Download Piemonte

New developments of
Silicon Photomultipliers
(for PET systems)
Claudio Piemonte
[email protected]
FBK – Fondazione Bruno Kessler, Trento, Italy
Outline
SiPMs for PET systems
 Critical SiPM properties:
• signal shape
• intrinsic timing
• photo-detection efficiency
• temperature dependence
 Energy and timing resolution
 2 examples of innovative systems using SiPMs
• TOF-PET/MR
• multilayer detector
The data shown in the talk always refer to FBK SiPMs.
C. Piemonte
TOF-PET workshop, Baia delle Zagare, 4 September
2
The (analog) SiPM
• tiny micro GM-APD connected in parallel.
• each element gives the same signal
when fired by a photon
 proportional information
with extremely high gain
 Very fast response
Solid-state device
• compact (thin)
• robust
• not sensitive to mag. fields
INNOVATIVE SYSTEMS
C. Piemonte
Some of the main producers:
• FBK
• Hamamatsu, (MPPC)
• MPI-Munich
• RMD (SSPM)
• SensL (SPM)
• ST microelectronics - Catania
• Zecotek (MAPD)
•…
TOF-PET workshop, Baia delle Zagare, 4 September
3
What is available?
SiPM size:
-from 1x1mm2 up to 4x4mm2
Cell size:
- from 25x25 to 100x100um2
SEM picture
Most common technology:
- epi silicon
- poly silicon resistor
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TOF-PET workshop, Baia delle Zagare, 4 September
4
Single cell signal shape
RQn
CQn
CG
VBDn
CDn
RSn
DIODE
nth MICRO-CELL
RQ = quenching resistor
CQ = parasitic cap.
CG = metal parasitic cap.
C. Piemonte
TOF-PET workshop, Baia delle Zagare, 4 September
Single cell signal shape
RQn
CQn
CG
VBDn
CDn
Current signal read out on 50W resistor
followed by a voltage amplifier:
RSn
DIODE
nth MICRO-CELL
RQ = quenching resistor
CQ = parasitic cap.
CG = metal parasitic cap.
C. Piemonte
TOF-PET workshop, Baia delle Zagare, 4 September
Single cell signal shape
Current signal read out on 50W resistor:
1x1mm2 SiPM
RQn
CQn
Amplitude (a.u.)
1.00
0.10
CG
VBDn
`
CDn
0.01
-1.0E-08
RSn
4.0E-08
9.0E-08
Time (s)
DIODE
nth MICRO-CELL
RQ = quenching resistor
CQ = parasitic cap.
CG = metal parasitic cap.
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T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C
TOF-PET workshop, Baia delle Zagare, 4 September
1.4E-07
fast component
due to CQ
layout dependent
slow component
due to microcell
recharge
Temp. dependent
because of poly res.
Single cell signal shape
Current signal read out on 50W resistor:
1x1mm2 SiPM
1.00
CQn
Amplitude (a.u.)
RQn
0.10
CG
VBDn
`
CDn
0.01
-1.0E-08
4.0E-08
RSn
DIODE
10.00
9.0E-08
Time (s)
Amplitude (a.u.)
RQ = quenching resistor
CQ = parasitic cap.
CG = metal parasitic cap.
1.4E-07
T = -5C
T = -15C
T = -25C
1mm2
1.00
0.10
0.01
-1.0E-08
slow component
due to microcell
recharge
Temp. dependent
because of poly res.
3x3mm2 SiPM
nth MICRO-CELL
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T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C
fast component
due to CQ
layout dependent
5.0E-08
1.1E-07
Time (s)
TOF-PET workshop, Baia delle Zagare, 4 September
larger cap. in parallel
to 50W reshapes the
signal from the
micro-cell:
- no fast comp.
- slower signal
1.7E-07
8
Intrinsic timing capability
laser pulses
Dt
Device illuminated with ultra-short
laser pulses at fixed repetition rate.
The fluctuations of the difference in
time between successive 1 p.e.
pulses have been measured.
1x1mm2 SiPM
40x40um2 cell size
G. Collazuol
NIMA 581 (2007) 461–464
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TOF-PET workshop, Baia delle Zagare, 4 September
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Intrinsic timing capability
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TOF-PET workshop, Baia delle Zagare, 4 September
10
Photo-detection efficiency
PDE = QE x Pt x FF
Quantum efficiency:
- dielectric stack:
Avalanche probability:
- electron/holes
choose appropriate
dielectrics thickness
and material
electrons should trigger
the avalanche
Fill factor:
- each microcell has a
dead border region.
