Speaker
Description
To face the higher levels of radiation due to the 10-fold increase in integrated luminosity during the High Luminosity LHC the CMS detector will replace the current endcap calorimeters with the new High Granularity Calorimeter (HGCAL). The electromagnetic section as well as the high-radiation regions of the hadronic section of the HGCAL (fluences above $10^{14} n_{eq}/cm^2$) will be equipped with silicon pad sensors, covering a total area of $620m^2$). Fluences up to $10^{16} n_{eq}/cm^2$ and doses up to 1.5 MGy are expected.
The sensors are processed on novel 8-inch p-type wafers with active thicknesses of $300\,\mu$m, $200\,\mu$m and $120\,\mu$m and with each main sensor several small sized test structures are hosted on the wafers, used for quality assurance and radiation hardness tests. In order to investigate the radiation-induced bulk damage, the diode test structures of these sensors have been irradiated with neutrons at JSI (Jožef Stefan Institute, Ljubljana) to fluences up to $1.5\cdot10^{16} n_{eq}/cm^2$.
In this talk, the electrical characterisation and charge collection measurements of the irradiated silicon diodes will be presented. The study focuses on the isothermal annealing behaviour of the bulk material at temperatures of 5.5°C, 20°C, 30°C, 40°C and 60°C in order to extract the temperature dependent annealing time constants that allow scaling to temperatures such as the 0°C foreseen as the shutdown temperature of the CE. Additionally, first results of a campaign investigating the effects of successive irradiation and annealing will be presented. This campaign mimics CMS' operating scenario at the HL-LHC, with a fraction of the end-of-life fluence accumulated in Run 4, annealing in the Long Shutdown 4, and remaining fluence accumulated in the final Run 5, by doing a two-step irradiation with in-between annealing.