Speaker
Description
This contribution presents the characterisation and the radiation-tolerance evaluation of MOSAIX, the wafer-scale monolithic active pixel sensor developed for the ALICE ITS3 upgrade. During LHC Long Shutdown 3, ITS3 will replace the three innermost layers of the Inner Tracking System with thin, bent, wafer-scale sensors, substantially reducing the material budget and bringing these layers closer to the interaction point. The resulting improvement in pointing resolution is essential for the low-transverse-momentum heavy-flavour measurements that probe the quark–gluon plasma. MOSAIX, fabricated in a 65 nm CMOS imaging process using stitching, is the first full-scale prototype of the ITS3 sensor, and validating it against both the detection-performance and the radiation-tolerance requirements is a prerequisite for the final design.
The detection performance was studied in test beam campaigns at the CERN PS, where the detection efficiency and the fake-hit rate were measured as a function of the pixel threshold, on chips subjected to different levels of irradiation. Raising the threshold reduces the efficiency while lowering it increases the fake-hit rate, and the range in which both requirements are met simultaneously defines the range of pixel thresholds available for ITS3 in LHC Run 4. The radiation tolerance was further assessed in dedicated campaigns with protons and with heavy ions, addressing single-event upsets in the on-chip logic and the sensitivity of the design to single-event latch-up. The current status and the outlook towards the final sensor will be presented.
