Overview

1
Overview

• 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
• Signal formation
• Isolation techniques
• Silicon detectors for SLHC
• n-p strip detectors
• n-p pixel detectors
• 3D detectors
• Electronics considerations
• Conclusions

2
History and basics
3
Position sensitive silicon detectors

• Planar diodes structured detectors (Kemmer
  1980) photolitografic processing

4
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
5
And we are we know now
LEP HERA , Tevatron LHC SLHC?
pp 1.41032 cm-2 s-1
pp 1035 cm-2 s-1
ee- 1.51031 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

6
Silicon detectors today
Signal 22500e in 300mm C1pF/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

7
LHC SLHC
8
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

9
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
10
Super LHC

• LHC upgrade ?LHC (2007), L 1034cm-2s-1
  f(r4cm) 31015cm-2
• ?Super-LHC (2015 ?), L 1035cm-2s-1
  f(r4cm)
  1.61016cm-2 TID4 MGy

5000e
CERN-RD48
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)

• Two main problems
• Occupancy increase
• Radiation damage

11
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!
12
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 hlt2.3

Long strips 12 cm x 80 mm
Short strips 3 cm x 50 mm
LHC
x10 if BCT25 ns x5 if BCT12.5 ns
Pixels 400x50 mm2
SLHC
13
Radiation damage in semiconductor detectors
14
The CERN RD50 Collaboration http//www.cern.ch/rd
50
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)
15
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 !

16
Frenkel pair
V
Vacancy Interstitial
Si
I
particle
s
EK gt 25 eV
EK gt 5 keV
Point Defects (V-V, V-O .. )
clusters
Influence of defects on the material and device
properties
Trapping (e and h)? CCEshallow defects do not
contribute at room temperature due to fast
detrapping
charged defects ? Neff , Vdepe.g. donors in
upper and acceptors in lower half of band gap
generation ? leakage currentLevels close to
midgap most effective
17
Selecting rad-hard materials for tracker
detectors at SLHC
? High CCE
High crystalline quality negligible rad-induced
deep traps
Negligible trapping effects
High E field close r-o elect.
? Low noise
Low leakage current
No type inversion
Low dielectric constant
? Low power
big bandgap
Thin thickness
? High speed
Low full depletion voltage
High resistivity
High mobility saturation field
but higher e-h creation energy
? Cost-effective
but higher capacitance
Commercially available in large scale
18
New Materials Diamond, SiC, GaN

• Wide band gap (3.3eV)
• lower leakage current than silicon
• SignalDiamond 36 e/mmSiC
  51 e/mmSi 80 e/mm
• more charge than diamond
• Higher displacement threshold than silicon
• radiation harder than silicon (?)

RD on diamond detectors RD42
Collaborationhttp//cern.ch/rd42/
CCE at high fluences degrades even more in SiC
and GaN than in Si.
19

• Approaches to develop radiation harder tracking
  detectors
• Material engineering
• Device engineering
• Change of detector
• operational conditions

• 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

CERN RD39Cryogenic Tracking Detectors
20
Change of Depletion Voltage Vdep(n-type
material RD48 results)
. with time (annealing)
. with particle fluence
Short term Beneficial annealing Long
term Reverse annealing - time constant
depends on temperature 500
years (-10C) 500 days (
20C) 21 hours ( 60C) -
Consequence Detectors must be cooled even
when the experiment is not running!
Type inversion Neff changes from positive to
negative (Space Charge Sign Inversion)
p
p
n
n
after inversion neglecting double junction
before inversion
21
The role of the oxygen in the Si (Vfd (I))

• In FZ detectors irradiation introduces
  effectively negative space charge!

