First international Conference on Radiation
and Dosimetry in Various Fields of Research,
April 25-27, 2012 Niš, Serbia
Effects of Radiation on
Particle Detector Performance
Michael Moll
CERN, Geneva, Switzerland
OUTLINE:
• Particle Detectors: LHC and LHC Detectors
• Radiation Levels & Radiation Damage
• Solid State Detector R&D for Particle Tracking Detectors
• Radiation Tolerant Solid State Detectors
• Conclusions and Outlook
LHC - Large Hadron Collider
• Installation in existing
LEP tunnel (27 Km)
•  4000 MCHF
(machine+experiments)
p
p
• 1232 dipoles B=8.3T
• pp s = 14 TeV
Ldesign = 1034 cm-2 s-1
• Heavy ions
(e.g. Pb-Pb at
s ~ 1000 TeV)
• LHC experiments located at 4 interaction points
• First beam: Sept.2008
• 2012: 2 x 4 TeV
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -2-
LHC Experiments
ATLAS
LHC-B
+ LHCf
CMS
ALICE
+
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -3-
LHC Experiments
ATLAS
LHC-B
+ LHCf
CMS
ALICE
+
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -4-
LHC example: CMS inner tracker
• CMS
• Inner Tracker
Outer Barrel
Inner Barrel
(TOB)
Inner Disks (TIB)
2.4 m
(TID)
End Cap
(TEC)
Total weight
12500 t
Diameter
15m
Length
21.6m
Magnetic field
4T
• CMS – “Currently the Most Silicon”







Pixel
• Pixel Detector
Micro Strip:
~ 214 m2 of silicon strip sensors, 11.4 million strips
Pixel:
Inner 3 layers: silicon pixels (~ 1m2)
66 million pixels (100x150mm)
Precision: σ(rφ) ~ σ(z) ~ 15mm
Most challenging operating environments (LHC)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -5-
Micro-strip Silicon Detectors
Highly segmented silicon detectors have been used in
Particle Physics experiments for nearly 30 years. They are
favourite choice for Tracker and Vertex detectors
(high resolution, speed, low mass, relatively low cost)
Pitch ~ 50mm
p+ in nMain application: detect the passage of
ionizing radiation with high spatial
resolution and good efficiency.
Segmentation → position
Reference: P.Allport, Sept.2010
Resolution ~ 5mm
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -6-
Signal degradation for LHC Silicon Sensors
Pixel sensors:
max. cumulated fluence for
Note: Measured partly
under different conditions!
Lines to guide the eye
(no modeling)!
LHC
signal [electrons]
25000
FZ Silicon
Strip and Pixel Sensors
20000
15000
10000
p-in-n-FZ (500V)
strip sensors
n-in-n (FZ), 285mm, 600V, 23 GeV p
p-in-n (FZ), 300mm, 500V, 23GeV p
p-in-n (FZ), 300mm, 500V, neutrons
n-in-n FZ (600V)
pixel sensors
References:
[1] p/n-FZ, 300mm, (-30oC, 25ns), strip [Casse 2008]
[2] n/n-FZ, 285mm, (-10oC, 40ns), pixel [Rohe et al. 2005]
5000
1013
5 1014
5 1015
eq [cm-2]
Strip sensors:
max. cumulated fluence for LHC
5 1016
M.Moll - 08/2008
Situation in 2005
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -7-
Signal degradation for LHC Silicon Sensors
Pixel sensors:
max. cumulated fluence for
LHC and
LHC upgrade
signal [electrons]
25000
FZ Silicon
Strip and Pixel Sensors
20000
15000
10000
Note: Measured partly
under different conditions!
Lines to guide the eye
(no modeling)!
p-in-n-FZ (500V)
strip sensors
n-in-n (FZ), 285mm, 600V, 23 GeV p
p-in-n (FZ), 300mm, 500V, 23GeV p
p-in-n (FZ), 300mm, 500V, neutrons
n-in-n FZ (600V)
pixel sensors
References:
[1] p/n-FZ, 300mm, (-30oC, 25ns), strip [Casse 2008]
[2] n/n-FZ, 285mm, (-10oC, 40ns), pixel [Rohe et al. 2005]
5000
1013
5 1014
5 1015
eq [cm-2]
5 1016
Strip sensors:
max. cumulated fluence for LHC and LHC upgrade
M.Moll - 08/2008
LHC upgrade will need more radiation
tolerant tracking detector concepts!
Boundary conditions & other challenges:
Granularity, Powering, Cooling, Connectivity,
Triggering, Low mass, Low cost!
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -8-
LHC - Upgrade
• LHC luminosity (Phase II) upgrade (L = 5x1034 cm-2s-1)
 planned for 2022; aiming to cumulate 3000 fb-1
Dominated by
pion damage
Dominated by
neutron damage
• Radiation hardness requirements (including safety factor of 2)
• 2 × 1016 neq/cm2 for the innermost pixel layers (Dose: 10 MGy)
• 7 × 1014 neq/cm2 for the innermost strip layers (Dose: 300 KGy)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -9-
Detector = “reverse biased p-i-n diode”
Positive space charge, Neff =[P]
(ionized Phosphorus atoms)
Poisson’s equation
q
d2
 2   x   0  N eff
dx
0
depleted
zone
neutral bulk
(no electric field)
• Depleted zone growth with
increasing voltage ( w  VB )
+VB<Vdep
Electrical
charge density
+VB>Vdep
particle
(mip)
Electrical
field strength
• Full charge collection only for
fully depleted detector (VB>Vdep)
Electron
potential energy
detector thickness d
depletion voltage Vdep
Vdep 
q0
0
 N eff  d 2
effective space charge density Neff
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -10-
Macroscopic Effects – I. Depletion Voltage
1000
500
102
 600 V
type inversion
100
50
101
1014cm-2
1
10-1
10
"p-type"
n-type
[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]
10
0
10
1
10
2
eq [ 10 cm ]
12
10
3
0
10
 Neff [1011cm-3]
5000
10
5
…. with time (annealing):
103
| Neff | [ 1011 cm-3 ]
Udep [V] (d = 300mm)
• Change of Depletion Voltage Vdep (Neff)
10-1
-2
• “Type inversion”: Neff changes from positive to
negative (Space Charge Sign Inversion)
before inversion
p+
n+
p+
n+
after inversion
8
6
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!
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -11-
Radiation Damage – II. Leakage Current
• Change of Leakage Current (after hadron irradiation)
I / V [A/cm3]
10-1
10-2
10-3
10-5
80 min 60C
1012
1013
1014
eq [cm-2]
1015
[M.Moll PhD Thesis]
Damage parameter  (slope in figure)
I
α
V   eq

