The CMS GEM Detector Front-end Electronics – Characterization and Implementation

This research work is a contribution to the CMS GEM upgrade. From 2026, the CERN Large Hadron Collider (LHC) will enter the High Luminosity phase, also known as phase-2, where the machine will almost double the number of proton collisions per second. This luminosity increase brings challenges to the LHC experiments, like CMS, particularly to their most forward detector sub-systems closer to the beamline. The higher particle rates and radiation levels challenge the detectors and their read-out electronics, the trigger, and the data acquisition systems of the experiment. In CMS, new Triple-GEM detectors are being installed in the forward part of the muon spectrometer. A first ring, called GE1/1, has been deployed during the current LHC Long Shutdown (2019-2021), and two other rings, GE2/1 and ME0, will be installed within a couple of years. The objective of the new Triple- GEM detector sub-system is to improve the CMS’s muon tracking and triggering capabilities. This thesis is devoted to the VFAT3, a front-end chip that has been designed for the CMS GEM upgrade project. The VFAT3 is a 128 channel ASIC providing both trigger and tracking data. In CMS, the VFAT3 chip is assembled on a small (5 x 5 cm2) PCB, called the VFAT3 hybrid. For GE1/1, 5,000 VFAT3 chips and hybrids had to be mass-produced. This mass production required a full characterization of the chip on the hybrid, including its radiation hardness and the study of the VFAT3 performance once it is integrated into the CMS GEM detectors. The objective of my work was to demonstrate the adequacy of the VFAT3 chip and VFAT3 hybrid for the CMS GEM phase-2 application and design the challenging hardware, software, and firmware tools required to reach that goal. The thesis is structured as follows: Chapter 1 introduces the CERN, the LHC, and the CMS projects. The phase-2 upgrade of the LHC is also described, and planned muon endcap upgrades are discussed. Chapter 2 details the GEM detectors and the first CMS GEM ring, GE1/1. The GE1/1 performance parameters achieved over ten years of GEM global collaboration R&D are also presented. Chapter 3 elaborated the VFAT3 chip, its design, and architecture. The key design goals of the chip design and optimization for GEM charge are also discussed. Chapter 4 presents the functional characterization of the VFAT3. The dedicated setup is described in detail, and the VFAT3 characterization performance is discussed. The phase-2 compatibility results of the VFAT3 are demonstrated as well. Chapter 5 is then devoted to the comprehensive study of the radiation hardness of the chip. Different test facilities and test setups designed to perform the radiation characterization are discussed. VFAT3 radiation-tolerance conformance to GEM operation is presented. In Chapter 6, the performance of the VFAT3 with the first CMS GE1/1 detector prototypes is evaluated. Various compatibility challenges and their mitigation strategies are presented as well. Chapter 7 presents the production of the VFAT3 hybrid, the manufacturing issues which had to be tackled, and finally, the results and final yield of the production of 5000 pieces for GE1/1 is described. Ultimately, Chapter 8 introduces the future CMS GEM rings, GE2/1 and ME0. The impact of my GE1/1 work and its future prospects towards GE2/1 & ME0 are also discussed.