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Development of SiPMs
a FBK-irst
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FBK – Fondazione Bruno Kessler, Trento, Italy
[email protected]
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Outline
• Important parameters of SiPM
• Characteristics of FBK-irst SiPMs
• Application of FBK-irst SiPM
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General view of the important
parameters in a SiPM
- Gain
- Noise
- Photo-detection efficiency
- Dynamic range
- Time resolution
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Gain
number of carriers produced per photon absorbed
i
~(VBIAS-VBD)/RQ
~exp(-t/RS*CD)
exp(-t/RQ*CD)
t
charge collected per event is the area of the exponential
decay which is determined by circuital elements and bias.
Gain = IMAX*t
(VBIAS-VBD)*t
(VBIAS-VBD)*CD
__Q = ________
__Q = ____________
q
RQ
q
q
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NOISE
1) Primary DARK COUNT
False current pulses triggered by non photogenerated carriers
Main source of carriers: thermal generation in the depleted region.
Critical points: quality of epi silicon; gettering techniques.
2) Afterpulsing:
secondary current pulse caused by a carrier released by a trap
which was filled during the primary event.
3) Optical cross-talk
Excitation of neighboring cells due to the emission of
photons during an avalanche discharge
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Photodetection efficiency
PDE = Npulses / Nphotons = QE x P01x FF
1. QE Quantum efficiency is the probability for a photon to
generate a carrier that reaches the high-field region.
Maximization: anti-reflective coating, drift region location
2. P01. triggering probability probability for a carrier traversing the
high-field to trigger the avalanche.
Maximization: 1. high overvoltage
2. photo-generation in the p-side of the junction
(electrons travel through the high-field region)
3. FF. Fill Factor
“standard” SiPMs suffer from low FF due to the
structures present around each micro-cell
(guard ring, trench)
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micro-cell
dead width
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Time resolution
Statistical Fluctuations in the first stages of the current growth:
1. Photo-conversion depth
2. Vertical Build-up at the very beginning of the avalanche
t=0
pair generation
0<t<t1 drift to the high-field region
t>t1
avalanche multiplication
* for short wavelength light
the first contribution is negligible
t1
t’1
single carrier
current level
3. Lateral Propagation
the avalanche spreading is faster if
generation takes place in the center
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FBK-irst SiPMs
Development of SiPMs started in 2005 in
collaboration with INFN.
• IRST:
development of the technology for the production of SiPMs
(large area devices/matrices) + functional characterization
• INFN (Pisa, Bari, Bologna, Perugia, Trento):
development of systems, with optimized read-out electronics,
based on SiPMs for applications such as:
- tracking with scintillating fibers;
- PET;
- TOF;
- calorimetry
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[C. Piemonte
“A new Silicon Photomultiplier
structure for blue light detection”
NIMA 568 (2006) 224-232]
IRST technology
20
n+
7E+05
p
guard region
n+
p
p epi
p+ subst.
Doping conc. (10^) [1/cm^3]
19
6E+05
Doping
Field
18
5E+05
17
4E+05
16
3E+05
15
2E+05
14
1E+05
13
0E+00
0
0.2
0.4
0.6
0.8
depth (um)
High field
region
1
1.2
1.4
Drift region
1) Substrate: p-type epitaxial
2) Very thin n+ layer
3) Polysilicon quenching resistance
4) Anti-reflective coating optimized for l~420nm
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E field (V/cm)
Shallow-Junction SiPM
Layout: from the first design…(2005)
SiPM structure:
- 25x25 cells
- microcell size: 40x40mm2
1mm
1mm
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Geometry NOT optimized
for maximum PDE
(max fill factor ~ 30%)
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… to the new devices (i) (2007)
Fill factor: 40x40mm2 => ~ 40%
50x50mm2 => ~ 50%
100x100mm2 => ~ 76%
Geometries:
1x1mm2
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2x2mm2
3x3mm2 (3600 cells)
4x4mm2 (6400 cells)
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…to the new devices (ii)
Circular: diameter 1.2mm
diameter 2.8mm
Matrices: 4x4 elements
of 1x1mm2 SiPMs
Linear arrays:
8,16,32 elements of
1x0.25mm2 SiPMs
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Tests performed at FBK
• IV measurement
fast test to verify functionality and uniformity of the properties.
