Open Archive Toulouse Archive Ouverte (OATAO)

To cite this document: Goiffon, Vincent and Hopkinson, Gordon R. and Magnan, Pierre and Bernard, Frédéric and Rolland, Guy and Saint-Pé, Olivier Multi level RTS in proton

irradiated CMOS image sensors manufactured in deep submicron technology. (2008) In:

Radiation Effects on Components and Systems - RADECS, 10 September 2008 - 12 September 2008 (Jyväskylä, Finland). (Unpublished)

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V. Goiffon1_{, G. R. Hopkinson}2_{, P. Magnan}1_{, F. Bernard}3_{, G. Rolland}3_{,O. Saint-Pé}4

1 Toulouse University, ISAE, Toulouse, France

2 Surrey Satellite Technology Limited, Sevenoaks, United Kingdom 3 CNES, Toulouse, France

4 EADS Astrium, Toulouse, France

*PhD research supported by CNES and EADS Astrium

8th European Workshop on Radiation Effects on Components and Systems September 12, 2008 in Jyväskylä, Finland

What is NIEL induced RTS? (1)

What is NIEL induced Random Telegraph Signal?

Dark current random discrete fluctuation (low frequency)

What do we know about NIEL induced RTS?

Induced by displacement damages only (not ionizing radiation) Due to switching generation centers in the depletion region Temperature activated (amplitudes and time constants)

0 10 20 30 40 50 1 1.5 2 2.5 3 3.5 4 Time (mn) D a rk c u rr e n t (f A ) Switching generation center

What is NIEL induced RTS? (2)

Why is RTS a problem for Image sensors?

Source of very intense dark current noise

Can be 100 times larger than dark current shot noise

Critical for low light level applications

RTS remaining mysteries :

RTS amplitudes

much larger than what can generate one single generation center?

Electric field enhancement? What is the responsible defect?

Can RTS distributions be predicted?

Studying RTS requires

The use of a dedicated detection technique Able to extract RTS parameters

The automated scan of an entire array

RTS Amplitude

Shot Noise

Talk outline

Proposed RTS detection method

Detection principle

Parameter extraction principle

Illustration

Proposed technique first results

Experimental details

RTS amplitude distribution

Photodiode bias effects on RTS

Conclusions and perspectives

0 50 100 150 200 250 0 2 4 6 8 10 12 Samples D a rk c u rr e n t (A U ) 0 50 100 150 200 250 0 2 4 6 8 10 12 Samples D a rk c u rr e n t (A U )

Proposed method principle (1)

Detection principle :

Based on a classical edge detection technique

Convolution of a digital step shaped filter and the signal

threshold

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Proposed method principle (2)

thresholds

Measured RTS

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Proposed method principle (2)

Transition time index extraction

T(1) T(2) T(3) _T(4)T(5) _{T(6) T(7) T(8)}T(9) T(10)

thresholds

Measured RTS

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Proposed method principle (2)

Transition time index extraction

Level value extraction

T(1) T(2) T(3) _T(4)T(5) _{T(6) T(7) T(8)}T(9) T(10)

L(4) L(3) L(2) L(1)

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Proposed method principle (2)

T(1) T(2) T(3) _T(4)T(5) _{T(6) T(7) T(8)}T(9) T(10)

L(4) L(3) L(2) L(1)

Transition time index extraction

Level value extraction

Amplitude

Proposed method feature

This automated process yields:

Levels L(i):

RTS maximum amplitude

Inter level amplitude

Number of levels

Transition time index T(i):

Level time constant

Mean time before a transition

Applied to a whole array

Automated detection of RTS pixels

Automated extraction of RTS characteristics

Result illustration

All the level are recognized

Most of the transition are detected

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Reconstituted RTS

Measured RTS

Experimental details

Test device

Custom 128 x128 pixel array Standard 3T pixel design

UMC CIS 0.18 µm CMOS process Technology dedicated to imaging

Proton irradiation

Facilities : KVI, Isotron, UCL Room temperature

Energies : from 7.4 to 184 MeV

Fluences : from 5 x 109 _{to 3 x 10}11 _H+_/cm2

Displacement damage dose : from 31.6 to 1022 TeV/g

Pixel

Area

RTS amplitude distribution (1)

Large amplitude RTS are exponentially distributed

0 0.5 1 1.5 2 100 101 102 103 104

RTS maximum amplitude (fA)

P ix e l c o u n t IC9 No irrad. IC5 19.4 TeV/g IC2 38.9 TeV/g IC4 77.6 TeV/g IC7 340.9 TeV/g IC8 1022.8 TeV/g

Amplitude

RTS amplitude distribution (2)

No significant change in slope with irradiation

A constant average amplitude exist:

A

=0.19

+/- 0.03 fA

0 0.5 1 1.5 2 100 101 102 103 104

RTS maximum amplitude (fA)

P ix e l c o u n t IC9 No irrad. IC5 19.4 TeV/g IC2 38.9 TeV/g IC4 77.6 TeV/g IC7 340.9 TeV/g IC8 1022.8 TeV/g Exp. fit

102 103 103

104 105

Displacement damage dose (TeV/g)

R T S d e fe c t c o u n t Y = 56.5 X

RTS defect counting

The number of RTS defects scales with total NIEL

The number RTS defects increases linearly with

displacement damage dose (whatever the proton energy)

50 MeV

7.4 MeV 100 MeV

Photodiode bias effects (1)

No sign of electric field enhancement

Mean dark current decreases with voltage

Due to depletion width reduction

No amplitude variation with voltage

0 20 40 60 80 100 120 140 160 1 1.5 2 2.5 3 Time (mn) D a rk c u rr e n t (f A ) VD = 2.4 V VD = 2 V VD = 1.6 V

0 0.2 0.4 0.6 0.8 1 1.2 1.4 100

101 102

Maximum amplitude (fA)

P ix e l c o u n t V D = 2.4 V V D = 2.0 V V D = 1.6 V

Photodiode bias effects (2)

The same trend is observed on the whole RTS population

No amplitude variation

with voltage

Electric field enhancement is not likely to

be the cause of large RTS amplitudes

Conclusions and perspectives

We have proposed a new RTS detection method

Based on a classical edge detection technique

Able to automatically extract multi level RTS parameters

First results indicate that:

Large RTS amplitudes are exponentially distributed

A universal mean RTS amplitude exists : ~0.19 fA

The number of RTS defects scales with total NIEL

RTS distributions can be predicted

Electric field enhancement can not explain RTS amplitudes

Future work

Explore the alternative explanation for RTS amplitudes inter center charge transfer?

Use of lower fluences and larger arrays to confirm these results with better statistics

Thank you!