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Overview
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History of silicon for tracking detectors & Basics
From LHC tracker to SLHC tracker
Radiation effects in silicon - defect engineering
Device engineering – radiation hard device design
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Silicon detectors for SLHC
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n+-p strip detectors
n+-p pixel detectors
3D detectors
Electronics considerations
Conclusions
DESY seminar
9.1.2007
Signal formation
Isolation techniques
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
1
History and basics
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
2
Position sensitive silicon detectors
Planar diodes – structured detectors (Kemmer 1980)
photolitografic processing
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
3
First considerations about radiation
hardness for HEP - SSC
(Detectors and Experiments for the
Superconducting Super Collider, pg.
491, Snowmass 1984
1984 considerations for SSC
(Detectors and Experiments for the
Superconducting Super Collider, pg.
491, Snowmass 1984
Now 105 upra
“Silicon strip detectors (near the beam pipe)
appear to be limited to…≤ 1032....the 1032
limit could be optimistic.” (PSSC Summary Report
pg. 130, 1984)
T. Kondo et al, Radiation Damage Test of Silicon Microstrip Detectors, pg. 612, Snowmass 1984
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
4
And we are we know now …
LEP
e+e-
1.5∙1031
cm-2 s-1
HERA , Tevatron
LHC
pp 1.4∙1032 cm-2 s-1
SLHC?
pp 1035 cm-2 s-1
•Silicon is a reliable detector technology
•Available on large scale (200 m2 CMS) by many vendors with high yield
•6’’ wafers are standard, 8’’ are coming
•Different silicon growing techniques can be exploited for sensor production
(CZ, MCz, FZ, epi-Si)
•Many different electronics read-out ASICs were developed
•Also other devices are interesting for tracking: CCD, MAPS, DEPFETs …
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
5
Silicon detectors today
Signal ~ 22500e in 300mm
C~1pF/cm
“Standard detector today” for HEP experiments (HERA (all), Belle, LEP, Tevatron)
•pitch 25 – few hundred microns
•readout strips in p+ side (for SSD) or both sides (for DSD) - around 6 cm long AC/DC coupled
•300 mm thick produced on n type-standard float zone silicon
•n-type silicon of 2-15 kWcm resistivity
•poly-silicon or FOXFET biased on the readout side
•Multi guarding structure
Physics reasons:
•superior position resolution (up to few microns), due to fine segmentation
•fast charge collection (tcol~ few ns) for 300 mm thick sensors – high rate operation
•dE/dx possible
•operational at moderate voltages
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
6
LHC & SLHC
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
7
LHC – new challenge
LHC properties
Proton-proton collider, 2 x 7 TeV
Luminosity: 1034
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
Main problems of a tracker at LHC:
•Loss of efficiency
•fast electronics (high series noise)
•charge trapping (loss of signal)
•high Ubias , danger of break-down
•High power dissipation (8W/module for ATLAS-SCT)
•Need for running cool (leakage current)
•Need for storing cool to reduce Vfd increase
•Large scale – complex services and links
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
8
CMS
Overall length: 21.5m, diameter: 15m,
total weight: 12500t, magnetic field: 4T
ATLAS
Overall length: 46m, diameter: 22m,
total weight: 7000t, magnetic field: 2T
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
9
• LHC upgrade
Super LHC
LHC (2007), L = 1034cm-2s-1
f(r=4cm) ~ 3·1015cm-2
500 fb-1
CERN-RD48
Super-LHC (2015 ?), L = 1035cm-2s-1
