GLAST Large Area Telescope:

1
GLAST Large Area Telescope Tracker
Subsystem WBS 4.1.4 2B Radiation
Evaluation-Testing Hartmut F.-W.
Sadrozinski Santa Cruz Institute for Particle
Physics University of California at Santa
Cruz Tracker Subsystem Scientist hartmut_at_scipp.uc
sc.edu
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LAT TKR Radiation Overview

• Radiation Levels are given in
• 433-SPEC-0001 GLAST Mission System Specification,
  CH 07
• LAT-SS-01165 TID Self-Shielding of the GLAST LAT
  TRK
• Applicable LAT documents
• LAT-SS-00152 Level-4 Electronics requirements
• LAT-DS-00011 LAT SSD Technical Specifications
• LAT-TD-00673 Constraints on the Temperature of
  TKR SSD
• LAT-TD-00401 LAT EE Parts List
• LAT-SS-00169 TKR Front-End (GTFE) Specification
• LAT-SS-00170 TKR Readout Controller (GTRC)
  Specification

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LAT TKR Radiation Overview

• Test plans
• LAT-CR-00082 LAT SSD Quality and Reliability
  Assurance
• LAT-TD-00085 Testing Procedures for the GLAST LAT
  SSDs
• LAT-PS-01325 Radiation Test Plan for the LAT TKR
  ASICs
• Test Results
• LAT-TD-00086 LAT Review of SSD RHA Test Results
• LAT-TD-00128 Results from Heavy Ion Irradiation
  (SSD)
• LAT-QR-01078 Q/A OF THE GLAST LAT SSD RHA
• LAT-TD-00333 SEE Test of the LAT TKR Front-End
  ASIC
• LAT-TD-01172 LAT TKR Readout Controller ASIC SEE
  Test
• LAT-TD-01632 LAT TKR Frontend ASIC SEE Test

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Radiation Levels TID
TID is caused by Charged Particles Trapped in SAA

• Shielding helps!
• Front Heat blanket, ACD
• Shielding 2 g/cm2 eliminates all electrons
• Back Mass of LAT
• Cuts TID by half
• Expected 5Y TID lt 0.8 kRad ( low ! )
• Design 5Y TID 4 kRad
• (5x Engineering Margin)
• Only in outer SSD layers
• for ASICS on outside
• Majority of TKR much less
• Testing TID 10 kRad

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Radiation Levels Heavy Ions
SEE Effects due to Galactic Cosmic Rays and
Solar Particle Events

• High energy particles due to Geomagnetic cut-off
• Shielding less effective!
• GCR
• For LET gt 2 F(5Y) 5/cm2
• LET lt 28 MeV/(mg/cm2)
• SPE
• For LET gt 5 F(5Y) 5/cm2
• (worst day/4)
• LET lt 100 MeV/(mg/cm2)
• Rates very low, but SEE effects potentially
  destructive
• GLAST Specs
• evaluate for LET lt 37 MeV/(mg/cm2)

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Radiation Effects on TKR Parts

• Use parts on the accepted parts list of GSFC as
  much as possible
• New Part Polyswitch re-settable device (3,456 in
  LAT)
• Do 100 kRad TID test ? NO (Parts are treated
  with 20 MRad during polymerization to enhance
  cross-linking!)
• Mitigates SEL risk!
• SSD (9,216 in LAT)
• SEE effects tested no effects observed, as
  expected
• TID (ionizing) tested with 60Co part of Q/A at
  Hiroshima U.
• Proton fluence generates leakage current and
  limits operating temperature
• ASICs (1,152 GTRC, 13,824 GTFE in LAT)
• SEE effects important (SEU and SEL) test plan
  results
• TID (ionizing) test plan results

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Radiation Effects on TKR SSD

• Displacement damage due to trapped protons
  increases leakage current
• DI aVolF
• Noise in frontend amplifier increases with
  leakage current
• ENC(DI) (DIt)0.5
• Exponential temperature dependence of DI limits
  operating temperature

Data apply to top TKR layers only
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Radiation Hardness Assurance on ASICs

