Silicon Photomultipliersa new device
for frontier detectorsin
HEP, astroparticle physics, nuclear medical and industrial applications
Nepomuk OtteMPI für Physik, Munich
Max-Planck-Institut für PhysikA. Nepomuk Otte
Outline
• Motivation for new photon detectors
• APDs in proportional and Geiger mode
• From single APDs in Geiger mode to Silicon Photomultipliers
• SiPM characteristics
• Current status of development
• PET as one example of application of SiPM
Max-Planck-Institut für PhysikA. Nepomuk Otte
Many future experiments will use>> 100,000 photon detectors
• robust and stable• easy to calibrate• blue sensitive• low cost (+ low peripheral costs)• compact• low power consumption• …• highest possible photon detection efficiency
Experiments that will use this photon detector
Requirements to be fulfilled by the photon detector candidate:
Max-Planck-Institut für PhysikA. Nepomuk Otte
Ground based Gamma Ray Astronomy
http://wwwmagic.mppmu.mpg.de/
Gamma Ray induces electromagnetic cascade
relativistic particle shower in atmosphere
Cherenkov light
fast light flash (nanoseconds)100 photons per m² (1 TeV Gamma Ray)
MAGIC: world largest air Cherenkov telescope
Max-Planck-Institut für PhysikA. Nepomuk Otte
to be achieved with
• Lowering Energy threshold down to 10 GeV
• Improve sensitivity by factor of 10
• Extend Observations into moonshine time
Future Plans
• High Performance Photon Detectors
and
• Large Array of Telescopes (10…20)
Max-Planck-Institut für PhysikA. Nepomuk Otte
Cosmic Ray Physics from Space
30°
400
km
≈ ≈
≈
ČerenkovFluorescence
EECR
230 kmEarth
Atmosphere
M .C .M . ‘0 2
30°
400
km
≈ ≈
≈
ČerenkovFluorescence
EECR
230 kmEarth
Atmosphere
M .C .M . ‘0 2
Atmospheric SoundingAtmospheric Sounding
http://www.euso-mission.org/
• Highest energy cosmic rays > 1020 eV• GZK mechanism• sources of CR• …
One promising photon detector candidate
The Silicon Photomultiplier
Max-Planck-Institut für PhysikA. Nepomuk Otte
A look into basic operationsof
semiconductor photon detectorswith
internal amplification
Max-Planck-Institut für PhysikA. Nepomuk Otte
• Bias: (10%-20%) ABOVEbreakdown voltage
• Geiger-mode: it’s a BINARYdevice!!
• Count rate limited
• Gain: “infinite” !!
• Bias: slightly BELOW breakdown
• Linear-mode: it’s an AMPLIFIER
• Gain: limited < 300 (1000)
• High temperature/bias dependence
• No single photo electron resolution
Linear/Proportional Mode
Geiger Mode
Slide adapted from Cova et al. NIST 2003Workshop on single photon detectors
log
(Ga
in)
Reverse Bias Voltage
Geigermode
Linearmode
0
Working modes of Avalanche Photodiodes
no gain
Max-Planck-Institut für PhysikA. Nepomuk Otte
Advantages of APDs in Geiger Modeor
Single Photon Avalanche Diodes (SPADs)
• Large standardized output signalhigh immunity against pickup
• High sensitivity for single photons
• Excellent timing even for single photo electrons (<<1ns)
• Good temperature stability
• Low sensitivity to bias voltage drifts
• Devices operate in general < 100 V
• Complete insensitive to magnetic fields
• No nuclear counter effect (due to standardized output)
Max-Planck-Institut für PhysikA. Nepomuk Otte
The principal 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
solved in SiPM concept
Max-Planck-Institut für PhysikA. Nepomuk Otte
Basic unit in a SiPM is a Single Photon Avalanche Diode (SPAD)
Breakdown in SPAD is quenched by individual polysilicon resistor (passive quenching)from B. Dolgoshein (ICFA 2001)
http://www.slac.stanford.edu/pubs/icfa/
Substrate p+
p+Guardring n-
n+ SiO2
Si Resistor* Al-conductorVbias
p-
Max-Planck-Institut für PhysikA. Nepomuk Otte
...
