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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).