1 Alberto Del Guerra – DASIPM2 Collaboration 1 st Workshop on “Photon Detection” (13-14...

1 Alberto Del Guerra – DASIPM2 Collaboration

1st Workshop on “Photon Detection”

(13-14 JUNE ,2007 PERUGIA)Risultati sperimentali ed applicazioni

dei SIPM a pixel ed a matrice dell’FBK-irst da parte della

collaborazione DASIPM

Alberto Del GuerraDepartment of Physics and INFN, Sezione di Pisa,

Pisa, I-56127 Italy

Spokesman of the DaSiPM2 collaboration:

University and INFN Bari, Bologna, Perugia, Pisa, Trento and FBK-irst (Trento), Italy


SUMMARY● SiPM features

● Gain● Noise● PDE● Dynamic Range● Time Resolution● Dependence upon temperature● Radiation Damage

● SiPM performance w/Scintillators (i.e., LSO/LYSO)● Energy resolution● Timing resolution● Magnetic field MRI● ASIC

● PET Application (FP7 project: COMPANION)


Example: SiPM technology at IRST (TN, Italy)

C.Piemonte NIM A 568 (2006) 224

≈≈

n+

p

epi

p+

Shallow-Junction GM-APD

13

14

15

16

17

18

19

20

0 0.2 0.4 0.6 0.8 1 1.2 1.4

depth (um)

Do

pin

g c

on

c. (1

0^) [

1/cm

^3]

0E+00

1E+05

2E+05

3E+05

4E+05

5E+05

6E+05

7E+05

E fi

eld

(V/c

m)

Doping

Field

n+ p

• n+-on-p layer structure• Anti-reflective coating (ARC) optimized for λ~420nm• Very thin (100nm) n+ layer (“low” doping min. recombination)

• Thin high-field region (max. doping of p layer also fixes low VBD )• Trenches for optical insulation of cell (low cross-talk)• Fill factor 20% - 30% (to be optimized)• RQ with doped polysilicon

Optimization for the blue light (420nm)1mm

1m

m

SiPM geometry: 1x1mm2

• 25x25 cells• cell size: 40x40 mm2

Substrate500 µm

fullydepletedregion4 µm


Dynamic range

SiPM output = sum of binary SPAD output !

The output signal is proportional to the number of fired cells as long as the number of photons in a pulse (Nphoton) times the photodetection efficiency PDE is significant smaller than the number of cells Ntotal.

)1( total

photon

N

PDEN

totalfiredcells eNNA

Saturation

Best working conditions: Nphoto-electrons < NSiPM cells

eg: 20% deviation from linearity if 50% of cells respond


Time resolution - Experimental Method

• SiPM exposed to pulsed femto-second laser in low light intensity conditions (single photon) • SiPM signal is sampled at high rate and the time of the pulses measured by waveform analysis

• Time resolution measured by studying the distribution of time differences between successive pulses (on the same SiPM device)(G.Collazuol et al. VCI 07)


Experimental Setup (CNR Pisa)

Pump LaserMillenia V (Spectra-physics)solid state CW visible laser

Mode-lockedTi:sapphire LaserTsunami (Spectra-physics)femtosecond pulsed laser

wavelength: tuned at 800±15 nmpulse width: ~ 60 fspulse period: ~ 80MHzpulse timing jitter < 100 fs

pump laser Ti:sappirelaser

SHG

Crystal for Second Harmonic Generation (SHG) conversion 800 nm 400 nmefficiency at % level

Filtersblue + neutralfor rejecting IR lightand tune intensity

Dark boxSiPM +

amplifier

Low noise LVsuppliers

LeCroy SDA 6020

Analog bandwidth: 6GHzSampling rate: 20GS/sVertical resolution: 8 bits

(Aknowledments: E.Marcon, LeCroy)

External trigger fromTi:sappire laser signal

ElectronicsI V conversion via RL (500Ω)Two stage voltage amplification (= x50)based on high-bandwidth low-noise RF amplifier: gali-5 (MiniCircuit) Zin= 50Ω

