Speaker
Description
The ALICE Collaboration at the Large Hadron Collider (LHC) will replace the three innermost layers of the Inner Tracking System (ITS) during the Long Shutdown 3 in 2026-2029. The new inner tracker, called ITS3, will consist of truly-cylindrical silicon barrels to improve the pointing resolution by a factor of two over a large momentum range and the tracking efficiency at very low transverse momenta ($p_{\rm T}$ < 0.3 GeV/$c$).
The first three layers will be equipped with stitched 27 cm long wafer-scale monolithic active pixel sensors built using a 65 nm CMOS imaging process technology. The sensors will be thinned to 50 $\mu$m to become flexible allowing the formation of truly-cylindrical barrels with an extremely low material budget of 0.09 % X/X$_{0}$ per layer. Starting from mid-2023, chip prototypes, the so-called MOnolithic Stitched Sensors (MOSS), have been produced to demonstrate the feasibility of the stitching process. A single chip has a dimension of 14 mm $\times$ 259 mm and a total of 6.7 million pixels organized in 10 repeated sensor units with pixel pitches of 18 and 22.5 $\mu$m. A second design is implemented in the MOnolithic Stitched Sensor with Timing (MOST) to evaluate on-chip powering segmentation containing 0.9 million pixels with 18 $\mu$m pitch distributed on a smaller area of 2.5 mm $\times$ 259 mm.
The primary goal of MOSS and MOST is to learn about the stitching technique implementation, yield and performance of wafer-scale sensors in view of the production of the ITS3 final-size full-functionality prototype sensor chip foreseen for summer 2025. The characterization campaign of the stitched sensors includes the verification of power domain impedances, DAC performance, pixel front-end readout response, threshold scans and fake-hit rate scans. This presentation will focus on the results and learnings from the characterisation campaign of the stitched sensors in the laboratory and in the test-beam facilities with an overview of the final chip features.
