1 / 32

Charge collection in irradiated pixel sensors

Charge collection in irradiated pixel sensors. Beam test measurements and simulation.

elmerlwilliams
Download Presentation

Charge collection in irradiated pixel sensors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Charge collection in irradiated pixel sensors Beam test measurements and simulation V. Chiochiaa, C.Amslera, D.Bortolettoc, L.Cremaldid, S.Cucciarellie, A.Dorokhova,b*, C.Hörmanna,b, M.Koneckie, D.Kotlinskib, K.Prokofieva,b, C.Regenfusa, T.Roheb, D.Sandersd, S.Sonc, T.Speera, D.Kimf, M.Swartzf a Physik Institut der Universität Zürich-Irchel, 8057, Zürich, Switzerlandb Paul Scherrer Institut, 5232, Villingen PSI, Switzerlandc Purdue University, Task G, West Lafayette, IN 47907, USA d Department of Physics and Astronomy, Mississippi State University, MS 39762, USAe Institut für Physik der Universität Basel, Basel, Switzerlandf Johns Hopkins University, Baltimore, MD, USA * Now at: Institut de Recherches Subatomiques, F67037 Strasbourg, France

  2. Outline • The CMS pixel detector and data reconstruction • Analysis ingredients: beam test data and detector simulation • Physical modelling of radiation damage: • Models with a constant effective doping concentration • EVL models (V.Eremin, E.Verbitskaya, Z.Li) • Advanced double junction models (V.C., M.Swartz) • Conclusions V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  3. The CMS pixel detector • 3-d tracking with 66 million channels • Barrel layers at radii = 4.3cm, 7.2cm and 11.0cm • Pixel cell size: 100x150 µm2 • Fluence 3(1)x1014 neq/cm2 year, inner layer for high(low) luminosity • Modules are unit cells of the system (1% of X0) • 704 barrel modules / 96 barrel half modules / 672 endcap modules • ~15k front end chips and ~1m2 of silicon V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  4. The LHC radiation environment • 4 cm layer F=3x1014 n/cm2/yr • Fluence decreases quadratically with the radius • Pixel detectors = 4-15 cm mostly pion irradiation • Strip detectors = 20-110 cm mostly neutron irradiation sppinelastic = 80 mb L = 1034 cm-2s-1 What is the sensors response after few years of operation? Fluence per year at full luminosity V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  5. Impact on reconstruction Charge Carriers Trapping Variation of the electric field profile Asymmetric pixel clusters Lorentz deflection Example: Long clusters along the z-coordinate at high h Example: Non-linear charge sharing in the r-f plane Sensor irradiation V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  6. Prototype sensors for beam tests 125 mm2 • p-spray design with biasing grid and punch through structures (CiS, Germany) • 125x125 mm2 cell size • 22x32 pixel matrix, 285 μm thick <111> DOFZ wafer, n-in-n type • Samples irradiated with 21 GeV protons at the CERN PS facility • Fluences: Feq=(0.47,2.0,5.9)x1014 neq/cm2 • Annealed for three days at 30º C • Bump bonded at room temperature to non irradiated front-end chips with non zero-suppressed readout, stored at -20ºC V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  7. 2004 Beam test setup Silicon strip beam telescope: 50 μm readout pitch,~1 μm resolution CERN Prevessin site H2 area beam: 150 GeV p B field pixel sensor support Cooling circuit T =-30 ºC or -10ºC 3T Helmoltz magnet V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  8. Charge collection measurement charge trapping n+side p-side ½ year LHC low luminosity 2 years LHC low luminosity 2 years LHC high luminosity Charge collection was studied with the cluster profiles in a row of pixels illuminated by a 15º beam and no magnetic field Temperature = -25 ºC and -10ºC Feq = (0, 0.5, 2, 6)x1014 n/cm2 V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  9. Detector simulation Charge transport ROOT Analysis Trapping ISE TCAD 9.0 Double traps models (DESSIS) 3-D Electric field mesh Trapping times from literature ROC+FED response Electronic response + data formatting Charge deposit PIXELAV V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  10. The classic picture after type inversion Neff<0 - • After irradiation the sensor bulk becomes more acceptor-like • The effective doping concentration is constant (and negative) across the sensor thickness • The p-n junction moves to the pixel implants side • Based on C-V measurements! V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  11. Models with constant Neff F = 6x1014 n/cm2 Amodel based on a type-inverted device with constant Neff across the bulk does not describe the measured charge collection profiles V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  12. Two traps models acceptor EC-0.525 eV donor EV+0.48 eV EConduction Electron traps 1.12 eV Hole traps EValence Given these parameters the charge carriers dynamics is governed by the Shockley-Read-Hall statistics Eremin-Verbitskaya-Li Model (EVL) NA and ND are fixed to TCT measurements V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  13. The double peak electric field c) Effective doping concentration a) Current density n+p junction np+ junction -HV b) Carrier concentration d) Electric field p-like n-like V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  14. EVL models F1=6x1014 n/cm2 100% observed leakage current s=1.5x10-15 cm2 30% observed leakage current s=0.5x10-15 cm2 The EVLmodel based on double traps can produce large tails but description of the data is still