(Aknowledments: F.Morsani and L.Zaccarelli, INFN-Pisa)

RLCC

CC CC

Cb

-Vb

GND

Vout

Rs

gali5 gali5

hn

SiPM

Data taking conditions:• different Vbias

• both at 800 nm and 400 nm• with different light intensities (counting rates in the range 10-20 Mhz ie 15-30 KHz per single cell)


Data at λ=800nm fit gives reasonable χ2 with an additional exponential term exp(-Δt/t)

•Δt ~ 0.2-0.8ns in rough agreement with diffusion tail lifetime: Δt ~ L2 / p2 D if L is taken to be the diffusion length• Contribution from the tails ~ 10-30% of the resolution function area

1 p.e.

2 p.e.

∆t

Laser period

Overvoltage=4V

λ=400nm

Overvoltage=4V

λ=800nm

FIT: gauss+const

FIT: gauss+const+exponential

Mod (∆t,Tlaser) [ns]

Mod (∆t,Tlaser) [ns]

Distributions of the difference in time between successive peaks (modulo the measured laser period Tlaser=12.367ns)

Single photon timing resolution


IRST – single photon timing

• λ = 800 nm• λ = 400 nm— contribution from noise and method (not subtracted)

eye guide

n+ pp

depletion region

p+

hν

e–h+

e–h+

high-field region

depletion regiondepletion region

neutralregion


CPTA – single photon timing

• l = 800 nm

• l = 400 nm

a) Green-Red sensitive SSPM 050701GR_TO18

b) Blue sensitiveSSPM 050901B_TO18

eye guideTwo different structures:a) thick n+/p b) p+/n deep junction


Comparison with Hamamatsu devices

• l = 800 nm

• l = 400 nm

eye guide

HPK-2HPK-3

1600 cells (25x25)

400 cells (50x50)


Over-voltage = 3V

Over-voltage = 5V

No p

inh

ole

Ø=

20

0m

m

Ø=

25

mm

Ø=

10

mm

No relevant spread Uniformity of rise-time among different cells

Dependence of single photon timingon the light spot size and positionBy using pinhole in front of the SiPM

IRST – timing studies

Poisson statistics: σt ∝ 1/√Npe

•contribution from noise subtracted

— fit to c/√Npe

λ=400nmOvervoltage = 4V

N of simultaneous photo-electrons

Dependence of SiPM timing on the number of simultaneous photons


Thermal-electrical characterization 1/4● Ileak vs Bias vs Temperature

M. Petasecca et al., Perugia (2007)


Thermal-electrical characterization 2/4● Vbreakdown vs Temperature

(**) K.G.McKay,Avalanche Breakdown in Silicon,Physical Review,Vol.94 Number 4, May 1954

M. Petasecca et al., Perugia (2007)


Thermal-electrical characterization 3/4● Gain vs Bias vs Temperature

The residual Gain dependence is due to the variation of Pt with temperature.

…but the Breakdown voltage is dependent with the temperature so…

M. Petasecca et al., Perugia(2007)


FBK-SiPM APD

∆Vbk /Vbk(@300K) % ~0.2 0.1

∆Vbk [mV] ~ 60 30 60-200 **

∆G/G(@300K) % ~ 3 1.5 3.4*

* Spanoudaki et al., IEEE NSS-MIC 2005

** J.P.R. David and G.J.Rees, RAD Hard Workshop 2003

Variation of Vbk and Gain with 1 °C ∆T

VARIATION with TEMPERATURE


Radiation damage

Expected effects:1) Increase of dark count rate due to introduction of generation centers

2) Increase of after-pulse rate due to introduction of trapping centers loss of single cell resolution

Dark rate increase DDC~ Pt/qe• α ΦeqVoleff

where α ~ 3 x 10-17 A/cm is a typical value ofthe radiation damage parameter for low E hadrons and Voleff ~ AreaSiPM x GF x Wepi

The effect is the same as in normal junction diodes: • independent of the substrate type• dependent on particle type and energy• proportional to fluence

