Transcript Folie 1

Radiation Tolerant Detectors
for Future HEP Experiments
Results from the
CERN-RD50 Collaboration
Gunnar Lindstroem
University of Hamburg
See also:
Michael Moll
Radiation Tolerant Sensors for Pixel Detectors
- CERN-RD50 project Pixel2005 Bonn September 05
http://www.cern.ch/rd50
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
1
Outline
 Silicon Detectors for Particle Tracking
 Motivation for R&D, the Challenge for Radiation Tolerance
 The RD50 Collaboration
 Radiation Damage, Deterioration of Detector Properties
 Approaches for Solutions, Material and Device Engineering
 Summary and Outlook
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
2
Silicon Detectors: Favorite Choice for Particle Tracking
Proton-proton collider, 2 x 7 TeV
Luminosity: 1034
LHC
properties
Bunch crossing: every 25 nsec, Rate: 40 MHz
event rate: 109/sec (23 interactions per bunch crossing)
Annual operational period: 107 sec
Expected total op. period: 10 years
Experimental requests
Detector properties
Reliable detection of mips
S/N ≈ 10
High event rate
time + position resolution:
high track accuracy
~10 ns and ~10 µm
Complex detector design
Intense radiation field
during 10 years
low voltage operation in
normal ambients
Radiation tolerance up to
1015 hadrons/cm²
Feasibility, e.g.
200 m² for CMS
large scale availability
known technology, low cost
! Silicon Detectors meet all Requirements !
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
3
LHC ATLAS Detector – a Future HEP Experiment
Overall length: 46m, diameter: 22m,
total weight: 7000t, magnetic field: 2T
ATLAS collaboration: 1500 members
principle of a silicon detector:
solid state ionization chamber
micro-strip detector
for particle tracking
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
4
Growing demand for Si-detectors in tracking applications
Covered area in m²
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
5
Main motivations for R&D on
Radiation Tolerant Detectors: Super - LHC
LHC upgrade
RD50
LHC (2007), L =
10 years
500
fb-1
SUPER - LHC (5 years, 2500 fb-1)
1034cm-2s-1
Pixel (?)
f(r=4cm) ~
3·1015cm-2
CERN-RD48
10
2500
fb-1
f(r=4cm) ~ 1.6·1016cm-2
CERN-RD50
• LHC (Replacement of components)
e.g. - LHCb Velo detectors (~2010)
- ATLAS Pixel B-layer (~2012)
Macropixel (?)
5
5
Super-LHC (2015 ?), L = 1035cm-2s-1
5 years
Ministrip (?)
16
total fluence eq
eq [cm-2]
•
1015
5
neutrons eq
pions eq
1014
5
ATLAS SCT - barrel
(microstrip detectors)
ATLAS Pixel
13
10
0
10
other charged
hadrons eq
20
30
40
50
60
[M.Moll, simplified, scaled from ATLAS TDR]
r [cm]
• Linear collider experiments (generic R&D)
Deep understanding of radiation damage will be fruitful for linear collider experiments where
high doses of e, g will play a significant role.
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
6
RD50
The CERN RD50 Collaboration
http://www.cern.ch/rd50
RD50: Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders
Collaboration formed in November 2001
Experiment approved as RD50 by CERN in June 2002
Main objective:
Development of ultra-radiation hard semiconductor detectors for the luminosity
upgrade of the LHC to 1035 cm-2s-1 (“Super-LHC”).
Challenges: - Radiation hardness up to 1016 cm-2 required
- Fast signal collection (Going from 25 ns to 10 ns bunch crossing ?)
- Low mass (reducing multiple scattering close to interaction point)
- Cost effectiveness (big surfaces have to be covered with detectors!)
