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Plasma display panels: problems and their analysis via computer simulationsPowerPoint Presentation

Plasma display panels: problems and their analysis via computer simulations

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### Plasma display panels: problems and their analysis via computer simulations

V.P. Nagorny, V.N. Khudik, P.J. Drallos

Plasma Dynamics Corporation, USA

A. Shvydky

University of Toledo, USA

Introduction computer simulations

- Could anybody imagined 5 years ago the question: PDP or LCD for large displays?
- Competition from LCD becomes really strong
- Rapid falling prices ( reaching $1/ sq in at retail )
- Response time (is approaching 3ms (<10ms))
- Color gamut (better than NTSC)
- High Contrast (> 500:1 1000:1)
- Large Pixel counts (~ 10M )
- The viewing angle is improving
- Color filter may disappear - going to LED illumination

- PDP – improved power consumption, image burning problem, …, but the main problems that we had 10 years ago are still there:
- Efficiency, and Brightness
- Addressing speed

- We better do something about these problems and quick.

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How we are doing with research computer simulations

- Matrix PDP – quasi 1D
- More Xe - higher efficiency, but also higher voltage (from 1D).
- Larger Secondary Emission – Good for efficiency (from 1D).
- Larger Gap– Good for efficiency (from 1D).

- Coplanar PDP is very complicated (many new elements – essential multi-D, barrier ribs, complex electric field configuration, cathode wave, striations, …)
- Qualitative results – good (2D, 3D, observations) :
- Discharge structure and dynamics
- Cathode and anode waves, striations
- New modes of the discharge
- New types ofinstabilities
- …

- Quantitative results – messy (lack of “tools”, difficulty due to a size):
- Efficiency – results can’t be trusted. Codes have built-in error ~XX%.
- Cathode wave – numerical diffusion is faster than the real wave
- Striations – no quantitative results
- Observations – sketchy. No comparison/control of ALL the factors.
- Some data are STILL ASSUMED (gXe,Ne, ePhos, other )

- Qualitative results – good (2D, 3D, observations) :

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Can we do better? computer simulations

- Yes – new powerful tools (kinetic codes), allowing quantitative investigations are developed or being developed. We can now investigate properties of all kinds of PDP discharges, including addressing speed, jitter, even efficiency... and make numerical experiments, that impossible or expensive to do in a real physical system.
- One still needs measurements of certain basic parameters, that affect the regime of operation of a pdp cell, so that investigation will be more focused. One also needs more detailed analysis of physical experiments, especially those made on the panel.

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New tools in action computer simulations Experimenting with Kinetic Codes

- Ramp discharge – dual nature, stability
- Sustain discharge
- Striations
- Cathode wave – speed

- Loading effects - Small vs. Large panel

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Ramp Discharge computer simulations

- L. F. Weber (1995-1998)I0=CdV/dt

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Ramp Discharge computer simulations

- Ideal for the test of 3D PIC/MC - Known solution (fluid theory –analytical and numerical).Faster than 3D fluid code<Ni>=ti (I0 /2e)=(ti /2e)CdV/dt ~ (1-6)104
- Stable if:
- Good priming
- dV/dt < Rmax(L,g )

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Ramp Discharge computer simulations

- 3D cell, 3D PIC/MC simulation vs. 3D Fluid

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Ramp Discharge computer simulations

- 1D cell, Ramp Rate = 1V/us, < Ni > ~ 3300 (3D PIC/MC)

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Ramp Discharge computer simulations

- 1D cell, < Ni > ~15000 (3D PIC/MC)

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Ramp Discharge computer simulations

- 1D cell, < Ni > ~15000 (3D PIC/MC)

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Ramp Discharge computer simulations

- Fluctuations in equilibrium d N ~ N1/2
N

- For < Ni > ~ 10000, dNi ~100 (1%) - fluid approximation seems good (99.7% less than 3s)

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Ramp Discharge computer simulations

- In the Townsend discharge Ni is the result of a balance, rather than equilibrium (d N ~ N1/2 ):
- Ni Ne = g Ni Ni = (g Ni ) exp(a L) = Ni
- Ne = g Ni + (g Ni )1/2 Ni + ( Ni /g )1/2 (sec. emis.)
- Ne=g Ni Ni + d Ni (avalanche), d Ni ~ ( Ni /g )1/2

- dNi ~ ( Ni /g )1/2 >>( Ni )1/2

- Ni Ne = g Ni Ni = (g Ni ) exp(a L) = Ni
- For the Ramp discharge PDP cell is statistically small.