5 years
2500 fb-1
f(r=4cm) ~ 1.6·1016cm-2
TID=4 MGy
CERN-RD50
Phase 1: no major change in LHC
L = 2.34 ∙1034cm-2s-1 (higher beam current)
Phase 2: major changes in LHC
L = 4.6 ∙1034 cm-2s-1 with (BL/2, qc)
L = 9.2 ∙1034 cm-2s-1 with (fill all bunches)
Phase 3: increase beam energy to 14 TeV
(9 to 17 T magnets)
DESY seminar
9.1.2007
Pixel (?)
Inner
Pixel
16
10
Ministrip (?)
Q>4000e
~5000e
Macropixel (?)
5
eq [cm-2]
10 years
SUPER - LHC (5 years, 2500 fb-1)
total fluence
eq
Q>9000e
1015
5
Mid-Radius
Short Strips
neutrons eq
Q>18000e
Outer-Radius
pions eq
“SCT”
1014
5
ATLAS SCT - barrel
(microstrip detectors)
ATLAS Pixel
13
10
0
10
20
30
40
50
other charged
hadrons eq
60
[M.Moll, simplified, scaled from ATLAS TDR]
r [cm]
Two main problems:
•Occupancy increase
•Radiation damage
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
10
ATLAS at SLHC (II)
Initial studies show that other sub-detectors can be kept with small
modifications and some with somewhat degraded performance also at SLHC!
ID requires complete replacement, but keeping services at the same level!
Long barrel proposal (other “Straw Man” design)
ID ATLAS @ LHC
ID ATLAS @ SLHC
Time plan: R&D 2009, 2010 Construction phase, 2014 Commissioning
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
11
ATLAS at SLHC (III)
Simulation studies done to
determine optimum segmentation
to cope with high track
multiplicities:
•230 min. bias collisions/BC
•10000 tracks for |h|<2.3
Long strips
12 cm x 80 mm
Short strips
3 cm x 50 mm
Pixels 400x50 mm2
DESY seminar
9.1.2007
LHC
SLHC
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
x10 if BCT=25 ns
x5 if BCT=12.5 ns
12
Radiation damage in
semiconductor detectors
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
13
The CERN RD50 Collaboration
http://www.cern.ch/rd50
RD50: Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders
 formed
in November 2001
 approved as RD50 by CERN 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 25ns 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 260 members from 53 institutes
Belarus (Minsk), Belgium (Louvain), Canada (Montreal), Czech Republic (Prague (3x)), Finland (Helsinki,
Lappeenranta), Germany (Berlin, Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe, Munich), 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, Oxford, Sheffield, Surrey), USA (Fermilab, Purdue University,
Rochester University, SCIPP Santa Cruz, Syracuse University, BNL, University of New Mexico)
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
14
Radiation damage
Two 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. Increase of leakage current (increase of shot noise, thermal runaway)
II. Change of effective doping concentration
(higher depletion voltage, under- depletion)
III. Increase of charge carrier trapping (loss of charge)
 Surface damage due to Ionizing Energy Loss (IEL)
- accumulation of charge in the oxide (SiO2) and Si/SiO2 interface –
affects: interstrip capacitance (noise factor), breakdown behavior, …
! Signal/noise ratio = most important quantity !
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
15
particle
Sis
Frenkel pair
Vacancy + Interstitial
EK > 25 eV
Point Defects (V-V, V-O .. )
V
I
EK > 5 keV
clusters
Influence of defects on the material and device properties
charged defects
 Neff , Vdep
e.g. donors in upper
and acceptors in
lower half of band
gap
DESY seminar
9.1.2007
Trapping (e and h)
 CCE
shallow defects do not
contribute at room
temperature due to fast
detrapping
generation
 leakage current
Levels close to
midgap
most effective
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
16
Selecting rad-hard materials for tracker detectors at SLHC
Main Selection
Parameters

