Si-detector macroscopic damage parameters during irradiation from measurements of dark current

evolution of with fluence

Craig Buttar, University of Sheffieldcollaborators

P Booth, I Dawson, PJ Dervan, C Grigson, RS Harper, R Nicholson, University of Sheffield

Maurice Glaser, CERN, Alick Macpherson, PSI/CERN

Craig Buttar NSS 2002 2

Outline

• Radiation damage in Si

• ATLAS SCT PS irradiation facility

• Current evolution with fluence

• Results from proton irradiation

• Pion irradiation at PSI

• Results from pion irradiation

• Summary of results-comparison to NIEL

Craig Buttar NSS 2002 3

Radiation effects

• Irradiation by heavy particles: s, ps,… results in displacement of atoms from their lattice sites.– Linear increase in leakage current with fluence: I=D

• Change in effective doping due to donor removal and acceptor creation– type inversion np at ~1013-1014neqcm-2

– Change in depletion voltage, primarily due to effN

At the Large Hadron Collider

•Expect levels ~1.4x1014(1MeV)neqcm-2 in regions closest to interactions-central tacking region of ATLAS and CMS

• Detector irradiation programme at CERN PS

Craig Buttar NSS 2002 4

PS Irradiation setup

30m

Temperatureand currentmonitoring

-7oC Dry N2

Atmosphere

Controlledenvironnmentbox

Proton Beam

Moving Stage

CirculatingChiller Coolant

PC

IEEE 488

RS 232

Detectors

IntelligentMotionController

Ethernet toSMTP server

• Irradiate detectors with voltage applied at ~-70C

• Monitor temperature and current during the irradiation between beam spills

• Small beam spot requires scanning of detectors

• Monitor fluence and uniformity of irradiation

• Measure fluence by activating Al foils

– measure 24Na peak at 1369keV, T1/2=16hrs

– Calibrate counter from secondary emission counter

Craig Buttar NSS 2002 5

Silicon Microstrip DetectorsBarrel detector specifications

Total area 63.6 x 64 mm2

Sensitive area 61.6 x 62 mm2

Thickness 285m

Number of strips 768+2

Pitch 80m

Readout AC-coupled Binary electronics

Craig Buttar NSS 2002 6

Model of bulk current during irradiation

e

Vd

2

ceffeff eNN 0

effNe

Vd

2

At low fluences, depletion depth is constant=> I~

Assume no annealing at ~-7oC

Depletion depth, d

1

At high fluences, depletion depth~=>I~

Current damage: I=D

Change in effective carrier concentration

5.02 e

VAI

Craig Buttar NSS 2002 7

Current evolution with proton fluence

Vb=100V

Craig Buttar NSS 2002 8

Proton Results-power laws

~I

High fluence gives good agreement with:

Results based 90 full-size ATLAS detectors

93.0~ I

Low fluence agreement is less good with

fluence rising sublinearly:

Craig Buttar NSS 2002 9

Proton Results-Damage parameters

-1-117 cm 0018.00630.0 Acm10x)13.084.4()20( Co

Craig Buttar NSS 2002 10

Module currents

4 detectors inModule

Use for on-linedosimetry

Craig Buttar NSS 2002 11

PSI-pion irradiation

• Πe1 beamline, T=191MeV

• Different operation due to beamstructure-switch-off beam to take I-Vs19ns beam with 1ns spacing

• Use ATLAS mini-detectors1cm2, from wafer with full-size detector

• ‘Portable’ cold box, chiller, monitoring system

• Guard and bulk biased seperately

Craig Buttar NSS 2002 12

Pion Irradiation Results

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 50 100 150 200 250 300 350 400

fluence (x1012cm-2)

Cu

rre

nt

(nA

)

-10.5

-10

-9.5

-9

-8.5

-8

0

2000

4000

6000

8000

10000

12000

14000

16000

0.00E+00 5.00E+13 1.00E+14 1.50E+14 2.00E+14 2.50E+14 3.00E+14 3.50E+14 4.00E+14

Integrated Fluence (x1012cm-2)

Cu

rre

nt

(nA

)1cm02.007.0)10(~

1-Acm1610x)2.02.1()20(

C

Co

o

fluencehigh - ~

fluence low- ~39.0

99.0

I

I

1.8 NIEL relative tocompare

4.05.2

*

p

Craig Buttar NSS 2002 13

Summary of results

24 GeV protons 300Mev pions

(+20oC) (4.8±0.1)x10-17Acm-1 (1.2±0.2)x10-16Acm-1

Low fluence power law 0.93 0.99

(+20oC) from [6,7] 2.5x10-17Acm-1 4.6x10-17cm-1

(-10oC) 0.063±0.002cm-1 0.07 ±0.02cm-1

High fluence power law 0.50 0.40

Craig Buttar NSS 2002 14

Summary

• A model for current evolution with fluence based on bulk current has been used to analyse detectors currents during irradiations with protons and pions

• The model appears to work well but there are deviations from the expected power laws

• Values of and have been extracted from the data and are larger than other results, but care required when comparing.

• Ratio of alpha agrees with relative NIEL-but need to reduce errors from fluence on pion measurements.

Craig Buttar NSS 2002 15

More work

• Improve model, why are there deviations from the power law ?

• Investigate effect of annealing

• Make measurements at other sites with a range of particle and energies