing method.
The dielectric layer 7 is made of low-melting glass (35
µm thick) that contains lead oxide (PbO), bismuth oxide
(Bi2O3) or phosphorus oxide (PO4) as the principal component.
[0025]
The dielectric layer 7 has a current limiting function
that is peculiar to the AC PDP, which is why the AC PDP
can realize a longer life than the DC PDP.
On the surface of the dielectric layer 7 that faces
the discharge space, the surface layer 8 with a thickness
of approximately 1 µm is layered. On the surface of the
surface layer 8, MgO powder 16 is disposed. The surface
layer 8 and the MgO powder 16 constitute a protective layer
17 disposed on the dielectric layer 7.
[0026]
The surface layer 8 is a thin film to protect the
dielectric layer 7 from ion bombardment during discharge
and to lower a firing voltage. The surface layer 8 is made
of MgO material that has high sputtering resistance and

a high secondary electron emission coefficient y. The MgO
material used in the embodiments of the present invention
also has even higher optical transparency and electric
insulation. On the other hand, as shown in FIGs. 5A-5D,
the MgO powder 16 is made up of MgO particles 16a-16d each
having a crystal structure with either one of the "two
specific crystal faces" and the "three specific crystal
faces . " The detail of the MgO powder 16 is described later.
[0027]
Note that, in FIG. 1, the MgO powder 16 that is disposed
on the surface of the surface layer 8 is schematically shown
in a larger size than the actual size for clearer explanation.
On the main surface of the back panel glass 10 that
is the substrate of the back panel 9, data electrodes 11
each with a width of 100 µm are formed in a stripe pattern
having a gap (3 60 µm) therebetween. The data electrodes
11 are adjacent to each other in the y direction, and each
extend in the x direction longitudinally. The data
electrodes 11 are made up of any one of an Ag thick film
(2 µm-10 µm thick) , an Al thin film (0.1 µm-1 µm thick) ,
a Cr/Cu/Cr layered thin film (0.1 µm-1 µm thick) and the
like. The dielectric layer 12 with a thickness of 30µm is
disposed on the entire surface of the back panel glass 9
to cover the data electrodes 11.
[0028]
On the dielectric layer 12, the grid-shaped barrier

ribs 13 (approximately 110 µm high and 40 µm wide) are each
disposed above the gap between the adjacent data electrodes
11. The barrier ribs 13 prevent erroneous discharge or
optical crosstalk by partitioning the discharge cells.
On the lateral surfaces of the barrier ribs 13 and
on the surface of the dielectric layer 12 between the lateral
surfaces, phosphor layers 14 of red (R), green (G) and blue
(B) colors are formed for color display. Note that the
dielectric layer 12 is inessential and that the phosphor
layer 14 may directly cover the data electrodes 11.
[0029]
The front panel 2 and the back panel 9 are disposed
such that the data electrodes 11 and the display electrode
pairs 6 are orthogonal to each other in plan view. The
edge portions around the panels 2 and 9 are sealed with
glass frit. In the space between the panels 2 and 9, a
discharge gas composed of inert gases such as He, Xe and
Ne is enclosed at a given pressure.
Between the barrier ribs 13 is a discharge space 15.
Where the adjacent display electrode pair 6 intersects the
data electrode 11 via the discharge space 15 corresponds
to a discharge cell (also referred to as a "sub-pixel")
that functions to display images . The discharge cell pitch
is 675 µm in the x direction and 300 µm in the y direction.
Three of the adjacent discharge cells whose colors are red,
green and blue compose one pixel (675 µm x 900 µm) .

As shown in FIG. 2, outside the panels, the scan
electrodes 5, the sustain electrodes 4 and the data
electrodes 11 are respectively connected to a scan electrode
driver 111, a sustain electrode driver 112 and a data
electrode driver 113 that are included in a driving circuit.
[0030]
(Driving of PDP)
As soon as the PDP 1 with the above structure is driven,
a heretofore-known driving circuit (unshown) including the
drivers 111-113 applies an AC voltage ranging from tens
to hundreds of kilohertz between the display electrode pairs
6 to selectably generate discharge in given discharge cells .
As a result, ultraviolet rays (shown as the dotted lines
and the arrows in FIG. 1) including resonance lines with
wavelengths of mainly 14 7 nm emitted by the excited Xe atoms
and molecular lines with wavelengths of mainly 172 nm emitted
by the excited Xe molecules irradiate the phosphor layers
14. Accordingly, the phosphor layers 14 are excited to
emit visible light. The visible light transmits the front
panel 2, and radiates through the front panel 2.
[0031]
As an example of the driving, the intra-field time
division grayscale display method is adopted. This method
divides one field of an image into a plurality of subfields
(S.F.) , and further divides each subfield into a plurality
of periods. One subfield is divided into four periods:

(1) an initialization period in which all discharge cells
are reset; (2) an address period in which discharge cells
are selectively addressed for display according to input
data; (3) a sustain period in which a sustain discharge
is generated in the discharge cells that are addressed to
display the images; and (4) an erase period in which wall
charges generated by the sustain discharge are erased.
[0032]
In each subfield, the following occurs so that the
PDP 1 emits light to display an image . In the initialization
period, an initialization pulse resets wall charges in all
discharge cells of the entire panel. In the address period,
an address discharge is generated in the discharge cells
that are intended to light. Subsequently in the sustain
period, an AC voltage (sustain voltage) is applied to all
the discharge cells simultaneously. Thus, the sustain
discharge is generated in the given length of time so as
to display the image.
FIG. 3 shows an example of driving waveforms in the
m-th subfield of one field when the PDP is driven. As shown
in FIG. 3, each subfield is divided into the initialization
period, the address period, the sustain period and the erase
period.
[0033]
The initialization period is set for erasing the wall
charges in all the discharge cells (initialization

discharge) so as not to be influenced by the discharge
generated prior to the m-th subfield (influence of the
accumulated wall charges) . In the example of the driving
waveforms in FIG. 3, a higher voltage (initialization pulse)
is applied to the scan electrode 5 than the data electrode
11 and the sustain electrode 4 to cause the gas in the
discharge cell to discharge. As a result, electric charges
generated by the discharge are accumulated on the wall
surface of the discharge cells in order to nullify the
potential difference among the data electrodes 11, the scan
electrodes 5 and the sustain electrodes 4. Therefore, on
the surface of the surface layer 8 around the scan electrodes
5 and on the surface of the MgO powder 16, negative wall
charges are accumulated as the wall charges. On the other
hand, positive wall charges are accumulated on the surface
of the phosphor layers 14 around the data electrodes 11
and the surfaces of the surface layer 8 and the MgO powder
16 around the sustain electrodes 4. These wall charges
cause a given value of wall potential between the scan 5
and data 11 electrodes as well as between the scan 5 and
sustain 4 electrodes.
[0034]
The address period (write period) is for addressing
the discharge cells that are selected according to image
signals divided into subfields (specifying the discharge
cells to light or not) . In this period, a lower voltage

