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IAP-PAI 25/05/20051 CMS Si Rad. Hardness Introduction Damage in Si Neutron tests => Beam => Irrad. Setup.

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Presentation on theme: "IAP-PAI 25/05/20051 CMS Si Rad. Hardness Introduction Damage in Si Neutron tests => Beam => Irrad. Setup."— Presentation transcript:

1 IAP-PAI 25/05/20051 CMS Si Rad. Hardness Introduction Damage in Si Neutron tests => Beam => Irrad. Setup => Electrical tests Results sample & overview

2 IAP-PAI 25/05/20052 Si in the CMS Tracker 25,000 wafers 15 sensor designs ~15,000 modules with 1-2 sensors (206m 2 ) I leak, R poly, N eff  V depl, C ac, C int, «pinholes» Requirement: ability to work for 10 years at LHC S/N > 10 Operating voltage < 300V

3 IAP-PAI 25/05/20053 Damage in Si (bulk) Tresholds: 25 eV (recoil atom) 2 keV (cluster) Scaling of the damage for STFZ silicon Non-Ionizing Energy Loss Successes… & problems

4 IAP-PAI 25/05/20054 Effects of radiations on the sensors I leak The current scales well, is material-independent, but NIEL scaling fails to explain the annealing beahaviour

5 IAP-PAI 25/05/20055 Effects of radiations on the sensors N eff  V depl Bulk type inversion Hamburg

6 IAP-PAI 25/05/20056 Effects of radiations on the sensors Increase of leakage current => increase of noise and power Variation of V dep -Type inversion => ! Overdepletion needed ! => beware of annealing Charge trapping => CCE deterioration Surface damage => Crosstalk, pinholes

7 IAP-PAI 25/05/20057 … At the LHC… Fluences all over the detector normalised to 1-MeV neutron equivalent… Using simulations to calculate fluxes, and NIEL to compute D tot … 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 IAP-PAI 25/05/20058 How many tests? QA during production: 1% sensors 4% test structures # 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 IAP-PAI 25/05/20059 T2 Neutron Beam Overview 9 Be (d,n) 10 B 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 Beam  max = 6.6 x n sr -1 s -1 Nominal LHC fluence reached in 6 to 18h

10 IAP-PAI 25/05/ 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 IAP-PAI 25/05/ Results overview: Bulk damage 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 IAP-PAI 25/05/ Recent results: R poly The average decrease is less than 1%. No effect of bias.

13 IAP-PAI 25/05/ Recent results: C ac ST average: pF.cm^2/1e14 HPK average: -0,07 pF.cm^2/1e 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. (Initial capacitance values around 60 pF)

14 IAP-PAI 25/05/ HPK thick structures: C int The ramp behaviour shows a late decrease of the C int with bias. The values are still around 1.2 pF/cm of strip length. No effect of bias.

15 IAP-PAI 25/05/ Recent results: R int The values are always well above 20 M . No effect of bias.

16 IAP-PAI 25/05/ Summary Big tracker + harsh environment => Simulations and QA scheme Bulk damage is predominant => Behaviour predictible, OK Strip damage only limited => within specifications

17 IAP-PAI 25/05/ Depletion voltage 7.5e & 1.06 e & 1.18 e14 + geometry correction factor + effective thickness correction Planar diode


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