  The Belle II experiment at KEK in Japan considers upgrading its vertex
detector system to address the challenges posed by high background levels
caused by the increased luminosity of the SuperKEKB collider. One proposal for
upgrading the vertex detector aims to install a 5-layer all monolithic pixel
vertex detector based on fully depleted CMOS sensors in 2027. The new system
will use the OBELIX MAPS chips to improve background robustness and reduce
occupancy levels through small and fast pixels. This causes better track
finding, especially for low transverse momenta tracks. This text will focus on
the predecessor of the OBELIX sensor, the TJ-Monopix2, presenting laboratory
and test beam results on pixel response, efficiency, and spatial resolution.