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
10-4
10-6 11
10

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
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

Strong temperature dependence
 E

I  exp  g ,eff

2
k
T
B


Consequence:
Cool detectors during operation!
Example: I(-10°C) ~1/16 I(20°C)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -12-
Radiation Damage – III. CCE (Trapping)
• Deterioration of Charge Collection Efficiency (CCE) by trapping
Trapping is characterized by an effective trapping time eff for electrons and holes:
Inverse trapping time 1/ [ns-1]


1

Qe ,h (t )  Q0 e ,h exp 
t
 

 eff e ,h 
1
where
 eff e,h
0.5
24 GeV/c proton irradiation
0.4
data for electrons
data for holes
 N defects
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]
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -13-
Radiation Damage in LHC detectors
• After about 5 fb-1 integrated luminosity first radiation damage effects are observed
 Remember: The aim is to build detectors resisting 3000 fb-1
• Examples (3/2012 - Preliminary Data!):
Change of Depletion Voltage
LHCb Velo (84 sensors, mainly n-in-n)
[Adam Webber, Uni Manchester, 2nd Inter-Experiment Workshop
on Radiation Damage in Silicon Detectors, CERN, 2.3.2012]
Increase of Leakage Current
ATLAS Pixel (Layer 0, 56 modules )
[Taka Kondo, KEK, 2nd Inter-Experiment Workshop on Radiation
Damage in Silicon Detectors, CERN, 2.3.2012]
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -14-
Approaches to develop
radiation harder solid state tracking detectors
• Defect Engineering of Silicon
Deliberate incorporation of impurities or defects into the
silicon bulk to improve radiation tolerance of detectors
Scientific strategies:
I.
Material engineering
II. Device engineering
III. Change of detector
operational conditions
CERN-RD39
“Cryogenic Tracking Detectors”
operation at 100-200K
to reduce charge loss
•
•
 Needs: Profound understanding of radiation damage
• microscopic defects, macroscopic parameters
• dependence on particle type and energy
• defect formation kinetics and annealing
 Examples:
• 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, Gallium Arsenide
Device Engineering (New Detector Designs)
 p-type silicon detectors (n-in-p)
 thin detectors, epitaxial detectors
 3D detectors and Semi 3D detectors, Stripixels
 Cost effective detectors
 Monolithic devices
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -15-
Silicon Growth Processes
• Floating Zone Silicon (FZ)
Poly silicon
 Czochralski Silicon (CZ)
 The growth method
used by the IC industry.
 Difficult to produce
very high resistivity
 [Oi ] ~ 5  1017 cm-3
RF Heating coil
Single crystal silicon
Czochralski Growth
Float Zone Growth
 Basically all silicon tracking detectors
made out of FZ silicon [Oi ]< 5  1016 cm-3
 Some pixel sensors: Diffusion Oxygenated
FZ (DOFZ)silicon [Oi ]~ 1-2  1017 cm-3
 Epitaxial Silicon (EPI)
 Chemical-Vapor Deposition (CVD) of Si
 up to 150 mm thick layers produced
 growth rate about 1mm/min
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -16-
Standard FZ, DOFZ, MCz and Cz Silicon
800
• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
Vdep (300mm) [V]
 Standard FZ silicon
FZ
12
<111>
10
600
8
400
6
4
200
|Neff| [1012 cm-3]
24 GeV/c proton irradiation
2
0
0
2
4
6
8
10
0
proton fluence [1014 cm-2]
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -17-
Standard FZ, DOFZ, MCz and Cz Silicon
800
• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
 Oxygenated
FZ (DOFZ)
• type inversion at ~ 21013 p/cm2
• reduced Neff increase at high fluence
12
FZ
<111>
DOFZ <111> (72 h 11500C)
10
600
8
400
6
4
200
|Neff| [1012 cm-3]
 Standard FZ silicon
Vdep (300mm) [V]
24 GeV/c proton irradiation
2
0
0
2
4
6
8
10
0
proton fluence [1014 cm-2]
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -18-
Standard FZ, DOFZ, MCz and Cz Silicon
800
• type inversion at ~ 21013 p/cm2
• strong Neff increase at high fluence
 Oxygenated
FZ (DOFZ)
• type inversion at ~ 21013 p/cm2
• reduced Neff increase at high fluence
 CZ silicon and MCZ silicon
 “no type inversion“ in the overall fluence range
600
12
FZ
<111>
DOFZ <111> (72 h 11500C)
MCZ <100>
CZ <100> (TD killed)
10
8
400
6
4
200
|Neff| [1012 cm-3]
 Standard FZ silicon
Vdep (300mm) [V]
24 GeV/c proton irradiation
2
0
0
2
4
6
8
10
0
proton fluence [1014 cm-2]
(for experts: there is no “real” type inversion, a more clear understanding of the observed effects is obtained by
investigating directly the internal electric field; look for: TCT, MCZ, double junction)
 Common to all materials (after hadron irradiation, not after  irradiation):
 reverse current increase
 increase of trapping (electrons and holes) within ~ 20%
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -19-
Proton vs. Neutron irradiation of oxygen rich silicon
• Epitaxial silicon
(EPI-DO, 72mm, 170cm, diodes)
irradiated with 23 GeV protons or reactor neutrons
500
[Data: I.Pintilie et al., NIMA 611 (2009) 52]
[Data: I.Pintilie et al., NIMA 611 (2009) 52]
100
Particle:
Particle:
300
Neff [1012 cm-3]
Vdep (300mm) [V]
400
23 GeV protons
reactor neutrons
200
100
50
positive space charge
0
negative space charge
-50
[M.Moll]
0
0
20
40
60
80 100
1 MeV neutron equivalent fluence eq [1014 cm-2]
depletion voltage
23 GeV protons
reactor neutrons
Vdep 
q0
0
[M.Moll]
0
20
40
60
80 100
1 MeV neutron equivalent fluence eq [1014 cm-2]
 N eff  d
2
absolute effective
space charge density
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -20-
Device engineering
p-in-n versus n-in-p detectors
n-type silicon after high fluences:
(type inverted)
p+on-n
p-type silicon after high fluences:
(still p-type)
n+on-p
p-on-n silicon, under-depleted:
n-on-p silicon, under-depleted:
• Charge spread – degraded resolution
•Limited loss in CCE
• Charge loss – reduced CCE
•Less degradation with under-depletion
•Collect electrons (3 x faster than holes)
Comments:
- Instead of n-on-p also n-on-n devices could be used
- Reality is much more complex: Usually double junctions form leading to fields at front and back!
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -21-
Electric Field in irradiated sensors
• Edge – TCT (Transient Charge Technique)