(scan pulse) is applied to the scan electrodes 5 than to
the data electrodes 11 or the sustain electrodes 4 in order
to light the intended discharge cells . More specifically,
a voltage is applied between the scan 5 and data 11 electrodes
in the same polar direction as the wall potential, as well
as between the scan 5 and sustain 4 electrodes in the same
polar direction as the wall potential, and thus, the address
discharge is generated. As a result, negative charges are
accumulated on the surface of the phosphor layers 14, on
the surface of the surface layer 8 around the sustain
electrodes 4, and on the surface of the MgO powder 16. In
addition, positive charges are accumulated as the wall
charges on the surface of the surface layer 8 around the
scan electrodes 5 and on the surface of the MgO powder 16.
Thus, a given value of the wall potential between the sustain
4 and scan 5 electrodes is generated.
[0035]
The sustain period is set to sustain the discharge
by extending the lighting period of each discharge cell
specified by the address discharge so as to keep luminance
according to a gradation level. In this period, in the
discharge cells that have the wall charges, a sustain
discharge voltage pulse (e.g. a rectangular waveform pulse
of approximately 200 V) is applied between a pair of the
scan electrode 5 and the sustain electrode 4 in such a manner
that the voltage pulse between the pair of the scan electrode

5 and the sustain electrode 4 is out of phase with each
other. Thus, the AC voltage is applied between the display
electrode pairs so that a sustain pulse discharge is
generated in the addressed discharge cells every time when
the polarities reverse at the electrodes.
[0036]
Due to the sustain discharge, in the discharge space,
resonance lines having wavelengths of 147 nm are emitted
from the excited Xe atoms, and molecular lines of 173 nm
are emitted from the excited Xe molecules. Thus, these
resonance lines and molecular lines are radiated to the
surface of the phosphor layers 14, and converted into visible
light. Thus, the image is displayed on the screen. The
ON-OFF combinations of the subfields of red, green and blue
colors enable an image to be displayed in multiple colors
and gradations. Note that in the discharge cells in which
the wall charges are not accumulated on the surface layer
8 , the sustain discharge is not generated, and the discharge
cells display black images.
[0037]
In the erase period, an erase pulse of a declining
waveform is applied to the scan electrodes 5. Thus, a
discharge is generated in order to erase the wall charges.
(Structure of Protective Layer 17)
FIG. 4A is a schematic view showing the protective
layer 17 of the PDP 1 and its nearby portion (the display

electrode pair 6 is omitted), and is also an enlarged view
of the nearby portion of the surface layer 8 and the MgO
powder 16 of FIG. 1. The protective layer 17 is made up
of the surface layer 8 and crystals of the MgO particles
of the MgO powder 16 disposed thereon.
[0038]
The surface layer 8 is an MgO thin film with a thickness
of approximately 1 µm formed on the dielectric layer 7 using
the heretofore-known thin-film processing method such as
the vacuum deposition method or the ion plating method.
Note that the surface layer 8 does not need to be made solely
of MgO but may be made of metal oxide materials that include
at least one of MgO, CaO, BaO, and SrO.
FIG. 5 is a schematic view showing the shape of each
Mgo particle included in the MgO powder 16. Particles of
the MgO powder 16 are roughly classified into four types
that are 16a, 16b, 16c and 16d according to their shapes.
[0039]
The MgO particles 16a and 16b respectively shown in
FIGs. 5A and 5B each have the NaCl type crystal structure
with the two specific crystal faces. The particles 16c
and 16d respectively shown in FIGs. 5C and 5D each have
the three specific crystal faces. The shape of each
particle 16a, 16b, 16c, and 16d shown in FIGs. 5 is merely
an example, and in reality, some distortion of the shape
can be observed. FIGs. 8A-8D are electron micrographs of

the shape of each MgO particle 16a, 16b, 16c, and an MgO
particle formed by the gas-phase method.
[0040]
The basic crystal structure of the MgO particle 16a
shown in FIG. 5A is hexahedral. Since the vertexes of the
hexahedral structure are truncated, the MgO particle 16a
is tetrakaidecahedral (having fourteen surfaces) with
truncated surfaces 82a. Each main surface 81a which is
in an octagonal shape is the (10 0) crystal face. Each
truncated surface 82a which is in a triangular shape is
the (111) crystal face. The MgO particle 16a has six main
surfaces 8la and eight truncated surfaces 82a.
In addition, the basic crystal structure of the MgO
particle 16b shown in FIG. 5B is octahedral. Since the
vertexes of the octahedral structure are truncated, the
MgO particle 16b is tetrakaidecahedral with truncated
surfaces 81b. Each main surface 82b in a hexagon shape
is the (111) crystal face. Each truncated surface 81b in
a quadrangular shape is the (100) crystal face. The MgO
particle 16b has eight main surfaces 82b and six truncated
surfaces 81b.
[0041]
In this embodiment, the main surface is, out of the
six surfaces or the eight surfaces, a surface that
constitutes the largest surface area with the same Miller
index. The truncated surface is a surface that is formed

by truncating the vertexes of the polyhedral crystal
structure.
In this embodiment, as shown in FIG. 5, a ratio of
the (10 0) crystal face to the total surface area of the
MgOparticle 16a ranges between 50%-98%, inclusive, whereas
that of the MgO particle 16b ranges between 30%-50%,
inclusive.
[0042]
The MgO particle 16c shown in FIG. 5C is
hexaicosahedral (having twenty-six surfaces). The MgO
particle 16c has a basically identical crystal structure
with that of the MgO particle 16b except for the following.
Each border area between the adjacent truncated surfaces
81c is truncated, and thus an oblique surface 83c is formed
on the border area. Hence, the MgO particle 16c is a
hexaicosahedron having six hexagonal truncated surfaces
81c each of which is the (100) crystal face, eight octahedral
main surfaces 82c each of which is the (111) crystal face,
and twelve quadrilateral oblique surfaces 83c each of which
is the (110) crystal face.
[0043]
The MgO particle 16d shown in FIG. 5D is
hexaicosahedral. The MgO particle 16d has a basically
identical crystal structure with that of the MgO particle
16a except for the following. Each border area between
the adjacent main surfaces 81d is truncated, and the

truncated area is called an oblique surface 83d. Hence,
the MgO particle 16d is a hexaicosahedron having six
octahedral main surfaces 81d each of which is the (100)
crystal face, eight hexagonal truncated surfaces 82d each
of which is the (111) crystal face, and twelve quadrangular
oblique surfaces 83d each of which is the (110) crystal
face. Note that the surface area of the (10 0) or (110)
crystal face can increase according to a burning condition,
and that in such a case, the (10 0) or (110) crystal face
is the main surface.
[0044]
Each oblique surface 83 in this embodiment is a surface
that is formed by truncating each side of the main surfaces
82c or 81d that connects two of the truncated surfaces 81c
or 82d.
FIGs. 6A, 6B, 6C, 6D, 6E and 6F are views showing
variations of the shape of each magnesium oxide particle
16a-16d.
The MgO particle 16a may have any hexahedral crystal
structure with at least one truncated surface. Examples
of such an MgO particles include an MgO particle 16al having
one truncated surface as shown in FIG. 6A, and an MgO particle
16a2 having two truncated surfaces as shown in FIG. 6B.
Herein, the truncated surface is the (111) crystal face,
and the main surface is the (10 0) crystal face. Note that
the hexahedral crystal structure with at least one truncated

