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Effects of Radiation on Particle Detector Performance

First international Conference on Radiation and Dosimetry in Various Fields of Research, April 25-27, 2012 Niš , Serbia. Effects of Radiation on Particle Detector Performance. Michael Moll CERN, Geneva, Switzerland. OUTLINE:. Particle Detectors: LHC and LHC D etectors

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Effects of Radiation on Particle Detector Performance

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  1. First international Conference on Radiation and Dosimetry in Various Fields of Research, April 25-27, 2012 Niš, Serbia Effects of Radiation on Particle Detector Performance Michael MollCERN, Geneva, Switzerland OUTLINE: • Particle Detectors: LHC and LHC Detectors • Radiation Levels & Radiation Damage • Solid State Detector R&D for Particle Tracking Detectors • Radiation Tolerant Solid State Detectors • Conclusions and Outlook

  2. LHC - Large Hadron Collider 27 Km p p • Installation in existing LEP tunnel (27 Km) •  4000 MCHF(machine+experiments) • 1232 dipoles B=8.3T • pps = 14 TeVLdesign = 1034 cm-2 s-1 • Heavy ions (e.g. Pb-Pb at s ~ 1000 TeV) • First beam: Sept.2008 • 2012: 2 x 4 TeV • LHC experiments located at 4 interaction points M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  3. LHC Experiments ATLAS LHC-B + LHCf CMS ALICE + M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  4. LHC Experiments ATLAS LHC-B + LHCf CMS ALICE + M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  5. LHC example: CMS inner tracker • Inner Tracker Outer Barrel (TOB) Inner Barrel (TIB) End Cap (TEC) Inner Disks(TID) 2.4 m 5.4 m Pixel • Pixel Detector 30 cm 93 cm • CMS • CMS – “Currently the Most Silicon” • Micro Strip: • ~ 214 m2 of silicon strip sensors, 11.4 million strips • Pixel: • Inner 3 layers: silicon pixels (~ 1m2) • 66 million pixels (100x150mm) • Precision: σ(rφ) ~ σ(z) ~ 15mm • Most challenging operating environments (LHC) M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  6. Micro-strip Silicon Detectors Highly segmented silicon detectors have been used in Particle Physics experiments for nearly 30 years. They are favourite choice for Tracker and Vertex detectors (high resolution, speed, low mass, relatively low cost) Pitch ~ 50mm p+ in n- • Main application: detect the passage of ionizing radiation with high spatial resolution and good efficiency. • Segmentation → position Resolution ~ 5mm Reference: P.Allport, Sept.2010 M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  7. Signal degradation for LHC Silicon Sensors Note: Measured partly under different conditions! Lines to guide the eye (no modeling)! Pixel sensors: max. cumulated fluence for LHC Situation in 2005 Strip sensors: max. cumulated fluence for LHC M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  8. Signal degradation for LHC Silicon Sensors Note: Measured partly under different conditions! Lines to guide the eye (no modeling)! Pixel sensors: max. cumulated fluence for LHC andLHC upgrade LHC upgrade will need more radiation tolerant tracking detector concepts!Boundary conditions & other challenges:Granularity, Powering, Cooling, Connectivity,Triggering, Low mass, Low cost! Strip sensors: max. cumulated fluence for LHC andLHC upgrade M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  9. LHC - Upgrade Dominated by pion damage Dominated by neutron damage • LHC luminosity (Phase II) upgrade (L = 5x1034 cm-2s-1) • planned for 2022; aiming to cumulate 3000 fb-1 • Radiation hardness requirements (including safety factor of 2) • 2 × 1016neq/cm2 for the innermost pixel layers (Dose: 10 MGy) • 7× 1014neq/cm2 for the innermost strip layers (Dose: 300 KGy) M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  10. Detector = “reverse biased p-i-n diode” Positive space charge, Neff =[P](ionized Phosphorus atoms) • Full charge collection only for fully depleted detector (VB>Vdep) Poisson’s equation neutral bulk(no electric field) • Depleted zone growth withincreasing voltage ( ) Electrical charge density Electrical field strength Electron potential energy detector thickness d depletion voltage Vdep effective space charge density Neff M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  11. Macroscopic Effects – I. Depletion Voltage …. with time (annealing): • Short term: “Beneficial annealing”• Long term: “Reverse annealing” - time constant depends on temperature:~ 500 years (-10°C)~ 500 days ( 20°C)~ 21 hours ( 60°C) - Consequence: Detectors must be cooled even when the experiment is not running! before inversion p+ n+ n+ p+ after inversion • Change of Depletion Voltage Vdep (Neff) •“Type inversion”: Neff changes from positive to negative (Space Charge Sign Inversion) M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  12. Radiation Damage – II. Leakage Current • Strong temperature dependence Consequence:Cool detectors during operation! Example: I(-10°C) ~1/16 I(20°C) • Change of Leakage Current (after hadron irradiation) 80 min 60C • Damage parameter  (slope in figure)Leakage current per unit volume and particle fluence •  is constant over several orders of fluenceand independent of impurity concentration in Si can be used forfluence measurement M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  13. Radiation Damage – III. CCE (Trapping) • Deterioration of Charge Collection Efficiency (CCE) by trapping Trapping is characterized by an effective trapping time eff for electrons and holes: where M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  14. Radiation Damage in LHC detectors • After about 5 fb-1 integrated luminosity first radiation damage effects are observed • Remember: The aim is to build detectors resisting 3000 fb-1 • Examples (3/2012 - Preliminary Data!): Change of Depletion Voltage Increase of Leakage Current LHCbVelo (84 sensors, mainly n-in-n) ATLAS Pixel (Layer 0, 56 modules ) [Taka Kondo, KEK, 2nd Inter-Experiment Workshop on Radiation Damage in Silicon Detectors, CERN, 2.3.2012] [Adam Webber, Uni Manchester, 2nd Inter-Experiment Workshop on Radiation Damage in Silicon Detectors, CERN, 2.3.2012] M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  15. Approaches to develop radiation harder solid state tracking detectors • Defect Engineering of SiliconDeliberate incorporation of impurities or defects into the silicon bulk to improve radiation tolerance of detectors • Needs:Profound understanding of radiation damage • microscopic defects, macroscopic parameters • dependence on particle type and energy • defect formation kinetics and annealing • Examples: • Oxygen rich Silicon (DOFZ, Cz, MCZ, EPI) • Oxygen dimer & hydrogen enriched Si • Pre-irradiated Si • Influence of processing technology • New Materials • Silicon Carbide (SiC), Gallium Nitride (GaN) • Diamond (CERN RD42 Collaboration) • Amorphous silicon, Gallium Arsenide • Device Engineering (New Detector Designs) • p-type silicon detectors (n-in-p) • thin detectors, epitaxial detectors • 3D detectors and Semi 3D detectors, Stripixels • Cost effective detectors • Monolithic devices Scientific strategies: Material engineering Device engineering Change of detectoroperational conditions CERN-RD39“Cryogenic Tracking Detectors”operation at 100-200K to reduce charge loss M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  16. Silicon Growth Processes • Czochralski Silicon (CZ) • Floating Zone Silicon (FZ) • The growth method used by the IC industry. • Difficult to producevery high resistivity • [Oi] ~5 1017 cm-3 Poly silicon RF Heating coil Single crystal silicon Czochralski Growth Float Zone Growth • Epitaxial Silicon (EPI) • Basically all silicon tracking detectors made out of FZsilicon [Oi]< 5  1016 cm-3 • Some pixel sensors: Diffusion Oxygenated FZ (DOFZ)silicon [Oi]~1-2 1017cm-3 • Chemical-Vapor Deposition (CVD) of Si • up to 150 mm thick layers produced • growth rate about 1mm/min M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  17. Standard FZ, DOFZ, MCz and Cz Silicon 24 GeV/c proton irradiation • Standard FZ silicon • type inversion at ~ 21013 p/cm2 • strong Neffincreaseat high fluence M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  18. Standard FZ, DOFZ, MCz and Cz Silicon 24 GeV/c proton irradiation • Standard FZ silicon • type inversion at ~ 21013 p/cm2 • strong Neffincreaseat high fluence • Oxygenated FZ (DOFZ) • type inversion at ~ 21013 p/cm2 • reduced Neffincreaseat high fluence M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  19. Standard FZ, DOFZ, MCz and Cz Silicon 24 GeV/c protonirradiation • Standard FZ silicon • type inversion at ~ 21013 p/cm2 • strong Neffincreaseat high fluence • Oxygenated FZ (DOFZ) • type inversion at ~ 21013 p/cm2 • reduced Neffincreaseat high fluence • CZ siliconand MCZ silicon • “no type