Space Research Centre Silicon Carbide X-Ray detectors for Planetary Exploration Dr. John E. Lees University of Leicester 8 th International Conference on Position Sensitive Detectors September 2008
Jan 21, 2016
Space Research Centre
Silicon Carbide X-Ray detectors for Planetary Exploration
Dr. John E. LeesUniversity of Leicester
8th International Conference on Position Sensitive Detectors
September 2008
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Introduction
Limitations of silicon based detectors for planetary explorationcoolingradiation damage
Search for other materials – wide band gapGaAs
DiamondSilicon Carbide
SiC imaging arrays Collaboration with University of Newcastle
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Ideal requirements for X-ray detectors
• Photon counting• Imaging• Good timing resolution• High spatial resolution• Solar blind – not sensitive to visible light• High quantum efficiency• High dynamic range• Low background• Radiation hard• Energy resolution
X
SiC
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Semi-Transparent SiC Schottky Diode
LHS: A 280m2 Schottky contact and gold bond pad
RHS: Die layout with a range of diode sizes
1.0x10-3cm-2
1.81x10-3cm-2
4.93x10-4cm-2
400m
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STSSD structure
20 m epitaxial layer on a 370 m substrate
Semi-transparent Schottky contact.
3 nm Ti / 12 nm Ni
25 nm thermallygrown SiO2
4nm Cr / 200nm Au
5 nm Cr / 250nm Au 4nmCr/100nmNiOhmic Contact
n 4H-SiC
n+ 4H-SiC
Lees et al.,Nucl. Inst. Meth A 578 (2007) 266-234
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Improving the Low Energy ResponseK-shell emission lines of elements: Na (Z=11, E=1.04 keV) to Zn (Z=30, E=8.64 keV)
STSSD has an 18nm thick electrode
Absorption in SiC Schottky diode electrode structure
0.0001
0.001
0.01
0.1
1
0 5 10 15 20 25 30
Energy (keV)
Ab
so
rpti
on
100 nm Au [14]
200 nm Ni [15]
Semi-transparent diode
Au-M
Au-LIII Au-LII Au-LI
Ti-K
Ni-K
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Planetary Exploration
General Multi-spectral: X-rays/UV/Optical/Infra-red
Imaging pixel arrays
Environment Radiation environment
Shielding
Radiation hard electronics
Operating temperatures
Spacecraft Mass
Power
Cost
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Some current and planned planetary missions
Mercury Messenger and BepiColombo
Venus Venus Express and Venus Climate Orbiter
Mars Mars Reconnaissance Orbiter,
Mars Express, ExoMars
Saturn Cassini-Huygens and Tandem
Jupiter JUNO and Laplace
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Jupiter
X-rays (Chandra)
FUV (HST)
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Auroral Processes
Precipitation of energetic ions and electrons along field lines from the planetary magnetosphere into the atmosphere produces emissions in IR, visible, UV, and X-ray wavelengths
Table shows typical values for the magnetised planets
Planet Earth Jupiter Saturn Uranus Neptune
Electron input power (GW) 10 1000 100 10 1
UV output (GW) 1 100 10 1 0.1
X-ray brem output (MW) 1 100 10 1 0.1
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Radiation environment
Alessandro Atzei and Peter Falkner, ESA technical note, SCI-AP/2004/TN-085/AA
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Radiation environment
Jupiter - Total Radiation Dose - r=3*Rj
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
0 5 10 15 20
Shielding [mm Al]
Ra
dia
tio
n d
os
e [
kra
d/d
ay
]Onera model (total)
Onera model (electrons)Onera model (brems)
Onera model (protons)
ESA ref. D&G (Total)ESA ref. D&G (electrons)
ESA ref. D&G (brems)ESA ref. D&G (protons)
Comparison between ONERA-full (D&G + GIRE + Salammbô) and ESA ref. D&G at an equatorial distance of 3 Rj from Jupiter centre
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Irradiation of STSSDs
Phase 1 - irradiation at Paul Scherrer Institut
• 63 MeV protons
• Total fluence 1x1011 cm-2
Phase 2 - irradiation at Theodor Svedberg Laboratory
• 50 MeV.
• Total fluence ~1 x 1013 protons cm-2.
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STSSD Radiation Tolerance
I-V measurements
0.1
1
10
100
1000
10000
0 20 40 60 80 100
Reverse voltage bias (Volts)
Cu
rren
t (p
A)
2nd irradiation
Pre-Irradiated
1st irradiation
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STSSD Radiation Tolerance
55Fe X-ray spectra
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Energy (keV)
Co
un
ts p
er c
han
nel
2nd Irradiation
Pre-Irradiation
1st Irradiation
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STSSD Radiation Tolerance
109Cd X-ray spectra
0
20
40
60
80
100
120
140
160
5 10 15 20 25 30
Energy (keV)
Co
un
ts p
er c
han
nel
2nd Irradiation1st IrradationPre-Irradiation
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Next Steps
• Material characterisation
• Improve electronics better energy resolution
• Extend radiation fluences
• Protons, neutrons, electrons and X-ray/gamma-ray
• Modelling
• New device structures
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Acknowledgements
Nigel Bannister University of Leicester
David Bassford
Emma Bunce
Stan Cowley
George Fraser
Mark Sims
Dean Talboys
Chris Whitford
Alton Horsfall University of Newcastle