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Silicon Pixel and Strip Detectors for LHC Experiments

Silicon Pixel and Strip Detectors for LHC Experiments. 1 st Coordination Meeting of the CBM Experiment at the future GSI facility GSI, Nov. 15-16, 2002. P. Riedler ALICE Silicon Pixel Team CERN. Acknowledgements:

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Silicon Pixel and Strip Detectors for LHC Experiments

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  1. Silicon Pixel and Strip Detectors for LHC Experiments 1st Coordination Meeting of the CBM Experiment at the future GSI facility GSI, Nov. 15-16, 2002 P. Riedler ALICE Silicon Pixel Team CERN

  2. Acknowledgements: M. Campbell, P. Collins, H. Dijkstra, F. Faccio, H. Pernegger, G. Stefanini and the ALICE SPD Team P.Riedler - CERN

  3. Outline - The LHC and its experiments • Radiation damage in silicon • Electronics • Detectors • A closer look at the ALICE SPD ALICE Silicon Pixel Telescope Reconstructed event: Testbeam 2002 P.Riedler - CERN GSI - 15/11/2002 P.Riedler - CERN 3

  4. P.Riedler - CERN

  5. The LHC and its Experiments • head-on collisions of protons (7TeV on 7 TeV) • and heavy ions • Lmax~1034cm-2 s-1 f(4cm)~3 1015 (neq) cm-2 in 10 years (>85% charged hadrons) • ! RADIATION DAMAGE ! • Detectors for LHC under full construction now • Installation: 2006, First Beam: 2007 • => RD groups (e.g. RD48, now RD50) already work on solutions for next generation of detectors P.Riedler - CERN

  6. P.Riedler - CERN

  7. 2 general purpose detectors: Higgs in SM and in MSSM, supersymmetric Particles, B physics (CP violation, ...),… CMS ATLAS Strips: 61m2, 6.3 x 106 channels Pixels: ~2m2, 80 x 106 channels 210m2, 9.6 x 106 channels ~2m2, 33 x 106 channels P.Riedler - CERN

  8. Heavy ion physics CP violation and rare decays ALICE LHCb Strips: 4.9m2, 2.6 x 106 channels Drifts: 1.3m2, 1.33 x 105 channels Pixels: 0.2m2, 9.83 x 106 channels VELO: 0.32m2, 2 x 105 channels Tracker: 14m2, ~8 x 105 channels HPD: ~ 0.02m2,~1 x 106 channels P.Riedler - CERN

  9. Silicon Strip Detectors Silicon Pixel Detectors amplifier Detector Al strip p+ + + SiO2/Si3N4 - Chip - + n bulk + n+ - + Vbias • Each strip is connected to one readout channel • N-in-n detectors • Double sided detectors • Floating intermediate strips • … • 2-dim matrix of cells • Each cell is connected to its own processing electronics • high granularity P.Riedler - CERN

  10. Electronics Detectors Full bulk is sensitive to passing charged particles Sensitive components are located close to the surface Radiation Damage in Silicon Surface Damage Bulk Damage e.g. ATLAS Pixel Detector P.Riedler - CERN

  11. Electronics Single Event Effects (SEE) Cumulative Effects Permanent (e.g. single event gate rupture SEGR) Static (e.g. single event upset SEU) Transient SEEs Total Ionizing Dose (TID) Ionisation in the SiO2 and SiO2-Si interface creating fixed charges (all devices can be affected) Displacement Defects (bipolar devices, opto-components) In the following the effects of TID only will be discussed : P.Riedler - CERN

  12. Total Ionizing Dose • Ionization due to charged hadrons, g, electrons,… in the SiO2 layer and SiO2-Si interface • Fixed positive oxide charge • Accumulation of electrons at the interface • Additional interface states are created at the SiO2-Si border R. Wunstorf, PhD thesis 1992 P.Riedler - CERN

  13. Effects of TID in CMOS devices Threshold voltage shift, transconductance and noise degradation, source drain leakage, leakage between devices E.g.: transistor level leakage and threshold voltage shift F. Faccio, ELEC2002 Parasitic channel between source and drain P.Riedler - CERN

