inaf - osservatorio astrofisico catania ii prin 2006 meeting news from single photons sergio...

INAF - Osservatorio Astrofisico CataniaINAF - Osservatorio Astrofisico Catania

II PRIN 2006 Meeting II PRIN 2006 Meeting

NEWS FROM SINGLE PHOTONSNEWS FROM SINGLE PHOTONS

Sergio BillottaSergio Billotta

II PRIN 2006 meeting - Bled 26-28 Mar '08 Sergio Billotta - NEWS FROM SINGLE PHOTONS

2

SummarySummary

Single Photon Avalanche Diode (SPAD)Single Photon Avalanche Diode (SPAD)What it isHow it worksDarkAfter pulsePhoton Detection Efficiency (PDE)

Silicon PhotoMultiplier (SiPM)Silicon PhotoMultiplier (SiPM)What it isDarkAfter pulseLinearityCharge spectrumTime jitterPhoton Detection Efficiency (PDE)

Conclusions


3

SPADSPADwhat it iswhat it is

OXIDE

METAL

N+

N+

GetteringP+

Sinker

SPAD = Single Photon Avalanche DiodeSPAD = Single Photon Avalanche Diode

STMicroelectronics SPADSTMicroelectronics SPAD Planar device Thin junction depletion layer (~ 1m) Low breakdown voltage (15 – 30 V) Photodetector active area: defined by the metal ring used to contact the N+ thin polysilicon layer doped with

arsenic (Diameter: 10 ÷ 100m) High-electric field active region: defined by an P+ enrichment diffusion Local gettering sites: provided by an external ring doped by a heavy POCl

3 diffusion (to reduce the defectivity

in the device active area)


4

SPADSPADhow it workshow it works

OXIDE

METAL

N+

N+

GetteringP+

Sinker

Semiconductor junction diodes reverse-biased few Volt above the breakdown voltage.

The electric field within SPAD depletion layer is so high (higher than 3 x 105 V/cm) that a single carrier (photo / thermal electron) injected in this region can trigger a self-sustaining avalanche multiplication process.

A sharp current pulse of few milliamps and with sub-nanosecond rise time is produced.( If the first carrier is photogenerated, the current rising edge marks the photon arrival time).

Once the breakdown current has been detected, it is quenched by a large series resistor (passive quenching) or by a suitable quenching circuit (active quenching).

The diode is thus turned off for a suitable hold-off time that allows the charge stored within the depletion layer to dissipate.

The voltage is restored to the bias value and the device is ready to detect another photon.


5

SPADSPADdarkdark

STM SPAD arrayIt is manufactured by the integration of 25 pixels with a square geometry of 5 x 5. For these devices, STMicroelectronics has designed three different pixel diameters: 20, 40 and 60 m. Separation distances between adjacent pixels are in the range of 160 and 240 m according to different diameters.

Anode contacts are in common for each row, while each cathode is separately contacted and available from outside by different pads. The typical breakdown voltage is about 30 V.

We have measured the dark counts rate of each pixel of several array of SPADs, and we have found a fairly good uniformity of it.

Median room temperature dark count rate at 4V overbias as a function of SensL SPAD device area.

Applications of Silicon Photon Counting Detectors, Stewart et al., JMO in press


6

SPADSPADaafter pulsefter pulse

It depends on:Trap concentration in the junction depletion layernumber of carriers generated during a Geiger pulse.

It could strongly enhance the total dark count rate.

During an avalanche some carriers are trapped by deep levels in the multiplication region

released after a statistically fluctuating delay

they can re-trigger a Geiger event correlated with the previous avalanche pulse

Dark count rate at several hold-off time

estimation of the afterpulsing effects

Lo t:7 0 3 0 1 2 wf4 2 - S a mple s : k 3 / k 4 - S ing le - P ix e l:3 2 b9 3 P a dA-3 2 mic ro nD a rk (c o rre c te d fo r the H .O .) v s H o ld o ff

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

0 5 10 15 20 25 30 35 40 45

H o ld o f f t i m e (s )

Dark

(cnt

s/s)

_

s a m p le k 3 - 3 2 V - 2 4 ° C s a m p le k 3 - 3 5 V - 2 4 ° C s a m p le k 4 - 3 2 V - 2 1 ° C s a m p le k 3 - 3 5 V - 2 2 ° C