inversion“ in the overall fluence range (for experts: there is no “real” type inversion, a more clear understanding of the observed effects is obtained by investigating directly the internal electric field; look for: TCT, MCZ, double junction) • Common to all materials (after hadron irradiation, not after  irradiation): • reverse current increase • increase of trapping (electrons and holes) within ~ 20% M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  20. Proton vs. Neutron irradiation of oxygen rich silicon • Epitaxial silicon (EPI-DO, 72mm, 170Wcm, diodes)irradiated with 23 GeV protonsorreactor neutrons absolute effective space charge density depletion voltage M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  21. Device engineeringp-in-n versus n-in-p detectors p-type silicon after high fluences:(still p-type) n-type silicon after high fluences:(type inverted) n+on-p p+on-n • n-on-p silicon, under-depleted: • Limited loss in CCE • Less degradation with under-depletion • Collect electrons (3 x faster than holes) • p-on-n silicon, under-depleted: • Charge spread – degraded resolution • Charge loss – reduced CCE Comments:- Instead of n-on-p also n-on-n devices could be used- Reality is much more complex: Usually double junctions form leading to fields at front and back! M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  22. Electric Field in irradiated sensors • Edge – TCT (Transient Charge Technique) • Technique pioneered by GregorKramberger, Ljubljana [IEEE TNS, 57, AUGUST 2010,2294-2302] • Illumination of sensor from the side with pulsed IR laser • Scan across detector thickness and measure charge and induced current as function of depth • Reconstruct electric field Example: n-in-p sensor after 1016 p/cm2 [N.Pacifico, CERN, 2012] Collected Charge To analog, time resolved, readout Focusing optics Si Strip Detector • Heavily irradiated detectors • Even at low voltage, charge collected from all depth • High fields at front (strips) and also back side (Double junctions) • Large fields observed which lead to charge multiplication (avalanche) and thus increased signal (increased noise) Depth in sensor [mm] IR Laser Cooling plate Z positioning (detector) XY positioning (laser) M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  23. FZ n-in-p microstrip detectors (n, p, p - irrad) • n-in-p microstrip p-type FZ detectors(Micron, 280 or 300mm thick, 80mm pitch, 18mm implant ) • Detectors read-out with 40MHz(SCT 128A) [A.Affolder, Liverpool, NIMA 623, 2010, 177–179] Signal(103 electrons) 800V Fluence(1014 neq/cm2) 500V • CCE: ~7300e (~30%) after ~ 11016cm-2 800V • n-in-p sensors are strongly considered for ATLAS upgrade(previously p-in-n used) M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  24. FZ n-in-p microstrip detectors (n, p, p - irrad) • n-in-p microstrip p-type FZ detectors(Micron, 280 or 300mm thick, 80mm pitch, 18mm implant ) • Detectors read-out with 40MHz(SCT 128A) [A.Affolder, Liverpool, NIMA 623, 2010, 177–179] Signal(103 electrons) Fluence(1014 neq/cm2) • CCE: ~7300e (~30%) after ~ 11016cm-2 800V • n-in-p sensors are strongly considered for ATLAS upgrade(previously p-in-n used) • no reverse annealing in CCE measurementsfor neutron and proton irradiated detectors M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  25. Good performance of planar sensors at high fluence • Why do planar silicon sensors with n-strip readout give such high signals after high levels (>1015 cm-2 p/cm2) of irradiation? • Extrapolation of charge trapping parameters obtained at lower fluences would predict much lower signal! • Explanation: ‘Charge multiplication effects’ as even CCE > 1 was observed 1700V 800V 500V • Which voltage can be applied? M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  26. Silicon materials for Tracking Sensors Note: Measured partly under different conditions! Lines to guide the eye (no modeling)! • Signal comparison for p-type silicon sensors LHC SLHC n-in-p technology should be sufficient for Super-LHC at radii presently (LHC) occupied by strip sensors highest fluence for strip detectors in LHC: The used p-in-n technology is sufficient M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  27. 