Radiation hardness of the
Avalanche Photodiodes
for ECAL CMS detector
at CERN
A. Singovski
The University of Minnesota
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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APD’s in the CMS detector
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Radiation level after 10 years
Crystal
calorimeter
100
Radiation doses are in red, 104 Gy.
Neutron fluence in green 1013 neutrons/cm 2 with E > 100 keV.
Levels outside of the detector are down by a factor of 100 or more.
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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APD’s for CMS
Manufacturer:
• Hamamatsu Photonics, Japan.
Quantity:
• Two APD’s per crystal– 124,000 APD’s with
spares.
Accessibility during operation:
• None.
Radiation levels:
• Maximum expected dose 200 kGy and 2 1013
neutrons/cm2.
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Basic APD Structure:
Junction
Si2N4 AR
coating
5  5 mm2
active area
Groove to
minimize surface
leakage current.
RESMDD02 July 10-12 2002, Florence,
APD is grown
epitaxially on
an n++ wafer.
A.Singovski, University of Minnesota
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APD radiation damage
Radiation damage of APD can influence ECAL
performance by essentially two effects:
-rise of the bulk current  increase APD
noise contribution to the energy resolution
-early breakdown  breakdown happens
before APD can reach operation point at
Gain=50
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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APD contribution to the ECAL resolution
E
Resolution:
a

E
b
E ( GeV )
c
E
where,
a : due to intrinsic shower fluctuations & photo statistics
b : related to stability and reproducibility
c : noise contributions
CMS design goal : a ~3%, b~0.5%, c~200 MeV
APD contributions:
a - photo statistics (area, QE) & excess noise factor
b - gain variation with bias voltage and temperature
c - capacitance as series noise and dark current as parallel noise

to ta l

parallel

series




2
p a r a lle l
I
ds
 
2
s e r ie s
 I db M
4 kT  C
2
2
2
F
 q 
 0 .7

 
 R 
g


RESMDD02 July 10-12 2002, Florence,
M = A P D g ain
F = ex cess n o ise facto r
  = sh ap in g tim e co n stan t
q = electro n ch arg e
I d s = d ark su rface cu rren t
I d b = d ark b u lk cu rren t
R = series resistan ce
C = cap acitan ce o f A P D an d am p lifier
k = B o ltz m an n co n stan t
T = ab so lu te tem p eratu re
g = tran sco n d u ctan ce o f am p lifier
first stag e
A.Singovski, University of Minnesota
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Irradiation Tests.
Irradiation with protons:
• 70 MeV protons beam at PSI – Switzerland.
• 11013 hadrons/cm2 in ~ 2 hours.
Irradiation with gammas.
• All irradiation with
60C0
source.
Irradiation with neutrons.
• Californium source (252Cf) for irradiation at
the University of Minnesota.
• 2 1013 neutrons/cm2 in ~ 2 days.
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Device failure
Irradiation in a 70
35 beam.
MeV proton
Dark Current (mA)
30
25
20
15
10
5
0
0
1000
2000
3000
4000
5000
6000
7000
8000
Time (s)
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Neutron irradiation facility
Use old tandem
laboratory facility in
Minneapolis to store
and operate two 7 mg
sources for irradiation
samples.
•High and low flux
areas 1013 and 1011
n/cm2 in 2 – 4 days.
•Must provide biases to
components during
irradiation.
Draws for irradiation
RESMDD02 July 10-12 2002, Florence,
•Return sources after 4
years of operation.
A.Singovski, University of Minnesota
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Neutron irradiation results
7 0 5 A P D 's Irra d ia te d - In c lu d e s S o u rc e D e c a y
300
I d /M (n A ) at G a in 5 0
y = 1 .3 9 5 4 E -1 1 x
250
2
R = 8 .6 3 3 3 E -0 1
200
150
100
50
0
0 .0 E + 0 0
5 .0 E + 1 2
1 .0 E + 1 3
1 .5 E + 1 3
2 .0 E + 1 3
-2
In te g ra te d N e u tro n F lu x (n e u tro n s c m )
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Durk current
Current [m A]
Total Current (dark current + ionisation current)
20
18
16
14
12
10
8
6
4
2
0
0.00E+00
70 MeV
protons
5.00E+12
1.00E+13
1.50E+13
total Neutron Flux / cm
2.00E+13
2
Current vs Flux
25
3003006176
2802004514
Current at M=50, mkA
20
1 MeV
neutrons
from 252Cf
15
10
5
0
0
2E+12
4E+12
6E+12
8E+12
1E+13
1.2E+13
1.4E+13
Total neutron flux
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Neutron irradiation summary
1. All APD tested so far survived -> no
significant shift in breakdown voltage.
2. The mean bulk current after 2x1013
neutrons/cm2 is Id280nA (non-amplified
value).
3. It corresponds to 14mA at Gain=50 and
~ 80MeV noise contribution (no-recovery
case, CMS TDR).
Acceptable for CMS ECAL detector
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Gamma irradiation
60Co
irradiation
facility at PSI
APDs
32 wires containing 60Co
surround the probe and give
a very uniform irradiation
field.
Present activity is 2.5 kGy/h
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Gamma irradiation results
Lot 34 Breakdown Voltage Comparison
V B(irradiated)-VB(Hamamatsu) [V]
5
0
-5
-10
-15
Rejected
-20
-25
-30
8900
9000
9100
9200
9300
9400
9500
9600
APD #
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Gamma irradiation results 2
Id/Gain
APD with a
significant shift
of Vb after 60Co
irradiation
(vs. good one)
Noise
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Screening
Method:
- irradiate 100% of APD`s (0.5 Mrad) with Co-60 gamma source
(at PSI);
- measure VB and Id(V) of all irradiated APD`s 1 day after
irradiation (at PSI);
- measure noise at M=1, 50, 150, 300 before annealing (at
CERN APD Lab)
- anneal all APD`s in the oven (for 4 weeks at T=80C, at CERN
APD Lab);
- measure VB, Id(V) after annealing/ageing (at CERN APD Lab);
-reject
potentially non-reliable APD`s: ones showing
-Shift
of Vb more than 5V
-high
Id
-high
noise
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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APD rejection
High dark current
RESMDD02 July 10-12 2002, Florence,
High noise
A.Singovski, University of Minnesota
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Screening efficiency
Double irradiation (225 APDs from lot##33,34)
3
Change of VB [V]
2
1
0
-1
-2
dVB(after first Co-irr.)
-3
dVB(after annealing)
-4
dVB(after second Co-irr.)
-5
0
50
100
150
200
250
APD #
225 APD`s which passed 1st irradiation and annealing were irradiated
the 2nd time. No change of VB>2V was found for all APD`s !!!
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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Gamma irradiation summary
1. APDs are sensitive to the gamma irradiation.
2. Several percents “die” after irradiation ->
get a breakdown close to the operation point.
3. Screening, applied to 100% of APDs make
them 99.9% rad. Hard.
RESMDD02 July 10-12 2002, Florence,
A.Singovski, University of Minnesota
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