A silicon 3D detector with a single cell of 50 × 50 µm 2 was produced and evaluated for timing applications. The measurements of time resolution were performed for 90 Sr electrons with dedicated electronics used also for determining time resolution of Low Gain Avalanche Detectors (LGADs). The measurements were compared to those with LGADs and also simulations. The studies showed that the dominant contribution to the timing resolution comes from the time walk originating from different induced current shapes for hits over the cell area. This contribution decreases with higher bias voltages, lower temperatures and smaller cell sizes. It is around 30 ps for a 3D detector of 50 × 50 µm 2 cell at 150 V and -20 • C, which is comparable to the time walk due to Landau fluctuations in LGADs. It even improves for inclined tracks and larger pads composed of multiple cells. A good agreement between measurements and simulations was obtained, thus validating the simulation results. PACS: 85.30.De; 29.40.Wk; 29.40.Gx Work performed in the framework of the CERN-RD50 collaboration.

Abstract:3D silicon pixel detectors have been investigated as radiation-hard candidates for the innermost layers of the HL-LHC upgrade of the ATLAS pixel detector. 3D detectors are already in use today in the ATLAS IBL and AFP experiments. These are based on 50×250 µm 2 large pixels connected to the FE-I4 readout chip. Detectors of this generation were irradiated to HL-LHC fluences and demonstrated excellent radiation hardness with operational voltages as low as 180 V and power dissipation of 12-15 mW/cm 2 at a fluence of about 10 16 n eq /cm 2 , measured at -25 • C. Moreover, to cope with the higher occupancies expected at the HL-LHC, a first run of a new generation of 3D detectors designed for the HL-LHC was produced at CNM with small pixel sizes of 50×50 and 25×100 µm 2 , matched to the FE-I4 chip. They demonstrated a good performance in the laboratory and in beam tests with hit efficiencies of about 97% at already 1-2 V before irradiation.

A : Small-pitch 3D silicon pixel detectors have been investigated as radiation-hard candidates for the innermost layers of the HL-LHC pixel detector upgrades. Prototype 3D sensors with pixel sizes of 50×50 and 25×100 µm 2 connected to the existing ATLAS FE-I4 readout chip have been produced by CNM Barcelona. Irradiations up to particle fluences of 3 × 10 16 n eq /cm 2 , beyond the full expected HL-LHC fluences at the end of lifetime, have been carried out at Karlsruhe and CERN. The performance of the 50×50 µm 2 devices has been measured in the laboratory and beam tests at CERN SPS. A high charge collected and a high hit efficiency of 98% were found up to the highest fluence. The bias voltage to reach the target efficiency of 97% at perpendicular beam incidence was found to be about 100 V at 1.4 × 10 16 n eq /cm 2 and 150 V at 2.8 × 10 16 n eq /cm 2 , significantly lower than for the previous IBL 3D generation with larger inter-electrode distance and than for planar sensors. The power dissipation at -25 • C and 1.4 × 10 16 n eq /cm 2 was found to be 13 mW/cm 2 . Hence, 3D pixel detectors demonstrated superior radiation hardness and were chosen as the baseline for the inner layer of the ATLAS HL-LHC pixel detector upgrade. K: Particle tracking detectors, HL-LHC upgrade, 3D silicon pixel detectors, Radiationhard detectors A X P : 1805.10208