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New developments of Silicon Photomultipliers (for PET systems) Claudio Piemonte FBK – Fondazione Bruno Kessler, Trento, Italy.

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Presentation on theme: "New developments of Silicon Photomultipliers (for PET systems) Claudio Piemonte FBK – Fondazione Bruno Kessler, Trento, Italy."— Presentation transcript:

1 New developments of Silicon Photomultipliers (for PET systems) Claudio Piemonte FBK – Fondazione Bruno Kessler, Trento, Italy

2 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 2 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.

3 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 3 tiny micro GM-APD connected in parallel. each element gives the same signal when fired by a photon 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

4 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 4 What is available? SEM picture SiPM size: -from 1x1mm2 up to 4x4mm 2 Cell size: - from 25x25 to 100x100um 2 Most common technology: - epi silicon - poly silicon resistor

5 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte Single cell signal shape C Dn R Sn V BDn R Qn DIODE C Qn CGCG n th MICRO-CELL R Q = quenching resistor C Q = parasitic cap. C G = metal parasitic cap.

6 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte Single cell signal shape C Dn R Sn V BDn R Qn DIODE C Qn CGCG n th MICRO-CELL R Q = quenching resistor C Q = parasitic cap. C G = metal parasitic cap. Current signal read out on 50 resistor followed by a voltage amplifier:

7 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte Single cell signal shape C Dn R Sn V BDn R Qn DIODE C Qn CGCG n th MICRO-CELL 1x1mm 2 SiPM R Q = quenching resistor C Q = parasitic cap. C G = metal parasitic cap. fast component due to CQ layout dependent slow component due to microcell recharge Temp. dependent because of poly res. Current signal read out on 50 resistor:

8 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 8 Single cell signal shape C Dn R Sn V BDn R Qn DIODE C Qn CGCG n th MICRO-CELL 1x1mm 2 SiPM 3x3mm 2 SiPM R Q = quenching resistor C Q = parasitic cap. C G = metal parasitic cap. fast component due to CQ layout dependent slow component due to microcell recharge Temp. dependent because of poly res. larger cap. in parallel to 50 reshapes the signal from the micro-cell: - no fast comp. - slower signal Current signal read out on 50 resistor:

9 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 9 Intrinsic timing capability 1x1mm 2 SiPM 40x40um 2 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

10 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 10 Intrinsic timing capability

11 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 11 Photo-detection efficiency PDE = QE x P t 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.

12 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 12 Photo-detection efficiency PDE = QE x P t x FF Quantum efficiency: - dielectric stack - doping profiles Avalanche probability: - electron/holes - over-voltage Fill factor: - each microcell has a dead border region. 50x50 m 2 micro-cell FF~50% Data obtained counting pulses from uniform low-level illumination n-on-p structure QE optimized at 420nm (>90%) in air for perpendicular light

13 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 13 Temperature dependence Breakdown -30C +30C

14 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte Temperature dependence Breakdown Dark count -30C +30C

15 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 15 Temperature dependence Breakdown Dark count Quenching resistor -30C +30C

16 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 16 Temperature dependence Breakdown Dark count Quenching resistor -30C +30C Temperature must be stable and possibly low!

17 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 17 SiPMs 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% 4x4mm 2 SiPM 50x50 m2 cell Example of energy spectrum with FBK SiPMs measured by Philips Research Aachen (corrected from saturation) dE/E ~ 1/sqrt(N) LYSO 4x4x20mm 3 LYSO 4x4x20mm 3

18 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 18 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

19 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 19 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

20 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 20 SiPMs in PET – timing resolution Two 3x3mm 2 SiPMs in coincidence measurement by Philips Research Aachen CRT<430ps FWHM Measurement at room temperature. Decreasing temperature better results. LYSO 3x3x15mm 3

21 TOF-PET workshop, Baia delle Zagare, 4 September C. 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?

22 TOF-PET workshop, Baia delle Zagare, 4 September C. 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?

23 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 23 HYPERImage 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

24 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 24 Ultra compact solid-state PET detector based on SiPMs Research on ToF-PET/MR TypePMTAPDSiPM MR compliantnoyes ToF compliantyesnoyes Why SiPMs?

25 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 25 The stack The SiPM tile The ASIC tile Building block of the PET system Mounting and measurements at Uni. Heidelberg and Philips

26 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 26 2x2 array of ~4x4mm 2 SiPMs The SiPM tile 32.7mm Overall fill factor ~ 84% Flat surface for crystal mounting 700 working arrays have been delivered by FBK

27 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 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 The stack works

28 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 28 DaSiPM2 project PET tomograph for small animals proposed by Pisa Univ. 4 rotating heads 3 stacked layers: 4x4cm 2 ~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

29 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte cm 1.3cm 8x8 array 1.5mm element pitch read-out on one side Our largest area monolithic array!! The DASiPM2 SiPM

30 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte DaSiPM2 SiPM: breakdown IV curves of the 64 elements of one array 30

31 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 31 DaSiPM2 SiPM: breakdown IV curves of the 64 elements of one array V bd distributions on different wafers σ ~ 0.15÷0.4V V bd -V bd_mean distributions in a matrix grouped by wafer σ ~ 0.12V

32 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 32 Δ 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 dElba- Italy, May 24-30, 2009 Measurements at INFN Pisa DaSiPM2 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

33 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 33 Δ 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 dElba- Italy, May 24-30, 2009 Measurements at INFN Pisa DaSiPM2 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

34 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 34 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 short wavelengths - decrease dark count: difficult task - new simplified interconnection with electronics

35 TOF-PET workshop, Baia delle Zagare, 4 September C. Piemonte 35 Acknowledgments HyperImage project Philips Volkmar Schulz Torsten Solf Uni heidelberg Peter Fischer Michael Ritzer FBK Mirko Melchiorri Alessandro Piazza Alessandro Tarolli Nicola Zorzi DaSiPM2 project Alberto Del Guerra Giuseppina Bisogni Gabriela Llosa Sara Marcatili Gian-Franco Dalla Betta


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