Design and Characterization of The Silicon Strip Sensors for The Future Hadron Colliders

Silicon sensors play a key role in High Energy Physics (HEP) experiments due to their superior performance in terms of robust and reliable charged particle tracks and vertex reconstruction. Owing to the placement of these sensors in a harsh radiation environment imposed by current and future HEP experiments like Compact Muon Solenoid (CMS) in the Large Hadron Collider (LHC) phase and the high luminosity LHC (HL-LHC) phase, the radiation hardness study is inevitable. It is imperative to optimize the sensor design or develop new sensor configurations which can withstand such radiation scenario. This has generated an interest in the development and improvement of the radiation tolerance of the sensors which require better designs and better engineering technologies.\\ This thesis is devoted to the characterization studies of the silicon sensors for their performance and study of novel sensor designs through Technological Computer Aided Design (TCAD) simulations for their survival in harsh radiation sectors.\\ The characterization studies involved development and characterization of AC-coupled, poly-silicon biased, p-on-n silicon strip sensors. While the fabrication of the sensors were carried out in Bharat Electronics Limited (BEL), the characterization study was performed in Karlsruhe Institute of Technology (KIT). The non-irradiated sensors were subject to several tests defined in the characterization scheme for the quality assurance of the fabricated sensors. The details of the process steps involved in the fabrication cycle and the performance characteristics of the fabricated sensors are discussed. The measured data shows a good control of the process parameters governing the poly-silicon deposition and the quality and uniformity of the coupling oxide layer. The radiation tolerance of the fabricated sensors has also been evaluated and results are presented in the thesis. It is to be noted that this is the first radiation hardness study performed on AC-coupled sensors developed in India.\\ As part of the characterization study, various automated and programmable characterization systems were developed to carry out a `Quality Assurance' inspection of the pad and strip sensors. The system consists of a current-voltage, capacitance-voltage (CVIV) setup, and a Transient Current Technique (TCT) setup; capable of measuring global sensor, strip, inter-strip parameters and charge collection. The thesis lists the most noticeable features of the setups, their operation, and measurement results. The system, is proposed to be used as a `Sensor Qualification Centre' and will be utilized for the qualification of the 2S multi-strip sensors of the CMS outer tracker in the HL-LHC phase.\\ The n-on-p silicon sensors employed in strip configurations in the CMS experiment experience a rapid fall in the collected charge (CC) with progressing radiation damage. This results in an inefficient signal read-out and hence silicon sensors become unfit for particle tracking in extremely high radiation environment. Hence, it is important to develop and evaluate new thin sensor technologies which can provide intrinsic charge multiplication (gain) for a high signal to noise ratio (S/N), and survive at high fluences. In this thesis, the behaviour of Low Gain Avalanche Detector (LGAD) in radiation environment is explored through TCAD device simulations. The simulation predictions provide a reasonable qualitative description of both the non-irradiated and irradiated LGAD device behaviour. It has been emphasized that the gain of the non-irradiated LGAD devices is strongly influenced by the overall doping profiles of the p-well and n$^{+}$ implantations.\\ Design optimization of pixel sensors using TCAD device simulations has been carried out for the Phase-II CMS tracker upgrade. Simulations were carried out on two n-on-p planar pixel sensor geometries, 50 $\times$ 50 $\mu$m$^2$ and 100 $\times$ 25 $\mu$m$^2$, for two wafer thicknesses of 150 $\mu$m and 200 $\mu$m. A stepwise approach for identification of a radiation hard design is described.\\ The requirement for reduced material budget has made the silicon sensor community to explore thinner sensor options. Simulation studies of low resistivity or high bulk doping concentration silicon substrate sensors with respect to thickness and radiation hardness (for proton damage) are presented. It is found that thin and highly doped substrates are attractive candidates as the radiation hard sensors for the reported values of resistivities and bias voltage.\\ The research work carried out on the development of the AC-coupled, poly-silicon biased silicon sensors and establishment of characterization laboratory at DU has laid a foundation for future advancements of the silicon sensor instrumentation technology in India. The radiation hardness simulation studies on LGAD, pixel, and low resistivity silicon sensors has provided useful inputs for the development of novel sensor technology for high luminosity HEP experiments.