Properties of FBK UFSDs after neutron and proton irradiation up to 6⋅ 1015 neq/cm2

Abstract

The properties of 60-μm thick Ultra-Fast Silicon Detectors (UFSD) detectors manufactured by Fondazione Bruno Kessler (FBK), Trento (Italy) were tested before and after irradiation with minimum ionizing particles (MIPs) from a 90Sr β-source. This FBK production, called UFSD2, has UFSDs with gain layer made of Boron, Boron low-diffusion, Gallium, carbonated Boron and carbonated Gallium. The irradiation with neutrons took place at the TRIGA reactor in Ljubljana, while the proton irradiation took place at CERN SPS. The sensors were exposed to a neutron fluence of 4⋅1014, 8⋅1014, 1.5⋅1015, 3⋅1015, 6⋅ 1015 neq/cm2 and to a proton fluence of 9.6⋅ 1014 p/cm2, equivalent to a fluence of 6⋅ 1014 neq/cm2. The internal gain and the timing resolution were measured as a function of bias voltage at -20oC. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction method for both.