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R adiation tolerance of M onolithic A ctive P ixel S ensors (MAPS)

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,

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R adiation tolerance of M onolithic A ctive P ixel S ensors (MAPS)

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  1. 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) 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

  2. The operation principle of MAPS Sensor design: P-Well Diode (N-Well) • The Active volume (Epitaxial layer) is not depleted. • Charge gets collected via thermal diffusion. EpitaxialLayer Substrate Diode 1-2µm 4-14µm Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  3. The operation principle of MAPS Particle trajectory Preamplifier (one per pixel) Diffusing free electrons ~20-40µm Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  4. Some simple preamplifiers 3 Transistor Pixel Multi-diode pixel Amplifier (Source Follower) Classical MAPS-design +Better charge collection efficiency - Higher leakage current -Less gain - More noise Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  5. The MIMOSA - Technology Minimum Ionizing Particle MOSActive Pixel Sensor • Features of the MIMOSA – detectors: • Single point resolution 1.5µm - 2.5µm • Typical Pixel – pitch ~20µm • Thinning achieved to 120µm (50µm under study) • S/N for MIPs 20 – 40 • Detection efficiency > 99% • Column parallel readout is demonstrated • Produced in various commercial CMOS-Processes MIMOSA IV Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  6. Radiation tolerance against ionising doses Noise of: The standard structure The advanced structure Not irradiated, 10°C Noise [e-] Noise [e-] After 1 MRad, 10°C Tint [ms] Leakage current was reduced by removing thick oxide from the diodes and adding P++ guard rings. Recent beamtests (MIMOSA-15) prove the resistance against 1 MRad X-Rays: • Results (- 25 °C, Tint ~ 170 µs): • Det. eff: > 99.9 % • S/N: 19.5 MPV Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  7. 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 – 1013neq / cm² MAPS are highly P-doped, not depleted => No problems with Neff. Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  8. Leakage current of irradiated MAPS Increase of leakage current after 1013 neq / cm² ? An increase of leakage current is observed. Reasonably low at moderate cooling. of the chip support Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  9. Noise of irradiated MAPS Data taken at 10°C, tInt = 3.3 ms 2 diodes per pixel 1 diode per pixel No clear trend. Increase of ~10% is expected because of shot noise. More shot noise expected at high temperatures. Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  10. CCE of irradiated MAPS Data taken at 10°C, tInt = 3.3 ms with 55Fe-photons. Summed signal of 4 pixels of a cluster. Pixel pitch: 20 µm Active Medium: MIMOSA-1: ~ 14 µm MIMOSA-2: ~ 4 µm Pixels with more than one diode have a better CCE Detectors with thin active medium degrade slower (gray points) Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  11. S/N estimate of irradiated MAPS Previous slide normalized with: Measured signal and noise (non irrad. pixels) Test beam data for comparision A combination of thick sensors and multiple diodes shows the best performances. (Direct measurements are needed to confirm the extrapolation) Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  12. S/N and det. efficiency Thick sensor (MIMOSA-9) irradiated up to 1012 neq / cm²(Beamtest): Small pixels detect better than big ones A S/N of ~10 (MPV) is required for good detection efficiency Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  13. S/N and det. efficiency Thick sensor (MIMOSA-15) irradiated up to 1013 neq / cm²(Beamtest): A radiation tolerance of  2 x 1012 neq / cm²has been demonstrated Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

  14. Summary and Conclusion • The radiation tolerance of MAPS against 1MRad has been demonstrated. • The radiation tolerance of MAPS against neutron has been tested: • with 5 different Chips, 4 different processes • ~ 10 slightly different pixel designs • Leakage current and noise increase were observed. • Can be tolerated if the chip is moderately cooled • A reduction of the charge collection efficiency is the dominant problem • Origin: Probably reduced lifetime of the charge carriers • Can be reduced by: • Using a thick sensitive volume (high initial signal) • Using a high diode density (small pixels): Small diffusion paths • Tolerance against 2 x 1012 neq / cm² has been demonstrated • We hope to reach 1013 neq / cm²in the next years In contrast to J. Velthuis et al.* (2005) we see no evidence for radiation tolerance of MAPS above 1013 neq / cm² * J.J. Velthuis et al., IEEE Transactions on Nuclear Science, Vol. 52, No. 5, October 2005

  15. Thank you MIMOSA V More information in the internet: http://ireswww.in2p3.fr/ires/recherche/capteurs/index.html

  16. STAR Upgrade • Radiation doses @ Star: ~50 kRad • Specific complication: • Integration time envisaged: 4 ms • Temperature: Up to 40 °C • => Leakage current and noise? • Status: • Beamtests were undertaken. Preliminary result: • Current designs seem compatible with ~ 50kRad and 30°C • Integration time = 2 ms => ok also at 40°C • Refined data analysis is ongoing

  17. S/N looks good, but analyse signal an noise separately: J.J. Velthuis et al., IEEE Transactions on Nuclear Science, Vol. 52, No. 5, October 2005 (some points and error bars were removed for clearity)

  18. Potential explaination for “radiation tolerance” against 1014 neq Signal and noise plot where superposed: Red Points: Noise Black Points: Signal Some where removed for clarity * J.J. Velthuis et al., IEEE Transactions on Nuclear Science, Vol. 52, No. 5, October 2005 Threshold: 8 S/N (Seed pixel) + 2 S/N (Cluster) 1010 1011 1012 1013 1014 Hypothesis: Signal measurements reflect the moving threshold (Only event with highest charge were selected, poor det. eff)

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