C. Piemonte 1

Development of SiPMsa FBK-irst

C.Piemonte

FBK – Fondazione Bruno Kessler, Trento, Italy

piemonte@fbk.eu

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Outline

• Important parameters of SiPM

• Characteristics of FBK-irst SiPMs

• Application of FBK-irst SiPM

C. Piemonte 3

- Gain

- Noise

- Photo-detection efficiency

- Dynamic range

- Time resolution

General view of the important parameters in a SiPM

C. Piemonte 4

Gain = IMAX*Q = (VBIAS-VBD)*Q = (VBIAS-VBD)*CD __ ________ __ ____________ q RQ q q

charge collected per event is the area of the exponential decay which is determined by circuital elements and bias.

t

i

~exp(-t/RS*CD)

~(VBIAS-VBD)/RQ

exp(-t/RQ*CD)

Gain

number of carriers produced per photon absorbed

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1) Primary DARK COUNT

False current pulses triggered by non photogenerated carriers

Main source of carriers: thermal generation in the depleted region. Critical points: quality of epi silicon; gettering techniques.

NOISE

2) Afterpulsing: secondary current pulse caused by a carrier released by a trap which was filled during the primary event.

3) Optical cross-talk Excitation of neighboring cells due to the emission of photons during an avalanche discharge

C. Piemonte 6

PDE = Npulses / Nphotons = QE x P01x FF

1. QE Quantum efficiency is the probability for a photon to generate a carrier that reaches the high-field region.

Maximization: anti-reflective coating, drift region location

Photodetection efficiency

2. P01. triggering probability probability for a carrier traversing the

high-field to trigger the avalanche.

Maximization: 1. high overvoltage 2. photo-generation in the p-side of the junction (electrons travel through the high-field region)

3. FF. Fill Factor “standard” SiPMs suffer from low FF due to the structures present around each micro-cell (guard ring, trench)

micro-cell

dead width

C. Piemonte 7

Time resolution

Statistical Fluctuations in the first stages of the current growth:

1. Photo-conversion depth

2. Vertical Build-up at the very beginning of the avalanche

3. Lateral Propagation

t=0 pair generation0<t<t1 drift to the high-field regiont>t1 avalanche multiplication

* for short wavelength light the first contribution is negligible

t1

t’1

single carrier current level

the avalanche spreading is faster ifgeneration takes place in the center

C. Piemonte 8

Development of SiPMs started in 2005 in collaboration with INFN.

• IRST: development of the technology for the production of SiPMs (large area devices/matrices) + functional characterization

• INFN (Pisa, Bari, Bologna, Perugia, Trento): development of systems, with optimized read-out electronics, based on SiPMs for applications such as: - tracking with scintillating fibers; - PET; - TOF; - calorimetry

FBK-irst SiPMs

C. Piemonte 9

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. (

10^

) [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+ pShallow-Junction SiPM

1) Substrate: p-type epitaxial2) Very thin n+ layer 3) Polysilicon quenching resistance4) Anti-reflective coating optimized for ~420nm

p+ subst.

epi

n+

[C. Piemonte “A new Silicon Photomultiplier structure for blue light detection” NIMA 568 (2006) 224-232]

IRST technology

Drift regionHigh field region

p

guard region

C. Piemonte 10

Layout: from the first design…(2005)

SiPM structure:- 25x25 cells- microcell size: 40x40m2

1mm

1mm

Geometry NOT optimizedfor maximum PDE (max fill factor ~ 30%)

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… to the new devices (i) (2007)

1x1mm2 2x2mm2 3x3mm2 (3600 cells) 4x4mm2 (6400 cells)

Fill factor: 40x40m2 => ~ 40% 50x50m2 => ~ 50% 100x100m2 => ~ 76%

Geometries:

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…to the new devices (ii)

Circular: diameter 1.2mm diameter 2.8mm

Matrices: 4x4 elements of 1x1mm2 SiPMs

Linear arrays: 8,16,32 elements of 1x0.25mm2 SiPMs

C. Piemonte 13

• IV measurement fast test to verify functionality and uniformity of the properties.

