Characterisation of small scale MLR1 devices for ALICE ITS3

During the upcoming Long Shutdown 3 (scheduled for 2026–2029), the ALICE Inner Tracking System (ITS), currently at its second version (ITS2), will be further upgraded to ITS3. After the upgrade, the 3 innermost ITS2 layers (Inner Barrel, or IB) will be replaced by 3 flexible, truly cylindrical layers of stitched large-scale MAPS, produced with the TPSCo 65 nm technology. The reduced need for supporting frames, as well as the substitution of the present water cooling system with air cooling, is expected to lead to a dramatic drop in material budget per layer from 0.36% X_0 to an average of 0.09% X_0 , improving ITS tracking precision and pointing resolution compared to ITS2. A wide range of Multi-Layer Reticle 1 (MLR1) small test devices have been developed to validate 65 nm technology for ITS3, including Analog and Digital Pixel Test Structures (APTS and DPTS), designed to optimise the pixel charge collection process and front-end configuration, respectively. In this contribution results of MLR1 device tests will be shown. Measurements have been performed both with charged particle beams and in laboratory with a 55-Fe source, in order to investigate the MLR1 65 nm small test device performances and to compare them with the upcoming ITS3 goals (99% detection efficiency and 5 μm spatial resolution under up to 10 kGy TID + 10^13 1 MeV n_eq /cm^2 NIEL). APTS laboratory measurements have shown high charge collection efficiency after a low-dose n-type blanket implantation, while test beam results both on APTS and DPTS have proven that the expectations for ITS3 sensor detection efficiency and spatial resolution are met.