Speaker
Description
The Inner Tracking System 3 (ITS3) for the ALICE experiment at CERN, to be installed during the LHC Long Shutdown 3 (2026-2030), will replace the current three innermost ITS2 layers. ITS3 introduces a novel ultra-light and high-precision vertex detector based on monolithic active pixel sensors that are thinned to 50 µm, bent to radii of 19, 25, and 32 mm to form truly cylindrical layers, and extended to unprecedented lengths of 27 cm through a wafer-scale stitching process. Stitching multiple reticle-sized blocks into a single large sensor eliminates the need for flexible printed circuits, reducing complexity and mass. These design choices aim to meet the stringent ITS3 requirements of minimal material budget (< 0.09 % X$_0$ per layer), low power consumption (∼ 40 mW/cm$^2$ ), a lightweight mechanical support structure based on carbon foam, air-cooled mechanics, and high spatial resolution (∼ 5 µm). The core of this upgrade is the development of a new family of stitched CMOS sensors — MOSS, MOST, and MOSAIX — fabricated in the 65 nm Tower Semiconductor (TPSCo) process.
MOSS and MOST prototypes have demonstrated the feasibility of this approach, achieving excellent performance in laboratory and beam tests: detection efficiency above 99%, low fake-hit rate (< 10$^{−2}$ /pixel/s), and radiation tolerance up to 4 × 10$^{12}$ 1 MeV n$_{eq}$ /cm$^2$ and 4 krad. Building on these results, the final full-size full-functionality ITS3 sensor prototype, MOSAIX, is under development.
This contribution will present the development path from MOSS and MOST to MOSAIX with focus on the sensor performance validation and highlighting key technological breakthroughs such as large-area sensor stitching, sensor bending and thinning, radiation-tolerant design, and integration using carbon foam and air cooling.