3D detector concept n-columns p-columns wafer surface PLANAR 3D p+ p+ p+ n+ 50 mm - 300 mm n-type substrate - - - - - - - - - + + + + + + + + + + • “3D” electrodes: - narrow columns along detector thickness, - diameter: 10mm, distance: 50 - 100mm • Lateral depletion: - lower depletion voltage needed - thicker detectors possible - fast signal - radiation hard M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  28. Example: Testbeam of 3D-DDTC • DDTC – Double sided double type column front column [G.Fleta, RD50 Workshop, June 2007] • Testbeam data – Example: efficiency map[M.Koehler, Freiburg University] • Processing of 3D sensors is challenging,but many good devices with reasonableproduction yield produced. • 3D sensors will be part of ATLAS IBL detector! back column 40V applied~98% efficiency M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  29. Use of other semiconductor materials? • Diamond: wider bandgap lower leakage current less cooling needed less noise • Signal produced by m.i.p: Diamond 36 e/mm Si 89 e/mm Si gives more charge than diamond • GaAs, SiC and GaN strong radiation damage observed no potential material for LHC upgrade detectors(judging on the investigated material) • Diamond (RD42)  good radiation tolerance (CCE degradation similar to silicon) already used in LHC beamcondition monitoring systemsconsidered as potential detector material for sLHC pixel sensors poly-CVD Diamond –16 chip ATLAS pixel module single crystal CVD Diamond of few cm2 Diamond sensors are heavily used in LHC Experiments for Beam Monitoring! M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  30. Summary – Radiation Damage • Radiation Damage in Silicon Detectors • Change ofDepletion Voltage(internal electric field modifications, “type inversion”, reverse annealing, loss of active volume, …) (can be influenced by defect engineering!) • Increase ofLeakage Current(same for all silicon materials) • Increase ofCharge Trapping(same for all silicon materials) Signal to Noise ratio is quantity to watch (material + geometry + electronics) • Microscopic defects & Damage scaling factors • Microscopic crystal defects are the origin to detector degradation. • NIEL – Hypothesis used to scale damage of different particles with different energy • Different particles produce different types of defects! (NIEL – violation!) • There has been an enormous progress in the last 5 years in understanding defects. • Approaches to obtain radiation tolerant devices: • Material Engineering: -explore and develop new silicon materials (oxygenated Si) - use of other semiconductors (Diamond) • Device Engineering: - look for other sensor geometries- 3D, thin sensors, n-in-p, n-in-n, … Details in talk by IoanaPintilieon defects. M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  31. Detectors for the LHC upgrade • At fluences up to 1015cm-2(outer layers – ministrip sensors) The change of the depletion voltage and the large area to be covered by detectors are major problems. • n-MCZ silicon detectors show good performance in mixed fields due to compensation of charged hadron damage and neutron damage (Neff compensation) (however, more work needed) • p-type siliconmicrostrip detectors show very encouraging results“base line option” for the ATLAS SCT upgrade • At fluences > 1015cm-2 (Innermost tracking layers – pixel sensors)The active thickness of any silicon material is significantly reduced due to trapping.Collection of electrons at electrodes essential: Use n-in-p or n-in-n detectors! • Recent results show that planar siliconsensors still give sufficient signal, • 3D detectors : very promising but difficult technology, will be installed in ATLAS IBL! • Diamond is still an interesting option (Higher damage due to low energy protons?) • Solutions for the upgrade available, but still some questions to be answered/explored: • Can we profit from avalanche effects and control them? • Can we profit from compensation effects in mixed fields (i.e. MCZ)? • Can we understand detector performance on the basis of simulations? ? ? ? M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  32. Acknowledgements & References • Most references to particular works given on the slides • Some additional material taken from the following presentations: • RD50 presentations: http://www.cern.ch/rd50/ • Anthony Affolder: Presentations on the RD50 Workshop in June 2009 (sATLASfluence levels) • Frank Hartmann: Presentation at the VCI conference in February 2010 (Diamond results) • Books containing chapters about radiation damage in silicon sensors • HelmuthSpieler, “Semiconductor