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CMS Si Rad. Hardness

CMS Si Rad. Hardness. Introduction Damage in Si Neutron tests => Beam => Irrad. Setup => Electrical tests Results sample & overview. Si in the CMS Tracker. I leak , R poly , N eff V depl , C ac , C int , «pinholes». 25,000 wafers 15 sensor designs

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CMS Si Rad. Hardness

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  1. CMS Si Rad. Hardness • Introduction • Damage in Si • Neutron tests • => Beam • => Irrad. Setup • => Electrical tests • Results sample & overview

  2. Si in the CMS Tracker Ileak, Rpoly, NeffVdepl , Cac, Cint, «pinholes» 25,000 wafers 15 sensor designs ~15,000 modules with 1-2 sensors (206m2) • Requirement: ability to work for 10 years at LHC • S/N > 10 • Operating voltage < 300V

  3. Damage in Si (bulk) Tresholds: 25 eV (recoil atom) 2 keV (cluster) Non-Ionizing Energy Loss Successes… & problems Scaling of the damage for STFZ silicon

  4. Effects of radiations on the sensors Ileak The current scales well, is material-independent, but NIEL scaling fails to explain the annealing beahaviour

  5. Effects of radiations on the sensors NeffVdepl Hamburg Bulk type inversion

  6. Effects of radiations on the sensors • Increase of leakage current • => increase of noise and power • Variation of Vdep-Type inversion • => ! Overdepletion needed ! • => beware of annealing • Charge trapping • => CCE deterioration • Surface damage • => Crosstalk, pinholes

  7. … At the LHC… Using simulations to calculate fluxes, and NIEL to compute Dtot… Fluences all over the detector normalised to 1-MeV neutron equivalent… Eg: Tracker TDR, study by M. Huhtinen Aim of the irradiation tests: study the radiation hardness of the sensors => Quality and stability of the production => Electrical behaviour after irradiation (previsions) => Check the relevantness of the tests (bias)

  8. How many tests? QA during production: 1% sensors 4% test structures 300 1200 • # of irradiations foreseen: • Irradiating 5 sensors or 10 test structures/set => 180 irrad. • Over 3 years, made by 2 « IQC » and 2 sets/irrad => 15 irrad./year 39 have been performed, but with less sensors in total

  9. T2 Neutron Beam Overview 9Be (d,n) 10B Beam Fmax = 6.6 x 1012 n sr-1 s-1 Nominal LHC fluence reached in 6 to 18h Irradiation has to be made in the more « CMS-like » environment… => Biasing of the sensors, Cooling and low RH using dry air and liquid N2 All controls are outside the irradiation zone => HV, temperature, deuteron beam and leakage current monitoring Post-irradiation dose measurement using alanine films

  10. Electrical Tests Dry air generator (typ. RH ~1 %) Accuracy: Current measurements: < 10 pA (dielectrics) Capacitance measurement (CV): < 1 pA (stable parasitics < 12 pF) Capacitance measurement (strip): < 0.05 pA (stable parasitics < 10 pF)

  11. Results overview: Bulk damage parameter a With an experimental temperature correction factor of 20, one finds the alpha parameter quoted in literature. No effect of bias. More detailed studies show an agreement with literature, although no effect of bias has been observed so far (further tests in progress).

  12. Recent results: Rpoly The average decrease is less than 1%. No effect of bias.

  13. Recent results: Cac (Initial capacitance values around 60 pF) ST average: -0.58 pF.cm^2/1e14 HPK average: -0,07 pF.cm^2/1e14 Thick HPK average -0.41 pF.cm^2/1e14 The coupling capacitances are barely affected by irradiation. There is an influence of the sensor thickness : thicker sensors are a bit more sensitive. No effect of bias.

  14. HPK thick structures: Cint The ramp behaviour shows a late decrease of the Cint with bias. The values are still around 1.2 pF/cm of strip length. No effect of bias.

  15. Recent results: Rint The values are always well above 20 M. No effect of bias.

  16. Summary • Big tracker + harsh environment • => Simulations and QA scheme • Bulk damage is predominant • => Behaviour predictible, OK • Strip damage only limited • => within specifications

  17. Depletion voltage 7.5e13 1.04 & 1.06 e14 1.17 & 1.18 e14 Planar diode + geometry correction factor + effective thickness correction

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