Electron Multiplying CCDs

An IntroductionSimon Tulloch

www.qucam.com

CCD60 128 x 128 CCD87/97 512x512 CCD201 1K x 1K

Image Area Store Area

Norm

al Seri

al re

gis

ter

Multiplication register

Multip

licatio

n re

giste

r

Multiplication register

Standard MOSFETamplifier

1e- in

1000e- signal out

Avalanche multiplication takesplace in Multiplication Register,using an HV clock (40-45Volts).

Commercially available :

Electron Multiplying CCDs

Flexible OperationE2V CCD201

3e noiseTo Observe:Absorption linesBright Emission LinesEmission lines superimposed on bright continuum

<<1e noiseTo Observe: Faint Emission Lines

clock left clock right

Conventional Amp.Electron Multiplying

Amplifier

Pot

enti

al E

nerg

yMultiplication Clocking 1

Gain electrode

In this diagram we see a small section of the gain register

Pot

enti

al E

nerg

yMultiplication Clocking 2

Pot

enti

al E

nerg

y

Gain electrode energised. Charge packets accelerated strongly into deep potential well.Energetic electrons loose energy through creation of more charge carriers (analogous tomultiplication effects in the dynodes of a photo-multiplier) .

Gain electrode

Pot

enti

al E

nerg

yMultiplication Clocking 3

Pot

enti

al E

nerg

y

Clocking continues but each time the charge packets pass through the gain electrode, furtheramplification is produced. Gain per stage is low, <1.015, however the number of stages is high so the total gain can easily exceed 10,000

Multiplication Noise

L3 CCD Noise Characteristics

0

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12000

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18000

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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Mean of Signal

Var

ianc

e of

Sig

nal

Normal CCD

L3 Gain=12

L3 Gain=39

L3 Gain=283

2Effect is to increase the photon noise by a a factor of

Flat fields taken with an EMCCD show unusual statistics. The variancein the flat fields is no longer equal to the mean signal as is expectedwith photon statistics.

EMCCD becomes competitiveat lower exposure levels

With EM Gain: At low illumination, photons are resolved. Without EM Gain: object only just visible above noise.Also visible is the Clock Induced Charge (CIC) which is the dominant noise source (typical value 0.03e-)

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0 10 20 30 40 50 60

Photons per pixel per f rame

SN

R

Conventional CCD 5e- noise

L3 CCD with no CIC

photon noise limit

EMCCD wins due to zero read noiseEMCCD loses due to multiplication noise

EMCCD range of operation

EMCCD

So at higher expsoure levels the EMCCD actually performs worse than a normal CCD

Raw input frames Thresholded and accumulated

Particles? Waves?

Cry

ogen

ic C

CD

87 im

agin

g a

fain

t pin

hole

Early EMCCD Demonstrations

1) Crab Nebula pulsar at 180fps

2) Photon interference in the lab

Threshold