Presently 251 members from 51 institutes
Belarus (Minsk), Belgium (Louvain), Canada (Montreal), Czech Republic (Prague (3x)), Finland (Helsinki,
Lappeenranta), Germany (Berlin, Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe), Israel (Tel Aviv), Italy
(Bari, Bologna, Florence, Padova, Perugia, Pisa, Trento, Turin), Lithuania (Vilnius), Norway (Oslo (2x)), Poland
(Warsaw(2x)), Romania (Bucharest (2x)), Russia (Moscow), St.Petersburg), Slovenia (Ljubljana), Spain
(Barcelona, Valencia), Switzerland (CERN, PSI), Ukraine (Kiev), United Kingdom (Exeter, Glasgow, Lancaster,
Liverpool, Sheffield, University of Surrey), USA (Fermilab, Purdue University,
Rochester University, SCIPP Santa Cruz, Syracuse University, BNL, University of New Mexico)
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
7
Scientific Organization of RD50
Spokesperson
Mara Bruzzi
Deputy-Spokesperson
Michael Moll
INFN and University of Florence
CERN
Defect / Material
Characterization
Bengt Svensson
Defect
Engineering
Eckhart Fretwurst
New
Materials
Juozas V.Vaitkus
Macroscopic
Effects
Jaakko Härkönen
(Oslo University)
(Hamburg University)
(Vilnius University)
(Helsinki HIP)
•Characterization:
(pre/post irradiation)
SIMS, IR, PL, Hall,
TSC, DLTS, EPR,…
- V2O, O-dimers,…
- high res. CZ, …
- clusters, ..
•Theory:
Defect formation,
defect annealing,
energy states,…..
•DOFZ/Oxygenation
•High resistivity CZ
•Epitaxial Silicon
•Dimerization
•Other impurities
H, N, Ge, …
•Thermal donors
•Pre-irradiation
treatments
• SiC
• CdTe
• other materials
•Test structure
characterization
IV, CV, CCE
•NIEL
•Device modeling
•Operational
conditions
New
Structures
Mahfuzur Rahman
(Glasgow University)
Full Detector
Systems
Gianluigi Casse
(Liverpool University)
•3D detectors
•Thin detectors
•Cost effective
solutions
•LHC-like tests
•Links to HEP
•Links to R&D
of electronics
•Comparison:
pad-mini-full
detectors
CERN contact: Michael Moll
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
8
Radiation Damage in Silicon Sensors
 Two general types of radiation damage in detector materials:
 Bulk (Crystal) damage due to Non Ionizing Energy Loss (NIEL)
- displacement damage, built up of crystal defects –
I. Change of effective doping concentration (higher depletion voltage,
under- depletion)
II. Increase of leakage current (increase of shot noise, thermal runaway)
III. Increase of charge carrier trapping (loss of charge)
 Surface damage due to Ionizing Energy Loss (IEL)
- accumulation of positive in the oxide (SiO2) and the Si/SiO2 interface –
affects: interstrip capacitance (noise factor), breakdown behavior, …
 Impact on detector performance and Charge Collection
(depending on detector type and geometry and readout electronics!)
Signal/noise ratio is the quantity to watch
 Sensors can fail from radiation damage !
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
9
Non Ionizing Energy Loss NIEL: displacement damage
Point defects
+ clusters
Dominated by
clusters
Damage effects generally ~ NIEL, however differences between proton & neutron damage
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
10
Radiation Damage I. – Effective doping concentration
Change of Depletion Voltage Vdep (Neff)
1000
500
10
 600 V
2
type inversion
100
50
10
5
101
1014cm-2
n-type
1
10-1
100
"p-type"
[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]
10
0
10
1
10
2
eq [ 1012 cm-2 ]
10
3
10-1
“Type inversion”: Neff changes from positive to
negative (Space Charge Sign Inversion)
after inversion
before inversion
p+
n+
p+
Gunnar Lindstroem – University of Hamburg
n+
 Neff [1011cm-3]
5000
…. with time (annealing):
10
103
| Neff | [ 1011 cm-3 ]
Udep [V] (d = 300m)
…. with particle fluence:
8
6
„Hamburg model“
NY
NA
4
NC
gC eq
2
NC0
[M.Moll, PhD thesis 1999, Uni Hamburg]
0
1
10
100
1000 10000
annealing time at 60oC [min]
Short term: “Beneficial annealing”
Long term: “Reverse annealing”
- time constant depends on temperature:
~ 500 years (-10°C)
~ 500 days ( 20°C)
~ 21 hours ( 60°C)
- Consequence: Detectors must be cooled
even when the experiment is not running!
Warsaw University 19-Oct-05
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Radiation Damage II. – Leakage current
…. with time (annealing):
Change of Leakage Current (after hadron irradiation)
I / V [A/cm3]
10
10-2
10-3
n-type FZ - 780 cm
n-type FZ - 410 cm
n-type FZ - 130 cm
n-type FZ - 110 cm
n-type CZ - 140 cm
p-type EPI - 380 cm
-5
10
12
10
13
10
14
eq [cm ]
-2
10
10
I
V   eq
Leakage current
per unit volume
and particle fluence
 is constant over several orders of fluence
and independent of impurity concentration in Si
 can be used for fluence measurement
Gunnar Lindstroem – University of Hamburg
5
4
3
3
2
2
.
