Piemonte 2

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C. Piemonte 1

Development of SiPMs

a FBK-irst

C.Piemonte

FBK – Fondazione Bruno Kessler, Trento, Italy

[email protected]



C. Piemonte

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*tQ = (VBIAS-VBD)*tQ = (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



C. Piemonte 5

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


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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 generation

0<t<t1 drift to the high-field region

t>t1 avalanche multiplication

* for short wavelength light

the first contribution is negligible

t1t’1

single carrier

current level

the avalanche spreading is faster if

generation takes place in the center



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



13

14

15

16

17

18

19

20

0 0.2 0.4 0.6 0.8 1 1.2 1.4

depth (um)

D o p i n g c o

n c .

( 1 0 ^ ) [ 1 / c m ^ 3 ]

0E+00

1E+05

2E+05

3E+05

4E+05

5E+05

6E+05

7E+05

E

f i e l d ( V / c m )

Doping

Field

n+ p Shallow-Junction SiPM

1) Substrate: p-type epitaxial

2) Very thin n+ layer

3) Polysilicon quenching resistance

4) Anti-reflective coating optimized for l~420nm

p+ subst.

p epi

n+

[C. Piemonte

“A new Silicon Photomultiplier

structure for blue light detection”

NIMA 568 (2006) 224-232]

IRST technology

Drift regionHigh fieldregion

p

guard region



Layout: from the first design…(2005)

SiPM structure:

- 25x25 cells

- microcell size: 40x40mm2

1mm

1mm

Geometry NOT optimized

for maximum PDE

(max fill factor ~ 30%)



… to the new devices (i) (2007)

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

Fill factor : 40x40mm2 => ~ 40%

50x50mm2 => ~ 50%100x100mm2 => ~ 76%

Geometries:



C. Piemonte 12

…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 measurementfast test to verify functionality and uniformity of the properties.

• Functional characterization in darkfor 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 FBK



C. Piemonte 14

Leakage current: mainly due to

surface generation at the

micro-diode periphery

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 35

Vrev [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 of

devices at wafer level



C. Piemonte 15

Dark signals are exactly equal to photogenerated signals

functional measurements in dark give a completepicture of the SiPM functioning

Signal 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)

A m p l i t u d 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: 50x50mm2



C. Piemonte 16

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120

Charge (a.u.)

C o u n t s

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)

G a i n

Pulse gen.

Laser

Pulse area

= charge

histogram

collection

SiPM

~ns

1p.e. 2

3

4

pedestal.

Excellentcell

uniformity

Linear

gain

Signal properties – NO amplifier



C. Piemonte 17

s = single

d = double pulses

a = after-pulse

VBIAS

SiPM

50

Digital

Scope

Pulses at the scope.

Av

100x

Signal properties – with amplifier

A voltage amplifier allows an easier characterization,

but attention must be paid when determining the gain



C. Piemonte 18

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

Let’s look at the electro-optical characteristics of

these devices:

Micro-cell size: 50x50mm2



C. Piemonte 19

1x1mm2 SiPM - 50x50mm2 cell

0.01

0.10

1.00

-1.0E-08 4.0E-08 9.0E-08 1.4E-07

Time (s)

A m p l i t u d e ( a . u . )

T = 25C

T = 15C

T = 5C

T = -5C

T = -15C

T = -25C

Signal shapeFast transient:

avalanche current

through parasitic

capacitance in

parallel with

quenching res.

Slow transient:

Exponential recharge

of 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 50W

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)

A m p l i t u d e

( a . u . )

T = 25C

Signal shape



C. Piemonte 20

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)

C o

u n t s

DC 28

DC 28.5

DC 29

DC 29.5

DC 30

DC 30.5DC 31

DC 32

DC 33

1x1mm2 SiPM – 50x50mm2 cell

Dark count

Growing

thresholdT = -30C VBD = 27.2V

From this plot we get

idea of dark rate and

optical cross-talk

probability



C. Piemonte 21


1.0E+05

1.0E+06

1.0E+07

27 28 29 30 31 32 33 34 35Voltage (V)

D a r k c o u n t

( H z

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)

G a i n

T = 25C

T = 15C

T = 5C

T = -5CT = -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)

B r e a k d o w n v o l t a g e

( 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 4.2

1000/T (1/K)

D a r k c o u n t ( H z )

DC 2V

DC 3V

DC 4V

• 2V overvoltage

• 3V overvoltage

• 4V overvoltage



C. Piemonte 22

4x4mm2 SiPM - 50x50mm2 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)

A m p l i t u d 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)

D a r k c o u n t

( H z )

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)

G a i n

-15C

-25CGain

Dark count



C. Piemonte 23


Same conclusions as forthe 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

1

2 3

4

5

1

2

3 45 6

12

3

4 5 6 7

8

T=-25C Vbd=27.6V

Charge spectra whenilluminating the device

with short light pulses



C. Piemonte 24

Photo-detection efficiency (1)



C. Piemonte 25

Photo-detection efficiency (2)

dark pulses light pulses

DC curr

with light

DC curr.

wo light



C. Piemonte 26

…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)

P D E

L=400nm

L=425nm

L=450nm

L=475nmL=500nm

L=550nm

50x50mm 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)

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



C. Piemonte 28

Time resolution (2)

Distribution of thetime difference

Timing performance (s)

as a function of theover-voltage



C. Piemonte 29

Microcell functionality measurement

(measurement at RWTH Aachen)



C. Piemonte

Measurement of microcell

eficiency with a 5 umLED spot diameter




C. Piemonte




C. Piemonte 32

Some applications and

projects in which we areinvolved



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 35

Vrev [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: 40x40mm2



C. Piemonte 34

Na22 spectrum with LSO

on a single SiPM(1x1mm2, 40x40mm2 cell)

Res = 18%

Tests are ongoing in Pisa(DASiPM project, A. Del Guerra)

on these devices coupled with pixellated

and 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)

M u o n E f f i c i e n c y f o r 1 k H z n o i s e

2.8 mm round IRST

SiPM for CMS- Outer Hadron calorimeter

Muon response in YB2 using SiPMs

Muon Efficiency in YB2Baseline HPD response at 8 kV

Circular SiPM - 50x50mm2 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 bundle

of 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 project

Development 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



• 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

Piemonte 2

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