Silicon Detector Development for Future Lepton Colliders & Quality Control of the ATLAS Strip Tracker Production

Abstract

Future high energy physics aims to probe the Standard Model with unprecedented precision, through upgrades of existing collider experiments and the development of future collider facilities. Achieving the ambitious physics goals requires detector instrumentation with a performance beyond the current state of the art. This challenge motivates dedicated studies of detector technologies for future upgrades and the next generation of collider experiments. In this context, this thesis is divided into two parts. <br/>

In the first part, the H2M (Hybrid-to-Monolithic) test chip, developed envisioning tracking applications at a future lepton collider, is characterised through sensor simulations and laboratory and test beam measurements. The H2M is a monolithic pixel sensor designed and fabricated in a modified 65 nm CMOS imaging process with a small collection electrode. The chip matrix consists of 64×16 square pixels with a pitch of 35 μm. Each pixel includes an analog front-end and digital logic with an 8-bit pulse processing counter. A minimum ionising particle detection efficiency of 99% has been achieved at a threshold of approximately 205 electrons, demonstrating that the sensor modifications maintain a high efficiency at relatively large pixel pitches, which are beneficial for large-area tracking applications. The spatial resolution has been measured to be 9.3 ± 0.1 μm at a threshold of 178 electrons, consistent with the sensor design and large pitch. A non-uniform in-pixel response has been observed in the measurements, which has been attributed to the formation of local potential wells in regions with low electric field and interpreted further with the aid of simulation. The timing resolution, limited by this effect, has been determined to be 28.4 ± 0.2 ns. Furthermore, single-die chips have been thinned to a total chip thickness of 21 μm without performance degradation, proving that the technology is suitable for ultra-low material budget applications. <br/>

The second part of the thesis presents the quality assurance and quality control of the End of-Substrature (EoS) cards. These cards will be installed in the Inner Tracker detector, the upgrade of the current Inner Detector of the ATLAS experiment at the Large Hadron Collider (LHC) for the High-Luminosity LHC. Acting as the interface between the on- and off-detector systems, the EoS cards are a critical component. Therefore, all the 1 552 cards that will be placed in the detector are undergoing strict non-destructive testing. In particular, a card flatness tolerance of 300 μm has been set to ensure proper gluing to the detector’s carbon-fiber core and effective heat dissipation. To verify this, a capacitive sensor setup has been developed to perform fast flatness measurements of all cards, demonstrating results consistent with those obtained using a smartscope.