• Functional characterization in dark for a complete characterization of the output signal and noise properties (signal shape, gain, dark count, optical cross-talk, after-pulse)

• Photo-detection efficiency

C. Piemonte et al. “Characterization of the first prototypes of SiPM fabricated at ITC-irst” IEEE TNS, February 2007

Tests performed at FBKTests performed at FBK

C. Piemonte 14

Leakage current: mainly due to surface generation at the micro-diode periphery

Static characteristic (IV)Static characteristic (IV)

Matrix 4x4 1-9

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0 5 10 15 20 25 30 35Vrev [V]

I [A

]

SiPM4 - W12

Breakdown voltage

Breakdown current: determined by dark events

Very useful fast test. Gives info about:- Device functionality- Breakdown voltage- (Dark rate)x(Gain) uniformity- Quenching resistance (from forward IV)

Reverse IV

Performed on several thousands ofdevices at wafer level

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Dark signals are exactly equal to photogenerated signals functional measurements in dark give a complete picture of the SiPM functioning

Signal properties – NO amplifierSignal properties – NO amplifier

0.E+00

1.E-03

2.E-03

3.E-03

4.E-03

5.E-03

6.E-03

7.E-03

0.0E+00 1.0E-07 2.0E-07 3.0E-07 4.0E-07

Time (s)

Am

pli

tud

e (V

)

Thanks to the large gain it is possible to connect the SiPM directly to the scope

VBIAS

SiPM

50

DigitalScope

SiPM: 1x1mm2

Cell: 50x50m2

C. Piemonte 16

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120Charge (a.u.)

Co

un

ts

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

31 32 33 34 35 36

Bias voltage (V)

Ga

in

Pulse gen.

Laser

Pulse area= charge

histogram collection

SiPM

~ns

1p.e. 23

4

pedestal.

Excellent cell uniformity

Lineargain

Signal properties – NO amplifierSignal properties – NO amplifier

C. Piemonte 17

s = singled = double pulsesa = after-pulse

VBIAS

SiPM

50

DigitalScope

Pulses at the scope.

Av100x

Signal properties – with amplifierSignal properties – with amplifier

A voltage amplifier allows an easier characterization,but attention must be paid when determining the gain

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1x1mm2 (400 cells) 4x4mm2 (6400 cells)

Let’s look at the electro-optical characteristics of these devices:

Micro-cell size: 50x50m2

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1x1mm2 SiPM - 50x501x1mm2 SiPM - 50x50m2 cellm2 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`

Signal shapeFast transient:avalanche currentthrough parasiticcapacitance inparallel with quenching res.

Slow transient:Exponential rechargeof the diode capac. through the quenching resistor

Important to note:The value of the quenching resistor increases with decreasing temperature and so the time constant follows the same trend

Set up: SiPM current signal converted into voltage on a 50 resistor and amplified with a wide-band voltage amplifier.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-1.00E-08 4.00E-08 9.00E-08 1.40E-07

Time (s)

Am

plitu

de (

a.u.

)T = 25C

Signal shape

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1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

-0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00

Threshold (V)

Cou

nts

DC 28DC 28.5DC 29DC 29.5DC 30DC 30.5DC 31DC 32DC 33

1x1mm2 SiPM – 50x501x1mm2 SiPM – 50x50m2 cellm2 cell Dark count Dark count

Growing threshold

T = -30C VBD = 27.2V

From this plot we get idea of dark rate and optical cross-talk probability

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1x1mm2 SiPM - 50x50m2 cell

1.0E+05

1.0E+06

1.0E+07

27 28 29 30 31 32 33 34 35

Voltage (V)

Da

rk c

ou

nt

(Hz)

25.00

15.00

5.00

-5.00

-15.00

-25.00

0.0E+00

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

27 28 29 30 31 32 33 34 35

Voltage (V)

Ga

in

T = 25C

T = 15C

T = 5C

T = -5C

T = -15C

T = -25C

Gain

Dark count

y = 0.0674x + 29.2

27

27.5

28

28.5

29

29.5

30

30.5

31

31.5

-30 -10 10 30Temperature (C)

Bre

akd

ow

n v

olta

ge

(V

)

y = 1E+14e-5.213x

1.E+05

1.E+06

1.E+07

3.2 3.4 3.6 3.8 4.0 4.21000/T (1/K)

Dar

k co

unt (

Hz)

DC 2V

DC 3V

DC 4V

• 2V overvoltage• 3V overvoltage• 4V overvoltage

C. Piemonte 22

4x4mm2 SiPM - 50x50m2 cell4x4mm2

0.01

0.10

1.00

10.00

-1.0E-08 5.0E-08 1.1E-07 1.7E-07 2.3E-07Time (s)

Am

plit

ud

e (

a.u

.)