High CCE
Main
Operative Characteristics
Main Material
Characteristics
High crystalline
quality & negligible
rad-induced deep
traps
Negligible trapping effects
High E field close r-o elect.

Low noise

Low power

High speed
Low leakage current
No type inversion
Low dielectric constant
big bandgap
Thin thickness
Low full depletion voltage
High resistivity
but: higher e-h
High mobility & saturation field
creation energy

Cost-effective
but: higher capacitance
Commercially available
in large scale
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
17
New Materials: Diamond, SiC, GaN
Property
Eg [eV]
Ebreakdown [V/cm]
me [cm2/Vs]
mh [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
20
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
R&D on diamond detectors: RD42 – Collaboration
http://cern.ch/rd42/
CCE at high fluences degrades even
more in SiC and GaN than in Si.
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC






Wide band gap (3.3eV)
lower leakage current
than silicon
Signal:
Diamond 36 e/mm
SiC
51 e/mm
Si
80 e/mm
more charge than
diamond
Higher displacement
threshold than silicon
radiation harder than
silicon (?)
18
Approaches to develop radiation harder
tracking detectors
•Material engineering
•Device engineering
•Change of detector
operational conditions

CERN RD39
“Cryogenic Tracking Detectors”

DESY seminar
9.1.2007
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
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
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
19
Change of Depletion Voltage Vdep
(n-type material – RD48 results)
…. with time (annealing):
103
1000
500
102
 600 V
type inversion
100
50
101
1014cm-2
10
5
1
10-1
100
"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
10
10-1
-2
• “Type inversion”: Neff changes from positive to
negative (Space Charge Sign Inversion)
p+
before inversion
DESY seminar
9.1.2007
n+
p+
n+
after inversion
neglecting double junction
 Neff [1011cm-3]
5000
| Neff | [ 1011 cm-3 ]
Udep [V] (d = 300mm)
…. with particle fluence
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!
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
20
The role of the oxygen in the Si
(Vfd (I))
8
Carbon-enriched (P503)
Standard (P51)
O-diffusion 24 hours (P52)
O-diffusion 48 hours (P54)
O-diffusion 72 hours (P56)
Carbonated
500
MCz-n Helsinki
6
Standard
Oxygenated
2
0
0
400
300
4
200
100
1
2
3
4
24 GeV/c proton [10 cm ]
14
-2
In FZ detectors irradiation introduces
effectively negative space charge!
600
5
Vdep [V] (300 mm)
|Neff| [1012cm-3]
10
For detectors irradiated with charged hadrons
RD48: Higher oxygen content
 less negative space charge
For detectors irradiated with charged hadrons
RD50: High initial oxygen dimmer (O2i)
MCz/Cz and Epitaxial silicon detectors
positive space charge (Bi-stable donors)
Increase of Vfd at high fluences is roughly the same
in all O rich materials |Neff|~7·10-3 cm-1 p !
Almost independent of oxygen content:
Donor removal
“Cluster damage”
 negative charge
DESY seminar
9.1.2007
After neutron irradiation all materials behave
similarly and neutrons are 3x (except epi-Si)
more damaging than charged hadrons!
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
21
Proton irradiated oxygen rich detectors
(Vfd (II))
4.00E+02
8.E+12
500 V
MCz - n (CNM)
3.50E+02
MCz - n (2e14)
6.E+12
3.00E+02
DOFZ n (2e14)
5.E+12
2.50E+02
7.E+12
Vfd [V]
|Neff| [1/cm3]
DOFZ n (CNM)
4.E+12
2.00E+02
3.E+12
1.50E+02
2.E+12
1.00E+02
300 mm thick sensors
1.E+12
End of
LHC
5.00E+01
0.00E+00
0.E+00
0
2E+14
4E+14
6E+14
8E+14
1E+15
Fluence [24 GeV p/cm2]
Do we undergo SCSI
NO verified by TCT & annealing curves
1.2E+15
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
Annealing time @ 80C [min]
beneficial and reverse annealing similar to
that of n-type STFZ, DOFZ materials
•Positive space charge is compensated by negative
formed during RA
•Reverse annealing time constants are prolonged by
high concentration of O
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
22
Thin n-type epitaxial Si detectors-CERN-scenario experiment
S-LHC: L=1035cm-2s-1
Most inner pixel layer
250
50 mm after 50 min@80C annealing
Parameters
operational period per year:
100 d, -7°C, Φ = 3.48·1015cm-2
beam off period per year 265 d, +20°C
positive stable damage
negative space charge
during RA
9.1.2007
200
Vfd [V]
extracted at elevated
annealing fit measurements at room
temperatures very well
Very good reproducibility and working
model
(BA, constant damage, 1st order RA, 2nd
order RA)
DESY seminar
(Vfd (III))
150
25 mm after 50 min@80C annealing
50 mm simulation
100
50
25 mm simulation
G. Lindström et al.
0
0
2.1015
4.1015
6.1015 8.1015
eq [cm-2]
1016
Compensation
The scenario can be found where the Neff can
be controlled. Increase of Vfd is not a limiting
factor for efficient use of Si detectors!
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
23
Neutron irradiated epitaxial Si detectors (V
fd (IV))
8.00E+13
neutrons
7.00E+13
no SCSI
Neff [cm-3]
6.00E+13
n-type
detectors
5.00E+13
SCSI
4.00E+13
3.00E+13
Epi75 - ST (CiS); 150 Ohm cm
Epi75 - DO (CiS); 150 Ohm cm
2.00E+13
Epi150 (IRST); 500 Ohm cm
1.00E+13
Epi25 - (CiS); 50 Ohm cm
Epi50 - (CiS); 50 Ohm cm
0.00E+00
0.00E+00
2.00E+15
4.00E+15
G. Kramberger et al., 8th RD50 workshop
SMART coll., 8th RD50 workshop
6.00E+15
8.00E+15
1.00E+16
1.20E+16
Equivalent fluence [cm-2]
Neutrons: smaller increase of |Neff| with fluence than in any other material |gc|~5·10-3 cm-1
no SCSI for r=50 Wcm ; SCSI for r>150 Wcm
20<r<60 cm
200 mm , max=2∙1015 cm-2
Vfd < 300 V
Not easy to produce
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
24
Trapping of the drifting charge (I)
(-10oC,
Vfd)
t=min
[10-16 cm2/ns]
24 GeV protons
200 MeV/c pions
(average )
Electrons 5.6 ± 0.7
Holes
6.6 ± 0.8
1
reactor neutrons
4.1 ± 0.5
6.0 ± 0.4
 eff ,e,h
  e,h (T , t )  eq
The e,h was so far found independent on material;
resistivity
[O], [C]
type (p,n)
wafer production (FZ, Cz, epitaxial)
somewhat lower trapping at eq>1015 cm-2
extrapolated values
Remember we have a mixture of
pions and neutrons in experiments!
r~4cm
r~20cm
r~60cm
electrons
for higher fluences
 eff ,e,h  t drift
holes
DESY seminar
9.1.2007
300 mm
 3ns
vsat
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
25
Trapping of the drifting charge (II)
 e,h (T , t )
   0 exp( 

