Silicon Detector Technologies for Future Particle Collider Experiments

Future collider experiments are typically motivated by the search for new particles and precision measurements of physical observables. The goal is to find deviations from existing theories. In practice, this requires advances towards higher luminosities at higher collision energies, finally resulting in a more difficult experimental environment. At the same time, more precise measurements are required. One such collider is the high luminosity upgrade of the LHC (HL-LHC), that is planned to start operation in 2026. Compared to LHC, the number of simultaneous collisions (pile-up) will increase by roughly a factor four and the radiation exposure of the detectors will be an order of magnitude larger than for LHC. Another proposed collider is the Compact Linear Collider (CLIC) that would provide electron- positron collisions at a centre-of-mass energy of up to 3 TeV. As the collision partners are fundamental particles, the initial state and energy are well known. This allows for precision measurements of Higgs and Top quark observables, including a wide variety of measurements that are particularly sensitive to physics beyond the standard model. Here, the detector is required to deliver an unprecedented precision on the measurement of jet energy, impact parameter and particle momentum. For both colliders and their associated experiments, silicon detectors play an essential role in meeting the detection requirements. For CLIC, the desired momentum resolution together with the flavour tagging performance will require a vertex detector with a spatial resolution of around 3 um and a time resolution better than 5 ns, all at a material budget of only 0.2% X0 per layer. This can be achieved by using thin silicon pixel sensors of around 50 um thickness. The design of the CLIC calorimeter is driven by the need of an unprecedented jet energy resolution. To achieve this, CLIC will employ a highly granular sampling calorimeter optimised for Particle Flow techniques. Silicon pad sensors will be used as active material in the electromagnetic calorimeter due to their compactness, operational stability, excellent signal-to-noise ratio and good segmentation properties. More recently, the CMS collaboration has decided to adopt a similar concept in the upgrade of their endcap calorimeters for the HL-LHC phase, a project commonly called HGCAL. Here, the reasoning to use silicon as active calorimeter material is however broader. It is additionally driven by the need for radiation hardness and precise time stamping for pile-up mitigation. In this work, the role of silicon detectors in the CLIC vertex detector as well as the calorimeters for CLIC and HGCAL, is explored. The focus is put on the performance of thin detector substrates, issues of characterisation and calibration in connection with the high granularity, as well as the possible time resolution that can be reached. The first part explores the performance of thin silicon pixel detectors that are considered for the CLIC vertex detector. The Timepix3 ASIC is used as a test vehicle to study several aspects of thin silicon pixel sensors and to determine the specifications for the CLIC frontend electronics. A calibration method suited for a channel density of O(10^4/cm^2) and addressing time-over-threshold and time-of-arrival readouts with a non-linear behaviour is investigated. Laboratory measurements and beam test results are presented and a special focus is put on the time resolution of ASIC and sensor. The second part covers the electrical characterisation of large area silicon pad sensors for fine-grained calorimeters. It describes the design and commissioning of a system for testing the voltage dependence of electrical current and capacitance of each pad. The system consists of an active multiplexer matrix and a passive probe card that handles only the contacts to the sensor. Results for a wide range of prototype silicon pad sensors are presented. The third part focusses on the sub-nanosecond timing capabilities the same sensors have when operated in a calorimeter environment. A prototype sensor is equipped with a dedicated readout and used to sample electromagnetic showers. It is shown that, on a module level, time resolutions of less than 15 ps can be achieved. Finally, the outlook on the time resolutions achievable at the system level is discussed.