Technique pioneered by Gregor Kramberger, Ljubljana [IEEE TNS, 57, AUGUST 2010,2294-2302]
Illumination of sensor from the side with pulsed IR laser
Scan across detector thickness and measure charge and induced current as function of depth
Reconstruct electric field
Example: n-in-p sensor after 1016 p/cm2
To analog, time resolved, readout
Focusing optics
Si Strip Detector
IR Laser
Cooling plate
Z positioning
(detector)
XY positioning (laser)
• Heavily irradiated detectors
Collected Charge
[N.Pacifico, CERN, 2012]
Depth in sensor [mm]
 Even at low voltage, charge collected from all depth
 High fields at front (strips) and also back side (Double junctions)
 Large fields observed which lead to charge multiplication (avalanche) and thus increased signal (increased noise)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -22-
FZ n-in-p microstrip detectors (n, p, p - irrad)
• n-in-p microstrip p-type FZ detectors (Micron, 280 or 300mm thick, 80mm pitch, 18mm implant )
• Detectors read-out with 40MHz (SCT 128A)
Signal(103 electrons)
[A.Affolder, Liverpool, NIMA 623, 2010, 177–179]
800V
500V
Fluence(1014 neq/cm2)
 CCE: ~7300e (~30%)
after ~ 11016cm-2 800V
 n-in-p sensors are strongly considered
for ATLAS upgrade (previously p-in-n used)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -23-
FZ n-in-p microstrip detectors (n, p, p  irrad)
• n-in-p microstrip p-type FZ detectors (Micron, 280 or 300mm thick, 80mm pitch, 18mm implant )
• Detectors read-out with 40MHz (SCT 128A)
time [days at 20oC]
CCE (103 electrons)
Signal(103 electrons)
[A.Affolder, Liverpool, NIMA 623, 2010, 177–179]
Fluence(1014 neq/cm2)
 CCE: ~7300e (~30%)
after ~ 11016cm-2 800V
20
18
16
14
12
10
8
6
4
2
0
0
500
1000
1500
2000
2500
6.8 x 1014cm-2 (proton - 800V)
1.6 x 1015cm-2 (neutron - 600V)
2.2 x 1015cm-2 (proton - 500 V)
4.7 x 1015cm-2 (proton - 700 V)
[Data: G.Casse et al., NIMA 568 (2006) 46 and RD50 Workshops]
M.Moll
0
100
200
300
400
o
time at 80 C[min]
500
 no reverse annealing in CCE measurements
for neutron and proton irradiated detectors
 n-in-p sensors are strongly considered
for ATLAS upgrade (previously p-in-n used)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -24-
Good performance of planar sensors at high fluence
• Why do planar silicon sensors with n-strip readout give such high signals after
high levels (>1015 cm-2 p/cm2) of irradiation?
Collected Charge [103 electrons]
 Extrapolation of charge trapping parameters obtained at
lower fluences would predict much lower signal!
 Explanation: ‘Charge multiplication effects’ as even CCE > 1 was observed
n-in-p-Fz (1700V)
25
1700V
20
n-in-p-Fz (800V)
15
800V
10
p-in-n-FZ (500V)
1014
5 1015
eq [cm-2]
n-in-p (FZ), 300mm, 500V, 23GeV p [1]
n-in-p (FZ), 300mm, 500V, neutrons [1,2]
n-in-p (FZ), 300mm, 500V, 26MeV p [1]
n-in-p (FZ), 300mm, 800V, 23GeV p [1]
n-in-p (FZ), 300mm, 800V, neutrons [1,2]
n-in-p (FZ), 300mm, 800V, 26MeV p [1]
n-in-p (FZ), 300mm, 1700V, neutrons [2]
p-in-n (FZ), 300mm, 500V, 23GeV p [1]
p-in-n (FZ), 300mm, 500V, neutrons [1]
References:
500V
5
FZ Silicon Strip Sensors
n-in-p-Fz (500V)
5 1016
M.Moll - 09/2009
[1] G.Casse, VERTEX 2008
(p/n-FZ, 300 mm, (-30 oC, 25ns)
[2] I.Mandic et al., NIMA 603 (2009) 263
(p-FZ, 300 mm, -20 oC to -40oC, 25ns)
 Which voltage can be applied?
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -25-
Silicon materials for Tracking Sensors
Collected Charge [103 electrons]
• Signal comparison for p-type silicon sensors
n-in-p-Fz (1700V)
25
20
Note: Measured partly
under different conditions!
