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Kinetic and Cell-Geometry Effects in AC-PDP Simulation
Y.K. Shin, C.H. Shon, H.S. Lee, W. Kim, and J.K. Lee
Department of Physics, POSTECH, Hyo-Ja Dong, Pohang 790-784,Korea
Abstract
A hollow-cathode with the electrodes
embedded into the barrier rib and dielectric
ditched surface discharge are simulated and
compared with a coplanar geometry. The
kinetic simulation for the hollow-cathode
and ion energy distribution near the sheath is
discussed.
Introduction
The difficulty of experimental measurement makes the numerical simulation [1][2] a useful tool and an alternative studying
the phenomena in AC-PDP. The new panelmanufacture time is reduced through the
numerical benchmark such as changes in cell
size. We present the coplanar geometry and
the modified geometries with the coplanar
geometry.
While the fluid simulation has an
advantage of short computing time, it has the
shortcomings that the rate coefficients are
obtained under the assumption of uniform
electric field in space. These rates are
overestimated in the high electric field
region of the sheath. Since the rate
coefficients are exponentially proportional to
the gas discharge, the use of accurate rates is
important to describe the discharge. The
more accurate rate coefficients are obtained
from hybrid [1] and kinetic [3] simulations
using the Monte-Carlo collision. Sometimes
the energy distribution of the incoming ion
on the MgO and the phosphor is needed for
studying the lifetime of the materials.
Results
Figure 1(a) shows the voltage pulse
form. 250 V is applied to Vx and Vy
electrode during 2 us. Va electrode is
grounded during simulation. Coplanar
geometry is shown in Fig. 1(b). Cell size is
1260 X 210 um. Gas pressure is 500 Torr.
Dielectric layers of 30 um are deposited with
the dielectric constant 10. The distance
between Vx and Vy electrode is 80 um.
Figure 1. (a) pulse form, (b) coplanar structure with
1260x210 um, (c) hollow-cathode with electrode
embedded into the barrier ribs, and (d) ditched
dielectric structure.
The modified geometries are shown in Figs
1(c) and Figs. 1(d) with the cell size of Fig.
1(b). Figure 1(c) has the grounded electrode
in the barrier ribs. The embedded electrode
increases the ionization and confinement of
charged particles. The single substrate
structure is shown in Fig. 1(d). The time
evolutions of electron density and electric
potential in the coplanar geometry are shown
in Fig. 2.
(a)
Unlike the coplanar structure the discharge is
spread toward the embedded electrode and
(a)
-7.5 V
30 V
30 V
80 V
(b)
Xe*: 6.69E13 cm-3
-3
ne : 3.4E12 cm
(c)
6.00E+014
H=100 m
(b)
4.00E+014
100 V
(c)
H=50 m
d = 50 m
n :e 5.37E12 cm-3
2.00E+014
H=50 m
d=0
200.00
0.00E+000
(d)
m
0.00
0.00
10 V
200.00
4040
4060
4080
4100
Time (ns)
-15 V
60 V
10 V
400.00
600.00
m
800.00
1000.00
1200.00
Fig. 2 Coplanar structure: (a) and (b) electron
density and potential for first pulse (70 ns), (c)
and (d) electron and potential for the second
pulse (4100 ns).
The cell ignition between Vx and Vy
electrodes is shown in Figs. 2(a) and Figs.
2(b). The charge neutrality is achieved in the
flat potential. The density and the potential
in second pulse are shown in Figs. 2(c) and
Figs. 2(d). The high electric field due to the
negative wall voltage near Vx electrode
creates the high charged particles between
Vx and Vy electrodes. The potential and
density profiles show the discharge moving
to Vx electrode.
Figures 3(a) and 3(b) show the
potential and the Xe* profiles of the hollow
cathode with electrode embedded into the
barrier ribs at 4050 ns. When the discharge
cell is ignited, the impinging ions toward the
barrier rib due to the grounded electrode
causes the secondary electron emission.
