Claudio Piemonte, FBK 1
Single-photon detectorsin micro-electronics technology
Claudio PiemonteChief Scientist, Fondazione Bruno [email protected]
Claudio Piemonte, FBK 2
Outlook• Micro-electronics technology
• Single-photon detection why and where
• Approaches at single photon detection
• Single photon detection using impact ionization
in semiconductors
• Overview of SiPM parameters
• New trends in SPAD/SiPM
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Micro-electronics
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valves and
discrete components
transistors
and discrete
components
integrated
circuits
Electronics evolution
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Nel 1961, Fairchild
commercializes first
integrated circuit
1958, Jack Kilby,
Texas Instruments.
First integrated circuit.
Nobel prize 2000 SSI 10 components
(small scale integration)
Micro-electronics
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1970 VLSI
very large scale integration
thousands of components
(first microprocessors)
1980 ULSI
ultra large scale integration
millions of components
(advanced microprocessors)
Micro-electronics
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10 micron
digital electronics
analog electronics
Micro-electronics
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Micro-electronics
Present: going vertical!
Picture from: https://www.semiwiki.com/forum/content/860-physical-verification-3d-ic-designs-using-tsvs.html
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Micro-electronics
technology
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Starting material: silicon.
Sand: silicon oxide
Growth of silicon ingot
Silicon wafer
Pictures from: http://apcmag.com/picture-gallery-
how-a-chip-is-made.htm/
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Circuit design
Simulation
CAD design
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IC production
Silicon Foundry
Silicon wafer lotSilicon wafer
with thousands
of ICs
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IC production
Lithography: core of a foundry
Present CMOS technologies have 30-50 lithos
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Wafer testing and dicing
Automatic probers for
wafer level testing
Dicing in single ICs
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Packaging
“Pick and place”
IC in package
Pictures from: http://apcmag.com/picture-gallery-
how-a-chip-is-made.htm/
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Larger IC producers
http://anysilicon.com/top-semiconductor-foundries-capacity-2015-2016-infographic/
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CMOS technology
Complementary metal–oxide–semiconductor is a
technology for constructing integrated circuits.
Typically CMOS designs use complementary and
symmetrical pairs of p-type and n-type MOSFETs for logic
functions.
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CMOS image sensors
1um
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CMOS image sensors: evolution
Backside illumination
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CMOS image sensors
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Main features of the
micro-electronics technology
compact
rugged
low power consumption
Reliable, reproducible, mass-production
COST
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Micro-electronics
technology is the
ideal platform for the
development/production of
any sensor
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Low-level light detectionapplications
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Low-level light detection
we refer to this part
of the spectrum
~100 nm~2um
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Christopher Chunnilal, et al. Opt. Eng. 53(8), 081910 (July 10, 2014).
Single-photon applications
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Nuclear PhysicsCherenkov light detection Noble liquids TPCs
Spectroscopy
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Bio-medical applicationsPositron Emission Tomography Flow cytometry
TCSPC
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Lidar
Applications:Autonomus cruise controlSpeed gunLanding AidRendezvous and dockingEarth science….
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Quantum Random Number Gen.
The problem
of secure
communication
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Low-level light detectiontechnologies
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The problem: processing of extremely weak signals
Current signal:
1 pair/photon
Detector noise:
fluctuation of leakage
current
Electronics noise:
shot + thermal noise
Need of a detector with internal amplification to reduce
the impact of electronic noise!
Dominating
noise
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Vacuum-based photodetectorswith internal gain.
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PMT (photomultiplier tube)
MOST USED for low level light detection!
Pros:
• very mature technology
• low dark noise
• good QE in the whole light spectrum
Cons:
• sensible and bulky (vacuum-based)
• requires high voltage
• sensitivity to magnetic fields
• damaged with high light levels
Vacuum technologies
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MCP (micro-channel plate)
Vacuum technologies
Pros:
• low dark noise
• very fast
• large size possible
Cons:
• sensible and bulky (vacuum-based)
• requires high voltage
• damaged with high light levels
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HPD (hybrid photodetector)
Vacuum technologies
Pros:
• good photon resolution
• fast
• can be operated in magnetic field
Cons:
• sensible and bulky (vacuum-based)
• requires high voltage
• damaged with high light levels
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Transmission dynode
(Tynode/Trynode)
Vacuum technologies
TiN + Al2O3
ERC Membrane project
(H. Van Der Graaf)Patent US6657385
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Solid-state photodetectorswith internal gain.
(produced with micro-electronic technologies)
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+-
photon
semicon
n+
p+
V-
V+
time
Current
Photon
arrival
Photodiode (cross-section)
The photodiode
Movement of carriers
induces a current at the
electrodes according to
the Ramo theorem.
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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)
Ioniz
ation R
ate
s (
1/u
m)
Impact ionization:
carrier has enough kinetic
energy to break a bond, i.e.
to move an electron from
valence to conduction band
Ionization rates:
number of pairs created by
a carrier per unit distance
travelled
a field of ~3x105V/cm is
needed to create on average
a pair in 1mm travelled.