t
t 
t
)    1  exp(  )  ( 0    ) exp(  )   
 ta


ta 
ta

Neutron irr.
0  
0
Electrons
Holes
an @60oC
Eta[eV]
0.3±0.15
~650 min
1.06±0.1
-0.4±0.2
~550 min
0.98±0.1
 Ea 

 k BT 
 an   0 exp 
Confirmed also by ATLAS pixel test beam!
T. Lari, Nucl. Inst. Meth. A518 (2004) 349.
 e,h (T , t )
Trapping probability decreases with temperature, but mobility also!
Operation at lower T doesn’t improve CCE !
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
26
Leakage current
10-2
10-3
…. with particle fluence:
-5
10
1012
1013
eq [cm-2]
1014
1015
[M.Moll PhD Thesis]
Damage parameter  (slope in figure)
I
α
V   eq

n-type FZ - 780 Wcm
n-type FZ - 410 Wcm
n-type FZ - 130 Wcm
n-type FZ - 110 Wcm
n-type CZ - 140 Wcm
p-type EPI - 380 Wcm
10-4
10-6 11
10

6
n-type FZ - 7 to 25 KWcm
n-type FZ - 7 KWcm
n-type FZ - 4 KWcm
n-type FZ - 3 KWcm
p-type EPI - 2 and 4 KWcm
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
DESY seminar
9.1.2007
(t) [10-17 A/cm]
I / V [A/cm3]
10-1
with time (annealing):
6
80 min
60C
5
4
5
4
3
3
2
2
.
1
0
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:
 E