Detector Systems”, Oxford University Press 2005 • Frank Hartmann, “Evolution of silicon sensor technology in particle physics”, Springer 2009 • L.Rossi, P.Fischer, T.Rohe, N.Wermes “Pixel Detectors”, Springer, 2006 • Gerhard Lutz, “Semiconductor radiation detectors”, Springer 1999 • Research collaborations and web sites • CERN RD50 collaboration (http://www.cern.ch/rd50 ) - Radiation Tolerant Silicon Sensors • CERN RD39 collaboration – Cryogenic operation of Silicon Sensors • CERN RD42 collaboration – Diamond detectors • Inter-Experiment Working Group on Radiation Damage in Silicon Detectors (CERN) • ATLAS IBL, ATLAS and CMS upgrade groups M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  33. The RD50 CollaborationDevelopment of Radiation Hard Semiconductor Devices for High Luminosity Colliders • RD50: 47 institutes and 261 members 38 European and Asian institutesBelarus (Minsk), Belgium (Louvain), Czech Republic (Prague (3x)), Finland (Helsinki, Lappeenranta ), Germany (Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe, Munich), India (Delhi), Italy(Bari, Florence, Padova, Perugia, Pisa, Trento), Lithuania (Vilnius), Netherlands (NIKHEF), Norway (Oslo)), Poland (Warsaw(2x)), Romania (Bucharest (2x)),Russia (Moscow, St.Petersburg), Slovenia (Ljubljana), Spain (Barcelona(2x), Santander, Valencia), Switzerland (CERN, PSI), Ukraine (Kiev), UnitedKingdom (Glasgow, Liverpool) 8 North-American institutesCanada (Montreal), USA (BNL, Fermilab, New Mexico, Purdue, Santa Cruz, Syracuse) 1 Middle East instituteIsrael (Tel Aviv) Detailed member list and further details: http://cern.ch/rd50 M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  34. Spares • Spare slides M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  35. Detector Module 128 mm • Detector Modules “Basic building block of silicon based tracking detectors” Silicon Sensors Mechanical support (cooling)Front end electronics and signal routing (connectivity) • Example: ATLAS SCT Barrel Module SCT = SemiConductor Tracker ASICS = Application Specific Integrated CircuitSTPG = Thermal Pyrolytic Graphite Silicon sensors (x4)- 64 x 64 mm2-p-in-n, single sided - AC-coupled - 768 strips - 80m pitch/12mm width ASICS (x12) -ABCD chip (binary readout) - DMILL technology - 128 channels Wire bonds (~3500)-25 mm Al wires Mechanical support- TPG baseboard - BeO facings • ATLAS – SCT - 15.552 microstrip sensors-2.112 barrel modules - 1.976 forward modules - 61 m2 silicon, 6.3.106strips Hybrid (x1)- flexible 4 layer copper/kapton hybrid-mounted directly over two of the four silicon sensors - carrying front end electronics, pitch adapter, signal routing, connector s(rf) ~ 16 mm, s(z) ~ 850mm [NIMA538 (2005) 384]

  36. Hybrid Pixel Detectors Solder Bump: Pb-Sn • HAPS – Hybrid Active Pixel Sensors • segment silicon to diode matrix with high granularity( true 2D, no reconstruction ambiguity) • readout electronic with same geometry(every cell connected to its own processing electronics) • connection by “bump bonding” • requires sophisticated readout architecture • Hybrid pixel detectors will be used in LHC experiments: ATLAS, ALICE, CMS and LHCb ~ 15mm (VTT/Finland) Flip-chip technique M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  37. The LHC Upgrade Program • LHC luminosity upgrade (Phase II) (L=5x1034 cm-2s-1) in 2022 Challenge: Build detectors that operate after 3000 fb-1 M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  38. Radiation Damage – II. Leakage Current …. with time (annealing): 80 min 60C • Leakage current decreasing in time (depending on temperature) • Strong temperature dependence Consequence:Cool detectors during operation! Example: I(-10°C) ~1/16 I(20°C) • Change of Leakage Current (after hadron irradiation) …. with particle fluence: 80 min 60C • Damage parameter  (slope in figure)Leakage current per unit volume and particle fluence •  is constant over several orders of fluenceand independent of impurity concentration in Si can be used forfluence measurement M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  39. Radiation Damage – III. CCE (Trapping) ….. and change with time (annealing): • Deterioration of Charge Collection Efficiency (CCE) by trapping Trapping is characterized by an effective trapping time eff for electrons and holes: where Increase of inverse trapping time (1/) with fluence M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  