Lines to guide the eye
(no modeling)!
FZ Silicon Strip Sensors
n-in-p (FZ), 300mm, 500V, 23GeV p [1]
n-in-p (FZ), 300mm, 500V, neutrons [1,2]
n-in-p (FZ), 300mm, 500V, 26MeV p [1]
n-in-p (FZ), 300mm, 800V, 23GeV p [1]
n-in-p (FZ), 300mm, 800V, neutrons [1,2]
n-in-p (FZ), 300mm, 800V, 26MeV p [1]
n-in-p (FZ), 300mm, 1700V, neutrons [2]
p-in-n (FZ), 300mm, 500V, 23GeV p [1]
p-in-n (FZ), 300mm, 500V, neutrons [1]
n-in-p-Fz (800V)
15
10
References:
5
n-in-p-Fz (500V)
p-in-n-FZ (500V)
1014
5 1015
eq [cm-2]
LHC
highest fluence for strip detectors
in LHC: The used
p-in-n technology is sufficient
5 1016
[1] G.Casse, VERTEX 2008
(p/n-FZ, 300 mm, (-30 oC, 25ns)
[2] I.Mandic et al., NIMA 603 (2009) 263
(p-FZ, 300 mm, -20 oC to -40oC, 25ns)
M.Moll - 09/2009
SLHC
n-in-p technology should be sufficient for Super-LHC
at radii presently (LHC)
occupied
by
strip
sensors
[3]
285
m
pixel
[Rohe
et
al. 2005]
[1] n/n-FZ,
[2]
[3]
3D, double
Diamond
p/n-FZ,
300
[RD42
sided,
mm,
m, (-10
(-30
Collaboration]
250C,
C,
mm40ns),
25ns),
columns,
strip300
[Casse
mm substrate
2008]
[Pennicard 2007]
o
o
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -26-
3D detector concept
 Lateral depletion: - lower depletion voltage needed
- thicker detectors possible
- fast signal
- radiation hard
n-columns
p-columns
PLANAR
3D
p+
p+
n
50 mm
- - -++
+
+ +
p+
+
300 mm
 “3D” electrodes: - narrow columns along detector thickness,
- diameter: 10mm, distance: 50 - 100mm
- ++
+ +
+
wafer surface
n-type substrate
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -27-
Example: Testbeam of 3D-DDTC
[G.Fleta, RD50 Workshop, June 2007]
 DDTC – Double sided double type column
front
column
 Testbeam data – Example: efficiency map
[M.Koehler, Freiburg University]
 Processing of 3D sensors is challenging,
but many good devices with reasonable
production yield produced.
 3D sensors will be part of ATLAS IBL detector!
40V applied
~98% efficiency
back column
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -28-
Use of other semiconductor materials?
Property
Eg [eV]
Ebreakdown [V/cm]
me [cm2/Vs]
mh [cm2/Vs]
vsat [cm/s]
e-h energy [eV]
e-h pairs/X0
Diamond
5.5
107
1800
1200
2.2·107
13
4.4
GaN
3.39
4·106
1000
30
8.9
~2-3
4H SiC
3.3
2.2·106
800
115
2·107
7.6-8.4
4.5
Si
1.12
3·105
1450
450
0.8·107
3.6
10.1
 Diamond: wider bandgap
 lower leakage current
 less cooling needed
 less noise
 Signal produced by m.i.p:
Diamond 36 e/mm
Si
89 e/mm
 Si gives more charge
than diamond
 GaAs, SiC and GaN  strong radiation damage observed
 no potential material for LHC upgrade detectors
(judging on the investigated material)
 Diamond (RD42)  good radiation tolerance (CCE degradation similar to silicon)
 already used in LHC beam condition monitoring systems
 considered as potential detector material for sLHC pixel sensors
poly-CVD Diamond
–16 chip ATLAS
pixel module
single crystal CVD
Diamond of few cm2
Diamond sensors are heavily used in LHC Experiments for Beam Monitoring!
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -29-
Summary – Radiation Damage
 Radiation Damage in Silicon Detectors
 Change of Depletion Voltage (internal electric field modifications, “type inversion”,
reverse annealing, loss of active volume, …)
(can be influenced by defect engineering!)
 Increase of Leakage Current (same for all silicon materials)
 Increase of Charge Trapping (same for all silicon materials)
Signal to Noise ratio is quantity to watch (material + geometry + electronics)
 Microscopic defects & Damage scaling factors