surface means a polyhedral structure having at least seven
surfaces and that at least one of the surfaces is the
truncated surface. The MgO particle 16b may have any
octahedral crystal structure with at least one truncated
surface. Examples of such an MgO particle include an MgO
particle 16bl having one truncated surface as shown in FIG.
6C, and the MgO particle 16b2 having two truncated surfaces
as shown in FIG. 6D. Herein, the truncated surface is the
(100) crystal face, and the main surface is the (111) crystal
face. Note that the octahedral crystal structure with at
least one truncated surface means that a polyhedral
structure has at least nine surfaces and that at least one
of the surfaces is the truncated surface.
[0045]
The MgO particle 16c may have any octahedral crystal
structure with at least one truncated surface and one oblique
surface. Examples of such an MgO particle include an MgO
particle 16cl having six truncated surfaces and one oblique
surface as shown in FIG. 6E. Herein, the main surface is
the (111) crystal face, the truncated surface is the (100)
crystal face, and the oblique surface is the (110) crystal
face. Note that the octahedral crystal structure with at
least one truncated surface and one oblique surface means
that a polyhedral structure has at least ten surfaces and
that at least one of the surfaces is the truncated surface
and that at least another one is the oblique surface.

[0046]
The MgO particle 16d may have any hexahedral crystal
structure with at least one truncated surface and one oblique
surface. Examples of such an MgO particle include an MgO
particle 16dl having eight truncated surfaces and one
oblique surface as shown in FIG. 6F. Herein, the main
surface is the (100) crystal face, the truncated surface
is the (111) crystal face, and the oblique surface is the
(110) crystal face. Note that the hexahedral crystal
structure with at least one truncated surf ace and one oblique
surface means a polyhedral structure has at least eight
surfaces and that at least one of the surfaces is the
truncated surface and that at least another one is the oblique
surface.
[0047]
In the case where the MgO powder 16 including the MgO
particles 16a and 16b are disposed on the dielectric layer
7, the two specific crystal faces are exposed to the discharge
space 15. Thus, such an arrangement produces synergistic
effects on the properties of the two specific crystal faces .
When the MgO powder 16 further includes the MgO particles
16c and 16d, the three specific crystal faces are exposed
to the discharge space 15.
The MgO crystal with the NaCl type crystal structure
of a cubic lattice has the (111) , (110) and (100) crystal
faces as its main crystal faces. Among the three, the (100)

crystal face is the densest surface (surface in which atoms
are the most densely packed) with the lowest surface free
energy. Accordingly, the Mgo crystal having the (100)
crystal face is chemically stable, barely absorbing
impurity gases (water, hydrocarbon, carbon dioxide, and
etc .) over the wide temperature range from a low temperature
to a temperature equal to or higher than a normal temperature .
That is, the MgO crystal does not have to suffer from
unnecessary chemical reactions that may be caused by the
impurity gases. Thus, it is expected that the MgO crystal
with the (100) crystal face is chemically stable even at
a temperature lower than a normal temperature at which a
conventional MgO crystal suffers from the impurity gas
absorption (See Hyomen Gijutsu (Journal of the Surface
Finishing Society of Japan) Vol. 41, No.4, 1900, P.50).
When the MgO crystal with the (100) crystal face is used
for the PDP, the absorption of the impurity gases (especially
a carbon dioxide gas) inside the discharge space 15 can
be suppressed over the wide temperature range, and therefore
the discharge delay as a result of temperatures can be avoided.
(See Journal of Chemical Physics Vol.103, No. 8, 3240-3252,
1995) . However, the (100) crystal face suffers from a small
amount of secondary electron emission over the wide
temperature range from a low temperature and a temperature
equal to or higher than a normal temperature. Accordingly,
the (100) crystal face alone is not sufficient to prevent

the discharge delay. Especially when the address discharge
period is reduced as a result of the development of the
high-definition PDP, this problem of the discharge delay
occurs more evidently.
[0048]
The (111) crystal face is a surface that smoothly emits
secondary electrons at a normal temperature or higher, which
can prevent the discharge delay in such a temperature range .
However, the (111) crystal face has the highest surface
free energy of the three, and therefore the (111) crystal
face is disadvantageous that the impurity gases (especially
a carbon dioxide gas) are easily absorbed. The impurity
gases are likely to be accumulated on the crystal face
especially at a temperature lower than a normal temperature,
which obstructs the electron emission. Accordingly, the
(111) crystal face alone is not sufficient to prevent the
discharge delay caused by temperatures (especially
discharge delay in the low temperature range).
[0049]
For the above reasons, the MgO powder 16 in the
embodiments of the present invention is composed of the
MgO particles 16a and 16b each having the NaCl type crystal
structure with the two specific crystal faces (100) and
(111) and the MgO particles 16c and 16d each having the
NaCl type crystal structure with the three specific crystal
faces (100) , (110) and (111) .

Accordingly, the MgO powder 16 including the MgO
particles 16a-16d each having the two or three specific
crystal faces exposed to the discharge space 15 suppresses
the impurity gas absorption and maintains the stable
electron emission in the wide temperature range from a low
temperature (when the PDP is initially driven and the PDP
is used in an area where an environmental temperature is
low) to a temperature equal to or higher than a normal
temperature (when a given length of time has passed since
the initial driving of the PDP and the PDP is used at a
high environmental temperature) as well as effectively
suppressing the "discharge delay" and "dependence of
discharge delay on temperatures." Consequently, the PDP
1 can stably display excellent images.
[0050]
Note that the crystal faces may not have the above
properties when the particle is small in size or a ratio
of each crystal face to the total surface area of the particle
is small. As described later, MgO particles formed by the
gas -phase method have various diameters, and an MgO particle
with a diameter of below 3 00 nm causes problems associated
with the discharge delay dependence on temperatures even
though the particle has the (100) crystal face. However,
the MgO particles formed by burning the precursor each have
a uniform diameter, and almost all the particles have a
diameter of 3 00 nm and over. Thus, the MgO particles formed

by burning the precursor achieve the discharge properties
of each crystal face.
[0051]
When the MgO particle 16c having the NaCl type crystal
structure with the three specific crystal faces (100), (110)
and (111) is employed in the PDP 1, the PDP 1 demonstrates
the same properties as that with the MgO particles 16a and
16b. In addition, the MgO particle 16c enables a sufficient
amount of secondary electrons to be emitted without the
aid of space charges generated at the start of discharge
in the initial stage of driving the PDP 1. More specifically,
since the (110) crystal face emits secondary electrons over
the wide temperature range from low to high temperatures,
the MgO particles 16c and 16d with the three specific crystal
faces can emit more secondary electrons than the MgO
particles 16a and 16b with the two specific crystal faces.
[0052]
For the reasons mentioned above, using the MgO
particles 16c and 16d is advantageous that the stable
secondary electron emission is ensured regardless of the
number of pulses (the number of sustain pulses) applied
to the display electrode pairs 6 during the sustain period.
(In other words, the advantage that the discharge delay
dependence on space charges can be reduced.) Thus, the
MgO particles 16c and 16d can suppress the "dependence of
discharge delay on space charges" as well as "discharge