The few existing preliminary measurements are in agreement with expectations for the radiation damage parameter a within a factor of 2 (Musienko and Danilov, VCI07)

C.PiemonteFNAL 25/10/2006


Radiation damage

Dark count rate increase

M.Danilov - VCI07

CALICE collaboration

MEPhI/Pulsar SiPM

~ Positron 28 MeV (8*10**10 cm**2)

Photonique/CPTA deviceY.Musienko – Vienna VCI 2007


Summary of SiPM featuresMost important features of a SiPM are:• sensitivity to extremely low photon fluxes providing proportional information with excellent resolution and high photon detection efficiency• extremely fast response with low fluctuation (sub-ns risetime and <100ps jitter)

More features:• low bias voltage (<100V)• low power consumption (<50µW/mm2)• long term stability• insensitive to magnetic fields (up to 15T) and EM pickup• robust and compact• low cost (in the future! now ~140$/mm2) + low peripheral costs

Technology parameters: may be tuned to match the specific application● silicon quality (dark rate, after-pulse)● doping concentration (operating voltage and its range)● layer structure and thickness (PDE wavelength range, optical cross-talk)● optical cell insulation (optical cross-talk)● effective area of the cells (gain, fill factor, dynamic range, recovery time)● quenching resistor (recovery time, dynamic range)


Great variety of possible applications

● Calorimetry in magnetic fields● Fiber tracking (spectrometers, beam monitoring)● Particle ID (TOF, RICH, fast timing with cherenkov, Transition Radiation)● Astroparticle (Imaging Air Cherenkov Telescopes)● Space applications (calorimetry, traking, TOF)● Medical imaging (PET) + timing + magnetic and RF fields (MRI)● Thin scintillators read-out● Time resolved X-Ray correlation spectroscopy● Fast timing applications


Medical imaging (PET)

Aims: PET detectors with• high spatial resolution (sub-millimeter)• high sensitivity (low dose or high signal/background ratio)• high time resolution (TOFPET background rejection)• DOI capability (no or less parallax)• no sensitivity to magnetic fields, EM pickup and RF (simultaneous NMR scan)

Key issues:• Granularity: matrices of SiPM

• High PDE for short wavelengths (420nm): • for coupling to high light yield crystals (scintillators)• max E resolution high efficiency to reject background Compton scattering

• Optical coupling with scintillator • Dynamic range and recovery time: multi cell signal saturation and fluctuation • Gain stability with V and T: individual control of O(10000) channels

Many photons applicationBlue sensitive SiPM


Matrices of SiPM - IRST

G.LLosa et al. IEEE NSS 2006 CD record M06-88

The first matrices of 2x2 blue sensitive SiPMs have been developed at IRST

SEM photograph of a section of a 3D detector

To avoid the anode wire bonding on the active surfaceaim to use the 3D technology at IRST to have a conducting contact to bring the anode to the backside.


A 22Na spectrum was obtained with a 1 mm x 1 mm x 10 mm LSO crystal coupled to a SiPM (GF~30.9%) Two devices were operated in time coincidence. A typical energy resolution of 21% FWHM was obtained.

World best resolution w/ LSO (3x3x20) and PT XP2020 10%(FWHM) [intrinsic 8.9% at 511 keV] [Balcerzyk et al., IEEE TNS 47(2000)1319]

SiPMs

22Na Source

Scintillatorcrystals

R ~ 17.6 % FWHM

Best spectrum

Typical spectrumR ~ 21.0 % FWHM

9/18/06 23

Energy resolution vs. different bias

poiché…

9/18/06 24

Scintillator readout with SiPM matrices

- LSO crystal (1x1 mm2) coupled to one pixel - time coincidence with a PMT

R ~ 29%

M6 @ 35.7

9/18/06 25

Scintillator readout with SiPM matrices

R ~ 30%

- LSO crystal (1x1 mm2) put in the centre - time coincidence with a PMT - gain calibration with a LED

M6 @ 35.7

9/18/06 26

Timing: set up

CFD

Timecoincidence delay

scope

∆t

SiPM LSO

trigger

thresh1

thresh2

9/18/06 27

Timing: cosa ci aspettiamo dalla teoria?