Microscopic crystal defects are the origin to detector degradation.
NIEL – Hypothesis used to scale damage of different particles with different energy
Different particles produce different types of defects! (NIEL – violation!)
There has been an enormous progress
Details in talk by
in the last 5 years in understanding defects.
Ioana Pintilie on defects.
 Approaches to obtain radiation tolerant devices:
 Material Engineering:
 Device Engineering:
- explore and develop new silicon materials (oxygenated Si)
- use of other semiconductors (Diamond)
- look for other sensor geometries
- 3D, thin sensors, n-in-p, n-in-n, …
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -30-
Detectors for the LHC upgrade
 At fluences up to 1015cm-2 (outer layers – ministrip sensors)
The change of the depletion voltage and the large area to be covered by detectors are major problems.
 n-MCZ silicon detectors show good performance in mixed fields due to compensation of
charged hadron damage and neutron damage (Neff compensation) (however, more work needed)
 p-type silicon microstrip detectors show very encouraging results
“base line option” for the ATLAS SCT upgrade
 At fluences > 1015cm-2 (Innermost tracking layers – pixel sensors)
The active thickness of any silicon material is significantly reduced due to trapping.
Collection of electrons at electrodes essential: Use n-in-p or n-in-n detectors!
 Recent results show that planar silicon sensors still give sufficient signal,
 3D detectors : very promising but difficult technology, will be installed in ATLAS IBL!
 Diamond is still an interesting option (Higher damage due to low energy protons?)

