Transcript Investigation of radiation hard sensors for the ILC forward calorimeter

.
Investigation of radiation hard sensors
for the ILC forward calorimeter
K. Afanaciev, Ch. Grah, A. Ignatenko,
W. Lange, W. Lohmann, M. Ohlerich
International school-seminar
Actual problems of microworld Physics
Gomel 2007
1-Apr-16
Actual problems of microworld physics. Gomel 2007
Very Forward Region of the ILC Detector
BeamCal
Interaction
point
EM calorimeter with sandwich structure:
30 layers of 1 X0
3.5mm W and 0.3mm sensor
Angular coverage from 5 mrad to 28 mrad
Moliére radius RM ≈ 1cm
Segmentation between 0.5 and 0.8 x RM
• The purpose of the instrumentation of the very forward region is:
– Hermeticity: increase the coverage to polar angles > 5mrad
– Fast beam diagnostics
1-Apr-16
Actual problems of microworld physics. Gomel 2007
The Challenges for BeamCal
Creation of beamstrahlung at the ILC
e-
e+
Bethe-Heitler process
e+e- pairs from beamstrahlung are
deflected into the BeamCal
≈ 1 MGy/y
15000 e+e- per BX => Edep  10 – 20 TeV
~ 5 MGy per year strongly dependent on
the beam and magnetic field configuration
=> radiation hard sensors
Detect the signature of single high energetic
particles on top of the background.
≈ 5 MGy/y
=> high dynamic range/linearity
For 1 layer, per cell
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Actual problems of microworld physics. Gomel 2007
Irradiation facility
Superconducting DArmstadt LINear ACcelerator
Technical University of Darmstadt
V.Drugakov
2X0
Energy spectrum of
shower particles in BeamCal
Irradiation up to several MGy using the injector line of the S-DALINAC:
10 ± 0.015 MeV and beam currents from 2 to 100 nA
corresponding to doses about 10 to 600 kGy/h
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Actual problems of microworld physics. Gomel 2007
Irradiation facility
1-Apr-16
Actual problems of microworld physics. Gomel 2007
Investigated materials
 Gallium arsenide (GaAs),
 Polycristalline CVD Diamond (pCVD)
. Silicon (radiaton-hard and common detector-grade for comparison)