Vbias
The Silicon Photomultiplier or Geiger-APD
typically 100…2000 small SPADs / mm²
All SPADs connected in parallel
30µm
1mm
Bias andOutput
Only one common signal line
SiPM
Max-Planck-Institut für PhysikA. Nepomuk Otte
SiPM output is the analog sum of all SPADs
Well defined output signal per SPAD multi pixel resolution
Max-Planck-Institut für PhysikA. Nepomuk Otte
Dynamic Range
Dynamic range naturally limited by number of available SPADs
working condition:Number of photo electrons < SPADcells
⎥⎥⎦
⎤
⎢⎢⎣
⎡−⋅=
⋅−
available
photon
NPDEN
availablefiredcells eNN 1
From probability considerations:
1 10 100 1000 100001
10
100
1000
Number of pixels fired
Number of photoelectrons
576 1024 4096
from B. Dolgoshein Light06
workin
g range
20% deviation from linearity if 50% of cells respond
Max-Planck-Institut für PhysikA. Nepomuk Otte
Photon Detection Efficiency (PDE)or
Effective Quantum Efficiency
Most important parameter of a photon detector!!
limiting factors:
• Fraction of sensitive area (20% - 80%)
• Intrinsic quantum efficiency
• Surface reflection losses
• Probability for Geiger breakdown(depends on electric field)
W.Oldham, P.Samuelson, P.Antognetti, IEEE Trans. ED (1972)
In total: Currently claimed best PDE values are ~40% >60% seem feasible
• SPAD recovery time (passive quenching
• Active volume / absorption length
Max-Planck-Institut für PhysikA. Nepomuk Otte
Problems:
Optical Crosstalk
High Dark Count Rate
Max-Planck-Institut für PhysikA. Nepomuk Otte
• Hot-Carrier Luminescence 105 avalanche carriers 3 emitted photon
e.g A. Lacaita et al, IEEE TED (1993)
• SPADs not only detect photonsthey also emit photons during breakdown
Emission microscopy picture of a prototype SiPM
Optical Crosstalk
Max-Planck-Institut für PhysikA. Nepomuk Otte
Optical crosstalk
Artificial increase in signal
Excess Noise Factor of SiPM
Photons can trigger additional cells
Sketch from Cova et al. NIST 2003Workshop on single photon detectors
can be quite significant
Max-Planck-Institut für PhysikA. Nepomuk Otte
How to suppress Optical Crosstalk?
Possible counter measures:
• Lowering bias voltage decrease in breakdown probability
• Lowering SPAD cell capacity
• Optical insulation between SPAD cells
(Price to pay: lower PDE)
Max-Planck-Institut für PhysikA. Nepomuk Otte
Blocking Photons with Grooves
0 100 200 300 400 500 6001
10
100
1000
10000
eve
nts
channel
200 400 600 800 1000
1
10
100
1000
10000
1
0
Co
unts
QDC channel
SiPM Z-type. U-Ubd
=8V. kopt
=1,85. tgate
=80ns.
QDC LeCroy 2249A. Noise.
Gain: 3•106; No grooves
Gain: 3•107; with grooves
from B. Dolgoshein MEPhI
Suppression of crosstalk seems possibleExcess Noise Factor ~1
Max-Planck-Institut für PhysikA. Nepomuk Otte
Dark Count Rate
Two main contributions:
Free Carrier Generation: Tunneling:
It is a Complex Topic; here only the very basics:
Depends on temperature(Can be cooled away)
Depends on operation voltage Influenced by design of the device
Max-Planck-Institut für PhysikA. Nepomuk Otte
Dark Count Rate
high single electron dark rate (105 – 106 1/sec*mm² at room temp.)