unsatisfactory V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  15. Advanced EVL models • The recipe: • Relax the assumption on the cross sections • Let the parameters (NA, ND, sA/De, sA/Dh) vary • Keep the traps energy levels (EA, ED) to the EVL values • Constraints to the model: • Charge collection profiles (at different Vbias and Feq) • Trapping rates • Generated leakage current be/h from literature Feq known within 10% V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  16. Best fit: F1=6x1014 n/cm2 • Data --- Simulation F1=6x1014 n/cm2 NA/ND=0.40 sh/se=0.25 V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  17. Temperature dependence F1=6x1014 n/cm2 • Charge collection profiles depend on temperature • T-dependent recombination in TCAD and T-dependent variables in PIXELAV (me/h, Ge/h, ve/h) • The model can predict the variation of charge collection due to the temperature change T=-25ºC T=-10ºC V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  18. Scaling to lower fluences (1) Preserve linear scaling of Ge/h and of the current with Feq F2=2x1014 n/cm2 NA/ND=0.68 sAh/sAe=0.25 sDh/sDe=1.00 ! Not shown: Linear scaling of trap densities does not describe the data! V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  19. Scaling to lower fluences (2) • Near the ‘type-invesion’ point: the double peak structure is still visible in the data! • Profiles are not described by thermodynamically ionized acceptors alone • At these low bias voltages the drift times are comparable to the preamp shaping time (simulation may be not reliable) F3=0.5x1014 n/cm2 NA/ND=0.75 sAh/sAe=0.25 sDh/sDe=1.00 V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  20. Scaling summary • Donors concentration increases faster than acceptors • NA/ND increases for decreasing fluences • Electric field peak at the p+ backplane increases with irradiation V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  21. Lorentz angle vs depth Lorentz angle Electric field • Lorentz angle and electric field extracted from the test beam measurements • The Lorentz angle is not constant across the sensor thickness V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  22. Conclusions (1) • A simulation based on a constant effective doping (or “type inverted”) across the sensor bulk does not describe the measured charge collection profiles • A effective model based on two defect levels can be tuned to describe the observed charge collection profiles • Trapping of the leakage current produces an electric field profile with two maximaat the detector implants. Is it time to leave the classical notion of ‘partial depletion’? • The model can: • account for the expected leakage current and, within the uncertainties, for free carriers trapping • predict the temperature dependence of charge collection V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  23. Conclusions (2) • In reality the chemistry of Si defects is more complicated and there are several trap states • The levels in this model have no physical reality and have to be considered as an ‘effective sum’ of multiple charged states • The simulation is a very nice tool for predicting the behavior of our pixel sensors during the operation in CMS. The hit reconstruction algorithms need to be fine tuned to cope with radiation effects V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  24. References • V. Eremin, E. Verbitskaya, and Z. Li, “The origin of double peak electric field distribution in heavily irradiated silicon detectors”, Nucl. Instr. Meth.A476, pp. 556-564 (2002) • M.Swartz, “CMS Pixel simulations”, Nucl.Instr.Meth. A511, 88 (2003) • V.Chiochia, M.Swartz et al., “Simulation of Heavily Irradiated Silicon Pixel Sensors and Comparison with Test Beam Measurements”, accepted for publication on IEEE Trans.Nucl.Sci., eprint:physics/0411143 • A.Dorokhov et al., • ISE TCAD 9.0: http://www.synopsys.com/products/acmgr/ise/dessis_ds.html V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  25. Backup slides V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  26. CMS pixel sensor design Gold Nickel Titanium Indium-Bump Si3N4 cross section nitride Al punch-through biasing p+ pspray n+ metal line n- bulk n+/Al opening p+ nitride + LTO Bump-bond contact Al Si3N4 passivation Vendor: CiS, Erfurt - www.cismst.de V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  27. Test beam setup pixel sensor Magnetic field = 3 T • Four modules of silicon strip detectors • Beam telescope resolution ~ 1 m • Sensors enclosed in a water cooled box (down to -30ºC) • No zero suppression, unirradiated readout chip • Setup placed in a 3T Helmoltz magnet  or  PIN diode trigger V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  28. ISE TCAD simulation V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  29. PIXELAV simulation V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  30. SRH statistics V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  31. SRH generation current V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

  32. Lorentz angle vs bias • ‘Effective’ Lorentz angle as function of the bias voltage • Strong dependence with the bias voltage (electric field) • Weak dependence on irradiation • This is a simplified picture!! Magnetic field = 4 T V. Chiochia – Charge collection in irradiated pixel sensors 10th European Symposium on Semiconductor Detectors - Wildbad Kreuth, June 12 -16, 2005

More Related