  14. Radiation Levels in some LHC experiments total dosefluence 1MeV n eq. [cm-2] after 10 years ATLAS Pixels 50 Mrad 1.5 x 1015 ATLAS Strips 7.9 Mrad ~2 x 1014 CMS Pixels ~24Mrad ~6 x 1014 * CMS Strips 7.5Mrad 1.6 x 1014 ALICE Pixel 500krad ~2 x 1013 LHCb VELO - 1.3 x 1014/year** *Set as limit, inner layer reaches this value after ~2 years **inner part of detector (inhomogeneous irradiation ) A radiation tolerant design is important to ensure the functionality of the read out over the full life-time! P.Riedler - CERN

  15. A B C D Solution -Technology Hardening Flatband-voltage shift as function of the oxide thickness • Tunneling of trapped charge in thin oxides • D VT~ 1/tox2 for tox > 10nm • D VT ~ 1/tox3 for tox < 10nm After N.S. Saks, M.G. Ancona, and J.A. Modolo, IEEE Trans.Nucl.Sci., Vol. NS-31 (1984) 1249 P.Riedler - CERN

  16. Using a 0.25µm CMOS process reduces th-shift significantly P.Riedler - CERN

  17. Enclosed Geometry Standard Geometry Leakage path Gate S D S D Gate Enclosed gate (S-D leakage) Guard ring (leakage between devices) Enclosed geometrie to avoid leakage P.Riedler - CERN

  18. F. Faccio, ELEC2002 P.Riedler - CERN

  19. Front end technology choices of the different experiments Technology Chip ALICE Pixel 0.25µm CMOS ALICE1 ALICE Strips 0.25µm CMOS HAL25 ALICE Drift 0.25µm CMOS PASCAL ATLAS Strips DMILL ABCD ATLAS Pixel DMILL->0.25µm CMOS FE-D25 CMS Pixel DMILL->0.25µm CMOS PSI CMS Strips 0.25µm CMOS APV25 LHCb VELO DMILL/0.25µm CMOS SCTA/Beetle LHCb Tracker 0.25µm CMOS Beetle Deep sub-µm means also: speed, low power, low yield, high cost P.Riedler - CERN

  20. Bulk Damage Displacement of an Si atom and creation of a vacancy and interstitial • Point like defects (g, electrons) • Cluster Defects (hadrons, ions) Radiation Damage in Detectors • Surface Damage • Creation of positive charges in the oxide and additional interface states. • Electron accumulation layer. P.Riedler - CERN

  21. Macroscopic Effects • Surface Damage • Increase of interstrip • capacitance (strips!) • Pin-holes (strips!) • Bulk Damage • Increase of leakage current • Increase of depletion voltage • Charge trapping Effects signal, noise, stability (thermal run-away!) • Annealing effects will not be discussed here. • But: Do not neglect these effects, esp. for long term running! • All experiments have set up annealing scenarios to simulate the damage after 10 years. P.Riedler - CERN

  22. But: I prop. Exp(-Eg/2kT) ATLAS Strip detector P. Riedler Phd-thesis M. Moll - Vertex 2002 Cooling will help! e.g: ATLAS Strips: -7°C CMS Pixel: -8°C Linear increase of leakage current with fluence: DIvol=a fne (a=4-6 x 10-17 A/cm) Leakage current P.Riedler - CERN

  23. Before Inversion p+ V depletion n+ After Inversion V depletion M. Moll - Vertex 2002 Depletion Voltage Type-Inversion: n-type bulk starts to behave like p-type bulk -> depletion from the backside of the diode! Vdep increases with fluence (after inversion) If depletion voltage has increased too so much that underdepleted operation is necessary-> charge loss and charge spread! P.Riedler - CERN

  24. p-in-n n-in-n Efficiency ATLAS ATLAS Vbias NIM A 450 (2000) 297 At LHC: ATLAS pixel CMS pixel LHCb VELO (special case) Fluences close to 1015 cm-2 Possible Solutions n-in-n detectors Underdepleted operation is possible! P.Riedler - CERN

  25. 2. Oxygenated Silicon Defect engineering (RD48) - to reduce reverse annealing => Lower depletion voltage can be expected after several years sunning (including warm-up times) But: improvement only for charged hadrons and g. No effect for neutrons observed. Also: spread of depletion voltage of detectors from different suppliers can reduce the beneficial effect ATLAS pixel uses oxygenated Si P.Riedler - CERN

