High voltage CMOS monolithic active pixel sensor for high energy physics experiments
Creators: name: Bui, Tuan Anh
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400908
subject: Microelectronics

description: Position sensitive detectors are widely used in the tracking system of High Energy Physics (HEP) experiments such as ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid) at the Large Hadron Collider (LHC), the world¿s largest particle accelerator at CERN mainly due to their outstanding performance. The future upgrade of the LHC to its high luminosity (HL) will enable the use of maximal physics potential of the facility for searching beyond the Standard Model of particle physics. After ten years of operation, the expected radiation fluence will result in a radiation environment that is beyond the capacity of the present tracking system design. The required upgrade of the silicon central tracker will include higher granularity and radiation hard sensors that can tolerate the increased occupancy and the higher radiation levels. The radiation hardness of new sensors must be roughly ten times higher than in the current LHC detectors. Extensive measurements and simulation studies have been performed to investigate different designs and materials for silicon sensors to cope with such that high radiation hardness.<br> <br>High Voltage CMOS (HV-CMOS) Monolithic Active Pixel Sensor (MAPS) is currently a promising candidate technology for the new inner pixel detector at the LHC. The HV-CMOS MAPS was proposed in 2007, since then it has been very attracting since it has overcome most of the disadvantages of the standard MAPS design. The HV-CMOS MAPS has been demonstrated to have excellent performance for charged particle tracking, such as higher charge collection efficiency, better sensitivity and faster response speed. The capability of fabricating sensors and readout electronics on the same substrate helps to reduce the material budget and the complexity in term of mounting small size pixels. Several prototypes of the HV-CMOS MAPS have been fabricated through a series of large-scale collaboration in the ATLAS and Mu3e program with very promising results.<br> <br>This thesis presents works on numerical simulation studied for the HV-CMOS MAPS design. The simulation process is an essential part of the device development process since it can provide further analysis and optimisation of the design. It can significantly shorten the development time, especially for the new technology with non-standard process of fabrication. A complete Technology Computer Aided Design (TCAD) model of a single pixel HV-CMOS MAPS is developed based on Sentaurus TCAD simulation framework of Synopsys. A single pixel of HV-CMOS MAPS model is used to determine and predict the electrical characteristics and performance of the device regrading device dimensions, doping concentrations of the structural layer and bias conditions. The interaction with Minimum Ionising Particles (MIP) is also simulated to study its effect on the sensors' performance.<br> <br>A comprehensive analysis to study the effect of radiation hardness on a pixel of HV-CMOS MAPS is also performed. The radiation induced damage creates bulk damage in silicon and alters the sensor¿s characteristics, such as an increase in leakage current and a reduction of charge collection efficiency, thus deteriorates the detector performance. The radiation damage simulation, based on a four-level trap model, can reproduce experimentally observed detector characteristics such as leakage current, full depletion voltage and charge collection efficiency.<br> <br>Lastly, a model for multi-channel pixels of HV-CMOS MAPS is developed. The model comprises of nine pixels arranged in a 3×3 array. The model is used to analysing and predicting interpixel crosstalk and charge sharing effects between pixels. The radiation incidents at different positions and directions are simulated to investigate the performance of the HV-CMOS MAPS and the impacts on adjacent cells. The performance degradation of the whole sensor system due to radiation induced damage is also studied.<br><br>The combined results of this thesis demonstrate the advantage and power of the TCAD simulations of semiconductor radiation detectors as a tool to bridge the gap from experiments to simulations.