development of the first prototypes of silicon photomultiplier at itc-irst

10th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006

Development of

the first prototypes of

Silicon 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

Nicoleta Dinu 210th Pisa Meeting on Advanced Detectors, Isola d’Elba, May 2006

• Motivations for new photon detectors

• What is a Silicon PhotoMultiplier (SiPM)?

• Characteristics of the first SiPM prototypes developed at ITC-irst

• Summary and outlook

Outline


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


A look on photon detectors characteristicsVACUUM

TECHNOLOGY

SOLID-STATE

TECHNOLOGY

PMT MCP-PMT HPD PN, PIN APD GM-APD

Photon detection efficiency

Blue 20 % 20 % 20 % 70 % 50 %

Green-yellow 40 % 40 % 40 % 80-90 % 60-70 %

Red 6 % 6 % 6 % 80 % 80 %

Timing / 10 ph.e 100 ps 10 ps 100 ps few ns tens of ps

Gain 106 - 107 106 - 107 3 - 8x103 1 200 V 105 - 106

Operation voltage 1 kV 3 kV 20 kV 100-500V 100 V

Operation in the magnetic field

10-3 T Axial magnetic

field 2 T

Axial magnetic field 4

T

No sensitivity

No sensitivity

No sensitivity

Threshold sensitivity (S/N1)

1 ph.e 1 ph.e 1 ph.e 100 ph.e

10 ph.e 1 ph.e

Shape characteristics sensible

bulky

compact sensible, bulky

robust, compact, mechanically rugged

VACUUM

TECHNOLOGY

SOLID-STATE

TECHNOLOGY

PMT MCP-PMT HPD PN, PIN APD GM-APD

Photon detection efficiency

Blue 20 % 20 % 20 % 60 % 50 % 30%

Green-yellow 40 % 40 % 40 % 80-90 % 60-70 % 50%

Red 6 % 6 % 6 % 90-100 % 80 % 40%

Timing / 10 ph.e 100 ps 10 ps 100 ps tens ns few ns tens of ps

Gain 106 - 107 106 - 107 3 - 8x103 1 200 105 - 106

Operation voltage 1 kV 3 kV 20 kV 10-100V 100-500V 100 V

Operation in the magnetic field

10-3 T Axial magnetic

field 2 T

Axial magnetic field 4

T

No sensitivity

No sensitivity

No sensitivity

Threshold sensitivity (S/N1)

1 ph.e 1 ph.e 1 ph.e 100 ph.e

10 ph.e 1 ph.e

Shape characteristics sensible

bulky

compact sensible, bulky

robust, compact, mechanically rugged


Rquenching

-Vbias

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

Current (a.u.)

Time (a.u.)

Standardized output signal

Planar diodeR. H. Haitz, J. App.Phys. Vol. 36, No. 10 (1965) 3123

Reach-through diodeJ.R. McIntire, IEEE Trans. El. Dev. ED-13 (1966) 164

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


What is a SiPM ?

- Vbias

n pixels

One pixel fired

Two pixels fired

Three pixels fired

Current (a.u.)

Time (a.u.)

Al

ARC

-Vbias

Back contact

ppnn++

ppnn++

Rquenching

hh

p+ silicon wafer

Front contact

• matrix of n microcells in parallel

• each microcell: GM-APD + Rquenching

Main inventors: V. M. Golovin and A. Sadygov

Russian patents 1996-2002

Out

The advantage of the SiPM in comparison with GM-APDANALOG DEVICE – the output signal is the sum of the signals from all fired pixels

SiPM – photon detector candidate for many future applications


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


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)

avalanchegeomSiPM QE


Layout & Fabrication Process

• 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

• Layout includes:• several SiPM designs with different implant geometries• test structures for process monitoring• test structures for analysis of the SiPM behavior


Wafer and SiPM designMain blockWafer

SiPM geometric characteristics:• area: 1 x 1 mm2

• number of micro-cells: 625• micro-cell size: 40 x 40 m2

SiPM

1 mm

1 m

m


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

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

Vback [V]

Lea

kag

e cu

rren

t [A

]

pixel/ block1

pixel/ block2

pixel/ block3

pixel/ block4

pixel/ block5

pixel/ block6

pixel/ block7

pixel/ block8

pixel/ block9

pixel/ block10

VBD = 31 V

Single micro-cell test structures

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

Vback [V]

Le

ak

ag

e c

urr

en

t [A

]

SiPM/ block1SiPM/ block2SiPM/ block3SiPM/ block4SiPM/ block5SiPM/ block6SiPM/ block7SiPM/ block8SiPM/ block9SiPM/ block10

VBD = 31 V

SiPM (625 micro-cells)


Quenching resistance

Ωmicrocell

Nmicrocell

R

SiPMR 499

-2.5E-03

-2.0E-03

-1.5E-03

-1.0E-03

-5.0E-04

0.0E+00

0.0 0.5 1.0 1.5 2.0

Vback [V]

For

war

d cu

rren

t [A

]

SiPM-block4

SiPM-block5

y = -0.002x + 0.0011

R = 500 ohm

SiPM (625 micro-cells)

Uniform micro-cell quenching

resistance over the wafer

Uniform SiPM quenching resistance over the wafer

Very good correlation between Rmicro-cell and RSiPM

kR cellmicro 312

-1.E-05

-8.E-06

-6.E-06

-4.E-06

-2.E-06

0.E+00

0 1 2 3 4

Vback [V]

Fo

rwa

rd c

urr

en

t [A

]

Pixel block 1

Pixel block 2

Pixel block 3

Pixel block 4

Pixel block 5

y = -0.0000032x + 0.0000018

R = 312 kohm

Single micro-cell test structures


SiPM internal gain

Gain:• linear variable with Vbias

• in the range 5 x 105 2 x 106

micro-cell capacitance• Cmicro-cell = 48 fF

rise time recovery time micro-cell recovery time• = Rquenching · Cmicro-cell ~ 20 ns

Rise time• 1 ns (limited by the read-out system)

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

1.6E+06

1.8E+06

2.0E+06

30 31 32 33 34 35 36

Bias Voltage (V)

Gai

n


1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 50 100 150 200 250

threshold (mV)

dar

k co

un

t ra

te (

Hz)

Room temperature (~ 23°C)•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 thefirst run

SiPM dark count

32.0 V32.5 V 33.0 V

33.5 V 34.0 V34.5 V

Dark count rate•linear variable with Vbias

•increases with the temperature

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

30 31 32 33 34 35 36

Voltage (V)

Dar

k C

ount

rat

e (H

z


Single photon counting capability

0

1 p.e.

2 p.e.

3 p.e.

4 p.e.5 p.e.

6 p.e.

7 p.e.

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

Excellent single photoelectron resolution


• 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 @ 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

Summary and outlook

development of the first prototypes of silicon photomultiplier at itc-irst

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