Gunnar Lindstroem – University of HamburgHamburg workshop 24-Aug-061 Radiation Tolerance of Silicon Detectors The Challenge for Applications in Future

Gunnar Lindstroem – University of Hamburg Hamburg workshop 24-Aug-06 1

Radiation Tolerance of Silicon Detectors The Challenge for Applications

in Future High Energy Physics Experiments

Gunnar Lindstroem, University of Hamburg


LHCproperties

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 secExpected 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 low voltage operation in normal ambients

Intense radiation field Radiation tolerance up to during 10 years 1015 hadrons/cm²

Feasibility, e.g. large scale availability200 m² for CMS known technology, low cost

Silicon Detectors: Favorite Choice for Particle Tracking

! Silicon Detectors meet all Requirements !

Example: Large Hadron Collider LHC, start 2007


LHC ATLAS Detector – a Future HEP Experiment

Overall length: 46m, diameter: 22m, total weight: 7000t, magnetic field: 2TATLAS collaboration: 1500 members

micro-strip detectorfor particle tracking

principle of a silicon detector: solid state ionization chamber

For innermost layers: pixel detectors 2nd general purpose experiment:

CMS, with all silicon tracker!


Main motivations for R&D on Radiation Tolerant Detectors: Super - LHC

• LHC upgrade LHC (2007), L = 1034cm-2s-1

(r=4cm) ~ 3·1015cm-2

Super-LHC (2015 ?), L = 1035cm-2s-1

(r=4cm) ~ 1.6·1016cm-2

• LHC (Replacement of components) e.g. - LHCb Velo detectors (~2010) - ATLAS Pixel B-layer (~2012)

• Linear collider experiments (generic R&D)Deep understanding of radiation damage will be fruitful for linear collider experiments where high doses of e, will play a significant role.

10 years

500 fb-1

5 years

2500 fb-1

5

0 10 20 30 40 50 60

r [cm]

1013

5

1014

5

1015

5

1016

eq

[cm

-2]

total fluence eqtotal fluence eq

neutrons eq

pions eq

other charged

SUPER - LHC (5 years, 2500 fb-1)

hadrons eqATLAS SCT - barrelATLAS Pixel

Pixel (?) Ministrip (?)

Macropixel (?)

(microstrip detectors)

[M.Moll, simplified, scaled from ATLAS TDR]

CERN-RD48

CERN-RD50


Radiation Damage in Silicon Sensors

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 !


Deterioration of Detector Properties by displacement damage NIEL

10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104

particle energy [MeV]

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

D(E

) / (

95 M

eV m

b)

neutronsneutrons

pionspions

protonsprotons

electronselectrons

100 101 102 103 104

0.4

0.60.8

1

2

4

neutronsneutrons

pionspions

protonsprotons

Point defects + clusters

Dominated by clusters

Damage effects generally ~ NIEL, however differences between proton & neutron damage important for defect generation in silicon bulk


Radiation Damage – Leakage current

1011 1012 1013 1014 1015

eq [cm-2]

10-6

10-5

10-4

10-3

10-2

10-1

I /

V

[A/c

m3 ]

n-type FZ - 7 to 25 Kcmn-type FZ - 7 Kcmn-type FZ - 4 Kcmn-type FZ - 3 Kcm

n-type FZ - 780 cmn-type FZ - 410 cmn-type FZ - 130 cmn-type FZ - 110 cmn-type CZ - 140 cm

p-type EPI - 2 and 4 Kcm

p-type EPI - 380 cm

[M.Moll PhD Thesis][M.Moll PhD Thesis]

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

Increase of Leakage Current

eqV

I

α

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

Consequence: Cool detectors during operation! Example: I(-10°C) ~1/16 I(20°C)

1 10 100 1000 10000annealing time at 60oC [minutes]

0

1

2

3

4

5

6

(t)

[10

-17 A

/cm

]

1

2

3

4

5

6

oxygen enriched silicon [O] = 2.1017 cm-3

parameterisation for standard silicon [M.Moll PhD Thesis]

80 min 60C

with time (annealing):

Tk

EI

B

g

2exp

…. with particle fluence:


Radiation Damage – Effective doping concentration

n+ p+ n+

10-1 100 101 102 103

eq [ 1012 cm-2 ]

1

510

50100

5001000

5000

Ude

p [V

] (

d =

300

m)

10-1

100

101

102

103

| Nef

f | [

1011

cm

-3 ]

600 V

1014cm-2

type inversion

n-type "p-type"

[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]

p+

Change of Depletion Voltage Vdep (Neff)

“Type inversion”: Neff changes from positive to

negative (Space Charge Sign Inversion)

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)

…. with time (annealing):

NC

NC0

gC eq

NYNA

1 10 100 1000 10000annealing time at 60oC [min]

0

2

4

6

8

10

N

eff [

1011

cm-3

]

[M.Moll, PhD thesis 1999, Uni Hamburg]

before inversion after inversion

„Hamburg model“

…. with particle fluence:

Consequence: Cool Detectors even during beam off (250 d/y)alternative: acceptor/donor compensation by defect enginrg.,e.g. see developm. with epi-devices (Hamburg group)


Radiation Damage – Charge carrier trapping

Deterioration of Charge Collection Efficiency (CCE) by trapping

Trapping is characterized by an effective trapping time eff for electrons and holes:

tQtQ

heeffhehe

,,0,

1exp)(

defects

heeff

N,

1

where:

0 2.1014 4.1014 6.1014 8.1014 1015

particle fluence - eq [cm-2]

0

0.1

0.2

0.3

0.4

0.5

Inve

rse

trap

ping

tim

e 1

/ [n

s-1]

data for electronsdata for electronsdata for holesdata for holes

24 GeV/c proton irradiation24 GeV/c proton irradiation

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

….. and change with time (annealing):

5 101 5 102 5 103

annealing time at 60oC [min]

0.1

0.15

0.2

0.25

Inve

rse

trap

ping

tim

e 1

/ [n

s-1]

data for holesdata for holesdata for electronsdata for electrons

24 GeV/c proton irradiation24 GeV/c proton irradiationeq = 4.5.1014 cm-2 eq = 4.5.1014 cm-2

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

Increase of inverse trapping time (1/) with fluence

Consequence: Cooling does not help but:use thin detectors (~100m) and p-type Si,

listen to Gregors talk!

Charge trapping leads to very small e,h at eq = 1016/cm²


Summary

Silicon Detectors in the inner tracking area of future colliding beam experiments have to tolerate a hadronic fluence of up to eq = 1016/cm²

Deterioration of the detector performance is largely due to bulk damage caused by non ionizing energy loss of the particles

Reverse current increase (originating likely from both point defects and clusters) can be effectively reduced by cooling. Defect engineering so far not successful

Change of depletion voltage severe, also affected by type inversion and annealing effects. Modification by defect engineering possible, for standard devices continuous cooling essential (freezing of annealing)

Charge trapping lilely the ultimate limitation for detector application, responsible trapping centers widely unknown, cooling and annealing have little effects

Documents

Gunnar Lindstroem – University of HamburgHamburg workshop 24-Aug-061 Radiation Tolerance of Silicon Detectors The Challenge for Applications in Future