Irradiation studies of L1 sensors for D

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Irradiation studies of L1 sensors for DØ 2b

• Regina Demina
• University of Rochester

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Outline

• Radiation environment and silicon sensor specs
• Results on prototypes
• Conclusions

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Requirements for silicon sensors

• Main challenge for silicon sensors - radiation
• Depletion voltage (F)
• Leakage current (F) ? noise
• Doses comparable to LHC use their RD
• NB Uncertainty in F estimate conservative
  approach 1.5 safety margin

10 years of CMS at inner radius
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Depletion voltage
Specification on breakdown voltage derived based
on depletion voltage evolution
T-10oC with warm up periods
Hamburg model
20fb-1
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Signal to noise ratio

• Noise contributions
• Capacitive load 45043C(pF)
• Al strip resistance analogue cables (L0)
• Shot noise IleakI0aFAd (a3E-17A/cm)
• Thermal noise in Rbias

Ileak16mA/cm2
Goal S/Ngt 10 Possible if Tlt-10oC for L0 and
L1 Tlt-5oC for L2 L5 Important to test Ileak
after irradiation on prototype sensors and on
test structures during production
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Irradiation studies at KSU

• More details in T. Boltons talk
• 10 MeV p, sweep the beam using electrostatic
  deflector
• Anneal at 60oC for 80 min, then keep cold
• Measure I at 1oC, extrapolate to 20oC

HPK
Single sided low r sensors with guard band
structure produced by HPK
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Leakage current

• Raw currents measured at T1oC
• Vbreakgt700V (spec)

19fb-1 at r1.8 cm Corresponds to 17mA/cm2
_at_-10oC (need 16 for s/ngt10)
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I leak vs T

• Measure at 1oC, extrapolate to 20oC
• Verify temperature dependence

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I leak vs F

• I ap Fp
• ap11.6?10-17 A?cm for 10 MeV p
• Hardness of 10MeV protons vs 1 MeV neutrons k
  a(10MeVp)/a(1 MeVn)11.6/4.562.54 (compared
  to3.87)

N.B. a3.0e-17A ?cm for 1 MeV n, if use k3.87
D. Bechevet et al. NIM A 479(2002)487 At 10 MeV p
Montreal
G.P Summers et al., IEEE Trans Nucl. Sci
NS-40,6(1993)1372
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Depletion voltage vs flux

• Use 1/c2 vs V to determine V delp 30-50
  uncertainty

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V depl vs F, full size sensors
Use Hamburg model with stable damage, short and
long term annealing terms Flux in protons/cm2?
main effect on C (scales with 1/k)
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Other properties after irradiation

• Cint 3 pF(before) ? 6 pF (after 9.35E13 20
  fb-1) NC1680e(before) ? 1815 (after)

S/ngt9
No change in R poly after irradiation
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Conclusions

• Single sided low r sensor technology with guard
  band structure is used for the inner layers
• L1 sensors produced by HPK were tested up to 1E14
  10 MeV p/cm2
• Hardness factor was found to be 2.54 instead of
  theoretically predicted 3.87, but in agreement
  with a study by Rose collaboration
• Using this number and 1.5 safety factor we
  estimate 1E14 10 MeV p/cm2 to be equivalent to 20
  fb-1 at r1.8 cm (L0)
• After this dose
• No break down was observed up to 1000 V
• Sensors deplete at 350-400 V in agreement with
  the hamburg model
• Based on the observed increase in leakage current
  we expect Ileak 17 mA/cm2 at operating T of
  10oC ? s/n10
• Cint increased from 3 to 6 pF, which will lead to
  increase in Johnson noise from 1680e? 1815e
• R int did not change
• S/n is expected to be above 9 for L0 after 20
  fb-1
• We believe that these sensors will perform
  adequately after 20 fb-1

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Back up slidesdo not print
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Fluence estimations for Run IIb

• based on CDF silicon leakage current measurements
  in Run Iab
• observed radial dependence 1/r1.7
• measured CDF silicon sensor leakage currents are
  scaled to DØ sensor geometries and temperatures
  to give shot noise contributions of leakage
  currents
• for depletion voltage calculations, a 1 MeV
  equivalent neutron fluence is assumed
• ?1Mev n2.191013 rcm-1.7 cm-2/fb-1 (Matthew
  et al., CDF notes 3408 3937)
• safety factor 1.5 applied

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Performance extrapolations for Run IIb

• S/N extrapolations assume
• noise in front end of SVX4 45043C(pF)
• total silicon strip capacitance 1.4pF/cm
• L0 analog cable assumed (and measured) 0.4pF/cm
  
• noise due to series resistance of metal traces in
  silicon 210e-700e depending on module length
• noise due to finite value of bias resistor 250e
• shot noise due to increased leakage currents
• 1100e for L0 after 15fb-1 if T-5C
• 1000e for L2 (20cm long module) after 15fb-1 if
  T0C

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V depl vs F

• Test diods