0. A new generation photodetector
The VSiPMT Project

1. Our goal: increase the SiPM surface
Photocathode
Focusing Ring
SiPM
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
An innovative design for a modern hybrid photodetector based on the combination of a Silicon PhotoMultiplier (SiPM) with a hemispherical vacuum glass PMT standard envelope
IFAE - Roma 10/04/2015
Felicia Barbato

2. Advantages
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
excellent photon counting
high gain (>106)
negligible power consumption (nW)
small TTS (<ns)
simplicity, compactness and robustness
IFAE - Roma 10/04/2015
Felicia Barbato

3. Advantages
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
Thanks to the SiPM
the photon counting capability of the whole device
will be improved with respect to a classical PMT
excellent photon counting
high gain (>106)
negligible power consumption (nW)
small TTS (<ns)
simplicity, compactness and robustness
IFAE - Roma 10/04/2015
Felicia Barbato

4. Advantages
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
excellent photon counting
The BIGGEST DIFFERENCE with respect to classical HPDs
high gain (>106)
negligible power consumption (nW)
In a VSiPMT the high gain is obtained by the electrons crossing the Geiger region of the SiPM. Thus we need to supply a fair HV, only to obtain electrons with the right energy to enter in the silicon bulk
small TTS (<ns)
simplicity, compactness and robustness
A new generation photodetector for astroparticle physics: the VSiPMT,
G. Barbarino et al., DOI: /j.astropartphys
IFAE - Roma 10/04/2015
Felicia Barbato

5. Advantages
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
excellent photon counting
high gain (>106)
The absence of the voltage divider leads to a much lower power consumption
negligible power consumption (nW)
small TTS (<ns)
simplicity, compactness and robustness
GREAT DEAL for such experiments operating in hostile environments (underwater, ice, space)
IFAE - Roma 10/04/2015
Felicia Barbato

6. Advantages
In the VSiPMT the dynode chain is replaced by a SiPM, thus for such a device the TTS is simply due to the electron trajectories between the
photocathode and the SiPM and so we sistematically expect a lower TTS with respect to a classical PMT.
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
excellent photon counting
high gain (>106)
negligible power consumption (nW)
The TTS is smaller for the VSiPMT than for a standard PMT.
small TTS (<ns)
simplicity, compactness and robustness
IFAE - Roma 10/04/2015
Felicia Barbato

7. Advantages
The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector.
excellent photon counting
high gain (>106)
negligible power consumption (nW)
Thanks to the absence of the dynode chain the VSiPMT will be more compact and simpler having only 3 output connections: HV, SiPM bias voltage and the output signal.
small TTS (<ns)
simplicity, compactness and robustness
IFAE - Roma 10/04/2015
Felicia Barbato

8. The first industrial prototypes
An overview on
The first industrial prototypes

9. The industrial prototypes
32 mm
33 mm
In 2013 Hamamatsu realized for us two industrial prototype, by arranging a no-windowed SiPM inside a commercial Hamamatsu HPD.
The characterization of the devices pointed out features even better than expected
IFAE - Roma 10/04/2015
Felicia Barbato

10. Well separated waveforms Excellent photon counting capability
Waveforms and spectra
Peak values istogram
MEASUREMENT CONDITIONS:
VSiPMT illuminated by a pulsed laser light at low intensity (407nm)
Oscilloscope triggered in synch with the laser
Responses for multiple triggers are overlaid
Well separated waveforms
5 mV/div
20 ns/div
Excellent photon counting capability
IFAE - Roma 10/04/2015
Felicia Barbato

11. Excellent photon counting capability
Waveforms and spectra
MEASUREMENT CONDITIONS:
VSiPMT illuminated by a pulsed laser light at low intensity (407nm)
Oscilloscope triggered in synch with the laser
Responses for multiple triggers are overlaid
20 ns/div
Excellent photon counting capability
5 mV/div
IFAE - Roma 10/04/2015
Felicia Barbato

