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Development of the first prototypes of Silicon Photomultiplier at ITC-irst

Development of the first prototypes of Silicon Photomultiplier at ITC-irst. N. Dinu , R. Battiston, M. Boscardin, F. Corsi, GF. Dalla Betta, A. Del Guerra, G. Llosa-Llacer, M. Ionica, G. Levi, S. Marcatili, C. Marzocca, C. Piemonte, G. Pignatel, A. Pozza, L. Quadrani, C. Sbarra, N. Zorzi

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Development of the first prototypes of Silicon Photomultiplier at ITC-irst

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  1. Development of the first prototypes ofSilicon Photomultiplier at ITC-irst N. Dinu, R. Battiston, M. Boscardin, F. Corsi, GF. Dalla Betta, A. Del Guerra, G. Llosa-Llacer, M. Ionica, G. Levi, S. Marcatili, C. Marzocca, C. Piemonte, G. Pignatel, A. Pozza, L. Quadrani, C. Sbarra, N. Zorzi representing the INFN – ITC-irst collaboration for Development and Applications of SiPM to Medical Physics and Space Physics

  2. Outline • Motivations for new photon detectors • What is a Silicon PhotoMultiplier (SiPM)? • Characteristics of the first SiPM prototypes developed at ITC-irst • Summary and outlook Nicoleta Dinu

  3. Many fields of applications require photon detectors: • Astroparticle physics (detection of the radiation in space) • Nuclear medicine (medical imaging) • High energy physics (calorimetry) • Many others ..……… • Characteristics to be fulfilled by the photon detector candidate: • Highest possible photon detection efficiency • (blue –green sensitive) • High speed • High internal gain • Single photon counting resolution • Low power consumption • Robust, stable, compact • Insensitive to magnetic fields • Low cost Nicoleta Dinu

  4. A look on photon detectors characteristics Nicoleta Dinu

  5. Rquenching Current (a.u.) -Vbias Standardized output signal Time (a.u.) APDs in Geiger mode (GM-APD) • Quenching circuits development: • F. Zappa & all, Opt. Eng. J., 35 (1996) 938 • S. Cova & all, App. Opt. 35 (1996) 1956 Reach-through diode J.R. McIntire, IEEE Trans. El. Dev. ED-13 (1966) 164 Planar diode R. H. Haitz, J.App.Phys. Vol. 36, No. 10 (1965) 3123 The main disadvantage for many applications It is a binary device: One knows there was at least one electron/hole initiating the breakdown but not how many of them Nicoleta Dinu

  6. Front contact Out Current (a.u.) h Rquenching Two pixels fired Al Threepixels fired One pixel fired ARC n+ n pixels n+ p p  p+ silicon wafer Back contact Time (a.u.) - Vbias -Vbias What is a SiPM ? • matrix of n microcells in parallel • each microcell: GM-APD + Rquenching • Main inventors:V. M. Golovin and A. Sadygov • Russian patents 1996-2002 The advantage of the SiPM in comparison with GM-APD ANALOG DEVICE – the output signal is the sum of the signals from all fired pixels SiPM – photon detector candidate for many future applications Nicoleta Dinu

  7. Our activity for SiPM development • SiPM: INFN – ITC-irst research project • technological development of SiPM devices of 1 mm2 • matrix of few cm2 using SiPMs of 1 mm2 for Medical and Space Physics applications • Groups involved • ITC-irst – Institute for Scientific and Technological Research, Trento • simulations, design and layout • fabrication • electrical and functional characterization of the SiPM devices • INFN – Pisa, Perugia, Bologna, Bari, Trento branches • electrical and functional characterization of the SiPM devices • development of the read-out electronics • functional characterization of the system composed of SiPM and read-out electronics for medical (PET) and space (TOF) applications • 1.5 year activity • simulations, design and layout • first run fabrication • characterization of the first SiPM prototypes • the second run fabrication with optimised parameters finishes next week Nicoleta Dinu

