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

New developments of New developments of Silicon PhotomultipliersSilicon Photomultipliers

(for PET systems)(for PET systems)

Claudio [email protected]

FBK – Fondazione Bruno Kessler, Trento, Italy

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

OutlineOutlineSiPMs 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.


• tiny micro GM-APD connected in parallel.• each element gives the same signal

when fired by a photon

The (analog) SiPM 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


What is available?What is available?

SEM picture

SiPM size:-from 1x1mm2 up to 4x4mm2

Cell size:- from 25x25 to 100x100um2

Most common technology:- epi silicon- poly silicon resistor

TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte

Single cell signal shapeSingle cell signal shape

CDn

RSn

VBDn

RQn

DIODE

CQn

CG

nth MICRO-CELL

RQ = quenching resistorCQ = parasitic cap.CG = metal parasitic cap.



CDn

RSn

VBDn

RQn

DIODE

CQn

CG

nth MICRO-CELL


Current signal read out on 50 resistorfollowed by a voltage amplifier:



CDn

RSn

VBDn

RQn

DIODE

CQn

CG

nth MICRO-CELL

0.01

0.10

1.00

-1.0E-08 4.0E-08 9.0E-08 1.4E-07Time (s)

Am

plit

ud

e (

a.u

.)

T = 25C

T = 15C

T = 5C

T = -5C

T = -15C

T = -25C`

1x1mm2 SiPM


fast componentdue to CQlayout dependent

slow componentdue to microcellrechargeTemp. dependentbecause of poly res.

Current signal read out on 50 resistor:



CDn

RSn

VBDn

RQn

DIODE

CQn

CG

nth MICRO-CELL

0.01

0.10

1.00

-1.0E-08 4.0E-08 9.0E-08 1.4E-07Time (s)

Am

plit

ud

e (

a.u

.)

T = 25C

T = 15C

T = 5C

T = -5C

T = -15C

T = -25C`

0.01

0.10

1.00

10.00

-1.0E-08 5.0E-08 1.1E-07 1.7E-07Time (s)

Am

plit

ud

e (

a.u

.)

T = -5C

T = -15C

T = -25C

1mm2

1x1mm2 SiPM

3x3mm2 SiPM


fast componentdue to CQlayout dependent

slow componentdue to microcellrechargeTemp. dependentbecause of poly res.

larger cap. in parallelto 50 reshapes thesignal from themicro-cell:- no fast comp.- slower signal

Current signal read out on 50 resistor:


Intrinsic timing capabilityIntrinsic timing capability

1x1mm2 SiPM40x40um2 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


Intrinsic timing capabilityIntrinsic timing capability


Photo-detection efficiencyPhoto-detection efficiency

PDE = QE x Pt 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.

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+05 2E+05 3E+05 4E+05 5E+05 6E+05 7E+05

E field (V/cm)

Ioni

zatio

n R

ates

(1/

um)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

20 30 40 50 60 70 80 90 100Micro-pixel edge (um)

Are

a e

ffic

ien

cy

6um

4um


Photo-detection efficiencyPhoto-detection efficiency

PDE = QE x Pt x FF

Quantum efficiency:- dielectric stack- doping profiles

Avalanche probability:- electron/holes- over-voltage

Fill factor:- each microcell has a dead border region.

0

0.05

0.1

0.15

0.2

0.25

400 450 500 550 600 650 700

Ph

oto

-de

tect

ion

eff

icie

ncy

Wavelength (nm)

PDEi_1.5VPDEi_2.5VPDEi_3.5VPDEi_4.5V

50x50m2 micro-cell

FF~50% Data obtained countingpulses from uniform low-level illumination

• n-on-p structure• QE optimized at 420nm (>90%) in air for perpendicular light


0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

13

Temperature dependenceTemperature dependence

y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

Breakdown

-30C

+30C


0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)


y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C

BreakdownDark count

-30C

+30C


0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

15


y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C

0.0E+00

1.0E+05

2.0E+05

3.0E+05

4.0E+05

5.0E+05

-45 -35 -25 -15 -5 5 15 25 35 45

Que

nchi

ng re

sist

ance

(Ohm

)

Temperature (°C)

0.0E+00

1.0E+05

2.0E+05

3.0E+05

4.0E+05

5.0E+05

-45 -35 -25 -15 -5 5 15 25 35 45

Que

nchi

ng re

sist

ance

(Ohm

)

Temperature (°C)

BreakdownDark count

Quenching resistor

-30C

+30C


0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

4.5E+06

5.0E+06

28 30 32 34 36 38 40

Gai

n

Bias (V)

16


y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

y = 0.076x + 30.934

28

29

30

31

32

33

34

35

-40 -20 0 20 40

BV (V

)

Temperature (°C)

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 1 2 3 4 5 6 7

Dar

k co

uts (

Hz)

Overvoltage (V)

.-30° C

.-20° C

.-10° C

0° C

10° C

20° C

30° C

0.0E+00

1.0E+05

2.0E+05

3.0E+05

4.0E+05

5.0E+05

-45 -35 -25 -15 -5 5 15 25 35 45

Que

nchi

ng re

sist

ance

(Ohm

)

Temperature (°C)

0.0E+00

1.0E+05

2.0E+05

3.0E+05

4.0E+05

5.0E+05

-45 -35 -25 -15 -5 5 15 25 35 45

Que

nchi

ng re

sist

ance

(Ohm

)

Temperature (°C)

BreakdownDark count

Quenching resistor

-30C

+30C

Temperature must be stable and possibly low!


