Download - Radiation damage in the STAR environment and performance of MAPS sensors

IPHC-LBNL meeting

3-5 April 2008

Radiation damage in the STAR environment and performance of MAPS

sensors

Compilation of different test results mostly from Michael’s thesis

M.S. IPHC-LBNL meeting, 3-5 April 2008

22

Outline

What can we expect at STAR? Figure of merit – S/N Ionizing radiation effects Non-ionizing radiation effects Simple noise model Some solutions and issues


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Based on H.W. estimates (http://rnc.lbl.gov/~wieman/radiation dose straus oct 2007 HW.ppt)

For the radius of 2.5 cm:– Ionizing radiation:

Total dose: 155 kRad TLD projection: 300 kRad

– Non-ionizing radiation average pion count for 1 Yr: 3x1012 cm-2

TLD projection (pion assumption): 12x1012 cm-2

What can we expect at STAR?


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Figure of merit for high detection efficiency is S/N

Test results of MimoSTAR2 show that

– Measured with cuts on clusters– Similar performance can be expected from single threshold algorithm

for S/N>12 detection efficiency >99.6%


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Ionizing radiation effects

Increased leakage current– Increase of shot noise– Faster discharge time of the self-biased structure that

in extreme cases could lead to signal losses


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Time constant for discharge of the self-biased node

Dose (rad) τ

0 30 ms 11ms (~40 °C? ) measured at LBL

20 k 25 ms

500 k 7 ms

1 M 4 ms

from Michael’s thesis for the radiation tolerant diode layout and the operating temperature of 40 °C


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Discharge time

At LBL =130 ms at 30 °C and about 11 ms at the unknown (uncontrolled “ambient”) temperature for a non-irradiated sensor

– the charge collection efficiency (CCE) at the level of 77%, the sensor integration time was 1.7 ms

– at IPHC for the integration time of 4 ms CCE of 75%

short discharge time constant on the order of 10 ms (6 x integration time) did not affect signal collection

Degradation of the discharge time after integrated ionizing dose of a few hundred krad should not be a problem.


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Non-ionizing radiation

Charge losses due to bulk damage Increased leakage current (not negligible)

– Increase of shot noise


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Charge losses

-20 °C – minimized contribution from shot noise (negligible for fluences up to 2x1012 neq/cm2)

Mimosa-9 -20 °C Tint 0.7 ms

Mimosa-15 -20 °CTint 0.7 ms pixel pitch 20 μm.

Half of signal

0.7 signal

irradiation inherently added ionizing background that is approximately 100 krad for the fluence of 1x1013 neq/cm2. This background can be expected to scale linearly with the dose.

Mimosa-9 -20 °C Tint 0.7 ms

Half of signal


1010

Charge collection efficiency (CCE)

Beam Test Calibration of the Mimosa-15 prototype (S. Amar-Youcef, M. Deveaux, M. Goffe – 05.2006) At -20 °C and +20 °C:

– 20 μm pitch and 2.1x1012 neq/cm2 the CCE decrease to about 0.5– 30 μm pitch (MimoSTAR-like) CCE decreases to

0.66 (4.7 x 1011 neq/cm2) 0.39 (2.1 x 1012 neq/cm2)

20 °C

50 100 150 200 250 300 350ADC

0.2

0.4

0.6

0.8

1Entries

black chipRef, blue chip4, purple chip6, red chip10, green chip1120 °C

50 100 150 200 250 300 350ADC

0.2

0.4

0.6

0.8

1Entries

black chipRef, blue chip4, purple chip6, red chip10, green chip11

20 °C

50 100 150 200 250 300 350ADC

0.2

0.4

0.6

0.8

1Entries

black chipRef, blue chip4, purple chip6, red chip10, green chip1120 °C

50 100 150 200 250 300 350ADC

0.2

0.4

0.6

0.8

1Entries

black chipRef, blue chip4, purple chip6, red chip10, green chip11

Black: RefBlue: 4.7x1011

Purple: 2.1x1012

Red: 5.8x1012

Green: 1.1x1013

MimoSTAR2 pixel type


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Consequences

The charge losses after 2.1 x 1012 neq/cm2 will lead to the S/N reduction:– 28 to 14 for the 20 μm pitch– 20 to 8 for the 30 μm pitch

This results in an unacceptable degradation of S/N for the MimoSTAR2-like pixel.

MIP detection efficiency of irradiated prototypes was measured only at 0 °C due to the limited duration of the beam tests.

This limits the estimation of the detection efficiency achievable at STAR to theoretical considerations of the evolution of S/N.


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Leakage current (noise) from bulk damage

0

5

10

15

20

25

30

35

40

-20 0 20 40

T °C

no

ise

chip 3

chip 4

chip 5

chip 6

chip 7

chip 8

chip 9

chip 10

chip 11

after 2x1012 neq/cm2 the noise degrades from 15 to 18 e-

Chip 3 refChip 4 4.7x1011

Chip 6 2.1x1012

Chip 10 5.8x1012

Chip 11 1.1x1013 Chip 5 refChip 7 23 krad γChip 8 20 krad XChip 9 1 Mrad X

3T pitch 20 μm SB pitch 30 μm.


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Ni(I,Tint) = A × √I × √Tint N=√(N02+Ni2) Temperature

– Rule of thumb 2 x I every 10°C Ionizng radiation

– At 40 °C shot noise contribution is 0 krad => 10 e- 500 krad => 20 e- 1000 krad => 30 e-

– linear fit: (0.002 x Dose(krad)+1)– After tuning: (0.003 x Dose(krad)+1)

– Model fits data well (within 10%) Non-ionizing radiation

– At 20 °C shot noise contributions is 0 => 11 e- (incompatible with results for ionizing radiation) 2.1 x 1012 => 15 e- 5.8 x 1012 => 21 e- 1.1 x 1013 => 29 e-

– Linear fit: (0.14 x Dose(1012)+1)– Model fits data well but noise incompatible with the measurements on Mimosa-11

(leakage current needs to be x4 to fit the results)

Simple model for noise performanceMimosa-11(rad-hard)

N=√(N0^2+ (A × √I × √Tint × (0.003 x Dose(krad)+1) × (0.14 x Dose(1012)+1))^2)

A × √I = 10 at 40 °C


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Simple model for charge losses

Exponential dependency?


1515

MimoSTAR2 pixel

Single detector replacement – not sufficient Full elimination of shot noise – not sufficient Annealing ?


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MimoSTAR2 pixel

PHASE1 integration time


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Solutions

Decrease pixel pitch to 20 μm– # columns x 1.5 => power dissipation x 1.5– column length x 1.5 => integration time unchanged

SUZE can not run faster than designed (160 ns) Cluster size?

– Signal decrease to 0.5 from non-ionizing radiation damage (2.1 x 1012 neq/cm2)

– And noise increase 1.15 @ 0.2 ms integration time (assumption for 155 krad @ 40 °C)

– S/N goes down to about 0.44 (28 =>12) it looks OK but what is the accuracy of these estimations? (detector replacement S/N~16)


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Other solutions

Smaller pixel pitch (15, 18 μm) (power dissipation?) 30 μm pitch with multiple charge collecting diodes?

Graded substrate (!) Deep P implants

Latch up in SUZE and Mimosa22 needs to be investigated Hot pixels after non-ionizing irradiation (Function of dose?

Annealing?)– How to mask them for SUZE?

Irradiations with pions?

Other issues


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Noise from Mimosa15


2020

Distribution of discharge time constant (MimoSTAR2)

Download - Radiation damage in the STAR environment and performance of MAPS sensors

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