  The physics aims at the proposed high-energy $e^+e^-$ collider CLIC pose
challenging demands on the performance of the detector system. Precise hit-time
tagging, an excellent spatial resolutions, and a low mass are required for the
vertex and tracking detectors. To meet these requirements, an all-silicon
vertex and tracking detector system is foreseen, for which a broad R&D
programme on a variety of novel silicon detector technologies is being pursued.
For the ultra-low mass vertex detector, different hybrid technologies with
innovative sensor concepts and interconnection techniques are explored. For the
large-scale tracking detector, the focus of the R&D lies on monolithic HV-MAPS
and HR-CMOS technologies. This contribution gives an overview of the ongoing
activities with a focus on monolithic technologies for the CLIC tracking
detector. Recent results from laboratory and test-beam measurement campaigns of
the ATLASpix_Simple and the CLICTD sensor prototypes are presented.
