  The Mu3e experiment is searching for the charged lepton flavour violating
decay $ \mu^+\rightarrow e^+ e^- e^+ $, aiming for an ultimate sensitivity of
one in $10^{16}$ decays. In an environment of up to $10^9$ muon decays per
second the detector needs to provide precise vertex, time and momentum
information to suppress accidental and physics background. The detector
consists of cylindrical layers of $50\, \mu\text{m}$ thin High Voltage
Monolithic Active Pixel Sensors (HV-MAPS) placed in a $1\,\text{T}$ magnetic
field. The measurement of the trajectories of the decay particles allows for a
precise vertex and momentum reconstruction. Additional layers of fast
scintillating fibre and tile detectors provide sub-nanosecond time resolution.
The MuPix8 chip is the first large scale prototype, proving the scalability of
the HV-MAPS technology. It is produced in the AMS aH18 $180\, \text{nm}$
HV-CMOS process. It consists of three sub-matrices, each providing an
untriggered datastream of more than $10\,\text{MHits}/\text{s}$. The latest
results from laboratory and testbeam characterisation are presented, showing an
excellent performance with efficiencies $>99.6\,\text{\%}$ and a time
resolution better than $10\, \text{ns}$ achieved with time walk correction.
