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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
CMS Si Rad. Hardness
  • Introduction
  • Damage in Si
  • Neutron tests
  • => Beam
  • => Irrad. Setup
  • => Electrical tests
  • Results sample & overview
si in the cms tracker
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
damage in si bulk
Damage in Si (bulk)


25 eV (recoil atom)

2 keV (cluster)

Non-Ionizing Energy Loss

Successes… & problems

Scaling of the damage for STFZ silicon

effects of radiations on the sensors
Effects of radiations on the sensors


The current scales well, is material-independent, but NIEL scaling fails to explain the annealing beahaviour

effects of radiations on the sensors1
Effects of radiations on the sensors



Bulk type inversion

effects of radiations on the sensors2
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
at the lhc
… 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)

how many tests
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

t2 neutron beam overview
T2 Neutron Beam Overview

9Be (d,n) 10B


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

electrical tests
Electrical Tests

Dry air generator

(typ. RH ~1 %)


Current measurements: < 10 pA (dielectrics)

Capacitance measurement (CV): < 1 pA (stable parasitics < 12 pF)

Capacitance measurement (strip): < 0.05 pA (stable parasitics < 10 pF)

results overview bulk damage
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).

recent results r poly
Recent results: Rpoly

The average decrease is less than 1%.

No effect of bias.

recent results c ac
Recent results: Cac

(Initial capacitance

values around 60 pF)

ST average: -0.58^2/1e14

HPK average: -0,07^2/1e14

Thick HPK average


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.

hpk thick structures c int
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.

recent results r int
Recent results: Rint

The values are always well above 20 M.

No effect of bias.

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


1.04 & 1.06 e14

1.17 & 1.18 e14

Planar diode

+ geometry correction factor

+ effective thickness correction