Heavy ion irradiation on silicon strip sensors for GLAST

We investigated the damage of silicon strip sensors due to heavy-ion radiation, as a check of the in-orbit stability of silicon strip sensors under cosmic-ray irradiation in the 5 year GLAST mission. In order to study single-event effects (SEE), we used Fe ions slowed-down in an absorber, with a resulting LET of 8 MeV/(mg/cm²) on the surface of the sensor. The total doses achieved in two runs were about 8 krd and 22 krd, corresponding to a fluence of about 5*10⁷ and 1.5*10⁸ ions/cm², respectively. Silicon strip sensor with two different crystal orientations, <111> and <100>, were irradiated. We measured leakage currents and capacitances before and after irradiation to evaluate the damage. The leakage current was found to increase by about 10 nA/cm²/krd, as expected for the ionizing irradiation. No significant changes of capacitances were found. In addition, no coupling capacitors were broken. The observed effects are well within the in-orbit requirements of the GLAST mission.