Solutions for the upgrade available, but still some questions to be answered/explored:
 Can we profit from avalanche effects and control them?
 Can we profit from compensation effects in mixed fields (i.e. MCZ)?
 Can we understand detector performance on the basis of simulations?
?? ?
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -31-
Acknowledgements & References

Most references to particular works given on the slides

Some additional material taken from the following presentations:




Books containing chapters about radiation damage in silicon sensors





RD50 presentations: http://www.cern.ch/rd50/
Anthony Affolder: Presentations on the RD50 Workshop in June 2009 (sATLAS fluence levels)
Frank Hartmann: Presentation at the VCI conference in February 2010 (Diamond results)
Helmuth Spieler, “Semiconductor Detector Systems”, Oxford University Press 2005
Frank Hartmann, “Evolution of silicon sensor technology in particle physics”, Springer 2009
L.Rossi, P.Fischer, T.Rohe, N.Wermes “Pixel Detectors”, Springer, 2006
Gerhard Lutz, “Semiconductor radiation detectors”, Springer 1999
Research collaborations and web sites





CERN RD50 collaboration (http://www.cern.ch/rd50 ) - Radiation Tolerant Silicon Sensors
CERN RD39 collaboration – Cryogenic operation of Silicon Sensors
CERN RD42 collaboration – Diamond detectors
Inter-Experiment Working Group on Radiation Damage in Silicon Detectors (CERN)
ATLAS IBL, ATLAS and CMS upgrade groups
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -32-
The RD50 Collaboration
Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders
• RD50: 47 institutes and 261 members
38 European and Asian institutes
Belarus (Minsk), Belgium (Louvain), Czech Republic (Prague (3x)),
Finland (Helsinki, Lappeenranta ), Germany (Dortmund, Erfurt,
Freiburg, Hamburg, Karlsruhe, Munich), India (Delhi), Italy (Bari,
Florence, Padova, Perugia, Pisa, Trento), Lithuania (Vilnius),
Netherlands (NIKHEF), Norway (Oslo)), Poland (Warsaw(2x)), Romania
(Bucharest (2x)), Russia (Moscow, St.Petersburg), Slovenia (Ljubljana),
Spain (Barcelona(2x), Santander, Valencia), Switzerland (CERN, PSI),
Ukraine (Kiev), United Kingdom (Glasgow, Liverpool)
8 North-American institutes
Canada (Montreal), USA (BNL, Fermilab, New Mexico, Purdue,
Santa Cruz, Syracuse)
1 Middle East institute
Israel (Tel Aviv)
Detailed member list and further details:
http://cern.ch/rd50
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -33-
Spares
•Spare slides
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -34-
Detector Module
• Detector Modules “Basic building block of silicon based tracking detectors”
 Silicon Sensors
 Mechanical support (cooling)
 Front end electronics and signal routing (connectivity)
• Example: ATLAS SCT Barrel Module
 Silicon sensors (x4)
128 mm
- 64 x 64 mm2
- p-in-n, single sided
- AC-coupled
- 768 strips
- 80mm pitch/12mm width
SCT = SemiConductor Tracker
ASICS = Application Specific
Integrated CircuitS
TPG = Thermal Pyrolytic Graphite
 ASICS (x12)
- ABCD chip (binary readout)
- DMILL technology
- 128 channels
 Wire bonds (~3500)
- 25 mm Al wires
 Mechanical support
- TPG baseboard
- BeO facings
 Hybrid (x1)
• ATLAS – SCT
s(r) ~ 16 mm, s(z) ~ 850mm [NIMA538 (2005) 384]
- flexible 4 layer copper/kapton hybrid
- mounted directly over two of the four silicon sensors
- carrying front end electronics, pitch adapter, signal routing, connector
- 15.552 microstrip sensors
- 2.112 barrel modules
- 1.976 forward modules
- 61 m2 silicon, 6.3.106strips
Hybrid Pixel Detectors
• HAPS – Hybrid Active Pixel Sensors
• segment silicon to diode matrix with high granularity
•
•
•
•
( true 2D, no reconstruction ambiguity)
readout electronic with same geometry
(every cell connected to its own processing electronics)
connection by “bump bonding”
requires sophisticated readout architecture
Hybrid pixel detectors will be used in LHC experiments:
ATLAS, ALICE, CMS and LHCb
Solder Bump: Pb-Sn
~ 15mm
(VTT/Finland)
Flip-chip technique
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -36-
The LHC Upgrade Program
• LHC luminosity upgrade (Phase II) (L=5x1034 cm-2s-1) in 2022
Challenge: Build detectors that operate after 3000 fb-1
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -37-
Radiation Damage – II. Leakage Current
• Change of Leakage Current (after hadron irradiation)
-1
…. with time (annealing):
…. with particle fluence:
6
10-2
10-3
-4
10
10-5
10-6 11
10

