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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

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Recent advances in silicon single photon avalanche diodes and their applications

Massimo Ghioni

Politecnico di Milano, Dipartimento di Elettronica e Informazione

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  • M. Ghioni

Pavia, April 3, 2007

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Outline

  • 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
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Why single photon counting? For ultimate sensitivity in optical signal measurement !

straight digital technique

  • vercomes 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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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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Photon counting/timing applications

photon count

Quantum Information Processing Metrology Medical Physics Military Space Applications Electronics Biotechnology Meteorology

detector calibration primary radiometric scales quantum standards lighting displays IR detectors lidar quantum cryptography quantum computing single photon sources entertainment robust imaging devices nuclear radioactivity medical / non interactive imaging remote sensing night vision security single molecule detection medical imaging\ bioluminescence quantum imaging hyper-spectral imaging neutrino/ cherenkov/ dark matter detection environmental monitoring chemical – bio agent detection

photon counting

Quantum Information Processing Metrology Medical Physics Military Space Applications Electronics Biotechnology Meteorology

detector calibration primary radiometric scales quantum standards lighting displays IR detectors lidar quantum cryptography quantum computing single photon sources entertainment robust imaging devices nuclear radioactivity medical / non interactive imaging remote sensing night vision security single molecule detection medical imaging\ bioluminescence quantum imaging hyper-spectral imaging neutrino/ cherenkov/ dark matter detection environmental monitoring chemical – bio agent detection

source: www.photoncount.com

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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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SPAD: reverse I-V characteristic

VREV [V] VBD No avalanche Avalanche IREV [mA]

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APD vs. SPAD

APD SPAD

Avalanche ON Quenching Reset

Avalanche PhotoDiode Single-Photon Avalanche Diode

  • Bias: well ABOVE breakdown
  • Geiger-mode: it’s a TRIGGER device!!
  • Gain: meaningless !!
  • Bias: slightly BELOW breakdown
  • Linear-mode: it’s an AMPLIFIER
  • Gain: limited < 1000
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for SPAD operation…

mandatory

  • to avoid local Breakdown, i.e.
  • edge breakdown guard-ring feature
  • microplasmas

uniform area, no precipitates etc.

but but for for good good SPAD performance..... SPAD performance..... further requirements!!

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Earlier Diode Structures

Haitz’s planar diode (early 60’s) p

+

n

  • xide

metal

guard ring

  • n

metal

5 µm 5 µm

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)

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Earlier Diode Structures

RCA reach-through diode (circa 1970)

  • perated 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

  • 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
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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

10 10 10 10 10

5 4 3 2 1

1 3 4 2 5 10

Time (ns) Counts

  • Shorter tail duration
  • p+ implantation for VBD control
  • Fully isolated devices on wafer
  • Guard Ring still employed 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

10 10 10 10 10

5 4 3 2 1

1 3 4 2 5 10

Time (ns) Counts

  • 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

neutral p layer thickness w tail lifetime τ = w2 / π2Dn

A.Lacaita, M.Ghioni, S.Cova, Electron.Lett. 25, 841 (1989)

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Double-junction SPAD structure

FWHM = 35ps FW(1/1000)M = 214ps FW(1/100)M = 125ps FWHM = 35ps FW(1/1000)M = 214ps FW(1/100)M = 125ps

p-epi

hν

+

n

+

p++ 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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Custom SPAD technology

  • Full process flexibility makes it possible to address the most

demanding requirements

n p + p p hν + n +

→ Top epi-layer thickess/doping adjusted to increase PDE

0.1 0.2 0.3 0.4 0.5 0.6 0.7 400 500 600 700 800 900 1000 Wavelength (nm) Photon Detection Efficiency

10 V 7 V 5 V Excess Bias Voltage

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Custom SPAD technology

n p + p p hν + n +

400 800 1200 1600 2000

Time (ps) Counts

10

1 2 3 4 FWHM = 35 ps FW1/100M = 370 ps

10 10 10 10

→ Bottom epi-layer thickess adjusted to achieve short diffusion tail

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Custom SPAD technology

n p + p p hν + n +

heavy phosphorus diffusion p/p+ segregation gettering

→ 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 Field-Enhanced Generation

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Field-enhanced generation

Coulombic well Dirac well

  • Poole-frenkel effect

barrier height lowered

  • Phonon-assisted tunneling

barrier width decreased Phonon process is thermally activated Tunneling is temperature independent Overall temperature dependence is a function of electric field

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0.1 1 10 100 1000 10000

  • 80
  • 60
  • 40
  • 20

20

Temperature (°C) Counts (c/s)

SPAD with "standard" electric SPAD with "engineered" electric field

Custom SPAD technology

n p + p p hν + n +

→ Electric field engineered to avoid band-to band tunneling

  • Field-enhanced generation less intense
  • DCR strongly reduces with temperature
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Large area SPADs: dark count rate

Practical Exploitation of DCR vs T

Peltier cooling to -20°C

is simple / cheap / rugged reduces DCR by a factor 25 – 100

0.1 1 10 100 1000 10000 100000

  • 50
  • 40
  • 30
  • 20
  • 10

10 20

Temperature (°C) Counts (c/s) 200 µm 50 µm 100 µm

25 100

Dark Count Rate (DCR)

