  The CLIC Tracker Detector (CLICTD) is a monolithic pixel sensor. It is
fabricated in a 180 nm CMOS imaging process, modified with an additional deep
low-dose n-type implant to obtain full lateral depletion. The sensor features a
small collection diode, which is essential for achieving a low input
capacitance. The CLICTD sensor was designed as a technology demonstrator in the
context of the tracking detector studies for the Compact Linear Collider
(CLIC). Its design characteristics are of broad interest beyond CLIC, for
HL-LHC tracking detector upgrades. It is produced in two different pixel
flavours: one with a continuous deep n-type implant, and one with a segmented
n-type implant to ensure fast charge collection. The pixel matrix consists of
$16\times128$ detection channels measuring $300 \times 30$ microns. Each
detection channel is segmented into eight sub-pixels to reduce the amount of
digital circuity while maintaining a small collection electrode pitch. This
paper presents the characterisation results of the CLICTD sendor in a particle
beam. The different pixel flavours are compared in detail by using the
simultaneous time-over-threshold and time-of-arrival measurement
functionalities. Most notably, a time resolution down to $(5.8 \pm 0.1)$ ns and
a spatial resolution down to $(4.6 \pm 0.2)$ microns are measured. The hit
detection efficiency is found to be well above 99.7% for thresholds of the
order of several hundred electrons.
