Comparison of 35 and 50μm thin HPK UFSD after neutron irradiation up to 6 ⋅ 1015 neq/cm2

We report results from the testing of 35 μm thick Ultra-Fast Silicon Detectors (UFSD) produced by Hamamatsu Photonics (HPK), Japan and the comparison of these new results to data reported in a previous paper on 50 μm thick UFSD produced by HPK. The 35 μm thick sensors were irradiated with neutrons to fluences of 1 ⋅ 1014, 1 ⋅ 1015, 3 ⋅ 1015, 6 ⋅ 1015 neq/cm2. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particles (MIPs) from a 90Sr β-source. The leakage current, capacitance, internal gain and the timing resolution were measured as a function of bias voltage at −20 °C and −27 °C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction discrimination method for both devices. Within the fluence range measured, 35 μm thick UFSD present advantages in timing accuracy, bias voltage and power consumption.