Pixel-Strip Modules for the CMS Tracker Phase-2 Upgrade: From DAQ test system development to module assembly and qualification

The Large Hadron Collider (LHC) will undergo a major “High Luminosity” upgrade with the goal of delivering a peak instantaneous luminosity of $\mathrm{5-7.5 \times 10^{34}\ cm^{-2}s^{-1}}$ by 2029. In order for the CMS experiment to cope with the higher radiation levels and data rates, the current CMS Silicon Tracker will be replaced. In particular, the outer part of the Tracker, referred to as the Outer Tracker, will introduce a new module concept, made of two vertically stacked silicon sensors. It will exploit the strong magnetic field inside the CMS detector to perform an on-module transverse momentum ($\mathrm{p_{T}}$) discrimination, detecting high $\mathrm{p_{T}}$ particles locally and sending the corresponding information, referred to as stubs, to the CMS Level-1 Trigger system. This thesis focuses on one of the two foreseen module designs, namely the Pixel-Strip (PS) module. The module is made of a $\mathrm{10 \times 5\ cm^{2}}$ strip sensor, with 2.5 cm long strips and 100 μm pitch, stacked on top of a macro pixel sensor with 1467 × 100 μm macro pixels bump-bonded to macro pixel ASICs. The latter are of particular importance as they implement the logic for the on-module $\mathrm{p_{T}}$ discrimination. The sensor stack is surrounded by peripheral front-end, readout and power hybrid circuits. The front-end hybrids host the strip sensor ASICs and a data concentration ASIC. The readout hybrid handles the control of the front-end ASICs and the bi-directional optical data communication with the back-end system. Finally, the power hybrid ensures power distribution to all the front-end electronic components. The presented work describes the latest developments with respect to three main aspects: the PS module assembly, the module production test systems, and the PS module qual- ification. On the one hand, the module assembly relies on a semi-automated procedure capable of fulfilling the high precision requirements of the sensor-to-sensor alignment. On the other hand, the development of the production test systems is driven by the core principle of versatility, flexibility and high throughput such that they are able to sup- port the qualification of the wide range of hybrid circuits and module types. As far as performance studies are concerned, the preliminary laboratory qualification of the lat- est assembled prototype PS modules demonstrates the electrical integrity of the readout chain but still yields a relatively high electronic noise affecting the strip sensor. Never- theless, test-beam qualification of a prototype module shows excellent performance with cluster efficiencies above 99% for the strip sensor and 98% for the pixel sensor. Finally, the test-beam qualification demonstrates the pT discrimination capabilities of the module, yielding stub efficiencies above 98%.