New developments of New developments of Silicon PhotomultipliersSilicon Photomultipliers
(for PET systems)(for PET systems)
Claudio [email protected]
FBK – Fondazione Bruno Kessler, Trento, Italy
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 2
OutlineOutlineSiPMs 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.
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 3
• tiny micro GM-APD connected in parallel.• each element gives the same signal
when fired by a photon
The (analog) SiPM The (analog) SiPM
Some of the main producers:• FBK• Hamamatsu, (MPPC)• MPI-Munich• RMD (SSPM) • SensL (SPM)• ST microelectronics - Catania • Zecotek (MAPD)• …
Solid-state device
• compact (thin)• robust
• not sensitive to mag. fields
INNOVATIVE SYSTEMS
proportional information with extremely high gain Very fast response
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 4
What is available?What is available?
SEM picture
SiPM size:-from 1x1mm2 up to 4x4mm2
Cell size:- from 25x25 to 100x100um2
Most common technology:- epi silicon- poly silicon resistor
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
Single cell signal shapeSingle cell signal shape
CDn
RSn
VBDn
RQn
DIODE
CQn
CG
nth MICRO-CELL
RQ = quenching resistorCQ = parasitic cap.CG = metal parasitic cap.
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
Single cell signal shapeSingle cell signal shape
CDn
RSn
VBDn
RQn
DIODE
CQn
CG
nth MICRO-CELL
RQ = quenching resistorCQ = parasitic cap.CG = metal parasitic cap.
Current signal read out on 50 resistorfollowed by a voltage amplifier:
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
Single cell signal shapeSingle cell signal shape
CDn
RSn
VBDn
RQn
DIODE
CQn
CG
nth MICRO-CELL
0.01
0.10
1.00
-1.0E-08 4.0E-08 9.0E-08 1.4E-07Time (s)
Am
plit
ud
e (
a.u
.)
T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C`
1x1mm2 SiPM
RQ = quenching resistorCQ = parasitic cap.CG = metal parasitic cap.
fast componentdue to CQlayout dependent
slow componentdue to microcellrechargeTemp. dependentbecause of poly res.
Current signal read out on 50 resistor:
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 8
Single cell signal shapeSingle cell signal shape
CDn
RSn
VBDn
RQn
DIODE
CQn
CG
nth MICRO-CELL
0.01
0.10
1.00
-1.0E-08 4.0E-08 9.0E-08 1.4E-07Time (s)
Am
plit
ud
e (
a.u
.)
T = 25C
T = 15C
T = 5C
T = -5C
T = -15C
T = -25C`
0.01
0.10
1.00
10.00
-1.0E-08 5.0E-08 1.1E-07 1.7E-07Time (s)
Am
plit
ud
e (
a.u
.)
T = -5C
T = -15C
T = -25C
1mm2
1x1mm2 SiPM
3x3mm2 SiPM
RQ = quenching resistorCQ = parasitic cap.CG = metal parasitic cap.
fast componentdue to CQlayout dependent
slow componentdue to microcellrechargeTemp. dependentbecause of poly res.
larger cap. in parallelto 50 reshapes thesignal from themicro-cell:- no fast comp.- slower signal
Current signal read out on 50 resistor:
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 9
Intrinsic timing capabilityIntrinsic timing capability
1x1mm2 SiPM40x40um2 cell size
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.
t
G. Collazuol NIMA 581 (2007) 461–464
laser pulses
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 10
Intrinsic timing capabilityIntrinsic timing capability
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 11
Photo-detection efficiencyPhoto-detection efficiency
PDE = QE x Pt x FF
Quantum efficiency:- dielectric stack: choose appropriate dielectrics thickness and material- doping profiles: shallow implants for blue light
Avalanche probability:- electron/holes electrons should trigger the avalanche- over-voltage as high as possible
Fill factor:- each microcell has a dead border region.
1E-03
1E-02
1E-01
1E+00
1E+01
1E+02
1E+05 2E+05 3E+05 4E+05 5E+05 6E+05 7E+05
E field (V/cm)
Ioni
zatio
n R
ates
(1/
um)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
20 30 40 50 60 70 80 90 100Micro-pixel edge (um)
Are
a e
ffic
ien
cy
6um
4um
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 12
Photo-detection efficiencyPhoto-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.
