1. 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

2. M.S. IPHC-LBNL meeting, 3-5 April 2008 2 2 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

3. M.S. IPHC-LBNL meeting, 3-5 April 2008 3 3 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: 3x10 12 cm -2 TLD projection (pion assumption): 12x10 12 cm -2 What can we expect at STAR?

4. M.S. IPHC-LBNL meeting, 3-5 April 2008 4 4 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%

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

6. M.S. IPHC-LBNL meeting, 3-5 April 2008 6 6 Time constant for discharge of the self-biased node Dose (rad)τ 030 ms11ms (~40 °C? ) measured at LBL 20 k25 ms 500 k7 ms 1 M4 ms from Michael’s thesis for the radiation tolerant diode layout and the operating temperature of 40 °C

7. M.S. IPHC-LBNL meeting, 3-5 April 2008 7 7 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.

8. M.S. IPHC-LBNL meeting, 3-5 April 2008 8 8 Non-ionizing radiation Charge losses due to bulk damage Increased leakage current (not negligible) – Increase of shot noise

9. M.S. IPHC-LBNL meeting, 3-5 April 2008 9 9 Charge losses -20 °C – minimized contribution from shot noise (negligible for fluences up to 2x10 12 n eq /cm 2 ) Mimosa-9 -20 °C Tint 0.7 ms Mimosa-15 -20 °C Tint 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 1x10 13 n eq /cm 2. This background can be expected to scale linearly with the dose. Mimosa-9 -20 °C Tint 0.7 ms Half of signal

10. M.S. IPHC-LBNL meeting, 3-5 April 2008 10 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) Black: Ref Blue: 4.7x10 11 Purple: 2.1x10 12 Red: 5.8x10 12 Green: 1.1x10 13 MimoSTAR2 pixel type

11. M.S. IPHC-LBNL meeting, 3-5 April 2008 11 Consequences The charge losses after 2.1 x 10 12 n eq /cm 2 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.

12. M.S. IPHC-LBNL meeting, 3-5 April 2008 12 Leakage current (noise) from bulk damage after 2x10 12 n eq /cm 2 the noise degrades from 15 to 18 e- Chip 3 ref Chip 44.7x10 11 Chip 6 2.1x10 12 Chip 105.8x10 12 Chip 11 1.1x10 13 Chip 5ref Chip 723 krad γ Chip 820 krad X Chip 91 Mrad X 3T pitch 20 μm SB pitch 30 μm.

13. M.S. IPHC-LBNL meeting, 3-5 April 2008 13 Ni(I,Tint) = A × √I × √Tint N=√(N0 2 +Ni 2 ) 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(10 12 )+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 performance Mimosa-11(rad-hard) N=√(N0^2+ (A × √I × √Tint × (0.003 x Dose(krad)+1) × (0.14 x Dose(10 12 )+1))^2) A × √I = 10 at 40 °C

14. M.S. IPHC-LBNL meeting, 3-5 April 2008 14 Simple model for charge losses Exponential dependency?

15. M.S. IPHC-LBNL meeting, 3-5 April 2008 15 MimoSTAR2 pixel Single detector replacement – not sufficient Full elimination of shot noise – not sufficient Annealing ?

16. M.S. IPHC-LBNL meeting, 3-5 April 2008 16 MimoSTAR2 pixel PHASE1 integration time

17. M.S. IPHC-LBNL meeting, 3-5 April 2008 17 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 10 12 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)

18. M.S. IPHC-LBNL meeting, 3-5 April 2008 18 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

19. M.S. IPHC-LBNL meeting, 3-5 April 2008 19 Noise from Mimosa15

20. M.S. IPHC-LBNL meeting, 3-5 April 2008 20 Distribution of discharge time constant (MimoSTAR2)