recent advances in silicon single photon avalanche diodes and...

Recent advances in silicon single photon avalanche diodes and their applications

Massimo GhioniPolitecnico di Milano, Dipartimento di Elettronica e Informazione

M. Ghioni Pavia, April 3, 2007

2Outline

• Single photon counting: why, what and how

• SPAD device technology: origin and evolution

• Single element SPAD detectorsrecent advancescustom SPAD vs standard CMOS technologyapplication cases

• SPAD array detectorsapplication cases

• Conclusions


3Why 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)


4Why 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.)


5Photon counting/timing applications

photoncount

QuantumInformationProcessing

Metrology

MedicalPhysics

Military

Space Applications

Electronics

Biotechnology

Meteorology

detector calibration

primaryradiometric

scales

quantum standards

lighting

displays

IR detectors

lidar

quantum cryptography

quantum computing

single photonsources

entertainment

robust imagingdevices

nuclear

radioactivity

medical / non interactiveimaging

remote sensing

night vision

security

single moleculedetection

medicalimaging\

bioluminescencequantum imaging

hyper-spectralimaging

neutrino/cherenkov/ dark matter detection

environmental monitoring chemical – bio agent detection

photoncounting

QuantumInformationProcessing

Metrology

MedicalPhysics

MilitarySpace

Applications

Electronics

Biotechnology

Meteorology

detector calibration

primaryradiometric

scales

quantum standards

lighting

displays

IR detectors

lidar

quantum cryptography

quantum computing

single photonsources

entertainment

robust imagingdevices

nuclear

radioactivity

medical / non interactiveimaging

remote sensing

night vision

security

single moleculedetection

medicalimaging\

bioluminescencequantum imaging

hyper-spectralimaging

neutrino/cherenkov/ dark matter detection

environmental monitoring chemical – bio agent detection

source: www.photoncount.com


6Available detectors

Vacuum TubePMT

Currently used in photon counting/timing applicationsLimited 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 ratesLimited time resolution

SSPD (Superconducting Single Photon Detector)Limited active areaNeed to be operated at < 4 K

SPAD (Single Photon Avalanche Diode)Best suited for photon counting/timing applications


7SPAD: reverse I-V characteristic

VREV [V]VBD

No avalanche

Avalanche

I REV

[mA

]


8APD vs. SPADAPD 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


9for SPAD operation…

mandatory

• to avoid local Breakdown, i.e.

• edge breakdown guard-ring feature

• microplasmas uniform area, no precipitates etc.

butbut forfor goodgood SPAD performance.....SPAD performance.....

further requirements!!


10Earlier Diode Structures

Haitz’s planar diode (early 60’s)

p

+n oxidemetal

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)


11Earlier 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


12Haitz’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


13Haitz’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).


14Epitaxial SPAD structure

10

10

10

10

10

5

4

3

2

1

0 1 3 42 5100

Time (ns)

Cou

nts

- 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)


15Double-epitaxial SPAD structure

10

10

10

10

10

5

4

3

2

1

0 1 3 42 5100

Time (ns)

Cou

nts

• 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 wtail lifetime τ = w2 / π2Dn

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


16Double-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)


17Device 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


18Custom SPAD technology

• Full process flexibility makes it possible to address the mostdemanding requirements

n

p+p

p

hν +n

+

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

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

400 500 600 700 800 900 1000Wavelength (nm)

Phot

on D

etec

tion

Effic

ienc

y 10 V7 V5 V

Excess Bias Voltage



n

p+p

p

hν +n

+

0 400 800 1200 1600 2000Time (ps)

Cou

nts

100

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



n

p+p

p

hν +n

+heavy phosphorus diffusion

p/p+ segregation gettering

→ Specific designed gettering processes for removing transition metal impuritiesresponsible for:

- thermal carrier generation (dark count rate - DCR)- carrier trapping (afterpulsing effect)


21Dark 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


22Field-enhanced generation

Coulombic well Dirac well

• Poole-frenkel effect

barrier height lowered

• Phonon-assisted tunneling

barrier width decreased

Phonon process is thermally activatedTunneling is temperature independentOverall temperature dependence is a function of electric field


23

0.1

1

10

100

1000

10000

-80 -60 -40 -20 0 20Temperature (°C)

Cou

nts

(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 tunnelingField-enhanced generation less intenseDCR strongly reduces with temperature


24Large area SPADs: dark count rate

Practical Exploitation of DCR vs TPeltier cooling to -20°C

is simple / cheap / rugged

reduces DCR by a factor 25 – 1000.1

1

10

100

1000

10000

100000

-50 -40 -30 -20 -10 0 10 20Temperature (°C)

Cou

nts

(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


25Large 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


26Large area SPADs: time response

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

FWHM not dependent on the detector diameter35ps FWHM checked for 200µm deviceat room temperatureVery stable response up to 4 Mc/s1

10

100

1000

10000

100000

11.5 12.0 12.5 13.0 13.5 14.0 14.5Time (ns)

Cou

nts

(c/s

)

FWHM = 35 ps

λλ = 820 = 820 nmnm

- 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)


27Custom 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 circuitcomponents specifically designed in the detector technology

• Dedicated silicon foundry is required


28CMOS 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)


29CMOS-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


30CMOS-SPAD: experimental results

Afterpulsing Time response

1E-06

1E-05

1E-04

1E-03

1E-02

0 5 10 15 20 25 30 35 40

Time (ns)

Afte

rpul

sing

Pro

babi

lity

Den

sity

(1/n

s)

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)


31CMOS-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 detectorsbut 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


32

Quenching circuits


33Quenching 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)


34Quenching circuits

Active quenching...

Output Pulses

P.Antognetti, S.Cova, A.LongoniIEEE 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


35iAQC: 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


36Signal pick-up for improved photon-timing

• Avalanche current sensingat 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)

0 40 80 120 160 200Threshold voltage (mV)

25

75

125

0

50

100

150

Tim

e re

solu

tion

FWH

M (p

s)

50 µm activearea diameter


37Improved 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)


38

Single element SPAD: application cases

Single molecule fluorescence spectroscopy

Fluorescence Lifetime Imaging (FLIM)


39Single 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


40Single 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


41Single 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)


42SPTM 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)


43Fluorescence 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


44

SPAD arrays


45SPAD arrays

Photon Counting inAdaptive optics in astronomyParallel Fluorescence Correlation SpectroscopyMultiphoton multifocal microscopyChemiluminescent 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


46SPAD 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


47

SPAD arrays: application cases

Tip-tilt and curvature sensors for adaptive optics

Large element SPAD array for protein microarray detection


48

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


49Hybrid 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 PerkinElemerCourtesy of A. Silber (ESO)


50

100µm, 80µm, 50µm pixel diameter

Replace the single SPAD chips in STRAP modules

Monolithic four-quadrant SPAD detector


51SPAD-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)


52SPADA detector head


536x8 SPAD array detector

Chemiluminescent protein microarray for “in-vitro” allergy diagnosis

50 µm pixel diameter

240 µm pitch


542-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

Collectingoptics

Focusingoptics

Optical filters


552-D photon counting module: mechanics

Filter holder

20cm20cm

8.5cm8.5cm17cm17cm

Slide tray

X Y

θ


56Conclusion

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’sand 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

recent advances in silicon single photon avalanche diodes and...

Documents