1mm2

T = -15C

T = -25C

Signal shape

1mm2 SiPM

0.E+00

1.E+06

2.E+06

3.E+06

4.E+06

5.E+06

6.E+06

7.E+06

28 29 30 31 32 33

Voltage (V)

Da

rk c

ou

nt (

Hz)

16 x Dark Count of 1mm2 SiPM

-15C -25C

0.E+00

1.E+06

2.E+06

3.E+06

28 29 30 31 32 33

Voltage (V)

Ga

in

-15C

-25CGain

Dark count

C. Piemonte 23

4x4mm2 SiPM - 50x50m2 cell

Same conclusions as for the previous device:

• Excellent cell response uniformity over the entire device (6400 cells) Width of peaks dominated by electronic noise

-5.E-10 2.E-09 4.E-09 6.E-09 8.E-09

Charge (V ns)

28.6V

29.2V

29.6V

12 3

4

5

1

2

34 5 6

12

3

4 5 6 7

8

T=-25C Vbd=27.6VCharge spectra when illuminating the device with short light pulses

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Photo-detection efficiency (1)Photo-detection efficiency (1)

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Photo-detection efficiency (2)Photo-detection efficiency (2)

dark pulses light pulses

DC currwith light

DC curr. wo light

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……what is the PDE of these devices?what is the PDE of these devices?

Measured on 1x1mm2 SiPM using photon counting technique

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

30 31 32 33 34 35

Bias voltage (V)

PD

E

L=400nm

L=425nm

L=450nm

L=475nm

L=500nm

L=550nm

50x50m cell - ~50% fill factor

400nm

Broad peak between 450 and 600nm

500nm

425nm

450nm

C. Piemonte 27

• Laser: - wavelength: 400 or 800nm - pulse width: ~60fs - pulse period: 12.34ns with time jitter <100fs• Filters: to have less than 1 photodetection/laser pulse• SiPMs: 3 devices from 2 different batches measured

Time resolution (1)Time resolution (1)

G. Collazuol, NIMA, 581, 461-464, 2007.

C. Piemonte 28

Time resolution (2)Time resolution (2)

Distribution of thetime difference

Timing performance ()as a function of the over-voltage

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Microcell functionality measurementMicrocell functionality measurement

(measurement at RWTH Aachen)

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Measurement of microcell eficiency with a 5 um LED spot diameter

Microcell functionality measurementMicrocell functionality measurement

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Microcell functionality measurementMicrocell functionality measurement

C. Piemonte 32

Some applications and Some applications and projects in which we are projects in which we are

involvedinvolved

C. Piemonte 33

SiPM matrix – for PET (1)

Matrix 4x4 1-9

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0 5 10 15 20 25 30 35Vrev [V]

I [A

]

SiPM4 - W12IV curves of 9 matrices of one wafer

1mm

9x16 IV curvesNon working SiPM

• Uniform BD voltage• Uniform dark rate

First, small monolithic matrix of SiPM:Element 1x1mm2

Micro-cell size: 40x40m2

C. Piemonte 34

Na22 spectrum with LSOon a single SiPM (1x1mm2, 40x40m2 cell)

Res = 18%

Tests are ongoing in Pisa (DASiPM project, A. Del Guerra) on these devices coupled with pixellatedand slab LSO scintillators

SiPM matrix – for PET (2)

NEXT STEP: Larger monolithic matrices

C. Piemonte 35

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 1 2 3 4

SiPM dark current (microAmps/mm^2)

Mu

on

Eff

icie

ncy

fo

r 1

kHz

no

ise

2.8 mm round IRST

SiPMfor CMS-Outer Hadroncalorimeter

Muonresponse in YB2 using SiPMs

MuonEfficiency in YB2Baseline HPD response at 8 kV

Circular SiPM - 50x50m2 cellfor CMS – Outer Hadron Calorimeter

Muon response using SiPMs

Muon response using HPD at 8kV

package designed by Kyocera

module with 18 SiPMs

Each SiPM reads a bundleof 5 fibers

6mm2 area SiPM

C. Piemonte 36

Array of SiPM for Fiber Tracking

32x array connected to ASIC designed for strip detectors=> capacitive divider at the input to reduce signal

Response uniformity under LED illumination

INFN PG (R. Battiston) + Uni Aachen

C. Piemonte 37

HYPERimage project

Seventh Framework programme, FP7-HEALTH-2007-A

coordinator

C. Piemonte 38

HYPERimage projectDevelopment of hybrid TOF-PET/MR test systems

with dramatically improved effective sensitivity

First clinical whole body PET/MR investigations of breast cancer

TOF-PET building blocks

C. Piemonte 39

• The SiPM is going to play a major role as a

detector for low intensity light, because of:

- comparable/better proprieties than PMT;

- the inherent characteristics of a solid-state det..

• IRST has been working on SiPMs (GM-APDs) for about

3 years obtaining very good results in:

- performance;

- reproducibility;

- yield;

- understanding of the device.

Conclusion