12. Work function
HV: photoelectron transfer NO power consumption (NULL current) unlike PMTs.
LV-based gain EASY STABILIZATION
Reducing the SiO2 coating layer it will be possible to reach the plateau region at even lower voltages
Efficiency is highly stable over 3200 V.
No need for high voltage stabilization.
IFAE - Roma 10/04/2015
Felicia Barbato

13. Surface increase factor ≈ 7
Photocathode XY scan
CHARACTERISTICS:
7mm x 7mm entrance window
3 mm Ø GaAsP photocathode
1mm2 MPPC
Homogeneous efficiency
≈ 0.2 over a 7mm2 surface
Surface increase factor ≈ 7
IFAE - Roma 10/04/2015
Felicia Barbato

14. Total Gain = GVSiPMT x GAMP
Peak values hystogram
High gain (105÷106)
Linear trend
Area hystogram
Total Gain = GVSiPMT x GAMP
Ideal Working Point: 72.2V
G ≈ 6x106 (GAMP = 20);
Dark Count ≈ 60 kcps;
72.2V ≈ 3x105
IFAE - Roma 10/04/2015
Felicia Barbato

15. Transit Time Spread Laser Trigger DT distribution DT VSiPMT
spe signal DT
VSiPMT
TTS (σ) < 0.5 ns
DT distribution
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16. Decisively looks like a weak point
Dark Count Rate
High DC rates
100 – 1000 kcps
Decisively looks like a weak point
However...
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17. New generation Hamamatsu MPPCs
Dark Count Rate
New generation Hamamatsu MPPCs
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Felicia Barbato

18. ZJ4991 (100mm) has a too limited linearity
Dynamic range
What we measured
robust hint for a too strong focusing
small size of the photoelectrons beam
ZJ4991 (100mm) has a too limited linearity
The output signal saturates soon, with Nfired not exceeding 20 even under high illumination conditions
IFAE - Roma 10/04/2015
Felicia Barbato

19. VSiPMT dynamic range depends on two factors:
Focusing
VSiPMT dynamic range depends on two factors:
SiPM: linearity strongly related to the total number of pixels.
Focusing: linearity is maximized if for a photocathode uniformly illuminated all pixels are hit by the accelerated photoelectrons.
Differently from the cases of a PMT or an HPD, a too strong focusing would be deleterious because a too squeezed photoelectron spot means that not all pixels are involved, thus drastically reducing the linearity.
IFAE - Roma 10/04/2015
Felicia Barbato

20. Realization of a larger VSiPMT
A new project for the
Realization of a larger VSiPMT

21. Optimizing a prototype
We will pay a close attention on the optimization of this two parameters
VSiPMT
Main aspects
Focusing optimization
SiPM
selection
Thus we organized a plan in 5-phases
IFAE - Roma 10/04/2015
Felicia Barbato

22. How we expect the VSiPMT to be
Photocathode
How we expect the VSiPMT to be
Focusing metallic ring
SiPM
SiPM frame
HV Tab
Feedthrough
IFAE - Roma 10/04/2015
Felicia Barbato

23. Simulation for an optimized focusing
Work-plan
Phase 5
Phase 4
Phase 1
Phase 2
Phase 3
SiPM
selection
And
characteri
zation
Simulation for an optimized focusing
VSiPMT
characteri
zation
PMT
cut
VSiPMT
assembly
IFAE - Roma 10/04/2015
Felicia Barbato

24. Simulation for an optimized focusing
Phase 1
Phase 1
Simulation for an optimized focusing
The prototypes by Hamamatsu showed a linearity range much lower than expected
Focusing the photoelectrons in a wider spot will help to damp the problem
IFAE - Roma 10/04/2015
Felicia Barbato

25. Phase 1 Simulations Equipotential surfaces inside the VSiPMT.
Electroctatic potential distribution inside the VSiPMT.
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Felicia Barbato

26. Electron trajectories
Phase 1
Simulations
Electrons emission: E=1eV α=40°
Focusing ring: V=-1.95kV d=18mm
Spot: ø=3mm
Timing: TT=7.01ns TTS=0.60ns
Electron trajectories
IFAE - Roma 10/04/2015
Felicia Barbato

