10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006 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 representing the INFN – ITC-irst collaboration for Development and Applications of SiPM to Medical Physics and Space Physics

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 2 Motivations for new photon detectors What is a Silicon PhotoMultiplier (SiPM)? Characteristics of the first SiPM prototypes developed at ITC-irst Summary and outlook Outline

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta 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

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 4 A look on photon detectors characteristics VACUUM TECHNOLOGY SOLID-STATE TECHNOLOGY PMTMCP-PMTHPDPN, PINAPDGM-APD Photon detection efficiency Blue20 % 70 %50 % Green-yellow40 % %60-70 % Red  6 % 80 % Timing / 10 ph.e  100 ps  10 ps  100 ps few nstens of ps Gain x  200 V Operation voltage1 kV3 kV20 kV V  100 V Operation in the magnetic field  T Axial magnetic field  2 T Axial magnetic field  4 T No sensitivity Threshold sensitivity (S/N  1) 1 ph.e  100 ph.e  10 ph.e  1 ph.e Shape characteristicssensible bulky compactsensible, bulky robust, compact, mechanically rugged VACUUM TECHNOLOGY SOLID-STATE TECHNOLOGY PMTMCP-PMTHPDPN, PINAPDGM-APD Photon detection efficiency Blue20 % 60 %50 %30% Green-yellow40 % %60-70 %50% Red  6 % %80 %40% Timing / 10 ph.e  100 ps  10 ps  100 ps tens nsfew nstens of ps Gain x  Operation voltage1 kV3 kV20 kV10-100V V  100 V Operation in the magnetic field  T Axial magnetic field  2 T Axial magnetic field  4 T No sensitivity Threshold sensitivity (S/N  1) 1 ph.e  100 ph.e  10 ph.e  1 ph.e Shape characteristicssensible bulky compactsensible, bulky robust, compact, mechanically rugged

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 5 R quenching -V bias 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 Current (a.u.) Time (a.u.) Standardized output signal Planar diode R. H. Haitz, J. App.Phys. Vol. 36, No. 10 (1965) 3123 Reach-through diode J.R. McIntire, IEEE Trans. El. Dev. ED-13 (1966) 164 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

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 6 What is a SiPM ? - V bias n pixels One pixel fired Two pixels fired Three pixels fired Current (a.u.) Time (a.u.) Al ARC -V bias Back contact p n+n+n+n+ p n+n+n+n+  R quenching h p + silicon wafer Front contact matrix of n microcells in parallel each microcell: GM-APD + R quenching Main inventors: V. M. Golovin and A. Sadygov Russian patents Out 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

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 7 Our activity for SiPM development SiPM: INFN – ITC-irst research project technological development of SiPM devices of 1 mm 2 matrix of few cm 2 using SiPMs of 1 mm 2 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

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta 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 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  geom optimisation minimize the dead area around each micro-cell (uniform breakdown and optical isolation through trenches)

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 9 Layout & Fabrication Process 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 Layout includes: several SiPM designs with different implant geometries test structures for process monitoring test structures for analysis of the SiPM behavior

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 10 Wafer and SiPM design Main block Wafer SiPM geometric characteristics: area: 1 x 1 mm 2 number of micro-cells: 625 micro-cell size: 40 x 40  m 2 SiPM 1 mm

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 11 IV & breakdown  Uniform breakdown voltage V BD for different micro-cell and SiPM devices over the wafer  Uniform working point V bias for different SiPM devices V bias = V BD +  V,  V  3 V very important when matrix of many SiPMs devices of 1 mm 2 are built V BD = 31 V Single micro-cell test structures V BD = 31 V SiPM (625 micro-cells)

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 12 Quenching resistance SiPM (625 micro-cells)  Uniform micro-cell quenching resistance over the wafer  Uniform SiPM quenching resistance over the wafer  Very good correlation between R micro-cell and R SiPM Single micro-cell test structures

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 13 SiPM internal gain  Gain: linear variable with V bias in the range 5 x 10 5  2 x 10 6  micro-cell capacitance C micro-cell = 48 fF rise time recovery time  micro-cell recovery time  = R quenching · C micro-cell ~ 20 ns  Rise time  1 ns (limited by the read-out system)

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 14  Room temperature (~ 23°C) 1 p.e. dark count rate: ~ 3 MHz 3 p.e. dark count rate: ~ 1 kHz  Mention: trenches for the optical isolation between micro-cells were not implemented in the first run SiPM dark count 32.0 V 32.5 V 33.0 V 33.5 V34.0 V 34.5 V  Dark count rate linear variable with V bias increases with the temperature

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 15 Single photon counting capability 0 1 p.e. 2 p.e. 3 p.e. 4 p.e. 5 p.e. 6 p.e. 7 p.e.  A LED was pulsed at low-light-level to record the single photoelectron spectrum Excellent single photoelectron resolution

10 th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006Nicoleta Dinu 16 SiPM - a research project of our INFN – ITC-irst collaboration team Characteristics of the first SiPM prototypes developed by ITC-irst SiPM area: 1 mm 2, 625 micro-cells, size: 40 x 40  m 2 Uniform breakdown voltage (V BD ~ 31 V)  uniform working point Uniform micro-cell quenching resistance: R quenching ~ 320 k  Fast signals (rise time ~ 1 ns, small recovery time  ~ 20 ns) High internal gain, linear variable with the overvoltage: 5 x 10 5  2 x 10 6 Dark count rate: ~ 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 Summary and outlook