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S tatus of the R&D on MAPS in Strasbourg and Frankfurt

S. Amar, G. Bartone, J. Baudot, A. Besson, G. Claus, C. Colledani, M.Deveaux , A. Dorokhov, G. Dozière, W. Dulinski, C. Dritsa, X.Fang, J.C. Fontaine, I. Fröhlich, M. Goffe, D. Grandjean, S. Heini, A. Himmi, C. Hu, M. Koziel, K. Jaaskelainen, F. Morel, C. Muentz, N. Pillet, C. Schrader,

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S tatus of the R&D on MAPS in Strasbourg and Frankfurt

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  1. S. Amar, G. Bartone, J. Baudot, A. Besson, G. Claus, C. Colledani, M.Deveaux, A. Dorokhov, G. Dozière, W. Dulinski, C. Dritsa, X.Fang, J.C. Fontaine, I. Fröhlich, M. Goffe, D. Grandjean, S. Heini, A. Himmi, C. Hu, M. Koziel, K. Jaaskelainen, F. Morel, C. Muentz, N. Pillet, C. Schrader, A. Shabetai, J. Stroth, M. Szelezniak, I. Valin, B. Wiedemann, M. Winter (Project coordinator MAPS) Status of the R&D on MAPS in Strasbourg and Frankfurt • Outline: • Operation principle of MAPS (a reminder) • Fast readout • Radiation hardness • System integration and material budget • Summary and Conclusion

  2. Particle trajectory Diode Preamplifier (one per pixel) Diffusing free electrons ~20µm The operation principle of MAPS A Minimum Ionising Particle creates ~80 e-/h-pairs perµm in Si Collection with build in voltages and thermal diffusion P++ = Highly P-doped ~ 30µm N P++ P- P++

  3. The MIMOSA - Technology Minimum Ionizing Particle MOSActive Pixel Sensor • Features of the MIMOSA – detectors: • Single point resolution 1.5µm - 2.5µm • Pixel – pitch 10-40 µm • Thinning achieved 50 - 120µm • S/N for MIPs 20 – 40 • Detection efficiency > 99% • Radiation hardness: 1MRad ; 2 x 1012 neq/cm² • Produced in various commercial CMOS-Processes MIMOSA IV

  4. Main R&D Directions • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression • Thinning and material budget • Thinning of Chips • Feasibility studies on thin support structures • System integration and reliability • Study complex sys-tems composed of numerous chips • Radiation hardness • Search for improved sensors (pixel design, production process…)

  5. Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Concept: ~1000 on - chip discriminators Pixel array Data sparsifi-cation logic Output: Cluster information (zero suppressed) Blind area Sensor Column parallel readout is demonstrated but needs improvement. Data sparsification logic remains to be developed. Goal: A readout time of ~ 10µs for CBM

  6. ~ On - chip discriminator • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Pixel array Data sparsifi-cation logic • MIMOSA-16 • Designed in AMS-0.35µm Opto • 32 columns of 128 pixels (25 µm pitch) • On-pixel CDS • On-chip discriminator • Improved version of the successful MIMOSA-8 Beam test at CERN – SPS in early September Some results are labelled „Private and preliminary“: Data is roughly 2 weeks old, very preliminary analysis. Only the few results shown are stabilized (might still get better). CAD – Layout of MIMOSA-16

  7. MIMOSA-16 • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Good reference design (4.5 x 4.5 µm² diode) Collection diode too small (2.4 x 2.4 µm²) Detection efficiency [%] Detection efficiency of reference design is > 99 % For some pixels, the collection diode was chosen to small (insufficient CCE) Fake hit rate at typical discriminator threshold (> 4 mV) < O(10-4) S/N (MIMOSA-8) = ~ 8-9 S/N (MIMOSA-16) = ~ 16-17 A. Besson 10-2 • Note: • Spatial resolution: 5-6 µm • Digital resolution: 7.2 µm • Clustering helps despite of digital output  A. Besson 10-8

  8. MIMOSA-16 • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Significant pixels / hit A. Besson Mean number of firing pixels/hit varies between 2.5 and 6

  9. MIMOSA-16 • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression 4.5 x 4.5µm² - diode 7.8 mV IPHC-Strasbourg CEA-Saclay 3.5 mV A. Besson (modified) Pixel multiplicity in clusters has a wide distribution. One can hardly accept only clusters with >1 significant pixel!