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
80 min 60C
1012
eq [cm ]
-2
1014
 is constant over several orders of fluence
and independent of impurity concentration in Si
 can be used for fluence measurement
80 min 60C
5
4
4
3
3
2
2
0
1
oxygen enriched silicon [O] = 2.1017 cm-3
parameterisation for standard silicon
1
[M.Moll PhD Thesis]
10
100
1000
o
10000
annealing time at 60 C [minutes]
[M.Moll PhD Thesis]
Leakage current
per unit volume
and particle fluence
6
5
1
1015
Damage parameter  (slope in figure)
I
α
V   eq

1013
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
(t) [10-17 A/cm]
I / V [A/cm3]
10


Leakage current decreasing in time
(depending on temperature)
Strong temperature dependence
 E

I  exp  g ,eff

2
k
T
B


Consequence:
Cool detectors during operation!
Example: I(-10°C) ~1/16 I(20°C)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -38-
Radiation Damage – III. CCE (Trapping)
• Deterioration of Charge Collection Efficiency (CCE) by trapping
Trapping is characterized by an effective trapping time eff for electrons and holes:


1

Qe ,h (t )  Q0 e ,h exp 
t
 

 eff e ,h 
where
Increase of inverse trapping time (1/) with fluence
1
 eff e,h
 N defects
….. and change with time (annealing):
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -39-
Impact of Defects on Detector Properties
• Microscopic defects are the reason for the degradation of the sensor performance
Shockley-Read-Hall statistics
charged defects
 Neff , Vdep
Trapping (e and h)
 CCE
e.g. donors in upper
and acceptors in lower
half of band gap
shallow defects do not
contribute at room
temperature due to fast
detrapping
generation
 leakage current
Levels close to midgap
most effective
Impact on detector properties can be calculated if all defect parameters are known:
sn,p : cross sections
E : ionization energy
Nt : concentration
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -40-
How to normalize radiation damage
from different particles?
 NIEL - Non Ionizing Energy Loss scaling using hardness factors
D( E )  ( E ) dE
1