• Testing done by INFN Padova collaborators
• SEE testing at INFN Legnaro tandem Van der Graff
  facility (?)
• TID testing at INFN Legnaro 60Co source
• We have done 2 SEE runs, 1 TID irradiation with
  fully functional pre-production prototype TKR
  ASICs
• All LAT ASICs are fabed in epitaxial 0.5um
  Agilent CMOS
• TID not a problem, SEL Threshold gt 56
  MeV/(mg/cm2)
• TID Test Plan for each of the 5 lots of GTFE, 1
  lot of GTRC
• 7 parts each mounted on mini-MCM with 2 GTRC
• TID 10 kRad in 4 steps
• Measure power, gain, noise rate and functionality
• SEU Test Plan for of each of the 5 lots of GTFE,
  1 lot of GTRC
• 2 parts each mounted on mini-MCM with 2 GTRC
• Heavy ions with LET from 8 (Si) to 83 (Au)
  MeV/(mg/cm2).
• Measure Single Event Upset(SEU), Single Event
  Functional Interrupt (SEFI) and Single Event
  Latch-up (SEL) cross sections

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TID Test Results on TKR ASICs

• Testing by INFN Padova (R. Rando, D. Bisello, J.
  Wyss et. al.)
• Irradiate both GTRC and GTFE pre-production
  prototypes
• Use mini-MCM and DAQ set-up
• After TID of 10 krad for GTFE, 20 krad for GTRC
• Power dissipation did not change
• Gain stable
• Noise rate under control
• GTRC and GTFE function at 20MHz

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SEE Test Results on TKR ASICs

• Testing by INFN Padova (R. Rando, D. Bisello, J.
  Wyss et. al.)
• Irradiate both GTRC and GTFE pre-production
  prototypes
• Fluence from GTRC Test
• NO SEL observed ? Upper limit on expected rate of
  Latch-up
• SEU cross sections sensitive to layout details as
  expected
• Rockett cell proves to be SEU hardened
• No TID effects
• Radiation Testing well in hand

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SEE Test Results on TKR ASICs cont.

• Very consistent results wrt. to previous data on
  test chips
• Cross sections different
• for 0 gt 1 and 1 gt 0 etc

• Cross section threshold
• 5-8 MeV/(mg/cm2)
• SEL Upper Limit
• lt 10-6 cm2 /GTRC

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SEE Test Results on TKR ASICs cont.

• Communication errors and SEFI error cross
  sections and upper limits for SEL for the
  entire GTRC.
• The Weibul fit s S(1-e-(LET-THR)/W)
• gives S 410-6, THR 5 - 8, W 40-48.

• SEL Probability lt 0.5 for entire TKR in 5
  years
• SEU Probability 1 for entire TKR in 5 years

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SEL Testing Using the right H.I. Range

• Single Event Upset (SEU) is essentially a surface
  phenomen
• Large charges in the gate flips the bit, no
  special H. I. range
• Single Event Latch-up (SEL)
• Caused by parasitic transistor inside the bulk
• Epitaxial structures should reduce charge
  collection
• Range of Heavy Ions has to exceed the charge
  collection distance
• Collection Distance
• A.H. Johnston an ion range that is approximately
  twice the dimension of the epitaxial layer
  thickness is generally adequate.
• For our 6um epi process this means 17 um
  required range.
• J. Howard et al. find charge collection distance
  of 26 um for high energy heavy ions in 7 um
  epitaxial structures.
• ESA/SCC Basic Specification No. 25100 ion range
  gt 30 um .
• Heavy Ion Range for LET 37 MeV/(mg/cm2)
• LNL Legnaro (Br) 31um LAT TKR Preference
• BNL (Br) 39um
• TAMU (Ag) 130um GSFC Rad Branch Preference

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TKR Radiation Evaluation Conclusions

• SSD
• Radiation issues well understood used to Q/A the
  lots (Hiroshima)
• Increase in leakage current not expected to
  diminish TKR performance as long as the
  temperature is controlled to lt30?C
• ASICs
• Require radiation testing for each of the lots (5
  GTFE, 1 GTRC)
• Radiation testing well in hand at INFN Padova
• Expected TID and SEE risk very small
• SEL mitigation from polyswitch resettable devices
• Concern
• Schedule ASIC radiation testing has to start in
  April, yet test plan has not been signed off by
  GSFC.
• Cost New requirements could introduce schedule,
  cost and man-power problems. We are talking with
  GSFC rad group