Investigation of radiation damage in n+-in-n planar pixel sensors for future ATLAS pixel detector upgrades

Abstract

The ATLAS detector is a multi-purpose detector within the large hadron collider at CERN in Geneva. Its inner-most sub detector is the pixel detector which is an important part of the tracker system. It is a hybrid detector where readout electronics and sensors are manufactured separately and connected subsequently through bump bonds. Due to the location next to the interaction point sensors have to withstand high radiation. Test sensors were irradiated with neutrons at the JSI in Ljubljana and with protons at the irradiation center Karlsruhe and at CERN-PS. The radiation hardness of planar silicon n-in-n sensors was demonstrated in this thesis up to a fluence of 2E16 n_eq/cm², which is the expected end of life fluence for the inner layer after the HL-LHC upgrade of ATLAS. More charge than calculated with a simple trapping model is collected, indicating that some sort of stable charge amplification is taking place. The measurements were done with a beta particle source and with high energy beams of electrons and pions at test beam sites. An excellent hit efficiency of 97% was achieved.