1. GLAST Large Area Telescope:
Gamma-ray Large Area Space Telescope
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

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

3. LAT TKR Radiation Overview
Test plans:
LAT-CR LAT SSD Quality and Reliability Assurance
LAT-TD Testing Procedures for the GLAST LAT SSDs
LAT-PS Radiation Test Plan for the LAT TKR ASICs
Test Results
LAT-TD LAT Review of SSD RHA Test Results
LAT-TD Results from Heavy Ion Irradiation (SSD)
LAT-QR Q/A OF THE GLAST LAT SSD: RHA
LAT-TD SEE Test of the LAT TKR Front-End ASIC
LAT-TD LAT TKR Readout Controller ASIC SEE Test
LAT-TD LAT TKR Frontend ASIC SEE Test

4. TID is caused by Charged Particles Trapped in SAA
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 < 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

5. 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 > 2 : F(5Y) ~ 5/cm2
LET < 28 MeV/(mg/cm2)
SPE:
For LET > 5 : F(5Y) ~ 5/cm2
(worst day/4)
LET < 100 MeV/(mg/cm2)
Rates very low, but SEE effects potentially destructive
GLAST Specs:
evaluate for LET < 37 MeV/(mg/cm2)

6. 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

7. Radiation Effects on TKR SSD
Displacement damage due to trapped protons increases leakage current
DI ~ a*Vol*F
Noise in frontend amplifier increases with leakage current
ENC(DI) ~ (DI*t)0.5
Exponential temperature dependence of DI limits operating temperature:
Data apply to top TKR layers only

8. 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 fab’ed in epitaxial 0.5um Agilent CMOS
TID not a problem, SEL Threshold > 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

9. 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

10. 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

11. SEE Test Results on TKR ASICs cont.
Very consistent results wrt. to previous data on test chips
Cross sections different
for 0 —> 1 and 1 — > 0 etc
Cross section threshold:
~ 5-8 MeV/(mg/cm2)
SEL Upper Limit
< 10-6 cm2 /GTRC

12. 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 = 4*10-6, THR = 5 - 8, W =
SEL Probability < 0.5 % for entire TKR in 5 years
SEU Probability ~ 1% for entire TKR in 5 years

13. 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 : ion range > 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

14. 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 <30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 …