Custom SPAD technology

Transcription

Recent advances in silicon single photon
avalanche diodes and their applications
Massimo Ghioni
Politecnico di Milano, Dipartimento di Elettronica e Informazione
Outline
2
• Single photon counting: why, what and how
• SPAD device technology: origin and evolution
• Single element SPAD detectors

recent advances

custom SPAD vs standard CMOS technology

application cases
• SPAD array detectors

application cases
• Conclusions
M. Ghioni
Pavia, April 3, 2007
Why single photon counting?
For ultimate sensitivity in optical signal measurement !
straight digital technique
overcomes limits of analog measurements (circuit noise)
photon timing with picosecond precision
measurement of ultrafast optical signals
by Time Correlated Single Photon Counting (TCSPC)
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3
Why high sensitivity?
• Low sample concentration
• Minute samples
• Short exposure time
• Photon losses (poor collection, absorption, etc.)
• Low excitation power
• Greater magnification
• Ultra-weak emission (Raman scattering etc.)
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4
Photon counting/timing applications
bioluminescence
single molecule
detection
detector
calibration
primary
radiometric
scales
quantum
standards
quantum
imaging
quantum
cryptography
hyper-spectral
imaging
medical
imaging\
Metrology
Metrology
Quantum
Information
Processing
Biotechnology
lighting
Electronics
displays
5
photon
counting
count
Medical
Physics
Space
Applications
single photon
sources
medical / non
interactive
imaging
entertainment
neutrino/
cherenkov / dark
matter detection
quantum
computing
radioactivity
Military
Military
Meteorology
Meteorology
nuclear
night vision
IR detectors
robust imaging
devices
remote sensing
environmental monitoring
source: www.photoncount.com
M. Ghioni
lidar
security
chemical – bio agent detection
Available detectors
Vacuum Tube
PMT
Currently used in photon counting/timing applications
Limited quantum efficiency
Solid State
APD (ordinary Avalanche PhotoDiodes)
No single photon detection
Special CCD (EM-CCD, I-CCD)
Photon counting possible only at low frame rates
Limited time resolution
SSPD (Superconducting Single Photon Detector)
Limited active area
Need to be operated at < 4 K
SPAD (Single Photon Avalanche Diode)
Best suited for photon counting/timing applications
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6
SPAD: reverse I-V characteristic
7
No avalanche
VBD
Avalanche
IREV [mA]
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VREV [V]
APD vs. SPAD
8
APD
SPAD
ON
Avalanche
Quenching
Reset
Avalanche PhotoDiode
Single-Photon Avalanche Diode
•
Bias: slightly BELOW breakdown
•
Bias: well ABOVE breakdown
•
Linear-mode: it’s an AMPLIFIER
•
Geiger-mode: it’s a TRIGGER device!!
•
Gain: limited < 1000
•
Gain: meaningless !!
M. Ghioni
for SPAD operation…
mandatory
• to avoid local Breakdown, i.e.
• edge breakdown Æ guard-ring feature
• microplasmas
Æ uniform area, no precipitates etc.
but for good SPAD performance.....
further requirements!!
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9
Earlier Diode Structures
10
Haitz’s planar diode (early 60’s)
n+
metal
5 µm
oxide
5 µm
n-
guard ring
p
metal
Avalanche physics investigation
• operated at low voltage (a few tens of Volt)
• limited power dissipation during the avalanche (a few hundred milliwatt)
• fabricated in ordinary silicon wafer with a planar technology
R.Haitz, J.Appl.Phys. 35, 1370 (1964), J.Appl.Phys. 36, 3123 (1965)
M. Ghioni
Earlier Diode Structures
RCA reach-through diode (circa 1970)
• operated at high voltage (a few hundred Volts)
• high power dissipation during the avalanche (around ten watt)
• proprietary non-planar technology on a ultra-pure high-resistivity silicon
wafers
R. McIntyre, H. Springings, P.Webb, RCA Engineer 15, 1970
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Haitz’s planar diode
•
12
Deep diffused guard ring

