CMS Pixel Radiation Damage Measurements F.Feindt and T. Prousalidi* on behalf of CMS Collaboration University of Hamburg, *NTUA February 14, 2019 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 1 / 20
Table Of Contents Simulation vs. Measurements 1 Z-Dependence of Leakage Current 2 Summary and Conclusion 3 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 2 / 20
Introduction – Continuous Radiation Damage in CMS CMS Pixel Barrel Radiation damage during CMS operation Continuous degradation of detector properties 1 MeV n-equivalent in silicon, 3000 fb − 1 Focus on Leakage current I leak p s = 13 TeV CMS Integrated Luminosity, pp, 2018, Full depletion voltage V depl Data included from 2018-04-17 10:54 to 2018-08-20 14:44 UTC 45 45 Total Integrated Luminosity ( fb ¡ 1 ) LHC Delivered: 42.20 fb ¡ 1 These properties need to be 40 40 CMS Recorded: 39.75 fb ¡ 1 35 35 Measured CMS Preliminary Offline Luminosity 30 30 Compared to models 25 25 Predicted 20 20 15 15 Taking into account operation conditions 10 10 (temperature) 5 5 0 0 17 Apr 1 May 8 May 15 May 22 May 29 May 5 Jun 12 Jun 19 Jun 26 Jun 3 Jul 10 Jul 17 Jul 24 Jul 31 Jul 7 Aug 14 Aug 24 Apr Date (UTC) F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 3 / 20
Introduction – NIEL Two Types of Radiation-Induced Damage Ionizing energy loss - reversible, but not in SiO 2 ⇒ surface damage N on- I onizing E nergy L oss (NIEL) - displacing atoms ⇒ various types of bulk defects Bulk Defects Introduce new states in the band gap Close to the conduction or valence band – donor or acceptor like defects ⇒ change the effective doping concentration Shallow levels – trapping of electrons and holes Close to the midgap ⇒ generation of leakage current May interact (annealing) so the concentrations of these defects may change in time F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 4 / 20
Introduction – Leakage Current Modeling Leakage Current Model from M. Moll Change in leakage current due to irradiation ∆ I leak = α Φ eq V Φ eq is the neutron equivalent fluence V is the volume α is the current related damage rate t τ I ( T ) − β ln ( t − α ( t , T ) = α 0 ( T ) + α I e t 0 ) subject to annealing All relevant parameters given in M. Molls thesis (for annealing 80 min at 60 ◦ C) F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 5 / 20
Introduction – Full Depletion Voltage Modeling Hamburg Model Change in the effective doping concentration ∆ N eff (Φ eq , t , T ) = N C , 0 (Φ eq ) + N A (Φ eq , t , T ) + N Y (Φ eq , t , T ) N c , 0 is the constant term N A is the beneficial (short term) annealing N Y is the reverse (long term) annealing There are several parameter sets available "RD48 oxy" and "CB-oxy" relevant for (measured as irradiated) oxygenated Si In addition saturation of N Y implemented F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 6 / 20
Introduction – Simulation Procedure Input Full irradiation and temperature history Radiation Damage Model Hamburg or α parameters FLUKA fluence predictions* Sensor position and geometry Thermal contacts* * these introduce significant uncertainties Procedure Each days deposited dose is annealed respecting the temperature history Previous days contributions are superimposed for leakage current or depletion voltage predictions F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 7 / 20
Simulation vs. Measurements Simulation vs. Measurements – Leakage Current Layer 1 Data granularity: Per sector, not resolved in z Temp measured near cooling loops ≈ − 11 . 5 ◦ C If detector on: Add an offset ⇒ Si at ≈ -8.5 ± 2 ◦ C Leakage current simulations are corrected by a factor of 1.0 Final fluence from FLUKA: ≈ 7 . 9 × 10 14 n eq / cm 2 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 8 / 20
Simulation vs. Measurements Simulation vs. Measurements – Leakage Current Layer 2 Data granularity: Per sector, not resolved in z Temp measured near cooling loops ≈ − 11 . 5 ◦ C If detector on: Add an offset ⇒ Si at ≈ -8.5 ± 2 ◦ C Leakage current simulations are corrected by a factor of 2.2 Final fluence from FLUKA: ≈ 1 . 8 × 10 14 n eq / cm 2 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 9 / 20