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
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GaAs
Density
5.32 g/cm3
Pair creation E
4.3 eV/pair
Band gap
1.42 eV
Electron mobility 8500 cm2/Vs
Hole mobility
400 cm2/Vs
Dielectric const. 12.85
Radiation length 2.3 cm
Ave. Edep/100 m
(by 10 MeV e-)
69.7 keV
Ave. pairs/100 m 13000
Structure
p-n or insul.
Si
2.33
3.6
1.14
1350
450
11.9
9.4
Diamond
3.51
13
5.47
1800
1200
5.7
18.8
53.3
9200
p-n
34.3
3600
insul.
Actual problems of microworld physics. Gomel 2007
Methodology. Irradiation
•Irradiation under bias voltage
•Monitoring of beam and sample currents, sample temperature
exit window
of beam line
collimator (IColl)
sensor box (IDia, TDia, HV)
1-Apr-16
Faraday cup (IFC, TFC)
Actual problems of microworld physics. Gomel 2007
Methodology. CCD Setup
Sr90
sample
Sr90 source
Preamplifier
Scint
.
PA
PM1
PM2
discr
discr
delay
&
ADC
Gate
Sensor box
Trigger box
typical spectrum of an E6 sensor
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Actual problems of microworld physics. Gomel 2007
pCVD Diamond Detector
• pCVD diamonds are an
interesting material:
– radiation hardness
– advantageous properties like: high
mobility, low εR = 5.7, thermal
conductivity
– availability on wafer scale
– Solid-state ionisation chamber (no pn junction)
• Samples from two manufacturers
were investigated:
(courtesy of IAF)
(courtesy of IAF)
– Element SixTM (ex-DeBeers)
– Fraunhofer Institute for Applied
Solid-State Physics – IAF
•
•
•
1 x 1 cm2
200-500 μm thick
(typical thickness 300μm)
Ti(/Pt)/Au metallization
1-Apr-16
Actual problems of microworld physics. Gomel 2007
CVD Diamond. Irradiation
Thickness,
µm
500
Dose,
MGy
>1
DESY 8 (IAF)
FAP 5 (IAF)
300
470
>1
>5
E6_4p (E6)
470
>5
Sample
E6_B2 (E6)
100 nA (E6_4p)
100 nA (FAP5)
E6_4p
After absorbing 7MGy:
CVD diamonds still
operational.
1-Apr-16
Actual problems of microworld physics. Gomel 2007
CVD Diamond. Irradiation results
~ -80%
Signal decreased by  80 % after absorbed dose of about 7 Gy
But signal is still visible.
Slight increase in current, but still in pA range
1-Apr-16
Actual problems of microworld physics. Gomel 2007
CVD Diamond. Irradiation results
Signal from sample decreases with time after irradiation
further decrease after ‘purging’ trapping levels with UV light
Signal increases back after irradiation with small dose - ‘pumping’
1-Apr-16
Actual problems of microworld physics. Gomel 2007
GaAs Detector
Supplied by FCAL group at JINR
Produced by Siberian Institute of Technology, Tomsk
Sample is semi-insulating GaAs doped by Sn
(shallow donor) and compensated by Cr (deep
acceptor). This is done to compensate electron
trapping centers EL2+ and provide i-type
conductivity.
Sample works as a solid state ionisation chamber
Structure provided by metallisation (similar to diamond)
500 m thick detector is divided into 87 5x5 mm pads
and mounted on a 0.5mm PCB with fanout
Metallisation is V (30 nm) + Au (1 m)
1-Apr-16
Actual problems of microworld physics. Gomel 2007
I-V and C-V
current-voltage-curve: Ring 6
0.0000012
0.0000010
0.0000008
0.0000006
0.0000004
Constant pad capacity
no dependence on V =>
no structure
Pad-Nummer
1
3
5
7
current [A]
0.0000002
0.0000000
-0.0000002
Pad capacity about 12 pF
-0.0000004
-0.0000006
-0.0000008
-0.0000010
-0.0000012
-0.0000014
-0.0000016
-500
Zeitkonstante Spannung
Guardring nicht angeschlossen
-400
-300
-200
-100
0
100
200
300
400
500
Almost linear IV characteristics => resistor
Currents in the order of 0.2 A @ 100V
capacitance [F]
Voltage [V]
1.30E-011
r8p5
r6p4
r3p3
r11p6
1.20E-011
Rpad  500 MOhm
0
20
40
60
Stepnummer [Dealy = 2000ms]
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Actual problems of microworld physics. Gomel 2007
80
100
GaAs. Signal
S8 pad4
ring 4
Clear separation of peaks from Sr90 source
Quite homogeneous response
over different pads
Saturation of signal @ about 200V bias
S8 pad4
ring 6
Collection efficiency  60%
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Actual problems of microworld physics. Gomel 2007
GaAs. Irradiation
 Sample 7
 Sample 8
Preliminary
Samples 7&8, pad4, ring6 @ 200V
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Actual problems of microworld physics. Gomel 2007
GaAs. Irradiation results
Sample 8 pad4 ring6
Results: CCE dropped to about 6% from 60% (by ~ 90%)
but signal is visible for absorbed dose of about 1 MGy
Dark current increased  2 times (from 0.4 to 1 A @ 200V)
1-Apr-16
Actual problems of microworld physics. Gomel 2007
Silicon. Comparison
For comparison purposes two silicon detectors were irradiated
(detector grade by Micron)
Degradation of signal starts at doses  40 kGy
At higher doses dark current and noise level
increases dramatically (from  10 nA to A).
No clear signal visible
Tested this year Radiation hard silicon - no final results yet
but general behavior similar => high currents after about 70 kGy
1-Apr-16
Actual problems of microworld physics. Gomel 2007
Conclusion
New results - two more diamond samples from E6 irradiated this year
Single crystal CVD diamond sample irradiated
Radiation-hard silicon sample irradiated

Analysis in progress
Further work is planned for CVD diamond and GaAs
Possible new material - SiC
At the moment CVD diamond and GaAs prove to be sufficiently
radiation hard for application in BeamCal
Inconsistent results from different diamond samples
could be a problem
Pumping behavior could be a problem for calorimetry
1-Apr-16
Actual problems of microworld physics. Gomel 2007