*Post, Schiff Phys. Rev. 80 p.1113 (1950)

Dove…<N> = numero medio di fotoniQ = CFV * <N> = tempo di decadimento dello scintillatore

Se… = 40 ns per LSO<N> ~ 100 per il fotopicco

~ 400 ps

Triggerando sul primo fotone Q=1 Triggerando al 20% Q=20

~ 1.78 ns

*

9/18/06 28

Timing: risultati

Miglior risultatoottenuto

= 600 ps

9/18/06 29

External trigger from gradient amplifier

Pulse generator

SiPMLED

55 µs

Shielded electronics

Magnet 1T

LED trigger

SiPM signal is acquired while the gradient is increasing

scope

SiPM signal integrated and histogrammed

SiPM in ststic magnetic field + gradient

9/18/06 30

single SiPM in magnetic resonance: Z gradient on

Black: reference spectrum acquired inside the magnet with

the gradient off

Red: spectrum acquired with the gradient on

SiPM dark signal

Pickup coil signal

9/18/06 31

single SiPM in magnetic resonance: Z gradient on

Black: reference spectrum acquired inside the magnet with

the gradient off

R~30.4%

LSO (1x1 mm^2) - 22Na - no coincidence

R~29.6%

Red: spectrum acquired with the gradient on

Spectra can be superimposed if acquired in a short time

9/18/06 32

SiPM electrical model

Rq: quenching resistor (hundreds of k)

Cd: photodiode capacitance (few tens of fF) Cq: parasitic capacitance in parallel to Rq (smaller than Cd)

Cg : parasitic capacitance due to the routing of the bias voltage to the N microcells, realized with a metal grid (few tens of pF)

IAV: current source modelling the total charge delivered by a microcell during the avalanche

A parameter extraction procedure has been developed, based on both static and dynamic measurements, to perform realistic simulations.

9/18/06 33

Validation of the parameter extraction procedure

Two different amplifiers have been used to read-out the detector

a) Transimpedance amplifier

BW=80MHz, Gain=2.7k

b) Voltage amplifier

BW=360MHz, Gain=140

The fitting between simulations and measurements is quite good

9/18/06 34

Front-end electronics: main specifications

Self-triggered electronics

Dynamic range: about 50% of SiPM micro-cell occupancy ( SiPM gain 106 , no of micro-cells = 625 total charge 48pC )

The required jitter for the self-trigger signal (few hundreds of picoseconds) calls for large bandwidth (about 250MHz)

Power consumption: about 2mW per channel

Threshold for the self-trigger signal: adjustable, from few micro-cells to the full dynamic range

Important feature: fine adjustment of the SiPM bias voltage

9/18/06 35

Front-end architecture

Current buffer

Baseline holder

To current discriminatorCf

Vdd

Vbl-

+

SiPM

VBIAS

M : 1

Rf

Shaper

Peak detector

Vdd

-

+

-

+

The front-end is based on an input current buffer, which allows to achieve large bandwidth and dynamic range.

An output branch of the current buffer, suitably scaled, is sent to an integrator, which extracts the charge information.

Another output branch goes to a current discriminator, which provides the self-trigger signal.

9/18/06 36

The current buffer

Vg1

Vg2

Vref

Iout

M0

M1

M2

M3 M4

M5

SiPM

Vcc

A prototype of the input current buffer has been designed, based on a current feedback scheme

Vref can be used to vary the bias voltage of the detector, which is DC coupled to the front-end

The technology used is a standard 0.35m CMOS

Simulated input impedance 20

Simulated bandwidth (including the SiPM model connected at the input) 250MHz

Noise negligible

Dynamic range equivalent to about 300 micro-cells

9/18/06 37

Current buffer: first measurements

A test board which performs current-to-voltage conversion and amplification has been realized

An infrared pulsed laser has been used as optical source (about 260 micro-cells hit)

The bias voltage of the detector has been varied from 32.5V to 36V

The measurements show the good linearity performance of the current buffer.

