Michael Moll ( CERN – PH-DT2-SD) CERN – PH-DT2 – Scientific Tea meeting 13.10.2006 Radiation Tolerant Silicon Detectors Michael Moll ( CERN – PH-DT2-SD) Outline What is a silicon detector? – How does it work? What is radiation damage? – What are the problems? Radiation damage in future experiments: Super-LHC + (LHCb Upgrade) The CERN RD50 collaboration Strategies to obtain more radiation tolerant detectors Some examples how to obtain radiation tolerant detectors Material Engineering Device Engineering Summary Bonjour tout le monde. Premièrement j'aime vous remercier de l'invitation. Deuxièmement j'aime dire que je suis désolé pour mon Français Si vous pensez à un moment qui mon Français est trop mauvais, je m'arrêterai et continuerai en anglais. Cependant, je voudrais vraiment essayer de donner cette présentation en français Alors je commence: Aujourd'hui je voudrais parler au sujet du développement des détecteurs de semi-conducteur pour le futurs générations de collisionneurs avec de très haute luminosité ….et en particulier au sujet des développements pour le remise a niveau (upgrade) du LHC (le Grand Collisionneur Hadronique), le Super LHC. ..la plus grande partie des développements que je vais présenter .. ont été effectuées par la collaboration CERN-RD50

Silicon Detector – Working principle Take a piece of high resistivity silicon and produce two electrodes (not so easy !) Apply a voltage in order to create an internal electric field (some hundred volts over the 0.3mm thick device) Traversing charged particles will produce electron-hole pairs The moving electrons and holes will create a signal in the electric cicuit Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -2 / 20-

Silicon Strip Detector Segmentation of the p+ layer into strips (Diode Strip Detector) and connection of strips to individual read-out channels gives spatial information pitch typical thickness: 300mm (150m - 500m used) using n-type silicon with a resistivity of  = 2 KWcm (ND ~2.2.1012cm-3) results in a depletion voltage ~ 150 V Resolution  depends on the pitch p (distance from strip to strip) - e.g. detection of charge in binary way (threshold discrimination) and using center of strip as measured coordinate results in: typical pitch values are 20 mm– 150 mm  50 mm pitch results in 14.4 mm resolution Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -3 / 20-

Example – The ATLAS module Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -4 / 20-

LHCb – VELO: Silicon sensor details R-measuring sensor (45 degree circular segments) 300 mm thick sensors n-on-n, DOFZ wafers 42 mm radius AC coupled, double metal 2048 strips / sensor Pitch from 40 to 100 mm Produced by Micron Semiconductor 42 mm 8 mm F-measuring sensor (radial strips with a stereo angle) [Martin van Beuzekom, STD6, September 2006] Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -5 / 20-

LHCb-VELO - Module construction Beetle 4 layer kapton circuit Heat transport with TPG Readout with 16 Beetle chips 128 channels, 25 ns shaping time, analog pipeline 0.25 mm CMOS no performance loss up to 40 Mrad Yield > 80 % Kapton hybrid Carbon fibre Thermal Pyrolytic Graphite (TPG) [Martin van Beuzekom, STD6, September 2006] Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -6 / 20-

