que, NM, September 20 gy Conference, Albuque craft Charging …€¦ · Spacecraft Charging at GEO...

Comparison of numerical and experimentalComparison of numerical and experimental investigations on the ESD onset in the Inverted

Potential Gradient situation in GEO

P. Sarrailh, J.-C. Matéo-Vélez, J.-F. Roussel, B. Dirassen (ONERA)

11th Spacecraft Charging Technology Conference, Albuquerque, NM, September 20-24, 2010

, , , ( )J. Forest, B. Thiébault (ARTENUM)

D. Rodgers, A. Hilgers (ESA)

Outline

• General overview on the ESD risk• Experimental setup

p p• SPIS ESD tool• Parametric study: comparison experimental/numerical results

General overview on the ESD risk

Spacecraft Charging at GEO in sunlight

• S/C structure at a negative potential several kV due to electron collection• Photoemission on solar cell cover glass:

• Dielectrics in sunlight more positive than S/C structure

g p• Barrier of potential on the front side due to rear side negative potential

• This situation is the Inverted Potential Gradient (IPG)

net photo electron current

saddle point - 2010 V

- 1500 V

hυrecollected electrons

S/C SA SA

- 2800 V

- 2000 Vfront side

rear side - 3000 V

electrons

- 2500 V

- 2200 V ibl t j t i f

2010 V

- 2010 V

- 1500 V

IPG situation at the solar cell scale

• At the solar cell edge:• Gap surface covered with (photoconductive) kapton = S/C structure voltage• Solar cell voltage ~ S/C structure voltage (strings voltage ~100 V)

• Cover Glass top surface is more positive than solar cell = differential voltage• Triple point between conductor, dielectric and vacuum

• Uses of a simplified geometry (valid for interconnects) to compare experimental and

0- numerical results

-2200 V-2400 V

-2600 V

-2800 VFront surface

barrier potential

Triple point

Coverglass

-2000 V

Front surface

Side surface

Differential voltage

Dielectric layer

Triple point

Solar Cell ~ -3000 V

-3000 V~ -3000 V

dielectrics

Differential voltage

Structure S/C stucture potential

Microscopic structure and electron avalanche

Simulation at mesoscopic scale

Microscopic scale model

Fowler-Nordheim e-

electric field amplification due to micron tipdielectrics

Differential potential

Electric field onSecondaryElectron avalanche

Secondary emission by electron impact + recollection

Electric field on the tip

Fowler-Nordheim

Secondary emission > 1 Cathode spot creation

=> ESD

electron emission

Tip geometry and field enhancement factor

• Field enhancement factor from 300 to 800• Tip length: 1 m • Tip radius (from emitting area): 1 - 10 nm

• Figure 5 and figure 8 extracted from:Effect of electrode surface finish on electrical breakdown in vacuum, D W Williams and W T

Williams, J. Phys. D: Appl. Phys. (5), 1972.

Experimental setup

Experimental Setup

• ONERA CEDRE vacuum chamber• Pressure: 3.10-6mbar• Barrier potential controlled by Vbias

Barrier potential controlled by Vbias

• Differential voltage by photoemission (as in flight)

Rotatingcubic holder

UV sourceElectrostatic probe

HV Feedthroughs Electrostatic probecubic holder

Dielectric

UV sourceSample

tank walls

Csat =

CCD Camera

CEDRE chamber

VbiasCsat 10nF

Nominal case – Perpendicular TP with Aluminum and Teflon

• The triple point is irradiated by the UV source• Only the chosen triple point line can generate

Irradiated zone

y p p gESDs thanks to a protecting mask 40mm

Dielectric FEP with aluminization on the rear side Protecting mask

UV Irradiation zone

sample

UV protection

200 mmUV protection mask

Nominal case – Perpendicular TP with Aluminum and Teflon

• The voltage on the FEP is close to 0V • 8 ESDs have been obtained at 1 5

ESD #1ESD #2ESD #3

different locations of the triple point edge

• The ESD threshold is about -800V -0,5

nt, A ESD #4

ESD #5ESD #6ESD #7ESD #8

0- -1-5 0 5 10 15 20

Time, µs

00 200 400 600 800 1000

Differential voltage threshold, V

Results of the parametric study

6Nominal caseMetal length 15mm

Metal length 15mmCMX AR dielectricChange of incidence angleGold

e Co planar (5nF)

00 500 1000 1500 2000 2500

Differential voltage threshold, V

SPIS ESD tool

The mock-up geometry and the boundary conditions

UV• Simulation conditions:

• Teflon (127 m) / aluminum (1.5 mm)• External box : 4 cm x 4 cm x 0.6 cm

Irradiated zone

• TP zone : 1 m• tip length = 1 m• Barrier potential from 500 V to 2000V• from 800 to 300;

Barrier potential(Dirichlet condition) Refinement

boxTriple point with field

enhancement

;Dielectric FEP

Symmetry conditions

enhancement

PerpendicularX

Metal plane + triple point(Dirichlet; V = 0)