Output waveform of the test board as a function of the SiPM bias voltage

Peak of the output waveform as a function of the SiPM bias voltage


Proposal COMPANION for FP7

● Development of a combined PET/MRI scanner for small animals.

● [Submitted 19 April. Results end June. (Start 1 Jan 2008?)] - 8 groups from 4 countries:

Institution Main tasks

1 UP University of Pisa Pisa, Italy Simulation+ PET construction + testing

2 FBK IRST Trento, Italy Photodetectors development

3 PB Politechnic Institute of Bari

Bari, Italy ASIC development

4 WBIC Wolfson Brain Imaging Center

Cambridge,UK Gradient development + preclinical application in neurology

5 CC Cancer Institute of Cambridge

Cambridge,UK Preclinical application in oncology

6 UV University of Valencia Valencia, Spain Simulation+ image reconstruction + attenuation correction

7 UM Technical University of Madrid

Madrid, Spain Readout system + image reconstruction

8 TEI Technological Educational

Institute of Athens

Athens, Greece Simulation +Image fusion and motion correction

COMPANION - COmbined MRI-PET for small ANimal-Imaging in Oncology and Neurology CONFIDENTIAL


Design● PET/MRI imposes hard restrictions:

● Space limitation inside the MR scanner.● Sensitivity to magnetic fields.

● Attempts with light guides and APDs.

20 cm

~12 cm

8 cm

Split gradient

≤ 2.5 cm

PET ring

• Split gradient coil with the PET tomograph placed inside (20 cm outer radius to fit inside standard magnets from 7 to 11T).

• PET inner diameter: ~12 cm to accommodate inside RF coils and rat/mouse bed. • Maximum axial length: 8 cm. Maximum transaxial thickness: 2.5 cm.


● The PET tomograph consists of a ring composed of 16 detector heads. ● The heads are: LSO slab 7.2 cm long x 2.4 cm wide x 1 cm thick;● Read out by SiPM matrices. Total thickness ~1.8 cm.

7.2 cm

≤ 2.5 cm

2.4 cm

12.4 cm

12.4 cm

2.4 cm

≤ 2.5 cm

PET design


● LSO continuous scintillator slab 7.2 cm x 2.4 cm x 1 cm thick with matrix readout.

● Simulations predict better performance than detector heads with pixellated crystals. Better spatial resolution, possible DOI (even with one layer).

● Readout by SiPM matrices and dedicated ASIC

SiPM matrix LSO crystal slab:72 mm x 24 mm10 mm thick

10 mm

72 mm

24 mm

Scintillator


● Matrices: Aim- backplane readout● Phase 1: Matrices with lateral readout (1 mm x 1 mm SiPM

elements in 1.5 mm x 1.5 mm pitch).● Phase 2: Matrices with backplane readout (1.5 mm x 1.5 mm in

1.5 mm x 1.5 mm pitch -Almost no dead area).● Improved PDE (PET efficiency).● Same layout, number of channels● Development in parallel. Not delaying the PET scanner

construction.● Technology already developed at IRST.● Final decision according to performance, yield...

Matrices


LATERAL READOUT.

coolingpipes TOP VIEW

SIDE VIEW

scintillator support

SiPM matrix ASICs

72 mm

24 mm

~1.8 mm

… … …

… … …

support

fan-out

holes to reach the sensor

BACKPLANE READOUT.

Possible layout


Simulation results● Expected performance (GEANT4):

● FOV axial 7 cm, transaxial FOV ~6 cm. ● spatial resolution at the CFOV , below 1mm3.● efficiency around 11% for an energy threshold of 250 keV.