• For detectors irradiated with charged hadrons
• RD48 Higher oxygen content
• ? less negative space charge

22
Proton irradiated oxygen rich detectors (Vfd
(II))
500 V
End of LHC
300 mm thick sensors

• Do we undergo SCSI
• NO verified by TCT annealing curves

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

23
Thin n-type epitaxial Si detectors-CERN-scenario
experiment (Vfd (III))
S-LHC L1035cm-2s-1Most inner pixel layer

• Parameters 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)

operational period per year100 d, -7C, F
3.481015cm-2beam off period per year 265 d,
20C
G. Lindström et al.
positive stable damage negative space charge
during RA
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!
24
Neutron irradiated epitaxial Si detectors (Vfd
(IV))
neutrons
no SCSI
n-type detectors
SCSI
G. Kramberger et al., 8th RD50 workshop SMART
coll., 8th RD50 workshop
Neutrons smaller increase of Neff with
fluence than in any other material gc510-3
cm-1 no SCSI for r50 Wcm
SCSI for rgt150 Wcm
200 mm , Fmax21015 cm-2 Vfd
lt 300 V
20ltrlt60 cm
Not easy to produce
25
Trapping of the drifting charge (I)
b(-10oC, tmin Vfd) 10-16 cm2/ns 24 GeV protons 200 MeV/c pions (average ) reactor neutrons
Electrons 5.6 0.7 4.1 0.5
Holes 6.6 0.8 6.0 0.4

• The be,h was so far found independent on
  material
• resistivity
• O, C
  
• type (p,n)
• wafer production (FZ, Cz, epitaxial)
• somewhat lower trapping at Feqgt1015 cm-2

26
Trapping of the drifting charge (II)
Neutron irr. tan _at_60oC EtaeV
Electrons 0.30.15 650 min 1.060.1
Holes -0.40.2 550 min 0.980.1
Trapping probability decreases with temperature,
but mobility also! Operation at lower T doesnt
improve CCE !
27
Leakage current
. with particle fluence

• Leakage current decreasing in time
  (depending on temperature)
• Strong temperature dependence

• Damage parameter ? (slope in figure)
  Leakage current
  per unit volume
  and particle fluence
• ? is constant over several orders of fluenceand
  independent of impurity concentration in Si ?
  can be used for fluence measurement

Consequence Cool detectors during
operation! Example I(-10C) 1/16 I(20C)
28
Device engineering
29
Device engineering - Signal in Si detectors (I)
p
Weighting field
hole
sensing electrode all other electrodes
280 mm
electron
n
n
Contribution of drifting carriers to the total
induced charge depends on DUw ! Uw simple in
diodes and complicated in segmented devices! For
track Qe/(QeQh)19 in ATLAS strip detector
diode
QhQe0.5 q
80 mm pitch 18 mm implant
30
Device engineering - Signal in Si detectors (II)
drift current
scalar field in which the carrier drifts
Terms different for holes and electrons

• trapping term ( teff,eteff,h )
• drift velocity ( me3mh )

electrons get less trapped
example of inverted p-n 280 mm fully depleted
detector with 25 mm pitch
31
Device engineering - Signal in Si detectors (III)
n
p
Segmented readout
Segmented readout
diode
better ?
worse ?
good ?
even worse p readout (p-n detector)
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 pitchltltthickness
• implant width close to pitch (depends on FE elec.
  inter-electrode capacitance)
• for a given cell size of a pixel detector

32
Device engineering - Signal in Si detectors (IV)
p
p
n
n
Segmented readout
Segmented readout
electrons
Carriers in this region would be trapped before
reaching high Ew! It doesnt matter if the
region is depleted or not - under-depleted
detectors would perform almost as good as fully
depleted!
33
Device engineeringTrapping induced charge sharing
Incomplete charge collection due to trapping
results in appearance of the charge in the
neighboring strips!
bipolar pulse
n strips (higher signal)
diode
p strips (wider cluster)
0
81
Signals in the neighbors few of the hit
strip Depends strongly on fluence position of
the hit and electrode geometry!
observed in atlas test beam Y. Unno et al., IEEE
Trans. NS 49(4) (2002) 1868
34
Device engineeringIsolation techniques n-side
readout (I)
isolation structure needed to interrupt
the inversion layer between the strip
3 techniques available (from n-on-n technology)
p-stop
p-spray/p-stop
p-spray
high-field region depends on Qox
high-field regions
high-field regions
?
Cint, VBR degrade with radiation (Oox), better
initially
Cint, VBR improve with radiation (Oox), worse
initially
compromise
Simulations needed for each design of a detector
to find an optimum!
35
Silicon detectors for SLHC
36
n-p short strip detectors (20ltrlt60 cm)
Detector geometry Thickness300 mm, strip
pitch80 mm, implant width 18 mm, LHC speed
readout (SCT128A-HC), beta source measurements