delay" and "dependence of discharge delay on temperatures . "
Consequently, the PDP 1 is expected to display even better
images.
[0053]
FIG. 9 shows the measurement results of the
conventional MgO crystal formed by the gas-phase method
and the MgO particles 16c and 16d with the three specific
crystal faces measured by Cathodoluminescence (CL)
measurement.
As shown in FIG. 9, when the spectra of the MgO crystal
formed by the gas-phase method were measured, the spectra
with wavelengths of approximately 200-300 nm were hardly
detected. On the other hand, when the spectra of the MgO
particles 16c and 16d were measured, the luminescence
intensity peaks at approximately 200-300 nm. The light
with the same wavelengths are also emitted during discharge
of a PDP. Since the energy of the light with wavelength
of about 200 nm-300 nm is approximately 5 eV, the light
can excite the electrons of the MgO particles whose energy
level in the band structure is up to 5 eV below the vacuum
level. As a result, the secondary electrons are easily
emitted to the discharge space.
[0054]
As the light with wavelengths of approximately 200-300
nm are emitted during the discharge, the space charges alone
can sufficiently promote secondary electron emission

without any other special assistance. In a PDP that
includes a protective layer having the MgO crystals formed
by the gas-phase method dispersed thereon, the discharge
delay is changed by the number of discharge pulses . However,
with the light, the discharge delay does not need to depend
on the space charges since the special assistance is
unnecessary. Accordingly, such a discharge delay change
does not occur.
[0055]
As described above, when the PDP has the MgO particles
16c and 16d with the three specific crystal faces that emit
deep ultraviolet (DUV) rays detectable by CL measurement,
due to the MgO particles 16c and 16d, the PDP emits light
with wavelengths of approximately 200-300 nm during the
discharge. Accordingly, using the MgO particles 16c and
16d realizes the PDP that is not influenced by the space
charges.
[0056]
Subsequently, the surface ratios of the crystal faces
in the crystal structure of each MgO particle 16a, 16b,
16c and 16d in accordance with this embodiment are described
as follows.
According to the investigation by the inventors, the
following surface ratios are desirable so as to effectively
achieve the above effects.
The surface ratio of the (100) crystal face to the

total surface area of the MgO particle 16a favorably falls
within a range between 50%-98%, inclusive.
[0057]
The surface ratio of the (100) crystal face to the
total surface area of the MgO particle 16b favorably falls
within a range between 3 0%-50%, inclusive.
The surface ratio of the (111) crystal face to the
total surface area of the MgO particle 16c favorably falls
within a range between 10%-80%, inclusive.
[0058]
The surface ratio of the (100) crystal face to the
total surface area of the MgO particle 16c favorably falls
within a range between 5%-50%, inclusive.
The surface ratio of the (110) crystal face to the
total surface area of the MgO particle 16c favorably falls
within a range between 5%-50%, inclusive.
The surface ratio of the (111) crystal face to the
total surface area of the MgO particle 16d favorably falls
within a range between 10%-40%, inclusive.
[0059]
The surface ratio of the (100) crystal face to the
total surface area of the MgO particle 16d favorably falls
within a range between 40%-80%, inclusive.
The surface ratio of the (110) crystal face to the
total surface area of the MgO particle 16d favorably falls
within a range between 10%-40%, inclusive. To fix the MgO

powder 16 to the surface layer 8, note that some of the
MgO particles 16a-16d may be partially embedded in the
surface layer 8 in addition to the arrangement that the
MgO powder 16 is dispersed on the surface layer 8 as shown
in FIG. 4A. Such an arrangement of the MgO powder 16 enables
the MgO particles 16a-16d to be more firmly fixed to the
surface layer 8. Thus, when the PDP 1 is shaken or shocked,
thanks to the arrangement, the MgO powder 16 does not easily
come off from the surface layer 8, as is expected. Thus,
this arrangement is favorable.
[0060]
Although FIGs. 1 and 4 each show the structure of the
protective layer 17 having the MgO powder 16 disposed over
the entire surface of the surface layer 8, the present
invention is not limited to the above structure. More
specifically, in Embodiment 1, the surface layer 8 covers
the entire surface of the dielectric layer 7 so as to protect
the dielectric layer 7. In view of the protection, the
MgO powder 16 may be disposed on a partial surface area
of the surface layer 8. For example, the MgO particles
can be disposed on a partial surface area above the
transparent electrodes 41 and 51, and alternatively can
be disposed on a partial surface area above the discharge
space 15 (i.e. an area that does not correspond to the barrier
ribs 13) . Furthermore, the density of the MgO particles
16a-16d may be variable in a given range. All of the above

variations are expected to have the similar effects to that
of the PDP 1 of Embodiment 1.
[0061]

Following is a description of a PDP la in accordance
with Embodiment 2 of the present invention. The differences
between the PDP 1 and the PDP la are mainly described. FIG.
7 is a cross-sectional view of the PDP la. FIG. 4B is a
schematic view showing the protective layer of the PDP la
and its nearby portion.
The feature of the PDP la is that the protective layer
is composed of the MgO powder 16 disposed directly on the
dielectric layer 7 does not include the surface layer 8.
The MgO powder 16 includes the MgO particles 16a-16d as
with Embodiment 1.
[0062]
The PDP la with the above feature promotes the smooth
secondary electron emission in the wide temperature range
from low to a normal temperature or higher when the PDP
la is initially driven. Thus, the PDP la can display
excellent images by effectively suppressing the "discharge
delay" and "dependence of discharge delay on temperatures."
In addition, the MgO particle 16c included in the MgO powder
16 can improve the dependence of discharge delay on space
charges. Thus, the PDP la is expected to display images
even more stably.

[0063]
Furthermore, since the PDP la is not provided with
the surface layer 8, the process to form the surface layer
8 (thin-film processing such as the sputtering method, ion
plating method, and electron-beam deposition method) is
completely unnecessary. That is, due to the omission of
the process, the production cost can be reduced, which
ensures the effectiveness and great advantage to the PDP
la.
Note that, in the PDP la, it is the MgO powder 16 that
protects the dielectric layer 7. From the standpoint of
the protection, the MgO powder 16 needs to be disposed over
the entire surface of the dielectric layer 7.
[0064]