causes the photon detection efficiency (PDE) to be non uniform in the active zone
PDE = QE x η
- QE = quantum efficiency
- η = avalanche triggering probability
M. Ghioni
Haitz’s planar diode
-
Haitz’s structure has drawbacks in applications requiring high-resolution
photon-timing
-
Long diffusion tail
Multi-exponential tail makes deconvolution more difficult
G. Ripamonti and S. Cova, Solid State Electron. 28, 925 (1985)
T.A.Louis et al, Rev.Sci.Instrum. 59, 1148 (1988).
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Epitaxial SPAD structure
14
5
10
4
Counts
10
3
10
2
10
1
10
0
10
0
1
2
3
4
Time (ns)
- Shorter tail duration
- p+ implantation for VBD control
- Fully isolated devices on wafer
- Guard Ring still employed Æ non-uniform PDE, non-exponential tail
M.Ghioni, S.Cova, A.Lacaita, G.Ripamonti, Electron. Lett. 24, 1476 (1988)
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Double-epitaxial SPAD structure
15
5
10
4
Counts
10
3
10
2
10
1
10
0
10
0
1
2
3
4
Time (ns)
•
Short diffusion tail with clean exponential shape
•
Active area defined by p+ implantation
•
No guard-ring (uniform PDE)
•
Adjustable VBD and E-field
•
SUITABLE for array fabrication
A.Lacaita, M.Ghioni, S.Cova, Electron.Lett. 25, 841 (1989)
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neutral p layer thickness w
tail lifetime τ = w2 / π2Dn
5
Double-junction SPAD structure
16
FWHM = 35ps
n+
hν
FW(1/100)M = 125ps
p+
FW(1/1000)M = 214ps
p-epi
p++
p++
n-substrate
• Patterned p++ buried layer
• No Tail (no carrier collection from neutral layer)
• Suitable for small area devices (Φ ~ 10µm)
A.Spinelli, M.Ghioni, S.Cova and L.M.Davis, IEEE J. Quantum Electron. QE-34, 817 (1998)
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Device technology: prospect
• Two different approaches

standard CMOS technology

custom SPAD technology
have to face most requested improvements:
higher photon detection efficiency (especially in the red region)
larger active area (~ 100 µm)
shorter diffusion tail
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Full process flexibility makes it possible to address the most
demanding requirements
0.7
hν
p
p+
n
n+
p+
Photon Detection Efficiency
•
18
Excess Bias Voltage
0.6
10 V
7V
5V
0.5
0.4
0.3
0.2
0.1
0
400
500
600
700
800
Wavelength (nm)
→ Top epi-layer thickess/doping adjusted to increase PDE
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900
1000
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4
10
FWHM = 35 ps
p
n+
10
p+
p+
Counts
hν
3
FW1/100M = 370 ps
2
10
n
1
10
0
10
0
400
800
1200
1600
Time (ps)
→ Bottom epi-layer thickess adjusted to achieve short diffusion tail
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2000
20
hν
¾heavy phosphorus diffusion
p
n+
p+
p+
¾p/p+ segregation gettering
n
→ Specific designed gettering processes for removing transition metal impurities
responsible for:
- thermal carrier generation (dark count rate - DCR)
- carrier trapping (afterpulsing effect)
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Dark Count Rate (primary noise)
• Thermally generated carriers trigger avalanche pulses
• Shot noise, equivalent to dark current in PINs / APDs
Thermal Generation via GR centers
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Field-Enhanced Generation
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Field-enhanced generation
Coulombic well
•
Poole-frenkel effect
barrier height lowered
22
Dirac well
• Phonon-assisted tunneling
barrier width decreased
¾ Phonon process is thermally activated
¾ Tunneling is temperature independent
¾ Overall temperature dependence is a function of electric field
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10000
hν
n+
1000
p+
p
p+
Counts (c/s)
SPAD with "standard" electric
100
10
n
SPAD with "engineered" electric field
1
0.1
-80
-60
-40
-20
Temperature (°C)
→ Electric field engineered to avoid band-to band tunneling