C. Piemonte et al.
“Characterization of the first prototypes
of SiPM fabricated at ITC-irst”
IEEE TNS, February 2007
• Functional characterization in dark
for a complete characterization of the output signal and
noise properties (signal shape, gain, dark count, optical cross-talk, after-pulse)
• Photo-detection efficiency
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Static characteristic (IV)
Matrix 4x4 1-9IV
Reverse
SiPM4 - W12
1.E-05
Breakdown current:
determined by dark events
1.E-06
1.E-07
I [A]
Breakdown voltage
1.E-08
1.E-09
Leakage current: mainly due to
surface generation at the
micro-diode periphery
1.E-10
1.E-11
0
5
10
15
20
Vrev [V]
25
30
35
Very useful fast test. Gives info about:
- Device functionality
- Breakdown voltage
- (Dark rate)x(Gain) uniformity
- Quenching resistance (from forward IV)
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Performed on
several thousands of
devices at wafer level
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Signal properties – NO amplifier
Dark signals are exactly equal to photogenerated signals
functional measurements in dark give a complete
picture of the SiPM functioning
Thanks to the large gain it is possible to connect the SiPM
directly to the scope
7.E-03
VBIAS
SiPM: 1x1mm2
Cell: 50x50mm2
SiPM
Digital
Scope
50W
Amplitude (V)
6.E-03
5.E-03
4.E-03
3.E-03
2.E-03
1.E-03
0.E+00
0.0E+00
1.0E-07
2.0E-07
3.0E-07
4.0E-07
Time (s)
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Signal properties – NO amplifier
pedestal.
1p.e. 2
800
700
~ns
Counts
Pulse gen.
Excellent
cell
uniformity
3
600
500
4
400
300
200
100
Laser
0
0
20
40
SiPM
60
80
Charge (a.u.)
100
120
3.5E+06
3.0E+06
Pulse area
= charge
Gain
histogram
collection
2.5E+06
2.0E+06
1.5E+06
Linear
gain
1.0E+06
5.0E+05
0.0E+00
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33
34
Bias voltage (V)
35
36
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Signal properties – with amplifier
A voltage amplifier allows an easier characterization,
but attention must be paid when determining the gain
Pulses at the scope.
VBIAS
SiPM
Av
100x
50W
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Digital
Scope
s = single
d = double pulses
a = after-pulse
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Let’s look at the electro-optical characteristics of
these devices:
1x1mm2 (400 cells)
4x4mm2 (6400 cells)
Micro-cell size: 50x50mm2
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1x1mm2 SiPM - 50x50mm2 cell
Set up: SiPM current signal converted into voltage on a 50W
resistor and amplified with a wide-band voltage amplifier.
1.2
1.00
Signal shape
1.0
Amplitude(a.u.)
(a.u.)
Amplitude
Fast transient:
avalanche current
through parasitic
capacitance in
parallel with
quenching res.
0.8
0.6
0.10
0.4
`
= 25C
T =T25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C
0.2
0.0
0.01
-1.00E-08
-1.0E-08
4.00E-08
4.0E-08
9.00E-08
9.0E-08
Time
Time (s)
(s)
Slow transient:
Exponential recharge
of the diode capac.
through the
quenching resistor
1.40E-07
1.4E-07
Important to note:
The value of the quenching resistor increases with decreasing
temperature and so the time constant follows the same trend
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1x1mm2 SiPM – 50x50mm2 cell
Dark count
Growing
threshold
1.0E+06
1.0E+03
DC 28
DC 28.5
DC 29
DC 29.5
DC 30
DC 30.5
DC 31
DC 32
DC 33
1.0E+02
-0.70
-0.60
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Counts
1.0E+05
From this plot we get
idea of dark rate and
optical cross-talk
probability
T = -30C VBD = 27.2V
1.0E+04
-0.50
-0.40
-0.30
Threshold (V)
-0.20
-0.10
20
0.00
1x1mm2 SiPM - 50x50mm2 cell
5.0E+06
3.0E+06
31.5
Breakdown voltage (V)
4.0E+06
Gain
Gain
T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C
2.0E+06
1.0E+06
0.0E+00
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30.5
30
29.5
29
y = 0.0674x + 29.2
28.5
28
27.5
27
27
28
29
30
31
32
33
34
35
-30
-10
10
Temperature (C)
Voltage (V)
25.00
15.00
5.00
-5.00
-15.00
-25.00
1.0E+06
1.E+07
Dark count
Dark count (Hz)
Dark count (Hz)
1.0E+07
30
2V
• 2V DC
overvoltage
3V
• 3V DC
overvoltage
4V
• 4V DC
overvoltage
1.E+06
y = 1E+14e-5.213x
1.E+05
3.2
1.0E+05
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29
30
31
32
Voltage (V)
33
34
35
3.4
3.6
3.8
1000/T (1/K)
4.0
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4.2
4x4mm2 SiPM - 50x50mm2 cell
4x4mm2
3.E+06
Gain
-25C
-15C
Gain
2.E+06
1.E+06
0.E+00
28
29
30
31
32
33
Voltage (V)
Signal shape
1mm2
T = -15C
T = -25C
1.00
0.10
1mm2
0.01
-1.0E-08
Dark count
7.E+06
SiPM
16 x Dark Count
of 1mm2 SiPM
6.E+06
Dark count (Hz)
Amplitude (a.u.)