Following is a description of the production method
of the PDP 1 and the PDP la in accordance with each embodiment
of the present invention. The difference between the PDP
1 and la is simply the structure of the protective layer.
The production processes of the PDP 1 and la are basically
identical with each other.
(Manufacturing Back Panel)
On the surface of the back panel glass 10 made up of
soda-lime glass with a thickness of approximately 2.6 mm,
conductive materials mainly composed of Ag are applied with
the screen printing method in a stripe pattern at a given

interval. Thus, the data electrodes 11 with a thickness
of some micrometers (e.g. approximately 5µm) are formed.
The data electrodes 11 are made up of a metal such as Ag,
Al, Ni, Pt, Cr, Cu, and Pd or a conductive ceramic such
as metal carbide and metal nitride. The data electrodes
11 may be made of the composition of these materials, or
may have a layered structure of these materials as necessary.
[0065]
The gap between each two adjacent data electrodes 11
is set to 0.4 mm or below so that the PDP 1 has a 40-inch-
screen in conformity with the NTSC or VGA specification.
Following that, a glass paste with a thickness of
approximately 20-30µm made of lead-based or lead-free
low-melting glass or SiO2 material is applied and burned
over the back panel glass 10 and the data electrodes 11
in order to form the dielectric layer 12.
Subsequently, the barrier ribs 13 are formed on the
dielectric layer 12 as follows . The low-melting glass paste
is applied and burned on the dielectric layer 12 . The paste
is formed, using a sandblast method or a photolithography
method, in a grid pattern dividing the borders of a plurality
of adjacent discharge cells (unshown) arranged in rows and
columns.
[0066]
After forming the barrier ribs 13, on the lateral
surface of each barrier rib 13 and on the exposed surface

of the dielectric layer 12, phosphor ink including one of
red (R), green (G) and blue (B) phosphors commonly used
for the AC PDP is applied. The phosphor ink is then dried
and burned to form the phosphor layers 14.
Following is an example of the chemical composition
of the applicable phosphors of the red, green and blue colors.
[0067]
Red phosphor; (Y, Gd) BO3: Eu,
Green phosphor; Zn2SiO4: Mn,
Blue phosphor; BaMgAl10O17: Eu
It is desirable that each phosphor (powder) has a
particle diameter of 2.0 µm on average. Into a server,
50 mass percent of the phosphors are put, and 1.0 mass percent
of ethycellulose and 49 mass percent of solvent
(?-terpineol) are added. The phosphors, the ethycellulose
and the solvent are stirred and mixed by a sand mill so
as to manufacture the phosphor ink whose viscosity is 15
* 10-3 Pa.s. When this phosphor ink is jetted into the gaps
between the barrier ribs 13 from a nozzle with a diameter
of 60 urn, the panel is moved in the longitudinal direction
of the barrier ribs 13. Accordingly, the ink is applied
in a stripe pattern on the panel. Then, the ink is burned
for 10 minutes at 500°C. Thus, the phosphor layers 14 are
formed.
[0068]
Hence, the manufacturing of the back panel 9 is

completed.
(Manufacturing Front Panel 2)
On the surface of the front panel glass 3 made of
soda-lime glass with a thickness of approximately 2.6 mm,
the display electrode pairs 6 are formed. Embodiment 2
adopts the printing method as an example to form the display
electrode pairs S. However, the display electrode pairs
6 may be formed by a dye coat method, blade coat method
or the like.
[0069]
To begin with, on the front panel glass 3 , transparent
electrode materials such as ITO, SnO2, and ZnO are applied
in a given pattern such as a stripe pattern and dried. Thus,
transparent electrodes 41 and 51 with thicknesses of
approximately 100 nm are formed.
Meanwhile, a photosensitive paste is prepared by
blending Ag powder and an organic vehicle with a
photosensitive resin (photodegradable resin). The
photosensitive paste is applied on the transparent
electrodes 41 and 51, and the transparent electrode 41 and
51 are covered with a mask having an opening that matches
the pattern of the bus lines. After a development process
in which exposure is performed on the mask, the
photosensitive paste is burned at a burning temperature
of approximately 590-600°C. Thus, the bus lines 42 and
52 with a final thickness of some micrometers are formed
51
on the transparent electrodes 41 and 51. Though the screen
method can conventionally produce a bus line with a width
of 100 µm at best, this photomask method enables the bus
lines 42 and 52 to be formed as thin as 30 µm. Besides
Ag, the bus lines 42 and 52 can be made of other metal materials
such as Pt, Au, Al, Ni, Cr, tin oxide and indium oxide.
Other than the above methods, the bus lines 42 and 52 can
be formed by etching a film having been formed by the
deposition method or the sputtering method.
[0070]
Subsequently, a paste is prepared by mixing (i)
lead-based or lead-free low-melting glass or SiO2 powder
whose softening point is 550°C -600°C with (ii) organic
binder such as butyl carbitol acetate . The paste is applied
on the display electrode pairs 6, and burned at a temperature
ranging from 550°C to 650°C. Thus, the dielectric layer
7 with a final thickness of some micrometers to some tens
of micrometers is formed.
(Forming Method of MgO Particles Having Crystal
Structure with Two Specific Crystal Faces or Three Specific
Crystal Faces)
In order to form the crystalline body of the MgO powder
16, each MgO particle 16a-16d is formed. As an example
of the forming method, high-purity magnesium oxide compound
(MgO precursor) is equally treated with heat (burned) in
oxygen-containing atmosphere at a high temperature (700°C

or higher).
[0071]
In the embodiments of the present invention, the
magnesium compound for the MgO precursor may be at least
one of (may be a mixture of two or more) magnesium hydroxide,
magnesium alkoxide, acetylacetone magnesium, magnesium
nitrate, magnesium chloride, magnesium carbonate,
magnesiumsulfate, magnesium oxalate, and magnesium acetate.
Some of the compounds listed above are present generally
in hydrated form. Such magnesium hydrate is also
applicable.
[0072]
The purity of the magnesium compound for the MgO
precursor is favorably 99.95% or more, and more favorably
99.98% or more because of the following reason. When many
impurity elements such as alkali metals, boron, silicon,
iron and aluminum are contained in the magnesium compound,
there is a risk that the particles of the compound fuse
and sinter together during the heat treatment (especially
at a high burning temperature) , and therefore the
high-crystalline MgO particles are unlikely to grow. On
the other hand, the high-purity magnesium compound prevents
such a problem.
[0073]
When such a high-purity magnesium oxide precursor is
burned in oxygen-containing atmosphere, the MgO particles

16a-16d can be formed as highly pure as 99.95% or more,
or as 99.98% or more.
Aburning temperature of the magnesium oxide precursor
is favorably 700°C or more, and more favorably 1000°C or
more. This is because the crystal faces do not growproperly,
having crystal defects, at a burning temperature lower than
700°C, and therefore the particles absorb much impurity
gas . Note that when the burning temperature reaches 2000°C
or higher, the oxygen escapes from the particles, which
results in the crystal defects causing the absorption of
much impurity gas . Thus, the favorable burning temperature
is 1800°C or below.
The MgO precursor burned at a temperature ranging from
700°C to 2000°C, inclusive, turns to the MgO particles
16a-16d with the two or three specific crystal faces.
According to another experiment carried out by the inventors,
it was observed that the (110) crystal face tends to shrink
when the precursor is burned at a temperature of
approximately 1500°C or higher. Thus, in order to enhance
the yield of the MgO particles 16c and 16d having the three
specific crystal faces, the burning temperature desirably
ranges_from 700°C to no higher than 1500°C. On the other
hand, in order to enhance the yield of the MgO particles
16a and 16b, the burning temperature desirably falls in
a range of 1500°C-2000°C, inclusive,.
[0074]