k

D(1MeV neutrons)
  ( E ) dE
Hardness factor k
of a radiation field (or monoenergetic particle) with respect to 1 MeV neutrons
•E
energy of particle
• D(E) displacement damage cross section for a certain particle at energy E
D(1MeV neutrons)=95 MeV·mb
• (E) energy spectrum of radiation field
The integrals are evaluated for the interval [EMIN,EMAX], being EMIN and EMAX
the minimum and maximum cut-off energy values, respectively, and covering
all particle types present in the radiation field
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -41-
NIEL - Displacement damage functions
104
D(E) / (95 MeV mb)
103
4
neutrons
102
2
101
1
0.8
0.6
100
10-1
10-2
10
protons
protons
pions
1
0.4
100
101
102
103
pions
104
neutrons
1 MeV
neutron
equivalent
damage
electrons
-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]
• NIEL - Non Ionizing Energy Loss
1MeV
• NIEL - Hypothesis: Damage parameters scale with the NIEL
 Be careful, does not hold for all particles & damage parameters (see later)
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -42-
Summary: Radiation Damage in Silicon Sensors
• Two general types of radiation damage to the detector materials:
 Bulk (crystal) damage due to Non Ionizing Energy Loss (NIEL)
- displacement damage, built up of crystal defects –
Influenced by
impurities
in Si – Defect
Engineering
is possible!
I.
Change of effective doping concentration (higher depletion voltage,
under- depletion)
II.
Increase of leakage current (increase of shot noise, thermal runaway)
Same for
III. Increase of charge carrier trapping (loss of charge)
all tested
Silicon
materials!  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 Efficiency
(depending on detector type and geometry and readout electronics!)
Signal/noise ratio is the quantity to watch
 Sensors can fail from radiation damage !
Can be
optimized!
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -43-
Are diamond sensors radiation hard?
23 GeV p
[RD42, LHCC Status Report, Feb. 2010]
70 MeV p
[RD42, LHCC Status Report, Feb. 2010]
 Most published results on 23 GeV protons
23 GeV p
70 MeV p
 70 MeV protons 3 times more damaging
than 23 GeV protons
 25 MeV protons seem to be even more
damaging (Preliminary: RD42 about to cross check
the data shown to the left)
26 MeV p
 In line with NIEL calc. for Diamond
[W. de Boer et al. Phys.Status Solidi 204:3009,2007]
[V.Ryjov, CERN ESE Seminar 9.11.2009]
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -44-
Advantage of non-inverting material
p-in-n detectors (schematic figures!)
Fully depleted detector
(non – irradiated):
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -45-
Advantage of non-inverting material
p-in-n detectors (schematic figures!)
Be careful, this is a very schematic
explanation, reality is more complex !
Fully depleted detector
(non – irradiated):
heavy irradiation
inverted
non inverted
inverted to “p-type”, under-depleted:
non-inverted, under-depleted:
• Charge spread – degraded resolution
•Limited loss in CCE
• Charge loss – reduced CCE
•Less degradation with under-depletion
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -46-
Silicon materials for Tracking Sensors
• Signal comparison for various Silicon sensors
25000
Silicon Sensors
p-in-n (EPI), 150 mm [7,8]
n-in-p-Fz (500V)
n-in-p-Fz (800V)
signal [electrons]
20000
3D simulation
15000
n-FZ(500V)
10000
p-in-n (EPI), 75mm [6]
n-in-p (FZ), 300mm, 500V, 23GeV p [1]
n-in-p (FZ), 300mm, 500V, neutrons [1]
n-in-p (FZ), 300mm, 500V, 26MeV p [1]
n-in-p (FZ), 300mm, 800V, 23GeV p [1]
n-in-p (FZ), 300mm, 800V, neutrons [1]
n-in-p (FZ), 300mm, 800V, 26MeV p [1]
p-in-n (FZ), 300mm, 500V, 23GeV p [1]
p-in-n (FZ), 300mm, 500V, neutrons [1]
Double-sided 3D, 250 mm, simulation! [5]
150mm n-EPI
SiC, n-type, 55 mm, 900V, neutrons [3]
Diamond (pCVD), 500 mm [4] (RD42)
75mm n-EPI
References:
SiC
1014
Higher Voltage
leads to charge
multiplication
Other materials
pCVD Diamond
5000
Note: Measured partly
under different conditions!
Lines to guide the eye
(no modeling)!
5 1015
eq [cm-2]
5 1016
[1] p/n-FZ, 300mm, (-30oC, 25ns), strip [Casse 2008]
[2] p-FZ,300mm, (-40oC, 25ns), strip [Mandic 2008]
[3] n-SiC, 55mm, (2ms), pad [Moscatelli 2006]
[4] pCVD Diamond, scaled to 500mm, 23 GeV p, strip [Adam et al. 2006, RD42]
Note: Fluenze normalized with damage factor for Silicon (0.62)
[5] 3D, double sided, 250mm columns, 300mm substrate [Pennicard 2007]
[6] n-EPI,75mm, (-30oC, 25ns), pad [Kramberger 2006]
[7] n-EPI,150mm, (-30oC, 25ns), pad [Kramberger 2006]
[8] n-EPI,150mm, (-30oC, 25ns), strip [Messineo 2007]
Beware:
Signal shown
and not S/N !
M.Moll - 08/2008
 All sensors suffer from radiation damage
 Presently three options for innermost pixel layers under investigation:

Silicon planar sensors, 3-D silicon sensors, Diamond sensors
M.Moll, RAD2012, 25.4.2012, Niš, Serbia -47-