Radiation tolerance of Monolithic Active Pixel Sensors (MAPS) Outline: Operation principle of MAPS Radiation tolerance against ionising doses (update)

Radiation tolerance of Monolithic Active Pixel Sensors (MAPS)

Outline:• Operation principle of MAPS• Radiation tolerance against ionising doses (update)• Radiation tolerance against non-ionising doses• Summary

S. Amar, A. Besson, J. Baudot, G. Claus, C. Colledani, G. Deptuch, M.Deveaux, A. Dorokhov, W. Dulinski, A. Gay, M. Goffe, Y. Gornushkin, D. Grandjean, F. Guilloux, S. Heini, A. Himmi, C. Hu, K.

Jaaskelainen, C. Muentz, M. Pellicioli, N. Pillet, O. Robert, A. Shabetai, M. Szelezniak, J. Stroth, I. Valin, M. Winter (Project coordinator)

Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux ([email protected])

Radiation tolerance against non-ionising doses

The measurement procedure:• Chips were irradiated and bonded consecutively• Comparisons were made between irradiated and new chips

Parameters measured were:• Leakage current of the pixels• Noise of the pixels• Charge Collection Efficiency (CCE) by means of a 55Fe-source• Detection efficiency in beam tests (~ 5 GeV e- and 120 GeV Pions)

Data was taken as function of:• The pixel pitch • The thickness of the sensitive volume• „Temperature“

Region of interest: 1011 – 1013 neq / cm²

MAPS are highly P-doped, not depleted => No problems with Neff. Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux ([email protected])

Leakage current of irradiated MAPS

Increase of leakage current after 1013 neq / cm² ?

An increase of leakage currentis observed. Reasonably lowat moderate cooling.

of the chip support


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Radiation Dose [neq/cm²]

Lea

kag

e C

urr

ent

[fA

]

T=-20°C T=+20°C

Impact of the temperature on leakage current

=> Cooling helps

Mimosa-15Preliminary

Noise of irradiated MAPS

0,0 2,0x1012 4,0x1012 6,0x1012 8,0x1012 1,0x1013 1,2x1013

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Noise

[ e

_ ]

Neutron Flux [ neq / cm²]

T= -20 °C SB-Pixel 3T-Pixel

T=-20°C T=+20°C

Origin of scattering is not understood

Noise is reduced by more than 50% at -20°C. Expect additional benefitfor combined radiation doses (ionising and non-ionising)

MIMOSA-15

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Radiation dose [neq]

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arg

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ixe

ls

T=-20°C

T=+20°C

Preliminary

Substantialsystematicuncertainties!

Impact of temperature on the charge collection efficiency

Slight trend: Higher temperature => Better CCE BUT: Can also be explained as artefact of higher noise => Not considered as significant today

S/N and det. efficiency


Pitch effect on the radiation tolerance of MAPS

20 µm pitch reaches 2x1012 neq (MIMOSA-15)

Reducing the pixel pitch is the only known mean to recover CCE

1,00E+13

2,00E+121,00E+12

3,00E+11

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2E+12

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Pixe l pitch [µm ]

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Well established(beam test results)

Friendly speakingpreliminary

Radiation hardness as a function of pixel pitch(at -20°C, < 1 ms integration time )

Highest radiation level tested „good“: 2.00E+12 might also be 3.00E+12

t [200 = 1s]

True hit

Ground state: Noise ~ 30 e-

Excitation 1: Noise ~ 31 e-

Excitation 2: Noise ~ 33 e-

Threshold

Sig

nal [

AD

C]

Random Telegraph Signal

So far observed at doses >> 1011 neq/cm²

Observed withMIMOSA-2 (3T-Pixel),reproduced withMIMOSA-15 (3T-Pixel)

Leakage current (?)

Potential Danger for SB-Pixels

Really crucial? Will be studied with MIMOSA-18 (in Frankfurt). Expect results early next year.

SB-Pixels may adapt themselfes to slow fluctuations.But also to those ones?

Temperature Dependence of RTS

Cooling helps!

Summary and Conclusion

Non-Ionising radiation damage:

• Increases the leakage current of MAPS• Increases the (shot)-noise of MAPS• Reduces the collected charge !!! (Most crucial)• Generates Random Telegraph Signal

Cooling may:• Reduce leakage current and shot noise• Dimm amplitude of Random Telegraph Signalbut has no beneficial effect on charge collection.

Reducing the pixel pitch:• May substantially increase the charge collection(half the pixel pitch, roughly factor 5 more radiation hardness)

Documents

Radiation tolerance of Monolithic Active Pixel Sensors (MAPS) Outline: Operation principle of MAPS Radiation tolerance against ionising doses (update)