Lo t: 7 0 3 0 1 2 wf3 2 - S a mple : e ps ilo n - S ing le - P ix e l: 3 2 b9 3 P a dA - nume ro 2 9 -3 2 mic ro nD a rk (c o rre c te d fo r H .O .) v s H o ld o ff

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

8 0 0 0

9 0 0 0

1 0 0 0 0

0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5

H o ld o ff t im e (s )

Da

rk (

cnts

/s)

_

3 2 V - 2 2 ° C


7

PDE = QE x Pt x A

e

QE = Quantum EfficiencyP

t= Avalanche

ProbabilityA

e= Geometrical

Efficiency Probability for a photon to generate an e–h pair in the active thickness of the device

QE = (Dielectric layer transmittance) x QEinternal

Probability for a photon that has crossed the dielectric layer to generate an e–h pair in the active thickness.

wavelength dependent.

Can be maximized, implementing an anti-reflective coating (ARC)

ARC

SPADSPADphoton detection efficiency (1)photon detection efficiency (1)


8

PDE = QE x Pt x A

e


t= Avalanche

ProbabilityA

e= Geometrical

Efficiency

There is a finite probability for a carrier to initiate an avalanche when passing through a high-field region. In case of a photogeneration event, 2 carriers are created travelling in opposite directions

Pt = P

e + P

h - P

eP

h

Electron and hole breakdown initiation probabilities

In case of photogeneration on the right side, the situation is symmetrical and only electrons contribute to the triggering probability, thus, P

t = P

eM.

In the central region, both carriers contribute to a different extent as a function of the interaction position and the Pt value is between P

eM and P

hM

When a pair is generated in the left side of the high-field region, the electron is directly collected at the n+ terminal; thus, it does not contribute to the triggering probability. The hole is forced to cross the whole high-field region and so its triggering probability is maximized and P

t = P

hM.



9

PDE = QE x Pt x A

e


t= Avalanche

ProbabilityA

e= Geometrical

EfficiencyA

active / A

total for SPAD = 1


OXIDE

METAL

N+

N+

GetteringP+

Sinker

All the exposed area is active

Photon Detection Probability (PDP)


10

Pho

ton

Det

ectio

n E

ffic

ienc

y %

PDE of a 40 m STM SPAD

SPADSPADphoton detection efficiencyphoton detection efficiency

0 %

1 0 %

2 0 %

3 0 %

4 0 %

5 0 %

6 0 %

7 0 %

3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1 1 0 0W a v e le n g th (n m )

Qua

ntum

Effi

cien

cyP

hoto

n D

etec

tion

eff

icie

ncy

L ot: 7 0 3 0 1 2 w f3 2 - S am p le: k E p s i lon - S in g le - P ix e l : 3 2 b 9 3 P ad A -3 2 m icron

0

1 0

2 0

3 0

4 0

5 0

6 0

3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0

W a v eleg th (nm )

Qu

antu

m D

etec

tion

Eff

icie

ncy

(%

)

_

2 0 ,6 % (3 4 ,9 7 4 V ) - [H o ld o ff : 4 0 u s - Tsenso r :1 7 °C - R =3 7 0 k+ 2 9 0 k] 1 0 ,5 % (3 2 ,0 4 5 V ) - [H o ld o ff : 4 0 u s - Tsenso r :1 7 °C - R =3 7 0 k+ 2 9 0 k]

3 0 ,2 % (3 7 ,7 5 8 V ) - [H o ld o ff : 4 0 u s - Tsenso r :1 7 °C - R =3 7 0 k+ 2 9 0 k] 1 0 % (3 1 .9 V ) - [H o ld o ff : 4 5 u s - Tsenso re2 2 °C - R :3 9 0 k+ 2 7 0 k]

STMSTMPixel size: 40mV

Brk: 26V

VBIAS

: 10% -> 15%H.O.: 6 s

STMSTMPixel size: 32mV

Brk: 29V

VBIAS

: 10% -> 30%H.O.: 40/45 s

SensLSensLPixel size: 50mV

Brk: 28V

Vovervoltage

: 1.5V -> 4V

MPDMPDPixel size: 50mOperating conditions set by the electronics inside the module



11

Single Photon Avalanche Diode (SPAD)Single Photon Avalanche Diode (SPAD)What it isHow it worksDarkAfter pulsePhoton Detection Efficiency (PDE)

