The ALICE ITS upgrade

A major upgrade of the Inner Tracking System (ITS) of the ALICE experiment at LHC is currently under preparation with the aim of exploiting the increased Pb-Pb luminosity expected during Run 3 and Run 4 after 2020, which will enable to make a detailed study of the properties of the Quark-Gluon Plasma. The new ITS, which will be installed during the Long Shutdown 2 (2019-2020), will increase the readout rate capability by more than two orders of magnitude while, at the same time, improving the tracking capability and the impact parameter resolution, especially at low transverse momentum.The new ultra-light tracker will be constructed with Monolithic Active Pixel Sensors to instrument the ~10 m2 ITS active surface, arranged on seven layers, with the inner layer as close as 23 mm from the interaction point.The CMOS chip (ALPIDE) which will equip the ITS is built in the TowerJazz 180 nm -CMOS imaging sensor process and has been custom designed to fulfil the stringent requirements of the new tracker.The chip R&D; phase finished in 2016 with the development of a chip whose performances fulfil and often exceed the project requirements. The start of production of ALPIDE in December 2016 marked the beginning of the production phase of the ITS upgrade.