Radiation Tolerance of Monolithic Active Pixel Sensors: Impact of Non-Ionising Doses

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 Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

2. 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)

3. 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)

4. Impact of the temperature on leakage current Mimosa-15 Preliminary => Cooling helps

5. Noise of irradiated MAPS T=-20°C T=+20°C MIMOSA-15 Origin of scattering is not understood Noise is reduced by more than 50% at -20°C. Expect additional benefit for combined radiation doses (ionising and non-ionising)

6. Impact of temperature on the charge collection efficiency Preliminary Substantial systematic uncertainties! Slight trend: Higher temperature => Better CCE BUT: Can also be explained as artefact of higher noise => Not considered as significant today

7. 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 Resmdd 2006, 13. 0ct. 2006, Florence, Michael Deveaux (michael.deveaux@ires.in2p3.fr)

8. Radiation hardness as a function of pixel pitch (at -20°C, < 1 ms integration time ) Friendly speaking preliminary Well established (beam test results) Highest radiation level tested „good“: 2.00E+12 might also be 3.00E+12

9. Random Telegraph Signal So far observed at doses >> 1011 neq/cm² True hit Signal [ADC] Excitation 2: Noise ~ 33 e- Excitation1: Noise ~ 31 e- Threshold Ground state: Noise ~ 30 e- t [200 = 1s] Leakage current (?) Observed with MIMOSA-2 (3T-Pixel), reproduced with MIMOSA-15 (3T-Pixel)

10. Potential Danger for SB-Pixels SB-Pixels may adapt themselfes to slow fluctuations. But also to those ones? Really crucial? Will be studied with MIMOSA-18 (in Frankfurt). Expect results early next year.

11. Temperature Dependence of RTS Cooling helps!

12. 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 Signal • but 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)