Impact ionization
an
ap
Silicon
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1E-16
1E-15
1E-14
1E-13
1E-12
1E-11
1E-10
1E-09
1E-08
1E-07
1E-06
-30 -25 -20 -15 -10 -5 0Reverse Bias Voltage (V)
Curr
ent (A
)
Simulated diode reverse current
IMPACT IONIZATION ONIMPACT IONIZATION OFF
VBD VAPD
Reverse current in a diode
Low field region (V<VAPD)
Leakage current is given by
thermal generation
in the depletion region:
I = q * G * Wdep = q * ni * 1/Tg *Wdep
High field region (V>VAPD)
Leakage current deviates from the
expected constant value because
some carriers “impact ionize”
A sort of “GAIN” could be defined
Very high field region (V>VBD)
the current rises indefinetly
“avalanche”
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Impact ionization
Avalanche Photo-Diode
Geiger-Mode Avalanche Photo-Diode/Single-Photon Avalanche Diode
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Avalanche photodiode (APD)
Electrons photo-generated in the drift region are
multiplied (on average) by the same factor!
n+
p+
p
-
+ Efield thin
multiplication
region
drift
region
p
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Noise in an APD
Fluctuation of leakage current
SHOT NOISEStatistical fluctuation of gain
(additional noise vs PD)
EXCESS NOISEIt deterioratess with gain
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Excess Noise Factor (F) in an APD
F = M*k + (2-1/M)(1-k) k = ah/ae for electron
injection
1
10
100
1000
0 1 2 3 4
F
k
G=100
G=20
K must be as small as
possible to minimize F.
Ideally = 0 =>
holes do not ionize
In silicon, k depends strongly on the field,
at low fields (~2x105V/cm) k<<1
Silicon
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n+
p+
p
-
+ Efield
p
photon
Reach-through APD
The structure can be designed
for backside illumination to
allow usage also at short
wavelengths.
photon
front-side illumination
suitable for red/IR light
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Features of an APD
1. Spatially uniform avalanche multiplication
No micro-plasmas dislocation-free process
2. Reduction of the field along the edges
guard-ring
beveled structure
n+
p+
p
p
n+
p+
p
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Features of an APD
3. Choice of semiconductor material based on:
- quantum efficiency at particular wavelength
- response speed
- noise
Germanium: Sensitivity from 1 to 1.6um
k~1 high F
High speed
Silicon: Sensitivity from 0.1 to 1um
k~0.1 low F
Hetero-junct.: sensitivity from 1 to 1.7um
k depends on materials
high speed
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t = 0 ……..let’s bias the diode at V>VBD
t < t0 ……..i=0 (if no free carriers in the high field region)
t = t0 ..........photocarrier initiates the avalanche
t0 < t < t1….avalanche spreading
t > t1 ……..self-sustaining current (limited by series resistances)
t
i
t0
i=iMAX
t1
GM-APD/SPAD: principle (i)
n+
p+
p
-
+ Efield
p
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We need to quench the avalanche to detect another photon
VBIAS
VD
• large resistance: passive quenching
• analog circuit: active quenching
t
i
t0 t1 t2
t
vD
vBD
GM-APD/SPAD: principle (ii)
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GM-APD/SPAD: model
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The GM-APD can be modeled with an electrical circuit and
two probabilities:
CD
RS
VBD
RQVBIASVD
SPAD
- CD = diode capacitance
- Rs = series resistance (~1kW)
- VBD = breakdown voltage
- RQ = quenching resistance (>300kW)
- VBIAS > VBD
- P01 = Triggering probability
- P10 = turn-off probability
which govern the switch transition
GM-APD/SPAD: model
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OFF condition: switch open,
(capacitance charged to VBIAS, no current
flowing)
Avalanche triggering (P01 ) [t0]
ON condition: switch closed
CD discharges to VBD with
a time constant RSxCD, at the same time
the external current grows to (VBIAS-VBD)/RQ
Avalanche quenching (P10) [t1]
OFF condition: switch open
diode capacitance recharghes from VBD
to VBIAS with a time constant RQxCD
Ready for new detection [t2]
CD
RS
VBD
RQVBIAS
IINTID
VD
DIODE
t
ID
t0
t2
t
IINT
~(VBIAS-VBD)/RQ
t1
~(VBIAS-VBD)/RQ
t0
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P01 – Triggering probability
MC simulations of the
current growth during an
avalanche build-up process[Spinelli, IEEE TED, vol. 44, n. 11, 1997]
avalanche failed
=> no photon detection
Triggering probability depends on the ionization rates.
Important factor in the photo-detection efficiency.
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1E-09
1E-07
1E-05
1E-03
1E-01
1E+01
1E+03
0E+00 1E-05 2E-05 3E-05 4E-05 5E-05 6E-05 7E-05
Current (A)
Avera
ge p
uls
e length
(s)
Quenching resistance must be high enough!!
R. Haitz, JAP vol.35, n.5 1964
P10 – Turn-off probability
probability to quench the avalanche by a fluctuation
to zero of the number of carriers crossing the HF
Steady current through junction (A)
Tim
e for
quench
ing (
s)
t
IINT
t1
~(VBIAS-VBD)/RQ
t0