I  exp   g
2k BT 

Consequence:
Cool detectors during operation!
Example: I(-10°C) ~1/16 I(20°C)
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
27
Device engineering
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
28
Device engineering - Signal in Si detectors (I)
t

r (t )
t 0

r0
 

Q   Idt  q  v Ew dt  q  Ew dr
t
t 0


Q  q[U w (r )  U w (r0 )]
p+
280 mm
Weighting field
hole
electron
Qe  h  Qe  Qh
U w  0
sensing electrode
Uw 1
all other electrodes
Uw  0
n+
Contribution of drifting carriers to
the total induced charge depends
on Uw !
Uw simple in diodes and complicated in
segmented devices!
For track:
Qe/(Qe+Qh)=19%
in ATLAS strip detector
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
n+
diode
Qh=Qe=0.5 q
segmentation
80 mm pitch
18 mm implant
29
Device engineering - Signal in Si detectors (II)

I  qv Ew
Q(t ) 
drift current
tint
tint
 Idt  q  exp(  
t
0
t 0
t 0
 
) me,h E  Ew dt
eff ,e , h
scalar field in which the carrier drifts
Terms different for holes and electrons
•trapping term ( eff,e~eff,h )
•drift velocity ( me~3mh )
electrons get
less trapped
example of inverted p+-n 280 mm fully
depleted detector with 25 mm pitch
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
30
Device engineering - Signal in Si detectors (III)


 
E , Ew , E  Ew
p+
diode
good 
n+
Segmented readout
 
small
Ew E


worse 
even worse: p+ readout
(p+-n detector)
Segmented readout
 
large
Ew E


better 
even better: n+ readout
(n+-p, n+-n detector)
How to get maximum signal?
use of n+-n or n+-p device (electron collection) with pitch<<thickness
implant width close to pitch (depends on FE elec. – inter-electrode capacitance)
for a given cell size of a pixel detector
DESY seminar
9.1.2007
pitchx
 0, 
pitchy
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
31
Device engineering - Signal in Si detectors (IV)
 eff ,e,h  tdrift
p+
n+
Segmented readout
electrons

Ew

p+
n+
Segmented readout

Ew
Carriers in this region would be trapped before reaching high Ew!
It doesn’t matter if the region is depleted or not - under-depleted
detectors would perform almost as good as fully depleted!
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
32
Device engineering
Trapping induced charge sharing
Incomplete charge collection due to trapping results in appearance of the charge in the
neighboring strips!
bipolar pulse
measuring
 Idt  0
n+ strips
(higher signal)
p+
p+ strips
(wider cluster)
p bulk
n+
diode
0
±U
81%
Signals in the neighbors few % of the hit strip
observed in atlas test beam
Y. Unno et al., IEEE Trans. NS 49(4) (2002) 1868
DESY seminar
9.1.2007
Depends strongly on fluence position of the hit
and electrode geometry!
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
33
Device engineering
Isolation techniques n+-side readout (I)
strip 1
strip 2
++++++++
oxide
isolation structure
needed to interrupt the
inversion layer between
the strip
n+
n+
p- substrate
electron layer
p+
backplane
3 techniques available (from n+-on-n technology):
p-stop
p-spray
S1
S2
high-field regions
S1
p-spray/p-stop
S2
S1
high-field regions
Cint, VBR improve with radiation Cint, VBR degrade with radiation
(Oox), better initially
(Oox), worse initially
S2
high-field region
depends on Qox
compromise

Simulations needed for each design of a detector to find an optimum!
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
34
Silicon detectors for SLHC
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
35
n+-p short strip detectors (20<r<60 cm)
Detector geometry: Thickness=300 mm, strip pitch=80 mm, implant width= 18 mm,
LHC speed readout (SCT128A-HC), beta source measurements
n-in-p : standard FZ
p-in-n : oxygenated and standard FZ