Silicon PhotoMultiplier (SiPM)Silicon PhotoMultiplier (SiPM)What it isDarkAfter pulseLinearityCharge spectrumTime jitterPhoton Detection Efficiency (PDE)

Conclusions


12

SiPMSiPMwhat it iswhat it is

Silicon PhotoMultiplierSilicon PhotoMultiplier

Matrix of n pixels in parallel Each pixel: SPAD + R

quenching

Analog Device => the output signal is the sum of the signals from all fired pixel

Qout

= C x (VR – V

BR) x N

fired

Schematic cross-section of a half single cell of the SiPM fabricated at STMicroelectronics Catania R&D clean room facility

a) SEM top view of a SiPM prototype fabricated at STMicroelectronics Catania R&D clean room facility; b) detail of optical trenches between adjacent pixels


13

SiPMSiPMdarkdark

Dark count pulses:s => single pixel pulsed => two simultaneously pixels pulsea = >

Characteristics of the single-pixel dark pulse (equal of single photon pulse)rise time~ hundreds of psrecovery timeτ = R

quenching · C

micro-cell ~ 20-30 ns

Measured noise rate as a function of V − Vbd

afterpulses

Dark rate as a function of overbias for a SensL SiPM at room temperature and at -20°C



14

SiPMSiPMafter pulseafter pulse

Sketch of the electronics for the self-correlated timing, employed forafterpulse measurements.

For uncorrelated events (SiPM without cross-talk and afterpulses):The random noise follows the Poisson lawThe distribution of the arrival time between two events is exponential

We measured the distribution of time intervals between two consecutive dark pulses at 20°C for several bias voltages, and built the corresponding histograms.The lower time threshold was around 15-20ns, therefore preventing us from attaining a direct measurement of cross-talk.

The afterpulse effect shows up in such a distribution as a pronounced deviation from the perfect exponential distribution of the uncorrelated dark noise, namely a prominent peak around 200ns.


15

If Nphoton x PDE << Ntotal Output signal Nfired

When 50% of the cells fire the deviation from linearity is 20%

Best working condition => Nphotons

< Ncells

)1( total

photon

N

PDEN

totalfiredcells eNNA

If t > R the SiPM dynamic range is larger.

t = duration of the light signal

R = single pixel recovery time

SiPMSiPMdynamic range - linearitydynamic range - linearity


16

SiPMSiPMcharge spectrumcharge spectrum

By making use of a dedicated data acquisition system one can characterize the SiPM on an event-by-event basis. Using this method we built the charge distribution histogram under several different light intensity values. We employed a red laser diode (650nm) pulsed at 1kHz, whose light was conveyed onto the sensor by means of an optical fiber.

A typical charge spectrum under very low light level for a 10x10 device biased at 6% OV.The multipeak structure reflects the detection of 1-18 photons per event. For this sensor we measured a 3resolving power around 20 and a 2resolving power around 45.

Sketch of the electronics for the charge and time measurements, employed for SiPM response characterization.


17

SiPMSiPMtime jittertime jitter

STM SiPM:SiPM area: 0,5 x 0,5 mm2

Pixel active area: 32 x 32 m2

Fill factor: 36%N° pixels: 10 x 106% overvoltage Apparatus:Pulsed laser diode ( = 650 nm, 1kHz, pulse: 40ps)Optical fiber

A typical timing spectrum under very low light level for a 10x10 device biased at 6% OV. The average number of detected photons was around 6. The time calibration of the TDC was 50ps/channel, therefore the time resolution (sigma) is 135ps.

Sketch of the electronics for the charge and time measurements, employed for SiPM response characterization.

The width (FWHM) of the statistical distribution of the delay between the true arrival time of the photon at the sensor and the measured time marked by the output pulse current leading edge.


18

PDE = QE x Pt x A

e


t= Avalanche

ProbabilityA

e= Geometrical

Efficiency

dead region:determined by the guard ringstructure preventing optical cross-talk space between the cells for the individual resistors

Considering that the area of a cell can be very small (in the order of 30x30 m2) even few microns of dead region around the cell have a very detrimental effect on the geometrical efficiency.

Best filling can be achieved with a small number of big cells => SATURATION !!!

