1. 1 Radiation Hardness of Monolithic Active Pixel Sensors Dennis Doering, Goethe-University Frankfurt am Main on behalf of the CBM-MVD-Collaboration Outline - Operation principle of MAPS - Radiation damage effects - MAPS with high-resistivity epitaxial layer - Parameters of radiation hardness - Conclusion

2. /17/21 Applications of MAPS Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 2 Picture STAR Picture CBM International Linear Collider CBM-Experiment (FAIR, GSI) STAR-Experiment MAPS are developed for applications as vertex detector since 1999 at IPHC (Strasbourg).

3. /17/21 Operation principle Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 3 SiO 2 N+ P+ P- P+ Sensing diode Epitaxial Layer P-Well Substrate N+ 50 µm ~50 µm thin sensors ⇒ low material budget High granularity ⇒ good spatial resolution 10-40 µm => a few µm resolution

4. /17/21 Operation principle Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 4 SiO 2 N+ P+ P- P+ Epitaxial Layer P-Well Substrate e- N+ e- Particle Sensing diode

5. /17/21 Non-ionizing radiation effects: Signal response Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 5 SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate N+ e- Sensing diode Defects

6. /17/21 Signal response Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 6

7. /17/21 Non-ionizing radiation effects: Leakage current/Noise Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 7 SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate N+ - - Sensing diode Defects

8. /17/21 Noise Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 8 Radiation damage

9. /17/21 Noise Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 9 Radiation damage

10. /17/21 Noise Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 10 Radiation damage Cooling 2 times higher noise with respect to unirradiated

11. /17/21 Non-ionizing radiation effects Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 11 SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate N+ e- - - Sensing diode Defects

12. /17/21 Non-ionizing radiation effects Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 12 SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate N+ e- - - Radiation damage Sensing diode Defects

13. /17/21 Non-ionizing radiation effects Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 13 SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate N+ e- - - Radiation damage Sensing diode Defects

14. /17/21 Signal to Noise ratio Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 14 S/N limit (MIPS) Technical feasible limits reached: - Pixel pitch - Operating temperature Region of interest ?

15. /17/21 High-resistivity Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 15 Larger depleted volumes ⇒ guided charge collection ⇒ Improved charge collection efficiency (CCE) SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate depleted volume Low-resistivity High-resistivity High-resistivity: Decrease of doping concentration in epitaxial layer. Sensing diode

16. /17/21 Signal response Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 16

17. /17/21 Signal response Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 17 More charge collected in a high resistivity epitaxial layer.

18. /17/21 Signal response Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 18 Radiation damage effect after 3·10 14 n eq /cm²: Some signal get lost due to recombinations. However, the high resistivity sensor is even irradiated better than the low resistivity sensor unirradiated.

19. /17/21 Improvements using high resistivity Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 19 Error bars: Signal fit uncertainty * 10% noise uncertainty *Beam test is pending S/N limit (MIPS) * Parameters: - Pixel pitch - Operating temperature - Resistivity of epitaxial layer

20. /17/21 How to improve the non-ionizing radiation hardness of MAPS: -Operate the sensor at low temperature ( -30°C) -Small pixel pitch ( 10µm) -High-resistivity epitaxial layer (used here 400 Ωcm) Conclusion Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 20

21. /17/21 How to improve the non-ionizing radiation hardness of MAPS: -Operate the sensor at low temperature ( -30°C) -Small pixel pitch ( 10µm) -High-resistivity epitaxial layer (used here 400 Ωcm) ⇒ Radiation hardness beyond 3·10 14 n eq /cm² Conclusion Dennis Doering: Radiation hardness of MAPS DPG Mainz March 2012 21