Dielectric(implicit solver)

SPIS ESD tool

• ESD prediction scenario, two imbricate loops:• Barrier potential prediction• Tip geometry evaluation: field enhancement factor

loop (for a fixed tip length – 1m standard)

Tip and potential P t ti l

ESD prediction scenario

Data from UI

Init simulationFN current calculation

TipRecession interactor

FN current calculation

TipRecession interactor

Simulation Loop

Next time-step

Same potentialNext tip (lower

p pre-initializationPotential sweep

Plasma integration

SC/Plasma interactions simulationDt

ScenarioPower balance on tip

Tip temperature

Mass losses by evaporation

Neutral density

Power balance on tip

Tip temperature

Mass losses by evaporation

Neutral density

noESD ?

Is the tip melted ?

Circuit solver

simulationDuration

Scenario end ?

simulationLoop

Tip length

evaporation

Ionization probability

Tip length

evaporation

Ionization probability

nolo L

Scenario end ?

Results to UI

• Tip model (tipRecession interactor):• Tip model based on a cylindrical geometry

• Tip model based on a cylindrical geometry• Zero dimensional thermal model (compared to Rossetti ….)

Barrier potential and emitted currentste

rier p

ESD T i

ESD Trig. = 650

ESD Trig. = 600

1ESD Trig. = 800

ESD Trig. = 750

ESD Trig. = 700

Ph t i i

Fowler-Nordheim emission

Photoemission

0 50 100 150 200 250 300 350 40010-20

0 50 100 150 200 250 300 350 400

Time (s)

Electron emission : densities in volume-2

Dielectric Metal Dielectric Metal

S d l t d itF l N dh i l t d it

DielectricMetal

nolo Secondary electrons densityFowler-Nordheim electrons density

• F-N primary electrons:• directed toward the barrier potential

M d it h 1020 3 (S h ff t)

• Max density can reach 1020 m-3 (Space charge effect)• Secondary electrons are present on the top side of the dielectric due to hoping

Parametric study: comparison of the numerical and experimental results

Parametric study – reference case

5 Reference caseAluminum-Teflon 127 m3 mm Gap

Irradiated Gap

ESD Trig. = 800

ESD Trig. = 600

Pea 800 600

500 1000 1500 2000 2500

Experimental resultsNumerical results

Differential voltage (V)

Parametric study – Sun incidence angle

Not Irradiated Gap

5 Reference caseAluminum-Teflon 127 m3 mm Gap

Not Irradiated GapAluminum-Teflon 127 m3 mm Gap

) Irradiated Gap

400V 3mm

500 1000 1500 2000 2500

Differential voltage threshold (V)

Parametric study – Gap length

15mm Gap

5Reference caseAluminum-Teflon 127 m3 mm Gap

15mm GapAluminum-Teflon 127 mIrradiated Gap

Irradiated Gap

900V 3mm

500 1000 1500 2000 2500

Differential voltage threshold (V)

Parametric study – Dielectric material

Aluminum-CMX 100 m3 mm Gap

Reference caseAluminum-Teflon 127 m

3 mm GapIrradiated Gap

) 3 mm GapIrradiated Gap

CMX-AR □ = 2.6×1016

CMX-AR □ = 1016

CMX-AR □ = 5×1015

Teflon □ = 1016

500 1000 1500 2000 2500

500 1000 1500 2000 2500Differential voltage threshold (V)

Lessons to be taken from the experiments and numerical simulations

• The numerical results qualitatively agree with the experiments• It is definitely more difficult to trig ESDs in the following cases

• Low photon incidence angle• Longer metallic plate• Co-planar geometry

More conductive dielectric

0- • More conductive dielectric

• Strong effect of • surface resistivity of the front edge

r • surface resistivity of the front edge• Tip geometry (radius and shape)

• Need for complementary experimental data (surface resistivity measurement,

p y p ( y ,surface distribution and type of microscopic structures)

Conclusion

• Large experimental parametric study

• SPIS ESD tool:• Complete ESD scenario:

• 3D Electron avalancheThermal model of the tip

0- • Thermal model of the tip• ESD threshold estimation

• Simulation of the charging and electron avalanche well described• Automatically adapted time steps: from 1s to 10-12s

r Automatically adapted time steps: from 1s to 10 s• 3 length scales simulated

• Good qualitative agreement between experiments and numerical results

• Need of further experimental data to provide design engineers with quantitative/predictive ESD risk tool

Perspective

• Experimental investigation on surface resistivity to get more data

• Photo conductivity modeling improvement

• More complex geometry:

p g y• solar cell edge • here, it is close to the interconnects

• Effect of multiple tips (tip distribution on the surface)

• Emission from semi-conductors

• Model the plasma generation during the transition to arc

Questions ?

que, NM, September 20 gy Conference, Albuque craft Charging …€¦ · Spacecraft Charging at GEO...

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