1
[M.Moll PhD Thesis]
80 min 60C
4
0
15
6
5
1
Damage parameter  (slope in figure)
α

n-type FZ - 7 to 25 Kcm
n-type FZ - 7 Kcm
n-type FZ - 4 Kcm
n-type FZ - 3 Kcm
p-type EPI - 2 and 4 Kcm
10-4
10-6 11
10

6
…. with particle fluence:
(t) [10-17 A/cm]
-1
17
-3
oxygen enriched silicon [O] = 2 10 cm
parameterisation for standard silicon
1
[M.Moll PhD Thesis]
10
100
1000
o
10000
annealing time at 60 C [minutes]
 Leakage current decreasing in time
(depending on temperature)
 Strong temperature dependence:
 Eg

I  exp 

2
k
T
B


Consequence:
Cool detectors during operation!
Example: I(-10°C) ~1/16 I(20°C)
Warsaw University 19-Oct-05
12
Radiation Damage III. – Charge carrier trapping
 Deterioration of Charge Collection Efficiency (CCE) by trapping
Trapping is characterized by an effective trapping time eff for electrons and holes:
where:
Inverse trapping time 1/ [ns-1]
Increase of inverse trapping time (1/) with fluence
0.5
24 GeV/c proton irradiation
0.4
data for electrons
data for holes
0.3
0.2
0.1
[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]
0
0
2.1014 4.1014 6.1014 8.1014
1015
particle fluence - eq [cm-2]
1
 eff e,h
 N defects
….. and change with time (annealing):
Inverse trapping time 1/ [ns-1]


1
Qe,h (t )  Q0 e,h exp 
t
  eff e,h 


0.25
24 GeV/c proton irradiation
eq = 4.5.1014 cm-2
0.2
0.15
data for holes
data for electrons
0.1
[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]
5 101
5 102
5 103
annealing time at 60oC [min]
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
13
Impact on Detector: Decrease of CCE
 Two basic mechanisms reduce collectable charge:
- trapping of electrons and holes  (depending on drift and shaping time !)
- under-depletion
 (depending on detector design and geometry !)
Example: ATLAS microstrip detectors + fast electronics (25ns)
p-in-n : oxygenated versus standard FZ
- beta source
- 20% charge loss after 5x1014 p/cm2 (23 GeV)
Laser (1064nm) measurements
max collected charge (overdepletion)
CCE (arb. units)
Q/Q0 [%]
100
n-in-n versus p-in-n
- same material, ~ same fluence
- over-depletion needed
80
60
collected at depletion voltage
40
oxygenated
standard
20
1.00
0.80
0.60
1
2
3
4
p [1014 cm-2]
0.20
5
p-in-n
0.40
M.Moll [Data: P.Allport et all, NIMA 501 (2003) 146]
0
0
n-in-n
n-in-n (7.1014 23 GeV p/cm2)
p-in-n (6.1014 23 GeV p/cm2)
[M.Moll: Data: P.Allport et al. NIMA 513 (2003) 84]
0
100 200 300 400 500 600
bias [volts]
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
14
Approaches for Radiation Hardening
Scientific strategies:
I. Material engineering
II. Device engineering
III. Change of detector
operational conditions
CERN-RD39
“Cryogenic Tracking Detectors”
„Lazarus Effect“
Defect Engineering of Silicon
Understanding radiation damage
Macroscopic effects and Microscopic defects
Simulation of defect properties & kinetics
Irradiation with different particles & energies
Oxygen rich Silicon
DOFZ, Cz, MCZ, EPI
Oxygen dimer & hydrogen enriched Si
Pre-irradiated Si
Influence of processing technology
New Materials
Silicon Carbide (SiC), Gallium Nitride (GaN)
Diamond: CERN RD42 Collaboration
Amorphous silicon
Device Engineering (New Detector Designs)
p-type silicon detectors (n-in-p)
thin detectors
3D and Semi 3D detectors
Stripixels
Cost effective detectors
Simulation of highly irradiated detectors
Monolithic devices
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
15
Different Sensor mMaterials
Example: is SiC an option?