Aactive

/ Atotal

SiPMSiPMphoton detection efficiencyphoton detection efficiency


19

PDE SiPM 1mm - 32V - Guadagno 8E+5 - temp = 24°C - Trigger:0,5

0%

5%

10%

15%

20%

25%

300 400 500 600 700 800 900 1000

lamda (n m)

PD

E

STMSTM1 x 1 mm2

20 x 20 pixelsPixel size: 32mFill factor: 36%V

BIAS: 32V

Gain = 8 x 105

Temp: 24°C

SiPMSiPMphoton detection efficiencyphoton detection efficiency

SensLSensL1 x 1 mm2

1144 pixelsPixel size: 20 mFill factor: 43%V

BIAS: 29.5V, 30V, 31V and 32V

Temp: 20°C

S T M S iP M - 1 0 x1 0 p ixel s - 0 ,5 m m x 0 ,5 m m

0

2

4

6

8

10

12

14

300 400 500 600 700 800 900 1000

W av elength (nm )

Ph

oto

n D

etec

tio

n E

ffic

ien

cy (

%)

_

1 0 % (3 2 ,5 V ) - [T a m b ie n te 2 0 ° C - S o g lia 4 4 m V (0 .7 p h s ) - Ga te 5 0 0 n s ] 1 0 % (3 2 ,5 V ) - [T a m b ie n te 2 0 ° C - S o g lia 4 4 m V (0 .7 p h s ) - Ga te 5 0 n s ]

1 2 % (3 3 V ) - [T a m b ie n te 2 1 ° C - T v ic in o S e n s o re 2 2 ° C - S o g lia 4 7 m V (0 .7 p h s ) - Ga te 5 0 n s ] 7 % (3 1 ,5 V ) - [T a m b ie n te 2 0 ° C - T v ic in o S e n s o re 2 0 ° C - S o g lia 3 8 m V (0 .7 p h s ) - Ga te 5 0 n s ]

5 % (3 1 V ) - [T a m b ie n te 2 1 ° C - T v ic in o S e n s o re 2 0 ° C - S o g lia 3 4 m V (0 .7 p h s ) - Ga te 5 0 n s ]

STMSTM0.5 x 0.5 mm2

10 x 10 pixelsPixel size: 32mFill factor: 36%Temp: 20°CV

Brk: 29.5V

HamamatsuHamamatsu1 x 1 mm2

20 x 20 pixelsFill factor: 61%V

BIAS: 70V

Gain = 7 x 105

Temp: 25°C

10%

12%

5%

7%

Gate 500 ns

11stst method methodGainGain

overestimated: after overestimated: after pulsepulse

22ndnd method methodunderestimated: no underestimated: no

amplitudeamplitudediscriminationdiscrimination



20

ConclusionsConclusions

SiPMSiPMAdvantages:Advantages: robust and compact sensitivity to extremely low photon fluxes providing

proportional information with excellent resolutionand high photon detection efficiency

extremely fast response with low fluctuation (sub-ns rise time and <100ps jitter)

low bias voltage (<100V) low power consumption (<50μW/mm2) long term stability insensitive to magnetic fields (up to 15T) and EM

pickup low cost (in the future! now ~140$/mm2) + low

peripheral costs

Disadvantages:Disadvantages: silicon quality (dark rate, after-pulse) effective area of the cells (gain, fill factor, dynamic

range, recovery time optical cell insulation (optical cross-talk) quenching resistor (recovery time, dynamic range)

SPADSPADAdvantages:Advantages: solid state technology: robust, compact, mechanically

rugged and less expensive Geiger mode high internal gain of 105 - 106

faint sources high quantum efficiency large standardized output signal no Read Out Noise high sensitivity for single photons excellent timing event for single photo electrons (<<

1ns) good temperature stability devices operate in general < 100V no nuclear counter effect (due to the standardized

output)

Disadvantages:Disadvantages: BINARY DEVICE – one knows there was at least one

electron/hole initiating the breakdown but not how many of them !!!!!

Max diameter 100 m.


21

INAF - Osservatorio Astrofisico CataniaINAF - Osservatorio Astrofisico Catania

II Meeting PRIN 2006II Meeting PRIN 2006

NEWS FROM SINGLE PHOTONSNEWS FROM SINGLE PHOTONS

Sergio BillottaSergio Billotta

GrazieGrazie

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