New developments of Silicon Photomultipliers (for PET systems)

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New developments of Silicon Photomultipliers(for
PET systems)

• Claudio Piemonte
• piemonte_at_fbk.eu

FBK Fondazione Bruno Kessler, Trento, Italy
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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.
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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

• Some of the main producers
• FBK
• Hamamatsu, (MPPC)
• MPI-Munich
• RMD (SSPM)
• SensL (SPM)
• ST microelectronics - Catania
• Zecotek (MAPD)

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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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Single cell signal shape
RQ quenching resistor CQ parasitic cap. CG
metal parasitic cap.
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Single cell signal shape
Current signal read out on 50W resistor followed
by a voltage amplifier
RQ quenching resistor CQ parasitic cap. CG
metal parasitic cap.
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Single cell signal shape
Current signal read out on 50W resistor
1x1mm2 SiPM
fast component due to CQ layout dependent
slow component due to microcell recharge Temp.
dependent because of poly res.
RQ quenching resistor CQ parasitic cap. CG
metal parasitic cap.
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Single cell signal shape
Current signal read out on 50W resistor
1x1mm2 SiPM
fast component due to CQ layout dependent
slow component due to microcell recharge Temp.
dependent because of poly res.
3x3mm2 SiPM
larger cap. in parallel to 50W reshapes
the signal from the micro-cell - no fast comp. -
slower signal
RQ quenching resistor CQ parasitic cap. CG
metal parasitic cap.
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Intrinsic timing capability
laser pulses
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.
Dt
1x1mm2 SiPM 40x40um2 cell size
G. Collazuol NIMA 581 (2007) 461464
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Intrinsic timing capability
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Photo-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

• Fill factor
• each microcell has a
• dead border region.

• Avalanche probability
• electron/holes
• electrons should trigger
• the avalanche
• over-voltage
• as high as possible

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Photo-detection efficiency
PDE QE x Pt x FF

• Quantum efficiency
• dielectric stack
• doping profiles

• Fill factor
• each microcell has a
• dead border region.

• Avalanche probability
• electron/holes
• over-voltage

50x50mm2 micro-cell

• n-on-p structure
• QE optimized at 420nm
• (gt90) in air for
• perpendicular light

Data obtained counting pulses from uniform
low-level illumination
FF50
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Temperature dependence
Breakdown
-30C
30C
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Temperature dependence
Dark count
Breakdown
-30C
30C
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Temperature dependence
Dark count
Breakdown
-30C
30C
Quenching resistor
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Temperature dependence
Dark count
Breakdown
-30C
30C
Quenching resistor
Temperature must be stable and possibly low!
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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
• dead time

4x4mm2 SiPM 50x50mm2 cell
Example of energy spectrum with FBK SiPMs
measured by Philips Research Aachen (corrected
from saturation)
dE/E14
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SiPMs in PET timing resolution

• Critical SiPM parameters
• intrinsic timing
• extremely good -gt no significant impact when
  used with LSO
• photo-detection efficiency
• statistics of emitted light plays a very
  important -gt
• we must see as much light as possible -gt
• PDE as high as possible
• dark noise
• for large SiPMs can be quite high

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SiPMs in PET timing resolution (2)

• signal shape
• output signal is the convolution of SiPM
  response and light emission

response to LSO (40ns dec. time) for exponential
SiPM current signal with different time constants
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SiPMs in PET timing resolution
Two 3x3mm2 SiPMs in coincidence
LYSO 3x3x15mm3
CRTlt430ps FWHM
Measurement at room temperature. Decreasing
temperature better results.
measurement by Philips Research Aachen
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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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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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HYPERImage project
consortium
final goals
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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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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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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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The stack works
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
More results at next NSS, Orlando (FL), October
2009
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DaSiPM2 project
INFN Pisa Bari Bologna
Perugia Trento
PET tomograph for small animals proposed by Pisa
Univ.
S. Moehrs et al., Phys. Med. Biol, pp.
11131127 (2006)
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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The DASiPM2 SiPM

• 8x8 array
• 1.5mm element pitch
• read-out on one side

1.2cm
1.3cm
Our largest area monolithic array!!
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DaSiPM2 SiPM breakdown
IV curves of the 64 elements of one array
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DaSiPM2 SiPM breakdown
Vbd distributions on different wafers
IV curves of the 64 elements of one array
s 0.150.4V
Vbd-Vbd_mean distributions in a matrix grouped by
wafer
s 0.12V
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DaSiPM2 functional tests
Measurements at INFN Pisa

• 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
A. Del Guerra., Advantages and Pitfalls of the
Silicon Photomultiplier (SiPM) as Photodetector
for the Next Generation of PET scanners,
presented at the 11th Pisa Meeting on advanced
detectors, La Biodola Isola dElba- Italy, May
24-30, 2009
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DaSiPM2 functional tests
Measurements at INFN Pisa

• 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
A. Del Guerra., Advantages and Pitfalls of the
Silicon Photomultiplier (SiPM) as Photodetector
for the Next Generation of PET scanners,
presented at the 11th Pisa Meeting on advanced
detectors, La Biodola Isola dElba- Italy, May
24-30, 2009
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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 RD at FBK
• increase PDE _at_ short wavelengths
• decrease dark count difficult task
• new simplified interconnection with electronics

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Acknowledgments
FBK Mirko Melchiorri Alessandro
Piazza Alessandro Tarolli Nicola Zorzi
DaSiPM2 project Alberto Del Guerra Giuseppina
Bisogni Gabriela Llosa Sara Marcatili Gian-Franco
Dalla Betta
HyperImage project Philips Volkmar
Schulz Torsten Solf
Uni heidelberg Peter Fischer Michael Ritzer