Property
Eg [eV]
Ebreakdown [V/cm]
e [cm2/Vs]
h [cm2/Vs]
vsat [cm/s]
Z
r
e-h energy [eV]
Density [g/cm3]
Displacem. [eV]
Diamond
5.5
107
1800
1200
2.2·107
6
5.7
13
3.515
43
GaN
3.39
4·106
1000
30
31/7
9.6
8.9
6.15
15
4H SiC
3.26
2.2·106
800
115
2·107
14/6
9.7
7.6-8.4
3.22
25
Si
1.12
3·105
1450
450
0.8·107
14
11.9
3.6
2.33
13-20
Wide bandgap (3.3eV)
lower leakage current
than silicon
Signal:
Diamond 36 e/m
SiC
51 e/m
Si
89 e/m
more charge than diamond
Higher displacement threshold
than silicon
radiation harder than silicon (?)
Result for SiC: very low CCE even for very thin devices
R&D on diamond detectors:
RD42 – Collaboration
http://cern.ch/rd42/
Recent review: P.J.Sellin and J.Vaitkus on behalf of RD50
“New materials for radiation hard semiconductor detectors”, submitted to NIMA
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
16
Monocrystalline Material: Float Zone Silicon (FZ)
 Float Zone process
 Mono-crystalline Ingot
 Using a single Si crystal seed, melt
the vertically oriented rod onto the
seed using RF power and “pull” the
monocrystalline ingot
 Wafer production
 Slicing, lapping, etching, polishing
 Oxygen enrichment (DOFZ)
 Oxidation of wafer at high temperatures
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
17
Czochralski Silicon (Cz) & Epitaxial Silicon (EPI)
Czochralski silicon
• Pull Si-crystal from a Si-melt contained
in a silica crucible while rotating.
• Silica crucible is dissolving oxygen into
the melt  high concentration of O in CZ
• Material used by IC industry (cheap)
• Recent developments (~2 years) made CZ
available in sufficiently high purity (resistivity) to
allow for use as particle detector.
 Epitaxial silicon
•
•
•
•
•
•
Chemical-Vapor Deposition (CVD) of Silicon
CZ silicon substrate used  in-diffusion of oxygen
growth rate about 1m/min
excellent homogeneity of resistivity
up to 150  m thick layers produced (thicker is possible)
price depending on thickness of epi-layer but not
extending ~ 3 x price of FZ wafer
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
18
Oxygen in FZ, Cz and EPI
Epitaxial silicon
5
1018
5
Cz as grown
1017
5
1016
5
0
1017
5
DOFZ 72h/1150oC
DOFZ 48h/1150oC
DOFZ 24h/1150oC
50
100
[G.Lindstroem et al.]
150
depth [m]
200
250
1016
5
• DOFZ: inhomogeneous oxygen distribution
• DOFZ: oxygen content increasing with time
at high temperature
Gunnar Lindstroem – University of Hamburg
5
75 mu
1018
5
CZ substrate
25 mu
5
EPI
layer
O-concentration [1/cm3]
O-concentration [cm-3]
• CZ: high Oi (oxygen) and O2i (oxygen dimer)
concentration (homogeneous)
• CZ: formation of Thermal Donors possible !
50 mu
 Cz and DOFZ silicon
1018
5
1017
5
1016
5
0
SIMS 25 m
SIMS 50 m
SIMS 75 m
simulation 25 m
simulation 50 m
simulation 75m
[G.Lindström et al.,10th European Symposium on
Semiconductor Detectors, 12-16 June 2005]
10 20 30 40 50 60 70 80 90 100
Depth [m]
• EPI: Oi and O2i (?) diffusion from substrate
into epi-layer during production
• EPI: in-homogeneous oxygen distribution
Warsaw University 19-Oct-05
19
Change of Neff: FZ, DOFZ, Cz and MCz Silicon
24 GeV/c proton irradiation
800
• Oxygenated FZ (DOFZ)
• type inversion at ~ 21013 p/cm2
• reduced Neff increase at high fluence
• CZ silicon and MCZ silicon
Vdep [V]
• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
600
10
8
400
6
4
200
Neff [1012 cm-3]
• Standard FZ silicon
12
CZ <100>, TD killed
MCZ <100>, Helsinki
STFZ <111>
DOFZ <111>, 72 h 11500C
2
0
0
2
4
6
8
10
0
proton fluence [1014 cm-2]
 no type inversion in the overall fluence range (verified by TCT measurements)
(verified for CZ silicon by TCT measurements, preliminary result for MCZ silicon)
 donor generation overcompensates acceptor generation in high fluence range
• Common to all materials (after hadron irradiation):
 reverse current increase