Note that the MgO particles 16a-16d may be screened
through a screening process. The following is a concrete
description of a process for forming magnesium hydroxide
that is a magnesium oxide precursor with use of liquid phase
methods. The description also shows a process for forming
the MgO powder including the MgO particles 16a-16d from
the magnesium hydroxide.
(1) As a starting material, liquid-phase magnesium
alkoxide (Mg(OR)2) or liquid-phase acetylacetone magnesium
at a purity greater than or equal to 9 9.95% is prepared.
The solution of magnesium alkoxide (Mg(OR)2) or
acetylacetone magnesium is hydrolyzed with a small amount
of acid, and therefore magnesium hydroxide gel that is the
MgO precursor is obtained. Subsequently, the gel is burned
in an atmosphere at a temperature ranging from 700°C to
2000°C, inclusive, for dehydration. Thus, the powder
having the MgO particles 16a-16d is formed.
[0075]
(2) As a starting material, liquid-phase magnesium
nitrate (Mg(NO3)2) at a purity greater than 99.95% is
prepared. An alkali solution is added to the solution of
magnesiumnitrate (Mg(NO3)2), and thus a magnesium hydroxide
precipitation is obtained. The magnesium hydroxide
precipitation is separated from the solution, and then is
burned in an atmosphere at a temperature ranging from 700°C
to 2000°C, inclusive, for dehydration. Consequently, the

precipitation forms into the powder having the MgO particles
16a-16d.
[0076]
(3) As a starting material, liquid-phase magnesium
chloride (MgCl2) at a purity greater than or equal to 99 . 95%
is prepared. Calcium hydroxide (Ca(OH)2) is added to the
solution of magnesium chloride (MgCl2), and thus, a
magnesium hydroxide (Mg(OH)2) precipitation that is the
magnesium oxide precursor is obtained. Subsequently, the
magnesium hydroxide precipitation is separated from the
solution, and then is burned in an atmosphere at a temperature
ranging from 700°C to 2000°C, inclusive, for dehydration.
Thus, the precipitation forms into the powder having the
MgO particles 16a-16d.
[0077]
With use of the liquid phase methods (1) - (3) in which
the solution of magnesium alkoxide (Mg(OR)2), magnesium
nitrate (Mg(NO3)2), or magnesium chloride (MgCl2) each of
which is at a purity greater than or equal to 99.95% is
hydrolyzed with the acids or alkalis whose concentrations
are controlled, the magnesium hydroxide (Mg(OH)2)
precipitation having extremely fine crystal grains can be
achieved. Burning the precipitation in the atmosphere at
700°C or higher separates H2O (water) from (Mg(OH)2) , and
thus the MgO powder is formed. The MgO powder formed as
above has few crystal defects, and accordingly scarcely

absorbs a hydrocarbonic gas.
[0078]
Generally, the MgO particles formed by a conventional
gas-phase oxidation method comparatively exhibit more
variations in diameter. Because of this, in a conventional
forming process, the screening process is necessary to
select particles with a roughly uniform diameter so that
the particles have uniform discharge properties.
(Disclosed in Japanese Laid-open Patent Application
Publication No. 2006-147417)
In accordance with the embodiments of the present
invention, on the other hand, although the MgO particles
are also obtained by burning the MgO precursor, compared
with those formed by the conventional method, the MgO
particles each have a uniform diameter within a given size
range. More specifically, the size of the MgO particles
in accordance with the embodiments falls within a range
of 3 00 nm-2 µm. Each particle in the embodiments has a
smaller surface area than a crystal formed by the gas-phase
oxidation method, which is why the MgO particles 16a-16d
do not absorb much impurity gas and thereby efficiently
emitting secondary electrons. In addition, since the
particles each have a uniform diameter, the screening
process to screen unnecessary particles can be omitted.
The simplified process brings about significant advantage
to the production efficiency and the production cost.

[0079]
Note that Mg(OH)2, the magnesium oxide precursor, is
a compound that has a hexagonal crystal structure, which
is different from MgO having octahedral (having eight
regular surfaces) cubic structure. Although the crystal
growth process in which Mg(OH)2 is pyrolyzed to form the
MgO crystal is complicated, the MgO crystal keeps the
hexagonal crystal structure of Mg (OH)2 in the crystal growth.
As a result, the (100) , (111) and (110) crystal faces are
formed.
[0080]
On the other hand, when the MgO crystal is formed with
a vapor phase synthetic method, only a particular crystal
face is likely to grow. For example, direct oxidation of
Mg (magnesium metal) is used for forming the MgO powder
as follows. A small amount of an oxygen gas is added to
the magnesium metal while the magnesium metal is heated
at a high temperature in a bath filled with an inert gas.
However, this method causes the crystal faces to grow only
in the (100) direction because Mg absorbs the oxygen gas.
Consequently, the crystal faces oriented in other
directions are unlikely to grow.
[0081]
The MgO particles can also be obtained by the following
method similarly to the above method in which magnesium
hydroxide is burned. The magnesium compound that does not

have a sodium chloride type crystal structure (cubic
structure) is directly burned as a magnesium oxide precursor
at a temperature of 70 0°C or higher to be in a thermal
equilibrium state. Such a magnesium compound includes
magnesium alkoxide, magnesium nitrate, magnesium chloride,
magnesium carbonate, magnesium sulfate, magnesium oxalate,
and magnesium acetate. When a (OR)2, Cl2, (NO3)2, CO3, or
C2O4 group, a coordinating atom of Mg, is separated from
the magnesium compound, such a mechanism works that the
(110) and (111) crystal faces grow as well as the (100)
crystal face. Thus, the powder of the MgO particles 16a-16d
having the two or three specific crystal faces can be
achieved.
[0082]
(Forming Process of Protective Layer)
The protective layer according to Embodiments 1 and
2 are formed in the following process.
In order to form the protective layer 17 in accordance
with Embodiment 1, the surface layer 8 made of the MgO
material is formed on the dielectric layer 7 by the
heretofore-known thin-film processing such as the vacuum
deposition method or the ion plating method.
Subsequently, on the surface of the surface layer 8,
the powder including the MgO particles 16a-16d are applied
by the screen printing method or the spraying method.
Subsequently, the solvent are dried and removed, and the

MgO particles 16a-16d are fixed to the surface layer 8,
and the protective layer 17 according to Embodiment 1 is
formed.
[0083]
In order to form the protective layer in accordance
with Embodiment 2, on the surface of the dielectric layer
7 , the powder including the MgO particles 16a- 16d are applied
by the screen printing method or the spraying method. The
MgO particles 16a-16d are fixed to the dielectric layer,
and thus the protective layer according to Embodiment 2
is formed.
The front panel 2 is completed after the protective
layer has been formed in the above process.
(Completion of PDP)
The front panel 2 and the back panel 9 are sealed
together with use of sealing glass. Thereafter, the
interior of the discharge space 15 is highly vacuumed (1.0
x 10"4 Pa) thereby removing the atmosphere and impurity gas
from the discharge space 15. In the discharge space 15,
Xe mixed gas such as Ne-Xe-based, He-Ne-Xe-based, or
Ne-Xe-Ar-based gas is enclosed as discharge gas at a given
pressure (66.5 kPa-101 kPa in this embodiment). The
concentration of the Xe gas in the mixed gas falls in a
range of 15%-100%.
[0084]
The PDP 1 or la is completed after having gone through

the above processes.
In Embodiments 1 and 2, the front panel glass 3 and
the back panel glass 10 are made of soda-lime glass . However,
this is merely an example, and note that other materials
may be used.