M. Ghioni
Field-enhanced generation less intense
DCR strongly reduces with temperature
0
20
Large area SPADs: dark count rate
24
Dark Count Rate (DCR)
• Avalanche pulses triggered by
thermally generated carriers
25 • Equivalent to the dark current in
PINs and APDs
100000
10000
Counts (c/s)
200 µm
1000
100
100
100 µm
Practical Exploitation of DCR vs T
10
Peltier cooling to -20°C
50 µm
1
is simple / cheap / rugged
0.1
-50
-40
-30
-20
-10
0
10
20
Temperature (°C)
Typical performance @5V excess bias voltage
M. Ghioni
reduces DCR by a factor 25 – 100
Large area SPADs: afterpulsing
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Afterpulsing Effect
• Carriers trapped during
avalanche
• Carriers released later trigger the
avalanche
• Increases noise and affects
correlation measurements
Characterization of afterpulsing
• 200 µm detector
• 80ns deadtime
• Time Correlated Carrier Counting
(TCCC) method
• Afterpulsing negligible after 1 µs
• Total afterpulsing probability:
~ 2% @ RT
~ 6% @ -25°C
M. Ghioni
Large area SPADs: time response
26
100000
By using a current pick-up circuit* and
sensing the avalanche current at very
low level (< 100 µA):
10000
Counts (c/s)
FWHM = 35 ps
1000
λ = 820 nm
100
FWHM not dependent on the detector
diameter
35ps FWHM checked for 200µm device
10
at room temperature
1
11.5
12.0
12.5
13.0
13.5
14.0
14.5
Very stable response up to 4 Mc/s
Time (ns)
- clean exponential tail with 240 ps lifetime
* S.Cova, M.Ghioni, F.Zappa, US patent No. 6,384,663 B2, 2002
A.Gulinatti et al, Electron. Lett. 41, 272 (2005)
M. Ghioni
Custom SPAD technology: pros & cons
PROs
•
Flexibility: designer can modify process parameters & conditions
•
Optimization of device structure can be pursued
•
High-performance SPADs demonstrated with diameter up to 200 µm
•
Progress of technology driven by detector requirements
CONs
•
Monolithic integration of detector and electronics requires circuit
components specifically designed in the detector technology
•
Dedicated silicon foundry is required
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CMOS based SPAD
•
standard HV-CMOS technology
•
deep n-well to cut off the diffusion tail
•
p+n junction (intrinsically low PDE)
A. Rochas et al, Rev. Sci. Instrum. 74, 3263 (2003)
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CMOS-SPAD: experimental results
DCR
PDE
•
low PDE @ 600-700 nm
•
fairly high DCR @ Vexc>3V (φ = 12µm)
•
DCR decreases slowly with T
F. Zappa et al, Optics Letters 30, 1327 (2005)
S.Tisa et al, IEEE-IEDM, 815 (2005)
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0.8 µm HV-CMOS
CMOS-SPAD: experimental results
Afterpulsing
Time response
Afterpulsing Probability
Density (1/ns)
1E-02
55ns hold-off
1E-03
1E-04
1E-05
1E-06
0
5
10
15
20
25
30
35
40
Time (ns)
•
2.6% total afterpulsing probability @ 55ns hold-off
•
35 ps time resolution FWHM
•
long diffusion tail
F. Zappa et al, Optics Letters 30, 1327 (2005)
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CMOS-SPAD: pros & cons
PROs
•
Standard fabrication in silicon foundry, mature technology
•
Straightforward integration: on-chip detector & electronics
•
Small parasitic capacitance Æ small avalanche charge for small detectors
but NOT for wide devices (higher junction cap: 100 µm diam. Æ CJ~ 1pF )
CONs
•
High voltage CMOS process required
•
No flexibility in processing
•
SPAD’s with diameter > 50 µm not yet demonstrated
•
Progress of technology driven by circuit requirements