40. Impact of Defects on Detector Properties • Microscopic defects are the reason for the degradation of the sensor performance Shockley-Read-Hall statistics Details in previous talk by IoanaPintilieon defects. charged defects Neff , Vdepe.g. donors in upper and acceptors in lower half of band gap Trapping (e and h) CCEshallow defects do not contribute at room temperature due to fast detrapping generation leakage currentLevels close to midgap most effective Impact on detector properties can be calculated if all defect parameters are known:n,p : cross sections E : ionization energy Nt : concentration M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  41. How to normalize radiation damage from different particles? • NIEL - Non Ionizing Energy Loss scaling using hardness factors Hardness factor kof a radiation field (or monoenergetic particle) with respect to 1 MeV neutrons • Eenergy of particle • D(E) displacement damage cross section for a certain particle at energy E D(1MeV neutrons)=95 MeV·mb • f(E)energy spectrum of radiation field • The integrals are evaluated for the interval [EMIN,EMAX], being EMIN and EMAX the minimum and maximum cut-off energy values, respectively, and covering all particle types present in the radiation field M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  42. NIEL - Displacement damage functions 1 MeV neutron equivalent damage 1 • NIEL - Non Ionizing Energy Loss • NIEL - Hypothesis: Damage parameters scale with the NIEL • Be careful, does not hold for all particles & damage parameters (see later) 1MeV M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  43. Summary: Radiation Damage in Silicon Sensors • Two general types of radiation damage to the detector materials: • Bulk (crystal) damage due to Non Ionizing Energy Loss (NIEL)- displacement damage, built up of crystal defects – • Change of effective doping concentration (higher depletion voltage, under- depletion) • Increase of leakage current (increase of shot noise, thermal runaway) • Increase of charge carrier trapping (loss of charge) • Surface damagedue to Ionizing Energy Loss (IEL) - accumulation of positive in the oxide (SiO2) and the Si/SiO2 interface –affects: interstrip capacitance (noise factor), breakdown behavior, … • Impact on detector performance and Charge Collection Efficiency(depending on detector type and geometry and readout electronics!) Signal/noise ratio is the quantity to watch Sensors can fail from radiation damage ! Influenced by impuritiesin Si – Defect Engineeringis possible! Same for all tested Silicon materials! Can be optimized! M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  44. Are diamond sensors radiation hard? 23 GeV p 70 MeV p [RD42, LHCC Status Report, Feb. 2010] [RD42, LHCC Status Report, Feb. 2010] • Most published results on 23 GeV protons • 70 MeV protons 3 times more damaging than 23 GeV protons • 25 MeV protons seem to be even more damaging (Preliminary: RD42 about to cross check the data shown to the left) • In line with NIEL calc. for Diamond [W. de Boer et al. Phys.Status Solidi 204:3009,2007] 23 GeV p 70 MeV p 26 MeV p [V.Ryjov, CERN ESE Seminar 9.11.2009] M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  45. Advantage of non-inverting materialp-in-n detectors (schematic figures!) Fully depleted detector(non – irradiated): M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  46. Advantage of non-inverting materialp-in-n detectors (schematic figures!) non inverted • non-inverted, under-depleted: • Limited loss in CCE • Less degradation with under-depletion Fully depleted detector(non – irradiated): Be careful, this is a very schematic explanation, reality is more complex ! heavy irradiation inverted • inverted to “p-type”, under-depleted: • Charge spread – degraded resolution • Charge loss – reduced CCE M.Moll, RAD2012, 25.4.2012, Niš, Serbia

  47. Silicon materials for Tracking Sensors Higher Voltageleads to charge multiplication Beware:Signal shown and not S/N ! Note: Measured partly under different conditions! Lines to guide the eye (no modeling)! • Signal comparison for various Silicon sensors • All sensors suffer from radiation damage • Presently three options for innermost pixel layers under investigation: • Silicon planar sensors, 3-D silicon sensors, Diamond sensors M.Moll, RAD2012, 25.4.2012, Niš, Serbia

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