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Wir schaffen Wissen – heute für morgen
G. Casse, University of Liverpool and M. Moll, CERN (RD50)
A. Dierlamm, KIT; D. Eckstein, DESY;
A. Junkes, University of Hamburg; T. Rohe, PSI (CMS)
D. Muenstermann, University of Geneva (ATLAS)
Pion induced change of material parameters in Silicon
PSI, 8. Juli 2017
Introduction
All LHC experiments use silicon
detectors for tracking. The size of
the trackers exceeds previous
projects by an order of magnitude
CDF (Tevatron, largest pre LHC
silicon tracker):
• Barrel only: layer00 +
SVX-II (5 layers) +
ISL (1.5 layers), total < 10m2
ATLAS:
• Pixel: 3 barrel layers, 2×3 disks,
total ~1.7m2
• Strip: 4 barrel layers, 2×9 disks, total ~40m2
CMS:
• Pixel: 3 barrel layers, 2×2 disks, total ~1.1m2
• Strip: 4 inner + 6 outer barrel layers, 2×3 inner + 2×9 outer disks, total ~200m2
PSI, 08.07.2017
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Motivation for pion irradiation
LHC (2009)
• Planned for ~500/fb within 10years
• F(r=4cm) ~ 3×1015 Neqcm-2
– Long and intensive R&D phase
for all LHC experiments
– Maximum fluence specified so
far is
– Radiation field is dominated
by pions for
– r < 20 cm (ATLAS)
– r < 60 cm (CMS)
Pions
Fluences in CMS (500/fb)
All
1.00E+14
– Proton and neutron irradiation
facilities available
1.00E+13
– pE1 is the only pion beam in the
world suitable for irradiation
HL-LHC (2022 ?)
• Planned for ~2500/fb within ~5years
1.00E+12
• F(r=4cm) ~ 1×1016 Neqcm-2
• New detector concept needed (scope of RD50)
0
• New developments in the recent years
– Other materials: Epitaxial, mCz, p-type
sensors, diamond
– Other device types: optimisation of device thickness,
“n-in-p”, 3D, ...
PSI, 08.07.2017
Neutrons
1.00E+15
F [cm^-2]
– 0.6-1×1015 Neqcm-2 (present
experiments)
– 1.5-5×1015 Neqcm-2
phase I upgrades (CMS) and
IBL (ATLAS)
1.00E+16
20
40
60
80
100
120
r [cm]
Seite 3
[A. Affolder at 13th RD50 workshop]
Charge collection
•
•
•
The signal height is the “figure” of merit for the operation of pixel detectors (threshold presetly installed
ROCs ~3000 electr., next generation ~1500 electrons)
First results on very highly irradiated indicate that such levels of radiation hardness might be reachable
Pion data cover < 5% of the total range
PSI, 08.07.2017
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Radiation damage in Silicon
•
•
Surface damage
– Mainly by ionisation in the covering layers
– Built up of positive surface charge
– Danger of breakdown close to n-side electrodes
 careful choice of n-side isolation
Crystal damage by displacement
• Leakage current increase proportional to F
F ~ ?? (depending much on T)
– power load (cooling), power
– Preamplifier (if DC coupled)
• Change of internal electric field
F > a few 1014 Neq/cm2 (L > ~100/fb)
– Bias voltage has to be
– Charge is focused  spatial resolution degrades
– Complicated annealing behaviour
• Reduced signal (trapping)
F > ~1015 Neq/cm2 (L > ~250/fb):
– Possibly charge amplification > 1kV  RD50
– High voltage is presently limited by connectors,
cables and power supplies
PSI, 08.07.2017
10 MeV p
24 GeV p
1 MeV n
[Mika Huhtinen NIMA 491(2002) 194]
generation
 leakage current
Levels close to midgap
most effective
Electrons
Holes
charged defects
 Neff , Vdep
Donor +
e.g. donors in upper and
acceptors in lower half of Acceptor band gap
Trapping (e and h)  CCE
shallow defects do not
contribute at room
temperature due to fast
detrapping
Ec
Ev
Ec
Ev
Ec
Ev
Seite 5
NIEL
104
103
neutrons
2
2
101
1
0.8
0.6
10
D(E) / (95 MeV mb)
4
100
10-1
10-2
protons
protons
pions
0.4
100
101
102
103
pions
104
neutrons
electrons
10-3
10-4
10-5 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
10 10 10 10 10 10 10 10 10 10 100 101 102 103 104
particle energy [MeV]
How to compare different types of radiation?
• Assume the damaging parameters scale with deposited
energy, not used for the (reversible) process of ionization,
the so called NIEL
PSI, 08.07.2017
Use 1MeV neutrons as standard (most present in the
outer tracker regions)
• Calculate “hardness factor” for each type of irradiation
•
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Dependence on particle type
Leakage current
• calculate damage constant a
• Increase of leakage current scales
with the hardness factors calculated from NIEL
hypothesis
• Leakage current is nowadays used to measure the
hardness factors
→ Other properties (internal electric field, trapping)
need a more detailed understanding
<5.3 MeV> neutrons
6
1.47

a80/60 [10-17A/cm]
8
1.14
4
192 MeV pions
0.62
2
23 GeV protons
1011
1012
1013
F [cm-2]
1014
VOi-/0 + CiCs(A)-/0 (E2)
VV-/0 + ? (E4)
VV--/- (E3)
27 MeV protons
23 GeV protons
192 MeV pions
5.3 MeV neutrons
50
PSI, 08.07.2017
27 MeV protons
2.22
DLTS-signa (arb. units)
DLTS (deep level transient spectroscopy)
• Measure capacitance of a diode as
function of the temperature
• Data scaled with a
• Level E4 is correlated to leakage
current (and damage clusters)
• Concentration scales with a
• Other defect levels do not scale
10
100
CiOi+/0 (H1)
150
200
Temperature [K]
250
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Built up of space charge (NIEL violation)
•
•
•
•
•
•
n-type epitaxial material (Oxygen rich)
Shallow donor (positive space charge) at E(30K) produced with
protons much more efficiently than with neutrons
This donor overcompensates the deep acceptors responsible for
“type inversion” in proton irradiated samples
Macroscopic behaviour differs
Also the case for different energies of protons
What about pions?