  • Avalanche pulses triggered by

thermally generated carriers

  • Equivalent to the dark current in

PINs and APDs

Typical performance @5V excess bias voltage

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Large area SPADs: afterpulsing

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

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Large area SPADs: time response

By using a current pick-up circuit* and sensing the avalanche current at very low level (< 100 µA):

FWHM not dependent on the detector

diameter

35ps FWHM checked for 200µm device

at room temperature

Very stable response up to 4 Mc/s

1 10 100 1000 10000 100000 11.5 12.0 12.5 13.0 13.5 14.0 14.5

Time (ns) Counts (c/s) FWHM = 35 ps

λ λ = 820 = 820 nm nm

  • 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)

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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

  • low PDE @ 600-700 nm
  • fairly high DCR @ Vexc>3V (φ = 12µm)
  • DCR decreases slowly with T

PDE

  • F. Zappa et al, Optics Letters 30

DCR

, 1327 (2005) S.Tisa et al, IEEE-IEDM, 815 (2005) 0.8 µm HV-CMOS

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CMOS-SPAD: experimental results

Afterpulsing Time response

1E-06 1E-05 1E-04 1E-03 1E-02 5 10 15 20 25 30 35 40

Time (ns) Afterpulsing Probability Density (1/ns)

55ns hold-off

  • 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 small avalanche charge for small detectors

but NOT for wide devices (higher junction cap: 100 µm diam. 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

Passive quenching is simple... … but suffers from

  • not well defined deadtime
  • τreset > 100 ns for (Cd + Cs) > 1 pF
  • photon timing spread
  • et al

τreset=RL (Cd + Cs)

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Quenching circuits

Active quenching...

Output Pulses P.Antognetti, S.Cova, A.Longoni IEEE Ispra Nucl.El.Symp. (1975) Euratom Publ. EUR 5370e

...provides: :

  • short, well-defined deadtime
  • high counting rate > 1 Mc/s
  • good photon timing
  • standard logic output
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iAQC: integrated Active Quenching Circuit

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)

Practical advantages

  • Miniaturization mini-module detectors
  • Low-Power Consumption portable modules
  • Rugged and Reliable

Plus improved performance

  • Reduced Capacitance
  • Improved Photon Timing
  • Reduced Avalanche Charge
  • Reduced Afterpulsing
  • Reduced Photoemission reduced crosstalk

in arrays

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Signal pick-up for improved photon-timing

  • 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)

40 80 120 160 200

Threshold voltage (mV)

25 75 125 50 100 150

Time resolution FWHM (ps)

50 µm active area diameter

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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

Single molecule fluorescence spectroscopy Fluorescence Lifetime Imaging (FLIM)

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Single molecule fluorescence spectroscopy 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

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Single molecule fluorescence spectroscopy

  • Correlation analysis revealed

conformational fluctuation at multiple time scales spanning from hundreds of microsecond to seconds

Yang, H., et al., Science, 302(5643), 2003

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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

Instrument Response Function (IRF) with SPTM and with PerkinElmer SPCM

  • Time-resolution: 60ps
  • Dark Counts: down to 5 c/s
  • Quantum Efficiency: 45% @ 500nm
  • 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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SPAD arrays

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SPAD arrays

Photon Counting in

Adaptive optics in astronomy Parallel Fluorescence Correlation Spectroscopy Multiphoton multifocal microscopy Chemiluminescent assay analysis

Photon Timing in

Fluorescence lifetime imaging

Basic goals

  • increase throughput
  • miniaturization, lower system cost

Two approaches

  • Dense CMOS-based SPAD arrays

3D imaging

  • SPAD arrays with limited pixel number (< 100) and large pixel area
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SPAD arrays and optical crosstalk

Origin: hot-carrier luminescence 105 avalanche carriers 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

Tip-tilt and curvature sensors for adaptive optics Large element SPAD array for protein microarray detection

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STRAP = System for Tip-tilt Removal with Avalanche Photodiodes

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

Adaptive Optics

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Hybrid four-quadrant SPAD module

2x2 lenslet array

Peltier

Spacer Ceramic Centering Ceramic

  • Quenching, protection circuit and other

electronics developed by Polimi and Microgate

  • 4 SPAD chips supplied by PerkinElemer

Courtesy of A. Silber (ESO)

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100µm, 80µm, 50µm pixel diameter Replace the single SPAD chips in STRAP modules

Monolithic four-quadrant SPAD detector

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SPAD-Array (SPADA)

60 element array with circular geometry Fully parallel – 20 kfps 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

Chemiluminescent protein microarray for “in-vitro” allergy diagnosis

50 µm pixel diameter 240 µm pitch

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2-D photon counting module: optics

  • NA = 0.3
  • FOV = 2,064 mm
  • η ~ 8%
  • Magnification 1:1

Ottica di raccolta Ottica di focalizzazione Filtri ottici Microarray SPADA Collecting

  • ptics

Focusing

  • ptics

Optical filters

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2-D photon counting module: mechanics

Filter holder 20cm 20cm 8.5cm 8.5cm 17cm 17cm Slide tray

X Y

θ

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Conclusion

  • 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