ALICE ITS3 - A bent wafer-scale monolithic pixel detector

by Alex Kluge (CERN)

Friday 11 Apr 2025, 11:00 → 12:15 Europe/Zurich

40/S2-C01 - Salle Curie (CERN)

ALICE is upgrading its inner three silicon tracker layers with a bent wafer-scale monolithic pixel detector (ITS3).
Each layer comprises two sensors, 27 cm long, 50 µm thick and bent to concentric half-layers around the beam pipe (radii: 19, 25, 32 mm) supported by carbon foam stiffeners. The sensors with 40 mW/cm² consumption and a material budget of 0.07% X0 per layer are air-cooled.
Fabrication of 27 cm long sensors, requires stitching at foundry level connecting identical reticle-sized sensor elements, bypassing the need for flexible printed circuits.
Pixel test structures on a 300 mm, 65 nm TPSCo technology were validated with a resolution of 5 µm, an efficiency of > 99%, a fake hit rate of < 10-2/pixel/s and a radiation load of 4*1014 1 MeV neq cm-2. These findings were further corroborated with 26 cm long Monolithic Stitched Sensor prototypes, confirming the stitching and integration process in laboratory and beam tests.
Prototype silicon sensors thinned to ≤ 50 µm were successfully bent to the ITS3's required radii while retaining full functionality. Mechanical engineering models with 50 µm thick dummy sensors demonstrated a mechanical stability of ± 0.5 μm under an 8 m/s airflow, consistent with the sensor’s power consumption and the interconnection scheme.
The design of the final full-function sensor prototype (MOSAIX) with a pixel size of 22.8 x 20.8 µm2 is underway. The seminar will report on the R&D phase, the final sensor design and detector integration.

Coffee will be served at 10:30