In most applications trigger threshold at several photoelectrons
accidental trigger rate << single electron dark rate
Silicon photomultipliers are sensitive to every single electron
But:
Strong reduction of noise by lowering operation temperature(Factor two every 8°C)
In addition:
Y. Musienko
Max-Planck-Institut für PhysikA. Nepomuk Otte
Let’s go shopping
In general devices are still in prototype stage
Various very intense developments ongoing in Industry (>4) and Research Institutes:
• Center of Perspective Technology and Apparatus CPTA, Moscow
• MEPhI/Pulsar Enterprise, Moscow
• JINR(Dubna)/Micron Enterprise
• HAMAMATSU
• RMD (Abstract 218)
• SensL, Ireland
• Max-Planck Semiconductor Lab, Munich
Max-Planck-Institut für PhysikA. Nepomuk Otte
MEPhI/Pulsar/MPI
In collaboration with MPI for Physics (Munich)
Intended application:
Air Cherenkov Telescopes (MAGIC)
Cosmic Ray space missions (e. g. EUSO)
Development aimed at:
sensor area 10x10 mm²
Photon Detection Efficiency >60%Largest existing SiPM 5x5 mm²
2500 APD cells
Current device parameters @ 56V:
Dark rate: 500kHz at -60°C
Gain: 107
PDE: (see next slide)
Max-Planck-Institut für PhysikA. Nepomuk Otte
5x5mm² SiPM: Photon Detection Efficiency
QETPDE GeigerpackingSiO ⋅⋅⋅= εε2
εpacking = 0.5 εGeiger ≈ 1
300 350 400 450 500 550 600 650 7000
10
20
30
40
50
60
70
80
90
Absorption length x0, µm
T (70 nm SiO2)
SiPM (T = -60 0C)
Eff
icie
ncy
ε,
%
Wavelength λ, nm
PMT XP2020Q
0,00573 4,433,31,721,380,3120,09740,0145
B.Dolgoshein,LIGHT06
No antireflection coating of SiPM
QETPDE GeigerpackingSiO ⋅⋅⋅= εε2
εpacking = 0.5 εGeiger ≈ 1
300 350 400 450 500 550 600 650 7000
10
20
30
40
50
60
70
80
90
Absorption length x0, µm
T (70 nm SiO2)
SiPM (T = -60 0C)
Eff
icie
ncy
ε,
%
Wavelength λ, nm
PMT XP2020Q
0,00573 4,433,31,721,380,3120,09740,0145
B.Dolgoshein,LIGHT06
No antireflection coating of SiPM
limiting above400nm
Max-Planck-Institut für PhysikA. Nepomuk Otte
Hamamatsu: Digital Pixel Photon Detector
Device from early 2005
T. TakeshitaSnowmass 05
Max-Planck-Institut für PhysikA. Nepomuk Otte
Hamamatsu
0-100-1.5 (100 pixels), U=48.9V, T=22.6C
0
5
10
15
20
25
30
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
PDE
[%]
D. Renker (2005)Latest devices achieve ~40% PDE @ 450nm (D. Renker)
Gain: 107
Dark noise: 550kHz @ room temperatureCrosstalk: 30%
Max-Planck-Institut für PhysikA. Nepomuk Otte
Metal Resistive layer Semiconductor (MRS)
from K. Voloshin NIM A 539 (2005)
~100% Geometrical occupancy
PDE limited by semitransparent metal electrode
10,000 cells/mm² are possiblewith this technology
See results on PET later
Max-Planck-Institut für PhysikA. Nepomuk Otte
MRS: PDE
Photon detection efficiency (Room temperature)
0
5
10
15
20
25
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
PDE
[%]
XP2020 PMT
INR/JINR APD
CPTA APD
Y.Musienko (2005)
Max-Planck-Institut für PhysikA. Nepomuk Otte
Ongoing Development:SiPM exploiting Backillumination
predicted characteristics:
• PDE > 80%• Single photo electron time jitter ~ nsec• Cooling is mandatory
By the Semiconductor Laboratory affiliated to the MPIs for Physics and Extraterrestrial Physics
Si
photondepleted bulk
