BIDIMENSIONAL ARRAYS OF SPAD FOR TIME RESOLVED SINGLE

PHOTON IMAGING

ST-MicroelectronicsLNS

Salvatore Tudisco

New Developments In Photodetection 2008Aix-les-Bains, France

Time Resolved Single Photon Imaging-TRSPIone of the most challenging goals in the field of photonics

Lifetime images of tissue

Applications

TRSPI – Main Requirements:

Sensitivity

Image Definition

Timing

Single Photon DetectionHigh Photo Detection Efficiency

High number of pixelsHigh Fill-Factor

Information on arrival time of photonsExcellent Resolution

Elementary device, PixelArray realization Read–out strategy

Fundamental Steps

SPAD – Single Photon Avalanche Diode

SPADp-n junction reversely biased above the breakdown voltageoperating in Geiger mode

ST-Microelectronics CMOS planar technology

P+

N-

High Boron (P+) concentration reduce the Breakdown voltage

E. Sciacca et al., IEEE Trans. on el. dev. 50 (2003) 4E. Sciacca et al., IEEE Photonics Tech. Lett. 18 (2006) 15

N- gettering region: impurities reduction

Si <100>

cathode

When a carrier enter inside the high field region it can trigger the avalanche multiplication

process

avalanche multiplication process requires a quenching strategy

QuenchingPassive Quenching

50 Ω

Quenchingresistor

Finocchiaro et al. IEEE Trans. Nucl. Scie. 52(2005)3040

Active Quenching

S. Tisa et al. Sensors and Actuators A 140 (2007) 113–122

Mixed Active-PassiveMingguo Liu et al. IEEE J. Q. E. 44 (2008) 430

Quenching strategy affects the time performance

Time jitter, Hold-off

SPAD PERPORMANCEGainPhotodetection EfficiencyTiming Dark Counting RateAfterpulsing

105÷107, depending on the quenching strategy (QS) and supply voltage

E. Sciacca et al., IEEE Trans. on el. dev. 50 (2003) 4

M. Belluso et al. Mem. SAIT Suppl. 9 (2006) 430

Photodetection Efficiency

E.V. 10%

15% at 400 nm, 45% at 600 nm, 20% at 800 nm

Gain

SPAD PERPORMANCEGainPhotodetection EfficiencyTiming Dark Counting RateAfterpulsing

105÷107, depending on the quenching strategy (QS) and supply voltage

15% at 400 nm, 40% at 600 nm, 20% at 800 nmdepending on QS, from tens up to few hundred of ps (AQ or PQ)

laser pulse408 nm60 ps FWHM

Many photons regime

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10,5 11 11,5Time [ns]

Cou

nts

FWHM ≅ 150 ps

Finocchiaro et al. IEEE Trans. on Nucl. Scie. 52(2005)3040

Single photon regime

0

50

100

150

200

250

300

350

400

10 10,5 11 11,5 12Time [ns]

Cou

nts

FWHM ≅ 300 ps

Technique

Passive Quenching

SPAD PERPORMANCEGainPhotodetection EfficiencyTiming Dark Counting RateAfterpulsing

105÷107, depending on the quenching strategy (QS) and supply voltage

15% at 400 nm, 40% at 600 nm, 20% at 800 nmdepending on QS, from tens up to few hundred of ps (AQ or PQ)

~ 400 cps for 20 μm φ, func( T [ C], O.V. [Volts], φ)

S. Privitera et al. submited to SENSORS

Events following a primary avalanchePassive Quenching

d=20 μm

total probability ~ 10-3 func( T [ C], O.V. [Volts], φ)

SPAD Arrays

Read-out StrategyPhoton identification in space and time with bi-dimensional array lead to an electrical complexity that grows as n2 (n number of pixels for side)

reading technique should minimize the number of connections !

Optical Cross-TalkAvalanche multiplication process produce photons -1÷80 μm attenuation length- 10-5 photons per carrier crossing the junction

Optical Isolation trench

Total cross-talk probability is ~ 10-3

Electrical Cross-Talk Small contribution

Read-out StrategyProposed solution

Avalanche signal is extracted simultaneously from anode and cathode.

PQ

All electric anode and cathode contacts are shared between diodes of the same row and column.

Simultaneous information on position and time of

arrival of photons

10x10 Array

60µm diameter 245µm pitch

Using passive quenching, the cathode signal extraction requires a dedicated electronics to preserve the overall performance of the system.

Cathode BufferColumn and row bus

Results Measure Set-Up

Single photon images

Row and column signals are sent to a standard nuclear electronics based on VME modules (Constant Fraction Discriminators and Time to Digital Converters)

Webcam’s optical system allows to focus on the surface of sensor images positioned at about 20 cm, and of 10x10 cm2

of dimension.

ConclusionSPAD arrays are good candidates for TRSPIFirst results show the single photon imaging capability

Next step:

Time Resolved Imaging Arrays with large number of pixels

INFN - Laboratori Nazionali del Sud and Catania University

S.Tudisco, L.Lanzanò, F.Musumeci, L.Neri, S.Privitera, A.Scordino,

ST – Microelectronics and IMM-CNR

G.Condorelli, G.Fallica, S.Lombardo, M.Mazzillo, D.Sanfilippo, E.Sciacca, G.Valvo

Collaboration