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Quenching circuits
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Quenching circuits
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Passive quenching is simple...
τreset=RL (Cd + Cs)
… but suffers from
• not well defined deadtime
• photon timing spread
• τreset > 100 ns for (Cd + Cs) > 1 pF
• et al
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Quenching circuits
34
Active quenching...
Output Pulses
...provides:
• short, well-defined deadtime
• high counting rate > 1 Mc/s
P.Antognetti, S.Cova, A.Longoni
• good photon timing
IEEE Ispra Nucl.El.Symp. (1975)
• standard logic output
M. Ghioni
Euratom Publ. EUR 5370e
iAQC: integrated Active Quenching Circuit
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Practical advantages
• Miniaturization Æ mini-module detectors
• Low-Power Consumption Æ portable modules
• Rugged and Reliable
Plus improved performance
•
•
•
•
•
Reduced Capacitance
Improved Photon Timing
Reduced Avalanche Charge
Reduced Afterpulsing
Reduced Photoemission Æ reduced crosstalk
in arrays
F.Zappa, S.Cova, M.Ghioni, US patent 6,541,752 B2, 2003 (prior. March 9, 2000)
F.Zappa et al., IEEE J. of Solid State Circuits 38, 1298 (2003)
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Signal pick-up for improved photon-timing
Time resolution FWHM (ps)
150
125
100
75
50 µm active
area diameter
50
25
0
0
40
80
120
160
Threshold voltage (mV)
• Avalanche current sensing
at very low level (< 100 µA)
• Can be added to any existing AQC
S.Cova, M.Ghioni, F.Zappa, US patent No. 6,384,663 B2, 2002 (prior. March 9, 2000)
A.Gulinatti et al., Electron. Lett. 41, 20047445 (2005)
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Improved i-AQC
with on-chip current pick-up and timing circuit
A. Gallivanoni, I. Rech, D. Resnati, M. Ghioni, and S. Cova, Optics Express 14, 5021 (2006)
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Single element SPAD: application cases
¾ Single molecule fluorescence spectroscopy
¾ Fluorescence Lifetime Imaging (FLIM)
M. Ghioni
Single molecule fluorescence spectroscopy
39
Fre-FAD complex
• Conformational dynamics of of biomolecules is crucial to their biological functions
• Electron transfer used as a probe for angstrom-scale structural changes
• Measure fluorescence lifetimes (down to < 100ps) to gauge conformational dynamics
H. Yang, G. Luo, P. Karnchanaphanurach, T.M. Louie, I. Rech, S.Cova, L. Xun,
and X. Sunney Xie, Science, 302(5643), 2003
M. Ghioni
Single molecule fluorescence spectroscopy
40
• Correlation analysis revealed
conformational fluctuation at
multiple time scales spanning
from hundreds of microsecond
to seconds
Yang, H., et al., Science, 302(5643), 2003
M. Ghioni
Single Photon Timing Module SPTM
• Compact (82x60x30mm)
• Single power supply (+15V)
• Controlled Temperature
(Peltier cell)
• Software controlled settings
• On-board fast counters
• RS-232 data transmission
• Time-resolution: 60ps
• Dark Counts: down to 5 c/s
• PDE: 45% @ 500nm
• I.Rech et al., IEEE J. of Sel. Topics in Quantum Electronics, vol.10, 788 (2004)
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SPTM performance in the Harvard set-up
42
• Time-resolution: 60ps
• Dark Counts: down to 5 c/s
• Quantum Efficiency: 45% @ 500nm
Instrument Response Function (IRF)
with SPTM and with PerkinElmer SPCM
• I.Rech et al., IEEE J. of Sel. Topics in Quantum Electronics, vol.10, 788 (2004)
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Fluorescence Lifetime Imaging (FLIM)
