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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

Jupiter

X-rays (Chandra)

FUV (HST)

Space Research Centre

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

Space Research Centre

Radiation environment

Alessandro Atzei and Peter Falkner, ESA technical note, SCI-AP/2004/TN-085/AA

Space Research Centre

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

Space Research Centre

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.

Space Research Centre

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

Space Research Centre

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

Space Research Centre

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

Space Research Centre

Next Steps

• Material characterisation

• Improve electronics better energy resolution

• Extend radiation fluences

• Protons, neutrons, electrons and X-ray/gamma-ray

• Modelling

• New device structures

Space Research Centre

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