  10. ~ On - chip discriminator • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Pixel array Data sparsifi-cation logic • MIMOSA-16 works very well . . . • but leaves room for improvement: • Too short col. lengths • Pixels still too big (25 x 25 µm²) => limited radiation hardness • Next generation prototype MIMOSA-22 under preparation : • Coll. length = 640 pixel (needs different design of steering and readout busses) • Pixels smaller (18.4 x 18.4 µm²), needs smaller discriminators • Slow control with JTAG • 128 colls. digital, (+ 8 analogue for debugging/test purpose) • Submission planned for 27. October 2007 • Tests planned February 2008

  11. ~ On - chip discriminator • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Pixel array Data spasifi-cation logic FPGA-based solution Flexible for testing different strategies Use existing chips as sensor Compatible with HADES – DAQ Test in HI-experiment is possible (MVD demonstrator) SUZE – 1 chip First test of on-chip implementation Close to hardware but inflexible Only digital part, (not yet combined with sensor) Not (yet) designed for beam tests See talk of C. Schrader

  12. Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression The readout architecture of SUZE-1: • Surface: ~ 3.6 x 3.6 mm² • Still too slow for CBM but sufficient for STAR-HFT and EUDET (FP6) • Submitted for fabrication, back from foundry in October • Test completed by end of year • Next generation chip is scheduled for 2008 (faster logic) 4 output memories ( 512 x 16 bits) • Integrated logic: • Step 1 (inside blocks of 64 colls) • identify up to 6 series of up to four • significant pixels / line • -Step 2 • Read-out outcome of step-1 in all blocks, • keep up to 9 series of four pixels

  13. ~ On - chip discriminator • Fast readout and good time resolution • Improvement of analog electronics • Integration of zero suppression Pixel array Data spasifi-cation logic MIMOSA-22+ = MIMOSA-22 + SUZE-1 • MIMOSA-22 sensor + discriminator: • 640 pixels per coll. x 1088 colls (more than Mi-22, surface ~1 x 2 cm²) • Pixel pitch 18.4 x 18.4 µm² • Integration time ~ 100 µs • + SUZE-1 data sparsification logic Final sensor for EUDET - Telescope Submission planned October 2008

  14. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Main concern for CBM: Non-ionizing radiation hardness Limitation of the non-ionizing radiation hardness: Reduced charge carriers lifetime => Signal electrons recombine before being collected Strategy to improve: A) Speed up charge collection time B) Use thicker sensor, produce more initial signal C) Recover lifetime of electrons How to do it: A) Reduce pixel pitch, shorter way, faster collection 40 µm => ~1011 neq / cm², 20 µm => ~1012 neq / cm² (MIMOSA-9) Try to modify pixel structure for faster collection (MIMOSA-21) B) Use sensors with thicker epitaxial layer (20µm instead 14µm) C)Try cryogenic detector operation

  15. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Study of MIMOSA-18 Smaller pixels, thicker sensor • MIMOSA-18 • Designed: 2006 • 512 x 512 pixels • 10µm pixel pitch (faster charge coll.) • Sensor thickness: 14µm and 20µm • Status: • First beam tests: June 2007 (DESY) – non irradiated chips • Irradiated samples now available • Systematic studies of irradiated chips: In Frankfurt by the end of the year

  16. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Room for Mi18 Beamtest results S/N Electrons [electrons] [ENC] ENC Study of MIMOSA-18: Thicker sensor, beam test at Desy (June 2007) C. Dritsa (preliminary) C. Dritsa (preliminary) C. Dritsa (preliminary) Results show no clear preference

  17. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation C. Dritsa (preliminary) Study of MIMOSA-18: Thicker sensor, beam test at Desy (June 2007) Additional charge is observed in the periphery of the clusters only. Benefit of thick sensor is smaller than expected. Next step: Confirm with irradiated chips => Frankfurt

  18. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Study of the ST-BICMOS 0.25µm process (MIMOSA-21) • Features: • Lowly doped (50 Ω cm) substrate for sensors • Allows depleting a bigger part of the volume => Faster charge collection • Deep N-Well implantation • Faster charge collection • Higher capacity (how much higher?) • Higher dark current (how much higher?) • Higher noise ? • Ionising radiation hardness? Signal electron starting point Possible trajectory 10 µm pitch N-Well N-Well Deep N-Well Deep N-Well Deep N-Well diode. Expect faster collection time. Standard N-Well diode. Diffusing electron may miss it.

