Development of the first prototypes of Silicon Photomultiplier at ITCirst

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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

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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

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• 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

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A look on photon detectors characteristics
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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
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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
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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

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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
• ?geom optimisation
• minimize the dead area around each micro-cell
  (uniform breakdown and optical
• isolation through trenches)

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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

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Wafer and SiPM design

• SiPM geometric characteristics
• area 1 x 1 mm2
• number of micro-cells 625
• micro-cell size 40 x 40 ?m2

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IV breakdown

• Uniform breakdown voltage VBD
• for different micro-cell and SiPM devices
  over the wafer
• Uniform working point Vbias for different SiPM
  devices
• Vbias VBD ?V, ?V ? 3 V
• very important when matrix of many SiPMs devices
  of 1 mm2 are built

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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

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SiPM internal gain

• Gain
• linear variable with Vbias
• in the range 5 x 105 ? 2 x 106
• micro-cell capacitance
• Cmicro-cell 48 fF

• micro-cell recovery time
• ? Rquenching Cmicro-cell 20 ns
• Rise time
• ? 1 ns (limited by the read-out
• system)

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SiPM dark count

• Room temperature ( 23C)
• 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

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

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Single photon counting capability

• A LED was pulsed at low-light-level to record
  the single
• photoelectron spectrum

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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 _at_ 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