piemonte 2
TRANSCRIPT
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C. Piemonte 1
Development of SiPMs
a FBK-irst
C.Piemonte
FBK – Fondazione Bruno Kessler, Trento, Italy
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C. Piemonte
Outline
• Important parameters of SiPM
• Characteristics of FBK-irst SiPMs
• Application of FBK-irst SiPM
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C. Piemonte 3
- Gain
- Noise
- Photo-detection efficiency
- Dynamic range
- Time resolution
General view of the important
parameters in a SiPM
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C. Piemonte 4
Gain = IMAX*tQ = (VBIAS-VBD)*tQ = (VBIAS-VBD)*CD __ ________ __ ____________
q RQ q q
charge collected per event is the area of the exponential
decay which is determined by circuital elements and bias.
t
i
~exp(-t/RS*CD)
~(VBIAS-VBD)/RQ
exp(-t/RQ*CD)
Gain
number of carriers produced per photon absorbed
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C. Piemonte 5
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.
NOISE
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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C. Piemonte 6
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
Photodetection efficiency
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)
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
3. Lateral Propagation
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
t1t’1
single carrier
current level
the avalanche spreading is faster if
generation takes place in the center
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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
FBK-irst SiPMs
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13
14
15
16
17
18
19
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4
depth (um)
D o p i n g c o
n c .
( 1 0 ^ ) [ 1 / c m ^ 3 ]
0E+00
1E+05
2E+05
3E+05
4E+05
5E+05
6E+05
7E+05
E
f i e l d ( V / c m )
Doping
Field
n+ p Shallow-Junction SiPM
1) Substrate: p-type epitaxial
2) Very thin n+ layer
3) Polysilicon quenching resistance
4) Anti-reflective coating optimized for l~420nm
p+ subst.
p epi
n+
[C. Piemonte
“A new Silicon Photomultiplier
structure for blue light detection”
NIMA 568 (2006) 224-232]
IRST technology
Drift regionHigh fieldregion
p
guard region
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Layout: from the first design…(2005)
SiPM structure:
- 25x25 cells
- microcell size: 40x40mm2
1mm
1mm
Geometry NOT optimized
for maximum PDE
(max fill factor ~ 30%)
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… to the new devices (i) (2007)
1x1mm2 2x2mm2 3x3mm2 (3600 cells) 4x4mm2 (6400 cells)
Fill factor : 40x40mm2 => ~ 40%
50x50mm2 => ~ 50%100x100mm2 => ~ 76%
Geometries:
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C. Piemonte 12
…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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C. Piemonte 13
• IV measurementfast test to verify functionality and uniformity of the properties.
• Functional characterization in darkfor a complete characterization of the output signal and
noise properties (signal shape, gain, dark count, optical cross-talk, after-pulse)
• Photo-detection efficiency
C. Piemonte et al.
“Characterization of the first prototypes
of SiPM fabricated at ITC-irst”
IEEE TNS, February 2007
Tests performed at FBK
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C. Piemonte 14
Leakage current: mainly due to
surface generation at the
micro-diode periphery
Static characteristic (IV)
Matrix 4x4 1-9
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
0 5 10 15 20 25 30 35
Vrev [V]
I [ A ]
SiPM4 - W12
Breakdown voltage
Breakdown current: determined by dark events
Very useful fast test. Gives info about:- Device functionality
- Breakdown voltage
- (Dark rate)x(Gain) uniformity
- Quenching resistance (from forward IV)
Reverse IV
Performed on
several thousands of
devices at wafer level
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C. Piemonte 15
Dark signals are exactly equal to photogenerated signals
functional measurements in dark give a completepicture of the SiPM functioning
Signal properties – NO amplifier
0.E+00
1.E-03
2.E-03
3.E-03
4.E-03
5.E-03
6.E-03
7.E-03
0.0E+00 1.0E-07 2.0E-07 3.0E-07 4.0E-07
Time (s)
A m p l i t u d e ( V )
Thanks to the large gain it is possible to connect the SiPM
directly to the scope
VBIAS
SiPM
50
DigitalScope
SiPM: 1x1mm2
Cell: 50x50mm2
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C. Piemonte 16
0
100
200
300
400
500
600
700
800
0 20 40 60 80 100 120
Charge (a.u.)
