Depleted Monolithic CMOS and Ultra-fast silicon detectors for particle physics and other applications
Science and Technology Facilities Council
University of Oxford
Semiconductor detectors are used widely in particle physics and other applications. This thesis concentrates on the development of two types of novel detectors. LGADs Both ATLAS and CMS are planning precision timing layers outside their trackers for the HL-LHC upgrades. These will be instrumented with a type of ultra-fast silicon detector called Low Gain Avalanche Detectors (LGADs) that achieve a timing resolution of ~30 ps. LGADs can be used to connect charged tracks to the correct production vertices and therefore reduce the effect of pile up at the High Luminosity LHC. Many other experiments nuclear and medical physics would also benefit from precision timing information.  LGADs use charge multiplication due to the avalanche initiated by a charge moving in large electrical fields to reach the picosecond regime. Unfortunately, the performance of these devices is limited by radiation damage when exposed to particle fluences higher than about 1014 particles/cm2.  Simulation of the doping profiles to improve LGAD radiation damage performance and prompt characterization of structures fabricated by Teledyne-e2V before and after radiation exposure will be conducted during this thesis. A study of the performance degradation (loss of signal, loss of gain, inhomogeneous spatial response, etc.) as a function of radiation fluence will also be performed. These studies will require careful laboratory measurements and test beam campaigns. The measurements will validate the TCAD simulations, improve our understanding of these devices, and lead to new optimised rad-hard designs.  Depleted Monolithic Active Pixels Sensors (DMAPS) DMAPS are position-sensitive detectors fabricates using standard CMOS processes. These sensors are extremely attractive for experiments in particle physics because they integrate the sensing and the readout electronics in a single layer of silicon. This removes the need for interconnection between the sensor and the readout-chip with the solder bump technology which is complex and expensive. DMAPS will become the sensor technology of choice for the next generation of experiments in particle physics. This thesis will focus on the optimization of the DMPAS technology for two different regimes: radiation-hard detector for further upgrades of the LHC pixel detectors and high-precision low-mass detector for future e+e- colliders. The R&D programme on DMPAS requires simulation with TCAD and sensor characterization, including radiation hardness studies for the HL-LHC application. This programme will be conducted in collaboration with TowerJazz using its 180 nm and 65 nm technologies.
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