Timing performance and gain degradation after irradiation with protons and neutrons of Low Gain Avalanche Diodes based on a shallow and broad multiplication layer in a float-zone 35μm and 50μm thick silicon substrate

Abstract

The high-luminosity upgrade of the ATLAS and CMS experiments includes dedicated sub-detectors to perform the time-stamping of minimum ionizing particles (MIPs). These detectors will be exposed up to fluences in the range of 1.5–2.5 × 10¹⁵ neq∕cm² and require a time resolution per detecting layer of 30 ps, for non-irradiated sensors, to 50–70 ps (depending on the exposed fluences) for sensors at the end of their lifetime. To cope with these requirements, the low-gain avalanche diode (LGAD) has been chosen as the baseline detection technology. In this article, an in-depth radiation tolerance study on LGADs manufactured at IMB-CNM using a so-called shallow junction is presented. Proton irradiation at CERN-PS up to fluences of 3 × 10¹⁵ neq∕cm² and neutron irradiation at JSI-Ljubljana up to 2.5 × 10¹⁵ neq∕cm² were performed. Two different active thicknesses were studied: 35 μm and 50 μm. Gain degradation, operation stability, and timing performance were evaluated.