R ecent developments on Monolithic Active Pixel Sensors (MAPS) for charged particle tracking.

1. Recent developments on Monolithic Active Pixel Sensors (MAPS) for charged particle tracking. Michael Deveaux on behalf of IPHC Strasbourg, IKF Frankfurt/M (Irradiations: F.M. Wagner, MEDAPP, FRM II reactor Munich) Outline The MAPS sensor (reminder) MIMOSA-22, a fast MAPS-sensor The SUZE-1 FEE chip Random Telegraph Signal and radiation damage Summary and Conclusion

2. The operation principle of MAPS +3.3V Reset +3.3V Output SiO2 SiO2 SiO2 N++ N++ P+ N+ P- P+ M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

3. How to build fast MAPS for the MVD: IPHC Strasbourg On - chip zero suppression Discriminators Sensor array Bondingpads + output Amplis. Expected time resolution: ~10 µs (~100 kFrame/s) Readout bus Pixel column SUZE-1 MIMOSA-16 and 22 M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

4. Last years status: MIMOSA-16 32 col. of 128 pixels (25 μm pitch, integrated CDS ) 1 Discriminator/column Tests at CERN-SPS ( 180 GeV pi−) in Summer 2007 Threshold: 6 mV Detection efficiency: 99.88 ± 0.05 (stat) % Fake rate: <10−5 Spatial resolution: 4.6 μm Proof of principle for MAPS with on-pixel CDS and on-chip discriminator (small size only). M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

5. MIMOSA-22, a fast and big chip • MIMOSA – 22: • Test the MIMOSA-16 concept with higher surface • 32 cols x 128 pixels => 128 cols x 576 pixels • 17 different (improved) pixels designs: • New high gain / low noise pixels • Radiation hard pixels • Build smaller pixels • 18.4 μm instead of 25 µm • Read-out time 100 μs ( 104 frames/s ) • JTAG slow control • Programmable test DACs for disciminator tests • 40 MHz digital data output Tested with Fe-55 source and CERN 100 GeV/c pion beam M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

6. Test results of the new preaplifyers • Standard SB-Pixel design (Mimosa-16): • Successfully used since MIMOSA-4 • No dead time • Noise: ~15e- with on-pixel CDS, else ~ 9e- New in MIMOSA-22 • Noise: • 10 < N < 14 e− ENC + 5 e− ENC Fix pattern noise (individual pixel offset) • Rad hard: 1e− ENC more than standard version • CCE : • 3x3 pixels : 70 – 80 % • 5x5 pixels : 80 – 90 % M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

7. Discriminator Threshold Discriminator Threshold Beam test results of MIMOSA-22 Detection efficiency Fake hit rate All pixels of interest show: Detection efficiency: >99.8% Fake hit rate: O(10-4 – 10-5) Spatial resolution: ~3.5 µm (~ Pitch / 5) M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

8. On - chip zero suppression Discriminators Sensor array Bondingpads + output Amplis. Readout bus SUZE – 1 data sparsification circuit • Chip with integrated Ø and output memories (no pixels) • Algorithm: • Step1: find up to 6 series of 4 neighbour pixels / raw in block of 64 cols. • Step2: Read-out all blocks, keep up to 9 series of 4 pixels. • Output memory: • 4 x (512x16 bits) taken from AMS I.P. lib. • Surface: • 3.9 × 3.6 mm² • Test result: • Works fine up to 115% clock frequency • Can handle up to 100 hits/frame at 104 frame/s Pixel column SUZE-1 How to build fast MAPS for the MVD M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

9. Next Step: MIMOSA-26 • MIMOSA-26 • Pixels + Ø-suppression • Expanded surface: • 1152 cols x 576 pixels • 21.2 x 10.6 mm² • 18.6 µm pixel pitch • Expanded data sparsification circuit • 18 blocks of 64 columns • Max. 9 clusters per row • Data rate: 80 Mbits/s • Submission November 2008 SUZE-1 Ø -suppression circuit MIMOSA-22 Sensor MIMOSA-26 M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

10. Radiation hardness studies together with M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

11. Signal [ADC] Time Random Telegraph Signal • Random Telegraph Signal: • Modulation of an output signal between two “quantum levels”. • Random period length. • RTS in MAPS sensors first described by Hopkinson (2000)* Output signal of two MAPS pixels * G.R. Hopkinson: “Radiation Effects in a CMOS Active Pixel Sensor”, IEEE-NSS Vol. 47, No. 6, P. 2480 D. Doering, Bachelor Thesis D. Doering, Bachelor Thesis RTS may generate fake-hits if amplitude exceeds discriminator threshold. Problem for MAPS being used in HEP – experiments? M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

12. Fake hit rate of MAPS with Random Telegraph Signal MIMOSA-18 (SB-pixel, irradiated at MEDAPP, FRM II, Munich) D. Doering, Bachelor Thesis Preliminary Affected SB-pixels remain sensitiv. The fake hit rate of MAPS shrinks with cooling. Identified RTS pixels contribute ~60 – 80 % of all fake hits. M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

13. Pixel Y Normal Pixel RTS Pixel Pixel X Distribution of RTS-pixels D. Doering, Bachelor Thesis • Up to ~10% of all pixels are affected. • Masking of pixels is not possible but pixels stay sensitiv • Operate pixels, tolerate fake hits ( ~ 104 / frame for full MVD) Note: Fast MAPS might show less RTS than MIMOSA-18 M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

14. Standard collection diode ( ~ 3 x 4 µm²) MIMOSA-Pixel with 10 x 10 µm² Sensors with improved charge collection efficiency M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

15. How to escape here? Diode 1 Diode 2 Sensors with improved charge collection efficiency Bigger collection diodes may improve CCE Improved CCE => improved radiation hardness Tested with MIMOSA-19 (by IPHC) M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

16. Results A. Büdenbender, Bachelor Thesis T= -20 °C Charge collection efficiency is indeed substantially increased But the bigger collection diodes generate more noise M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

17. S/N of the sensors A. Büdenbender, Bachelor Thesis Insufficient S/N Both MIMOSA-18 and MIMOSA-19 seem fairly radiation hard Big diodes have no advantages because of high noise M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia

18. Summary • At IPHC, a first sizable chip with column parallel readout was produced • and tested in the CERN – SPS pion beam: • Features: • reduced noise 15 e- => 10 – 14 e- , det. eff. > 99.8 % • pitch 18.4 μm, resolution = 3.5 µm • An FEE chip with cluster finding circuits (SUZE-1) was successfully tested. • MIMOSA-26 integrating the full discrimination chain will be submitted • in November. • Radiation hardness tests were undertaken at IKF: • A radiation hardness of 1013 neq/cm² has been shown for two pixel concepts • The effect of Random Telegraph Signal was identified as dominating source • of background hits in MAPS • Studies on RTS suggest, that RTS can be tolerated if chips are cooled M. Deveaux, 12th CBM Collaboration Meeting, 13 - 18 Oct. 2008 JINR Dubna, Russia