In order to confirm the performance effect according
to the embodiments of the present invention, the following
Experiments 1-6 were carried out, using PDP samples in
accordance with Examples (Samples 1-5) and Comparative
Examples (Samples 6-10).
[0085]
The structure that is common to all the samples is
as follows . The scan electrodes and the sustain electrodes
(display electrode pairs) are made of ITO electrodes and
bus electrodes made of Ag. Each ITO electrode is 150 µm
wide, and each bus electrode is 7 0 µm wide and 6 µm thick.
The discharge gap between display electrode pairs is 75
µm long. The glass substrate is 35 µm thick. Each barrier
rib is 110 µm high. The underside of each barrier rib is
approximately 8 0 µm wide, and the top thereof is
approximately 40µm wide. Each data electrode is 100 µm
wide, and 5 µm thick. Each phosphor layer is 15 µm thick.
[0086]
In the forming process of the protective layer, the
MgO particles with the two or three specific crystal faces

are formed. With the MgO particles, the protective layer
is formed. The heating condition for forming the MgO
particles from the MgO precursor (heat treatment condition) ,
the quantity of the MgO powder for applying, the Xe gas
concentration in the panel and such are as shown in Table
1 listed below.
In Example 1 (Samples 1 and 2) that is in accordance
with Embodiment 2, the protective layer is formed with the
MgO powder 16 of which approximately 90% are composed of
the (i) MgO particles 16a and 16b with the two specific
crystal faces (Sample 1), and (ii) the MgO particles 16c
and 16d with the three specific crystal faces (Sample 2).
[0087]
In Example 2 (Samples 3-5), the protective layer is
formed as follows. The MgO deposition layer is formed by
the vapor deposition method (EB) or the ion plating method.
Subsequently, the MgO powder 16 of which approximately 90%
are composed of (i) the MgO particles 16a and 16b with the
two specific crystal face or (ii) the MgO particles 16c
and 16d with the three specific crystal faces are disposed
on the MgO deposition layer.
In Comparative Example 6 (Sample 6), the protective
layer includes solely the MgO deposition layer with the
(111) crystal face formed by the vacuum deposition method.
[0088]
In Comparative Example 7 (Sample 7) , the protective

layer has single-crystal MgO particles formed by the
gas-phase method disposed thereon.
In Comparative Example 8 (Sample 8), the protective
layer is formed as follows . The single-crystal MgO particles
with a diameter of approximately 1 µm at the maximum formed
by the gas-phase method are disposed on the MgO deposition
layer formed by the vapor deposition method.
In Comparative Example 9 (Sample 9) , the protective
layer is formed as follows . The single-crystal MgO particles
with a diameter of approximately 3 µm at the maximum formed
by the gas-phase method are disposed on the MgO deposition
layer formed by the vapor deposition method.
[0089]
In Comparative Example 10 (Sample 10) , the protective
layer is formed as follows. The high-pure MgO precursor
is burned at 600°C to form the MgO particles, and the MgO
particles are disposed on the MgO deposition layer formed
by the vapor deposition method.
Experiment 1; (Evaluation of MgO Particle's Crystal
Face)
With use of Samples 1, 4 , 5, 7-9, a ratio of a surface
area of the (100) crystal face to a surface area of the
(111) crystal face of each MgO particle of the protective
layer was measured. Although the area ratio can be actually
measured by visual observation with an electron microscope,
the crystal faces are comprehensively identified by an

analysis with electron beams and the like in this experiment.
[0090]
Experiment 2; (Evaluation of MgO Particle with TDS
(Thermal Desorption Spectroscopy))
With use of Samples 1-10, an amount of impurity gas
(water, carbon dioxide gas, hydrocarbon gas) absorbed by
the MgO protective layer was measured with the thermal
desorption spectroscopy (TDS) technique. The measurement
results are shown in Table 1.
The amount of impurity gas (water, carbon dioxide gas,
hydrocarbon gas) absorbed by Sample 10 (total amount of
gas desorption between 10°C-1200°C) is set to 1 as the
standard value. Based on the standard value, relative
values are estimated to show the measurement results of
other samples. It is indicated that the smaller the
relative values are, the better the MgO particles that absorb
less impurity gas are.
[0091]
Experiment 3; (Evaluation of Discharge Delay)
With use of the following methods, evaluations were
made of a discharge delay of Samples 1-10 when a data pulse
is applied. The measurement results are shown in Table
1.
After an initialization pulse shown in FIG. 3 was
applied to a given pixel of each sample, data pulses and
scan pulses were repeatedly applied. Each pulse width of

the data pulses and the scan pulses is set to 100 µsec which
is longer than that when a PDP is generally driven at 5µsec.
A time lag (discharge delay) between the pulse application
and the discharge generation was measured for one hundred
times when the data pulses and the scan pulses were applied.
Using the maximum and minimum values of the measured time
lag, an average of the discharge delay was calculated.
[0092]
The discharge delay was observed with the following
apparatuses. Light emission of the phosphors as a result
of the discharge was received with the photosensor module
(H6780-20 manufactured by Hamamatsu Photonics K.K.), and
waveforms of the applied pulses and the received light
signals were observed with the digital oscilloscope (DL9140,
manufactured by Yokogawa Electric Cooperation).
The measurement result of the discharge delay of Sample
6 shown in Table 1 is set to 1 as the standard value. Based
on the standard value, relative values are estimated to
show the measurement results of other samples. It is
indicated that the smaller the relative value is, the shorter
the discharge delay is.
[0093]
Experiment 4; (Evaluation of Dependence of Discharge
Delay on Temperatures)
In the same way as Experiment 1, with use of a
temperature-controlled bath, evaluations were made of a

discharge delay of Samples 1-10 at -5°C and 25°C
environmental temperatures. Subsequently, a ratio of the
discharge delay at -5°C to at 25°C was calculated with use
of each sample.
The measurement results are shown in Table 1. It is
indicated that the closer to the value 1 the ratios of the
discharge delay are, the less dependent on the temperatures
the discharge delay is.
[0094]
Experiment 5; (Evaluation of Screen Flicker)
Evaluations were made of a screen flicker using Samples
1-10 as follows. A white image was displayed on a screen,
and then occurrence of the screen flicker was visually
checked.
Experiment 6; (Evaluation of Dependence of Discharge
Delay on Space Charges)
In the same way as Experiment 4 , evaluations were made
of a discharge delay of Samples 1-10 at the maximum and
the minimum number of pulses before an address discharge.
Subsequently, a ratio of the discharge delay at the maximum
to that at the minimum number was calculated. The
measurement results are shown in Table 1. The measurement
results indicate that the closer to the value 1 the ratio
of the discharge delay is, the less dependent on space charges
the discharge delay is.
[0095]