FLIM image of the autofluorescence of daisy pollen grains
• 64 µm x 64 µm area (256 pixels/axis)
• 0.6 ms/pixel acquisition time → 2 min total measurement time
Courtesy of Picoquant GmbH, Germany
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44
SPAD arrays
M. Ghioni
SPAD arrays
45
Two approaches
- Dense CMOS-based SPAD arrays
¾ 3D imaging
- SPAD arrays with limited pixel number (< 100) and large pixel area
¾ Photon Counting in
Adaptive optics in astronomy
Parallel Fluorescence Correlation Spectroscopy
Multiphoton multifocal microscopy
Chemiluminescent assay analysis
¾ Photon Timing in
Fluorescence lifetime imaging
Basic goals Æ
- increase throughput
- miniaturization, lower system cost
M. Ghioni
SPAD arrays and optical crosstalk
Origin: hot-carrier luminescence
105 avalanche carriers Æ 1 photon emitted
A. Lacaita et al, IEEE TED (1993)
Approach:
• Optical isolation between pixels
• Avalanche charge minimization
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SPAD arrays: application cases
¾ Tip-tilt and curvature sensors for adaptive optics
¾ Large element SPAD array for protein microarray detection
M. Ghioni
Adaptive Optics
48
STRAP Adaptive-Optics System of the VLT Observatory (Chile)
European Southern Observatory - ESO
D.Bonaccini et al,
Proc. SPIE Vol. 3126,
p. 580-588, Adaptive Optics
and Applications; R.K.Tyson,
R.Q.Fugate Eds., 1997
STRAP = System for Tip-tilt Removal with Avalanche Photodiodes
M. Ghioni
Hybrid four-quadrant SPAD module
49
2x2 lenslet array
Spacer Ceramic
Centering Ceramic
Peltier
¾
Quenching, protection circuit and other
electronics developed by Polimi and
Microgate
¾
4 SPAD chips supplied by PerkinElemer
Courtesy of A. Silber (ESO)
M. Ghioni
Monolithic four-quadrant SPAD detector
¾
100µm, 80µm, 50µm pixel diameter
¾
Replace the single SPAD chips in STRAP modules
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51
SPAD-Array (SPADA)
¾ 60 element array with circular
geometry
¾ Fully parallel – 20 kfps
¾ 4 sets of pixels
- Curvature sensor for AO systems
F. Zappa et al, IEEE PTL 17, 657 (2005)
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SPADA detector head
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6x8 SPAD array detector
53
Chemiluminescent protein microarray for “in-vitro” allergy diagnosis
M. Ghioni
¾
50 µm pixel diameter
¾
240 µm pitch
2-D photon counting module: optics
54
• NA = 0.3
Collecting
Ottica di raccolta
optics
Focusing
Ottica
di
optics
focalizzazione
Microarray
• FOV = 2,064 mm
SPADA
Optical
filters
Filtri ottici
• η ~ 8%
• Magnification 1:1
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2-D photon counting module: mechanics
55
Slide tray
X
Y
θ
8.5cm
17cm
20cm
Filter holder
M. Ghioni
Conclusion
56

SPADs in planar silicon technology offer high performance at low-cost

HV-CMOS industrial technologies produce remarkable devices:
Single SPAD’s (< 50µm diam); SPAD Arrays (<10% FF), Integrated PC-Systems

Custom CMOS-compatible technologies provide today’s top-performance SPAD’s
and flexibility to sustain continuing evolution and progress

Monolithic iAQCs open the way to miniaturized modules (down to the chip scale)

Remarkable results obtained in diversified applications: DNA and Protein
Analysis; Single-Molecule Spectroscopy; Wavefront Sensors in Adaptive Optics;
etc.

Results of decades of research made widely available by a new spinoff company
www.microphotondevices.com
M. Ghioni