25% charge loss after 5x1014 p/cm2 (23 GeV)
over-depletion is needed
Q/Q0 [%]
100


~40% charge loss after 3x1015 p/cm2 (23 GeV)
~7000 e after 7.5x1015 p/cm2 (23 GeV)
max collected charge (overdepletion)
Vfd
80
Vfd~1200 V
CCE~60%
60
collected at depletion voltage
40
Vfd>2500 V
oxygenated
standard
20
CCE~30%
M.Moll [Data: P.Allport et all, NIMA 501 (2003) 146]
0
0
1
2
3
4
p [1014 cm-2]
P.P. Allport et al.,
IEEE Trans. NS
52(5) (2005)
1903.
5
Much better performance
DESY seminar
9.1.2007
(same charge 6x the fluence + under-depleted operation)
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
36
n+-p short strip detectors (20<r<60 cm)
time [days at 20oC]
T=-20oC, Vbias=900 V
Trapping times tend to longer than
predicted at high fluences!
CCE (103 electrons)
recent neutron irradiated samples
20
18
16
14
12
10
8
6
4
2
0
0
500
1000
1500
2000
2500
800 V
1.1 x 1015cm-2
500 V
3.5 x 1015cm-2 (500 V)
7.5 x 1015cm-2 (700 V)
[Data: G.Casse et al., to be published in NIMA]
M.Moll
0
100 200 300 400 500
time at 80oC[min]
At first unexpected behavior of CCE(t)
Possible explanation:
•Increase of Vfd (not so important as electric field is still present close to electrodes)
•Annealing of electron trapping times
CONFIRMED also by simulations! The reverse annealing is not critical as for LHC!
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
37
n+-p short strip detectors – super modules
LBNL proposal
(evolved from
CDF run IIb)
Liverpool proposal
TPG
baseboard
DESY seminar
9.1.2007
Bridging
structure
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
38
n+-p short strip detectors – shot noise
STFZ detectors
Short strips at r=35 cm (3 cm x50 mm)
P. Allport et al.
ENCleak  12  I leak  shaping
CR-RC shaping
25 ns shaping time
Short strips should have noise
below 1000 e – dominated by
series noise ENCseries      C
In order to keep the noise
below the desired limit
ENCleak<500e , T<-15oC
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
39
Long strip detectors (r>60 cm)


Present technology (STFZ p+-n) pushed to the
higher radii may work – however practical
issues cold/warm during the beam-off must be
considered
Better would be n+-p type detectors (regardless
of the silicon type – neutron dominated
damage)



