ALPIDE: the Monolithic Active Pixel Sensor for the ALICE ITS upgrade

The upgrade of the ALICE vertex detector, the Inner Tracking System (ITS), is scheduled to be installed during the next long shutdown period(2019-2020) of the CERN Large Hadron Collider (LHC). The current ITS will bereplaced by seven concentric layers of Monolithic Active Pixel Sensors (MAPS) witha total active surface of∼10 $m^2$, thus making ALICE the first LHC experimentimplementing MAPS detector technology on a large scale. The ALPIDE chip, basedon TowerJazz 180 nm CMOS Imaging Process, is being developed for this purpose. A particular process feature, the deep p-well, is exploited so the full CMOS logiccan be implemented over the active sensor area without impinging on the deposited charge collection. The upgrade of the ITS presents two different sets of requirements for sensors of the inner and of the outer layers due to the signicantly different trackdensity, radiation level and active detector surface. The ALPIDE chip fulfils the stringent requirements in both cases. This paper summarises the ALPIDE features and main test results.