0
0.05
0.1
0.15
0.2
0.25
400 450 500 550 600 650 700
Ph
oto
-de
tect
ion
eff
icie
ncy
Wavelength (nm)
PDEi_1.5VPDEi_2.5VPDEi_3.5VPDEi_4.5V
50x50m2 micro-cell
FF~50% Data obtained countingpulses from uniform low-level illumination
• n-on-p structure• QE optimized at 420nm (>90%) in air for perpendicular light
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
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28 30 32 34 36 38 40
Gai
n
Bias (V)
0.0E+00
5.0E+05
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3.0E+06
3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
13
Temperature dependenceTemperature dependence
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
Breakdown
-30C
+30C
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
Temperature dependenceTemperature dependence
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C
BreakdownDark count
-30C
+30C
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
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5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
0.0E+00
5.0E+05
1.0E+06
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2.5E+06
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3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
15
Temperature dependenceTemperature dependence
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
-45 -35 -25 -15 -5 5 15 25 35 45
Que
nchi
ng re
sist
ance
(Ohm
)
Temperature (°C)
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
-45 -35 -25 -15 -5 5 15 25 35 45
Que
nchi
ng re
sist
ance
(Ohm
)
Temperature (°C)
BreakdownDark count
Quenching resistor
-30C
+30C
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
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3.0E+06
3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
0.0E+00
5.0E+05
1.0E+06
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2.0E+06
2.5E+06
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3.5E+06
4.0E+06
4.5E+06
5.0E+06
28 30 32 34 36 38 40
Gai
n
Bias (V)
16
Temperature dependenceTemperature dependence
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
y = 0.076x + 30.934
28
29
30
31
32
33
34
35
-40 -20 0 20 40
BV (V
)
Temperature (°C)
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
0 1 2 3 4 5 6 7
Dar
k co
uts (
Hz)
Overvoltage (V)
.-30° C
.-20° C
.-10° C
0° C
10° C
20° C
30° C
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
-45 -35 -25 -15 -5 5 15 25 35 45
Que
nchi
ng re
sist
ance
(Ohm
)
Temperature (°C)
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
-45 -35 -25 -15 -5 5 15 25 35 45
Que
nchi
ng re
sist
ance
(Ohm
)
Temperature (°C)
BreakdownDark count
Quenching resistor
-30C
+30C
Temperature must be stable and possibly low!
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 17
SiPMs in PET – energy resolutionSiPMs in PET – energy resolution
Critical SiPM parameters: • photo-detection efficiency
- optical window- internal QE- triggering probability- fill factor
• density of microcells• dead time
dE/E~14%
4x4mm2 SiPM 50x50m2 cell
Example of energy spectrumwith FBK SiPMs measuredby Philips Research Aachen(corrected from saturation)
dE/E ~ 1/sqrt(N)LYSO4x4x20mm3
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 18
SiPMs in PET – timing resolutionSiPMs in PET – timing resolution
Critical SiPM parameters:
• intrinsic timingextremely 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 noisefor large SiPMs can be quite high
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 19
SiPMs in PET – timing resolution (2)SiPMs in PET – timing resolution (2)
• signal shapeoutput signal is the convolution of SiPM response and light emission
0
0.002
0.004
0.0060.008
0.01
0.012
0.014
0.016
0.018
0 30 60 90 120 150
a.u.
Time (ns)
10ns
30ns
50ns
0
0.002
0.004
0.0060.008
0.01
0.012
0.014
0.016
0.018
0 30 60 90 120 150
a.u.
Time (ns)
10ns
30ns
50ns
response to LSO (40ns dec. time)for exponential SiPM current signalwith different time constants
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 20
SiPMs in PET – timing resolutionSiPMs in PET – timing resolutionTwo 3x3mm2 SiPMs in coincidence
measurement by Philips Research Aachen
CRT<430ps FWHM
Measurement at room temperature.Decreasing temperature better results.
LYSO 3x3x15mm3
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 21
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!
Real PET system with SiPMs?Real PET system with SiPMs?
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 22
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.
Real PET system with SiPMs?Real PET system with SiPMs?