C o u n t s
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
31 32 33 34 35 36
Bias voltage (V)
G a i n
Pulse gen.
Laser
Pulse area
= charge
histogram
collection
SiPM
~ns
1p.e. 2
3
4
pedestal.
Excellentcell
uniformity
Linear
gain
Signal properties – NO amplifier
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C. Piemonte 17
s = single
d = double pulses
a = after-pulse
VBIAS
SiPM
50
Digital
Scope
Pulses at the scope.
Av
100x
Signal properties – with amplifier
A voltage amplifier allows an easier characterization,
but attention must be paid when determining the gain
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C. Piemonte 18
1x1mm2 (400 cells) 4x4mm2 (6400 cells)
Let’s look at the electro-optical characteristics of
these devices:
Micro-cell size: 50x50mm2
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C. Piemonte 19
1x1mm2 SiPM - 50x50mm2 cell
0.01
0.10
1.00
-1.0E-08 4.0E-08 9.0E-08 1.4E-07
Time (s)
A m p l i t u d e ( a . u . )
T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C
Signal shapeFast transient:
avalanche current
through parasitic
capacitance in
parallel with
quenching res.
Slow transient:
Exponential recharge
of the diode capac.
through the
quenching resistor
Important to note:
The value of the quenching resistor increases with decreasing
temperature and so the time constant follows the same trend
Set up: SiPM current signal converted into voltage on a 50W
resistor and amplified with a wide-band voltage amplifier.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-1.00E-08 4.00E-08 9.00E-08 1.40E-07
Time (s)
A m p l i t u d e
( a . u . )
T = 25C
Signal shape
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C. Piemonte 20
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
-0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00
Threshold (V)
C o
u n t s
DC 28
DC 28.5
DC 29
DC 29.5
DC 30
DC 30.5DC 31
DC 32
DC 33
1x1mm2 SiPM – 50x50mm2 cell
Dark count
Growing
thresholdT = -30C VBD = 27.2V
From this plot we get
idea of dark rate and
optical cross-talk
probability
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C. Piemonte 21
1x1mm2 SiPM - 50x50mm2 cell
1.0E+05
1.0E+06
1.0E+07
27 28 29 30 31 32 33 34 35Voltage (V)
D a r k c o u n t
( H z
25.00
15.00
5.00
-5.00
-15.00
-25.00
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
27 28 29 30 31 32 33 34 35
Voltage (V)
G a i n
T = 25C
T = 15C
T = 5C
T = -5CT = -15C
T = -25C
Gain
Dark count
y = 0.0674x + 29.2
27
27.5
28
28.5
29
29.5
30
30.5
31
31.5
-30 -10 10 30Temperature (C)
B r e a k d o w n v o l t a g e
( V
y = 1E+14e-5.213x
1.E+05
1.E+06
1.E+07
3.2 3.4 3.6 3.8 4.0 4.2
1000/T (1/K)
D a r k c o u n t ( H z )
DC 2V
DC 3V
DC 4V
• 2V overvoltage
• 3V overvoltage
• 4V overvoltage
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C. Piemonte 22
4x4mm2 SiPM - 50x50mm2 cell4x4mm2
0.01
0.10
1.00
10.00
-1.0E-08 5.0E-08 1.1E-07 1.7E-07 2.3E-07Time (s)
A m p l i t u d e ( a . u . )
1mm2
T = -15C
T = -25C
Signal shape
1mm2 SiPM
0.E+00
1.E+06
2.E+06
3.E+06
4.E+06
5.E+06
6.E+06
7.E+06
28 29 30 31 32 33
Voltage (V)
D a r k c o u n t
( H z )
16 x Dark Count
of 1mm2 SiPM
-15C -25C
0.E+00
1.E+06
2.E+06
3.E+06
28 29 30 31 32 33
Voltage (V)
G a i n
-15C
-25CGain
Dark count
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C. Piemonte 23
4x4mm2 SiPM - 50x50mm2 cell
Same conclusions as forthe previous device:
• Excellent cell response uniformity
over the entire device (6400 cells)
Width of peaks dominated by
electronic noise
-5.E-10 2.E-09 4.E-09 6.E-09 8.E-09
Charge (V ns)
28.6V
29.2V
29.6V
1
2 3
4
5
1
2
3 45 6
12
3
4 5 6 7
8
T=-25C Vbd=27.6V
Charge spectra whenilluminating the device
with short light pulses
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C. Piemonte 24
Photo-detection efficiency (1)
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C. Piemonte 25
Photo-detection efficiency (2)
dark pulses light pulses
DC curr
with light
DC curr.