avalanche regionspath of the photo electron
output
50µm … 450µm
Blow up of one “cell”
Max-Planck-Institut für PhysikA. Nepomuk Otte
drift rings p+
shallow p+
avalanche region
photondrift path of the photo electron
µm100
µmµm 450...50
quenching resistor
output line
deep n
n type depleted bulk
• test structures of novel avalanche structure will be finished next month• After successful evaluation prototypes end 2007
Crosstalk problem can be a showstopper!!will be evaluated by dedicated structuressmall cell capacitance is of advantage
Max-Planck-Institut für PhysikA. Nepomuk Otte
Possible Applications of SiPM
The SiPM opens up a great variety of possible applications
• Calorimeter readout in magnetic fields (CALICE, ILC, …)• Space applications (EUSO, …)• Astroparticle experiments (MAGIC,…)• Medical imaging (PET)• Fast timing applications (<1nsec)• time resolved X-Ray correlation spectroscopy• Fiber trackers• Large pixilated photon detectors• …
In some applications the SiPM is already superior to PMT’s or APD’s
Some examples
Max-Planck-Institut für PhysikA. Nepomuk Otte
SiPMs in PET
Advantage: very compact, no sophisticated amplifier needed, …
Otte, et al. NIM A 545 (2005)
• direct coupling of SiPM to crystal
• no cooling
• Factor 4 area miss match between SiPM and crystal
• Energy resolution 22% FWHMon 22Na coincidence spectrum
• Time resolution 1.5 nsec FWHM
Things have quite improved since then
Max-Planck-Institut für PhysikA. Nepomuk Otte
First result of measurments with MW-3 (3x3 mm2) Geiger- mode APDs from Dubna (Z. Sadygov) + LYSO crystals (2x2x10 mm3)
0 200 400 6000
500
1000
1500
2000
150 200 2500
500
1000
1500
2000
Amplitude (pC)
Co
un
ts
511 keV : ∆A/A = 12.7% (FWHM)1275 keV : ∆A/A = 7.7% A
1275 / A
511 = 2.60
22Na + LSO (2x2x10 mm3; reflector = teflon)
MW-3 (3x3 mm2, n.1): RT, U = 138.0V, I = 1.05µA
Alexey Stoykov,Dieter Renker (PSI)
Energy Resolution:12% FWHM
Time Resolution:540ps
(limited by crystal)
MRS diode used
Max-Planck-Institut für PhysikA. Nepomuk Otte
CAlorimeter for the LInearCollider Experiment
High granularity needed
SiPM is equivalent to PMTs and APD (not shown)
Calicecollaboration
see also:Gerald EigenAbstract 211
Max-Planck-Institut für PhysikA. Nepomuk Otte
Things not discussed
30 minutes are by far not enough to give an overview on SiPM
• Cell recovery• Quenching mechanisms• Importance of parasitic capacitances• Afterpulsing• …
Max-Planck-Institut für PhysikA. Nepomuk Otte
Summary
The silicon photomultiplier is a real breakthrough in photon detection!!
CMOS like technology prospects for cheap mass production <10$ per mm²
It can not be damaged by exposure to strong source of light
Offers high internal amplification (>105)
Fast timing (<nsec)
No aging
Low power consumption (1…100µW/mm²)
High photon detection efficiency (>60%)
…
Max-Planck-Institut für PhysikA. Nepomuk Otte
Summary
High dark count rate not a showstopper for most applications
Optical crosstalk is a problem but solvable
Current parameters of available prototypes:
Detector area: 5x5 mm²
Photon detection efficiency: ~40%
Dark rate at room temperature: 105-106 counts/sec/mm²
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