  The Inner Tracking System (ITS) of the ALICE experiment at CERN will undergo
an upgrade during the LHC long shutdown 3, in which the three innermost
tracking layers will be replaced. This upgrade, named the Inner Tracking System
3 (ITS3), employs stitched wafer-scale Monolithic Active Pixel Sensors
fabricated in a 65 nm CMOS process. The sensors are 260 mm in length and
thinned to less than 50 um then bent to form truly half-cylindrical
half-barrels. The feasibility of this process for the ITS3 was explored with
the first test production run (MLR1) in 2021, whose goal was to evaluate the
charged particle detection efficiency and the sensor performance under
non-ionising and ionising radiation up to the expected levels for ALICE ITS3 of
$10^{13}$ $1$ MeV n$_{\mathrm{eq}}$ cm$^{-2}$ (NIEL) and 10 kGy (TID). Three
sensor flavours were produced to investigate this process: Analog Pixel Test
Structure (APTS), Circuit Exploratoire 65 (CE65) and Digital Pixel Test
Structure (DPTS).
  This contribution gives an overview of the MLR1 submission and test results,
describing the different sensor flavours and presenting the results of the
performance measurements done with particle beams for various chip variants and
irradiation levels.