  19. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Study of the ST-BICMOS 0.25µm process (MIMOSA-21) So far: Chips without epitaxial layer => Study diode properties Chips with epitaxial layer are under design Preliminary results (at 20°C, tInt = 40 ms => unfavorable conditions): N-Well N-Well Deep N-Well Deep N-Well Lower layer is missing! Lower layer is missing! Leakage current : 0.5 fA (OK) Noise : 19 ENC (still OK) (No shot noise) : 15 ENC (OK) CCE : Not Available Leakage current : 0.5 fA (OK) Noise : 19 ENC (still OK) (No shot noise) : 15 ENC (OK) CCE : Not Available Both pixels show satisfactory noise performances combined with extraordinary low leakage current. Next step: Address radiation hardness. Build chips with epi-layer

  20. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Recombination destroys the signal Cryogenic detector operation: Passivate signal traps by cooling Efficient approach for depleted N-doped detectors. BUT: MAPS are P-doped and undepleted.

  21. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Cryogenic detector operation: Passivate signal traps by cooling • Challenges: Build a test system • Chip operation at very low temperature => Isolate with vacuum • Operate readout board at warmer temperatures (reduce problems) • Transfer signals out of vacuum PCB MIMOSA-18 (?) Vias for thermal contact Mimosa – Readout board Support, LN2 cooled Support, “water” cooled @ room temperature Preliminary concept Input is welcome

  22. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Cryogenic detector operation: Passivate signal traps by cooling • A vacuum vessel is being • build at Frankfurt. • Mission: • Cryogenic MAPS operation • Test of MVD components under vacuum conditions. • Volume sufficient to test full detector stations • Status: • First vacuum tests are ongoing. • Experiments located in the device are still under design.

  23. Thinning and material budget • Thinning of Chips • Feasibility studies on thin support structures Operation Diamond Project goal: Build a super thin ladder of MAPS detectors with ~ 0.1 % X0 MIMOTel (50 µm) MIMOTel (50 µm) Contact Printed Circuits (Al, 3 µm) CVD – Diamond (50 – 100 µm) • Project partners: • IPHC – Strasbourg (MAPS production and coordination) • Diamond Materials, Freiburg (CVD- diamond production) • IZM – Munich (Lithography, system integration and bonding) Project is started but ambitious fundamental research. Risks are sizeable. Thickness of diamond aims to ILC, insufficient for our cooling requirements? (More about material budget: See talk of C. Müntz)

  24. Summary and Conclusion: • Fast column parallel architecture: • MIMOSA-16 beam tests demonstrated substantial improvements • First data sparsification chip is curently fabricated • Integrate sensors and data sparsification (MIMOSA-22+, in 2008) • FPGA board for studying interface MAPS to CBM-DAQ is under design • Radiation tolerance issues: • Interesting fab. processes are under study (20µm, deep N-Well) • Cryogenic chip operation is under preparation • Integration issues: • Design of MVD-Demonstrator is started at Frankfurt • Integration of CVD-Diamond + Silicon is under investigation by Strasbourg and partners.

  25. Radiation hardness • Study of pixel designs • Study of dedicated production processes • Cryogenic detector operation Study of MIMOSA-18, MIMOSA-19 Smaller pixels with modified structure MIMOSA-18 (Standard – pixel, 10 µm pitch) MIMOSA-19 (Particular diode, 12 µm pitch) Better charge collection? More charge/pixel? Higher capacity/lower gain Higher noise? Higher dark current? Hit and diff. e- Collecting diode Standard pixel (Mimosa-18) Mimosa – 19 pixel Status: MIMOSA-18 is running in Strasbourg and Frankfurt MIMOSA-19 produced, tests under preparation Irradiation is done

  26. General Status • Strasbourg: • Tests of the chips produced in 2006 are ongoing • (MIMOSA-16 to MIMOSA-21 + ADCs) • Chip design activities focus on fast readout • Specific prototypes are developed for radiation hardness issues • R&D on very thin support structures has started • Frankfurt: • Equipment still being completed • Preparation for tests on cryogenic chip operation • First simple radiation hardness studies were performed; systematic studies under preparation (MIMOSA-18, MIMOSA-19) • Intense R&D on MVD demonstrator

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