10.00
5.E+06
4.E+06
-15C
3.E+06
-25C
2.E+06
1.E+06
5.0E-08
1.1E-07 1.7E-07
Time (s)
2.3E-07
0.E+00
28
29
30
31
32
33
Voltage (V)
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4x4mm2 SiPM - 50x50mm2 cell
T=-25C Vbd=27.6V
2
1
3
28.6V
4
5
4
5
6
29.2V
3
2
Charge spectra when
illuminating the device
with short light pulses
Same conclusions as for
the previous device:
1
• Excellent cell response uniformity
4
5
6
7
8
3
29.6V
over the entire device (6400 cells)
Width of peaks dominated by
electronic noise
2
1
-5.E-10
2.E-09
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4.E-09
Charge (V ns)
6.E-09
8.E-09
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Photo-detection efficiency (1)
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Photo-detection efficiency (2)
DC curr
with light
DC curr.
wo light
dark pulses
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light pulses
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…what is the PDE of these devices?
Measured on 1x1mm2 SiPM using photon counting technique
50x50mm cell - ~50% fill factor
0.35
L=400nm
L=425nm
L=450nm
L=475nm
L=500nm
L=550nm
0.3
PDE
0.25
0.2
0.15
500nm
450nm
425nm
400nm
0.1
0.05
0
30
31
32
33
34
35
Bias voltage (V)
Broad peak between 450 and 600nm
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Time resolution (1)
• Laser: - wavelength: 400 or 800nm
- pulse width: ~60fs
- pulse period: 12.34ns with time jitter <100fs
• Filters: to have less than 1 photodetection/laser pulse
• SiPMs: 3 devices from 2 different batches measured
G. Collazuol, NIMA, 581, 461-464, 2007.
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Time resolution (2)
Distribution of the
time difference
Timing performance (s)
as a function of the
over-voltage
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Microcell functionality measurement
(measurement at RWTH Aachen)
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Microcell functionality measurement
Measurement of microcell
eficiency with a 5 um
LED spot diameter
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Microcell functionality measurement
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Some applications and
projects in which we are
involved
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SiPM matrix – for PET (1)
1mm
First, small monolithic matrix of SiPM:
Element 1x1mm2
Micro-cell size: 40x40mm2
IV
curves
of 9 matrices
of one wafer
SiPM4
- W12
Matrix 4x4 1-9
1.E-05
9x16 IV curves
Non working SiPM
1.E-06
I [A]
1.E-07
1.E-08
• Uniform BD voltage
• Uniform dark rate
1.E-09
1.E-10
1.E-11
0
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5
10
15
20
Vrev [V]
25
30
35
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SiPM matrix – for PET (2)
Tests are ongoing in Pisa
(DASiPM project, A. Del Guerra)
on these devices coupled with pixellated
and slab LSO scintillators
Na22
spectrum with LSO
on a single SiPM
Res = 18%
(1x1mm2, 40x40mm2 cell)
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NEXT STEP: Larger monolithic matrices
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Circular SiPM - 50x50mm2 cell
SiPM for CMS- Outer Hadron calorimeter
for CMS – Outer Hadron Calorimeter
Muon
in YB2
using SiPMs
SiPMs
Muonresponse
response
using
package designed by Kyocera
6mm2 area SiPM
Muon Efficiency in YB2
Baseline
HPD response
at 8 kV
Muon
response
using HPD
at 8kV
Muon Efficiency for 1 kHz noise
100%
module with
95%
18 SiPMs 90%
85%
80%
75%
70%
65%
60%
55%
50%
Each SiPM
reads a bundle
of 5 fibers
0
2.8 mm round IRST
1
2
3
4
SiPM dark current (microAmps/mm^2)
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Array of SiPM for Fiber Tracking
INFN PG (R. Battiston) + Uni Aachen
32x array connected to ASIC designed for strip detectors
=> capacitive divider at the input to reduce signal
Response uniformity under LED illumination
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HYPERimage project
Seventh Framework programme, FP7-HEALTH-2007-A
coordinator
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HYPERimage project
Development of hybrid TOF-PET/MR test systems
with dramatically improved effective sensitivity
First clinical whole body PET/MR investigations of
breast cancer
TOF-PET building blocks
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Conclusion
• The SiPM is going to play a major role as a
detector for low intensity light, because of:
- comparable/better proprieties than PMT;
- the inherent characteristics of a solid-state det..
• IRST has been working on SiPMs (GM-APDs) for about
3 years obtaining very good results in:
- performance;
- reproducibility;
- yield;
- understanding of the device.
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