Timing resolution from beam tests on thin LGADs down to 16.6 ps

The paper reports on the timing resolution achieved with Low-Gain Avalanche Diodes (LGADs), optimised for extreme-fluence conditions, at the DESY Test Beam Facility using 4 GeV/c electrons. The LGADs adopt an n-in-p technology with a p+-type boron gain implant, co-implanted with carbon to mitigate acceptor deactivation due to irradiation. The substrate thickness of the sensors varies from 20 to 45 μm, with an active area spanning from 0.75 × 0.75 to 1.28 × 1.28 mm2. The experimental setup consisted of a 45 μm-thick trigger sensor with an active area of 3.6 × 3.6 mm2, two device-under-test (DUT) planes, and a Photonis micro-channel plate photomultiplier tube (MCP) as a time reference. Data taking was performed at the ambient temperature of the facility, at 18 °C. The gain was measured between 7 and 40 across all non-irradiated sensors in the study. The timing resolution was calculated from a Gaussian fitting of the difference in times of arrival of a particle at the DUT and the MCP, using the constant fraction discriminator technique. A timing resolution of 26.4 ps was achieved in 45 μm-thick sensors, down to 16.6 ps in 20 μm-thick sensors, in the non-irradiation study. The combination of two 20 μm-thick LGADs reached a timing resolution of 12.2 ps. A set of 30 μm-thick sensors irradiated with neutrons at fluences between 0.4 × 1015 and 2.5 × 1015 neqcm−2 were tested in the beam. These irradiated sensors achieved a gain between 7 and 30 using a similar apparatus but cooled with solidified CO2 to −42 °C. A timing resolution of 20 ps was obtained in these irradiated sensors.