- over-voltage
- doping profiles:
as high as possible
shallow implants for
blue light
1E+02
0.9
0.8
0.7
Area efficiency
Ionization Rates (1/um)
1E+01
1E+00
1E-01
1E-02
0.6
0.5
0.4
0.3
6um
4um
0.2
0.1
1E-03
1E+05
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2E+05
3E+05
4E+05
5E+05
E field (V/cm)
6E+05
7E+05
TOF-PET workshop, Baia delle Zagare, 4 September
0
20
30
40
50
60
70
80
Micro-pixel edge (um)
90
100
11
Photo-detection efficiency
PDE = QE x Pt x FF
Quantum efficiency:
- dielectric stack
- doping profiles
Avalanche probability:
- electron/holes
- over-voltage
Fill factor:
- each microcell has a
dead border region.
50x50mm2 micro-cell
Photo-detection efficiency
0.25
• n-on-p structure
• QE optimized at 420nm
(>90%) in air for
perpendicular light
0.2
0.15
0.1
0.05
FF~50%
0
400
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450
PDEi_1.5V
PDEi_2.5V
PDEi_3.5V
PDEi_4.5V
500
550
600
Wavelength (nm)
650
700
Data obtained counting
pulses from uniform
low-level illumination
TOF-PET workshop, Baia delle Zagare, 4 September
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Temperature dependence
Breakdown
5.0E+06
4.5E+06
-30C
4.0E+06
3.5E+06
Gain
3.0E+06
2.5E+06
+30C
2.0E+06
1.5E+06
1.0E+06
5.0E+05
0.0E+00
28
30
32
34
Bias (V)
36
38
40
35
34
y = 0.076x + 30.934
BV (V)
33
32
31
30
29
28
-40
-20
0
20
40
Temperature (°C)
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TOF-PET workshop, Baia delle Zagare, 4 September
13
Temperature dependence
Dark count
Breakdown
5.0E+06
4.0E+06
.-30° C
3.5E+06
4.5E+06
Dark couts (Hz)
-30C
4.0E+06
3.5E+06
Gain
3.0E+06
2.5E+06
+30C
2.0E+06
3.0E+06
.-20° C
2.5E+06
.-10° C
2.0E+06
0° C
1.5E+06
10° C
1.0E+06
1.5E+06
1.0E+06
5.0E+05
5.0E+05
0.0E+00
0.0E+00
20° C
30° C
0
28
30
32
34
Bias (V)
36
38
1
2
40
35
34
y = 0.076x + 30.934
BV (V)
33
32
31
30
29
28
-40
-20
0
20
40
Temperature (°C)
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TOF-PET workshop, Baia delle Zagare, 4 September
3
4
Overvoltage (V)
5
6
7
Temperature dependence
Dark count
Breakdown
5.0E+06
4.0E+06
.-30° C
3.5E+06
4.5E+06
Dark couts (Hz)
-30C
4.0E+06
3.5E+06
Gain
3.0E+06
2.5E+06
+30C
2.0E+06
3.0E+06
.-20° C
2.5E+06
.-10° C
2.0E+06
0° C
1.5E+06
10° C
1.0E+06
1.5E+06
1.0E+06
5.0E+05
5.0E+05
0.0E+00
0.0E+00
30° C
0
28
30
32
34
Bias (V)
36
38
1
2
40
35
3
4
Overvoltage (V)
5
6
7
Quenching resistor
34
5.0E+05
32
31
30
29
28
-40
-20
0
20
Temperature (°C)
40
Quenching resistance (Ohm)
y = 0.076x + 30.934
33
BV (V)
20° C
4.0E+05
3.0E+05
2.0E+05
1.0E+05
0.0E+00
-45
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-35
-25
TOF-PET workshop, Baia delle Zagare, 4 September
-15
-5
5
15
Temperature (°C)
25
35
45
15
Temperature dependence
Dark count
Breakdown
5.0E+06
4.0E+06
.-30° C
3.5E+06
4.5E+06
Dark couts (Hz)
-30C
4.0E+06
3.5E+06
Gain
3.0E+06
2.5E+06
+30C
2.0E+06
3.0E+06
.-20° C
2.5E+06
.-10° C
2.0E+06
0° C
1.5E+06
10° C
1.0E+06
1.5E+06
1.0E+06
5.0E+05
5.0E+05
0.0E+00
0.0E+00
30° C
0
28
30
32
34
Bias (V)
36
38
1
2
40
3
4
Overvoltage (V)
5
6
7
Quenching resistor
35
34
5.0E+05
Quenching resistance (Ohm)
y = 0.076x + 30.934
33
BV (V)
20° C
32
31
30
29
28
-40
-20
0
20
Temperature (°C)
40
4.0E+05
3.0E+05
2.0E+05
1.0E+05
0.0E+00
-45
-35
-25
-15
-5
5
15
Temperature (°C)
25
35
45
Temperature must be stable and possibly low! 16
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TOF-PET workshop, Baia delle Zagare, 4 September
SiPMs in PET – energy resolution
dE/E ~ 1/sqrt(N)
LYSO
4x4x20mm3
Critical SiPM parameters:
• photo-detection efficiency
- optical window
- internal QE
- triggering probability
- fill factor
• density of microcells
4x4mm2 SiPM 50x50mm2 cell
• dead time
Example of energy spectrum
with FBK SiPMs measured
by Philips Research Aachen
(corrected from saturation)
C. Piemonte
dE/E~14%
TOF-PET workshop, Baia delle Zagare, 4 September
17
SiPMs in PET – timing resolution