SiPMs in PET – energy resolutionSiPMs 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%

4x4mm2 SiPM 50x50m2 cell

Example of energy spectrumwith FBK SiPMs measuredby Philips Research Aachen(corrected from saturation)

dE/E ~ 1/sqrt(N)LYSO4x4x20mm3


SiPMs in PET – timing resolutionSiPMs in PET – timing resolution

Critical SiPM parameters:

• intrinsic timingextremely 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 noisefor large SiPMs can be quite high


SiPMs in PET – timing resolution (2)SiPMs in PET – timing resolution (2)

• signal shapeoutput signal is the convolution of SiPM response and light emission

0

0.002

0.004

0.0060.008

0.01

0.012

0.014

0.016

0.018

0 30 60 90 120 150

a.u.

Time (ns)

10ns

30ns

50ns

0

0.002

0.004

0.0060.008

0.01

0.012

0.014

0.016

0.018

0 30 60 90 120 150

a.u.

Time (ns)

10ns

30ns

50ns

response to LSO (40ns dec. time)for exponential SiPM current signalwith different time constants


SiPMs in PET – timing resolutionSiPMs in PET – timing resolutionTwo 3x3mm2 SiPMs in coincidence

measurement by Philips Research Aachen

CRT<430ps FWHM

Measurement at room temperature.Decreasing temperature better results.

LYSO 3x3x15mm3


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?Real PET system with SiPMs?


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?Real PET system with SiPMs?


HYPERImage projectHYPERImage 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


Ultra compact solid-statePET detector based on SiPMs

Research on ToF-PET/MRResearch on ToF-PET/MR

Type PMT APD SiPM

MR compliant no yes yes

ToF compliant yes no yes

Why SiPMs?


The stack The SiPM tile

The ASIC tile

Building block of the PET systemBuilding block of the PET system

Mounting and measurementsat Uni. Heidelberg and Philips


2x2 array of ~4x4mm2 SiPMs2x2 array of ~4x4mm2 SiPMs

The SiPM tileThe SiPM tile

32.7mm32.7mm

• Overall fill factor ~ 84%• Flat surface for crystal mounting

700 working arrays have been delivered by FBK

TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 27 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

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 worksThe stack works

TOF-PET workshop, Baia delle Zagare, 4 SeptemberC. Piemonte 28 28

DaSiPM2 projectDaSiPM2 project

PET tomograph for small animals proposed by Pisa Univ.

4 rotating heads

3 stacked layers:• 4x4cm2

• ~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


1.2cm

1.3c

m

• 8x8 array • 1.5mm element pitch• read-out on one side

Our largest areamonolithic array!!

The DASiPM2 SiPMThe DASiPM2 SiPM


DaSiPM2 SiPM: breakdownDaSiPM2 SiPM: breakdown

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

0 5 10 15 20 25 30 35

I rev

[A]

Vrev [V]

IV curves of the 64 elements of one array

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

28 29 30 31 32 33

I rev[A

]

Vrev [V] 30


0

50

100

150

200

250

300

350

400

29 30 31 32 33 34

fre

qu

en

cy

Vbd [V]

DaSiPM2 SiPM: breakdownDaSiPM2 SiPM: breakdown

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

0 5 10 15 20 25 30 35

I rev

[A]

Vrev [V]

IV curves of the 64 elements of one array

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

28 29 30 31 32 33

I rev

[A]

Vrev [V]

Vbd distributions on different wafers

σ ~ 0.15÷0.4V

0

50

100

150

200

250

300

350

400

450

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

fre

qu

en

cy

Vbd-Vbd_mean [V]

Vbd-Vbd_mean distributions in a matrix grouped by wafer

σ ~ 0.12V


Δ

32

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 d’Elba- Italy, May 24-30, 2009


Measurements at INFN PisaMeasurements at INFN Pisa

DaSiPM2 functional testsDaSiPM2 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


Δ

33



Measurements at INFN PisaMeasurements at INFN Pisa

DaSiPM2 functional testsDaSiPM2 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


ConclusionConclusion

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 PDE @ short wavelengths- decrease dark count: difficult task- new simplified interconnection with electronics


AcknowledgmentsAcknowledgments

HyperImage project

PhilipsVolkmar SchulzTorsten Solf

Uni heidelbergPeter FischerMichael Ritzer

FBKMirko MelchiorriAlessandro PiazzaAlessandro TarolliNicola Zorzi

DaSiPM2 projectAlberto Del GuerraGiuseppina BisogniGabriela LlosaSara MarcatiliGian-Franco Dalla Betta

Documents

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