  8. Simulations • Aim: to identify the most promising configuration for: • Doping layers • the optimum dopant concentration of the implants which gives a breakdown voltage • in the range 20 - 50 V • Layout design • to avoid breakdown developing at junctions borders • Optimum photon detection efficiency in the blue region • QE (wavelength dependent) optimisation • minimize the amount of light reflected by the Si surface • maximize the generation of e-h pair in the depletion region • avalanche optimisation • maximization of the breakdown initiation probability • geomoptimisation • minimize the dead area around each micro-cell (uniform breakdown and optical • isolation through trenches) Nicoleta Dinu

  9. Layout & Fabrication Process • Layout includes: • several SiPM designs with different implant geometries • test structures for process monitoring • test structures for analysis of the SiPM behavior • First fabrication run completed in September 2005 • Main characteristics: • p-type epitaxial substrate • n+ on p junctions • poly-silicon quenching resistance • anti-reflective coating optimized for short wavelength light Nicoleta Dinu

  10. Main block Wafer SiPM 1 mm 1 mm Wafer and SiPM design • SiPM geometric characteristics: • area: 1 x 1 mm2 • number of micro-cells: 625 • micro-cell size: 40 x 40 m2 Nicoleta Dinu

  11. Single micro-cell test structures VBD = 31 V SiPM (625 micro-cells) VBD = 31 V IV & breakdown • Uniform breakdown voltage VBD for different micro-cell and SiPM devices over the wafer • Uniform working point Vbiasfor different SiPM devices • Vbias= VBD + V, V  3 V • very important when matrix of many SiPMs devices of 1mm2 are built Nicoleta Dinu

  12. Single micro-cell test structures Quenching resistance • Uniform micro-cell quenching resistance over the wafer SiPM (625 micro-cells) • Uniform SiPM quenching resistance over the wafer • Very good correlation between Rmicro-cell and RSiPM Nicoleta Dinu

  13. rise time recovery time SiPM internal gain • Gain: • linear variable with Vbias • in the range 5x105 2x106 • micro-cell capacitance • Cmicro-cell = 48fF • micro-cell recovery time •  = Rquenching · Cmicro-cell~ 20 ns • Rise time •  1 ns (limited by the read-out • system) Nicoleta Dinu

  14. SiPM dark count • Room temperature (~ 23°C) • 1 p.e. dark count rate: ~ 3MHz • 3 p.e. dark count rate: ~ 1kHz • Mention: • trenches for the optical • isolation between micro-cells • were not implemented in the • first run 34.5 V 32.0 V 33.5 V 34.0 V 32.5 V 33.0 V • Dark count rate • linear variable with Vbias • increases with the temperature Nicoleta Dinu

  15. 4 p.e. 5 p.e. 3 p.e. 6 p.e. 2 p.e. 7 p.e. 1 p.e. 0 Excellent single photoelectron resolution Single photon counting capability • A LED was pulsed at low-light-level to record the single photoelectron spectrum Nicoleta Dinu

  16. Summary and outlook • SiPM - a research project of our INFN – ITC-irst collaboration team • Characteristics of the first SiPM prototypes developed by ITC-irst • SiPM area: 1 mm2, 625 micro-cells, size: 40 x 40 m2 • Uniform breakdown voltage (VBD~ 31 V)  uniform working point • Uniform micro-cell quenching resistance: Rquenching ~ 320 k • Fast signals (rise time ~ 1 ns, small recovery time  ~ 20 ns) • High internal gain, linear variable with the overvoltage: 5 x 105  2 x 106 • Dark count rate: ~ MHz @ 3 V overvoltage and room temperature • Excellent photon counting resolution • Outlook • The characterization of the prototypes is in progress……. • The second run fabrication with optimised parameters (dark count rate and optical cross-talk) finishes next week Nicoleta Dinu

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