The measurement results in Table 1 shows that,
regardless of the existence of the MgO deposition layer,
each Sample 1-5 is dramatically advantageous regarding
discharge delay dependence on the temperatures or space
charges compared with Samples 6-10. Furthermore, Samples
1-5 show that the structure with the MgO deposition layer
has superiority in the discharge delay over the structure
without the MgO deposition layer.
[0096]
In each Sample 1-5, no screen flicker is observed,
and significant reduction of the absorption amount of the
impurity gas is observed.
These experiment results show that the excellent image
display performance is achieved because the MgO particles
with the two or three specific crystal faces have greatly
improved the protective layer properties. More
specifically, the reason the impurity gas absorption is
reduced in Samples 1-5 is that the MgO particles in the
protective layer has the (10 0) crystal face that does not
absorb much impurity gas in the low temperature region and
the (111) crystal face that smoothly emits secondary
electrons at a normal temperature or higher.
[0097]
When a comparison is made between Sample 2 and Sample
1, and between Sample 3 and Samples 4-5, Samples 2 and 3

each show a particular reduction in the dependence on the
space charges. This is because the MgO particles have the
(110) crystal face that emits secondary electrons in the
wide temperature range from low to high temperatures.
[0098]
Note that, in Samples 1-5, the MgO particles used for
the protective layer are formed by burning a high-pure
magnesium precursor at a heating temperature higher than
700°C (1400°C-1800°C). Using such a method, larger MgO
particles with fewer crystal defects can be obtained in
Examples than in Comparative Examples. Adopting the MgO
particles with such an excellent structure, Samples 1-5
achieve the above properties.
[0099]
On the other hand, Sample 6 of Comparative Example
shows a longer discharge delay and larger dependence of
the discharge delay on the temperatures than Samples 1-5.
This is because Sample 6 is not constituted from the MgO
particles with the two or three specific crystal faces in
accordance with the embodiments but solely from the MgO
deposition layer with the (111) crystal face formed by the
vacuum deposition method. Hence, Sample 6 does not have
the properties in accordance with the embodiments.
[0100]
Samples 7-9 of Comparative Example show a shorter
discharge delay and less dependence of the discharge delay

on the temperatures than Sample 6. However, Samples 7-9
still show a longer discharge delay and more dependence
on the temperatures than Samples 1-5 because of the following
reason. Although the MgO particles are included in the
protective layer, those MgO particles do not have the (110)
or (111) crystal face but have only the (10 0) crystal face
because the MgO particles are f ormedby the gas-phase method.
Thus, Samples 7-9 do not have the properties as with the
MgO particles with the two or three specific crystal faces
in accordance with the embodiments.
[0101]
In addition, Sample 10 of Comparative Example shows
a relatively short discharge delay. However, although
Sample 10 shows less dependence on the temperatures or space
charges than Sample 6, Sample 10 is more dependent on the
temperatures or space charges than Samples 1-5.
This is because Sample 10 has the MgO particles that
are achievedby burning the MgO precursor at a low temperature
(600°C) . Thus, a large amount of impurity gas is absorbed
in the MgO powder.
Industrial Applicability
[0102]
In view of industrial application, the PDP in
accordance with the embodiments of the present invention
can be applied to (i) a television used at transport or

public facilities, and at home, and (ii) a display for
computer, because the PDP offers the high-definition image
display at a low voltage.
In addition, the PDP in accordance with the present
invention is able to suppress a time lag (discharge delay)
between the application of driving voltage and discharge,
and the dependence of the discharge delay on temperatures
even when the partial pressure of xenon is high. Thus,
a high-definition television whose images are hardly
influenced by temperature environment can be achieved.

CLAIMS
1. A plasma display panel having a first substrate and a
second substrate that oppose each other with a discharge
space therebetween and are sealed together around edge
portions thereof, the first substrate including electrodes
and a dielectric layer that are disposed thereon in the
stated order, wherein
on or above a surface of the dielectric layer that
faces the discharge space, powder substantially made of
magnesium oxide particles each having a (100) crystal face
and a (111) crystal face is disposed.
2. The plasma display panel of Claim 1, wherein
the powder is disposed directly on the surface of the
dielectric layer.
3. The plasma display panel of Claim 1, wherein
a surface layer made of a metallic oxide is disposed
on the surface of the dielectric layer, the metallic oxide
being at least one selected from magnesium oxide, calcium
oxide, barium oxide, and strontium oxide, and
the powder is disposed on a surface of the surface
layer that faces the discharge space.
4. The plasma display panel of Claim 3, wherein

the magnesium oxide particles include particles that
are partially embedded in the surface layer so that each
magnesium oxide particle is exposed to the discharge space .
5. The plasma display panel of Claim 1, wherein
the magnesium oxide particles include particles each
having a hexahedral structure with at least one truncated
surface.
6. The plasma display panel of Claim 5, wherein
each hexahedral particle has a main surface which is
the (100) crystal face and the truncated surface which is
the (111) crystal face.
7. The plasma display panel of Claim 1, wherein
the magnesium oxide particles include particles each
having an octahedral structure with at least one truncated
surface.
8. The plasma display panel of Claim 7, wherein
each octahedral particle has a main surface which is
the (111) crystal face and the truncated surface which is
the (100) crystal face.
9. The plasma display panel of Claim 1,
the magnesium oxide particles include particles each

having a sodium chloride type crystal structure, and
each sodium chloride particle is a tetrakaidecahedron
that has six surfaces each of which is the (100) crystal
face and eight surfaces each of which is the (111) crystal
face.
10. The plasma display panel of Claim 9, wherein
each tetrakaidecahedral magnesium oxide particle has
a main surface which is the (100) crystal face and a truncated
surface which is the (111) crystal face.
11. The plasma display panel of Claim 9, wherein
each tetrakaidecahedral magnesium oxide particle has
amain surface which is the (111) crystal face and a truncated
surface which is the (100) crystal face.
12. The plasma display panel of Claim 1, wherein
the powder has been formed by burning a magnesium oxide
precursor.

"Discharge delay" and "dependence of discharge delay
on temperatures" are solved by improving a protective layer,
thus a PDP can be driven at a low voltage. Furthermore,
the PDP can display excellent images by suppressing
"dependence of discharge delay on space charges."
Liquid-phase magnesium alkoxide (Mg(OR)2) or acetylacetone
magnesium ate whose purity is 99.95% or more is prepared,
and is hydrolyzed by adding a small amount of acids to the
solution. Thus, a gel of magnesium hydroxide that is a
magnesium oxide precursor is formed. Burning the gel in
atmosphere at 700°C or more produces powder containing MgO
particles 16a-16d having the NaCl crystal structure with
(100) and (111) crystal faces or with (100) , (110) and (111)
crystal faces . By pasting the powder on a dielectric layer
7 or a surface layer 8, the MgO powder 16 is formed so as
to serve as the protective layer.