  26. Further solutions to allow a reasonable operating voltages even after high fluences and annealing: • Low resistive silicon • Thin detectors (also intersting for material budget reasons) • CZ starting material (under investigation) • <100> to reduce interstrip capacitance Choice of LHC experiments: ALICE pixel p-in-n standard FZ ATLAS pixel n-in-n oxygenated ATLAS strips p-in-n standard FZ CMS pixel n-in-n standard FZ CMS strips p-in-n standard FZ <100> LHCb VELO n-in-n standard FZ P.Riedler - CERN

  27. A closer look at the ALICE Silicon Pixel Detector (SPD) 2 barrel layers Dz= 28.3 cm r= 3.9 cm & 7.6 cm INFN Padova P.Riedler - CERN

  28. Sector - Carbon Fibre Support The two barrels will be built of 10 sectors, each equipped with 6 staves: stave INFN Padova INFN Padova Material budget(each layer) ≈ 0.9% X0 (Si ≈ 0.37, cooling ≈ 0.3, bus 0.17, support ≈ 0.1) (lowest material budget of all pixel detectors!) P.Riedler - CERN

  29. Bus Ladder: 5 chips+1 sensor MCM ALICE1LHCb chip Silicon sensor Grounding foil Cooling tube Carbon-fibre sector Each Stave is built of two HALF-STAVES, read out on the two sides of the barrel, respectively. 193 mm long P.Riedler - CERN

  30. 2mm 11mm SMD component 7 7 7 7 6 6 5 5 4 3 2 2 1 1 PIXEL DETECTOR Aluminum Polyimide READOUT CHIP Glue COOLING TUBE • Bus: • 7 layer Al-Kapton flex • Wire bonds to the ALICE1LHCb chip 240µm 200µm goal:150µm M.Morel P.Riedler - CERN

  31. ALICE1LHCb chip Multi Chip Module (MCM) AP DP GOL Laser and pin diode • Analog Pilot: • Reference bias • ADC (T, V and I monitor) Data out JTAG Clock • Digital Pilot: • Timing, Control and Readout P.Riedler - CERN

  32. 13.5 mm 15.8 mm ALICE1LHCb chip • Mixed signal (analogue, digital) • Produced in a commercial • 0.25µm CMOS process • Radiation tolerant design • (enclosed gates, guard rings) • 8192 pixel cells • 50 µm x 425 µm pixel cell • ~100 µW/channel P.Riedler - CERN

  33. Low minimum threshold: ~1000 electrons Low individual pixel noise:~100 electrons P.Riedler - CERN

  34. Fully developed test system for wafers: Class I - Mean Threshold Class I: 42-75% Class II: 6-12% Class III: 17-42% (sample: 4 wafer, 750µm) Production testing will start this autumn P.Riedler - CERN

  35. Ladders and Assemblies Detector • Detectors: • single chip detectors • 5 chip detectors for ladders • p-in-n • 300 µm thick(tests) - • final thickness: 200µm • Chips: • single chips • 750 µm thick (tests) - 150µm final Chip • Bump-bonding: • VTT/Finland • Pb-Sn solder bumps • AMS/Italy • In bumps P.Riedler - CERN

  36. First testbeam with full size ladder - July 2002 chip0 chip1 chip2 chip3 chip4 P.Riedler - CERN

  37. Detector Chips P.Riedler - CERN

  38. P.Riedler - CERN

  39. Sr-source measurement of thin ladder (300µm chip, 200µm detector) Chip 63 Chip 53 Chip 50 Chip 43 Chip 33 matrices P.Riedler - CERN

  40. Summary • All LHC experiments use silicon detectors to improve their tracking capabilities (up to >200m2!). • Installation foreseen in 2006. • The high radiation environment demands radiation tolerant technologies for front end chips and detectors. • Almost all silicon detectors use 0.25µm CMOS chips (future?). • P-in-n and n-in-n detectors are used depending on the expected fluences and the annealing damage. • The current challenges are the actual construction and integration of the detectors. P.Riedler - CERN

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