Critical SiPM parameters:
• intrinsic timing
extremely good -> no significant impact when used with LSO
• photo-detection efficiency
statistics of emitted light plays a very important ->
we must “see” as much light as possible ->
PDE as high as possible
• dark noise
for large SiPMs can be quite high
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TOF-PET workshop, Baia delle Zagare, 4 September
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SiPMs in PET – timing resolution (2)
• signal shape
output signal is the convolution of SiPM response and light emission
0.018
0.016
10ns
0.014
0.012
a.u.
response to LSO (40ns dec. time)
for exponential SiPM current signal
with different time constants
30ns
50ns
0.01
0.008
0.006
0.004
0.002
0
0
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30
60
90
Time (ns)
120
150
TOF-PET workshop, Baia delle Zagare, 4 September
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SiPMs in PET – timing resolution
Two 3x3mm2 SiPMs in coincidence
LYSO 3x3x15mm3
CRT<430ps FWHM
Measurement at room temperature.
Decreasing temperature better results.
measurement by Philips Research Aachen
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TOF-PET workshop, Baia delle Zagare, 4 September
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Real PET system with SiPMs?
 Results are very good but they are still a bit worse than recent PMTs.
 Possibility to build large area systems?
 Cost?
probably present SiPM technology will not replace
PMTs in present PET technology!
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TOF-PET workshop, Baia delle Zagare, 4 September
21
Real PET system with SiPMs?
 Results are very good but they are still a bit worse than recent PMTs.
 Possibility to build large area systems?
 Cost?
probably present SiPM technology will not replace
PMTs in present PET technology!
On the other side, due to its solid-state nature, the SiPM becomes an
essential component in innovative systems.
2 examples will be given:
• HYPERImage - EU/FP7 funded (www.hybrid-pet-mr.eu)
• DaSiPM2 - INFN
(http://www.df.unipi.it/~fiig/)
Both examples address the important issue:
covering a large area with SiPMs.
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TOF-PET workshop, Baia delle Zagare, 4 September
22
HYPERImage project
consortium
Development of hybrid TOF-PET/MR test system with
improved effective sensitivity
final goals
First clinical whole body PET/MR investigations of breast
cancer
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TOF-PET workshop, Baia delle Zagare, 4 September
23
Research on ToF-PET/MR
Ultra compact solid-state
PET detector based on SiPMs
Why SiPMs?
Type
PMT
APD
SiPM
MR compliant
no
yes
yes
ToF compliant
yes
no
yes
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TOF-PET workshop, Baia delle Zagare, 4 September
24
Building block of the PET system
The SiPM tile
The stack
The ASIC tile
Mounting and measurements
at Uni. Heidelberg and Philips
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TOF-PET workshop, Baia delle Zagare, 4 September
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The SiPM tile
32.7mm
32.7mm
• Overall fill factor ~ 84%
• Flat surface for crystal
mounting
2x2 array of ~4x4mm2 SiPMs
700 working arrays have been
delivered by FBK
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TOF-PET workshop, Baia delle Zagare, 4 September
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The stack works
M. Ritzert et al., “Compact SiPM
based Detector Module for Time-ofFlight PET/MR”, presented at the Real
Time Conference, May 10-15, Beijing,
2009
More results at next NSS, Orlando (FL), October 2009
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TOF-PET workshop, Baia delle Zagare, 4 September
27
DaSiPM2 project
PET tomograph for small
animals proposed by Pisa Univ.