wo light
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C. Piemonte 26
…what is the PDE of these devices?
Measured on 1x1mm2 SiPM using photon counting technique
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
30 31 32 33 34 35
Bias voltage (V)
P D E
L=400nm
L=425nm
L=450nm
L=475nmL=500nm
L=550nm
50x50mm cell - ~50% fill factor
400nm
Broad peak between 450 and 600nm
500nm
425nm
450nm
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C. Piemonte 27
• 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
Time resolution (1)
G. Collazuol, NIMA, 581, 461-464, 2007.
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C. Piemonte 28
Time resolution (2)
Distribution of thetime difference
Timing performance (s)
as a function of theover-voltage
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C. Piemonte 29
Microcell functionality measurement
(measurement at RWTH Aachen)
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C. Piemonte
Measurement of microcell
eficiency with a 5 umLED spot diameter
Microcell functionality measurement
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C. Piemonte
Microcell functionality measurement
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C. Piemonte 32
Some applications and
projects in which we areinvolved
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C. Piemonte 33
SiPM matrix – for PET (1)
Matrix 4x4 1-9
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
0 5 10 15 20 25 30 35
Vrev [V]
I [ A ]
SiPM4 - W12IV curves of 9 matrices of one wafer
1mm
9x16 IV curvesNon working SiPM
• Uniform BD voltage
• Uniform dark rate
First, small monolithic matrix of SiPM:Element 1x1mm2
Micro-cell size: 40x40mm2
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C. Piemonte 34
Na22 spectrum with LSO
on a single SiPM(1x1mm2, 40x40mm2 cell)
Res = 18%
Tests are ongoing in Pisa(DASiPM project, A. Del Guerra)
on these devices coupled with pixellated
and slab LSO scintillators
SiPM matrix – for PET (2)
NEXT STEP: Larger monolithic matrices
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C. Piemonte 35
50%
55%
60%
65%
70%
75%80%
85%
90%
95%
100%
0 1 2 3 4
SiPM dark current (microAmps/mm^2)
M u o n E f f i c i e n c y f o r 1 k H z n o i s e
2.8 mm round IRST
SiPM for CMS- Outer Hadron calorimeter
Muon response in YB2 using SiPMs
Muon Efficiency in YB2Baseline HPD response at 8 kV
Circular SiPM - 50x50mm2 cellfor CMS – Outer Hadron Calorimeter
Muon response using SiPMs
Muon response using HPD at 8kV
package designed by Kyocera
module with
18 SiPMs
Each SiPM
reads a bundle
of 5 fibers
6mm2 area SiPM
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C. Piemonte 36
Array of SiPM for Fiber Tracking
32x array connected to ASIC designed for strip detectors=> capacitive divider at the input to reduce signal
Response uniformity under LED illumination
INFN PG (R. Battiston) + Uni Aachen
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C. Piemonte 37
HYPERimage project
Seventh Framework programme, FP7-HEALTH-2007-A
coordinator
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C. Piemonte 38
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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• 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.
Conclusion