The present Inner Tracking System (ITS2) of the ALICE Experiment will be upgraded during the LHC Long Shutdown 3 (LS3). The upgrade foresees the replacement of the three innermost layers with a truly cylindrical vertex detector, the ITS3. Such tracker will be composed of two half barrels, comprising three self-supporting cylindrical half-layers, each made of two large-area (O(10×26 cm$^2$)) ultra-thin (≤50 μm) bent stitched Monolithic Active Pixel silicon Sensors (MAPS) fabricated in a 65 nm CMOS process. This novel technology will allow for an unprecedented low material budget of 0.05 %X/X0 per layer, strongly improving the tracking efficiency and the pointing resolution, especially for low-momentum particles.
An extensive campaign to validate the sensor technology through characterisation both in the laboratory and with in-beam measurements is ongoing. For this purpose, multiple test structures were included in the first test production (MLR1) to be tested: Analog Pixel Test Structure (APTS), Circuit Exploratoire 65 (CE65) and Digital Pixel Test Structure (DPTS). Excellent performance in terms of detection efficiency (>99%), spatial resolution (3-4 μm) and response to X-rays were
achieved. Moreover, good performance achieved on irradiated APTS and DPTS proved the 65 nm CMOS process tolerant far beyond 1×10$^{13}$ 1 MeV n$_{𝑒𝑞}$ cm$^{−2}$ (NIEL) and 10 kGy (TID), expected for the ALICE ITS3 operating environment.
This contribution will describe the different test structure flavours and the most recent results from laboratory and beam test measurements will be presented.