 increase of trapping (electrons and holes) within ~ 20%
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
20
Change of Neff: EPI Silicon
 Epitaxial silicon grown by ITME
G.Lindström et al.,10th European Symposium
on Semiconductor Detectors, 12-16 June 2005
Layer thickness: 25, 50, 75 m; resistivity: ~ 50 cm
Oxygen: [O]  91016cm-3; Oxygen dimers (detected via IO2-defect formation)
150
100
5.1013
50 m
50
25 m
0
0
2.1015 4.1015 6.1015 8.1015
eq [cm-2]
1016
0
23 GeV protons
2.1014
Neff(t0) [cm-3]
Neff (t0) [cm-3]
Reactor neutrons
Ta = 80oC
Vfd (t0)[V] normalized to 50 m
1014
105V
(25m)
25 m, 80 oC
50 m, 80 oC
75 m, 80 oC
230V
(50m)
1014
0
0
320V
(75m)
2.1015
4.1015 6.1015
eq [cm-2]
8.1015
1016
 No type inversion in the full range up to ~ 1016 p/cm2 and ~ 1016 n/cm2
(type inversion only observed during long term annealing)
Proposed explanation:
introduction of shallow donors bigger than generation of deep acceptors
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
21
Epitaxial Silicon - Annealing
50 m thick silicon detectors:
- Epitaxial silicon (50 cm on CZ substrate, ITME & CiS)
- Thin FZ silicon (4Kcm, MPI Munich, wafer bonding technique)
Vdep [V]
200
Ta=80oC
ta=8 min
150
100
EPI (ITME), 50m
FZ (MPI), 50m
50
0
0
•
•
1.4
1.2
1.0
0.8
0.6
0.4
0.2
150
Ta=80oC
EPI (ITME), 9.6.1014 p/cm2
100
Vfd [V]
250
|Neff| [1014 cm-3]
•
50
FZ (MPI), 1.7.1015 p/cm2
[E.Fretwurst et al., Hamburg]
20
40
60
80 100
proton fluence [1014 cm-2]
0 0
10
101
102
103
104
105
annealing time [min]
Thin FZ silicon: Type inverted, increase of depletion voltage with time
Epitaxial silicon: No type inversion, decrease of depletion voltage with time
 No need for low temperature during maintenance of SLHC detectors!
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
22
Damage Projection – SLHC
- 50 m EPI silicon: a solution for pixels ?

G.Lindström et al.,10th European Symposium on Semiconductor
Detectors, 12-16 June 2005 (Damage projection: M.Moll)
Radiation level (4cm): eq(year) = 3.5  1015 cm-2
SLHC-scenario: 1 year = 100 days beam (-7C)
30 days maintenance (20C)
235 days no beam (-7C or 20C)
600
Vfd [V]
S-LHC scenario
500
50 m cold
50 m warm
400
25 m cold
Detector with
cooling when not
operated
Detector without
cooling when not
operated
25 m warm
300
200
100
0
0
365
Gunnar Lindstroem – University of Hamburg
730
1095
time [days]
1460
1825
Warsaw University 19-Oct-05
23
Signal from irradiated EPI
 Epitaxial silicon: CCE measured with beta particles (90Sr)
25ns shaping time
proton and neutron irradiations of 50 m and 75 m epi layers
CCE (75 m)
= 2x1015 n/cm-2,
4500 electrons
CCE (50 m)
eq= 8x1015 n/cm-2,
2300 electrons
CCE (50 m):  1x1016cm-2 (24GeV/c protons)
2400 electrons
[G.Kramberger et al.,RESMDD - October 2004]
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
24
Microscopic defects
Damage to the silicon crystal: Displacement of lattice atoms
SiS
particle
EK>25 eV
V
I
EK > 5 keV
“point defects”, mobile in silicon,
can react with impurities (O,C,..)
point defects and defect clusters
Distribution of vacancies
created by a 50 keV Si-ion
in silicon (typical recoil
energy for 1 MeV neutrons):
I
V
Vacancy
+
Interstitial
I
V
Schematic
[Van Lint 1980]
Simulation
[M.Huhtinen 2001]
Defects can be electrically active (levels in the band gap)
- capture and release electrons and holes from conduction and valence band
 can be charged - can be generation/recombination centers - can be trapping centers
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
25
Characterization of microscopic defects
- gamma and proton irradiated silicon detectors -
 2003: Major breakthrough on g-irradiated samples
For the first time macroscopic changes of the depletion voltage and leakage current
can be explained by electrical properties of measured defects !