27. Phase 2
Phase 2
SiPM
selection
And
characteri
zation
The prototypes by Hamamatsu showed a linearity range much lower than expected
We selected a special non-windowed SiPM with a high pixel-number and a reasonable noise in order to achieve a wide dynamic range
IFAE - Roma 10/04/2015
Felicia Barbato

28. Phase 2 SiPM SiPM MPPC Hamamatsu S10943-3360 (X) n.1 V bias 67.15V
Gain
1.25 x 106
Dark Count Rate
≈ 400 kcps
Size
3x3 mm2
Pixel Size
50 µm
Number of pixels
3600
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Felicia Barbato

29. Phase 2
SiPM
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Felicia Barbato

30. Why cutting a PMT? Phase 3 Phase 3 PMT cut
We want to realize a larger prototype
We have time requirements that the collaboration with Hamamatsu can not satisfy
We are not able to deposit a photocathode, so we tried to cut a commercial PMT preserving its photocathode 1 2 3
IFAE - Roma 10/04/2015
Felicia Barbato

31. Phase 3 PRELIMINARY PMT cut Carried out in Argon gas (5.0 pure)
3-inches PMT
Band saw with diamond grinding disc
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32. Phase 3 PRELIMINARY PMT cut
The original PMT
The PMT after the cut
Unfortunately we succeed in maintaining only a fraction of the original photocathode
IFAE - Roma 10/04/2015
Felicia Barbato

33. Phase 4
Phase 4
VSiPMT
assembly
After the cut (still in Argon gas) we assemble the device by substituting a SiPM mounted on a PCB frame.
IFAE - Roma 10/04/2015
Felicia Barbato

34. VSiPMT Assembly – The SiPM frame
Phase 4
VSiPMT Assembly – The SiPM frame K A HV K A
Getters
GND
Grounded
copper mask
TOP VIEW
BOTTOM VIEW
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Felicia Barbato

35. Phase 4 PRELIMINARY VSiPMT Assembly HV tab SiPM frame 3x3mm2 SiPM
Vacuum feedthrough
Centering disc
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Felicia Barbato

36. Phase 4 PRELIMINARY VSiPMT Assembly IFAE - Roma 10/04/2015
Felicia Barbato

37. VSiPMT Assembly – The final product
Phase 4
VSiPMT Assembly – The final product
PRELIMINARY
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Felicia Barbato

38. Conclusions

39. Why should we realize a larger VSiPMT?
The VSiPMT key words
Photon counting capability
Low power consumption
Large sensitive surface
Good timing performances (low TTS)
High stability (not depending on HV)
All this features make the VSiPMT to be the answer to many big astroparticle physics experiments
IFAE - Roma 10/04/2015
Felicia Barbato

40. We hope to succeed by the end of the year
The idea
Start
Proof of feasibility
Proof
First prototype
Prototype
3-in prototype
3-inches
2007
2012
2013
2015
We hope to succeed by the end of the year
We are here
IFAE - Roma 10/04/2015
Felicia Barbato

41. Thank You !

42. Why we should choose the VSiPMT?
Features
PMT
VSiPMT
Comparison
Efficiency
QEphotocathodex ε1dynode(0.8)
QEphotocathodex FillFactor(twd 1)
≈equivalent
Gain
Timing ns
Fraction of ns
(no dynode spread)
Linearity
Depending on gain
Depending on #cells
Power Consumption
Divider Dissipation
VSiPMT: No dissipation
Amp. (G=10-20): <5mW
Power Supply Stability
HV Stabilization
LV easy stabilization
Dark counts rate (new)
≈ 0.5pe
≈ few
≈equivalent (today)
Photon Counting
Difficult
Excellent
Afterpulse (new)
VSiPMT (today)
Peak-to-valley ratio ≈3
>60
IFAE - Roma 10/04/2015
Felicia Barbato