higher signal and possible use potentially of longer
strips to reduce # of channels and have the same
S/N
No ballistic deficit with BCT=12.5 ns
Smaller operational voltage needed and no critical
issue if Vfd>operational bias (safety)
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
40
Planar n+-p pixel detectors (r<20
cm)
•Pion dominated damage – choice of material for these detectors MCz or epi-Si!
•Detectors of some 200 mm almost ideal choice if kept warm during beam-off period
Compensation of positive space charge with acceptors during RA (always fully depleted)
Annealing of electron trapping times – smaller effect of trapping
Smaller power dissipation due to smaller leakage current and bias voltage
Smaller shot noise
Epi-Si,75 mm
n. irr diodes
•after annealing (reduction of Vfd and electron trapping times)
•after segmentation (higher contribution of electrons)
DESY seminar
9.1.2007
~4000e@1016cm-2
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
41
10 years of LHC (4 cm)
at 1034 cm-2 s-1
10 years of SLHC (4 cm)
1034 cm-2 s-1
(60,100,160V)
Threshold needed on pixel
FE electronics is for
ATLAS and CMS pixels
around 3500-4000
electrons! Can we hope for
better electronics?
(500V)
more charge at lower
voltages (<300 V) with epi-Si
(600 V)
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
42
3D n+-p pixel detectors (r<20 cm)
Combine traditional VLSI processing and
MEMS (Micro Electro Mechanical Systems)
technology.
Both electrode types are processed inside the
detector bulk instead of being implanted on
the wafer's surface.
The edge is an electrode. Dead volume at the
Edge < 5 microns! Essential for forward
physics experiments and material budget
S.I. Parker, C.J. Kenny, J. Segal, Nucl. Instr. and Meth. A395 (1997) 328.
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
43
3D n+-p pixel detectors (r<20 cm)
Pros.
•Better charge collection efficiency
•Faster charge collection (depends on
inter-column spacing)
•Reduced full depletion voltage and
by that the power
•Larger freedom for choosing
electrode configuration
DESY seminar
9.1.2007
Cons.
•Columns are dead area (aspect ratio ~30:1)
•Spatially non-homogenous CCE
(efficiency=function of position)
•Much higher electrode capacitance (hence noise),
particularly if small spacing is desired – small drift
length
•Availability on large scale
•Time-scale and cost
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
44
•Volume = 1.2 x 1.33 x 0.23 mm3
•3 electrode Atlas pixel geometry
•n-electrode readout
•n-type before irradiation - 12 kW cm
•Irradiated with neutrons
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
45
Different geometry – 3D sct (RD50)
C. Piemonte et al., IRST
Sketch of the detector:
Functioning:
n-columns
ionizing particle
n+
p-type substrate
DESY seminar
9.1.2007
grid-like bulk contact
electrons are
swept away by
the transversal
field
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
n+
cross-section
between two
electrodes
holes drift in the
central region and
diffuse towards p+
Contact (long tail)
46
undepleted
300 or 500 mm
150 mm
Different geometry – 3D sct
3D-stc DC coupled detector
(64 x 10 columns)
80 mm pitch
80 mm between holes
10 mm hole diameter
Inter-column
region
depleted @
12 V
Active Thickness [um]
Diode like structure CCE measurements
(slow shaping time)
600
Focused IR laser of 7 mm spot size
3 strips connected to amplifier
Thickness calculated from signal
500
400
300
200
100
Florence
C-V
UCSC
0
0
50
100
150
200
Voltage [V]
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
47
Different geometry – 3D dct
1um
0.4um
Passivation
Oxide
50mm
Designed proposed by RD50
collaboration (IRST, CNM,
Glasgow)
Metal
5mm
n+ doped
P-stop
p+
10mm
TEOS 2um
300mm
Poly 3mm
p- type
substrate
p+ doped
50mm
p+ doped
•much simplified process – no
need for support wafer during
production
•single sided processing with
additional step of etching and
B diffusion
•Performance equal to original
design
Oxide
Metal
55um pitch
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
48
Electronics – deep sub micron CMOS
(ATLAS pixel, CMS all)
Vth  tox2
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
49
Electronics – BiCMOS
•Short shaping times (12.5 ns)
• large capacitances
Bipolar transistors perform better in terms of noise-power
(CMOS requires larger bias current)
BiCMOS in atlas not radiation hard enough and not available anymore
  100  1e14  40
Bipolar SiGe transistors “married” to DSM-CMOS
  200  3e15  50 @ I c  10mA
fT  50 GHz
DESY seminar
9.1.2007
Around 4 times smaller power consumption
than present design
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
50
Conclusions
The ideal detector is the one which can be depleted all the time and kept at
room temperature during beam-off periods – we are almost there!
 Sensor technology for SLHC tracker






Long strips (present p+-n cost effective or n+-p)
Short strips/pixel (n+-p on rad-hard material)
Pixel layers without innermost layer (n+-p pixels on rad-hard material)
Pixel layer at 4-6 cm (to be decided between diamond and silicon planar or 3D
pixels)
Electronics technology: all DSM-CMOS or BiCMOS (with SiGe bipolar
part) for strips
The most challenging will be engineering work (cooling, cabling,
shielding, other services)
Prospects are good, but work ahead is enormous!
Let’s wait to see first results from LHC, before …
DESY seminar
9.1.2007
G. Kramberger, Jožef Stefan Institute,
Towards Radiation Hard Silicon Detectros at SLHC
51