Fig. 3 (a) potential and (b) Xe* excitation for the
case of Fig. 1(b) at 4050 ns, respectively, (c)
discharge effect of barrier’s height.
increases the plasma density. In the second
pulse similar to the first pulse, right-side
electrode increases the plasma density than
that of the coplanar structure. The height of
barrier rib affects the discharge. The average
electron density during the second pulse is
shown in Fig. 3(c) to describe the effects of
barrier’s rib. The average electron density
for H=100 um is 25 % larger than that of
H=50 um, and 1.5 times large than that of
the barrier ribs without embedded electrode.
The single substrate geometry is
shown in Fig. 4. The potential profile shown
Fig. 4(a) is extended over the entire volume.
The high electric field in the ditched
dielectric region makes the ionization be the
dominant collision process. Since xenon
excited energy is low, most of electron
energy are transferred to the ionization
collision. Thus electron and ion density are
high in the ditched dielectric region.
Although the dominant electric field is a y
component, the small electric field, Ex,
exists near the edge of Vy electrode and
produces the xenon excited state. The xenon
excited state distributed along the x direction
is shown in Fig. 4(b).
about the damage of phosphor. Figures 5(a)
and 5(b) show the neon ion distribution and
energy distribution near the left-side barrier
rib.
(a)
(a)
120 V
100 V
140 V
20 V
(b)
Xe*: 1.52 E14 cm-3
(c)
Xe+ 1.05E13 cm-3
(b)
(d)
200.00
Xe*: 1.8E14 cm-3
1.08E14
m
1000
200.00
400.00
600.00
m
800.00
1000.00
1200.00
Fig. 4 (a) potential, (b) Xe* density, and (c)
Xe+ density (4050 ns), respectively, (d) Xe*
density (4100ns)
# of particles
0.00
0.00
100
10
0
UV photons of 147, 150, and 173 nm are
transported to the phosphor with less
radiation trapping because of a short
traveling distance. The ion bombardment on
the phosphor is related to the lifetime and
color purity of PDP. Although ions are
mainly created in the ditched region, the ion
bombardment on the dielectric is less due to
the upper-directed electric field. The charged
particle density increases toward the upper
region shown in Fig. 4(c). The other
discharge is initiated between Vx and Vy
electrodes after the flat potential is achieved
in the ditched dielectric. The dominant value
of electric field is a x component and
produces the ionization and excitation.
Figure 4(d) shows the xenon density
distributed near the dielectric along the x
direction.
The kinetic simulation [3] produces
the electron and ion energy distributions.
The ion energy distribution in the vicinity of
the phosphor gives important information
10
20
30
40
50
E (eV)
Fig. 5 (a) neon ion density (b) ion energy
distribution function near the left-side dielectric.
The ion energy distribution is obtained by
arranging the particle velocities existing in a
given region. The neon ion is drawn and
accumulated on the left-side barrier rib. The
low ion energy shown in Fig. 5(b) is due to
the frequent elastic collisions since the
sheath size is many times the ion-neutral
collisional mean-free-path and the voltage
drop between the dielectric layers resulted
from the charge accumulation [4].
We use a modest electron beam to
decrease the breakdown voltage. The
energetic electron of a beam enhances the
ionization and decreases the breakdown
voltage. The electron beam can be used as
the seed electron when the cell is ignited.
Conclusion
We present the fluid and kinetic
simulation for AC-PDP cell. The embedded
electrode structure increases the plasma
density and affects the discharge depending
on the barrier height. The ditched dielectric
structure enhances the plasma density and
discharge area. The low ion energy near the
barrier ribs results from the elastic collision
and charge accumulation.
Acknowledgment
This PDP project was supported by
the PDP Research Center, Korea.
References
1)
J. Meunier, Ph. Belenguer, and J.P.
Boeuf, J. Appl. Phys. 78(2),
731(1995); C. Punset, J.P. Boeuf, and
L.C. Pitchford, J. Appl. Phys. 83,
1884(1998).
2)
Y.K. Shin, J.K. Lee, and C.H. Shon,
IEEE Trans. Plasma Sci. (to appear in
Feb/1999).
3)
J.P. Verboncoeur, A.B. Langdon, and
N.T. Gladd, Comp. Phys. Commun. 87
199 (1995).
4)
Y. K. Shin, J.K. Lee, C. H. Shon, and
W. Kim, Jpn. J. Appl. Phys. Pt II. 38
L174 (1999).