Radiation testing of GLAST LAT tracker ASICs

Gamma-ray large area space telescope (GLAST) is a next generation high-energy gamma-ray space observatory designed for observations of celestial gamma-ray sources in the energy band extending from 10 MeV to more than 100 GeV. The main instrument, the large area telescope (LAT), consists of a microstrip silicon tracker, a calorimeter, an anticoincidence detector, and the data acquisition (DAQ) system. This paper summarizes the results obtained during the radiation testing of the ASIC chips used in the LAT tracker. Both single event effects (SEE) and total ionizing dose effect (TID) tests have been performed, as part of the radiation hardness assurance (RHA) for the planned 5-yr mission. Heavy-ion SEE tests have been performed at the SIRAD irradiation facility at the INFN National Laboratories of Legnaro, Italy (LNL) and at the Texas A&M University (TAMU) Cyclotron Institute, with LET values ranging up to ∼80 MeV×cm²/mg. The tolerance of the chips to ionizing radiation has been evaluated with heavy ions and by irradiating chips with the spherical ⁶⁰Co gamma source of the LNL CNR-ISOF laboratory.