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E computer simulationsmax

Ramp Discharge- Ramp discharge may be statistically unstable.

Vcell ~10 -5 cm3

n > nmin ~105cm-3

E< Emax

-----------------------------------

Fluctuations lead to diffusion between “fluid trajectories”. Oscillations increase or decrease until large oscillation occurs.

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Ramp Discharge computer simulations

- 1D cell, 3D PIC/MC : g Xe- dependence
- Statistical Instability is powerful – it works even when <Ni > and g are large. One needs external source to restart discharge.

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Ramp Discharge computer simulations

- Exoemission (1D test cell – initially empty, 3D PIC/MC,
<Ni >=15000,g Xe= 0.001, 7% mix )

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Ramp Discharge computer simulations

- Exoemission - 3D cell initially empty, 3D PIC/MC, < Ni > ~ 60000

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Ramp Discharge Summary computer simulations

- Ramp discharge (RD) exhibits dual nature – fluid and statistical.
- For the Ramp discharge PDP cell is statistically small.RD is statistically unstable unless external source of electrons is present. Average of simulations of 100 cells with different random seed numbers (no exoemission) showed much more fluid-like behavior, with much smaller fluctuations ramp measurements based on LINE current or/and light integration, can miss the statistical part of the ramp discharge behavior. Experiments on macrocell also miss statistical effects (very large N).
- In low-Xe mixtures some stabilization may be from metastables, but in hi-Xe mixtures only exoemission can stabilize the ramp.
- With larger gXe, the required level of exoemission may be smaller.
- Still no reliable data on gXe and exoemission rate, as well as gXe,Ne in the presence of exoemission – data critical for stability, efficiency, addressing, lifetime !!!!

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Sustain Discharge – Experiments computer simulations

- Current physical observations do not distinguish between different mechanisms of the processes. Special experiments would be very expensive to make, but 2D/3D PIC/MC simulations can do the job.

Mesh:

135x60x22

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Sustain Discharge – Striations computer simulations

- Guess: Anode striations caused by the ion-sound waves, or/and modulation of the surface charge on the cathode.
- Freeze ions above the part of the anode - Striation are even more pronounced, and stay. They are not a result of ion motion, have nothing to do with ion sound.
- Used uniform charge distribution, or no charge on the cathode

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Sustain Discharge – Striations computer simulations

- Guess : Anode striations – is a plasma ionization wave; the cathode wave – is the surface charging wave(there is no way to distinguish between these mechanisms just from observation).Reality – Almost opposite:
- 1. experiment with d/e =10-4(metal).

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Sustain Discharge – Striations computer simulations

- 2. “No Cathode” experiment, “frozen” ions. Results:
a) S ~ Qed/(e E), vf ~ Ie(t)

b) No significant difference between narrow (0-1eV), and wide (0-8eV) EDF of the source S.

Ion density (side) Potential (side)

Ion density (top) Charge Deposition Rate

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Sustain Discharge – Striations computer simulations

- Guess: There is about 12V ( IXe) between striations voltage across PC is about 12V x Nstr .
Reality – the voltage between striations decreases with time. Typically it starts with 12-13V, but by the time the last striation appears, the voltage between first ones may be just 2-3 V. Voltage across PC continue to decrease after the anode is completely covered by electrons.

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Sustain Discharge – Striations computer simulations

- Guess: Striations of PDP sustain discharge similar to those that occur in DC positive column.
- Reality: PDP striations appear in the process of charging dielectric, ion motion is not important for their formations, and they disappear due to an ion motion. In the DC positive column stationary striations require ion motion.

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Sustain Discharge – Striations computer simulations

- The formation of the striations follow the charging of the anode dielectric and formation of the conducting channel near the surface. The process of charging the surface limits the speed of the appearing of the striations.
- Ions inside the channel do not actively participate in the creation of dense areas – they may be considered immobilized. It is ionization by electrons, and the consequent decreasing of the electric field in the area makes a striation.
- Speed increases with thicker dielectric d/e (same current), larger current, lower normal electric field above the anode.

