1. C. Piemonte piemonte@fbk.eu
SiPM technology at FBK
C. Piemonte
Fondazione Bruno Kessler, Trento, Italy

2. Outline
FBK SiPM technology overview
FBK SiPM for TOF-PET
Conclusion

3. FBK expertise Silicon Radiation Sensors group (http://srs.fbk.eu)
Simulation & design
Fabrication
Device testing
750m2 clean room
equipped for
manufacturing of
silicon devices
Wafer-level testing
with manual and
fully automatic probe
stations
Lab for functional
testing
Process and
device physical
simulations
CAD design of
the sensor

4. SJ-SiPM Technology
Development started in 2005 in collaboration with INFN n+ p
Cross section
p+ subst.
p epi n+
Technology characteristics:
1) Integrated polysilicon resistor
2) Very shallow junction to enhance QE at short wavelengths
2) possible ARC to optimize QE at certain wavelengths

5. Device Layout: example of internal structure
Metal line connecting
all cells in parallel
(one common anode)
The cathode is
contacted on the
rear side.
Polysilicon
resistor
Resistor is located
around the active
area => no fill factor
loss
Field-plate
to reduce electric
field around the
junction
FF ~ 45% 40x40um2 cell
~ 55% 50x50um2 “
~ 72% 100x100um2 “

6. Device Layout: examples of SiPM geometries
Scale of the pictures is the same
2009
8x8 array of SiPMs
1.5x1.5mm pitch
50x50mm2 cell
2006
1x1mm2
40x40mm2 cell
2007
4x4mm2
50x50mm2 cell
Produced for DaSiPM (INFN project)

7. Process & Device characterization at FBK
Wafer level testing:
Automatic IVs: forward and reverse on all devices
Failure analysis in case of problems
Wafer dicing
Packaging of some samples
Functional tests:
- Dark analysis in climatic chamber
- Laser response
Photo-detection efficiency
Energy & timing resolution with scintillators

8. On-wafer automatic characterization
Reverse charact.
- Functionality of the device
- Breakdown voltage
- Dark count estimate
4 elements of the array
Forward charact.
- Functionality of the device
- Resistor value estimate
4 elements of the array

9. Example of faulty device
Most common defect is premature breakdown
Reverse IV plot
Working SiPM.
The current can
be roughly modeled
as I=q*DC*G
Vbd
light emission
SiPM with 1 defective cell.
I=(V-Vbd)/Rq

10. … after packaging… Reverse IV plot Forward IV plot
Temperature (C)
Reverse IV plot
Temperature (C)
Forward IV plot
(quenching resistor value
is temperature dependent)

11. Dark analysis in climatic chamber
For each bias voltage, Labview program performs following:
original data,
pulse identification
single-cell signal
(blue),
mean signal
(red)
Dark count rate vs
threshold (blue)
pulse area
histogram (blue),
baseline (red)
under
construction
pulse amplitude
distribution vs
distance
pulse distance
histogram

12. Dark analysis in climatic chamber
Gain
Bias Voltage (V)
Breakdown
&
Gain
Breakdown voltage (V)
Temperature (C)
76mV/C
Gain shift (1/K)
Bias Voltage (V)

13. Dark analysis in climatic chamber
Dark count
doubles every 10C
temperature increase
Dark count rate (HZ/mm2)
Over-Voltage (V)
Quenching resistor
increasing with
decreasing temperature
Quenching resistance (ohm)
Temperature (C)

14. Photo-detection efficiency
Measured with low level constant light
PoissonLight - PoissonDark
PDE =
Number of incident photons
50x50um2 cell
no after-pulses included

15. Application-oriented development
Many parameters to be considered for:
system performance optimization:
- Photo-detection efficiency
- Dark noise rate
- Correlated noise (after-pulse, optical cross-talk)
- Intrinsic timing capability
- Signal shape
- Geometry
Gain
and for real system implementation:
Temperature dependence
Operability range
packaging

16. Example: TOF-PET Time-Of-Flight Positron Emission Tomography w/o-ToF
With ToF
Info form the SiPM: Energy and timing

17. Critical SiPM parameters for TOF-PET
Photo-detection efficiency
Dark noise rate
Correlated noise
Intrinsic timing capability
Signal shape
Geometry
Gain
Temperature dependence
Operability range
packaging
SiPM parameters
Energy resolution
Timing resolution
Large complicated
system
System requirements