PSI, 08.07.2017
[A. Junkes, PhD thesis Uni Hamburg, 2011]
[A. Junkes, priv. comm 2013]
TSC (Thermally stimulated current):
Seite 8
Summary of known defects
Some identified defects
Phosphorus: shallow dopant
(positive charge)
positive charge (higher
positive charge (higher
introduction after proton than after
neutron irradiation, oxygen
dependent)
introduction after proton irradiation
than after neutron irradiation)
Leakage current
E4/E5: V3 (?)
leakage current
& neg. charge
Reverse
annealing
current after g irrad,
V2O (?)
(negative charge)
Boron: shallow dopant
(negative charge)
•
•
•
Trapping: Indications that E205a and H152K are important (further work needed)
Converging on consistent set of defects observed after p, p, n, g and e irradiation.
Defect introduction rates are depending on particle type and particle energy and (for some) on material!
PSI, 08.07.2017
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Simulation to predict device performance
Field in irradiated sensors becomes very complex
[Chiochia et al., IEEE Trans. Nucl. Sci. Vol. 52(4), 2005, p. 2294.]
Field in irradiated sensors becomes very complex
In order to be able to make predictions
using device simulation programs a strong
simplification to “effective” levels has to be
made
PSI, 08.07.2017
Measured defects → TCAD input
Seite 10
Simulation of trapping
TCAD simulations can reproduce TCT data, leakage current, depletion voltage and (partly) charge
trapping of irradiated sensors with one parameter set!
• Example: Input parameter set tuned to match TCT measurements (R.Eber, Uni.Karlsruhe)
[R.Eber, RD50 Workshop, June 2013]
•
Same set of data used to simulate CCE measurements taken in a CMS test beam
•
•
•
[T.Peltola, RD50 Workshop, June 2013]
PSI, 08.07.2017
•
Simulation predicts leakage current
correctly (not shown)
Simulation predicts CCE for proton and
neutron irradiated samples of different
thickness within 20%
Simulations start to get predictive
power; still the phase space of input
parameters is huge and input (defect)
parameters have to be tuned and adopted
to measured defect parameters.
Up to now, no data for pions
Seite 11
Previous irradiations
In the beginnings
• Test of n-type silicon with different oxygen content
• Before 2000 also: GaAs, MSGCs, .....
• Aim is to offer an irradiation time slot every 3 years
Last irradiations 2007 and 2010
• Irradiation was mainly used for charge collection measurements in strip and pixel detectors
– “New” detector types (e.g. single sided n-in-p) seem good candidates for upgrade of LHC detectors
[Affolder et. al presented at the TIPP09]
– Generate “mixed irradiations” (irradiate samples with neutrons afterwards to have the realistic particle
composition as later in the Experiment) [NIM A 612 (2010) 288-295]
– Pixels for signal height measurements [NIM A 612 (2010) 493-496], [NIM A 650 (2011) 136-139]
• Trapping and annealing studies [2011 JINST 6 P11008]
• Modelling of Electric fields (publication not yet released)
PSI, 08.07.2017
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Plans for 2014
Plan/Question
• How can pion damage be related to protons/neutron of different energies?
• Main activities
– Diodes (different materials mCz, epi, …)
– defect determination with spectroscopic methods (DLTS, TSC)
– Modelling of internal electric field (TCT)
– Segmented detectors (strips and pixels)
– Test with “real” particles (b-source tests, test beams)
Required beam time
• Assume that about 20% of the final fluence is necessary for meaningful extrapolation
• Intensity ~2×109 p/s focused on ~1cm2 1015Neq/cm2/week ~ 2× 1015Neq/cm2 in 2 weeks
• About 20 samples can be mounted in the “focus”
• Another ~40 in front and behind the focus for smaller fluences
Irradiation procedure
• Announce irradiation at web page of the CERN irradiation service
• Collect requests (normally overbooked)
• Select proposals according to scientific quality (with help of experts from RD50)
• So far many (oral) requests for epi-Silicon, mCz n- and p-type silicon and diamond
PSI, 08.07.2017
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Required resources
•
•
•
•
•
•
pE1-area has to be arranged with the shielding (redesigned “Gabathuler-hut”)
– no steering magnet in the area
– beam dump has to be provided (to prevent activation of the concrete blocks)
Equipment presently in WAKA:
– Ionisation chamber for on-line dosimetry
– XYZ-stage (provided by CERN)
– Wire chambers for beam tuning
Spectrometer for off-line dosimetry (will be provided by CERN)
– In the beginning help of the Hallendienst for calibration welcomed
Beam line support will be provided by T. Rohe (and occasionally by K. Deiters and D. Reggiani)
Irradiation will be run by
– Maurice Glaser and Federico Ravotti (CERN)
– PhD students for participating institutes
All visiting scientists are sufficiently supported by their home institutes/RD50
PSI, 08.07.2017
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Conclusions
• Joined request by all key players in the silicon tracker community (ATLAS/CMS/RD50)
• Study fundamental properties of silicon
• Defect formation in Silicon
• Description of pion damage by simulation and with other particla
• Important for the R&D strategy of LHC experiments
• PE1 is the only place in the world providing a sufficient pion flux
• Requested beam time (1 month every 3 years) and resources are very modest
PSI, 8. Juli 2017
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