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Sustain Discharge – Striations computer simulations

Striations near the address electrode

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Sustain Discharge – Striations computer simulations

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Sustain Discharge – Striations computer simulations

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Sustain Discharge – Striations computer simulations

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Sustain Discharge – Cathode Wave computer simulations

- Cathode wave speed investigation
- There is not enough experimental data that would allow distinguish one mechanism of the wave propagation from another. Speed changes during propagation, hard to say why.
- Fluid codes as well as kinetic Boltzmann codes suffer from numerical diffusion, rising from convective term or . Numerical diffusion of ions, is especially important, since it is responsible for artificial spread of ions ahead of the real cathode wave.
- Our previous 3D simulations have shown that the wave speed is of the order of the ion velocity in the cathode area, but we didn’t obtain self-similar behavior, since discharge dynamics affected the speed.

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plasma computer simulations

Dielectric, e

Cathode, V = 0

Sustain Discharge –Cathode Wave- “Experimental” setup for the CW speed investigation, using 3D/2D PIC/MC codes.

Anode, V=Va

dielectric: d, e

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Sustain Discharge – Cathode Wave computer simulations

- CW speed investigation (Fully-Conservative 2D PIC/MC)

self-similar behavior.

Dielectric thickness

d/e =10m,

Va= 500V,

g = 0.5 (pure Ne);

Resolution 600x320 (field).

jS,

s / C

j

ni

t = 90.5ns

V=2.2km/s

ne

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Sustain Discharge – Cathode Wave computer simulations

- CW speed investigation (Fully-Conservative 2D PIC/MC)

self-similar behavior.

Dielectric thickness

d/e=10m,

Va=500V,

g =0.5 (pure Ne);

Resolution 600x320 (field).

jS,

s / C

j

ni

t = 183 ns

v=2.2km/s

ne

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Sustain Discharge –Cathode Wave computer simulations

- Effect of diffusion on the cathode wave structure

De, Di≠ 0

De=Di=0

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Sustain Discharge – Cathode Wave computer simulations

- Speed of the CW, vCF (when it propagates) is about the ion speed near the surface in front of the CW, vCF ~ vi. Diffusion and the angle at which electric field enters the dielectric is very important for the propagation of the Cathode Wave.It is ironic that in the conditions of a pdp (d /e ~ a few microns) the cathode wave charges dielectric capacitor almost completely, so it may seem that it is a charging wave.
- vCF increases with
- Thinner dielectric: d /e
- Larger electric field near the tip.

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Single Cell vs. Row of Cells computer simulations

- Display line has ~ 3000-6000 cells; Number of lines ~500-1000.
- Wires have resistance, inductance, capacitance (R, L, C) – which may be important, when many cells work together. These parameters (R, L, C) change when one moves from 42 to 60in panel or from 840 to 1920 pixels/line even if pixels or wires stay the same.
- Interaction between cells may strongly affect the work of individual cell. Voltage applied to a cell may differ from the desirable. This may change the “rules of the game” - a cell design or driving waveform may work good in one panel and not so good in the other one, or in the same panel when many pixels are turned ON.
- Current measurements do not show the voltage and the current through an individual cell. What can we do about it?

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s computer simulations

Q

Single Cell vs. Row of Cells- Simplification: All lines work together, all lines are identical.

Single charge between

metal plates - difficult

Many charges - simple

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Single Cell vs. Row of Cells computer simulations

Single row – difficult:

One has to consider interaction with many rows

Many rows – simpler:

one may consider one row with

correct boundary conditions

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( I computer simulationsPositive direction )

Single Cell vs. Row of CellsFrom original 18 matrix elements in a cell C11 - C33, L11 - L33 , only 6 or 7 are independent(due to a symmetry of a cell), whichfor sustain dischargecan be organized in just five combinations: C1 - C3 ,LA , LB.

Transformers A and B : DVA=LA d/dt(I1 - I2 ), DVB=LB d/dt(I1+I2 - I3 )

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Single Cell vs. Row of Cells computer simulations

- Many cells, medium load (probably most important)

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Single Cell vs. Row of Cells computer simulations

- Many cells, large load

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Summary computer simulations

- Once again, what it’s gonna be: LCD or PDP? – My answer: It depends. It depends on the future progress of PDPs.
- The next generation of PDPs will be simpler, much more efficient, but we need to accelerate our progress NOW. We need a breakthrough, especially on efficiency and addressing speed. Using kinetic codes for making numerical experiments where it’s difficult to make or analyze a real ones, is essential. Today’s computer codes and computer power are good enough for this task.

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