18. Framework of the development
HYPERimage
Development of a hybrid TOF-PET/MR test system with improved effective sensitivity
First clinical whole body PET/MR investigations of breast cancer

19. Challenges in Simultaneous ToF-PET/MR
Ultra compact, stable and reliable ToF Solid State PET Detector
Modification of MRI to enable PET integration
Interference reduction of PET with MR
Stable and high accurate MR attenuation and motion correction techniques
Identification of key applications
Philips is committed to the clinical development of the PET/MR applications
Whole body support in both PET & MR
Full clinical support to drive application development
Core components are the PET from Gemini-TF and 3T MR Achieva XR
The PET detector here is equipped with mu-metal to shield the fringe field of the MR
Fully integrated WB PET/MR currently addressed in Philips Research and within an EU program.
Here, the Achieva XR system has to be modified in order to make room for the PET detector.
However, the most challenging component in this system is the development of a new PET detector that is able to handle the large B0, GC and RF fields plus the secondary effects like vibrations and temperature.
At the moment it has not been decided whether or not such a system will enter the development process within Philips.

20. HYPERimageToF-PET The Stack Pre-clinical system The module Why SiPMs?
PMT
APD
SiPM
MR compliant no
yes
ToF compliant
WB system

21. 2008 FBK SiPM technology g g 3x3x15mm3 LYSO crystal
3x3mm2 SiPM 50x50mm2 cell
Energy spectrum Na22
Measurements by
Philips Aachen
dE/E~14% FWHM
@511keV
Energy (a.u.)
Coincidence time resolution
unfolded timing
resol. ~305ps FWHM

22. HYPERimage SiPM geometry

23. HYPERimage SiPM - production
Wafer view
2x2 array of ~4x4mm2 SiPMs
3600 cells per element
Lot production time: ~3-4 months

24. Data analysis (1) - yield
white = OK
red = premature breakdown
green/blue = problems after breakdown

25. Data analysis (2)
Breakdown voltage
Polysilicon resistor
x105

26. Solution for Scintillator coupling
bonding pad
epoxy
epoxy (120mm) Si

27. Light transmittance vs wavel.
Epoxy layer properties
Light transmittance vs wavel.
layer thickness
bonding pad
epoxy
LSO/LYSO: OK
LaBr: epoxy can be removed from active area leaving only
a support frame around the device

28. The SiPM tile 1300 working arrays delivered for the preclinical system
32.7mm
Fill factor ~ 84%
(not including SiPM FF)
Flat surface for crystal
mounting
32.7mm
500mm
1300 working arrays
delivered for the
preclinical system
PCB design and mounting
at Uni. Heidelberg and Philips

29. The stack The module First very preliminary tests: SiPM tile ASIC tile
Mounting and
measurements
at Uni. Heidelberg
and Philips
First very preliminary tests:
Energy resolution ~16% FWHM
Coincidence res. time ~670ps FWHM
=> The stack works! Now, need to optimize the set up.

30. PET performance improvementg g
4x4x22mm3
LYSO crystal
4x4mm2 SiPM 67x67mm2 cell
Na22
511keV/1.2MeV
With 2008 technology: dE/E ~ 14% and CRT ~ 460ps
Optimizing geometry and technology:
dE/E ~ 11% FWHM
(corrected for
non linear.)
CRT ~ 380ps FWHM
(timing res.
of 270ps)
Energy spectrum
CRT vs threshold
Measurement
@ Philips

31. Conclusion SiPM technology is improving quickly, meeting
requirements of the most challenging applications
FBK has a competitive technology for TOF-PET
systems:
- excellent performance;
- efficient package solution to cover large areas;
- production capability;
- effective test methodology;
Work in progress:
- new technology for higher PDE;
- new package solution.

32. Acknowledgment Many thanks to all who contributed to this work.
In particular:
FBK SRS group:
Gabriele Giacomini
Alberto Gola
Elisabetta Mazzucca
Mirko Melchiorri
Alessandro Piazza
Nicola Serra
Alessandro Tarolli
Nicola Zorzi
HyperImage:
in particular
Philips Research Aachen
University of Heidelberg
DaSiPM & MEMS projects