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


33

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?


44

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%


55

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


66

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


77

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.


88

Non-ionizing radiation

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

– Increase of shot noise


99

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


1111

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.


1212

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.


1313

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


1414

Simple model for charge losses

Exponential dependency?


1515

MimoSTAR2 pixel

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


1616

MimoSTAR2 pixel

PHASE1 integration time


1717

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)


1818

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


1919

Noise from Mimosa15


2020

Distribution of discharge time constant (MimoSTAR2)

Documents

Radiation damage in the STAR environment and performance of MAPS sensors