[APL, 82, 2169, March 2003]
 2004: Big step in understanding the improved radiation tolerance of
oxygen enriched and epitaxial silicon after proton irradiation
[I.Pintilie, RESMDD, Oct.2004]
Levels responsible for depletion voltage
changes after proton irradiation:
Almost independent of oxygen content:
• Donor removal
•“Cluster damage”  negative charge
Influenced by initial oxygen content:
• I–defect: deep acceptor level at EC-0.54eV
(good candidate for the V2O defect)
 negative charge
Influenced by initial oxygen dimer content (?):
• BD-defect: bistable shallow thermal donor
(formed via oxygen dimers O2i)
 positive charge
See further: I. Pintilie et al, NIM A 556 (2005) 56 + NIM A, in press
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
26
Device Engineering: p-in-n versus n-in-n
n-type silicon after type inversion:
p+on-n
n+on-n
p-on-n silicon, under-depleted:
n-on-n silicon, under-depleted:
• Charge spread – degraded resolution
•Limited loss in CCE
• Charge loss – reduced CCE
•Less degradation with under-depletion
•Collect electrons (fast)
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
27
n-in-p microstrip detectors
n-in-p: - no type inversion, high electric field stays on segmented side
- collection of electrons
Miniature n-in-p microstrip detectors (280mm)
Detectors read-out with LHC speed (40MHz) chip (SCT128A)
Material: standard p-type and oxygenated (DOFZ) p-type
Irradiation:
25
CCE (103 electrons)
•
•
•
•
24 GeV/c proton irradiation
20
15
G. Casse et al.,
NIMA 535 (2004) 362
10
At the highest fluence
Q~6500e at Vbias=900V
5
0
0
1015
cm-2
CCE ~ 60% after 3
p
at 900V( standard p-type)
[Data: G.Casse et al., Liverpool, February 2004]
.
15
2 10
.
15
4 10
.
15
6 10
fluence [cm-2]
.
15
8 10
16
10
eq = 4.6 1015 cm-2
CCE ~ 30% after 7.5 1015 p cm-2
900V (oxygenated p-type)
Adopted from M. Moll,CERN, Bonn, Sep-05
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
28
Does thickness pay?
 Low fluence eq ≤ 1014 cm-2:
negligible trapping of charge carriers, signal for mip
(minimum ionizing particle) proportinal to detector thickness: S ~ d
 Trapping material independent, strong increase with fluence (see above)
 Large fluence eq ≥ 5·1015 cm-2:
signal height dominated by charge trapping, collection distance deff ≤ 100 m
signal for mip: S ~ deff
T. Lari, Milano
10 years at LHC
Signal vs. Φeq for 600V
Signal vs. bias for Φeq = 1016 cm-2
Equiv. Fluence in 1015 cm-2
5 y S-LHC
! After Φeq = 1016 cm-2 S(mip) = about 2000-2500 e regardless of material and thickness !
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
29
Summary
 At fluences up to 1015cm-2 (Outer layers of a SLHC detector) the change of depletion
voltage and the large area to be covered by detectors is the major problem.
 CZ silicon detectors could be a cost-effective radiation hard solution
(no type inversion, use p-in-n technology)
 p-type silicon microstrip detectors show very encouraging results:
CCE  6500 e; eq= 41015 cm-2, 300m, collection of electrons,
no reverse annealing observed in CCE measurement!
 At the fluence of 1016cm-2 (Innermost layer of a SLHC detector) the active thickness
of any silicon material is significantly reduced due to trapping.
The promising new options are:
⁃Thin/EPI detectors : drawback: radiation hard electronics for low signals needed
e.g. 2300e at eq 8x1015cm-2, 50m EPI,
…. thicker layers will be tested in 2005/2006
⁃ 3D detectors : drawback: technology has to be optimized
….. steady progress within RD50
 New Materials like SiC and GaN (not shown) have been characterized .
⁃ CCE tests show that these materials are not radiation harder than silicon
Further information: http://cern.ch/rd50/
Gunnar Lindstroem – University of Hamburg
Adopted from M. Moll,CERN, Bonn, Sep-05
Warsaw University 19-Oct-05
30
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
31
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
32
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
33
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
34
Gunnar Lindstroem – University of Hamburg
Warsaw University 19-Oct-05
35