Development of radiation hard pixel modules employing planar n-in-p siliconsensors with active edges for the ATLAS detector at HL-LHC

ATLAS is one of the two main experiments at LHC with the purpose of investigating the microscopic properties of matter to address the most fundamental questions of particle physics. After the achievements of the first years of running, the potential reach for new discoveries and precise measurements at LHC is being extended by pushing further the energy and luminosity frontiers through three upgrades of the accelerator culminating in the High Luminosity Large Hadron Collider (HL-LHC). To fully profit from the increased luminosity, two main upgrades of the ATLAS inner detector are planned.The first upgrade was already completed at the beginning of 2015 with the insertion of the IBL, a fourth pixel layer located at just 3.2 cm from the beam line. The new layer features modules with increased granularity and improved radiation hardness. These include sensors using the 3D technology which is employed for the first time in a high energy physics experiment. In this thesis the properties of these 3D sensors were characterised at beam tests before irradiation and the results used for the validation of the digitisation model implemented in the ATLAS simulation software.In the second major upgrade, foreseen for 2024, the full inner detector will be replaced by a completely new inner tracker fully made of silicon devices to cope with the high particle density and the harsh radiation environment at the HL-LHC, which during its operational period will deliver 3000 fb$^{−1}$, almost ten times the integrated luminosity of the full LHC program. The most severe challenges are to be faced by the innermost layers of the pixel detector which will have to withstand a radiation fluence up to 1.4 × 10$^{16}$n$_{eq}$/cm$$^{2}$, providing at the same time the maximum possible active area. A novel module concept was developed to fulfil the requirements for the pixel detector at the HL-LHC. This consists of thin planar n-in-p pixel sensors with active or slim edges, connected to the readout chip by a 3D integration concept including the Through Silicon Via technology. Thin sensors are designed to withstand high radiation fluence thanks to their enhanced charge collection efficiency and the possibility of operating at full depletion with moderate voltages. Moreover, the extension of the implantation to the sensor sides, allows to reduce the distance from the last pixel implant to the sensor edge, thus extending the active area up to a full active edge design. The Through Silicon Via technology allows to maximise the active area on the chip by removing the large wire-bond balcony and conveying the signal through the chip itself to the backside. In this thesis different sensor prototypes implementing the technologies described above are investigated before and after irradiation by means of radioactive sources and beam test measurements aiming at the development of a radiation hard four side buttable module for the innermost layers of the ATLAS pixel detector. The results for different sensor thicknesses ranging from 100 to 200 µm are compared with the performance of thicker and thinner sensors, including results from previous analysis. The behaviour at the edge of slim and active edge sensors is investigated and specific studies are presented in view of the future module geometries for the different layers and pseudorapidity regions of the pixel detector. Furthermore, n-in-p sensors were already demonstrated to be a cost effective alternative to the pixel technologies presently employed in ATLAS and are therefore suited to cover large areas in the outer layers for which first prototypes of four chip modules have been developed and characterised.