1. 1 Improved Non-Ionizing Radiation Tolerance of CMOS Sensors Dennis Doering 1 *, Michael Deveaux 1, Melissa Domachowski 1, Michal Koziel 1, Christian Müntz 1, Paul Scharrer 1, Joachim Stroth 1,2 1 Institut für Kernphysik, Goethe University Frankfurt/M, Germany 2 GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany Outline - CMOS Monolithic Active Pixel Sensors - Non-ionizing radiation damage effects - MAPS with high-resistivity epitaxial layer - Radiation tolerance - Triangle of non-ionizing radiation hardness

2. /17/23 CBM SIS300 MAPS* (2003) MAPS* (2012) MIMOSA-26 Binary, 0 Single point res. ~ 5 µm1.5 µm1 µm4 µm Material budget < 0.3% X 0 ~ 0.1% X 0 ~ 0.05% X 0 Rad. hard. non-io. >10 13 n eq 10 12 n eq /cm²>3·10 14 n eq >10 13 n eq Rad. hard. io > 3 Mrad200 krad> 1 Mrad> 500 krad Time resolution < 30 µs~ 1 ms~ 25 µs110 µs Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 CMOS Monolithic Active Pixel Sensors 2 Optimized for one parameter Current compromise Used by industry (digital camera) Have been modified for charged particle detection since 1999 by IPHC Strasbourg Foreseen for STAR, CBM, ALICE, ILC… => Sharing of R&D costs.

3. /17/23 Design of a MAPS Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 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. /17/23 Charge spectrum Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 4 e- Particle Epitaxial Layer Diode

5. /17/23 Non-ionizing radiation damage effect Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 5 Charge losses due to recombination at radiation-induced defects e- Particle Defects due to radiation Epitaxial Layer Diode

6. /17/23 Influence of radiation damage and pixel pitch Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 6 e- Large pixel pitch Small pixel pitch Defects due to radiation Small pixel pitch Large pixel pitch Epitaxial Layer Diode Epitaxial Layer Diode

7. /17/23 Pixel pitch effect Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 7 In most of the cases, the whole charge can be detected. Little losses for larger pixel pitch even unirradiated

8. /17/23 Pixel pitch effect Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 8 Signal losses depend on the pixel pitch.

9. /17/23 Pixel pitch effect Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 9 Smaller pixel pitch improves radiation tolerance. Drawback: Number of pixel Readout time Power consumption

10. /17/23 High-resistivity Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 10 Larger depleted volumes: ⇒ Accelerated charge collection ⇒ Improved non-ionizing radiation tolerance SiO 2 N+P+ P- P+ Epitaxial Layer P-Well Substrate depleted volume Low-resistivity ~ 30 Ωcm High-resistivity ~1k Ωcm New CMOS process available: High-resistivity: Decrease of doping concentration in epitaxial layer. Sensing diode

11. /17/23 MIMOSA-18 AHR Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 11 MIMOSA-18 AHR: Analog sensor with high-resistivity Epitaxial Layer. Main features: a)High-resistivity ~1k Ωcm EPI layer b)2.5V-3V depletion voltage c)Pixel pitch from 25µm down to 10µm Irradiation up to 3·10 14 n eq /cm² @ TRIGA reactor (Ljubljana/Slovenia)

12. /17/23 Signal response Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 12 More drift, less diffusion: ⇒ Signal charge focused to seed pixel ⇒ Signal amplitude doubled MIP-like β (Ru-106) Seed pixel

13. /17/23 Signal response Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 13 Radiation damage effect after 3·10 14 n eq /cm² : Signal losses due to recombinations observed. However, the irradiated high-resistivity sensor exhibits a higher signal amplitude than the unirradiated low-resistivity sensor. MIP-like β (Ru-106) Seed pixel

14. /17/23 Noise Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 14 Radiation damage Substantial increase in the bulk noise is observed.