Simulation vs. Measurements Simulation vs. Measurements – Leakage Current Layer 3 Data granularity: Per sector, not resolved in z Temp measured near cooling loops ≈ − 11 . 5 ◦ C If detector on: Add an offset ⇒ Si at ≈ -8.5 ± 2 ◦ C Leakage current simulations are corrected by a factor of 2.0 Final fluence from FLUKA: ≈ 9 × 10 13 n eq / cm 2 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 10 / 20
Simulation vs. Measurements Simulation vs. Measurements – Leakage Current Layer 4 Data granularity: Per sector, not resolved in z Temp measured near cooling loops ≈ − 11 . 5 ◦ C If detector on: Add an offset ⇒ Si at ≈ -7.5 ± 2 ◦ C Leakage current simulations are corrected by a factor of 1.8 Final fluence from FLUKA: ≈ 5 × 10 13 n eq / cm 2 F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 11 / 20
Simulation vs. Measurements Simulation vs. Measurements – Full Depletion Voltage Phase-1 Pixel - Full depletion voltage vs days 1000 Get N eff from the simulation Full depletion voltage /V CMS CMS FLUKA study v3.23.1.0 Sim: Vdep vs Day, L1 (z = 0 cm) 2018 Preliminary Data: From Cluster Charge, L1 (all z) 900 Data: From Cluster Size, L1 (all z) Calculating full depletion Voltage: Sim: Vdep vs Day, L2 (z = 0 cm) Data: From Cluster Charge, L2 (all z) Data: From Cluster Charge, Curvature Fit, L2 (all z) 800 Data: From Cluster Size, Curvature Fit, L2 (all z) qd 2 Data: From Cluster Size, L2 (all z) Sim: Vdep vs Day, L3 (z = 0 cm) Data: From Cluster Charge, L3 (all z) Data: From Cluster Charge, Curvature Fit, L3 (all z) V dep = N eff 700 Data: From Cluster Size, Curvature Fit, L3 (all z) Data: From Cluster Size, L3 (all z) Sim: Vdep vs Day, L4 (z = 0 cm) 2 ǫǫ 0 Data: From Cluster Charge, L4 (all z) Data: From Cluster Charge, Curvature Fit, L4 (all z) 600 Data: From Cluster Size, Curvature Fit, L4 (all z) Data: From Cluster Size, L4 (all z) Data from HV scan during operation: 500 Avg. cluster charge and size are 400 determined as a function of bias 300 voltage 200 The full depletion voltage is estimated 100 from the kink in the respective curves 02/07/17 01/10/17 01/01/18 02/04/18 02/07/18 02/10/18 2 data mean For Layer 1 ( ≈ 1 . 8 × 10 14 n eq / cm 2 ) simulation 1.5 double junction effects limit model 1 0.5 accuracy 02/07/17 01/10/17 01/01/18 02/04/18 02/07/18 02/10/18 Date F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 12 / 20
Simulation vs. Measurements Simulation vs. Measurements – Last Years Results Mayor Step With Respect to Last Year Last year, only full depletion voltage results for Phase-0 were shown For Phase-1 especially the high fluence for new Layer 1 is a challenge Modeling approach improved over the past year, especially our temperature assumptions For the on-state of the detector, offsets between the temperature sensor and the silicon have been deduced from a mock-up of the pixel barrel Scaling leakage current measurements to the temperatures at the time of measurement F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 13 / 20
Z-Dependence of Leakage Current Z-Dependence of Leakage Current – Measurements HV channels group modules with the same φ region in the detector. Individual cables group modules in z. By disconnecting cables from power supply backplanes in the CMS experimental cavern it was possible to isolate individual (layer 1) and groups of modules on same z-positions. The detector was at nominal operating temperature with a CO 2 set point of − 22 ◦ C. The measurements were taken after the end of the 2018 heavy ion run. F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 14 / 20
Z-Dependence of Leakage Current Z-Dependence of Leakage Current – Layer 1 - I Different z, I leak differs up to ≈ 150 µA Z-position measured mid of each module Measured volume 0 . 299 cm 3 (16 ROCs) Between sectors I leak differs up to ≈ Fluence 7 . 9 × 10 14 n eq / cm 2 (FLUKA, 50 µA Larger leakage currents towards smaller at z=0) z, not fully consistent between all Dose 41 Mrad (from occupancies) measured sectors (one outlier) F. Feindt (University of Hamburg) CMS Pixel Radiation Damage Measurements February 14, 2019 15 / 20
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