si-detector macroscopic damage parameters during irradiation from measurements of dark current...
TRANSCRIPT
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