Speaker
Description
The High-Luminosity LHC will challenge the detectors with a nearly 10-fold increase in integrated luminosity compared to the previous LHC runs combined, thus the CMS detector will be upgraded to face the higher levels of radiation and the larger amounts of data collected. The High-Granularity Calorimeter (HGCAL) will replace the current endcap calorimeters of the CMS detector. It will facilitate the use of particle-flow calorimetry with its unprecedented transverse and longitudinal readout/trigger segmentation, with more than 6M readout channels. The electromagnetic section as well as the high-radiation regions of the hadronic section of the HGCAL (fluences above 10^14 neq/cm2) will be equipped with silicon pad sensors, covering a total area of 620 m2. Fluences up to 10^16 neq/cm2 and doses up to 1.5 MGy are expected. The sensors are processed on novel 8-inch p-type wafers with an active thickness of 300 μm, 200 μm and 120 μm and cut into hexagonal shapes for optimal use of the wafer area and tiling. Each sensor contains several hundred individually read out cells of two sizes (around 0.5 cm2 or 1.2 cm2). 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 main sensors and single diodes from the test structures have been irradiated with neutrons at RINSC (Rhode Island Nuclear Science Centre, US) and JSI (Jožef Stefan Institute, Ljubljana, Slovenia) to fluences between 6.5·10^14 neq/cm2 and 1.5·10^16 neq/cm2. In this talk, the electrical characterisation and charge collection measurements of the irradiated silicon sensors will be presented. This includes first measurements with so-called partial sensors cut from multi-geometry wafers with internal dicing lines on the HV potential left in the active sensor area, the isothermal annealing behaviour of the bulk material and the CV-frequency and measurement-method dependence present in depletion voltage measurements in irradiated sensors. The observed behaviour of the electrical properties and charge collection efficiency is in agreement with the HGCAL specifications. The results are being used to optimize the HGCAL layout and to establish an operating and annealing scenario for HGCAL.