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 23
HYPERImage projectHYPERImage project
Development of hybrid TOF-PET/MR test system with improved effective sensitivity
First clinical whole body PET/MR investigations of breast cancer
consortium
final goals
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 24
Ultra compact solid-statePET detector based on SiPMs
Research on ToF-PET/MRResearch on ToF-PET/MR
Type PMT APD SiPM
MR compliant no yes yes
ToF compliant yes no yes
Why SiPMs?
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 25
The stack The SiPM tile
The ASIC tile
Building block of the PET systemBuilding block of the PET system
Mounting and measurementsat Uni. Heidelberg and Philips
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 26
2x2 array of ~4x4mm2 SiPMs2x2 array of ~4x4mm2 SiPMs
The SiPM tileThe SiPM tile
32.7mm32.7mm
• Overall fill factor ~ 84%• Flat surface for crystal mounting
700 working arrays have been delivered by FBK
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 27 27
More results at next NSS, Orlando (FL), October 2009
M. Ritzert et al., “Compact SiPM based Detector Module for Time-of-Flight PET/MR”, presented at the Real Time Conference, May 10-15, Beijing, 2009
M. Ritzert et al., “Compact SiPM based Detector Module for Time-of-Flight PET/MR”, presented at the Real Time Conference, May 10-15, Beijing, 2009
The stack worksThe stack works
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 28 28
DaSiPM2 projectDaSiPM2 project
PET tomograph for small animals proposed by Pisa Univ.
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
S. Moehrs et al., Phys. Med. Biol, pp. 1113–1127 (2006)
INFN Pisa Bari Bologna Perugia Trento
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 29
1.2cm
1.3c
m
• 8x8 array • 1.5mm element pitch• read-out on one side
Our largest areamonolithic array!!
The DASiPM2 SiPMThe DASiPM2 SiPM
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte
DaSiPM2 SiPM: breakdownDaSiPM2 SiPM: breakdown
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
1E-04
0 5 10 15 20 25 30 35
I rev
[A]
Vrev [V]
IV curves of the 64 elements of one array
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
28 29 30 31 32 33
I rev[A
]
Vrev [V] 30
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 31
0
50
100
150
200
250
300
350
400
29 30 31 32 33 34
fre
qu
en
cy
Vbd [V]
DaSiPM2 SiPM: breakdownDaSiPM2 SiPM: breakdown
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
1E-04
0 5 10 15 20 25 30 35
I rev
[A]
Vrev [V]
IV curves of the 64 elements of one array
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
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I rev
[A]
Vrev [V]
Vbd distributions on different wafers
σ ~ 0.15÷0.4V
0
50
100
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350
400
450
-0.6 -0.4 -0.2 0 0.2 0.4 0.6
fre
qu
en
cy
Vbd-Vbd_mean [V]
Vbd-Vbd_mean distributions in a matrix grouped by wafer
σ ~ 0.12V
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 32
Δ
32
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 Biodola – Isola d’Elba- Italy, May 24-30, 2009
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 Biodola – Isola d’Elba- Italy, May 24-30, 2009
Measurements at INFN PisaMeasurements at INFN Pisa
DaSiPM2 functional testsDaSiPM2 functional tests
• signal from all channels is summed;
• no gain correction
• crystal just standing on the SiPM, bad optical coupling
More functional results in a following talk by G. Bisogni
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 33
Δ
33
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 Biodola – Isola d’Elba- Italy, May 24-30, 2009
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 Biodola – Isola d’Elba- Italy, May 24-30, 2009
Measurements at INFN PisaMeasurements at INFN Pisa
DaSiPM2 functional testsDaSiPM2 functional tests
• signal from all channels is summed;
• no gain correction
• crystal just standing on the SiPM, bad optical coupling
More functional results in a following talk by G. Bisogni
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 34
ConclusionConclusion
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
TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 35
AcknowledgmentsAcknowledgments
HyperImage project
PhilipsVolkmar SchulzTorsten Solf
Uni heidelbergPeter FischerMichael Ritzer
FBKMirko MelchiorriAlessandro PiazzaAlessandro TarolliNicola Zorzi
DaSiPM2 projectAlberto Del GuerraGiuseppina BisogniGabriela LlosaSara MarcatiliGian-Franco Dalla Betta