Motivation for R&D on Radiation Tolerant Detectors: Super - LHC LHC upgrade LHC (2007), L = 1034cm-2s-1 f(r=4cm) ~ 3·1015cm-2 Super-LHC (2015 ?), L = 1035cm-2s-1 f(r=4cm) ~ 1.6·1016cm-2 LHC (Replacement of components) e.g. - LHCb Velo detectors (~2010) - ATLAS Pixel B-layer (~2012) Linear collider experiments (generic R&D) Deep understanding of radiation damage will be fruitful for linear collider experiments where high doses of e, g will play a significant role. 10 years 500 fb-1  5 5 years 2500 fb-1 Quelle est notre motivation? Nous avons trois raisons principales d'étudier les dommages du rayonnement et des détecteurs résistant au rayonnement 1. La première raison et le Super-LHC Si vous regardez les champs de rayonnement dans les expériences ATLAS et CMS du Grand Collisionneur Hadronique (LHC) vous trouvez déjà des niveaux de rayonnement très élevés. Par exemple, après 10 ans d'opération ils auront intégrés environ : 3 dix à la 15 (3 dix a la puissance 15 – 3 a la 15) particules par centimètres carrés à une distance de 4 centimètres du point d'interaction. Ceci correspond à la position de la couche intérieure des détecteurs a Pixel. Même si on regarde le niveau du rayonnement a un point plus extérieur, par exemple à 75 cm de distance du point d’interaction on trouve un très grand nombre du particules rapides après 10 ans d’opération. Aujourd'hui, nous sommes heureux que la technologie pour utiliser des détecteurs dans un tel environnement existe - les détecteurs survivront - mais ils souffriront fortement des dommages du rayonnement….. Pour le Super-LHC il est prévu d’augmenter la luminosité par un facteur dix; Après cinq ans d'opération du Super LHC, on aura un facteur cinq fois plus élevés de rayonnement comparés au LHC -- c'est un niveau de rayonnement pour lequel aucune technologie n'existe a ce jour -- pour les composants plus éloigné du point d'interaction on aura un problème - la technologie existe ; on pourrait employer par exemple des détecteurs Pixel a la place des détecteurs a micro piste. Cependant, ça serait beaucoup trop cher. donc nous avons besoin de détecteurs a bas prix qui sont résistant aux rayonnements 2. la deuxième raison est le LHC dans les expériences du LHC sont déjà employés, des détecteurs contenant des niveaux élevés d’oxygène. Ils sont plus résistant contre le rayonnement, leurs résistances ont déjà été démontré; mais ils ont besoin d'une caractérisation plus approfondie; on a prévu de changer une partie des détecteur après quelques années .(par exemple: le LHC-b Velo détecteur) 3. La troisième raison est la recherche pour les expériences de futurs collisionneurs linéaires où les détecteurs vont souffrir du rayonnement électromagnétique; Si on comprend les mécanismes du dommage du rayonnement électromagnétique, c’est déjà une première étape dans la compréhension des dommages du rayonnement hadronique qui sont beaucoup plus complexe. Plus tard je vais vous prouver que le silicium avec un concentration en oxygène très élevée est un très bon matériel pour ce type d’environnement Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -7 / 20-

Overview: 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 damage due 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 ! efficacité de collection de charge influencé par deux mécanisme piégeage – porteurs de charge sont pièges par les défaut profond déficit de collection de charge augmente en fonction de la fluence Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -8 / 20-

noise The charge signal Most probable charge ≈ 0.7 mean Mean charge Collected Charge for a Minimum Ionizing Particle (MIP) Mean energy loss dE/dx (Si) = 3.88 MeV/cm  116 keV for 300m thickness Most probable energy loss ≈ 0.7 mean  81 keV 3.6 eV to create an e-h pair  72 e-h / m (mean)  108 e-h / m (most probable) Most probable charge (300 m) ≈ 22500 e ≈ 3.6 fC Mean charge Most probable charge ≈ 0.7 mean Cut (threshold) efficacité de collection de charge influencé par deux mécanisme piégeage – porteurs de charge sont pièges par les défaut profond déficit de collection de charge augmente en fonction de la fluence noise Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -9 / 20-

What is signal and what is noise? Signal to Noise ratio Landau distribution has a low energy tail - becomes even lower by noise broadening Noise sources: (ENC = Equivalent Noise Charge) - Capacitance - Leakage Current - Thermal Noise (bias resistor) What is signal and what is noise? less signal more noise efficacité de collection de charge influencé par deux mécanisme piégeage – porteurs de charge sont pièges par les défaut profond déficit de collection de charge augmente en fonction de la fluence Good hits selected by requiring NADC > noise tail If cut too high  efficiency loss If cut too low  noise occupancy Figure of Merit: Signal-to-Noise Ratio S/N Typical values >10-15, people get nervous below 10. Radiation damage severely degrades the S/N. Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -10 / 20-