15. /17/23 Noise Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 15 Use of temperature dependence of bulk noise Radiation damage

16. /17/23 Noise Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 16 Cooling Noise is alleviated to a factor of 2 with decreasing temperature. Expect further noise reduction in case of faster readout. Radiation damage

17. /17/23 Signal to Noise ratio Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 17 S/N limit (MIPS)

18. /17/23 Signal to Noise ratio Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 18 Error bars: Fit uncertainty + 10% noise uncertainty S/N limit (MIPS) (High-resistivity)

19. /17/23 Signal to Noise ratio Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 19 Error bars: Fit uncertainty + 10% noise uncertainty S/N limit (MIPS) High-resistivity

20. /17/23 Signal to Noise ratio Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 20 Error bars: Fit uncertainty + 10% noise uncertainty S/N limit (MIPS) High-resistivity

21. /17/23 Radiation tolerance Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 21

22. /17/23 Summary Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 22 Radiation tolerance studies up to 3·10 14 n eq /cm² Results: CMOS sensors based on high-resistivity epitaxial layer exhibit substantially improved performance, (S/N ~ doubled) Radiation tolerance depends on the pixel pitch Laboratory test indicates: Radiation tolerance is beyond 3·10 14 n eq /cm² (Pitch 10µm, cooled sensor) Outlook: Ionizing radiation hardness addressed by MIMOSA-32 – fabricated in an 0.18µm process -> S. Senyukov (next talk)

23. /17/23 Triangle of non-ionizing radiation tolerant MAPS Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 23 Pitch Resistivity Temperature

24. /17/23 Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 24 BACKUP

25. /17/23 Radiation tolerance Noise increases Sensor: - Mi-18 AHR, SB-Pixel, 10 µm pitch - Epitaxial layer: 400  cm, 15 µm Irradiation: - fast reactor neutrons (Triga, Ljubljana) - Chip not powered during irradiation - Dose: 3 · 10 14 n eq /cm² + O(3 MRad) <20% less entries Thinner active vol.? CCE ok Gain ok Fe-55 (X-rays) Ru-106 (  -rays) 99% det. eff. after irrad. 620e (MPV) 490e (MPV) <20% less signal Thinner act. vol.? Noise increases => Compensate with cooling. 3 · 10 14 n eq /cm² + O(3 MRad) Not irradiated Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 25 Preliminary conclusion: Sensor tolerates 3 · 10 14 n eq /cm², to be confirmed in beam test

26. /17/23 Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 26 CCE ok Fe-55 X-ray CCE shifted MIMOSA-18 AHR 25µm (A2)MIMOSA-18 AHR 12µm (A1) gain ok 12 µm pitch: Average CCE is constant. 25µm pitch: Shift to lower values as observed in sensors based on low resistivity EPI layer. Pixel with 12µm and 25µm pitch (Fe-55) Seed pixel cluster

27. /17/23 Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 27 12 µm pitch: Shift of cluster peak now visible ⇒ some signal charges lost which diffuse longer distance (to neighbor pixels) 25µm pitch: Dramatic shift ⇒ 12µm pixel pitch: in a part of Epitaxial layer signal lost due to recombination can be neglected Pixel with 12µm and 25µm pitch (Fe-55) Cluster of 25 pixel => Larger diffusion paths

28. /17/23 Temperature measurement with infrared camera Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 28 Huber system CC 815 -70°C - + 35°C MIMOSA-18 Camera paint Sensor is operating Infrared -3°C /-20°C T of cooling liquidT of sensor

29. /17/23 High resistivity Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 29 Doping concentration Size of the depleted zone Idea: Decreasing the doping concentration from 10 15 should increase the size of the depleted zone:  Improved performance expected. Standard: 13 Ω cm; N A ≈10 15 cm -3 High resistivity: 400 Ω cm; N A ≈3.3 10 13 cm -3

30. /17/23 Applications of MAPS Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 30 MAPS are developed for applications as vertex detector since 1999 at IPHC (Strasbourg). CBM-Experiment (FAIR, GSI) STAR-Experiment Possible ITS-Upgrade ALICE International Linear Collider

31. /17/23 MIMOSA-26 - Working horse since several years Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 31 JTAG slow control On-chip voltage regulators 1152 discriminators zero suppr. logic Output memories Read out time: ~100 µs => ~ 10k frames/second Radiation tolerance: >300 kRad; > 21.2 x 10.6 mm² Pixel column Digital part Sensing part

32. /17/23 Pixel pitch effect Dennis Doering: Improved Non-Ionizing Radiation tolerance of CMOS sensors RESMDD Florence Oct 2012 32 Signal losses depend on the pixel pitch. Photons (Fe-55) Summed cluster charge