S. Moehrs et al.,
Phys. Med. Biol,
pp. 1113–1127 (2006)
INFN Pisa
Bari
Bologna
Perugia
Trento
4 rotating heads
3 stacked layers:
• 4x4cm2
• ~5mm-thick scintillator
(monolithic slab)
• SiPM read-out
Use of monolithic SiPM matrices will:
• improve spatial resolution and sensitivity
• simplify the assembly
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TOF-PET workshop, Baia delle Zagare, 4 September
28
The DASiPM2 SiPM
• 8x8 array
• 1.5mm element pitch
• read-out on one side
1.3cm
1.2cm
Our largest area
monolithic array!!
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TOF-PET workshop, Baia delle Zagare, 4 September
29
DaSiPM2 SiPM: breakdown
1E-04
IV curves of the
64 elements of
one array
1E-05
Irev [A]
1E-06
1E-07
1E-08
1E-09
1E-10
0
5
10
15
20
Vrev [V]
25
30
35
1E-05
1E-06
Irev [A]
1E-07
1E-08
1E-09
1E-10
28
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29
30
31
Vrev [V]
32
33
TOF-PET workshop, Baia delle Zagare, 4 September
30
DaSiPM2 SiPM: breakdown
1E-04
Vbd400distributions on different wafers
350
1E-05
IV curves of the
64 elements of
one array
1E-07
frequency
Irev [A]
1E-06
σ ~ 0.15÷0.4V
300
1E-08
250
200
150
100
50
1E-09
0
29
1E-10
0
5
10
15
20
Vrev [V]
25
30
30
31
32
33
34
Vbd [V]
35
Vbd-Vbd_mean distributions in a matrix
450
grouped
by wafer
1E-05
400
1E-06
350
Irev [A]
frequency
1E-07
1E-08
300
σ ~ 0.12V
250
200
150
100
1E-09
50
1E-10
28
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29
30
31
Vrev [V]
32
33
0
-0.6
-0.4
-0.2
TOF-PET workshop, Baia delle Zagare, 4 September
0
0.2
Vbd-Vbd_mean [V]
0.4
0.6
31
DaSiPM2 functional tests
Measurements
at INFN Pisa
• signal from all channels
is summed;
Δ
• no gain correction
More functional results in a following talk by G. Bisogni
• crystal just standing
on the SiPM, bad
optical coupling
A. Del Guerra., “Advantages and Pitfalls of the Silicon Photomultiplier (SiPM) as
Photodetector for the Next Generation of PET scanners””, presented at the 11 th Pisa
Meeting on advanced detectors, La
Biodolaworkshop,
– Isola d’ElbaItaly,Zagare,
May 24-30,
2009
TOF-PET
Baia delle
4 September
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32
DaSiPM2 functional tests
Measurements
at INFN Pisa
• signal from all channels
is summed;
Δ
• no gain correction
More functional results in a following talk by G. Bisogni
• crystal just standing
on the SiPM, bad
optical coupling
A. Del Guerra., “Advantages and Pitfalls of the Silicon Photomultiplier (SiPM) as
Photodetector for the Next Generation of PET scanners””, presented at the 11 th Pisa
Meeting on advanced detectors, La
Biodolaworkshop,
– Isola d’ElbaItaly,Zagare,
May 24-30,
2009
TOF-PET
Baia delle
4 September
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33
Conclusion
Status:
The SiPM is becoming a reliable and competitive object:
- performance is getting closer to PMT
- large area monolithic arrays have been produced with
satisfactory yield and first large area systems are
under construction.
Room from improvement in many aspects.
Ongoing R&D at FBK
- increase PDE @ short wavelengths
- decrease dark count: difficult task
- new simplified interconnection with electronics
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TOF-PET workshop, Baia delle Zagare, 4 September
34
Acknowledgments
FBK
Mirko Melchiorri
Alessandro Piazza
Alessandro Tarolli
Nicola Zorzi
HyperImage project
DaSiPM2 project
Alberto Del Guerra
Giuseppina Bisogni
Gabriela Llosa
Sara Marcatili
Gian-Franco Dalla Betta
Philips
Volkmar Schulz
Torsten Solf
Uni heidelberg
Peter Fischer
Michael Ritzer
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TOF-PET workshop, Baia delle Zagare, 4 September
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