Comparison of 35 and 50 ${\mu}$m thin HPK UFSD after neutron irradiation up to $6•10^15$ $neq/cm^2$

We report results from the testing of 35 μ m 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 μ m thick UFSD produced by HPK. The 35 μ m thick sensors were irradiated with neutrons to fluences of 1 ⋅ 10 14 , 1 ⋅ 10 15 , 3 ⋅ 10 15 , 6 ⋅ 10 15 neq/cm 2 . The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particles (MIPs) from a 90 Sr 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 μ m thick UFSD present advantages in timing accuracy, bias voltage and power consumption.