• n-in-p standard FZ
• 40 charge loss after 3x1015 p/cm2 (23 GeV)
• 7000 e after 7.5x1015 p/cm2 (23 GeV)

• p-in-n oxygenated and standard FZ
• 25 charge loss after 5x1014 p/cm2 (23 GeV)
• over-depletion is needed

Vfd
Vfd1200 V
CCE60
Vfdgt2500 V
CCE30
P.P. Allport et al., IEEE Trans. NS 52(5) (2005)
1903.
Much better performance (same charge 6x the
fluence under-depleted operation)
37
n-p short strip detectors (20ltrlt60 cm)
recent neutron irradiated samples
T-20oC, Vbias900 V
Trapping times tend to longer than predicted at
high fluences!

• 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!
38
n-p short strip detectors super modules
LBNL proposal (evolved from CDF run IIb)
Liverpool proposal
Bridging structure
TPG baseboard
39
n-p short strip detectors shot noise STFZ
detectors
Short strips at r35 cm (3 cm x50 mm)
P. Allport et al.
CR-RC shaping
Short strips should have noise below 1000 e
dominated by series noise
25 ns shaping time
In order to keep the noise below the desired
limit ENCleaklt500e , Tlt-15oC
40
Long strip detectors (rgt60 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 BCT12.5 ns
• Smaller operational voltage needed and no
  critical issue if Vfdgtoperational bias (safety)

41
Planar n-p pixel detectors (rlt20 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)

4000e_at_1016cm-2
42
10 years of LHC (4 cm) at 1034 cm-2 s-1
10 years of SLHC (4 cm) 1034 cm-2 s-1
Threshold needed on pixel FE electronics is for
ATLAS and CMS pixels around 3500-4000 electrons!
Can we hope for better electronics?
(60,100,160V)
(500V)
more charge at lower voltages (lt300 V) with
epi-Si
(600 V)
43
3D n-p pixel detectors (rlt20 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
lt 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.
44
3D n-p pixel detectors (rlt20 cm)

• Cons.
• Columns are dead area (aspect ratio 301)
• Spatially non-homogenous CCE (efficiencyfunction
  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

• 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

45

• 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

46
Different geometry 3D sct (RD50)
C. Piemonte et al., IRST
Functioning
Sketch of the detector
n-columns
p-type substrate
grid-like bulk contact
47
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 _at_ 12 V
150 mm
300 or 500 mm
undepleted
Diode like structure CCE measurements (slow
shaping time)
Focused IR laser of 7 mm spot size 3 strips
connected to amplifier
Thickness calculated from signal
48
Different geometry 3D dct
1um
Passivation
Metal

• Designed proposed by RD50 collaboration (IRST,
  CNM, Glasgow)
• 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

0.4um
Oxide
5mm
P-stop p
50mm
n doped
10mm
TEOS 2um
300mm
Poly 3mm
p- type substrate
p doped
p doped
50mm
Oxide
Metal
55um pitch
49
Electronics deep sub micron CMOS
(ATLAS pixel, CMS all)
50
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
Bipolar SiGe transistors married to DSM-CMOS
Around 4 times smaller power consumption than
present design
51
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!
Lets wait to see first results from LHC,
before