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 hartmut@scipp.ucsc.edu

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

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

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

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)

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

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

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

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

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

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

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 = 40-48. SEL Probability < 0.5 % for entire TKR in 5 years SEU Probability ~ 1% for entire TKR in 5 years

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 > 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

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 …