The CERN RD50 Collaboration http://www.cern.ch/rd50 RD50: Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders Collaboration formed in November 2001 Experiment approved as RD50 by CERN in June 2002 Main objective: Development of ultra-radiation hard semiconductor detectors for the luminosity upgrade of the LHC to 1035 cm-2s-1 (“Super-LHC”). Challenges: - Radiation hardness up to 1016 cm-2 required - Fast signal collection (Going from 25ns to 10 ns bunch crossing ?) - Low mass (reducing multiple scattering close to interaction point) - Cost effectiveness (big surfaces have to be covered with detectors!) Presently 261 members from 52 institutes Belarus (Minsk), Belgium (Louvain), Canada (Montreal), Czech Republic (Prague (3x)), Finland (Helsinki, Lappeenranta), Germany (Berlin, Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe), Israel (Tel Aviv), Italy (Bari, Bologna, Florence, Padova, Perugia, Pisa, Trento, Turin), Lithuania (Vilnius), The Netherlands (Amsterdam), Norway (Oslo (2x)), Poland (Warsaw (2x)), Romania (Bucharest (2x)), Russia (Moscow), St.Petersburg), Slovenia (Ljubljana), Spain (Barcelona, Valencia), Switzerland (CERN, PSI), Ukraine (Kiev), United Kingdom (Exeter, Glasgow, Lancaster, Liverpool, Sheffield, University of Surrey), USA (Fermilab, Purdue University, Rochester University, SCIPP Santa Cruz, Syracuse University, BNL, University of New Mexico) Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -11 / 20-

Approaches to develop radiation harder solid state tracking detectors Defect Engineering of Silicon Deliberate 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 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 detector operational conditions CERN-RD39 “Cryogenic Tracking Detectors” operation at 100-200K to reduce charge loss Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -12 / 20-

Silicon Materials under Investigation by RD50 Symbol  (cm) [Oi] (cm-3) Standard FZ (n- and p-type) FZ 1–710 3 < 51016 Diffusion oxygenated FZ (n- and p-type) DOFZ ~ 1–21017 Magnetic Czochralski Si, Okmetic, Finland (n- and p-type) MCz ~ 110 3 ~ 51017 Czochralski Si, Sumitomo, Japan (n-type) Cz ~ 8-91017 Epitaxial layers on Cz-substrates, ITME, Poland (n- and p-type) EPI 50 - 100 < 11017 DOFZ silicon Enriched with oxygen on wafer level, inhomogeneous distribution of oxygen CZ silicon high Oi (oxygen) and O2i (oxygen dimer) concentration (homogeneous) formation of shallow Thermal Donors possible Epi silicon high Oi , O2i content due to out-diffusion from the CZ substrate (inhomogeneous) thin layers: high doping possible (low starting resistivity) Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -13 / 20-

Standard FZ, DOFZ, Cz and MCz Silicon 24 GeV/c proton irradiation Standard FZ silicon type inversion at ~ 21013 p/cm2 strong Neff increase at high fluence Oxygenated FZ (DOFZ) reduced Neff increase at high fluence CZ silicon and MCZ silicon no type inversion in the overall fluence range (verified by TCT measurements) (verified for CZ silicon by TCT measurements, preliminary result for MCZ silicon)  donor generation overcompensates acceptor generation in high fluence range Common to all materials (after hadron irradiation): reverse current increase increase of trapping (electrons and holes) within ~ 20% Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -14 / 20-