Better than Siemens INVEON


Conclusions

SiPM might really replace PMT in many applications, due to their• sensitivity to extremely low photon fluxes• extremely fast response

IRST developed devices with excellent sensitivity to blue:• devices working as expected • very good reproducibility of the performances • very good yield • very good understanding of the device• flexible geometry (linear and 2-D matrices under development)

Photo-detection efficiency (IRST devices):• Quantum efficiency: > 95% in the blue region (optimized for 420nm)• Triggering probability: growing linearly with overvoltage • Geometrical fill factor: 15-30% to be optimized 44-76% soon available

Single photon timing resolution (IRST devices):• σt at the level of 50ps for typical working overvoltage (4V)

• σt at the level of 20ps for ~15 photoelectrons

Applications of SIPM in various fields are under development (e.g. PET)


Publications by the Collaboration (2006-2007)

1. F. Corsi, et al.. “Modelling a Silicon Photo Multiplier (SiPM) as a signal source for optimum front-end design”, NIM A, 2007, 572, 416-418.

2. V.Bindi, et al., “Preliminary Study of Silicon Photomultipliers for Space Missions”, NIM A 2007, 572, 662-667.

3. N.Dinu, et al., “Development of the first Prototypes of Silicon Photomultipliers (SiPM) at ITC-irst”, NIM A, 2007, 572, 422-426.

4. C.Piemonte, et al., “Characterization of the first prototypes of Silicon Photomultipliers fabricated at ITC-irst”, IEEE Trans Nucl Sci. 2007, 54(1), 236-244.

5. C.Piemonte, et al.,“ New results on the characterization of ITC-irst Silicon Photomultipliers”, Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, N42-4.

6. G.Llosa, et al.“Novel Silicon Photomultipliers for PET application” Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, M06-88, and submitted to IEEE Trans. Nucl. Sci.(2006).

7. F.Corsi, et al., “Electrical characterization of Silicon Photo-Multiplier Detectors for Optimal Front-End Design” Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, N30-222.

8. G. Collazuol, et al., “Single timing resolution and detection efficiency of the ITC-irst Silicon Photomultipliers”, presented at the XI VCI, Vienna 19-24 February 2007, accepted for publication in NIM A (2007)

9. G.Llosa, et al.,”Silicon Photomultipliers for very high resolution small animal PET and PET/MRI”, to be presented at the Second International Conference of the European Society for Molecular Imaging, Napoli, Italy, June 14-15, 2007 (Abstract)

10. G.Llosa et al. “ Novel Solid State detector and their application to very-high resolution PET and Hybrid Systems.” to be presented at the ENC 2007, Brussels, 16-19 September 2007, and submitted to Radiation Protection Dosimetry

11. A. Del Guerra “Silicon photomultiplier(SIPM): the Ideal Photodetector for the Next Generation of TOF, DOI, MRI compatible, High Resolution, High Sensitivity PET”, to be presented at the “Joint Molecular Imaging Conference” , Sept 8-11, 2007, Rhode Island, NY(USA)

● + 1 submission to X EFOMP (sept 2007)

1. + 4 submissions to IEEE NSS MIC 2007 (nov 2007)


International grants and collaborations (Pisa based)

Established● Marie Curie Individual Fellowship (2007-2008)● Italy-UK [Pisa-Cambridge (2007)]● Italy-Spain [Pisa-Valencia (2007-2008)]● Pisa University- UCI (US)Requested● NIH (US) (2nd revision) {P.I. w/ Univ. of

Washington} ● FP7

● COMPANION {P.I. w/ other seven partners}● PEM-MRI {partner}


Acknowledgments

Deepest thanks go to the members of the DASIPM2 collaboration:

● Claudio Piemonte & collaborators (FBK-irst and Trento)

● Francesco Corsi & collaborators (Bari)● Giovanni Ambrosi & collaborators (Perugia)● Giuseppe Levi & collaborators (Bologna)● Pisa TEAM (Gabriela Llosa, Sara Marcatili, Gianmaria Collazuol, S. Moehrs, N.Belcari, Maria G. Bisogni)


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1 Alberto Del Guerra – DASIPM2 Collaboration 1 st Workshop on “Photon Detection” (13-14...

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