EPI Devices – Irradiation experiments Epitaxial silicon Layer thickness: 25, 50, 75 m (resistivity: ~ 50 cm); 150 m (resistivity: ~ 400 cm) Oxygen: [O]  91016cm-3; Oxygen dimers (detected via IO2-defect formation) G.Lindström et al.,10th European Symposium on Semiconductor Detectors, 12-16 June 2005 G.Kramberger et al., Hamburg RD50 Workshop, August 2006 105V (25mm) 230V (50mm) 320V (75mm) Only little change in depletion voltage No type inversion up to ~ 1016 p/cm2 and ~ 1016 n/cm2 high electric field will stay at front electrode! reverse annealing will decreases depletion voltage! Explanation: introduction of shallow donors is bigger than generation of deep acceptors CCE (Sr90 source, 25ns shaping):  6400 e (150 mm; 2x1015 n/cm-2)  3300 e (75mm; 8x1015 n/cm-2)  2300 e (50mm; 8x1015 n/cm-2) Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -15 / 20-

Device engineering p-in-n versus n-in-p detectors n-type silicon after high fluences: p-type silicon after high fluences: p+on-n n+on-p p-on-n silicon, under-depleted: Charge spread – degraded resolution Charge loss – reduced CCE n-on-p silicon, under-depleted: Limited loss in CCE Less degradation with under-depletion Collect electrons (fast) Be careful, this is a very schematic explanation, reality is more complex ! Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -16 / 20-

n-in-p microstrip detectors n-in-p: - no type inversion, high electric field stays on structured side - collection of electrons n-in-p microstrip detectors (280mm) on p-type FZ silicon Detectors read-out with 40MHz no reverse annealing visible in the CCE measurement ! e.g. for 7.5  1015 p/cm2 increase of Vdep from Vdep~ 2800V to Vdep > 12000V is expected ! CCE ~ 6500 e (30%) after 7.5 1015 p cm-2 at 900V Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -17 / 20-

Introduced by: S.I. Parker et al., NIMA 395 (1997) 328 3D detector - concepts Introduced by: S.I. Parker et al., NIMA 395 (1997) 328 “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 ionizing particle carriers collected at the same time n-columns p-columns wafer surface n-type substrate Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -18 / 20-

3D detector - concepts Simplified 3D architecture Introduced by: S.I. Parker et al., NIMA 395 (1997) 328 “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 n-columns p-columns wafer surface n-type substrate Simplified 3D architecture n+ columns in p-type substrate, p+ backplane operation similar to standard 3D detector Simplified process hole etching and doping only done once no wafer bonding technology needed Simulations performed Fabrication: IRST(Italy), CNM Barcelona metal strip hole [C. Piemonte et al., NIM A541 (2005) 441] hole Hole depth 120-150mm Hole diameter ~10mm C.Piemonte et al., STD06, September 2006 First CCE tests under way Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -19 / 20-

Further information: http://cern.ch/rd50/ Conclusion New Materials like SiC and GaN have been characterized (not shown in this talk) .   CCE tests show that these materials are not radiation harder than silicon  Silicon (operated at e.g. -30°C) seems presently to be the best choice At fluences up to 1015cm-2 (Outer layers of SLHC detector) the depletion voltage change and the large area to be covered is major problem: MCZ silicon detectors could be a cost-effective radiation hard solution p-type (FZ and MCZ) silicon microstrip detectors show good results: CCE  6500 e; Feq= 41015 cm-2, 300mm, collection of electrons, no reverse annealing observed in CCE measurement! At the fluence of 1016cm-2 (Innermost layer of a SLHC detector) the active thickness of any silicon material is significantly reduced due to trapping. New options: Thin/EPI detectors : drawback: radiation hard electronics for low signals needed e.g. 3300e at Feq 8x1015cm-2, 75mm EPI, …. thicker layers (150 mm presently under test) 3D detectors : drawback: very difficult technology ….. steady progress within RD50 Further information: http://cern.ch/rd50/ Michael Moll – PH-DT2 – Scientific Tea, 11 October 2006 -20 / 20-